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Benthic megafauna of
the western Clarion-Clipperton Zone, Pacific Ocean
Guadalupe Bribiesca-Contreras1, omas G. Dahlgren2,3, Diva J. Amon4,
Stephen Cairns5, Regan Drennan1, Jennifer M. Durden6, Marc P. Eléaume7,
Andrew M. Hosie8, Antonina Kremenetskaia9, Kirsty McQuaid10,
Timothy D. O’Hara11, Muriel Rabone1, Erik Simon-Lledó6,
Craig R. Smith12, Les Watling13, Helena Wiklund2, Adrian G. Glover1
1Life Sciences Department, Natural History Museum, London, UK 2Department of Marine Sciences, University
of Gothenburg, Gothenburg, Sweden 3Norwegian Research Centre, NORCE, Bergen, Norway 4SpeSeas,
D’Abadie, Trinidad and Tobago 5Department of Invertebrate Zoology, National Museum of Natural History,
Smithsonian Institution, Washington, D.C., USA 6National Oceanography Centre, Southampton, UK 7UMR
ISYEB, Départment Origines et Évolution, Muséum national d’Histoire Naturelle, Paris, France 8Collections
& Research, Western Australia Museum, Perth, Australia 9Shirshov Institute of Oceanology, Russian Academy
of Sciences, Moscow, Russia 10School of Biological and Marine Sciences, University of Plymouth, Plymouth,
UK 11Museums Victoria, Melbourne, Australia 12Department of Oceanography, University of Hawai’i at
Mānoa, Honolulu, USA 13School of Life Sciences, University of Hawai’i at Mānoa, Honolulu, USA
Corresponding author: Guadalupe Bribiesca-Contreras (l.bribiesca-contreras@nhm.ac.uk)
Academic editor: Pavel Stoev | Received 12 February 2022|Accepted 5 May 2022 | Published 18 July 2022
http://zoobank.org/F503CB11-01EF-40D8-998C-135E8E8E44CE
Citation: Bribiesca-Contreras G, Dahlgren TG, Amon DJ, Cairns S, Drennan R, Durden JM, Eléaume MP, Hosie
AM, Kremenetskaia A, McQuaid K, O’Hara TD, Rabone M, Simon-Lledó E, Smith CR, Watling L, Wiklund H,
Glover AG (2022) Benthic megafauna of the western Clarion-Clipperton Zone, Pacic Ocean. ZooKeys 1113: 1–110.
https://doi.org/10.3897/zookeys.1113.82172
Abstract
ere is a growing interest in the exploitation of deep-sea mineral deposits, particularly on the abyssal
seaoor of the central Pacic Clarion-Clipperton Zone (CCZ), which is rich in polymetallic nodules. In
order to eectively manage potential exploitation activities, a thorough understanding of the biodiversity,
community structure, species ranges, connectivity, and ecosystem functions across a range of scales is
needed. e benthic megafauna plays an important role in the functioning of deep-sea ecosystems and
represents an important component of the biodiversity. While megafaunal surveys using video and still
images have provided insight into CCZ biodiversity, the collection of faunal samples is needed to conrm
species identications to accurately estimate species richness and species ranges, but faunal collections
are very rarely carried out. Using a Remotely Operated Vehicle, 55 specimens of benthic megafauna were
ZooKeys 1113: 1–110 (2022)
doi: 10.3897/zookeys.1113.82172
https://zookeys.pensoft.net
Copyright Guadalupe Bribiesca-Contreras et al. This is an open access ar ticle distributed under the terms of the Creative Commons Attribution License
(CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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collected from seamounts and abyssal plains in three Areas of Particular Environmental Interest (APEI 1,
APEI 4, and APEI 7) at 3100–5100 m depth in the western CCZ. Using both morphological and molecu-
lar evidence, 48 dierent morphotypes belonging to ve phyla were found, only nine referrable to known
species, and 39 species potentially new to science. is work highlights the need for detailed taxonomic
studies incorporating genetic data, not only within the CCZ, but in other bathyal, abyssal, and hadal re-
gions, as representative genetic reference libraries that could facilitate the generation of species inventories.
Keywords
Biogeography, deep-sea mining, DNA barcoding, DNA taxonomy, megafauna, polymetallic nodules
Table of contents
Introduction ............................................................................................................. 4
Materials and methods ............................................................................................. 5
Data resources ...................................................................................................... 5
Sampling .............................................................................................................. 6
DNA extraction, amplication, and sequencing ................................................... 7
Phylogenetic assignments ..................................................................................... 7
Taxonomic assignments ........................................................................................ 8
Comparison with seabed-imagery database ........................................................... 9
Results ...................................................................................................................... 9
Descriptions ....................................................................................................... 14
Genus Laetmonice Kinberg, 1856 ................................................................... 14
Laetmonice stet. CCZ_060 ......................................................................... 15
Genus Trianguloscalpellum Zevina, 1978 ........................................................ 17
Trianguloscalpellum gigas (Hoek, 1883) ...................................................... 17
Genus Catherinum Zevina, 1978 .................................................................... 20
Catherinum cf. albatrossianum (Pilsbry, 1907) ............................................ 20
Catherinum cf. novaezelandiae (Hoek, 1883) .............................................. 21
Genus Fungiacyathus Sars, 1872 ..................................................................... 29
Fungiacyathus (Fungiacyathus) cf. fragilis Sars, 1872 .................................... 29
Genus Chrysogorgia Duchassaing & Michelotti, 1864 .................................... 30
Chrysogorgia sp. CCZ_112 ......................................................................... 30
Genus Calyptrophora Gray, 1866 .................................................................... 35
Calyptrophora distolos Cairns, 2018............................................................. 35
Genus Protoptilum Kölliker, 1872 .................................................................. 36
Protoptilum stet. CCZ_068 ........................................................................ 36
Genus Freyastera Downey, 1986 ..................................................................... 42
Freyastera cf. tuberculata (Sladen, 1889) ..................................................... 42
Freyastera stet. CCZ_201 ........................................................................... 44
Genus Zoroaster Wyville omson, 1873 ....................................................... 46
Zoroaster stet. CCZ_065 ............................................................................ 46
Genus Porphyrocrinus Gislén, 1925 ................................................................ 47
cf. Porphyrocrinus sp. CCZ_165 ................................................................. 47
Benthic megafauna of the Clarion-Clipperton Zone 3
Genus Plesiodiadema Pomel, 1883 .................................................................. 53
Plesiodiadema cf. globulosum (A. Agassiz, 1898) .......................................... 53
Genus Kamptosoma Mortensen, 1903 ............................................................ 54
Kamptosoma abyssale Mironov, 1971 .......................................................... 54
Genus Molpadiodemas Heding, 1935 ............................................................. 56
Molpadiodemas stet. CCZ_102 .................................................................. 58
Molpadiodemas stet. CCZ_194 .................................................................. 59
Genus Synallactes Ludwig, 1894 ..................................................................... 62
Synallactes stet. CCZ_153 .......................................................................... 62
Genus Oneirophanta éel, 1879 ................................................................... 64
Oneirophanta stet. CCZ_100 ..................................................................... 64
Oneirophanta cf. mutabilis éel, 1879 ...................................................... 65
Genus Psychropotes éel, 1882 ...................................................................... 67
Psychropotes verrucicaudatus Xiao, Gong, Kou, Li, 2019 ............................. 67
Psychropotes dyscrita (Clark, 1920) .............................................................. 69
Genus Benthodytes éel, 1882 ....................................................................... 70
Benthodytes cf. sanguinolenta éel, 1882 ................................................... 70
Benthodytes marianensis Li, Xiao, Zhang & Zhang, 2018 ........................... 71
Genus Peniagone éel, 1882 ......................................................................... 72
Peniagone leander Pawson & Foell, 1986 .................................................... 72
Peniagone vitrea éel, 1882 ...................................................................... 74
Genus Psychronaetes Pawson, 1983 ................................................................. 75
Psychronaetes sp. CCZ_101 ........................................................................ 75
Genus Laetmogone éel, 1879 ...................................................................... 78
Laetmogone cf. wyvillethomsoni éel, 1979 ................................................ 78
Genus Ophiocymbium Lyman, 1880 ............................................................... 81
Ophiocymbium tanyae Martynov, 2010 ....................................................... 81
Ophiocymbium cf. rarispinum Martynov, 2010 ........................................... 83
Genus Ophiuroglypha Hertz, 1927 ................................................................. 84
Ophiuroglypha cf. irrorata (Lyman, 1878) ................................................... 84
Genus Hyalonema Gray, 1832 ........................................................................ 87
Hyalonema stet. CCZ_020 ......................................................................... 87
Hyalonema stet. CCZ_081 ......................................................................... 90
Genus Docosaccus Topsent, 1910 .................................................................... 92
Docosaccus sp. CCZ_021 ............................................................................ 92
Genus Holascus Schulze, 1886 ........................................................................ 93
Holascus stet. CCZ_078 ............................................................................. 93
Genus Bathyxiphus Schulze, 1899 .................................................................. 96
Bathyxiphus sp. CCZ_151 .......................................................................... 96
Discussion .............................................................................................................. 97
Conclusions ......................................................................................................... 100
Acknowledgements ............................................................................................... 101
References ............................................................................................................ 101
Supplementary material 1 ..................................................................................... 110
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
4
Introduction
e Clarion-Clipperton Zone (CCZ) in the central abyssal Pacic has become of
great interest for deep-sea mineral extraction. is large area of abyssal seaoor, ap-
proximately 6 million km2 (Wedding et al. 2013), has the largest concentrations of
high-grade polymetallic nodules, representing a vast source of commercially valuable
metals such as nickel, copper, and cobalt, many of which are currently used in high-
tech and green industries (Hein et al. 2020). Although new technological advances are
taking deep-sea mining closer to reality, the impacts of mining activities on deep-sea
ecosystems remain of concern and are still poorly understood (Jones et al. 2017). To
date, the International Seabed Authority (ISA), which governs seabed mining in this
area, has granted 17 exploration contracts to permit baseline surveys and resource as-
sessment (but not commercial mining) in the CCZ, and has adopted an environmen-
tal management plan establishing 13 areas where exploitation is currently prohibited
(called Areas of Particular Environmental Interest, or APEIs) (Smith et al. 2021). Four
of these were recently implemented, but the representativity of the APEI network still
needs to be assessed.
During the last few decades, there has been a dramatic increase in the scientic
exploration of the CCZ, but our knowledge of the faunal communities associated with
nodule elds is still limited, and taxonomic records for the area are scarce (Glover et
al. 2018). Although the CCZ was rst explored in 1875 by the H.M.S. Challenger
(omson and Murray 1885), relatively little taxonomic work has been carried out
in this vast area and hence very little biogeographic information is available (Simon-
Lledó et al. 2020). is is particularly problematic as such information is critical to
characterise the biodiversity, biogeographic ranges, and connectivity patterns across
the entire CCZ in order to make better predictions about the potential impacts of
deep-sea mining. In addition, the APEIs designated to preserve regional biodiversity
are severely understudied (Glover et al. 2016a; International Seabed Authority 2020;
Jones et al. 2021).
e CCZ abyssal seaoor is rich in topographic features such as hills, troughs,
fracture zones, and seamounts (Kaiser et al. 2017). It encompasses many habitats with
a range of dierent environmental conditions such as depth, nodule coverage, sedi-
ment composition, bathymetric relief, ow intensication on seamounts, and particu-
late organic carbon (POC) ux (Wedding et al. 2013; International Seabed Authority
2020; McQuaid et al. 2020; Washburn et al. 2021b). Benthic assemblages have been
found to change across the CCZ (Wilson 2017; Bonifácio et al. 2020; Simon-Lledó et
al. 2020), with POC ux inuencing regional megafaunal community patterns, and
local environmental factors (i.e., nodule coverage) and bathymetric features having
an eect at local scales (Amon et al. 2016; Simon-Lledó et al. 2019c). Seamounts are
abundant in the CCZ, most commonly in the eastern and western ends of the area,
with elevations of > 1000 m above the plain, and are a major source of hard-substrate
habitat (Wedding et al. 2013). Even though seamounts were hypothesised to provide
a potential refugia and to be larval sources of nodule-associated fauna that could aid
Benthic megafauna of the Clarion-Clipperton Zone 5
in recolonising nodule elds, of similar depths, disturbed by mining activities, a recent
study suggested that the seamounts sampled in the CCZ appear inadequate as refuge
areas (Cuvelier et al. 2020). Nonetheless, the biodiversity of the CCZ seamounts re-
mains largely unknown, with only few having been explored on the eastern (Cuvelier
et al. 2020; Jones et al. 2021) and western (Durden et al. 2021) margins.
Large benthic organisms (benthic megafauna) have been prioritised for monitor-
ing deep-sea ecosystems because they can be studied from seabed imagery (Dano-
varo et al. 2020), provide inferences on trophic interactions, ecosystem functioning
(Rex and Etter 2010), and processes of disturbances (Jones et al. 2017) and recovery
(Simon-Lledó et al. 2019a). In the CCZ, megafaunal benthic assemblages have been
studied almost exclusively from video and still images (e.g., Amon et al. 2016; Simon-
Lledó et al. 2019c, 2020; Cuvelier et al. 2020; Durden et al. 2021). While these studies
have vastly increased our understanding of biodiversity and community structure, un-
certainty remains as to the identity of operational taxonomic units (unique identiers
for dierent morphospecies) recognised in imaged-based survey, and whether they are
conspecic with other known species from elsewhere in the deep sea. It is thus criti-
cal to complement spatial/temporal analyses with detailed morphological and DNA-
sequence analyses of collected specimens (Amon et al. 2016, 2017b).
e DeepCCZ project was conceived to increase our understanding of faunal as-
semblages and biodiversity in the western CCZ, targeting both unexplored seamounts
and APEIs. Here, we provide the rst taxonomic synthesis of western CCZ megafauna,
which is also the largest megafaunal faunistic study from anywhere in the CCZ based
on collected specimens. We provide morphological descriptions, genetic data, and
high-resolution imagery for all megafauna specimens collected, including specimens
from both the abyssal plains and seamount habitats. It complements similar studies
of the high diversity of megafaunal xenophyophores (Gooday et al. 2020a, b), and
imagery-based community analysis of the megafauna in this area (Durden et al. 2021).
Materials and methods
e DeepCCZ expedition, aboard the RV Kilo Moana, from 14 May to 16 June 2018,
surveyed seamounts and abyssal plains in three Areas of Particular Environmental
Interest (APEIs 1, 4, and 7) located in the western Clarion-Clipperton Zone (CCZ;
Fig.1). All material presented here was collected during this expedition using the
Remotely Operated Vehicle (ROV) Lu’ukai, and specimens were processed following
the DNA taxonomy pipeline described in Glover et al. (2015).
Data resources
Sequences generated for this study have been deposited on GenBank: ON400681–
ON400730 (COI), ON406602–ON406622 (16S), ON406623–ON406643 (18S),
ON406596–ON406601 (28S), and ON411254–ON411256 (ALG11).
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
6
Sampling
Specimens were selected from across as many taxonomic groups as possible, with du-
plicates of similar morphotypes avoided; thus, the aim was to increase our understand-
ing of megafaunal diversity. A total of 55 specimens were collected during dierent
dives in three APEIs and three dierent geoforms (abyssal plain, seamount, and sea-
mount slope), 14 specimens were collected from abyssal seaoor in APEI 1; 13 from
abyssal seaoor, two from the seamount slope and six from a seamount in APEI 4; and
nine from abyssal seaoor and 11 from a seamount in APEI 7 (Fig. 1). In situ photo-
graphs and/or video frame grabs of each specimen were captured, with parallel lasers
for scale at 15 cm spacing. Megafaunal specimens were collected with the manipula-
tor (‘Orion’), suction sampler, or push cores, depending on the characteristics of each
specimen in order to best preserve morphological characters. Specimens collected with
the manipulator were placed into the biobox receptacle, while those collected with the
suction sampler were stored in a suction box. Collection data were recorded at the time
Figure 1. Map of the Clarion-Clipperton Zone (top left) indicating the nine Areas of Particular
Environmental Interest (APEIs) in red, exploration areas in green, and reserved areas in orange.
Shapeles were sourced from https://www.naturalearthdata.com/downloads/10m-physical-vectors/10m-
bathymetry/, and https://www.isa.org.jm/minerals/maps. Detailed maps of the study areas: APEIs 1
(top right), 4 (bottom left), and 7 (bottom right) show bathymetry from satellite values for the entire
APEI, and multibeam values obtained during the DeepCCZ expedition. Sites, and specic geoform,
where megafauna samples were collected are indicated as yellow stars in abyssal plains, green triangles in
seamounts, and pink hexagons in seamount slopes.
Benthic megafauna of the Clarion-Clipperton Zone 7
of capture (e.g., date and time, ROV latitude/longitude, seabed water depth, ROV
waypoint name).
After ROV recovery, specimens were transferred and maintained in cold (2–4 °C),
ltered seawater until processed. Following Glover et al. (2015), all specimens were
photographed, given a preliminary identication and assigned a unique voucher code
(e.g., CCZ_020). A tissue sample was taken from each specimen for downstream mo-
lecular analyses, and stored in 95% non-denatured ethanol at -20 °C. Specimens were
xed in 10% borax-buered formalin and transferred to 70% non-denatured ethanol
after 48 h, except for sponges, which were kept frozen at -80 °C. After the expedi-
tion, specimens and tissue sub-samples were sent to the University of Hawai’i Manoa.
Specimens were archived at the Natural History Museum, London (NHMUK), and
the Western Australian Museum (WAM ), following taxonomic inspection.
DNA extraction, amplification, and sequencing
DNA extraction was performed using the DNeasy Blood and Tissue Kit (Qiagen). e
barcode gene cytochrome oxidase I (COI) was the main target because this gene has
been used in previous studies on megafauna in the CCZ (e.g., Dahlgren et al. 2016;
Glover et al. 2016b). Additional markers for specic taxa (16S, 18S, 28S, and ALG11)
were amplied when either COI amplication was unsuccessful or to improve identi-
cation or phylogenetic inference. e PCR mix for each reaction contained 10.5µl
of Red Taq DNA Polymerase 1.1X MasterMix (VWR), 0.5 µl of each primer (10 µM),
and 1 µl of DNA template. PCR protocols and primers used for COI, 16S, and 18S
were following Glover et al. (2016b) and Dahlgren et al. (2016), and Hestetun et al.
(2016) for ALG11 and 28S. e PCR products were puried and sequenced at the
NHM Sequencing Facilities using a Millipore Multiscreen 96-well PCR Purication
System and ABI 3730XL DNA Analyser (Applied Biosystems), respectively. Sequenc-
ing primers used were the same as those for the PCR reactions, with the addition of
internal primers for 18S and only using primers from the second PCR for the ALG11
gene. DNA sequences were analysed using Geneious 7.0.6 (https://www.geneious.
com), with contigs assembled from both forward and reverse sequences and ambiguous
base calls corrected manually. DNA sequences generated in this study were submitted
to GenBank, with accession numbers ON400681–ON400730 for COI, ON406602–
ON406622 for 16S, ON406623–ON406643 for 18S, ON406596–ON406601 for
28S, and ON411254–ON411256 for ALG11.
Phylogenetic assignments
Phylogenetic relationships of the western CCZ megafauna were explored by estimating
phylogenetic trees for all taxa at dierent taxonomic levels: phylum Annelida: family
Aphroditidae; phylum Arthropoda: order Scalpellomorpha; phylum Cnidaria:
order Actiniaria, subclass Ceriantharia, subclass Octocorallia, and class Scyphozoa;
phylum Echinodermata: class Asteroidea, class Crinoidea, class Echinoidea, class
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
8
Holothuroidea, and class Ophiuroidea; and phylum Porifera. Dierent sets of genes
were used depending on published phylogenies and publicly available sequences for
each taxon, considering both nuclear and mitochondrial genes if available. For each
taxon, sequences were obtained from GenBank (Suppl. material 1: Table S1), except
for Porifera as a published alignment was used (Dohrmann 2018). Protein-coding
genes (COI, cytochrome oxidase III: COX3, mtMutS homolog: msh1, NADH-
dehydrogenase subunit 2 gene: ND2) were aligned using MUSCLE in MEGA-X. Non-
protein-coding genes (12S, 16S, 18S, 28S) were aligned using MAFFT v. 7 (Katoh
et al. 2019) using the auto strategy, and unalignable regions ltered in GBLOCKS
(Castresana 2000), allowing gap positions within nal blocks and less strict anking
positions. Individual gene-alignments were concatenated in Geneious, and the best
substitution model for each partition was determined using PartitionFinder 2 (Lanfear
et al. 2017). For Porifera, we manually aligned our sequences for the 18S, 28S, 16S,
and COI genes with the alignment provided in Dohrmann (2018).
Phylogenetic trees were estimated using partitioned maximum-likelihood (RAxML
v8.2.10; Stamatakis 2006) and Bayesian inference (BEAST v. 2.4.7; Bouckaert et al.
2014), with the best inferred substitution model for each partition. In RAxML, the
most common substitution model for each taxon was selected. RNA secondary struc-
ture, as in Dohrmann (2018), was also considered for Porifera, using the S16+G sub-
stitution model to paired sites of 18S and 28S. BEAST analyses were performed with
trees and clock models linked, a Yule tree model, and relaxed clock log normal. Two
independent runs of a maximum 100 M steps were combined after discarding 20%
as burn-in. Runs were checked for convergence and a median consensus tree was esti-
mated from the combined post-burn-in samples.
Taxonomic assignments
Taxonomic assignments considered information drawn from both molecular and mor-
phological analyses. For the latter, the collected specimens were sent to expert taxonomists
for morphological assignments. We assigned every specimen to the lowest Operational
Taxonomic Unit (OTU), each representing a species. However, we took a precautionary
approach when assigning species names (Dahlgren et al. 2016; Glover et al. 2016b; Hor-
ton et al. 2021), therefore recording species as ‘cf.’ when uncertain about their identity
based on (i) dierences in morphological characters, (ii) missing type locality DNA data,
or (iii) when type localities are at signicantly dierent depths or vast distances from the
western CCZ. Also, those species that could not be identied as a described species were
given a unique identier using the lowest taxonomic level condently identied and the
voucher code (assigned at sea; i.e., CCZ_060). In cases where more than one specimen
represented a species with a unique identier, this only included the voucher code of
the best-preserved voucher specimen of that species. Additionally, open taxonomic no-
menclature signs were used to indicate that the specimen was not identied any further
(‘stet’; e.g., ‘Laetmonice stet. CCZ_060’), or when the identication is still uncertain
(‘inc’; e.g., Bathymetrinae inc. CCZ_176), and ‘sp.’ was only used for potentially new
species (e.g., Psychronaetes sp. CCZ_101) after Glover et al. (2016b).
Benthic megafauna of the Clarion-Clipperton Zone 9
Current records available on OBIS, at a minimum depth of 3000 m, were re-
covered for each taxon on January 12, 2022 (robis::occurrence; Provoost and Bosch
2020). Records within a box dened by 13°N, 158°W; 18°N, 118°W; 10°N, 112°W;
2°N, 155°W were considered as occurring within the CCZ (Glover et al. 2015).
Comparison with seabed-imagery database
To gain preliminary insight into connectivity and distributions, morphology of speci-
mens was compared to and, where possible, aligned with a standardised megafauna
morphotype catalogue developed from in situ seabed imagery from across the north
Pacic abyss, mostly eastern CCZ (Simon-Lledó et al., pers. obs.). e catalogue aligns
invertebrate morphotypes, only for specimens larger than 1 cm, encountered in quan-
titative megafaunal assessments. At the time of writing, the survey areas so far encom-
passed in the standardised megafauna catalogue are, from east to west: UK-1 (Amon
et al. 2016); BGR, GSR, and APEI 3 (Cuvelier et al. 2020); APEI 6 (Simon-Lledó et
al. 2019b); TOML areas B, C, and D (Simon-Lledó et al. 2020); APEIs 1, 4, and 7
(this study; Durden et al. 2021); and the EEZ of Kiribati (Simon-Lledó et al. 2019d).
e catalogue assigns each documented taxon a 7-character, unique morphotype code
(e.g., POR_001) that diers from unique identiers used for the species in this study.
e level of taxonomic precision achieved in each catalogued taxon is indicated using
the open taxonomic nomenclature signs recommended for image-based identications
by Horton et al. (2021). A sux is added to each morphotype identication specifying
the taxonomic rank (e.g., "fam.", "family"; "gen.", "genus" or "sp.", "species") and the
signs "indet."or "inc.". e "indet." (indeterminabilis) indicates that further identica-
tion was not possible as diagnostic features are not typically visible in images, while
the "inc." (incerta) indicates that despite diagnostic features being visible in images,
the identication still has some uncertainty, needing further comparable material for
validation.
Results
A total of 55 specimens was collected in the western CCZ (Table 1). Based on mo-
lecular data these represent 48 species of invertebrate megafauna (43 singletons, four
doubletons, and a single species with four representatives) belonging to ten classes in
ve phyla. However, for three of the doubletons, each specimen was collected in a dif-
ferent APEI, but all were consistently found in the same geoform (i.e., abyssal plain,
seamount, or seamount slope). Most of the taxa were collected on the abyssal seaoor
(36 specimens from 33 species) > 4800 m deep, followed by seamounts (17 specimens
from 13 species) between 3095–3562 m deep, and only two specimens from two spe-
cies collected on a seamount slope at 4125 m deep. Out of the 48 taxa, only nine were
assigned to previously described species, all from adjacent regions such as the Kuril-
Kamchatka, Mariana, and Izu-Bonin Trenches, the South China Sea, and other areas
of the Northwest and Southwest Pacic.
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
10
Table 1. Megafauna specimens collected during the DeepCCZ expedition, including details of their collection such as collection site and geoform (S, seamount; AP,
abyssal plain; Sl, seamount slope), substrate or attachment (S, on sediment; E, epibiont, N, nodule; C, crust, Sa, anchored to sediment; B, attached to bone), depth,
decimal latitude and longitude, scientic collection and accession number, voucher number, and GenBank accession number.
