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Hydroids (Cnidaria: Hydrozoa: Leptothecata and Limnomedusae) on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i, with revisory notes on Hydrodendron Hincks, 1874 and a diagnosis of Plumaleciidae, new family


Abstract and Figures

Twenty-eight species of hydroids are now known from Japanese tsunami marine debris (JTMD) sent to sea in March 2011 from the Island of Honshu and landing between 2012 and 2016 in North America and Hawai‘i. To 12 JTMD hydroid species previously reported, we add an additional 16 species. Fourteen species (50%) were detected only once; given the small fraction of debris sampled, this suggests that the diversity of the total arriving hydroid fauna was likely larger. Our ongoing studies provide the first documentation of these species being rafted from one continental margin to another. Plumalecium plumularioides (Clark, 1877) is newly reported for the Japanese hydroid fauna. Fourteen species (52%), held to be either naturally amphi-Pacific or possibly introduced by ships at some earlier date, were already known from the Pacific coast of North America. We suggest that Obelia griffini Calkins, 1899, as represented in the JTMD fauna, may be a North Pacific oceanic neustonic species. We propose that Hydrodendron mirabile (Hincks, 1866) and its congeners be included in the family Phylactothecidae Stechow, 1921, here emended. We establish a new family, Plumaleciidae Choong and Calder, 2018, to accommodate the genus Plumalecium Antsulevich, 1982.
Content may be subject to copyright.
Aquatic Invasions (2018) Volume 13, Issue 1: 43–70
© 2018 The Author(s). Journal compilation © 2018 REABIC
Special Issue: Transoceanic Dispersal of Marine Life from Japan to North America and
the Hawaiian Islands as a Result of the Japanese Earthquake and Tsunami of 2011
Research Article
Hydroids (Cnidaria: Hydrozoa: Leptothecata and Limnomedusae)
on 2011 Japanese tsunami marine debris landing in North America
and Hawai‘i, with revisory notes on Hydrodendron Hincks, 1874 and
a diagnosis of Plumaleciidae, new family
Henry H.C. Choong
, Dale R. Calder
, John W. Chapman
, Jessica A. Miller
Jonathan B. Geller
and James T. Carlton
Invertebrate Zoology, Royal British Columbia Museum, 675 Belleville Street, Victoria, BC, Canada, V8W 9W2
Invertebrate Zoology Section, Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario,
Canada, M5S 2C6
Department of Fisheries and Wildlife, Oregon State University, Hatfield Marine Science Center, 2030 SE Marine Science Dr.,
Newport, Oregon 97365, USA
Moss Landing Marine Laboratories, Moss Landing, CA 95039, USA
Williams College-Mystic Seaport Maritime Studies Program, Mystic, Connecticut 06355, USA
Author e-mails: (HHCC), (DRC), (JWC), (JTC)
Corresponding author
Received: 13 May 2017 / Accepted: 14 December 2017 / Published online: 20 February 2018
Handling editor: Amy Fowler
Co-Editors’ Note:
This is one of the papers from the special issue of Aquatic Invasions on “Transoceanic Dispersal of Marine Life from
Japan to North America and the Hawaiian Islands as a Result of the Japanese Earthquake and Tsunami of 2011." The
special issue was supported by funding provided by the Ministry of the Environment (MOE) of the Government of Japan
through the North Pacific Marine Science Organization (PICES).
Twenty-eight species of hydroids are now known from Japanese tsunami marine debris (JTMD) sent to sea in March 2011 from
the Island of Honshu and landing between 2012 and 2016 in North America and Hawai‘i. To 12 JTMD hydroid species previously
reported, we add an additional 16 species. Fourteen species (50%) were detected only once; given the small fraction of debris
sampled, this suggests that the diversity of the total arriving hydroid fauna was likely larger. Our ongoing studies provide the first
documentation of these species being rafted from one continental margin to another. Plumalecium plumularioides (Clark, 1877) is
newly reported for the Japanese hydroid fauna. Fourteen species (52%), held to be either naturally amphi-Pacific or possibly
introduced by ships at some earlier date, were already known from the Pacific coast of North America. We suggest that Obelia
griffini Calkins, 1899, as represented in the JTMD fauna, may be a North Pacific oceanic neustonic species. We propose that
Hydrodendron mirabile (Hincks, 1866) and its congeners be included in the family Phylactothecidae Stechow, 1921, here emended.
We establish a new family, Plumaleciidae Choong and Calder, 2018, to accommodate the genus Plumalecium Antsulevich, 1982.