Classication Species Site Substrate /
Attachment
Depth (m) Coordinates
(Latitude, Longitude)
Collection Accession no. Voucher GenBank accession no.
Annelida Polychaeta
Phyllodocida
Aphroditidae
Laetmonice stet. CCZ_060 APEI 7 (S) S 3096 4.8897, -141.7500 NHMUK 2022.760 CCZ_060 ON400687 (COI)
Arthropoda
ecostraca
Scalpellomorpha
Scalpellidae
Trianguloscalpellum gigas APEI 7 (AP) E 4875 5.0442, -141.8165 WA M C74110 CCZ_074 ON400698 (COI),
ON406624 (18S)
Catherinum cf. albatrossianum APEI 7 (AP) E 4875 5.0442, -141.8165 WAM C74109 CCZ_073 ON400697 (COI),
ON406623 (18S)
Catherinum cf. novaezelandiae APEI 1 (AP) E 5241 11.2751, -153.7444 WAM C74111 CCZ_185 ON400722 (COI),
ON406625 (18S)
Cnidaria Anthozoa
Actiniaria
Metridioidea stet. CCZ_072 APEI 1 (AP) E 4875 5.0442, -141.8165 NHMUK 2021.19 CCZ_072 ON400696 (COI)
Metridioidea stet. CCZ_154 APEI 4 (AP) N 5009 6.9702, -149.9426 NHMUK 2021.27 CCZ_154 ON400715 (COI)
Metridioidea stet. CCZ_164 APEI 7 (AP) E 5001 6.9880, -149.9326 NHMUK 2021.5 CCZ_164 ON400717 (COI)
Actinostolidae Actinostolidae stet. CCZ_183 APEI 1 (AP) N 5241 11.2751, -153.7444 NHMUK 2021.28 CCZ_183 ON406626 (18S)
Actinostolidae stet. CCZ_202 APEI 4 (AP) N 5206 11.2518, -153.6059 NHMUK 2021.22 CCZ_202 ON406627 (18S)
Scleractinia
Caryophyllidae
Fungiacyathus (Fungiacyathus) cf. fragilis APEI 4 (S) S 3562 7.2647, -149.7740 NHMUK 2021.26 CCZ_107 NA
Alcyonacea
Chrysogorgiidae
Chrysogorgia sp. CCZ_112 APEI 4 (Sl) C 4125 7.2874, -149.8578 NHMUK* CCZ_112 ON400711 (COI),
ON406602 (16S)
Mopseidae Mopseidae sp. CCZ_088 APEI 4 (AP) N 5018 7.0089, -149.9109 NHMUK* CCZ_088 ON400705 (COI),
ON406603 (16S)
Primnoidae Calyptrophora distolos APEI 4 (Sl) C 4125 7.2874, -149.8578 USNM 1550968 CCZ_113 ON400712 (COI),
ON406604 (16S)
Pennatulacea
Protoptilidae
Protoptilum stet. CCZ_068 APEI 7 (S) Sa 3096 4.8897, -141.7500 NHMUK 2021.24 CCZ_068 ON400694 (COI),
ON406605 (16S)
Spirularia Spirularia stet. CCZ_067 APEI 7 (S) Sa 3132 4.8875, -141.7572 NHMUK 2021.23 CCZ_067 ON400693 (COI),
ON406606 (16S)
Scyphozoa
Somaeostomeae
Ulmaridae
Ulmaridae stet. CCZ_069 APEI 7 (S) S 3133 4.8876, -141.7572 NHMUK 2021.25 CCZ_069 ON400695 (COI)
Benthic megafauna of the Clarion-Clipperton Zone 11
Classication Species Site Substrate /
Attachment
Depth (m) Coordinates
(Latitude, Longitude)
Collection Accession no. Voucher GenBank accession no.
Echinodermata
Asteroidea
Brisingida
Freyellidae
Freyastera cf. tuberculata APEI 4 (AP) S 5000 6.9879, -149.9123 NHMUK 2022.79 CCZ_087 ON400704 (COI)
APEI 4 (AP) S 5000 6.9873, -149.9331 NHMUK 2022.80 CCZ_157 ON400716 (COI)
Freyastera stet. CCZ_201 APEI 1 (AP) S 5204 11.2518, -153.6059 NHMUK 2022.81 CCZ_201 ON400730 (COI)
Forcipulatida
Zoroasteridae
Zoroaster stet. CCZ_065 APEI 7 (S) S 3132 4.8877, -141.7569 NHMUK 2022.78 CCZ_065 ON400691 (COI),
ON406607 (16S)
Crinoidea
Comatulida
Phrynocrinidae
cf. Porphyrocrinus sp. CCZ_165 APEI 4 (AP) N 5002 6.9879, -149.9327 NHMUK 2022.76 CCZ_165 ON400718 (COI),
ON406616 (16S)
Antedonidae Bathymetrinae incert. CCZ_176 APEI 4 (AP) E 5009 6.9879, -149.9326 NHMUK 2022.77 CCZ_176 ON400719 (COI),
ON406617 (16S);
APEI 1 (AP) E 5241 11.2751, -153.7444 NHMUK 2022.60 CCZ_186 ON400723 (COI),
ON406618 (16S)
Echinoidea
Aspidodiadematoida
Aspidodiadematidae
Plesiodiadema cf. globulosum APEI 1 (AP) S 5204 11.2527, -153.5848 CASIZ 229305 CCZ_196 ON400726 (COI),
ON406628 (18S)
Echinothurioida
Kamptosomatidae
Kamptosoma abyssale APEI 4 (AP) S 5040 7.0360, -149.9395 CASIZ 229306 CCZ_082 ON400701 (COI)
Holothuroidea
Persiculida
Molpadiodemidae
Molpadiodemas stet. CCZ_102 APEI 4 (S) S 3552 7.2701, -149.7827 NHMUK 2022.66 CCZ_102 ON400708 (COI)
Molpadiodemas stet. CCZ_194 APEI 1 (AP) S 5205 11.2517, -153.6055 NHMUK 2022.71 CCZ_194 ON400725 (COI)
Synallactida
Synallactidae
Synallactes stet. CCZ_153 APEI 4 (AP) S 5009 6.9704, -149.9426 NHMUK 2022.69 CCZ_153 ON400714 (COI)
Synallactidae stet. CCZ_061 APEI 7 (S) S 3132 4.8877, -141.7569 NHMUK 2022.75 CCZ_061 ON400688 (COI),
ON406640 (18S)
Synallactidae stet. CCZ_066 APEI 7 (S) S 3095 4.8896, -141.7500 NHMUK 2022.63 CCZ_066 ON400692 (COI),
ON406642 (18S)
Deimatidae Oneirophanta stet. CCZ_100 APEI 4 (S) S 3550 7.2647, -149.7740 NHMUK 2022.84 CCZ_100 ON400706 (COI),
ON406643 (16S),
ON406620 (18S)
Oneirophanta cf. mutabilis APEI 1 (AP) S 5203 11.2520, -153.5847 NHMUK 2021.20 CCZ_193 ON400724 (COI),
ON406629 (16S),
ON406619 (18S)
Elasipodida
Psychropotidae
Psychropotes verrucicaudatus APEI 4 (AP) S 4999 6.9878, -149.9119 NHMUK 2021.19 CCZ_086 ON400703 (COI)
Psychropotes dyscrita APEI 4 (AP) S 5040 7.0212, -149.9355 NHMUK 2022.83 CCZ_083 ON400702 (COI)
Benthodytes cf. sanguinolenta APEI 1 (AP) S 5245 11.2953, -153.7420 NHMUK 2022.70 CCZ_178 ON400720 (COI)
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
12
Classication Species Site Substrate /
Attachment
Depth (m) Coordinates
(Latitude, Longitude)
Collection Accession no. Voucher GenBank accession no.
Elasipodida
Psychropotidae
Benthodytes marianensis APEI 7 (AP) S 4861 5.1043, -141.8865 NHMUK 2022.82 CCZ_019 ON400682 (COI)
Elpidiidae Peniagone leander APEI 7 (AP) S 4860 5.1042, -141.8861 NHMUK 2022.61 CCZ_018 ON400681 (COI),
ON406621 (16S)
Peniagone vitrea APEI 7 (AP) S 4875 5.0442, -141.8164 NHMUK 2022.64 CCZ_077 ON400699 (COI),
ON406622 (16S)
Laetmogonidae Psychronaetes sp. CCZ_101 APEI 4 (S) S 3562 7.2647, -149.7741 NHMUK 2022.65 CCZ_101 ON400707 (COI),
ON406631 (18S)
APEI 4 (S) S 3562 7.2647, -149.7741 NHMUK 2022.68 CCZ_104 ON400710 (COI),
ON406632 (18S)
APEI 7 (S) S 3132 4.8877, -141.7570 NHMUK 2022.62 CCZ_063 ON400690 (COI),
ON406630 (18S)
APEI 4 (S) S 3562 7.2647, -149.7741 NHMUK 2022.67 CCZ_103 ON400709 (COI),
ON406639 (18S)
Laetmogone cf. wyvillethomsoni APEI 7 (S) S 3132 4.8877, -141.7569 NHMUK 2021.18 CCZ_062 ON400689 (COI),
ON406641 (18S)
Ophiuroidea
Ophioscolecida
Ophioscolecidae
Ophiocymbium tanyae APEI 1 (AP) S 5204 11.2523, -153.5848 NHMUK 2022.74 CCZ_206 ON406633 (18S),
ON406596 (28S)
Ophiocymbium cf. rarispinum APEI 1 (AP) S 5206 11.2518, -153.6059 NHMUK 2022.73 CCZ_197 ON400727 (COI)
Ophiurida
Ophiopyrgidae
Ophiuroglypha cf. irrorata APEI 7 (S) S 3239 4.9081, -141.6813 NHMUK 2021.21 CCZ_058 ON400685 (COI)
APEI 7 (S) S 3096 4.8897, -141.7500 NHMUK 2022.72 CCZ_059 ON400686 (COI)
Porifera
Hexactinellida
Amphidiscosida
Hyalonematidae
Hyalonema stet. CCZ_020 APEI 7 (AP) Sa 4856 5.1149, -141.8967 NHMUK CCZ_020 ON400683 (COI),
ON406634 (18S),
ON406608 (16S),
ON406597 (28S),
ON411254 (ALG11)
APEI 1 (AP) Sa 5245 11.2954, -153.7422 NHMUK 2022.8 CCZ_179 ON400721 (COI),
ON406609 (16S)
Hyalonema stet. CCZ_081 APEI 4 (AP) Sa 5031 7.0360, -149.9395 NHMUK 2022.9 CCZ_081 ON406610 (16S)
Lyssacinosida
Euplectellidae
Euplectellinae stet. CCZ_199 APEI 1 (AP) Sa 5202 11.2518, -153.5853 NHMUK CCZ_199 ON400729 (COI),
ON406611 (16S)
Docosaccus sp. CCZ_021 APEI 7 (AP) Sa 4860 5.1043, -141.8867 NHMUK 2022.6 CCZ_021 ON400684 (COI),
ON406635 (18S),
ON406612 (16S),
ON406598 (28S),
ON411255 (ALG11)
Benthic megafauna of the Clarion-Clipperton Zone 13
Classication Species Site Substrate /
Attachment
Depth (m) Coordinates
(Latitude, Longitude)
Collection Accession no. Voucher GenBank accession no.
Lyssacinosida
Euplectellidae
Holascus stet. CCZ_078 APEI 7 (AP) Sa 4874 5.0443, -141.8162 NHMUK 2022.7 CCZ_078 ON400700 (COI),
ON406636 (18S),
ON406613 (16S),
ON406599 (28S),
ON411256 (ALG11)
Bolosominae stet. CCZ_198 APEI 1 (AP) Sa 5205 11.2518, -153.6053 NHMUK 2022.10 CCZ_198 ON400728 (COI),
ON406637 (18S),
ON406614 (16S),
ON406600 (28S)
Sceptrulophora
Euretidae
Bathyxiphus sp. CCZ_151 APEI 4 (AP) B 5001 6.9881, -149.9321 NHMUK CCZ_151 ON400713 (COI),
ON406638 (18S),
ON406615 (16S),
ON406601 (28S)
* Temporarily stored at University of Hawai’i at Mānoa, Honolulu, USA.
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14
Only two of these nine species had been previously found in the CCZ.
Juveniles of the brittle star Ophiocymbium tanyae Martynov, 2010 were collected
in the eastern IFREMER contract area and in APEI 3, but due to their early life
stage, they lacked taxonomically informative characters and were only assigned
to family level using DNA barcoding data (Christodoulou et al. 2020). In this
study, genetic data conrmed the taxonomic identity of these specimens. e other
species previously known from the CCZ is the sea cucumber Peniagone leander
Pawson & Foell, 1986, which also occurs in the Mariana Trench (Gong et al. 2020).
Additionally, ten species were assigned as ‘cf.’ based on morphological dierences
from similar described species, or because prior collections were in other ocean
basins or dierent bathymetric ranges. ese, and the remaining 30 taxa, likely
represent undescribed species. Based on morphological and genetic evidence, two
of these undescribed taxa have also been previously reported for the eastern CCZ
(Freyastera cf. benthophila and Crinoidea sp. NHM_055 from Glover et al. (2016b)
and (Amon et al. 2017b), referred to herein as Freyastera cf. tuberculata and cf.
Porphyrocrinus sp. CCZ_165, respectively).
e in situ images taken for 53 specimens were classied into a total of 45 mor-
photypes using the standardised megafauna imagery catalogue (Simon-Lledó et al.,
pers. obs.). From these, 11 (24%) were new additions to the existing catalogue, thus
representing morphotypes exclusively (to-date) encountered in the western CCZ (i.e.,
APEIs 1, 4 and 7), while 27 (60%) had already been encountered in other areas. More
specically, nine (20%) of the 45 morphotypes encountered in the western CCZ have
also previously been found both in abyssal areas of the Kiribati EEZ (west of the areas
studied) and in the eastern CCZ. Two (4%) of the morphotypes encountered in the
western CCZ have been found in Kiribati (but not in eastern CCZ locations), whereas
16 (36%) of the western CCZ morphotypes have been encountered in the eastern
CCZ, but not in Kiribati.
Descriptions
Phylum Annelida Lamarck, 1809
Class Polychaeta Grube, 1850
Subclass Errantia Audouin & H Milne Edwards, 1832
Order Phyllodocida Dales, 1962
Suborder Aphroditiformia Levinsen, 1883
Family Aphroditidae Malmgren, 1867
Genus Laetmonice Kinberg, 1856
Currently, there are no records from ≥ 3000 m depth for the genus Laetmonice Kin-
berg, 1856, in the Clarion-Clipperton Zone (OBIS 2022). A single polychaete speci-
men was collected, for which the genetic sequence of the COI gene was generated and
used to estimate a COI-only phylogenetic tree (Fig. 2).
Benthic megafauna of the Clarion-Clipperton Zone 15
Laetmonice stet. CCZ_060
Fig. 3
Material. C-C Z • 1 specimen; APEI 7; 4.8897°N, 141.75°W;
3096 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400687 (COI);
NHMUK 2022.76; Voucher code: CCZ_060.
Description. Single specimen (Fig. 3A). Body short, ovoid, attened ventrally
and somewhat arched dorsally. Specimen ~ 1 cm at widest point and 2 cm long, with
31 chaetigers. Dorsal felt not present. Specimen caked dorsally in dense layer of pale
sediment (Fig. 3B, E), easily removed from dorsum but adhering to prostomium,
parapodia, chaetae, and pygidium, obscuring respective features. Elytra 15 pairs,
semi-translucent, smooth, and overlapping to cover dorsum (Fig. 3C). Dorsal cirri
long, ne and tapering, extending beyond parapodia. Ventrum smooth. Ventral cirri,
short, mostly broken o, not extending to base of neurochaetae. Parapodia biramous.
Notochaetae include long, dark, brassy spines (Fig. 3E) with simple, tapered tips or
with harpoon-shaped tips bearing four or ve recurved fangs (Fig. 3D); both types of
notochaetae with tuberculated shafts (Fig. 3G); neurochaetae include ner, shorter,
paler chaetae with subdistal lateral spur and distal fringe of lamentous hairs (Fig. 3F),
tips frequently broken o or covered in sediment.
Figure 2. Rooted Bayesian phylogeny for the family Aphroditidae. COI-only BEAST median consensus
tree with posterior probability (PP) and bootstrap (BS) values indicated for each node. Only values of
PP > 0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle. Nodes
not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study are
highlighted in violet.
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
16
Remarks. e presence of harpoon-shaped notochaetae supports the placement of
this specimen within the genus Laetmonice (Fauchald 1977). Forms a monophyletic
clade with other species of the genus Laetmonice based on COI sequences. Genetically
distinct from Laetmonice stet. CCZ_060, the closest match is with Laetmonice licornis
Kinberg, 1856 (90.8% similarity). Laetmonice licornis is described from shelf depths
near Sweden in the North Atlantic.
Ecology. is specimen was observed crawling on the sedimented seaoor on the
seamount of APEI 7 at 3096 m depth.
Comparison with image-based catalogue. No exactly identical Aphroditiformia
morphotypes have been so far catalogued from seabed imagery collected in the eastern
CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of
Laetmonice stet. CCZ_060 was added as a new morphotype (i.e., Laetmonice sp. indet.,
ANN_019) in the megafauna imagery catalogue. Only one other Aphroditiformia
morphotype (i.e., Aphroditidae gen. indet., ANN_022; with much larger spines
and no sediment coating), was catalogued from seabed imagery in the eastern CCZ,
also found on a seamount. In vertically-facing seabed images, Aphroditiformia
Figure 3. Laetmonice stet. CCZ_060 A in situ image B ventral surface C elytra on dorsal surface Dhar-
poon-shaped chaeta E dorsal surface F neurochaeta with fringed tips G notochaetal spine shafts. Scale
bars: 2cm (A); 0.5 cm (B, E). Image attribution: Durden and Smith (A), Wiklund, Durden, Drennan,
and McQuaid (B, E ), Drennan (C , D, F, G).
Benthic megafauna of the Clarion-Clipperton Zone 17
morphotypes could potentially be confused with plate-shaped Xenophyophore tests
(e.g., Psamminidae), particularly a dense layer of sediment is found coating specimens,
as observed in Laetmonice stet. CCZ_060 (Fig. 3A).
Phylum Arthropoda von Siebold, 1848
Subphylum Crustacea Brünnich, 1772
Superclass Multicrustacea Regier, Shultz, Zwick, Hussey, Ball, Wetzer, Martin &
Cunningham, 2010
Class ecostraca Gruvel, 1905
Subclass Cirripedia Burmeister, 1834
Infraclass oracica Darwin, 1854
Superorder oracicalcarea Gale, 2015
Order Scalpellomorpha Buckeridge & Newman, 2006
Family Scalpellidae Pilsbry, 1907
To date, there is a single record at > 3,000 m depth for the order Scalpellomorpha in
the CCZ (OBIS 2022), but no collected material. ree specimens were collected dur-
ing the DeepCCZ expedition; these belong to three dierent species from which only
one was condently assigned to a previously described species. Sequences for the COI
and 18S genes were generated for the three specimens and included in a phylogenetic
tree estimated from 18S and COI sequences (Fig. 4).
Scalpellomorpha have been commonly found in image-based megafauna surveys
across the north Pacic abyss, usually attached to sponge stalks or nodules. However,
their classication beyond family level (e.g., Scalpellidae) from seabed imagery is con-
strained by their generally small size; only large specimens (> 3 cm) which are rarely
encountered can sometimes be classied to genus level from in situ images. Conse-
quently, scalpellid specimens usually are collated into a single, generic morphotype
(i.e., Scalpellidae gen. indet., ART_010) in image-based quantitative analyses.
Genus Trianguloscalpellum Zevina, 1978
Trianguloscalpellum gigas (Hoek, 1883)
Fig. 5
Material. C-C Z • 1 specimen; APEI 7; 5.0442°N, 141.8165°W;
4874 m deep; 28 May. 2018; Smith & Durden leg.; GenBank: ON400698 (COI),
ON406624 (18S); WAM C74110; Voucher code: CCZ_074.
Description. Single specimen, found attached to a glass sponge stalk (Fig. 5A).
Capitulum elongated, longer than wide (L = 8 mm, W = 5 mm), white, with short
peduncle (2 mm) covered by large scales (Fig. 5B, C). Capitulum is formed by 14
capitular plates, and growth lines are not visible. Carina is simply bowed, narrowing
distally but being approx. the same breath proximally. e tergum is somewhat oval-
shaped, long, ~ 2× as long as wide, with pointed basal angle, carinal margin arched,
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
18
Figure 4. Rooted Bayesian phylogeny of Scalpellomorpha. Concatenated (18S, and COI) BEAST me-
dian consensus tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of
PP > 0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle. Nodes
not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study are
highlighted in violet.
Benthic megafauna of the Clarion-Clipperton Zone 19
and occludent margin straight. Scutum is somewhat quadrangular, broad, 1.5× as long
as wide, with occludent margin much longer than the lateral margin. Inframedian
latus is triangular, reaching upper latus. Carinolatus triangular, umbo apical, higher
than rostrolatus.
Remarks. e specimen appears to be a juvenile of the species T. gigas based on
the plate arrangement, although diagnostic characters are not fully developed. ere
are no sequences available on public databases for T. gigas, but the 18S gene sequence is
very similar (> 99%) to other species within the family Scalpellidae, mostly within the
subfamily Arcoscalpellinae. However, the COI sequence is highly divergent (> 15%
nucleotide divergence and > 3% amino-acid divergence) from published sequences
of other species within the subfamily. e phylogenetic tree from concatenated data
for COI and 18S recovered a well-supported clade of species of Anguloscalpellum and
Trianguloscalpellum, but did not recover the genera as monophyletic. e type material
for T. gigas was collected during the H.M.S. Challenger expedition in the middle of the
North Pacic (Station 246: 36.1667°N, 178.0°E) at 3749 m depth (Hoek 1883). e
species has been recorded from the Northwest and Southwest Pacic, and the Indian
Ocean, from 3310 to 4820 m depth (Shalaeva and Boxshall 2014).
Ecology. e specimen was collected in the sedimented abyssal plain of APEI 7,
at 4874 m depth. It was attached to a glass sponge stalk, along with another barnacle
(Catherinum cf. albatrossianum; specimen CCZ_073), and an anemone (Metridioidea
stet. CCZ_072; specimen CCZ_072).
Comparison with image-based catalogue. No exactly similar Scalpellidae
morphotypes have been so far catalogued from seabed imagery collected in the eastern
Figure 5. Trianguloscalpellum gigas (Hoek, 1883). Specimen CCZ_074: A in situ photograph, attached
to a glass sponge stalk B left C and right lateral views. Scale bars: 5 cm (A); 1 mm (B, C ). Image attribu-
tion: Durden and Smith (A), Hosie (B, C). Arrows indicate position of T. gigas (specimen CCZ_074;
lower, yellow) and Catherinum cf. albatrossianum (specimen CCZ_073; upper, green).
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
20
CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of
Trianguloscalpellum gigas was catalogued as a new morphotype (i.e., Trianguloscalpellum
gigas sp. inc., ART_033). However, given the small size of specimen CCZ_074, this
morphotype could have easily been i.e., undetected in seabed image surveys conducted
in other areas of the CCZ.
Genus Catherinum Zevina, 1978
Catherinum cf. albatrossianum (Pilsbry, 1907)
Fig. 6
Material. C-C Z • 1 specimen; APEI 7; 5.0442°N, 141.8165°W;
4875 m deep; 28 May. 2018; Smith & Durden leg.; GenBank: ON400697 (COI),
ON406623 (18S); WAM C74109; Voucher code: CCZ_073.
Description. Single specimen 21 mm long, attached to glass sponge stalk
(Fig.5A; upper, green arrow). Capitulum elongated, white, ~ 2× as long as wide
(L= 16 mm, W = 8 mm); widest in the middle, tapering towards summit and base;
short peduncle (4 mm) with small scales (Fig. 6A, B). Fourteen capitular plates
fully calcied, showing growth lines, and separated by very narrow chitinous spaces.
Carina is strongly arched in the distal half, tapering proximally, with at roof and
apical umbo. Tergum is almost a right triangle, longer than wide, with slightly convex
occludent margin. Scutum is more than twice as wide as long, with arcuate occludent
margin, with a distal indent on the lateral margin for the reception of the apex of the
upper latus; baso-lateral margin rounded and next to the infra-median latus. Upper
latus is pentagonal; with apical umbo projecting into notch on the scutum; scutal
margin in concave; very short basal margin and carinolateral margin longer than
carinal margin. Rostrolatus has an umbo projecting from the rostral margin. Rostrum
minute. Large carinolatus, ~ 2× as long as wide, umbo sub-basal, abutting base of
carina, apex slightly extending approximately one fth of the carina. Inframedian
latus is > 2× as long as the widest section, widest distally and with rostral and carinal
margins concave, with umbo sub-basal.
Remarks. Morphological characters are in accordance with the description of
C. albatrossianum. e 18S sequence matches three genera within the subfamily
Arcoscalpellinae Zevina, 1978, while the closest match (85% similarity) for the COI
sequence is to another species of Catherinum. Like, C. cf. novaezelandiae it diers
morphologically from C. tortilum, reported from the CCZ by Poltarukha and Mel’Nik
(2012), in the form of the inframedian latus. e type locality of C. albatrossianum
is o Cape Hatteras, in the northwest Atlantic, at ~ 3740 m depth, but it has been
reported for the North Atlantic, Gulf of Mexico, and Indian Ocean between 760 and
4180 m depth (Zevina and Poltarukha 2014). e original description states that the
species lacks a rostrum, however, a minute rostrum is present in the specimen examined
herein. is in addition to the documented range of this species is the reason for the
use of cf. in the identication.
Benthic megafauna of the Clarion-Clipperton Zone 21
Ecology. Specimen was collected in a muddy abyssal area of APEI 7, at 4874 m
depth. It was attached to a glass sponge stalk (Fig. 5A; upper, green arrow), along with
another barnacle (Trianguloscalpellum gigas, specimen CCZ_074; lower, yellow arrow),
and an anemone (Metridioidea stet. CCZ_072; specimen CCZ_072). It had hydrozo-
ans and two serpulid polychaetes attached to it.
Comparison with image-based catalogue. A very similar morphotype
(Catherinum sp. indet., ART_032) has been encountered (e.g., large specimens > 3 cm
in length) in seabed image surveys conducted across the eastern CCZ and in abyssal
areas of the Kiribati EEZ.
Catherinum cf. novaezelandiae (Hoek, 1883)
Fig. 7
Material. C-C Z • 1 specimen; APEI 1; 11.2751°N, 153.7444°W;
5241 m deep; 09 Jun. 2018; Smith & Durden leg.; GenBank: ON400722 (COI),
ON406625 (18S); WAM C74111; Voucher code: CCZ_185.
Description. Single specimen 14 mm long; with elongated, white capitulum,
> 2× as long as wide (L = 12 mm, W = 5 mm), and short peduncle (2 mm) with
small scales (Fig. 7). Capitulum consists of 14 fully calcied capitular plates with
Figure 6. Catherinum cf. albatrossianum (Pilsbry, 1907). Specimen CCZ_073: A left B right lateral
views. Scale bars: 2 mm. Image attribution: Hosie (A, B ).
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growth lines, separated from each other by narrow chitinous sutures. Carina is sim-
ply bowed, with at roof. Tergum is triangular, shorter on the occludent margin,
with apical umbo; apical angle is similar to angle between the carinal and scutal mar-
gins. Upper latus somewhat pentagonal, with lower edge truncated, and apical edge
reaching over the scutum; with apical umbo. Rostrolatus with umbo apical on the
rostral margin, and arched lateral margin. Inframedian latus irregular in shape, nar-
row, almost 3× as long as the widest part, with umbo sub-medial; rostral and carinal
margins concave. Carinolatus is large, ~ 2× as long as wide, with umbo sub-carinal,
above basal angle.
Remarks. Morphological characters of the capitulum conform to the description
of the genus Catherinum. e sequence for the 18S gene is similar to sequences from
other species within the same family. Another species within the genus, C. tortilum
(Zevina, 1973), originally described from the Indian Ocean at 2760 m depth has
also been recorded for the CCZ at similar depths (4872–4877 m depth; Poltarukha
and Mel’Nik 2012). In C. tortilum, the inframedian latus’ umbo is conspicuously dis-
placed laterally away from the midline. e species C. novaezelandiae is distributed in
the Western and Eastern Indian Ocean, Western Central and Southwest Pacic, from
depths 455–4800 m (Shalaeva and Boxshall 2014), but was originally described from
East Cape, New Zealand (Southwest Pacic), at 1280 m.
Ecology. e specimen was collected in the sedimented abyssal plain of APEI 1
at 5241 m depth. It was attached to a glass sponge stalk, along with a crinoid (Bathy-
metrinae inc. CCZ_176; specimen CCZ_186), a polychaete, and anemones, that was
anchored in the mud.
Figure 7. Catherinum cf. novaezelandiae (Hoek, 1883). Specimen CCZ_185: A in situ photograph
Bright C left lateral views. Scale bars: 1 cm (A); 1 mm (B, C). Image attribution: Durden and Smith
(A), Hosie (B, C ).
Benthic megafauna of the Clarion-Clipperton Zone 23
Comparison with image-based catalogue. Relatively large abundances of a very
similar morphotype (Catherinum sp. indet., ART_031) were observed in seabed image-
ry collected within abyssal areas of the Kiribati EEZ, but not in eastern CCZ surveys.
Phylum Cnidaria Hatschek, 1888
A total of 12 cnidarians w collected, belonging to six orders in two classes (Anthozoa
and Scyphozoa).
Class Anthozoa Ehrenberg, 1834
Subclass Hexacorallia Haeckel, 1896
Order Actiniaria Hertwig, 1882
To date, there are 33 records of Actiniaria found at > 3000 m depth in the CCZ (OBIS
2022), but only two of these represent collected specimens. We collected ve speci-
mens, all belonging to dierent species, and for which genetic sequences of the COI
or 18S genes were generated and included in a phylogenetic tree built from a concat-
enated alignment of 12S, 16S, 18S, 28S, COI, and COX3 (Fig. 8).
Suborder Enthemonae Rodríguez & Daly in Rodríguez et al. 2014
Superfamily Metridioidea Carlgren, 1893
Metridioidea stet. CCZ_072
Fig. 9
Material. C-C Z • 1 specimen; APEI 1; 5.0442°N, 141.8165°W;
4875 m deep; 28 May. 2018; Smith & Durden leg.; GenBank: ON400696 (COI);
NHMUK 2021.19; Voucher code: CCZ_072.
Description. Single specimen, white (Figs 5, 9). Body subcylindrical, pedal disc
modied and attached to a glass sponge stalk, oral disc is > 2× column width; with
at least two cycles of slender, tapered, long, white tentacles, almost as long as the oral
disc diameter (Fig. 5A). Tubercles are evident on the top half of the column when pre-
served, but tentacles completely retracted (Fig. 9 A, B).
Remarks. COI sequence is similar (97.3%) to other species within the subfamily
Metridioidea but based on COI we were unable to delimit species because interspecic
divergence is very low. Additionally, only a few studies have included sequences for
COI, therefore hindering comparisons based solely on this gene. e COI divergence
between Metridiodea stet. CCZ_164 and Metridiodea stet. CCZ_072 (1.95% K2P
distance) was higher than the genetic distance between other species in the family
Metridiodea (Rodriguez et al. 2014), suggesting these to belong to separate species. e
phylogenetic tree recovered both CCZ specimens within the subfamily Metridioidea
(Fig. 8), in a clade belonging to Cuticulata. Clades within Cuticulata were not well
resolved in the phylogeny, but this group includes the Graspina clade (families
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Figure 8. Rooted Bayesian phylogeny of Actiniaria. Concatenated (12S, 16S, 18S, 28S, COI, and
COX3) BEAST median consensus tree with posterior probability (PP) and bootstrap (BS) values indi-
cated. Only values of PP > 0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated
with a circle. Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated
in this study are highlighted in violet.
Benthic megafauna of the Clarion-Clipperton Zone 25
Amphiantidae, Galantheanthenidae, and Actinoscyphiidae) that is characterised by a
modied pedal disc that enables them to attach to other substrates, such as sponge
stalks (Rodriguez et al. 2014), and is advantageous in deep-sea ecosystems. Based
on this modied pedal disc, the specimen very likely belongs to a family within the
Graspina clade.
Ecology. e specimen was collected in a muddy abyssal plain in APEI 7, at
4874m depth. It was attached to a glass sponge stalk (Fig. 5A; top of stalk), along
with two barnacles (Catherinum cf. albatrossianum, specimen CCZ_073; and
Triangulloscalpellum gigas, specimen CCZ_074).
Comparison with image-based catalogue. A very similar Actiniaria morphotype
(Metridioidea fam. indet., ACT_042) mostly attached to sponge stalks, has been com-
monly encountered in seabed image surveys conducted across the eastern CCZ but not
in abyssal areas of the Kiribati EEZ.
Figure 9. Metridioidea stet. CCZ_072 A oral B lateral views. Scale bars: 5 mm (A, B ). Image attribu-
tion: Wiklund, Durden, Drennan, and McQuaid (A, B ).
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Metridioidea stet. CCZ_154
Fig. 10
Material. C-C Z • 1 specimen; APEI 4; 6.9702°N, 149.9426°W;
5009 m deep; 06 Jun. 2018; Smith & Durden leg.; GenBank: ON400715 (COI);
NHMUK 2021.27; Voucher code: CCZ_154.
Description. Single specimen, completely white when alive (Fig. 10). Body of live
specimen is more or less cylindrical, wider proximally and distally, 29 mm long. Pedal
disc is the widest, 35 mm in diameter, attached to a manganese nodule, and oral disc 24
mm in diameter (Fig. 10B). Large and small conical, tapered tentacles alternating on the
margin of the oral disc in two cycles: ~ 20 + 20, with the larger ones being approx. half the
oral disc diameter and located above the smaller tentacles (Fig. 10A). Tentacles are only
visible in in situ images (Fig. 10A), as they are fully retracted in the preserved specimen.
Ecology. is specimen was attached to a nodule in abyssal sediments in APEI 4
at 5009 m depth.
Remarks. e COI sequence is similar to sequences of species within dierent
families, but in the phylogenetic tree it is recovered within the superfamily Metridi-
oidea (Fig. 8).
Comparison with image-based catalogue. No similar Actiniaria morphotypes
had been catalogued so far from seabed imagery in the eastern CCZ or in abyssal areas
of the Kiribati EEZ. e in situ image of Metridiodea stet. CCZ_154 was hence cata-
logued as a new morphotype (i.e., Metridioidea fam. indet., ACT_044).
Figure 10. Metridioidea stet. CCZ_154 A in situ image B specimen before preservation. Scale bars:
A, B 1 cm. Image attribution: Durden and Smith (A), Wiklund, Durden, Drennan, and McQuaid (B).
Metridioidea stet. CCZ_164
Fig. 11
Material. C-C Z • 1 specimen; APEI 7; 6.988°N, 149.9326°W;
5001 m deep; 06 Jun. 2018; Smith & Durden leg.; GenBank: ON400717 (COI);
NHMUK 2021.5; Voucher code: CCZ_164
Benthic megafauna of the Clarion-Clipperton Zone 27
Description. Single specimen, white (Fig. 11A). Specimen with a short, subcylin-
drical column, with pedal and oral discs almost the same diameter (Fig. 11A). Long,
slender, tapered, white tentacles arranged in at least two cycles (Fig. 11A). When pre-
served, column is more cylindrical, almost as long as wide (H = 18 mm, oral disc
diameter = 21 mm), and tubercles are evident on the top half of the column; tentacles
completely retracted (Fig. 11B, C).
Remarks. COI sequence is very similar to Metridiodea sp. CCZ_072 and they are
recovered as sister species, in the multi-gene phylogeny, within the Cuticulata in the
superfamily Metridioidea (Fig. 8). is species very likely belongs to a family within
the Graspina clade (Amphiantidae, Galantheanthenidae and Actinoscyphiidae) based
on the modied pedal disc that allows them to attach to substrates other than rocks
(Rodriguez et al. 2014).
Ecology. is specimen was collected in muddy abyssal sediments in APEI 4 at
5001 m depth, attached to a glass sponge stalk.
Comparison with image-based catalogue. As with specimen from Metridi-
odea stet. CCZ_072, a very similar morphotype has been commonly found in sea-
bed image surveys conducted across the eastern CCZ (i.e., Metridioidea fam. indet.,
ACT_042), but it does not seem possible to dierentiate between the species Metridi-
odea stet. CCZ_072 and Metridiodea stet. CCZ_164 from in situ imagery. Morpho-
type ACT_042 is hence likely to encompass, at least, these two species in image-based
analyses conducted across the CCZ.
Superfamily Actinostoloidea Carlgren, 1932
Family Actinostolidae Carlgren, 1932
Actinostolidae stet. CCZ_183
Fig. 12
Material. C-C Z • 1 specimen; APEI 1; 11.2751°N, 153.7444°W;
5241 m deep; 09 Jun. 2018; Smith & Durden leg.; GenBank: ON406626 (18S);
NHMUK 2021.28; Voucher code: CCZ_183.
Description. Single specimen, white, attached to a nodule (Fig. 12A). Column
is very short (3 mm), cylindrical (6 mm diameter), pedal disc much wider and com-
pletely attached to the nodule. Small tubercles scatter on the column (Fig. 12B).
Remarks. Closest matches for the 18S sequence are sequences from other members
of the family Actinostolidae (> 99.3%). In the phylogenetic tree, it is also recovered in
a well-supported clade with species of the family Actinostolidae (Fig. 8). However, this
clade also includes Capnea, which has been recovered within the same clade in previous
studies (Rodriguez et al. 2014), and a specimen collected in the eastern CCZ identied
as a member of the family Hormathiidae (Hormathiidae sp. NHM_416, Dahlgren et
al, 2016). No in situ photos are available.
Ecology. is specimen was collected in abyssal sediment in APEI 1 at 5241 m
depth, attached to a polymetallic nodule.
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Actinostolidae stet. CCZ_202
Fig. 13
Material. C-C Z • 1 specimen; APEI 4; 11.2518°N, 153.6059°W;
5206 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON406627 (18S);
NHMUK 2021.22; Voucher code: CCZ_202.
Description. Single, white specimen (Fig. 13A). Specimen with short column
(4mm), pedal and oral disc approx. the same diameter (8 mm). Between 8–10 white,
long tentacles, approx. as long as the oral disc diameter (Fig. 13A). Column with scale-
like pattern in preserved specimen (Fig. 13B), with tentacles fully retracted.
Remarks. e closest matches to the 18S sequence are species in dierent subor-
ders within the Actiniaria (98.3% sequence similarity), including Hormathiidae sp.
NHM_416 from the CCZ (Dahlgren et al. 2016). However, in the phylogenetic tree
it is condently recovered within the Actinostolidae (Fig. 8), along with the specimen
Hormathiidae sp. NHM_416.
Figure 11. Metridioidea stet. CCZ_164 A in situ image of specimen CCZ_164 B detail of oral disc
C lateral view of specimen. Scale bars: 2 cm (A); 2 mm (B); 5 mm (C). Image attribution: Durden and
Smith (A), Wiklund, Durden, Drennan, and McQuaid (B, C ).
Figure 12. Actinostolidae stet. CCZ_183 A specimen attached to nodule B close-up of specimen. Scale
bars: 1 cm (A), 2 mm (B). Image attribution: Wiklund, Durden, Drennan, and McQuaid (A, B ).
Benthic megafauna of the Clarion-Clipperton Zone 29
Ecology. is specimen was attached to a polymetallic nodule collected in abyssal
sediments of APEI 1 at 5206 m depth.
Comparison with image-based catalogue. No similar Actiniaria morpho-
types have been so far catalogued from seabed imagery in the eastern CCZ or
in abyssal areas of the Kiribati EEZ. e in situ image of Actinostolidae stet.
CCZ_202 was hence catalogued as a new morphotype (i.e., Actinostolidae gen.
indet., ACT_080). However, small actiniarians (e.g., oral disc < 2 cm) are usu-
ally dicult to classify from seabed imagery as basic morphological features (e.g.,
number of tentacles) are often not clearly visible. Consequently, ACT_080 could
be potentially confused with similarly small actinian morphotypes commonly en-
countered in the eastern CCZ (i.e., Hormathiidae gen. inc., ACT_022, also with
a short pedal approx. the same diameter as the oral disc, but with 16–18 long
thintentacles).
Order Scleractinia Bourne, 1900
For Scleractinia, there are only two records at > 3000 m depth in the CCZ (OBIS
2022), with no specimens collected. A single scleractinian was collected, for which
DNA amplication was unsuccessful.
Family Fungiacyathidae Chevalier & Beauvais, 1987
Genus Fungiacyathus Sars, 1872
Fungiacyathus (Fungiacyathus) cf. fragilis Sars, 1872
Fig. 14
Material. C-C Z • 1 specimen; APEI 4; 7.2647°N, 149.774°W;
3562 m deep; 03 Jun. 2018; Smith & Durden leg.; NHMUK 2021.26; Voucher code:
CCZ_107
Description. Single specimen, solitary, and unattached, ~ 27 mm in transverse
diameter. Live specimen with tapered, transparent tentacles, longer than half the coral-
lum diameter and arranged in two or three cycles (Fig. 14A). Corallum is light brown
distally and darker proximally on live specimen (Fig. 14B, C). e base is at and the
lower cycle septa are strongly arched upward; septa are arranged in ve cycles, those of
the fth are rudimentary.
Remarks. No genetic sequences were obtained from this specimen. Morphological
characters match the genus Fungiacyathus.
Ecology. is free-living specimen was found on a sedimented area on a seamount
in APEI 4, at 3561 m depth.
Comparison with image-based catalogue. A very similar scleractinian morpho-
type (i.e., Fungiacyathus sp. indet., SCL_003) has been encountered in seabed image
surveys conducted across the eastern CCZ but not in abyssal areas of the Kiribati EEZ,
usually on sediment. As with other solitary scleractinians, this taxon could be confused
with an anemone in seabed imagery (e.g., SCL_003 was originally catalogued as an
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Figure 13. Actinostolidae stet. CCZ_202 A in situ image B detail of specimen. Scale bars: 1 cm (A);
1 mm (B). Image attributions: Durden and Smith (A), Wiklund, Durden, Drennan, and McQuaid (B).
Actiniaria from in situ images, which was addressed following the collection and analy-
sis of the specimen collected in this study).
Subclass Octocorallia Haeckel, 1866
Order Alcyonacea Lamouroux, 1812
ere are 131 records of Alcyonacea at > 3000 m depth in the CCZ, only eight of
those representing preserved specimens (OBIS 2022). We collected three specimens
belonging to three dierent species, only one assigned to a previously described spe-
cies. Genetic sequences for both 16S and COI genes were amplied for each speci-
men, and included in a concatenated alignment (16S, COI, mtMutS, NADH2) used
to generate a phylogenetic tree of Octocorallia (Fig. 15). Classication of Alcyonacea
specimens from seabed imagery is often constrained by the lack of visibility of polyp
morphology, particularly when these are small (e.g., family Primnoidae). erefore,
classication from in situ images is mostly based on broader features like the branch-
ing pattern, the length of the main stem, and/or the number, size, and positioning of
polyps on branch nodes.
Suborder Calcaxonia Grassho, 1999
Family Chrysogorgiidae Verrill, 1883
Genus Chrysogorgia Duchassaing & Michelotti, 1864
Chrysogorgia sp. CCZ_112
Fig. 16
Material. C-C Z • 1 specimen; APEI 4; 7.2874°N, 149.8578°W;
4125 m deep; 04 Jun. 2018; Smith & Durden leg.; GenBank: ON400711 (COI),
ON406602 (16S); NHMUK; Voucher code: CCZ_112.
Benthic megafauna of the Clarion-Clipperton Zone 31
Description. Wide, long, sparsely branched colony, ~ 30 cm tall from the base
(Fig. 16A, B). Polyps constricted basally on the neck (Fig. 16C–E), placed on inter-
nodes and absent from the main stem (Fig. 16A, B). Polyps are light orange when alive
(Fig. 16C, D) and white after preservation (Fig. 16E). Sclerites near the polyp base are
scale-like, but throughout the body and along the tentacle rachis are all elongate at
rods; sclerites are absent from the tentacle pinnules.
Remarks. e sequence for the COI gene is 0% divergent from a sequence of a
specimen of Chrysogorgia abludo Pante & Watling, 2011 (specimen NAS102-3, Gen-
Bank accession number GQ180138) collected at Nashville Seamount, New England
Figure 14. Fungiacyathus (Fungiacyathus) cf. fragilis Sars, 1872. Specimen CCZ_107: A in situ image
Bdorsal view of live specimen C bleached skeleton. Scale bars: 1 cm (A); 3 mm (B, C ). Image attribu-
tion: Durden and Smith (A); Wiklund, Durden, Drennan, and McQuaid (B); Bribiesca-Contreras (C).
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32
Figure 15. Rooted Bayesian phylogeny of Octocorallia. Concatenated (16S, COI, mtMutS, NADH2)
median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only
values of PP > 0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle.
Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study
are highlighted in violet.
Benthic megafauna of the Clarion-Clipperton Zone 33
Figure 16. Chrysogorgia sp. CCZ_112 A, B in situ images of colony C closed polyp on live specimen
Dopened polyp on live specimen showing light orange colouration E closed polyp of preserved specimen.
Scale bars: 2 cm (A); 0.5 mm (C–E). Image attribution: Durden and Smith (A, B ); Wiklund, Durden,
Drennan, and McQuaid (C, D ); Bribiesca-Contreras (E).
Seamounts at 2246 m depth (Station 102; 34.5828°N, 56.8433°W) included as com-
parative material during the species description (Pante and Watling 2011). In octocor-
als, it has been found that COI evolves very slowly and therefore it is not suitable for
species discrimination, with dierent species having the same haplotype (McFadden et
al. 2011). Chrysogorgia abludo is distributed in the Atlantic Ocean, and morphological
characters of the specimen collected in this study dier from the original description of
C. abludo, as well as other species within the genus and hence considered a potentially
new species In the phylogenetic tree (Fig. 15) the specimen was also recovered along
with another specimen of Chrysogorgia, supporting its placement within the genus.
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Comparison with image-based catalogue. No similar Alcyonacea morphotypes
have been catalogued so far from seabed imagery in the eastern CCZ or in abyssal areas
of the Kiribati EEZ. Consequently, the in situ image of Chrysogorgia sp. CCZ_112 was
catalogued as a new morphotype (i.e., Chrysogorgia sp. indet., ALC_017).
Ecology. e specimen was attached to polymetallic crust on the slope of a sea-
mount in the APEI 4, at 4124 m depth.
Family Mopseidae Gray, 1870
Mopseidae sp. CCZ_088
Fig. 17
Material. C-C Z • 1 specimen; APEI 4; 7.0089°N, 149.9109°W;
5018 m deep; 02 Jun. 2018; Smith & Durden leg.; GenBank: ON400705 (COI),
ON406603 (16S); NHMUK XXX; Voucher code: CCZ_088.
Description. Single specimen, with white axis and polyps; polyps standing per-
pendicular to the axis when alive (Fig. 17A). Colony is long, ~ 45 cm tall, and un-
branched (Fig. 17A, B). Polyps are tall, ~ 2 mm, clavate, and standing parallel to the
branch (Fig. 17C).
Remarks. Both 16S (0.3% K2P) and COI (0.6% K2) sequences are very similar
to Mopseinae sp. NHM_330 (Dahlgren et al. 2016), which morphologically resembles
the genus Primnoisis. e specimen from the western CCZ likely belongs to the same
genus but based on genetic and morphological dierences represents a dierent species
from that of the eastern CCZ.
Figure 17. Mopseidae sp. CCZ_088 A in situ image B whole colony attached to a nodule C detail of
polyps before preservation. Scale bars: 5 cm (A); 2 cm (B); 5 mm (C). Image attribution: Durden and
Smith (A); Wiklund, Durden, Drennan, and McQuaid (B, C ).
Benthic megafauna of the Clarion-Clipperton Zone 35
Ecology. e specimen was found attached to a nodule in abyssal sediments of
APEI 4 at 5018 m depth.
Comparison with image-based catalogue. No similar Alcyonacea morphotypes
had been catalogued so far from seabed imagery in the eastern CCZ or in abyssal areas
of the Kiribati EEZ. Consequently, the in situ image of CCZ_088 was catalogued as
a new morphotype (i.e., Mopseidae gen. indet., ALC_018). However, it is often not
possible to determine whether such small and abundant polyps are arranged in pairs
or not, or the actual orientation of these with regards to the axis from seabed images.
Family Primnoidae Milne Edwards, 1857
Genus Calyptrophora Gray, 1866
Calyptrophora distolos Cairns, 2018
Fig. 18
Material. C-C Z • 1 specimen; APEI 4; 7.2874°N, 149.8578°W;
4125 m deep; 04 Jun. 2018; Smith & Durden leg.; GenBank: ON400712 (COI),
ON406604 (16S); USNM 1550968; Voucher: CCZ_131.
Description. Branching uniplanar, colony ~ 20.8 cm tall, with polyps perpen-
dicular to the stem in in situ images (Fig. 18A). Downward-oriented polyps, arranged
parallel to the branch, mostly paired, but a few whorls with three to four polyps are
present; polyps are ~ 2.7 mm tall and with an operculum longer than either of the body
wall scales (Fig. 18B, C).
Remarks. Morphological characters are concordant with the description of
Calyptrophora distolos (Cairns 2018). In addition to the paired polyps mentioned in
the species description, this specimen also presents a few whorls with three or four
polyps (Fig. 18C). Polyps are downward-oriented, therefore belonging to the wyvillei
complex (Cairns 2018). e species is most similar to C. persephone Cairns, 2015,
which has been described for the UK-1 and BGR areas in the CCZ (Cairns 2015).
However, C.persephone is characterised as having polyps oriented upwards, therefore
belonging to the japonica complex, and that are consistently arranged in whorls of
three or four, with each basal scale bearing two prominent distal spines. Calyptrophora
distolos was described from the Enigma Seamount, south of Guam, at 3737 m depth,
and has also been recorded for American Samoa at 2994 m depth (Cairns 2018). ere
are no genetic sequences available for other specimens of C. distolos, but the sequences
generated here cluster with other species of the genus (Fig. 15). However, the genus
was not recovered as monophyletic.
Ecology. e specimen was found attached to a polymetallic crust on the slope of
a seamount on APEI 4, at 4124 m depth.
Comparison with image-based catalogue. A similar primnoid morphotype (i.e.,
Calyptrophora distolos sp. inc., ALC_016) was catalogued from seabed imagery (also
collected on a seamount) in the eastern CCZ (e.g., Cuvelier et al. 2020), but not in
abyssal areas of the Kiribati EEZ.
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Order Pennatulacea Verrill, 1865
A total of 79 records of Pennatulacea occurring at > 3000 m depth in the CCZ have
been recorded in OBIS, but none represent preserved specimens (OBIS 2022). We
recovered a single specimen, for which sequences of both 16S and COI genes were
obtained, and which were included in the phylogenetic analysis of the Octocorallia
(Fig. 15).
Suborder Sessiliorae Kükenthal, 1915
Family Protoptilidae Kölliker, 1872
Genus Protoptilum Kölliker, 1872
Protoptilum stet. CCZ_068
Fig. 19
Material. C-C Z • 1 specimen; APEI 7; 4.8897°N, 141.75°W;
3096 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400694 (COI),
ON406605 (16S); NHMUK 2021.24; Voucher: CCZ_068
Description. Single specimen, ~ 12 cm tall, narrow sea pen; in situ colouration
orange with whitish polyps (Fig. 19A). Two rows, opposite to each other, of elongated
polyp calyces along the rachis (Fig. 19B, C).
Figure 18. Calyptrophora distolos Cairns, 2018. Specimen CCZ_132: A in situ image B whole colony
Cdetail of polyps before preservation. Scale bars: 2 cm (A, B ); 5 mm (C). Image attribution: Durden and
Smith (A); Wiklund, Durden, Drennan, and McQuaid (B, C ).
Benthic megafauna of the Clarion-Clipperton Zone 37
Figure 19. Protoptilum stet. CCZ_068 A in situ image B whole colony C detail of polyps before preser-
vation. Scale bars: 1 cm (A); 5 mm (B); 2 mm (C). Image attribution: Durden and Smith (A); Wiklund,
Durden, Drennan, and McQuaid (B, C).
Figure 20. Rooted Bayesian phylogeny of Ceriantharia. Concatenated (12S, 16S, 18S, 28S, and COI) median
consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of PP >
0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle. Nodes not recovered
on the RAxML tree are indicated with a hyphen. Sequences generated in this study are highlighted in violet.
Remarks. e COI sequence forms a clade with sequences from Protoptilum (<1%
genetic divergence), a genus within the family Protoptilidae, while the 16S sequence
is very similar to sequences of Protoptilum and Distichoptilum, both genera within the
same family. In the phylogenetic tree, the family Protoptilidae was not recovered as
monophyletic, but the CCZ specimen was recovered (with 1.00 posterior probability)
as sister to Protoptilum carpenterii Kölliker, 1872.
Ecology. e specimen was found anchored to soft sediment on a seamount of
APEI 7, at 3096 m depth.
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Comparison with image-based catalogue. No similar Pennatulacea morphotypes
have been catalogued so far from seabed imagery in the eastern CCZ or in abyssal areas
of the Kiribati EEZ. Consequently, the in situ image of Protoptilum stet. CCZ_068
was catalogued as a new morphotype (i.e., Protoptilum sp. indet., PEN_024). In seabed
images, PEN_024 can resemble other single-branched sea pens or even soft corals.
Subclass Ceriantharia Perrier, 1893
Order Spirularia den Hartog, 1977
To date, there are no records from a minimum of 3000 m depth in the CCZ for the
order Spirularia (OBIS 2022). We recovered a single specimen, for which the COI and
16S genes were successfully amplied and included in a concatenated matrix (12S,
16S, 18S, 28S, and COI) to estimate a phylogenetic tree of the Ceriantharia (Fig. 20).
Spirularia stet. CCZ_067
Fig. 21
Material. C-C Z • 1 specimen; APEI 7; 4.8875°N, 141.7572°W;
3132 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400693 (COI),
ON406606 (16S); NHMUK 2021.23; Voucher: CCZ_067.
Description. Single specimen, unattached, tube-dweller with tentacles extended
above the sediment in situ (Fig. 21A). Very long, conical, tapering, reddish brown
tentacles; capitulum whitish when alive (Fig. 21A). Column is 12 mm in height and 5
mm in width excluding tentacles (Fig. 21B). Tube consisting of soft sediment.
Remarks. e closest matches to the COI and 16S sequences were sequences
from other members of the family Cerianthidae: Pachycenrianthus, Cerianthus,
Ceriantheromorphe. However, in the concatenated phylogeny, it forms a clade
with Boctrunidifer sp. 1 and Ceriantheopsis americanus, belonging to the families
Botrucnidiferidae and Cerianthidae, respectively (Fig. 20). As Forero-Mejia et al. (2019)
recovered both families as non-monophyletic and a revision of these is suggested, we
were unable to assign it to a family.
Ecology. e specimen was found buried in the sediment on a seamount in APEI
7, at 3132 m depth.
Comparison with image-based catalogue. A very similar Ceriantharia morpho-
type (i.e., Spirularia sp. indet., CER_001) has been commonly encountered in seabed
image surveys conducted across the eastern CCZ, always found semi-buried with the
tentacles extending above the sediment surface.
Class Scyphozoa Goette, 1887
For the class Scyphozoa, there are currently 128 records from > 3000 m depth in the
CCZ, but none represent preserved specimens (OBIS 2022). We collected a single spec-
imen, for which the sequence for the COI gene was successfully amplied and included
in a multi-gene phylogeny (16S, 18S, 28S, and COI) of the Scyphozoa (Fig. 22).
Benthic megafauna of the Clarion-Clipperton Zone 39
Subclass Discomedusae Haeckel, 1880
Order Somaeostomeae Agassiz, 1862
Family Ulmaridae Haeckel, 1880
Ulmaridae stet. CCZ_069
Fig. 23
Material. C-C Z • 1 specimen; APEI 7; 4.8876°N, 141.7572°W;
3133 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400695 (COI);
NHMUK 2021.25; Voucher: CCZ_069.
Description. Single specimen, ~ 4.5 cm in diameter; with transparent bell and light
brown tentacles in situ (Fig. 23A). Rhopalia are evident around the bell (Fig.23B,C).
Figure 21. Spirularia stet. CCZ_067 A in situ image B specimen before preservation. Scale bars: 1 cm
(A); 2 mm (B). Image attribution: Durden and Smith (A); Wiklund, Durden, Drennan, and McQuaid (B).
Figure 22. Rooted Bayesian phylogeny of Scyphozoa. Concatenated (16S, 18S, 28S, and COI) median con-
sensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of PP >
0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle. Nodes not recovered
on the RAxML tree are indicated with a hyphen. Sequences generated in this study are highlighted in violet.
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Remarks. Only the sequence for the COI gene was successfully amplied, but
none of the matches on public databases were informative. In the phylogenetic tree
(Fig. 22), the CCZ specimen was recovered in a clade with other members of the class
Discomedusae. As both the Rhizostomeae and Semaeostomeae were not well support-
ed, the specimen was not condently assigned to any of both orders based on COI only.
However, the specimen morphologically resembles an undescribed ulmariid scypho-
zoan (Somaeostomeae) that was observed in the New Britain Trench (Gallo et al. 2015).
Ecology. e specimen was found on the sediment of a seamount in APEI 7 at
3095–3132 m depth. A similar species of ulmariid from the New Britain Trench was
found to skim the seaoor to feed on particulates on the sediment (Gallo et al. 2015).
Comparison with image-based catalogue. No similar Ulmaridae morphotypes have
been catalogued so far from seabed imagery in the eastern CCZ or in abyssal areas of the
Kiribati EEZ. Consequently, the in situ image of Ulmaridae stet. CCZ_069 was cata-
logued as a new morphotype (i.e., Ulmaridae gen. indet., SCY_010). A similarly shaped
Ulmaridae morphotype (e.g., Ulmaridae gen. indet., SCY_009; opaque reddish bell, dark
brown tentacles encircled with a white ring, and dark rhopalia around the bell), also even-
tually found crawling on the seabed surface, was previously catalogued from seabed image-
ry in nodule eld areas of the eastern CCZ. When photographed lying on the seabed (as
opposed to swimming in the water column), SCY_019 and SCY_010 may resemble an
anemone, particularly in images collected at high altitude above the seabed (e.g., > 5 m).
Figure 23. Ulmaridae stet. CCZ_069 A in situ image B specimen before preservation C rhopalia. Scale
bars: 1 cm (A); 5 mm (B). Image attribution: Durden and Smith (A); Wiklund, Durden, Drennan, and
McQuaid (B, C ).
Phylum Echinodermata
Class Asteroidea de Blainville, 1830
ere are currently 245 records of sea stars occurring at a minimum of 3000 m depth
in the CCZ, with only ve of those representing preserved specimens (OBIS 2022).
Four specimens were collected on the western CCZ, and sequences of the barcoding
gene COI were generated for all of them, and 16S for a single specimen. ese were
included in a concatenated alignment of 12S, 16S, 18S, COI, and H3 used to estimate
a phylogenetic tree (Fig. 24).
Benthic megafauna of the Clarion-Clipperton Zone 41
Figure 24. Rooted Bayesian phylogeny of Asteroidea. Concatenated (12S, 16S, 18S, COI, and H3)
median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only
values of PP > 0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle.
Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study
are highlighted in violet.
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Superorder Forcipulatacea Blake, 1987
Order Brisingida Fisher, 1928
Family Freyellidae Downey, 1986
Genus Freyastera Downey, 1986
Freyastera cf. tuberculata (Sladen, 1889)
Fig. 25
Material. C-C Z • 1 specimen; APEI 4; 6.9879°N, 149.9123°W;
5000 m deep; 02 Jun. 2018; Smith & Durden leg.; GenBank: ON400716 (COI);
NHMUK 2022.80; Voucher code: CCZ_157 • 1 specimen; APEI 4; 6.9873°N,
149.9331°W; 5000 m deep; 06 Jun. 2018; Smith & Durden leg.; GenBank: ON400704
(COI); NHMUK 2022.79; Voucher code: CCZ_087.
Comparative material. P O • 1 specimen, holotype of Freyella
benthophila Sladen, 1889; mid-South Pacic; 39.6833°S, 131.3833°W; 4663 m
deep; Challenger Expedition, Stn. 289; NHMUK 1890.5.7.1078. A O
•1specimen, syntype of Freyella tuberculata Sladen, 1889; between west coast of Africa
and Ascencion Islands; 22.3°N, 22.0333°W; 4389 m deep; Challenger Expedition,
Stn. 346; NHMUK 1890.5.7.1077. • 1 specimen, syntype of Freyella tuberculata;
between Canary Islands and Cape Verde Islands; 2.7° S, 14.6833°W; 4298 m deep;
Challenger Expedition, Stn. 89; NHMUK 1890.5.7.1076.
Description. Two specimens (R = 106 mm, r = 3 mm; R = 164 mm, r = 6 mm);
live specimens whitish on both actinal and abactinal surfaces, tube feet transparent with
bright orange attened discs (Fig. 25A, B). Disc is small, somewhat rounded, slightly
orange on actinal and abactinal surfaces (Fig. 25E, F); with six long, slender arms
(Fig.25A–C); lacking furrow spines (Fig. 25D). Each abactinal plate on the genital area
bears a single spinelet (Fig. 25E), covered with a membrane with pedicellariae. Each
mouth plate has two oral spines covered by a clear membrane bearing pedicellariae
(Fig. 25F); one located on the adoral margin of the mouth plate and the suboral spine
located above the centre of the mouth plate.
Remarks. e COI sequences were very similar to sequences of Freyastera cf.
benthophila (Sladen, 1889) collected in the UK-1 contract area from the CCZ (Glover
et al. 2016a), and which were recovered in a single clade (Fig. 24). Only arm segments
were recovered from the UK-1 specimens, and although they were found to resemble
F. benthophila, the whole specimens collected in the western CCZ dier from the
original description for the species. Only ve species are known for having six rays:
F. sexradiata (Perrier, 1885), F. benthophila, F. tuberculata (Sladen, 1889), F. basketa
Zhang et al., 2019, and F. delicata Zhang et al., 2019. However, F. benthophila is easily
distinguished from the other two species by its abactinal armament; each abactinal plate
bearing two or three spinelets covered with a simple membrane with no pedicellariae
(Sladen 1889). e specimens from the CCZ have abactinal spinelets covered by a
membrane that bears pedicellariae (Fig. 25E). ey also dier from F. benthophila
in having the spines on the adoral margin of the mouth-plates covered by a clear
Benthic megafauna of the Clarion-Clipperton Zone 43
Figure 25. Freyastera cf. tuberculata (Sladen, 1889). Specimen CCZ_175: A in situ image C whole specimen
D ventral surface of the arms before preservation. Specimen CCZ_087: B in situ image E details of dorsal disc
F ventral disc surface before preservation. Scale bars: 2 cm (A, B ); 1 cm (C); 2 mm (D); 1 mm (E); 0.5mm
(F). Image attribution: Durden and Smith (A, B); Wiklund, Durden, Drennan, and McQuaid (C–F).
membrane bearing pedicellariae instead of an opaque membrane with no pedicellariae
(Downey 1986). In addition, the suboral spines are located above the centre of the
mouth plate (Fig.25F), as in F.tuberculata, and not below the centre of the mouth
plate as described for F. benthophila (Downey 1986). Syntypes from F. tuberculata
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are from the Atlantic Ocean (Sladen 1889), but it has been reported for the Eastern
Tropical Pacic (0.05°N, 117.25°W) at 4243 m depth (Downey 1986). Unfortunately,
there are no genetic sequences available for this species, but COI sequences from
CCZ specimens are highly divergent from the sequence of F. benthophila collected in
the Mariana Trench (K2P distance: 13–14%). In the phylogenetic tree they are also
recovered in dierent clades, very close to another species reported herein, and to F.
delicata and Freyastera sp. Yap (in Zhang et al. 2019) (Fig. 24). e specimen collected
here represents the same species as found in the eastern CCZ, Freyastera cf. benthophila
(Glover et al. 2016b).
Ecology. One specimen was observed on the sedimented seaoor (CCZ_157),
while another was sitting on a nodule with the actinal surface against the muddy sea-
oor and lifting the tip of the arms like a basket (CCZ_087). Both seastars were col-
lected on abyssal sediments of APEI 4 at 5000 m depth. During morphological exami-
nation of these samples, the exoskeleton of a large (> 6 mm long), digested copepod
was found in the stomach of specimen CCZ_157.
Freyastera stet. CCZ_201
Fig. 26
Material. C-C Z • 1 specimen; APEI 1; 11.2518°N, 153.6059°W;
5204 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400730 (COI);
NHMUK 2022.81; Voucher code: CCZ_201.
Comparative material. P O • 1 specimen, holotype of Freyella
benthophila Sladen, 1889; mid-South Pacic; 39.6833°S, 131.3833°W; 4663 m
deep; Challenger Expedition, Stn. 289; NHMUK 1890.5.7.1078. A O
•1specimen, syntype of Freyella tuberculata Sladen, 1889; between west coast of Africa
and Ascencion Islands; 22.3°N, 22.0333°W; 4389 m deep; Challenger Expedition,
Stn. 346; NHMUK 1890.5.7.1077. • 1 specimen, syntype of Freyella tuberculata; be-
tween Canary Islands and Cape Verde Islands; 2.7°S, 14.6833°W; 4298 m deep; Chal-
lenger Expedition, Stn. 89; NHMUK 1890.5.7.1076.
Description. Single specimen, with very small disc and six long, slender, tapered
arms (R = 190 mm, r = 5 mm; Fig. 26A). Specimen before preservation has a slightly
orange adoral disc surface, white arms, and bright orange tube feet discs (Fig. 26A–D).
Disc is somewhat rounded, covered with short, scattered spines covered by a mem-
brane bearing pedicellariae (Fig. 26B). Arms with long, slender lateral spines, also cov-
ered with a membrane bearing pedicellariae (Fig. 26C). Each abactinal plate on the
genital area bears a one to few spinelets, completely covered with a membrane with
pedicellariae. Each mouth plate has two oral spines covered by a clear membrane bear-
ing pedicellariae; one located on the adoral margin of the mouth plate and the suboral
spine located above the centre of the mouth plate.
Remarks. e COI sequence is 4% divergent from the two specimens of Freyastera
cf. tuberculata reported herein, and hence considered a separate species. It is also
divergent (> 4% K2P distance) to sequences of other species of Freyastera, but forms a
Benthic megafauna of the Clarion-Clipperton Zone 45
monophyletic clade with those, conrming its placement within the genus (Fig. 24).
Morphologically it resembles Freyastera cf. tuberculata, but dier in having slightly
shorter and more scattered spinelets on the abactinal surface of the disc. Also, the
spinelets on the abactinal plates on the genital area are more numerous, and completely
covered by a membrane bearing pedicellariae, instead of having a membrane that does
not cover the spine all the way down to the base as in F. cf. tuberculata. In addition,
the genetic distance with specimens of that species corresponds to the genetic distance
between morphologically distinct species and hence considered a separate species.
Ecology. e specimen was collected on the sedimented abyssal plain of APEI 1 at
5204 m depth, with arms curled up like a basket (Fig. 26A).
Comparison with image-based catalogue. Freyastera spp. are commonly found in
image-based megafauna assessments across the CCZ (e.g., Amon et al. 2016; Amon et
al. 2017b), abyssal areas of the Kiribati EEZ, and other areas of the Pacic abyss (e.g.,
Peru Basin: Simon-Lledó et al. 2019a), both in nodule elds and in seamount areas.
e relatively large size of adult specimens facilitates the detection of these brisingids
even upon imagery collected at high altitudes (> 5 m) above the seabed. However,
only one Freyastera sp. morphotype (e.g., Freyastera sp. indet., AST_002) has been
catalogued so far, as dierences in structure of the abactinal armament and/or the
suboral spines are not visible from seabed images.
Figure 26. Freyastera stet. CCZ_201 A in situ image B whole specimen C dorsal disc surface D ventral
disc surface. Scale bars: 2 cm (A); 2 mm (B); 1 cm (C); 2 mm (D). Image attribution: Durden and Smith
(A); Wiklund, Durden, Drennan, and McQuaid (B–D).
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Order Forcipulatida Perrier, 1884
Family Zoroasteridae Sladen, 1889
Genus Zoroaster Wyville omson, 1873
Zoroaster stet. CCZ_065
Fig. 27
Material. C-C Z • 1 specimen; APEI 7; 4.8877°N, 141.7569°W;
3132 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400691 (COI),
ON406607 (16S); NHMUK 2022.78; Voucher code: CCZ_065.
Description. Single specimen (R = 16.6 cm, r = 1.3 cm). Actinal and abacti-
nal surfaces are bright orange when alive, with ambulacrum slightly darker orange
(Fig. 27A–D). Small disc; with ve long, slender arms, gradually tapering distally (Fig.
27B). Carinal plates bear conical primary spines, forming a single longitudinal row
that runs along the arm (Fig. 27A, C).
Remarks. Morphological characters are concordant with the description of the ge-
nus Zoroaster. e phylogenetic analyses also recovered the specimen in a well-support-
ed clade with other species of the genus (Fig. 24). However, COI divergence between
species in the genus is very low (K2P distance ≈ 1–2%) and species-level clades were not
recovered in the phylogeny, preventing us from assigning it to any species based on COI
sequences. e closest match to the COI sequence of the CCZ specimen is a sequence
from the long-armed morphotype (K2P distance 0.6%, GenBank accession number
AY225785.1) identied for Z. fulgens Wyville omson, 1873 in the Porcupine Sea-
bight, Atlantic Ocean (50.1987°N, 14.6593°W; 4001 m depth; Howell et al. 2004).
Although this value is concordant with intraspecic divergence in the genus, the 16S se-
quences divergence between the CCZ specimen and the long-armed morphotype (K2P
1.1%) is larger than between the long-armed morphotype and Z. spinulosus Fisher,
1906 (K2P 0.0%) and between Z. spinulosus and Z. ophiactis Fisher, 1916 (K2P 0.3%).
Ecology. e specimen was found partially buried in the sediment on the sea-
mount on APEI 7 at 3133 m depth.
Comparison with image-based catalogue. No similar Zoroasteridae morpho-
types have been catalogued so far from seabed imagery in the eastern CCZ nor in
abyssal areas of the Kiribati EEZ. Consequently, the in situ image of Zoroaster stet.
CCZ_065 was catalogued as a new morphotype (i.e., Zoroaster sp. indet., AST_025).
Class Crinoidea
To date, there are 66 records of crinoids occurring deeper than 3000 m in the CCZ,
with only seven of these representing preserved specimens (OBIS 2022). ree speci-
mens, belonging to two species, were collected in the western CCZ. e barcoding
gene COI was amplied for all specimens, and sequences were included in a concat-
enated alignment (16S, 18S, 28S, COI, and CytB) used to estimate a phylogenetic tree
for the class (Fig. 28).
Benthic megafauna of the Clarion-Clipperton Zone 47
Subclass Articulata Zittel, 1879
Order Comatulida
Suborder Bourgueticrinina Sieverts-Doreck, 1953
Family Phrynocrinidae AH Clark, 1907
Subfamily Porphyrocrininae AM Clark, 1973
Genus Porphyrocrinus Gislén, 1925
cf. Porphyrocrinus sp. CCZ_165
Fig. 29
Material. C-C Z • 1 specimen; APEI 4; 6.9879°N, 149.9327°W;
5002 m deep; 06 Jun. 2018; Smith & Durden leg.; GenBank: ON400718 (COI),
ON406616 (16S); NHMUK 2022.76; Voucher code: CCZ_165.
Description. Single specimen, attached to a nodule by a xenomorphic stalk
(Fig.29A). Crown (Fig. 29C) detached from stalk (Fig, 29B); L = 32 mm, composed
of a crown and short proximal part of stalk. Proximal stalk composed of 5 very thin
discoidal columnals up to 0.54 mm in diameter. Basal circlet truncated conical with
distal diameter 0.54 mm and adoral diameter 0.78 mm; basals ve, pentagonal
Figure 27. Zoroaster stet. CCZ_065 A in situ image B abactinal view of whole specimen C detail of
abactinal surface D detail of actinal surface before preservation. Scale bars: 3 cm (A); 2 cm (B); 5 mm
(C , D ). Image attribution: Durden and Smith (A); Wiklund, Durden, Drennan, and McQuaid (B–D).
Guadalupe Bribiesca-Contreras et al. / ZooKeys 1113: 1–110 (2022)
48
Figure 28. Rooted Bayesian phylogeny of Crinoidea. Concatenated (16S, 18S, 28S, COI, and CytB)
median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only
values of PP > 0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle.
Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study
are highlighted in violet.
Benthic megafauna of the Clarion-Clipperton Zone 49
in shape, with sunken lateral edges. Marked angle (~ 120°) between basals and
radials. Radials ve, pentagonal in shape; distal diameter 1.48 mm. Crown has
ve undivided arms. IBr1 are in close apposition with thin lateral anges. Brachial
formula 1+2 3+4 5+6 7+8 8+9 etc. First pinnule at IBr6; following pinnules every
second ossicle; P1 has eight segments 4.04 mm in length; P2 is similar with eight
pinnulars and 4.9 mm in length; P1 and P2 display lateral discoidal plates along
ambulacral groove.
Remarks. Morphological characters are concordant with those of the family
Phrynocrinidae and the genus Porphyrocrinus as understood by Messing (2016). is
is the rst record of the genus in the Eastern Pacic. Only two specimens have been
previously recorded from similar depths but collected from the Eastern Atlantic and
attributed to Porphyrocrinus cf. incrassatus (Eléaume et al. 2012). In the phylogenetic tree
the specimen is recovered in a monophyletic clade with other sequences from members
of the family (Fig. 28) and represents a new species. Based on genetic divergence of
the COI gene (0.5% K2P), the specimen found in the eastern CCZ (Crinoidea sp.
NHM_055; Glover et al. 2016b) belongs to the same species. However, the specimen
in Glover et al. (2016b) was not identied to family level or lower taxonomic level due
to its early developmental stage, lacking key diagnostic morphological features.
Ecology. e specimen was found attached to a nodule in the abyssal sediments of
APEI 4 at 5001 m depth.
Comparison with image-based catalogue. No similar Comatulida morphotypes
have been catalogued so far from seabed imagery in the eastern CCZ or in abyssal areas
of the Kiribati EEZ. Consequently, the in situ image of CCZ_065 was catalogued
as a new morphotype (i.e., Porphyrocrinus sp. indet., CRI_008). Note however, that
the in situ image of CCZ_065 was collected from an oblique angle and zoomed-in
camera, generating a detailed view of a specimen that, owing to its small size, would
be otherwise dicult to identify in quantitative assessments, e.g., where images are
usually collected vertically-facing, fully zoomed out, and at a higher altitude above
the seabed.
Figure 29. cf. Porphyrocrinus sp. CCZ_165 A in situ image B xenomorph stalk attached to a polymetal-
lic nodule C detached crown before preservation. Scale bars:1 cm (A). Image attribution: Durden and
Smith (A); Wiklund, Durden, Drennan, and McQuaid (B, C ).
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Superfamily Antedonoidea Norman, 1865
Family Antedonidae Norman, 1865
Subfamily Bathymetrinae AH Clark, 1909
Bathymetrinae inc. CCZ_176
Fig. 30
Material. C-C Z • 1 adult specimen; APEI 4; 6.9879°N,
149.9326°W; 5009 m deep; 06 Jun. 2018; Smith & Durden leg.; GenBank:
ON400719 (COI), ON406617 (16S); NHMUK 2022.77; Voucher code: CCZ_176.
• 1 specimen pentacrinoid stage; APEI 1; 11.2751°N, 153.7444°W; 5241 m deep; 09
Jun. 2018; Smith & Durden leg.; GenBank: ON400723 (COI), ON406618 (16S);
NHMUK 2022.60; Voucher code: CCZ_186.
Description. Two specimens, one adult (CCZ_176; Fig. 30A, B) and one pen-
tacrinoid stage (CCZ_186; Fig. 30C, D), both whitish when alive and attached to a
glass sponge stalk. Adult with 10 arms; centrodorsal low conical. Cirri ~ 17, length
7.5mm; c1 W > L; c2 W = L; c3 longest L = 0.95 mm, W at centre of ossicle = 0,25, W
distal = 0,45; following cirrals decreasing in length to c8 or c9; c3 to c17 with everted
distal edge; c8 to c14 with a spine on distal edge; c17 slightly longer than wide; claw
same length as c17; opposing spine small. No basal visible. Radial 5, visible, extending
beyond the rim of centrodorsal. First brachitaxis of two ossicles well separated laterally.
Ibr1 rectangular slightly incised by Ibr2; Ibr2 axillery, losangic. Subsequent brachials
very long; syzygies at 3+4, 9+10. First pinnule P1 on br2, 14 segments very thin and
slender, composed of very long segments starting at p3 with L < 6× W. In pentacrinoid
stage, ve arms are visible, with orals, and stalk.
Remarks. Morphological characters are concordant with those of the subfamily
Bathymetrinae in the family Antedonidae. e closest match (2.7% K2P) to the COI
sequences is a sequence of Psathyrometra fragilis (AH Clark, 1907) from Rodriguez
Seamount (1887 m; SIO-BIC E4433), within the family Zenometridae. However,
in the phylogenetic analysis the specimens were recovered in a dierent clade from
Psathyrometra spp. (Fig. 28), but in a well-supported clade with two species (Crinoidea
sp. NHM_056, Crinoidea sp. NHM_300) from the eastern CCZ (Glover et al.
2016b). e two species previously recorded in the eastern CCZ were delimited only
from genetic sequences, as they seem to be early pentacrinoid stages and thus lack
morphological characters for identication. However, based on the genetic divergence
values with the species Bathymetrinae inc. CCZ_176 (~ 10% K2P), the two eastern
CCZ species are most likely members of the subfamily Bathymetrinae.
Ecology. e adult specimen was found attached to a glass sponge stalk (Fig. 11A),
along with an anemone, in abyssal sediments of APEI 4 at 5001 m depth. After careful
examination of the material in the laboratory, a pentacrinoid stage was found attached
to a sponge stalk (Figs 6A, 30B), along with the cirriped Catherinum cf. novaezelandiae
(specimen CCZ_185) and the anemone Metridioidea stet. CCZ_164, in abyssal sedi-
ments of APEI 1 at 5241 m depth.
Benthic megafauna of the Clarion-Clipperton Zone 51
Figure 30. Bathymetrinae inc. CCZ_176 A side view of adult specimen. Specimen CCZ_186 B pentacri-
noid stage attached to a glass sponge stalk C pentacrinoid stage. Scale bars: 5 mm (A); 1 mm (B); 0.5 mm
(C). Image attribution: Wiklund, Durden, Drennan, and McQuaid (A, B ); Bribiesca-Contreras 2019 (C).
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Comparison with image-based catalogue. A very similar Comatulida morpho-
type (i.e., Bathymetrinae gen. indet., CRI_001) has been commonly encountered in
seabed image surveys conducted across the eastern CCZ, both in nodule elds and in
seamount areas (Amon et al. 2017b). In contrast, CRI_001 was not encountered in
image surveys conducted within abyssal areas of the Kiribati EEZ, where the presence
of Crinoids was substantially lower than at the eastern CCZ (e.g., only nine speci-
mens representing three morphotypes encountered in ~ 15,000 m2 of seabed surveyed;
Simon-Lledó et al. 2019d).
Class Echinoidea
To date, there are 1455 records of echinoids occurring deeper than 3000 m in the CCZ,
11 of these representing preserved specimens (OBIS 2022). Two specimens belonging
to dierent species were collected. Sequences for the barcoding gene COI were suc-
cessfully amplied for both specimens and included in a COI-only phylogenetic tree.
Figure 31. Phylogenetic tree of Echinoidea. COI-only median consensus BEAST tree with posterior
probability (PP) and bootstrap (BS) values indicated. Only values of PP > 0.70 and BS > 50 are shown,
with values of PP > 0.95 and BS > 90 indicated with a circle. Nodes not recovered on the RAxML tree are
indicated with a hyphen. Sequences generated in this study are highlighted in violet.
Benthic megafauna of the Clarion-Clipperton Zone 53
Subclass Euechinoidea Bronn, 1860
Infraclass Audolonta Jackson, 1912
Superoder Echinothuriacea Jensen, 1982
Order Aspidodiadematoida Kroh & Smith, 2010
Family Aspidodiadematidae Duncan, 1889
Genus Plesiodiadema Pomel, 1883
Plesiodiadema cf. globulosum (A. Agassiz, 1898)
Fig. 32
Material. C-C Z • 1 specimen; APEI 1; 11.2527°N, 153.5848°W;
5204 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400726 (COI),
ON406628 (18S); CASIZ 229305; Voucher code: CCZ_196.
Description. Single specimen, with a somewhat spherical, slightly attened
test (d = 2 cm, H = 1.5 cm). In situ colouration is purple, but the inated anal
cone is greyish blue (Fig. 32A). Primary spines are also purple, very long (up to
17cm), thin, exible, and strongly verticillate (Fig. 32B, C). Pedicellariae are tri-
dentate (Fig. 32C).
Remarks. In 1980, the RV Governor Ray collected several Aspidodiadematidae
specimens in the CCZ at ~ 4,800 m, and were assigned to the species P. globulosum.
e type localities of P. globulosum are the north of Malpelo Island, and from o
Galera Point, Ecuador in the Pacic Ocean, from 2877 to 3241 m depth (Agassiz
1898). ere are no genetic sequences available on public databases for the genus,
but both COI and 18S closest matches are to species of the genus Aspidodiadema A.
Agassiz, 1879, within the same family (18S: 99.4% similar to A. jacobyi A. Agassiz,
1880). e COI-only tree recovered a monophyletic clade including three specimens
of A. tonsum (Fig. 31), but the genetic divergence is within interspecic values for
COI (6.5–11.7%). Despite morphological characters being in accordance with the
diagnostic characters for P. globulosum, the specimen is listed as cf. as the collection site
is much deeper than the type locality.
Ecology. e specimen was collected on the sedimented abyssal plain of APEI 1,
at 5203 m depth.
Comparison with image-based catalogue. A very similar Plesiodiadema
sp. morphotype (i.e., Plesiodiadema globulosum sp. inc., URC_003) has been
commonly found in image-based megafauna assessments conducted in the eastern
CCZ (e.g., Amon et al. 2017b) and other areas of the eastern Pacic abyss (e.g.,
Yuzhmorgeologiya exploration area; Kamenskaya et al. 2013; Peru Basin; Simon-
Lledó et al. 2019a), both in nodule elds and in seamount areas. URC_003 is
usually the most abundant echinoid encountered in image-based megafauna
surveys conducted at the eastern CCZ. In contrast, URC_003 was not encountered
in surveys conducted in abyssal areas of the Kiribati EEZ, where kamptosomatids
(e.g., see below) appeared to dominate the echinoid community (Simon-Lledó
etal. 2019d).
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Order Echinothurioida Claus, 1880
Family Kamptosomatidae Mortensen, 1934
Genus Kamptosoma Mortensen, 1903
Kamptosoma abyssale Mironov, 1971
Fig. 33
Material. C-C Z • 1 specimen; APEI 4; 7.036°N, 149.9395°W;
5040 m deep; 01 Jun. 2018; Smith & Durden leg.; GenBank: ON400701 (COI);
CASIZ 229306; Voucher code: CCZ_082.
Other material. P O • 1 specimen, holotype of Kamptosoma asterias
(A. Agassiz); o the coast of Chile; 33.5167°S, 74.7167°W; 3950 m deep; Challenger
Expedition, Stn. 299; NHMUK 1881.11.22.114. • 2 specimens, Kamptosoma abyssale
Mironov, 1971; Tasman Sea; 0°N, 0°E; 4850–4800 m deep; Galathea Expedition, Stn.
574; NHMUK 1984.1.25.86-87.
Description. Single specimen (d = 3.4 cm, H = 1.6 cm). In situ, the body is reddish
brown, rounded and attened (Fig. 33A, B). Spines are the same reddish brown colour
of the body; oral primary spines are encased by a eshy, clear sac, swollen and brighter
at the tip. e test and covering skin are very thin and gonads are visible through; pri-
mary spines are projected upwards and tube feet extending downwards from the lower
half of the body. Whole abactinal surface (ambulacral and interambulacral) covered
by primaries arranged in irregular lines along the median lines of the plates, with few
secondaries or militaries near ambitus (Fig. 33C). Claviform (globiferous) pedicellariae
carries two saccules and two valves. Before preservation, colouration was bright orange.
Remarks. Only two species of Kamptosoma have been described to date.
Kamptosoma asterias (Agassiz, 1881) was rst described from o the coast of Chile
Figure 32. Plesiodiadema cf. globulosum (A. Agassiz, 1898). Specimen CCZ_196: A in situ image
Bspecimen after recovery C detail of pedicellaria of specimen CCZ_196. Scale bars: 2 cm (A); 1 cm (B).
Image attribution: Durden and Smith (A); Wiklund, Durden, Drennan, and McQuaid (B, C).
Benthic megafauna of the Clarion-Clipperton Zone 55
at 3950 m depth (type locality: H.M.S Challenger St. 299), and from the east of
Malden Island, Central Pacic, at 4750 m depth (type locality for K. indistinctum
synonymous with K. asterias: H.M.S. Challenger St. 272) (Agassiz 1881; 1904).
It has also been reported for the central Pacic Ocean, the Tasman Sea, Chile,
Antarctica, and the southern Indian Ocean from 3890–4950 m depth (Anderson
2016). Kamptosoma abyssale type locality is the Kuril-Kamchatka Trench, from
6090–6235 m (Mironov 1971), and occurs in the Northwest Pacic, from Aleutian
Islands to Kermadec Trench, and from Madagascar to east of Hawaii between
4374–6235 m depth (Mooi et al. 2004). ese two species are only dierentiated
by the shape of the claviform pedicellaria (previously referred to as globiferous
pedicellaria, but Mironov et al. (2015) suggested these to belong to the claviform
group as their rudimentary valves are not functional), with two valves in K. abyssale,
and three valves in K. asterias. e specimen from the CCZ has pedicellariae
Figure 33. Kamptosoma abyssale Mironov, 1971. Specimen CCZ_082: A, B in situ images C oral view
D aboral view of specimen before preservation. Scale bars: 1 cm (A, B); 5 mm (C , D ). Image attribution:
Durden and Smith (A, B ); Wiklund, Durden, Drennan, and McQuaid (C, D ).
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with two saccules and two valves, as described for K. abyssale. However, the COI
sequence is very similar (0.47–1.4% K2P distance) to sequences of K. asterias
collected in the Tasman Sea from 4570–4744 m depth, and are recovered in a
well-supported clade (Fig. 31). ese values of genetic divergence are within the
intraspecic divergence that has been reported for echinoids (Chow et al. 2016),
and therefore might belong to the same species. Nonetheless these specimens
identied as K. asterias were reported to have claviform pedicellariae with two
valves as described for K. abyssale (Anderson 2016). It has been suggested that K.
abyssale is a synonym of K. asterias, and the former species will only be validated
once material from both type localities is examined in detail (Anderson 2016;
Mironov et al. 2015; Mooi et al. 2004). Kamptosoma asterias from the Central
Pacic (St. 272) has been re-examined and was reported to have pedicellariae with
three valves (Mironov et al. 2015). e holotype from St. 299 was examined in this
study. Unfortunately, most pedicellariae have been lost and only a single claviform
pedicellariae was found, this with two valves.
Ecology. e specimen was found crawling rapidly across abyssal sediment in
APEI 4, at 5040 m depth. is morphotype has an unusually high crawling speed.
Comparison with image-based catalogue. A very similar Kamptosoma sp.
morphotype (i.e., Kamptosoma abyssale sp. inc., URC_010) has been encountered
in seabed image surveys conducted in abyssal areas of Kiribati’s EEZ, but not
in the eastern CCZ. URC_010 was the most abundant echinoid morphotype
encountered in the abyssal areas explored within Kiribati’s EEZ (Simon-Lledó
etal.2019d).
Class Holothuroidea
Holothurians are important components of the benthic deep-sea megafauna, and
currently there are 367 records at a minimum depth of 3000 m in the CCZ, with
141 representing preserved specimens (OBIS 2022). Holothurians are amongst
the most diverse invertebrate megafaunal taxa in the CCZ seaoor; a total of 106
dierent holothurian morphotypes has been so far catalogued in the image-based
assessments consulted for this study, across the CCZ and nearby locations. We
collected 18 specimens belonging to 15 dierent species, for which the COI gene
was successfully amplied for all but one specimen. e gene 18S was successfully
amplied for that specimen, as well as for other three. ese were included in a
concatenated alignment (12S, 16S, 18S, 28S, COI, and H3) used to estimate a
phylogenetic tree (Fig. 34).
Subclass Actinopoda Ludwig, 1891
Order Persiculida Miller, Kerr, Paulay, Reich, Wilson, Carvajal & Rouse, 2017
Family Molpadiodemidae Miller, Kerr, Paulay, Reich, Wilson, Carvajal & Rouse, 2017
Genus Molpadiodemas Heding, 1935
Benthic megafauna of the Clarion-Clipperton Zone 57
Figure 34. Phylogenetic tree of the class Holothuroidea. Concatenated (12S, 16S, 18S, 28S, COI, and
H3) median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated.
Only values of PP > 0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a
circle. Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this
study are highlighted in violet.
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Molpadiodemas stet. CCZ_102
Fig. 35
Material. C-C Z • 1 specimen; APEI 4; 7.2701°N, 149.7827°W;
3552 m deep; 03 Jun. 2018; Smith & Durden leg.; GenBank: ON400708 (COI);
NHMUK 2022.66; Voucher code: CCZ_102.
Description. Single specimen, ~ 32 cm long (Fig. 35A). Body subcylindrical when
alive, dorso-ventrally attened in preserved specimen (L = 22 cm, W = 9 cm; Fig. 35E,
F), tapering distally; body wall is completely covered in sediment and globigerinas,
rm, wrinkly, with transverse folds and ridges giving a partly serrated appearance to
the margin; brim present; anus and mouth ventral (Fig. 35D, E). Tube feet only visible
on the ventral surface, cylindrical, and orange (Fig. 35C). Dorsal surface is whitish and
ventral is yellowish in preserved specimen, but heavily covered by sediment. Ossicles in
tentacles; unbranched rods and branched rods, with branches intertwining at the ends
creating irregular perforated mesh (Fig. 35B).
Remarks. COI sequence forms a clade with other species of Molpadiodemas includ-
ing M. villosus (éel, 1886), M. morbillus O’Loughlin & Ahearn, 2005, M.crinitus
O’Loughlin & Ahearn, 2005 and M. involutus (Sluiter, 1901). Closest is to M. morbilus
(K2P 3.7–3.9%), and in the phylogenetic tree it is recovered in a well-supported clade
with other species within the genus (Fig. 34), but species were not separated within the
genus. ree species within the genus Molpadiodemas have been previously reported
in the CCZ: M. altanticus (R. Perrier, 1898), M. villosus and M. helios O’Loughlin &
Figure 35. Molpadiodemas stet. CCZ_102 A in situ image B tentacle ossicles C tube feet D dorsal
surface E ventral surface of specimen before preservation. Scale bars: 2 cm (A); 20 µm (B); 1 cm (D, E ).
Image attribution: Durden and Smith (A); Bribiesca-Contreras (B, C); Wiklund, Durden, Drennan, and
McQuaid (D, E).
Benthic megafauna of the Clarion-Clipperton Zone 59
Ahearn, 2005, with the latter species being recently described from the CCZ and so
far not reported elsewhere (O’Loughlin and Ahearn 2005). However, morphological
characters of Molpadiodemas stet. CCZ_102 are not in accordance with the description
of any of those three described species.
Ecology. is specimen was collected on the sediment seaoor of a seamount in
APEI 4 at 3552 m depth.
Comparison with image-based catalogue. A very similar Molpadiodemidae mor-
photype (i.e., Molpadiodemas sp. indet., HOL_103) has been commonly encountered
in seabed image surveys conducted across the eastern CCZ (e.g., Amon et al. 2017b)
and in abyssal areas of the Kiribati EEZ, mostly in nodule eld areas.
Molpadiodemas stet. CCZ_194
Fig. 36
Material. C-C Z • 1 specimen; APEI 1; 11.2517°N, 153.6055°W;
5205 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400725 (COI);
NHMUK 2022.71; Voucher code: CCZ_194.
Description. Single specimen (Fig. 36A). Colouration of live specimen is whitish
yellow, with skin somewhat translucent (Fig. 36A, E). Body subcylindrical in live spec-
imen, but dorso-ventrally attened when preserved, tapering anteriorly, ~ 4×as long
as wide (L = 25 cm, W = 8.2 cm); semi-translucent body wall, longitudinal muscles
visible through it; colouration of preserved specimen is yellowish (Fig. 36E), darker
on the ventral side (Fig. 36F). Ventral surface with small, black, unidentied epibionts
embedded in the skin (Fig. 36C, D). Specimen barely covered by sediment. Ossicles in
tentacles; unbranched rods with thick central swelling; and branched rods, often with
branches intertwining at the ends creating an irregular perforated mesh (Fig. 36B).
Remarks. e COI sequence of Molpadiodemas stet. CCZ_194 is similar to
sequences of other species of Molpadiodemas, including M. villosus, M. morbillus,
M.crinitus, M. involutus, and Molpadiodemas stet. CCZ_102. COI genetic divergence
between both specimens collected in the CCZ is 6%, in accordance with values of
genetic interspecic divergence for the genus. e specimen is recovered in a well-
supported clade along with other members of the genus (Fig. 34), but species are
not well delimited. As mentioned above, three species of Molpadiodemas have been
previously reported in the CCZ (O’Loughlin and Ahearn 2005). e tentacle ossicles
from specimen CCZ_194 are very similar to those of M. helios, but this latter species is
distinguished by the prominent tube feet that are barely visible in our specimen.
Ecology. is specimen was found on the sedimented seaoor of an abyssal plain
on APEI 1 at 5205 m depth.
Comparison with image-based catalogue. A very similar Molpadiodemas sp.
morphotype (i.e., Molpadiodemas sp. indet., HOL_004) has been commonly encoun-
tered in seabed image surveys conducted across nodule elds areas of the eastern CCZ
(e.g., Amon et al. 2017b), but not in abyssal areas surveyed within the Kiribati EEZ.
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Order Synallactida Miller, Kerr, Paulay, Reich, Wilson, Carvajal & Rouse, 2017
Family Synallactidae Ludwig, 1894
Synallactidae stet. CCZ_061
Fig. 37
Material. C-C Z • 1 specimen; APEI 7; 4.8877°N, 141.7569°W;
3132 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400688 (COI),
ON406640 (18S); NHMUK 2022.75; Voucher code: CCZ_061.
Description. Single specimen; description of external morphological features only
from in situ image as the specimen was damaged during collection (Fig. 37A). Body
semi-circular, with ventral surface attened, tapering distally; very wide, widest part
of body ~ 7 cm; anus posterodorsal; mouth anteroventral. Tegument seems thick. Os-
sicles present in tentacles, slightly curved rods, < 250 µm (Fig. 37B).
Remarks. ere are no close matches to the COI sequence of Synallactidae stet.
CCZ_061 in public databases. e closest match is to Synallactidae stet. CCZ_066
(14% K2P). Both specimens are recovered in a well-supported clade representing the
family Synallactidae (Fig. 34). ey are recovered very close to Paelopatides éel,
1886, but COI divergence suggest they belong to dierent genera.
Comparison with image-based catalogue. No similar Synallactidae morphotypes
have been so far catalogued from seabed imagery collected in the eastern CCZ or in
Figure 36. Molpadiodemas stet. CCZ_194 A in situ image B tentacle ossicles C epibionts on ventral sur-
face D detail of epibionts E dorsal surface F ventral view of specimen before preservation. Scale bars: 2cm
(A); 25 µm (B); 1 cm (E, F). Image attribution: Durden and Smith (A); Bribiesca-Contreras (B–D);
Wiklund, Durden, Drennan, and McQuaid (E, F).
Benthic megafauna of the Clarion-Clipperton Zone 61
abyssal areas of the Kiribati EEZ. Consequently, the in situ image of Synallactidae
stet. CCZ_061 was catalogued as a new morphotype (i.e., Synallactidae gen. indet.,
HOL_120).
Ecology. is specimen was collected on the sedimented seaoor of a seamount in
APEI 7 at 3132 m depth.
Synallactidae stet. CCZ_066
Fig. 38
Material. C-C Z • 1 specimen; APEI 7; 4.8896°N, 141.75°W;
3095 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400692 (COI),
ON406642 (18S); NHMUK 2022.63; Voucher code: CCZ_066.
Description. Single specimen, body semi-circular with ventral surface attened;
~ 3× longer than wide (L = 21 cm, W = 6 cm; Fig. 38A). Mouth anteroventral, anus
posterodorsal. Colouration in live specimen is bright red (Fig. 38D, E). Specimen
severely damaged during collection, guts separated from skin. Tegument is thick and
leathery, with wart-like protrusions on the dorsal surface, more evident on live speci-
men (Fig. 38A), and with a small, very short, triangular dorsal appendage. Brim evi-
dent on ventral surface. Small tube feet arranged in two irregular rows, one on each
side of ventrum, running longitudinally. Tentacles 18. Ossicles present in dorsal skin
(Fig. 38B) and tentacles (Fig. 38C).
Remarks. ere are no close matches to the COI sequence of Synallactidae
stet. CCZ_066 in public databases. e closest match is to specimen Synallactidae
stet. CCZ_061 (14% K2P). Both specimens are recovered in a well-supported
clade representing the family Synallactidae (Fig. 34). ey are recovered very
close to Paelopatides éel, 1886, but COI divergence suggest they belong to
dierentgenera.
Ecology. is specimen was collected on the sedimented seaoor of a seamount on
APEI 7 at 3095 m depth.
Figure 37. Synallactidae stet. CCZ_061 A in situ image B tentacle ossicles. Scale bars: 2 cm (A);
50µm(B). Image attribution: Durden and Smith (A); Bribiesca-Contreras (B).
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Comparison with image-based catalogue. No similar Synallactidae morphotypes
have been so far catalogued from seabed imagery collected in the eastern CCZ nor in
abyssal areas of the Kiribati EEZ. Consequently, the in situ image of CCZ_066 was
catalogued as a new morphotype (i.e., Synallactidae gen. indet., HOL_121). e dor-
sal protrusions that dierentiate HOL_121 from HOL_120 may not be clearly visible
in vertically-facing seabed imagery, and hence these two taxa might only be classiable
into a single, generic morphotype (i.e., HOL_120) in quantitative analyses.
Genus Synallactes Ludwig, 1894
Synallactes stet. CCZ_153
Fig. 39
Material. C-C Z • 1 specimen; APEI 4; 6.9704°N, 149.9426°W;
5009 m deep; 06 Jun. 2018; Smith & Durden leg.; GenBank: ON400714 (COI);
NHMUK 2022.69; Voucher code: CCZ_153.
Description. Single specimen (Fig. 39A). Body cylindrical, white, ~ 4× as long as
wide (L = 10 cm, W = 2.7 cm), attened proximally and rounded distally; attened
ventral surface. Two rows, upper and lower, of lateral, small, conical, thin processes,
similar to those around the proximal edge (Fig. 39D). ere is a row of yellowish, very
Figure 38. Synallactidae stet. CCZ_066 A in situ image B ossicles on dorsal skin C tentacle ossi-
cles D dorsal surface E ventral surface of specimen before preservation. Scale bars: 2 cm (A, D, E );
50 µm (B, C). Image attribution: Durden and Smith (A); Bribiesca-Contreras (B, C); Wiklund, Durden,
Drennan, and McQuaid (D, E).
Benthic megafauna of the Clarion-Clipperton Zone 63
small, tube feet in the mid-ventral surface, along the odd ambulacrum (Fig. 39E). Skin
rm but translucent. Colour on live and preserved specimen is white. Ossicles abun-
dant on dorsal body wall, spatulated crosses only with a long spinous apophysis, end
of arms spatulated with holes (Fig. 39B). Ventral ossicles also spatulated crosses with a
long spinous apophysis, smaller, sometimes with more than four arms, also spatulated
ends of arms with holes (Fig. 39C).
Remarks. e closest matches for the barcoding gene COI sequence are pub-
lished sequences from the genus Bathyplotes (89.9% similarity), also within the fam-
ily Synallactidae. e sequence is distinct from the only sequence of Synallactes sp.
(GenBank accession number: KX874365.1) included in the phylogeny (Fig. 34), and
they were not recovered as a monophyletic group. e DeepCCZ specimen was re-
covered sister to species of Bathyplotes, with Synallactes sp. recovered separately from
the other genera in the family Synallactidae, concordant with previous results (Miller
et al. 2017). Despite this, the specimen was assigned to the genus Synallactes based on
external morphological characters that are concordant with those described from the
genus. Species of Synallactes have previously been reported in the CCZ: Synallactes
profundus (Koehler & Vaney, 1905) and Synallactes aenigma Ludwig, 1894; the latter
being associated with manganese substrates. External morphology does not resemble
to S. profundus.
Ecology. is specimen was found on the sedimented seaoor of an abyssal plain
on APEI 4 at 5008 m depth.
Comparison with image-based catalogue. A very similar Synallactidae morpho-
type (i.e., Synallactes sp. indet., HOL_007) has been commonly encountered in seabed
Figure 39. Synallactes stet. CCZ_153 A in situ image B ossicles from dorsal skin C ossicles from ventral
skin D dorsal view of specimen before preservation, E ventral view. Scale bars: 2 cm (A); 50 µm (B, C);
5 mm (D, E ). Image attribution: Durden and Smith (A); Bribiesca-Contreras (B, C ); Wiklund, Durden,
Drennan, and McQuaid (D, E).
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image surveys conducted across nodule eld areas of the eastern CCZ (e.g., Amon et
al. 2017b), but not in abyssal areas of the Kiribati EEZ, where synallactid specimens
were very rarely encountered.
Family Deimatidae éel, 1882
Genus Oneirophanta éel, 1879
Oneirophanta stet. CCZ_100
Fig. 40
Material. C-C Z • 1 specimen; APEI 4; 7.2647°N, 149.774°W;
3550 m deep; 03 Jun. 2018; Smith & Durden leg.; GenBank: ON400706 (COI),
ON406643 (18S), ON406620 (16S); NHMUK 2022.84; Voucher code: CCZ_100.
Description. Single specimen; colouration of live specimen is beige, spotted with
light brown and yellow on dorsal surface (Fig. 40A, C, D), and lighter on ventral
surface, with suckers on tube feet and tentacles being dark brown (Fig. 40D). Body
cylindrical, ~ 33 cm long and 8.8 cm wide; mouth anteroventral, anus posteroventral.
Tentacles partly retracted. Papillae arranged in one or two rows along the dorsal radii,
and in a single row along the ventrolateral radii above the tube feet. Tube feet ~ 50
pairs, arranged in two or three rows on each ventrolateral ambulacrum; few tube feet
located along mid-ventral ambulacrum, among them two tube feet, one placed approx.
half the body length and the other approx. three quarter of the body length; and few
smaller feet close to anus. Dorsal ossicles spatulated crosses, crosses with open ramica-
tions, and small irregular perforated plates; ventral ossicles crosses with open ramica-
tions of dierent stage of development.
Remarks. Closest match for COI and 16S sequences is to Oneirophanta setigera
(Ludwig, 1893) (86.7% and 96.3%, respectively). In the phylogenetic tree, it is
recovered in a well-supported clade representing the family Deimatidae, including
Oneirophanta (Fig. 34). According to the external morphology Oneirophanta sp.
CCZ_100 diers from Oneirophanta mutabilis mutabilis éel, 1879, O. mutabilis
anis Ludwig, 1893 and O. conservata Koehler & Vaney, 1905 in high number of
tube feet arranged in two or three rows and by absence of large, perforated plates
on dorsum. It diers from O.setigera in high number of tube feet arranged in two
or three rows and by presence of small, perforated plates and bigger perforations on
spatulated crosses.
Ecology. e specimen was found on the sediment seaoor of a seamount on
APEI 4 at 3550 m depth.
Comparison with image-based catalogue. No exactly similar Deimatidae mor-
photypes have been so far catalogued from seabed imagery collected in the eastern
CCZ nor in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of
CCZ_100 was catalogued as a new morphotype (i.e., Oneirophanta sp. indet.,
HOL_063). However, HOL_063 could be potentially confused with a similar shaped
Benthic megafauna of the Clarion-Clipperton Zone 65
Deimatidae morphotype (e.g., Deimatidae gen. indet., HOL_062; also beige, cylindri-
cal, with conspicuous projections on the dorsal surface arranged in four rows) found
in the eastern CCZ (e.g., Amon et al. 2017b), with more abundant -though slightly
thinner- projections, that may be dicult to distinguish in vertically facing images.
Oneirophanta cf. mutabilis éel, 1879
Fig. 41
Material. C-C Z • 1 specimen; APEI 1; 11.252°N, 153.5847°W;
5203 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400724 (COI),
ON406629 (18S), ON406619 (16S); NHMUK 2021.20; Voucher code: CCZ_193.
Other material. I O • 3 specimens, syntypes of Oneirophanta mutabilis
éel, 1879; Eastern Indian, Antarctic Basin; 53.9167° S, 108.5833° E; 3566 m deep;
Challenger Expedition, Stn. 157; NHMUK 1883.6.18.33.
Description. Single specimen, body uniformly white (Fig. 41A). Body almost
cylindrical, > 2× as long as wide (L = 16 cm; W = 6.9 cm), being of almost equal
breadth throughout the whole length and tapering posteriorly; mouth anteroventral
and anus posteroventral. Tentacles 20, small, with a lightly brown tip, each with a
terminal part with 6–8 unbranched processes. Long, pointed processes, or dierent
lengths, arranged in four distinct rows, two rows running along the dorsal ambula-
cra with eight processes on each row, and the longest being approx. half of the body
Figure 40. Oneirophanta stet. CCZ_100 A dorsal view of specimen before preservation B in situ im-
age C ventral view D dorsal ossicles E ventral ossicles. Scale bars: 2 cm (A, C ); 5 cm (B); 200 µm (D);
100µm (E). Image attribution: Wiklund, Durden, Drennan, and McQuaid (A, C); Durden and Smith
(B); Kremenetskaia (D, E).
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length (Fig. 41C); the other two rows placed on the sides of the body, slightly above
the ventral lateral ambulacra. Ventral ambulacra with 11 and 13 tube feet, arranged
in two irregular rows; odd ambulacrum naked, except for two tube feet arranged
in the posterior half of the body, and ten surrounding the anus; processes crowded
anteriorly (Fig. 41D). in skin, translucent, but hard and brittle, with numerous
small and large perforated plates, with the small ones bearing two or three spines
near the centre, and the large ones ~ 30 spines; ossicles imbricated, almost forming
a skeleton (Fig. 41B).
Remarks. Sequences for the 18S, 16S, and COI genes were most similar to se-
quences from Oneirophanta setigera (99.07%, 95.6%, 88.51% similarity, respectively),
followed by other species within the family Deimatidae (i.e., Orphnurgus glaber Walsh,
1891 and Deima validum éel, 1879). e specimen was recovered in a well-sup-
ported clade including all members of Deimatidae (Fig. 34), closest to Oneirophanta
sp. CCZ_100 (K2P distance: 11%). Calcareous ossicles are concordant with those in
Oneirophanta mutabilis. is species was originally described west of the Crozet Is-
lands (H.M.S. Challenger station 146: 46.7667°S, 45.5167°E) at 2514 m depth (éel
Figure 41. Oneirophanta cf. mutabilis éel, 1879. Specimen CCZ_193 A in situ image B dorsal ossicles
C dorsal view before preservation D ventral view. Scale bars: 200 µm (B); 1 cm (C , D ). Image attribution:
Durden and Smith (A); Bribiesca-Contreras (B); Wiklund, Durden, Drennan, and McQuaid (C, D ).
Benthic megafauna of the Clarion-Clipperton Zone 67
1879) but has been further divided in two sub-species, O. mutabilis mutabilis and
O.mutabilis anis. e former has been reported to be cosmopolitan, while the later
has been recorded from the tropical eastern Pacic. Further analyses will be required
to determine the validity of the subspecies and if the CCZ specimen belongs to any of
those. It diers from the original description of O. mutabilis (éel, 1879) in having
an irregular number of pedicels around the ventral surface, the pedicels around the
anus arranged triangularly instead of a transversal row, as well as the arrangement of
the processes on bivium and trivium. However, éel (1879) mentioned that several
of the specimens examined diered from the specimen described in the number of
pedicels and the arrangement of processes, and further studies should clarify if these
are indeed subspecies.
Ecology. e specimen was found on the sediment surface of an abyssal plain on
APEI 1 at 5203 m depth.
Comparison with image-based catalogue. A very similar Oneirophanta sp. mor-
photype (i.e., Oneirophanta sp. indet., HOL_058) has been encountered in seabed
image surveys conducted across nodule elds areas of the eastern CCZ (e.g., Amon et
al. 2017b), but not in the abyssal areas surveyed at the Kiribati EEZ.
Order Elasipodida éel, 1882
Family Psychropotidae éel, 1882
Genus Psychropotes éel, 1882
Psychropotes verrucicaudatus Xiao, Gong, Kou, Li, 2019
Fig. 42
Material. C-C Z • 1 specimen; APEI 4; 6.9878°N, 149.9119°W;
4999 m deep; 02 Jun. 2018; Smith & Durden leg.; GenBank: ON400703 (COI);
NHMUK 2021.19; Voucher code: CCZ_086.
Description. Single specimen, colouration in situ is violet (Fig. 42A, B). Body
elongated and anteriorly depressed (L = 34.7 cm, W = 10.2 mm); with a broad brim.
Short (approx. one twelfth of body length), conical, single-pointed, dorsal unpaired
appendage, placed 2/5 of the body length from the posterior end (Fig. 42A–C). Dorsal
skin, including the dorsal appendage, covered in warts (Fig. 42C, F). Each wart has an
ossicle in the centre, a giant cross with a central apophysis and strongly curved arms,
all visible through the skin (Fig. 42E, F). Dorsal skin also contains smaller crosses with
spiny arms (Fig. 42E, F). Approximately 30 pairs of mid-ventral tube feet arranged
in two rows along the mid-ventral ambulacrum, arranged very close together on the
anterior two thirds of the body, and scattered after posteriorly, with the last pairs be-
ing very close together again. Colouration of preserved specimen is also purple, with
slightly lighter ventrum.
Remarks. COI sequence is very similar (K2P distance = 0.77%) to the holotype of
P. verrucicaudatus, and they were recovered together in the phylogenetic tree (Fig.34).
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is species was described from the Jiaolong seamount, in the South China Sea, west-
ern Pacic Ocean at 3615 m deep (Xiao et al. 2019). External morphological charac-
ters are in accordance with the original description.
Ecology. e specimen was found on the sedimented abyssal plain in APEI 4 at
4999 m depth.
Comparison with image-based catalogue. A very similar Psychropotes sp. mor-
photype (i.e., Psychropotes verrucicaudatus sp. inc., HOL_045) has been commonly
encountered in seabed image surveys conducted across nodule elds areas of the east-
ern CCZ (e.g., Amon et al. 2017b), but not in the abyssal areas surveyed within the
Kiribati EEZ.
Figure 42. Psychropotes verrucicaudatus Xiao, Gong, Kou, Li, 2019. Specimen CCZ_086: A, B in situ
images C dorsal view of specimen before preservation D ventral view E dorsal ossicles F detail of warts
and ossicles on dorsal body wall G mouth tentacles. Scale bars: 5 cm (B); 2 cm (C, D ); 100 µm (E). Image
attribution: Durden and Smith (A, B ); Wiklund, Durden, Drennan, and McQuaid (C, D ); Bribiesca-
Contreras (E–G).
Benthic megafauna of the Clarion-Clipperton Zone 69
Psychropotes dyscrita (Clark, 1920)
Fig. 43
Material. C-C Z • 1 specimen; APEI 4; 7.0212°N, 149.9355°W;
5040 m deep; 02 Jun. 2018; Smith & Durden leg.; GenBank: ON400702 (COI);
NHMUK 2022.83; Voucher code: CCZ_083.
Description. Single specimen, ~ 30 cm long (Fig. 43A). Colouration of live speci-
men is yellow (Fig. 43A, B), with reddish-light purple on ventral surface (Fig. 43C).
Tentacles 18, also reddish-light purple. Long, dorsal appendage with round end, slight-
ly longer than the total body length, and developed very close to the posterior end of
the body.
Remarks. Gebruk et al. (2020) morphologically examined the specimen collected
during the DeepCCZ and re-established the species Psychropotes dyscrita based on this
specimen. e holotype was collected in Peru, at 5206 m depth, and the species is
known from the Central Pacic Ocean at depths of 5040–5206 m (Gebruk et al. 2020).
Psychropotes dyscrita and P. moskalevi Gebruk & Kremenetskaia, 2020 are the two only
known yellow species for this genus and were recovered as sister species (Fig.34). e
COI sequence for the DeepCCZ specimen is 1.1 ± 0.4% divergent (K2P distance)
from specimens of P. moskalevi. Although this value seems low, the COI gene seems to
be more conserved in the genus Psychropotes (1.1–13.4%, mean=6.5%), with < 2%
Figure 43. Psychropotes dyscrita (Clark, 1920). Specimen CCZ_083: A, B in situ images C lateral view
D ventral view. Scale bars: 5 cm (A, B ); 2 cm (C , D ). Image attribution: Durden and Smith (A, B );
Wiklund, Durden, Drennan, and McQuaid (C, D ).
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70
interspecic divergence between some species pairs (P. dyscrita-P.moskalevi, P. moskale-
vi-P. raripes Ludwig, 1893).
Ecology. e specimen was found on the sediment seaoor of an abyssal plain in
APEI 4 at 5040 m depth.
Comparison with image-based catalogue. A very similar Psychropotes sp. mor-
photype (i.e., Psychropotes sp. indet., HOL_047) has been encountered in seabed image
surveys conducted across nodule elds areas of the eastern CCZ (e.g., Tilot 2006), and
in the Kiribati EEZ, where this taxon was the most abundant holothurian encountered
(Simon-Lledó et al. 2019d). In pioneer seabed image surveys conducted at the CCZ,
prior to the re-establishment of the species (Gebruk et al. 2020), this morphotype was
typically classied as P. longicauda. Based on seabed imagery (e.g., without analysis of
ossicles), it is not possible to determine whether HOL_047 specimens are P. dyscrita
or P. moskalevi.
Genus Benthodytes éel, 1882
Benthodytes cf. sanguinolenta éel, 1882
Fig. 44
Material. C-C Z • 1 specimen; APEI 1; 11.2953°N, 153.742°W;
5245 m deep; 09 Jun. 2018; Smith & Durden leg.; GenBank: ON400720 (COI);
NHMUK 2022.70; Voucher code: CCZ_178.
Description. Single specimen (Fig. 44A). Colouration of live specimen is light
pink dorsally (Fig. 44B), darker ventrally (Fig. 44C). Tentacles 18, yellow, digitiform.
Numerous dorsal papillae scattered on dorsal. Brim wide. Tube feet in double rows
along the mid-ventral ambulacrum, ~ 30 pairs, yellowish. Ossicles not found.
Remarks. e closest match for the COI sequence is a sequence from B. sanguinolenta
(GenBank: HM196505.1; 93.54% similarity) from the Ross Sea, Antarctica. A genetic
study revealed two separate clades within B. sanguinolenta (O’Loughlin et al. 2011): (1)
specimens from northwest Australia, and (2) Ross Sea. None of the samples included
in O’Loughlin et al. (2011) are from the type locality (34.1167° S 73.9399°’W, o
Chile, Pacic Ocean; 4000 m), but they identied at least two separate genetic species.
e COI sequence of the specimen collected in the CCZ forms a third clade within
the B. sanguinolenta species complex (Fig. 34). Genetic divergence (K2P distance)
between the CCZ specimens and both NW Australia and Ross Sea clades is 10.1% and
7.3%, respectively, corresponding to values of intraspecic divergence in the group.
In original description, éel (1882) describes the body to be 6–7× longer than wide,
whereas the preserved specimen collected in the CCZ is only ~ 3× longer than wide,
but might be due to preservation as in in situ images it appears longer. However, the
number of digitiform tentacles and appearance of small processes are concordant with
the description of B. sanguinolenta. e sequence of Benthodytes cf. sanguinolenta from
Glover et al. (2016b) does not form a clade with the CCZ specimen, with COI genetic
distance being large (K2P 23%).
Benthic megafauna of the Clarion-Clipperton Zone 71
Ecology. e specimen was found on the sedimented seaoor of an abyssal plain
in APEI 1 at 5249 m depth.
Comparison with image-based catalogue. No exactly similar Benthodytes sp.
morphotypes have been so far catalogued from seabed imagery collected in the eastern
CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of speci-
men CCZ_178 was catalogued as a new morphotype (i.e., Benthodytes sanguinolenta
sp. inc., HOL_124).
Benthodytes marianensis Li, Xiao, Zhang & Zhang, 2018
Fig. 45
Material. C-C Z • 1 specimen; APEI 7; 5.1043°N, 141.8865°W;
4861 m deep; 25 May. 2018; Smith & Durden leg.; GenBank: ON400682 (COI);
NHMUK 2022.82; Voucher code: CCZ_019.
Description. Single specimen (Fig. 45). Body is elongated, ~ 49.4 cm, dorso-ven-
trally attened with at ventral surface and inated dorsal surface; anteriorly depressed
and tapering posteriorly; colouration in live specimen is dark violet. Two irregular rows
of large conical papillae running along the paired dorsal ambulacra.
Remarks. e COI sequence is identical to the holotype of B. marianensis (K2P ge-
netic distance = 0%) collected in the Mariana Trench at 5567 m depth (Li et al. 2018).
ese two sequences are also recovered together in the phylogenetic tree (Fig.34). e
species is only known from this location. Morphological characters are also concordant
with the original description, including an uncommon, very peculiar, cross-shaped,
dorsal ossicle (Fig. 45B).
Ecology. e specimen was found on the sedimented seaoor of an abyssal plain
in APEI 7 at 4860 m depth.
Figure 44. Benthodytes cf. sanguinolenta éel, 1882. Specimen CCZ_178: A in situ image B dorsal
view of specimen before preservation C ventral view. Scale bars: 2 cm (A); 1 cm (B, C). Image attribution:
Durden and Smith (A); Wiklund, Durden, Drennan, and McQuaid (B, C).
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72
Comparison with image-based catalogue. CCZ_019 resembles a Benthodytes sp.
morphotype (i.e., Benthodytes sp. indet., HOL_111) encountered in seabed image sur-
veys conducted across nodule elds areas of the eastern CCZ (Amon et al. 2017b) and
the Kiribati EEZ. However, the vivid dark/violet colouration of HOL_011 (contrast-
ing with background bright sediment) can constrain the visibility of papillae features
in in situ photographed specimens, potentially making these hard to dierentiate from
other Benthodythes sp. morphotypes in vertically-facing seabed imagery.
Family Elpidiidae éel, 1882
Genus Peniagone éel, 1882
Peniagone leander Pawson & Foell, 1986
Fig. 46
Material. C-C Z • 1 specimen; APEI 7; 5.1042°N, 141.8861°W;
4860 m deep; 25 May. 2018; Smith & Durden leg.; GenBank: ON400681 (COI),
ON406621 (16S); NHMUK 2022.61; Voucher code: CCZ_018.
Description. Single specimen observed swimming (Fig. 46A). Specimen was se-
verely damaged during collection, with only a few tentacles recovered, and hence de-
scription of morphological characters is based on in situ images. Body ovoid, slightly
> 2× as long as it is wide. Velum composed of two pairs of fully fused papillae. Tube
feet four pairs; three posteriormost pairs fused together forming a posterior swimming
lobe; tube feet from the anteriormost pair very short.
Remarks. e specimen collected during the DeepCCZ expedition was recovered
in bits, so no morphological features can be distinguished. Only four reddish orange
tentacles were recovered, which are embedded in a transparent skin where ossicles
are evident. However, P. leander is one of the few species that can be identied
from images. e external morphological characters evident in in situ images from
the CCZ specimen are in accordance with the species description. e species was
Figure 45. Benthodytes marianensis Li, Xiao, Zhang & Zhang, 2018. CCZ_019: A in situ image B dorsal
ossicles including peculiar cross-shaped ossicle C ventral ossicles. Scale bar: 5 cm (A); 100 µm (B, C ).
Image attribution: Durden and Smith (A), Kremenetskaia (B, C).
Benthic megafauna of the Clarion-Clipperton Zone 73
originally described from in situ images and video footage collected across the eastern
CCZ (Pawson and Foell 1986) and subsequently observed in the area (e.g., Amon
et al. 2017b).
In the phylogenetic tree, the CCZ specimen was recovered in a well-supported
clade with other species of Peniagone (Fig. 34). It was recovered together with a sequence
of P. leander, which was recently rediscovered and collected for the rst time in the
Mariana Trench (Gong et al. 2020), both close to P. diaphana as reported by Gong et
al. (2020). e 16S sequence of the CCZ specimen is similar (K2P distance = 2%) to
the only available sequence from P. leander, but no COI sequence was made available.
Our COI sequence is > 12% divergent (K2P distance) from other species within the
genus. e COI gene seems to be highly divergent between species in this genus. Using
the data provided in Kremenetskaia et al. (2021) and including the CCZ sequence of
P. leander, COI mean interspecic divergence in the genus is 15.9% (min = 2.5% and
max = 22.7%), with our sequence of P. leander being 14.5%–21.2% divergent from
other species within the genus. Intraspecic divergence for species in the genus was
estimated between 0.9%–3.0%.
Ecology. e specimen was found swimming near the sediment surface on an
abyssal plain in APEI 7 at 4860 m depth.
Comparison with image-based catalogue. Peniagone leander (HOL_028) has
been commonly encountered in seabed image surveys conducted across the eastern
CCZ (e.g., Amon et al. 2017b) and in abyssal areas of the Kiribati EEZ, usually swim-
Figure 46. Peniagone leander Pawson & Foell, 1986. Specimen CCZ_018: A, B in situ images C tentacle
ossicles. Scale bars: 100 µm (C). Image attribution: Durden and Smith (A, B ); Bribiesca-Contreras (C).
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74
ming above the seabed but sometimes creeping on it. Body colour appears to be vari-
able; bright red, semi-transparent, purplish, and whitish HOL_028 specimens have
been encountered in seabed image surveys across the CCZ.
Peniagone vitrea éel, 1882
Fig. 47
Material. C-C Z • 1 specimen; APEI 7; 5.0442°N, 141.8164°W;
4875 m deep; 28 May. 2018; Smith & Durden leg.; GenBank: ON400699 (COI),
ON406622 (16S); NHMUK 2022.64; Voucher code: CCZ_077.
Other material. P O • 1 specimen, syntype of Peniagone vitrea var.
setosa Ludwig; South Pacic; 0.6°S, 86.7667°W; 2418 m deep; Albatross Expedition;
NHMUK 1895.11.12.7. • 3 specimens, syntypes of Peniagone vitrea éel, 1882; East
of St. Paul, Indian-Antarctic Ridge; 42.7167°S, 82.1833°W; 2652 m deep; Challenger
Expedition, Stn. 302; NHMUK 1883.6.18.82.
Description. Single specimen. Body long, ~ 3× as long as wide (Fig. 47C, D).
Mouth anterior, downwards; foremost neck-like part bent forwards in acute angle
Figure 47. Peniagone vitrea éel, 1882. Specimen CCZ_077: A, B in situ images C lateral view before
preservation D dorsal view E dorsal ossicles. Scale bars:2 cm (A); 3 cm (B); 200 µm (E). Image attribution:
Durden and Smith (A, B ); Wiklund, Durden, Drennan, and McQuaid (C, D ); Bribiesca-Contreras (E)
Benthic megafauna of the Clarion-Clipperton Zone 75
with ventral surface (Fig. 47C); with ten tentacles of similar sizes; anus terminal.
Velum consists of two pairs processes, fully fused by a membrane forming a lobe,
with only the tips free; the two middle processes are much larger (Fig. 47A, B, D).
Eight pairs of tube feet surrounding the posterior third of ventral surface, decreasing
in size distally. Skin translucent in live specimen (Fig. 47A, B), but white, hard, and
brittle after preservation, with numerous calcareous deposits (Fig. 47C, D). Dorsal
ossicles with four spinose arms, slightly arched, with mostly two long spinose pro-
cesses (Fig. 47E).
Remarks. Morphological external characters and ossicle morphology are in ac-
cordance with the original description of Peniagone vitrea. Unfortunately, no genetic
sequences of P. vitrea are available in public databases. is species was described from
o Patagonia at 2652 m depth. Using data from Kremenetskaia et al. (2021), the COI
sequence of P. vitrea is 16.5%–18.8% divergent (K2P) from other species of Peniagone,
and 17.9% divergent from the COI sequence of P. leander generated in this study. In
the phylogenetic tree, it is recovered in a well-supported clade with other species of
Peniagone (Fig. 34).
Ecology. e specimen was found feeding on the sedimented seaoor of an abyssal
plain in APEI 7 at 4874 m.
Comparison with image-based catalogue. A very similar Peniagone sp. morpho-
type (i.e., Peniagone vitrea sp. inc., HOL_059) has been commonly encountered in
seabed image surveys conducted across nodule elds areas of the eastern CCZ (e.g.,
Amon et al. 2017b), but not in the abyssal areas surveyed within the Kiribati EEZ.
Family Laetmogonidae Ekman, 1926
Genus Psychronaetes Pawson, 1983
Psychronaetes sp. CCZ_101
Fig. 48
Material. C-C Z • 1 specimen; APEI 7; 4.8877°N, 141.757°W;
3132 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400690 (COI),
ON406630 (18S); NHMUK 2022.62; Voucher code: CCZ_063. • 1 specimen;
APEI 4; 7.2647°N, 149.7741°W; 3562 m deep; 03 Jun. 2018; Smith & Durden
leg.; GenBank: ON400707 (COI), ON406631 (18S); NHMUK 2022.65; Voucher
code: CCZ_101. • 1 specimen; APEI 4; 7.2647°N, 149.7741°W; 3562 m deep;
03 Jun. 2018; Smith & Durden leg.; GenBank: ON400709 (COI), ON406639
(18S); NHMUK 2022.67; Voucher code: CCZ_103. • 1 specimen; APEI 4;
7.2647°N, 149.7741°W; 3562 m deep; 03 Jun. 2018; Smith & Durden leg.; Gen-
Bank: ON400710 (COI), ON406632 (18S); NHMUK 2022.68; Voucher code:
CCZ_104.
Description. Four specimens (Fig. 48A–D). Body dorso-ventrally attened
(L=15.9 cm, W = 3.4 cm), tapering at both ends; pronounced “neck” anteriorly;
mouth anteroventral, anus posterodorsal. Tentacles 18, with long stems and large
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76
elongate oval discs (Fig. 48G). Body wall rm and leathery, dark violet in preserved
specimen, with evident, numerous calcareous wheel-like ossicles that make the skin
sparkle under light. Mid-ventral ambulacrum is naked; one irregular row of ≥ 40
tube feet running along each ventrolateral ambulacra (Fig. 48G), very conspicu-
Figure 48. Psychronaetes sp. CCZ_101. Specimen CCZ_063 A in situ image. Specimen CCZ_101 B in
situ image F dorsal ossicles. Specimen CCZ_103 C in situ image H dorsal ossicles. Specimen CCZ_104
D in situ image E dorsal view of specimen before preservation G ventral view. Scale bars: 5 cm (A, D); 2
cm (B); 1 cm (E, G); 75 µm (F); 100 µm (H). Image attribution: Durden and Smith (A–D); Wiklund,
Durden, Drennan, and McQuaid (E, G); Bribiesca-Contreras (F, H ).
Benthic megafauna of the Clarion-Clipperton Zone 77
ous on live specimens (Fig. 48A–D), but fully retracted on preserved specimens.
Paired dorsal ambulacra with ~ 20 papillae each; ~ 7 long thick papillae distributed
along each ambulacrum, interspersed with smaller ones (Fig. 48A–E). ere are ~ 18
large conical papillae surrounding the anterior margin dorsally, fully fused forming a
fringe (Fig.48B, D). Dorsal ossicles numerous, wheel-like, of dierent sizes (ranging
from 77–340 µm in diameter) but mostly large; strongly concave; central primary
cross with 4–6 struts, mostly four; smooth rim; with 10–16, mostly 12, short spokes
(Fig. 48F, H).
Remarks. Based on ossicle morphology, the four specimens were considered to
belong to the same species. Sequence of the 18S were found to be identical between
specimens CCZ_063, CCZ_101, and CCZ_104 (0.0% K2P distance) but 1.3%
divergent from CCZ_103. e COI gene was amplied for the four specimens and
genetic divergence ranges between 0.8% to 7.4%. e two specimens collected in APEI
4 are less genetically divergent (CCZ_101-CCZ_104 = 0.8% K2P). e specimen
collected in APEI 7 (CCZ_063) is 2.3–2.9% divergent from the other three. e
specimen CCZ_103 is 7.4% divergent to CCZ_101 and CCZ_104, but only 2.9%
divergent from CCZ_063. While the former values are within the range of interspecic
genetic divergence, we considered the specimen to belong to the same species as both the
ossicle and external morphological characters are similar to the other three specimens. In
addition, the trace les for both 18S and COI for this specimen are messy and the high
genetic divergence could be an artifact of miss-called nucleotides. Unfortunately, there
are no sequences available for Psychronaetes, but we included sequences of other genera
within the family (Pannychia, Laetmogone, and Benthogone) for which COI genetic
divergence ranged from 23–31%. In the phylogenetic tree, the four specimens were
recovered in a well-supported clade (Fig.34), close to other Laetmogonidae (poorly
supported). is species has an anterior brim, which is characteristic of the monotypic
genus Psychronaetes. Psychronaetes hanseni Pawson, 1983 diers from the four specimens
in having smaller dorsal wheel ossicles (d = 50–80 µm) with 9–12 spokes, only 15 tube
feet on each of paired ventral ambulacrum, 15 mouth tentacles instead of 18, and in
the number of papillae on the dorsal paired ambulacra. e species and genus were
described from two specimens collected in the CCZ (Pawson 1983).
Ecology. e four specimens were found on the sedimented seaoor of seamounts
in APEIs 4 and 7 between 3132–3562 m depth.
Comparison with image-based catalogue. No exactly similar Psychronaetes sp.
morphotypes have been encountered in seabed image surveys conducted in the east-
ern CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ images
of these specimens were catalogued as a new morphotype (i.e., Psychronaetes sp. in-
det., HOL_110). However, HOL_110 can resemble at least two other Laetmogonidae
morphotypes catalogued from seabed imagery; Laetmogonidae gen. indet., HOL_030
(e.g., dark violet, but with 8+ long papillae) which is commonly found in the eastern
CCZ (but not in the Kiribati EEZ); and Psychronaetes sp. indet., HOL_122 (e.g., vio-
let, but only with six or seven long papillae and with fewer (< 20) and larger, thick tube
feet) which was also only found in the western CCZ.
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Genus Laetmogone éel, 1879
Laetmogone cf. wyvillethomsoni éel, 1979
Fig. 49
Material. C-C Z • 1 specimen; APEI 7; 4.8877°N, 141.7569°W;
3132 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400689 (COI),
ON406641 (18S); NHMUK 2021.18; Voucher code: CCZ_062.
Other material. P O • 1 specimen, holotype of Laetmogone spongiosa
éel, 1879; south of Japan; 34.1167°N, 138°E; 1033 m deep; Challenger Expedition,
Stn. 235; NHMUK 1883.6.18.47.
Description. Single specimen (Fig. 49A). Body cylindrical, ~ 3× as long as wide
(L = 15.6 cm, W = 5.2 cm), with convex dorsal surface and somewhat attened ventral
surface, tapering posteriorly; mouth anterior, subventral, terminal; anus posterior,
terminal, slightly dorsal; violet colouration in live and preserved specimen, with darker
ventral surface (Fig. 49A–C). Tentacles 15, of almost equal size, and very dark at the
tips. Odd ambulacrum is naked; 27 or 28 tube feet arranged in a single row on each
of the paired ventral ambulacra, forming a continuous line on the anterior ⅔ of the
body and scattered posteriorly, also decreasing in size (Fig. 49C). Each paired dorsal
ambulacrum with a single row of long processes, 12 on the left and 13 on the right;
longest processes longer than ⅓ of the body length. Twenty pedicels along each side
of the ventral surface, posterior pairs smaller than the others. Fourteen processes of
the bivium along the left ambulacra and thirteen along the right. Tegument is thick,
completely covered by calcareous ossicles. Dorsal ossicles are wheel-like of various sizes
(40–226 µm in diameter), with four or ve studs, mostly ve, on primary central
crosses, and with 8–17 spokes, mostly eight on large wheels; ossicle is convex, rim
smooth, interspoke areas small, and large central area on large wheels (Fig. 49D).
Remarks. Closest match on public databases for the COI gene sequence was
other sequences of Laetmogone wyvillethomsoni éel, 1879 (4.0–5.8% K2P genetic
distance) from the Ross Sea and Marie Byrd Seamounts (O’Loughlin et al. 2011).
e specimen from the CCZ and specimens from L. wyvillethomsoni from Antarctica
were recovered in our phylogeny (Fig. 34) in a well-supported clade (Fig. 34), which
is subdivided in three clades including the two Antarctic clades stratied by depth
reported in O’Loughlin et al. (2011), and the specimen from the CCZ. Type material
for L. wyvillethomsoni was collected during the H.M.S. Challenger expedition at
stations 300 (o the coast of South America; 33.7° S, 78.3°W; 2514 m depth) and 147
(west of the Crozet Islands; 46.2667° S, 48.45° E; 2926 m), and high morphological
variability was reported (éel 1879). e CCZ specimen morphologically resembles
L. wyvillethomsoni, but no rod-shaped ossicles were found in the dorsal skin, diering
from the original description.
Ecology. e specimen was found on the sedimented seaoor of a seamount in
APEI 7 at 3132 m depth.
Comparison with image-based catalogue. No similar laetmogonid morpho-
types have been encountered in seabed image surveys conducted in the eastern CCZ
Benthic megafauna of the Clarion-Clipperton Zone 79
or in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of speci-
men CCZ_062 was catalogued as a new morphotype (i.e., Laetmogone sp. indet.,
HOL_123).
Class Ophiuroidea
To date, there are 1201 records of ophiuroids occurring at > 3000 m depth in the
CCZ, with 117 representing preserved specimens (OBIS 2022). Four specimens
belonging to three dierent species were collected and the barcoding gene COI was
amplied for all but one, for which both 18S and 28S were amplied. ese se-
quences, excluding 18S, were included in a concatenated alignment (28S, and COI)
and used to estimate a phylogenetic tree (Fig. 50). Ophiuroidea is amongst the most
challenging groups to identify and classify based on seabed image data only; key
morphological features are too small to be appropriately visualised (e.g., plates and
scales) and/or are found on the ventral disc (not visible in images). As a result, the
taxonomic resolution of ophiuroid morphotypes catalogued from seabed imagery is
usually much lower than that in other echinoderm groups. Consequently, connectiv-
ity and distribution patterns of ophiuroids derived from seabed image data should
be interpreted cautiously.
Figure 49. Laetmogone cf. wyvillethomsoni éel, 1979. Specimen CCZ_062 A in situ image; B dorsal
view of specimen before preservation C ventral view D dorsal calcareous ossicles. Scale bars: 2 cm (A);
1 cm (B, C); 50 µm (D). Image attribution: Durden and Smith (A); Wiklund, Durden, Drennan, and
McQuaid (B, C ); Bribiesca-Contreras (D).
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Figure 50. Phylogenetic tree of Ophiuroidea. Concatenated (28S, and COI) median consensus BEAST
tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of PP > 0.70 and
BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle. Nodes not recovered on
the RAxML tree are indicated with a hyphen. Sequences generated in this study are highlighted in violet.
Benthic megafauna of the Clarion-Clipperton Zone 81
Subclass Myophiuroidea Matsumoto, 1915
Infraclass Metophiurida Matsumoto, 1913
Superorder Ophintegrida O’Hara, Hugall, uy, Stöhr & Martynov, 2017
Order Ophioscolecida O’Hara, Hugall, uy, Stöhr & Martynov, 2017
Family Ophioscolecidae Lütken, 1869
Genus Ophiocymbium Lyman, 1880
Ophiocymbium tanyae Martynov, 2010
Fig. 51
Material. C-C Z • 1 specimen; APEI 1; 11.2523°N, 153.5848°W;
5204 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON406633 (18S),
ON406596 (28S); NHMUK 2022.74; Voucher code: CCZ_206.
Description. Single specimen (disc diameter = 9 mm, maximum arm length
=25mm). Disc subpentagonal, attened (Fig. 51A, B). Dorsal disc surface covered
with numerous, imbricated, delicate disc scales, which are irregular in shape, decrease
in size distally and extend dorsally onto the rst arm segments (Fig. 51C). Radial
shields and genital plates apparently absent. Disc covered by thin skin, not obscuring
the scales. Ventral surface of the disc covered by scales similar to the dorsal disc scales
(Fig.51D). Oral shield somewhat triangular, approx. as long as wide, with convex
distal edge; separated from rst lateral arm plate by the adoral shields. Adoral shields
are wing-shaped, narrowing proximally. Each jaw bears a large, spiniform, apical
papillae and a smaller adjacent one on each side; additionally, there are two to three
modied papillae placed distally on each side of the jaws, block-shaped, the distalmost
being wing-shaped. Genital slit is not conspicuous. Arms are thin, longer than twice
the disc diameter (Fig. 51A, B). Dorsal arm plates are triangular, wider than long, with
pointed proximal and straight distal edges; separated by lateral arm plates and therefore
not overlapping with preceding dorsal arm plate (Fig. 51C). Arm spines are conical,
tapering distally but with rounded tips; two arm spines on rst three arm segments,
three arm spines on next three segments and four on the rest; middle arm spine is the
longest, but all are approx. the same length, approx. half the length of one arm segment.
First ventral arm plate is triangular, while the rest are pole-axe shaped, approx. as long
as wide, separated from the preceding plate by the lateral arm plates except for the rst
two ventral arm plates (Fig. 51D). Tentacle pores are large and evident throughout the
entire length of the arm. ree attened, rounded, large adoral shield papillae. First
four arms segments with two large papilliform tentacle scales attached to the lateral
arm plate; subsequent arm segment with a single tentacle scale; tentacle scales absent
on the remaining arm segments.
Remarks. Morphological characters of the specimen are in accordance with
the description of O. tanyae, which was collected in the Izu-Bonin Trench at
6740–6850 m depth. It diers from the original description in having arms ≥
2×as long as the disc diameter (dd), instead of being approx. the same. It also dif-
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fers on the tentacle scales, which extend to the fth segment, instead of just the
third, having two tentacle scales in the rst four segments instead of just one, and
in the number of arm spines of the rst arm segments. e number of arm spines
is discussed to vary amongst the paratypes (Martynov 2010), and it is very likely
that tentacle scales are easily lost and therefore the number could dier between
specimens. Only 18S and 28S were amplied for this specimen. e 28S sequence
of the CCZ specimen is identical (K2P = 0%) to the sequence of the species Ophi-
oscolecidae sp. 20 recently reported for the CCZ (Christodoulou et al. 2020).
Both specimens are recovered within the same clade, that includes other species
of the order Ophioscolescida (Fig. 50). Ophioscolescida sp. 20, Ophiocymbium
tanyae, and O.rarispinum Martynov, 2010 are recovered as a clade possibly rep-
resenting the genus Ophiocymbium. e species from Christodoulou et al. (2020)
was identied from DNA sequences only, as the four specimens collected (east-
ern IFREMER and APEI 3) are tiny juveniles with no distinctive morphological
characters. e species is therefore distributed in the Izu-Bonin Trench and the
Clarion-Clipperton Zone.
Ecology. e specimen was found on the sedimented seaoor of an abyssal plain
on APEI 1 at 5204 m depth.
Figure 51. Ophiocymbium tanyae Martynov, 2010 A dorsal view of specimen CCZ_206 before preserva-
tion B ventral view C detail of dorsal disc surface and dorsal arm plates D detail of jaws, ventral disc sur-
face and ventral arm plates. Scale bars: 2 cm (A, B); 5 mm (C , D ). Image attribution: Wiklund, Durden,
Drennan, and McQuaid (A–D).
Benthic megafauna of the Clarion-Clipperton Zone 83
Ophiocymbium cf. rarispinum Martynov, 2010
Fig. 52
Material. C-C Z • 1 specimen; APEI 1; 11.2518°N, 153.6059°W;
5206 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400727 (COI);
NHMUK 2022.73; Voucher code: CCZ_197.
Description. Single specimen, with white arms and greyish blue disc in situ
(Fig.52A). Disc is attened and somewhat pentagonal; brownish when alive and white
after preservation (Fig. 52B, D). Dorsal disc surface is covered by minute, thin, imbricat-
ed scales covered by a thin skin, not obscuring the scale margins; few granuliform spinel-
ets scattered on the dorsal surface (Fig. 52B). Small, oval, radial shields, approx. as long as
wide, arranged diagonally and touching proximally; distal margin extends beyond the disc
margin (Fig. 52D). Ventral surface of the disc covered by scales similar to the ones on the
dorsal surface, but lacking spinelets; gonads are visible through the thin scales (Fig.52C).
Each jaw bears two or three apical papillae, and three oral papillae on each side; two dis-
talmost are block-shaped while the third distalmost is spiniform. Oral shield is triangular,
longer than wide, rounded proximally; separated from the rst lateral arm plate by the
wing-shaped adoral shield. Supplementary oral shield, wider than long, located on the
distal margin of the oral shield. Two adoral shield papillae, with one placed in the middle
of each shield, resembling arm spines in shape and size. Arms are slender, ≥ 3× as long as
the disc diameter. Dorsal arm plates triangular, with rounded distal margin and slightly
convex distal edge, separated from preceding plates by lateral arm plates; rst two dorsal
arm plates absent but arm segments covered by thick skin with smaller plates embedded
(Fig. 52D). Adjacent lateral arm plates are slightly separated by soft tissue; each lateral arm
plate bears four long arm spines, similar in size; only two arm spines present in the rst
three arm segments and three on subsequent two arm segments. First ventral arm plate is
small, broad and triangular, with the rest being pole-axe shaped and separated from the
preceding plate except for the rst two segments. Tentacle pores are large throughout the
entire length of the arm, with no tentacle scales except for the rst arm segment, where
there is one attached to the lateral arm plate and resembles a small arm spine.
Remarks. In the phylogenetic tree, the specimen from the western CCZ is recov-
ered as closely related to Ophiocymbium tanyae (Fig. 50). Ophiocymbium rarispinum
was described from the Izu-Bonin Trench, between 6740 and 6850 m depth (ZMMU
D-798), and no genetic sequences have been published. Morphological characters are
concordant with the description of O. rarispinum, but diers in the length of the arms,
the number of oral papillae and the number of arm spines.
Ecology. e specimen was found crawling on the abyssal sediments of APEI 1 at
5206 m depth.
Comparison with image-based catalogue. A similar Ophiuroidea morphotype
(i.e., Ophiocymbium sp. indet., OPH_013) has been encountered in seabed image sur-
veys conducted across nodule elds areas of the eastern CCZ, but not in the abyssal
areas surveyed within the Kiribati EEZ.
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Figure 52. Ophiocymbium cf. rarispinum Martynov, 2010. Specimen CCZ_197 A in situ image B dor-
sal surface before preservation C detail of ventral surface, jaws and ventral arm plates D detail of dorsal
arm plates. Scale bars: 1 cm (A, B); 5 mm (C); 2.5 mm (D). Image attribution: Durden and Smith (A);
Wiklund, Durden, Drennan, and McQuaid (B–D).
Superorder Euryophiurida O’Hara, Hugall, uy, Stöhr & Martynov, 2017
Order Ophiurida Müller & Troschel, 1840 sensu O’Hara et al. 2017
Suborder Ophiurina Müller & Troschel, 1840 sensu O’Hara et al. 2017
Family Ophiopyrgidae Perrier, 1893
Genus Ophiuroglypha Hertz, 1927
Ophiuroglypha cf. irrorata (Lyman, 1878)
Fig. 53
Material. C-C Z • 1 specimen; APEI 7; 4.9081°N, 141.6813°W;
3239 m deep; 26 May. 2018; Smith & Durden leg.; GenBank: ON400685 (COI);
NHMUK 2021.21; Voucher code CCZ_058. • 1 specimen; APEI 7; 4.8897°N,
141.75°W; 3096 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400686
(COI); NHMUK 2022.72; Voucher code: CCZ_059.
Description. Two specimens, with greyish disc and pale arms in situ (Fig. 53A,
B). Disc rounded to pentagonal, attened, with slender, long arms, at least disc
diameter (disc diameter = 2.6 cm, arm length = 13.1 cm; Fig. 53C, D). Dorsal
disc surface covered by irregular, larger disc scales surrounded by small, imbricated
disc scales that also vary in size and shape. Radial shields are small, subtriangular,
Benthic megafauna of the Clarion-Clipperton Zone 85
almost as wide as long. Arm combs visible under the radial shields; with ve short
block-like arm-comb spinelets, not continuous on dorsal midline. Ventral surface
of the disc is covered by large, imbricated scales, increasing in size towards the
margin of the disc (Fig. 53F). Oral plates with 6–8 oral papillae, proximalmost
Figure 53. Ophiuroglypha cf. irrorata (Lyman, 1878). Specimen CCZ_059 A in situ image. Specimen
CCZ_058 B in situ image C dorsal view of specimen before preservation D ventral view E arm hooklets
F detail of ventral disc surface and ventral arm plates. Scale bars: 2 cm (A, B); 1 cm (C , D ); 2 mm (F).
Image attribution: Durden and Smith (A, B ); Wiklund, Durden, Drennan, and McQuaid (C–F).
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are pointed, becoming block-like towards the distal side of the oral plate. Oral
shield approx. as long as wide, subpentagonal, with somewhat concave proximal
margins, a convex distal margin, and with lateral margins slightly constricted in
the middle, where the genital slit begins. Adoral shields touching proximally, with
a similar width all along, and separating the oral shield from the rst lateral arm
plates. Genital slits run from the middle of the oral shield to the disc margin, bor-
dered by a continuous row of block-like genital papillae that continues dorsally as
an arm-comb.
Dorsal arm plates fan-shaped, contiguous. Lateral arm plates bear three short
(less than a third of the length of the arm segment) arm spines from the third arm
segment; two are located ventrally, very close together, and one located dorsally,
approx. halfway through the lateral arm plate; rst arm segment bears two arm
spines, the second two or three spines. Ventral arm plate trapezoidal, wider than
long, only touching the preceding plate only on rst three arm segments, after which
they are separated by the lateral arm plates and become fan-shaped to rhomboidal,
more than twice as wide as long, with pointed proximal edge and rounded distal
margin. Towards the distal end of the arms, the second lowest spine is modied into
a hyaline hooklet (Fig. 53E). Tentacle pores only on most proximal segments (8–11),
with six ventral and six lateral tentacle scales on rst arm segment and decreasing
in number until there is a single, very small, spiniform, tentacle scale remaining for
most of the arm length.
Remarks. Both specimens collected are only 0.4% divergent (K2P distance) in
COI sequences between them. Closest genetic match is Ophiuroglypha sp. (8% K2P
distance) collected in the CCZ (Christodoulou et al. 2020), and in the phylogenetic
tree they were recovered in a well-supported clade along with other species of
Ophiuroglypha (Fig. 50). Both specimens have an upturned hook in the second lowest
arm spine, which is characteristic of species of the genus Ophiuroglypha (previously a
subgenus but raised to genus by O’Hara et al. (2018)). Morphologically, the species
resembles to Ophiuroglypha irrorata concreta (Koehler, 1901) based on the arm spine
arrangement, dorsalmost spine separated from the two ventral spines. However, the
DeepCCZ specimens are listed as O. cf. irrorata, as a recent study suggested that the
arm spine arrangement might not be species specic, hence questioning the validity
of O. irrorata irrorata (Lyman, 1878) and O. irrorata concreta (Stöhr and O’Hara
2021). Additionally, molecular data has suggested that O. irrorata represents an
unresolved complex of species (Christodoulou et al. 2019).
Ecology. Both specimens were found on the sedimented seaoor of a seamount
in APEI 7, at 3096 (specimen CCZ_059) and 3239 m (specimen CCZ_058) depth.
Comparison with image-based catalogue. No similar Ophiuroidea morphotypes
have been encountered in seabed image surveys conducted in the eastern CCZ nor
in abyssal areas of the Kiribati EEZ. Consequently, the in situ images of CCZ_058
and CCZ_059 were catalogued as a new morphotype (i.e., Ophiuroglypha sp. indet.,
OPH_012).
Benthic megafauna of the Clarion-Clipperton Zone 87
Phylum Porifera Grant, 1836
A total of eight sponges was collected in the western CCZ. All these belong to the class
Hexactinellida and represent seven dierent species, but none was condently assigned
to any known species. To date, there are 255 records of hexactinellid sponges occur-
ring at > 3000 m depth in the CCZ, with only eight representing preserved specimens
(OBIS 2022). Several genes were targeted for amplication, but only 16S was success-
fully amplied for all of them. Other genes amplied were COI (7 specimens), 18S
(5), 28S (5), and ALG11 (3). Sequences of these genes were combined with the con-
catenated alignment from Dohrmann (2018), and the phylogenetic tree was estimated
using the same parameters (Fig. 54).
Class Hexactinellidae Schmidt, 1870
Subclass Amphidiscophora Schulze, 1886
Order Amphidiscosida Schrammen, 1924
Family Hyalonematidae Gray, 1857
Genus Hyalonema Gray, 1832
Hyalonema stet. CCZ_020
Fig. 55
Material. C-C Z • 1 specimen; APEI 7; 5.1149°N, 141.8967°W;
4856 m deep; 25 May. 2018; Smith & Durden leg.; GenBank: ON400683 (COI),
ON406634 (18S), ON406608 (16S), ON406597 (28S), ON411254 (ALG11);
NHMUK; Voucher code: CCZ_020. • 1 specimen; APEI 1; 11.2954°N, 153.7422°W;
5245 m deep; 09 Jun. 2018; Smith & Durden leg.; GenBank: ON400721 (COI),
ON406609 (16S); NHMUK 2022.8; Voucher code: CCZ_179.
Description. Two specimens. Lophophytous sponges (Fig. 55A–C). Body is
white, ovoid, almost as wide as long (CCZ_020 W = 4.7 cm, L = 5 cm; CCZ_179
W = 8 cm, L = 8 cm); with an osculum (CCZ_020 d = 1 cm; CCZ_179 d = 4 cm)
surrounded by a thin margin; separated atrial cavity. Attached to the sediment by a
thin tuft of basalia that extends from the central lower body (CCZ_020 L > 7 cm;
CCZ_179 L > 20 cm).
Remarks. Genetic sequences between specimens CCZ_020 and CCZ_179 are
1% and 0.8% divergent (K2P distance) for COI and 16S, respectively. COI and 16S
closest matches are sequences from Tabachnickia sp. within the Hyalonematidae. e
sequence for the 18S is > 95% similar to other species of Hyalonema. In the phylo-
genetic tree, both specimens were recovered together, in a well-supported clade with
other members from dierent subgenera within the genus Hyalonema and including
Tabachnickia sp. (Fig. 54).
Ecology. e specimens were collected attached to abyssal sediments of APEI 7
and APEI 1 at 4856 and 5245 m depth, respectively.
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Figure 54. Phylogenetic tree of Hexactinellida. Concatenated (16S, 18S, 28S, and COI) median con-
sensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of
PP > 0.70 and BS > 50 are shown, with values of PP > 0.95 and BS > 90 indicated with a circle. Nodes
not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study are
highlighted in violet.
Benthic megafauna of the Clarion-Clipperton Zone 89
Comparison with image-based catalogue. A very similar hyalonematid morpho-
type (i.e., Hyalonema sp. indet., HEX_002) has been commonly encountered in sea-
bed image surveys conducted across the eastern CCZ and in abyssal areas of the Kiri-
bati EEZ, mostly in nodule eld areas. In situ images of HEX_002 (Fig. 55A, C) show
that the aperture width of the central osculum is an unreliable character to distinguish
dierent Hyalonema sp. morphotypes (nor these from other genera) in seabed imagery,
as this contracts and expands episodically (e.g., Kahn et al. 2020).
Figure 55. Hyalonema stet. CCZ_020. Specimen CCZ_179 A in situ image B specimen before pres-
ervation. Specimen CCZ_020 C in situ image. Scale bars: 2 cm (A, C); 1 cm (B). Image attribution:
Durden and Smith (A, C ); Wiklund, Durden, Drennan, and McQuaid (B).
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Hyalonema stet. CCZ_081
Fig. 56
Material. C-C Z • 1 specimen; APEI 4; 7.036°N, 149.9395°W;
5031 m deep; 01 Jun. 2018; Smith & Durden leg.; GenBank: ON406610 (16S);
NHMUK 2022.9; Voucher code: CCZ_081.
Description. Single specimen (Fig. 56). Lophophytous sponge; body white, some-
what bowl-shaped, longer than wide (L = 3.9 cm, W = 2.8 cm); with a wide osculum
(d = 2.6 cm) surrounded by a thin margin. Attached to the sediment by a thin tuft of
basalia that extends from the central lower body.
Remarks. Morphological characters were found concordant with those of the
genus Hyalonema. e 16S sequence is very similar (99.34%) to sequences from
H.(Cyliconemaoida) ovuliferum Schulze, 1899, being the closest match on public databases.
It is recovered in a well-supported clade along with other hyalonematids (Fig. 54),
supporting its placement within the genus. It was not possible to assign it any subgenus,
as the dierent subgenera have not been recovered as monophyletic (Dohrmann 2018).
Figure 56. Hyalonema stet. CCZ_081 A in situ image, B. Scale bars: 1 cm (A); 5 mm (B). Image at-
tribution: Durden and Smith (A); Wiklund, Durden, Drennan, and McQuaid (B).
Benthic megafauna of the Clarion-Clipperton Zone 91
Ecology. is specimen was collected anchored to the sediment on the abyssal
plain of APEI 4 at 5031 m.
Comparison with image-based catalogue. A very similar hyalonematid mor-
photype (i.e., Hyalonema sp indet., HEX_003) has been commonly encountered in
seabed image surveys conducted across the eastern CCZ and in abyssal areas of the
Kiribati EEZ. As observed in HEX_002, the aperture width of the central osculum
in HEX_003 can vary owing to body contractions or expansions (Kahn et al. 2020),
and should hence not be used to guide identications of these morphotypes based on
seabed imagery.
Subclass Hexasterophora Schulze, 1886
Order Lyssacinosida Zittel, 1877
Family Euplectellidae Gray, 1867
Subfamily Euplectellinae Gray, 1867
Euplectellinae stet. CCZ_199
Fig. 57
Material. C-C Z • 1 specimen; APEI 1; 11.2518°N, 153.5853°W;
5202 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400729 (COI),
ON406611 (16S); NHMUK; Voucher code: CCZ_199.
Description. Single specimen (Fig. 57A). Lophophytous white sponge with tubu-
lar habitus (L = 5 cm). ere is a large, central osculum (d = 2cm), and protruding s-
tules with terminal suboscula, each with one or two, mostly two, openings (Fig.57B).
Long basalia (L = 6 cm) arranged as a tube, protruding from the lower end of the
habitus and anchored to the sediment (Fig. 57C).
Remarks. e 16S sequence is close to Corbitella discasterosa Tabachnick & Lévi,
2004 (2.3% K2P distance), and it is also similar to other species within the family
Euplectellidae. e closest COI match is Docosaccus maculatus Kahn, Geller, Reiswig
& Smith Jr., 2013 (91.5% similarity). Morphological characters are concordant with
those of the family Euplectellidae, and in the phylogenetic analysis it is recovered
within the Euplectellidae (Fig. 54), along with other species of Holascus Schulze,
1886, but poorly supported. Although the subfamilies were not recovered as
monophylectic, it is very likely it belongs to the subfamily Euplectillinae based on its
lophophytous form.
Ecology. is specimen was found anchored to the abyssal sediments of APEI 1
at 5202 m depth.
Comparison with image-based catalogue. A very similar Euplectellidae morpho-
type (i.e., Euplectellidae gen. indet., HEX_005) has been commonly encountered in
seabed image surveys conducted across nodule elds areas of the eastern CCZ, but not
in abyssal areas of the Kiribati EEZ. Kersken et al. (2019) collected a few specimens
of HEX_005 at the APEI 3 (Northeastern CCZ), identied as Corbitella discasterosa
based on morphological characters. Corbitella discasterosa is basiphytous, while our
specimen is lophophytous, but this would hardly be distinguished from seabed images.
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Genus Docosaccus Topsent, 1910
Docosaccus sp. CCZ_021
Fig. 58
Material. C-C Z • 1 specimen; APEI 7; 5.1043°N, 141.8867°W;
4860 m deep; 25 May. 2018; Smith & Durden leg.; GenBank: ON400684 (COI),
ON406635 (18S), ON406612 (16S), ON406598 (28S), ON411255 (ALG11);
NHMUK 2022.6; Voucher code: CCZ_021.
Description. Single specimen; lophophytous sponge. Plate-like, at, subcircular
body; 8.7 cm at its longest axis, 1 mm thick (Fig. 58A). Colouration is yellowish. Atrial
surface facing up (Fig. 58C), and dermal surface almost in contact with the seaoor,
with basalia protruding from it and anchoring it to the sediment (Fig. 58B).
Remarks. External morphological characters are concordant with the description
of D. maculatus (Kahn et al. 2013). However, sequences for the 16S and COI genes
Figure 57. Euplectellinae stet. CCZ_199 A in situ image B detail of body C whole specimen with
protruding basalia. Scale bars: 1 cm (A); 5 mm (B). Image attribution: Durden and Smith (A); Wiklund,
Durden, Drennan, and McQuaid (B, C).
Benthic megafauna of the Clarion-Clipperton Zone 93
from the holotype are 2.4% and 3.9% divergent (K2P distance), respectively, from
the western CCZ specimen. Sequences from 18S and 28S do not match to sequences
from D. maculatus. e species was described from Station M, o California, in the
Pacic Ocean at depths of 3,953–4,000 m, but the genus was originally thought to be
restricted to Antarctica (Kahn et al. 2013). is species has been recorded in the CCZ,
in the eastern IFREMER contract area and in APEI 3, from 4905–4998 m depth (Ker-
sken et al. 2019). e specimen collected in the western CCZ diers from the holotype
of D. maculatus in having more parietal oscula, and is smaller, and therefore considered
a dierent species. External morphological characters also dier from the other species
reported for the CCZ, D. nidulus Kersken, Janussen & Martínez Arbizu, 2019.
Ecology. is specimen was found anchored to abyssal sediments of APEI 7 at
4860 m depth.
Comparison with image-based catalogue. A very similar Docosaccus sp. morpho-
type (i.e., Docosaccus maculatus sp. inc., HEX_015) has been very frequently encoun-
tered in seabed image surveys conducted across nodule elds areas of the eastern CCZ
and in abyssal areas of the Kiribati EEZ.
Genus Holascus Schulze, 1886
Holascus stet. CCZ_078
Fig. 59
Material. C-C Z • 1 specimen; APEI 7; 5.0443°N, 141.8162°W;
48745 m deep; 28 May. 2018; Smith & Durden leg.; GenBank: ON400700 (COI),
ON406636 (18S), ON406613 (16S), ON406599 (28S), ON411256 (ALG11);
NHMUK 2022.7; CCZ_078.
Description. Single specimen; lophophytous white sponge (Fig. 59A). Band-like
body, collar formed from thin wall with two large openings, with lower opening being
larger than upper opening (Fig. 59B, C). Body height of 4.8 cm, lower body diameter
of 15.1 cm, and upper body diameter of 11.8 cm. Basalia almost as long as the body
height, protruding from the lower margin and anchoring it to the sediment (Fig. 59A).
Figure 58. Docosaccus sp. CCZ_021 A in situ image B dermal surface C and atrial surface. Scale
bars: 1 cm (A, B, C). Image attribution: Durden and Smith (A); Wiklund, Durden, Drennan, and
McQuaid (B, C ).
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94
Remarks. Morphological external characters are concordant with the description
of Holascus spinosus Kersken, Janussen & Martínez Arbizu, 2019, which was described
from the IOM area in the CCZ. e closest genetic matches on GenBank for the 16S
correspond to species within the genus Holascus (2.1–3.5% genetic divergence), with
the holotype of Holascus spinosus being the closest match (2.1% genetic divergence).
ere are no 18S sequences available for H. spinosus, but it is 0.23% divergent from
another species within the genus, H. euonyx (Lendenfeld, 1915), from which it diers
morphologically. In the phylogenetic tree it was recovered, with low support, as sister to
H. spinosus (Fig. 54), but 16S genetic divergence suggested these to be separate species.
Ecology. is specimen was found anchored to abyssal sediments of APEI 7 at
4874 m depth.
Comparison with image-based catalogue. A very similar Holascus sp. morpho-
type (i.e., Holascus sp. indet., HEX_014) has been commonly encountered in seabed
image surveys conducted across nodule elds areas of the eastern CCZ and in abyssal
areas of the Kiribati EEZ.
Subfamily Bolosominae Tabachnick, 2002
Bolosominae stet. CCZ_198
Fig. 60
Material. C-C Z • 1 specimen; APEI 1; 11.2518°N, 153.6053°W;
5205 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400728 (COI),
ON406637 (18S), ON406614 (16S), ON406600 (28S); NHMUK 2022.10; Vouch-
er code: CCZ_198.
Description. Single specimen; lophophytous white sponge (Fig. 60A, B). Body
is cup- to bell-shaped, slightly wider than long (L = 10 cm, W = 11 cm), with a long,
Figure 59. Holascus stet. CCZ_078 A in situ image B lateral view of specimen before preservation Ctop
view. Scale bars: 2 cm (A); 1 cm (B). Image attribution: Durden and Smith (A); Wiklund, Durden, Dren-
nan, and McQuaid (B, C ).
Benthic megafauna of the Clarion-Clipperton Zone 95
slender stalk (L = 70 cm) anchored to soft sediment. Central osculum with thick
body walls.
Remarks. e closest match with the 18S sequence is the holotype of Hyalostylus
microoricomus Kersken, Janussen & Martínez Arbizu, 2019 (99.8%), described from
the Heip Mountains in the GSR contract area in the CCZ at 3788 m depth (Kersken
et al. 2019). However, in the phylogenetic tree (Fig. 54) it was recovered in a well-
supported clade representing the subfamily Bolosominae, but subclades were not well
supported and hence the specimen is not attributed to any genera.
Ecology. is specimen was collected on abyssal sediments of APEI 1 at 5205 m
depth, and was anchored to the sediment.
Comparison with image-based catalogue. A very similar stalked sponge mor-
photype (i.e., Hexactinellidae ord. indet., HEX_026) has been encountered in seabed
image surveys conducted at the eastern CCZ, but not in abyssal areas of Kiribati’s EEZ.
In seabed images, HEX_026 highly resembles Hyalonema (Cyliconemaoida) campanula
Lendenfeld, 1915, as identied by Kersken et al. (2019) based on morphological traits
observed in specimens encountered in the eastern CCZ.
Figure 60. Bolosominae stet. CCZ_198 A, C in situ images B specimen before preservation. Scale bars:
5cm (A, C ). Image attribution: Durden and Smith (A, C ); Wiklund, Durden, Drennan, and McQuaid (B).
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Order Sceptrulophora Mehl, 1992
Family Euretidae Zittel, 1877
Subfamily Chonelasmatinae Schrammen, 1912
Genus Bathyxiphus Schulze, 1899
Bathyxiphus sp. CCZ_151
Figure 61
Material. C-C Z • 1 specimen; APEI 4; 6.9881°N, 149.9321°W;
5001 m deep; 06 Jun. 2018; Smith & Durden leg.; GenBank: ON400713 (COI),
ON406638 (18S), ON406615 (16S), ON406601 (28S); NHMUK 2022.11; Vouch-
er code: CCZ_151.
Description. Single specimen; basiphytous sponge (Fig. 61A, E). Body white,
elongated (L > 60 cm, W = 10 cm), thin (W = 11 mm), upright-blade shaped habitus
(Fig. 61B, C, E), attached to, possibly, a beaked-whale rostrum covered in manganese
crust (Fig. 61A).
Remarks. Morphological characters are concordant with those of the genus, being
very similar to Bathyxiphus subtilis Schulze, 1899, the only known species in the genus.
However, a midrib has been suggested as a key morphological feature absent in the
specimen presented here. e species was described from Isla Guadalupe at 1251 m
depth, and was recently recorded in APEI 3 at 4914 m (Kersken et al. 2019). However,
Figure 61. Bathyxiphus sp. CCZ_151. Specimen CCZ_151 A, E in situ images B, C , D specimen before
preservation. Scale bars: 2 cm (B, C). Image attribution: Durden and Smith (A, E ); Wiklund, Durden,
Drennan, and McQuaid (B–D).
Benthic megafauna of the Clarion-Clipperton Zone 97
16S sequences between the APEI 3 specimen and the western CCZ specimen are 3%
divergent (K2P distance). Additionally, they were not recovered as monophyletic in
the phylogenetic tree (Fig. 54) and hence considered dierent species. Measurements
of total length were estimated from in situ images as only approx. half the specimen
was recovered.
Ecology. e specimen was found attached to a beaked-whale rostrum covered in
polymetallic crust, on abyssal sediments of APEI 4 at 5001 m depth.
Comparison with image-based catalogue. A similar Bathyxiphus sp. morphotype
(i.e., Bathyxiphus sp. indet., HEX_025), though usually much smaller-sized, has been
commonly encountered in seabed image surveys conducted across nodule elds areas
of the eastern CCZ, but not in abyssal areas of the Kiribati EEZ.
Discussion
e DeepCCZ expedition surveyed three APEIs on the western CCZ, targeting both
abyssal seaoor and seamounts, and sampling the dierent megafaunal components.
e ROV survey for benthic megafauna yielded a remarkably diverse collection from
a small number of specimens, with 48 species from only 55 specimens (Table 1). Most
species were represented by a single specimen, but whenever more than one specimen
of the same species was collected, they were found at similar depths and same geoform
(i.e., seamount, abyssal plain or seamount slope), even if collected in dierent sites.
More than half of the species, 26, were sediment dwellers found both on seamounts
and abyssal plains, mostly representing mobile megafauna, such as sea urchins, sea
cucumbers, brittle stars, sea stars, a polychaete worm, and a jellysh observed skimming
the seaoor, and a single sessile species of cup coral. Eight species, mainly sponges,
were found anchored to the sediment, ve species were found attached to nodules, two
species attached to polymetallic crust found on seamount slopes, and a single species of
sponge was found attached to a fossilised beaked-whale rostrum covered in manganese
crust. Additionally, six species were found attached to old glass sponge stalks, including
scalpellids, crinoids, and actiniarians, with a few species co-occurring on the same
sponge stalks.
Many of the taxa presented here had been encountered in image-based surveys
from across the CCZ but never collected before, making our collections particularly
important for improving taxonomic knowledge (Glover et al 2018). We were able to
obtain genetic sequences for all but one specimen. e vast majority of taxa (29) could
not be attributed to described species, with only four having been previously reported
for the CCZ (Christodoulou et al. 2020; Glover et al. 2016b; Pawson and Foell 1986).
e high number of delimited but undescribed species reported here highlights our
still-limited knowledge on abyssal invertebrate megafauna in the CCZ, especially in the
protected APEI regions, and illustrates the importance of publishing open DNA taxo-
nomic data, even if full species identication and description are not always possible.
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98
Although the CCZ is often considered a vast and relatively homogeneous abys-
sal plain, this region has substantial, ecologically important, seaoor heterogeneity
(McQuaid et al. 2020; Washburn et al. 2021a). Variations in community structure and
biodiversity have been documented across the region (Smith et al. 2021), mainly in the
central and eastern CCZ, resulting from local and regional environmental conditions,
such as topographical changes, food input, and nodule abundance (Stoyanova 2012;
Vanreusel et al. 2016; Simon-Lledó et al. 2019c). While this study was not designed to
investigate drivers of benthic megafaunal assemblages, some dierences were observed
between seamounts and abyssal plains. In other areas, seamounts have been found to
harbour similar megafaunal taxonomic compositions as adjacent continental slopes
(Clark et al. 2010). However, little overlap between seamount and abyssal plain taxa
has been reported from surveys in the eastern CCZ (Cuvelier et al. 2020), and in west-
ern APEIs (Bribiesca-Contreras et al. 2021; Durden et al. 2021; Leitner et al. 2021).
Due to the sampling strategy of maximising diversity, most species were represented
by a single specimen, but whenever more than one specimen from the same species
was collected, they were found in the same geoform (i.e., seamount or abyssal seaoor)
even when collected in dierent APEIs (Table 1). Eight of the nine species that were as-
signed to previously described taxa were found in abyssal sites, except for Calyptrophora
distolos that was originally described from a seamount (Cairns 2018). is is possibly a
result of seamounts being understudied and undersampled compared to abyssal plains.
While the lack of shared species between habitats in this study could be a result of
undersampling, faunistic changes between habitats have been reported in the CCZ (Cuve-
lier et al. 2020; Durden et al. 2021). Dierences between abyssal plains and seamounts in
APEIs 4 and 7 (with only 16 and 19% overlap in Operational Taxonomic Units; OTUs)
have been observed from environmental-DNA sampling of sediments, with most OTUs
being rare and limited to small areas (Laroche et al. 2020). Similarly, image-based surveys
in the western APEIs observed very few common morphotypes shared across habitats, with
several rare morphotypes observed only once (Durden et al. 2021). In addition, Leitner
et al. (2021) have argued that even if some species are shared between seamounts and the
abyssal seaoor, the areal coverage of seamounts is a tiny proportion compared to the areal
of abyssal seaoor in the CCZ, so seamounts could supply only a very limited number of
propagules for recolonisation over ecological time scales. Previous ndings and our data
currently suggest that CCZ seamounts could not act as viable refugia for abyssal taxa and
provide propagules for recolonisation of areas disturbed by mining. Following the princi-
ples of a precautionary approach, representative and suitable refuge areas for megafaunal
communities needs to be dened and protected as source of propagules for recolonisation.
e study of deep-sea ecosystems presents several challenges, from the diculties
of collecting at great depths, to the resources required for an oceanographic survey, and
the labour to document and describe all the collected material (Glover et al. 2018).
With the pressing need to describe the biodiversity of these habitats, taxonomic stud-
ies that synthesise morphological, ecological, and genetic information, even for un-
described and indeterminate species (e.g., Dahlgren et al. 2016; Glover et al. 2016b;
Amon et al. 2017a, b; Wiklund et al. 2017; Christodoulou et al. 2020) contribute
Benthic megafauna of the Clarion-Clipperton Zone 99
fundamentally to the iterative building of biodiversity baselines (Engel et al. 2021;
Glover et al. 2015). For instance, based on DNA sequences, we found two taxa with
distributions likely spanning the entire CCZ, because they matched previously inde-
terminate juveniles collected in the eastern CCZ (Ophiocymbium tanyae as Ophioscol-
ecidae sp. 20 in Christodoulou et al. (2020), and cf. Porphyrocrinus sp. CCZ_165 as
Crinoidea sp. NHM_055 in Glover et al. (2016b)).
One of the limitations of this study is the scarcity of published barcodes for deep-see
invertebrates. For instance, an environmental DNA study in the western APEIs found
that only 25% and 1.5% of OTUs could be assigned to family level using reference
libraries for 18S and COI, respectively (Laroche et al. 2020). We mainly targeted the bar-
coding gene COI because it has been used before to document biodiversity in the CCZ
(e.g., Dahlgren et al. 2016; Glover et al. 2016b; Wiklund et al. 2017; Christodoulou et
al. 2020). However, while the gene is useful for species delimitation in most groups, it is
so variable that it does not accurately reect phylogenetic relationships. us, in several
cases it was not possible to assign our specimens to lower taxonomic levels based solely
on genetic information because comparisons of our generated sequences to public data-
bases showed that the closest taxa were only ~ 80% similar to multiple species belonging
to dierent higher taxonomic ranks (Order or Family levels). Hence, additional genes
were targeted to resolve higher rank relationships (16S, 18S, and 28S), but even for these
genes, the lack of reference libraries hindered taxonomic placement. is is not surprising
because the deep sea is severely undersampled and genetic sequences from bathyal and
abyssal species are scarce in public databases. Even though there is much greater availabil-
ity of genetic information for shallow water species, this did not inform our taxonomic
assignments for most groups, because it has been found that bathyal and abyssal taxa
often represent separate lineages from shallow-water ones (e.g., brittle stars: Bribiesca-
Contreras et al. 2017; Christodoulou et al. 2019; isopods: Lins et al. 2012).
Additional challenges result from the documentation that COI and other
mitochondrial genes show very little variation in anthozoan cnidarians (Hebert et al.
2003), preventing use of COI for species delimitation. For instance, the sequence of
Chrysogorgia sp. CCZ_112 collected in APEI 4 diered from the COI sequence of
C.abludo by a single nucleotide. Although the specimen was not assigned to the species
because previous ndings show that congeneric species of octocorals can share the same
COI haplotype (McFadden et al. 2011), we also took a precautionary approach when
assigning species to avoid overestimation of species ranges. In some syntheses, most deep-
sea species have been assumed to have wide distributional ranges (McClain and Hardy
2010), likely resulting from the greater ease of discovering abundant, wide-ranging species
than species with narrow distributions (Higgs and Attrill 2015), but also due to low
or overlooked morphological variability that hinders our ability to discriminate species.
Molecular studies have revealed dierent distinct lineages in some common, previously
considered wide-ranging species. For instance, genetic sequences and further detailed
morphological examination revealed at least two distinct species within the cosmopolitan
Psychropotes longicauda éel, 1882 (Gubili et al. 2017; Gebruk et al. 2020). One
represents the cosmopolitan species P. pawsoni Gebruk & Kremenetskaia in Gebruk et
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100
al. 2020 distributed in all four oceans, and the second represents a species only occurring
in the northwest Pacic, P. moskalevi Gebruk & Kremenetskaia in Gebruk et al. 2020.
While detailed taxonomic studies can reveal an overlooked biodiversity in deep-sea
taxa and are greatly improving our understanding of species ranges, they are time-con-
suming and usually target a small area or a few taxa (e.g., O’Loughlin and Ahearn 2005;
Molodtsova and Opresko 2017; Herzog et al. 2018; Kersken et al. 2019). In contrast,
the use of in situ seabed imagery to investigate megabenthic communities allows much
larger area surveys, but at a lower taxonomic resolution that can potentially underesti-
mate biodiversity and over-estimate species ranges. For instance, the sponge subfamilies
Euplectellinae and Corbitellinae are dierentiated by their mode of xation to substrata.
From seabed imagery, two hexactinellid sponges belonging to these subfamilies (Euplect-
ellinae stet. CCZ_199 herein, and Corbitella discasterosa in (Kersken et al. 2019), respec-
tively) were classied as the same morphotype because the mode of xation cannot be
observed when photographed from the top. However, the integration of both methods
can provide key insights into species composition and connectivity of benthic commu-
nities across the CCZ, which are fundamental aspects to guide conservation strategies.
e alignment of in situ specimen images from this study with invertebrate mor-
photypes previously catalogued from (and standardised across) dierent seabed image
surveys conducted in the CCZ (Amon et al. 2016; Simon-Lledó et al. 2019c, d, 2020;
Cuvelier et al. 2020; Durden et al. 2021) provided preliminary insight into the connec-
tivity of western megafauna populations. e 53 specimens that had an associated in situ
image were classied into a total of 45 morphotypes, from which 11 represented new
additions to the existing CCZ megafauna catalogue. Few morphotypes (9) were found
to have wider distributions, being reported from both the Kiribati EEZ to the west of
the CCZ, and from the eastern CCZ. Surprisingly, only two morphotypes were uniquely
shared with Kiribati, while 16 were uniquely shared with the eastern CCZ. ese results
suggest, rather tentatively, that western CCZ megafauna communities may share a much
larger species pool with (the more distant) eastern CCZ areas than with closer areas to-
wards the west, like Kiribati’s abyss. However, it is important to note that a much larger
sampling eort was previously conducted in eastern CCZ areas than around Kiribati. In
addition, the ROV sampling conducted for this study was limited and the number of
species identied in this study (48) is much lower than the number of morphotypes that
have been identied from seabed imagery in the western CCZ (143; Durden et al. 2021).
Further interpretation and synthesis of existing megafauna distribution data, as well as
additional sampling, will expand and contextualise these preliminary observations.
Conclusions
We provide the rst megafaunal faunistic study from the western CCZ based on
voucher specimens. Our ndings indicate a high diversity, represented mostly by un-
described species of megafauna in the western CCZ with little overlap between abyssal
plains and seamounts, and within similar habitats located in greater distances to one
Benthic megafauna of the Clarion-Clipperton Zone 101
another. Further studies should aim to increase our knowledge of patterns of biodiver-
sity across the entire CCZ in order to inform environmental management plans to pro-
tect its biodiversity. Our work also highlights the need for detailed taxonomic studies,
not only within the CCZ, an area targeted for deep-sea mining, but in other bathyal,
abyssal, and hadal regions. While species identication through genetic markers can
facilitate the generation of species inventories, this is only achievable when genetic
reference libraries are representative of the area and taxon of study, and these remains
limited for the CCZ megafauna.
Acknowledgements
We want to acknowledge the masters, crew and technical support sta on the R/V
Kilo Moana and ROV Lu’ukai during the DeepCCZ expedition. We are very grateful
for help with taxonomic identications provided by the expert taxonomists: Estefania
Rodriguez (AMNH) for anemones, Dhugal Lindsay (JAMSTEC) for scyphozoans;
Chris Mah (NMNH) for sea stars; Rich Mooi (CAS) and Carlos Andres Conejeros
Vargas (UNAM) for sea urchins; and Lenka Nealova (NHM) for annelids. We also
acknowledge Lauren Hughes (NHM), Miranda Lowe (NHM), Tom White (NHM),
Amanda Robinson (NMNH), Emma Sherlock (NHM), Andreia Salvador (NHM),
and Andrew Cabrinovic (NHM) for curatorial support; and Elena Luigli (NHM) and
Claire Grin (NHM) for lab support. Primary funding was from the Gordon and
Betty Moore Foundation grant no. 5596 and NOAA Oce of Ocean Exploration
(grant #NA17OAR0110209), and the University of Hawaii. We also acknowledge
funding from UK Seabed Resources, the UK Natural Environment Research Council
grant numbers NE/T003537/1 and NE/T002913/1 and through National Capability
funding to NOC as part of the Climate Linked Atlantic Section Science (CLASS)
programme (grant number NE/R015953/1), and e Norwegian Research Council
(JPIOMining Impact 2). DJA received funding from the EU’s Horizon 2020 research
and innovation programme under the Marie Sklodowska-Curie grant agreement
number 747946.
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