Key words: Pacific distributions, Leptothecata, Limnomedusae, anthropogenic debris, population connectivity,
transoceanic dispersal, systematics
The Great East Japan Earthquake and Tsunami of
March 11, 2011 sent into the North Pacific Ocean
a vast field of floating debris derived from the
Tōhoku coastline of northeast Honshu. Rafted objects
with living Japanese species began arriving on the
shores of North America in the spring and summer
H.H.C. Choong et al.
of 2012 and in the Hawaiian Islands in the fall of
2012 (Carlton et al. 2017). One of the most common
groups of organisms in the biofouling communities
on this debris was hydroids. Choong and Calder (2013)
reported on the presence of the Japanese hydroid
Sertularella mutsuensis Stechow, 1931 on a large
dock lost during the tsunami from the Port of Misawa
(Aomori Prefecture) that landed 14 months later, in
June 2012, on the Oregon coast. Calder et al. (2014)
reported upon collections of 11 additional coastal
thecate species (and one likely pelagic hydroid, Obelia
griffini Calkins, 1899) from biofouling on tsunami
debris intercepted in 2012 and 2013 landing in
Oregon and Washington.
We report here on additional collections of
hydroids recovered from Japanese tsunami marine
debris collected in Washington, Oregon, California,
and Hawai’i between 2012 and 2016, and analyze
the total hydroid fauna found to date.
Materials and methods
Morphological analyses
Samples were obtained from JTMD objects (identi-
fied as such through multiple lines of evidence; see
Carlton et al. 2017) landing in North America and
the Hawaiian Islands (Supplementary material Table
S1). Each object was assigned a unique identification
number preceded by JTMD-BF- (Japanese Tsunami
Marine Debris-BioFouling-). Specimens retrieved
from the field were either preserved directly in 95%
ethanol, or frozen and transferred into ethanol at a
later date. All specimens studied here are deposited
in the collections of the Invertebrate Zoology Section,
Department of Natural History, Royal Ontario
Museum (ROMIZ) and the Royal British Columbia
Museum (RBCM/BCPM). The classification and
implied relationships of hydroids adopted here gene-
rally follows Leclère et al. (2009), Maronna et al.
(2016), and Cunha et al. (2017). Species descriptions
are provided where warranted. Several taxa in this
study were described and illustrated in our previous
work (Calder et al. 2014).
Genetic analyses
Three approximately 20 × 20 cm scrapings were taken
from the sides of a floating dock (JTMD-BF-1)
originating from the Port of Misawa, Aomori Prefec-
ture, which landed on the central Oregon coast in early
June 2012 (Table S1). The samples were preserved
in 70% ethanol and sent to the Geller Laboratory at
Moss Landing Marine Laboratories, Moss Landing,
California USA. The ethanol was later decanted and
samples were rinsed with distilled water, drained,
and homogenized in an IKA (Wilmington, NC, USA)
A11 analytical mill. 10 g of homogenate were used
in a MoBio PowerSoil DNA extraction kit (Qiagen,
Germantown, Maryland, USA). Genomic DNA was
quantified using Nanodrop ND-1000 (ThermoFisher,
Waltham, Massachusetts USA). 5 ng of each total
DNA extraction were amplified in PCR cocktails
comprising a final concentration of 1 × Green Go Taq
Master Mix, 0.2 mg mL-1 BSA, 1.5 mM MgCl2, and
0.2 µM of each primer in a 50 µL reaction. We used
primers jgHCO2198 and jgLCO1490 from Geller et
al. (2013). Reaction conditions consisted of an initial
3 minute melt at 94 °C, followed by 32 cycles of a
1 minute at 95 °C, 45 seconds at 47 °C, and 90 seconds
at 72 °C. PCR amplicons were viewed on a 2%
agarose gel stained with ethidium bromide. Samples
were purified with 1.4 × the sample volume of
Agencourt Ampure (Brea, California USA) beads,
according to the manufacturer’s protocol.
Samples were quantified using Picogreen High
sensitivity DNA assay according to the manufacturer’s
protocol (Qiagen). 100 ng of sample were fragmented
with the IonXpress Ion Shear enzyme kit (Thermo-
Fisher). Samples were purified with 1.4 × the sample
volume of Agencourt Ampure beads. Samples were
then ligated with IonXpress barcodes and sequencing
adapters, size selected for ca. 400 bp using an e-gel
cassette, purified once more with 1.4 × Ampure beads.
Samples were quantified using the Agilent (Santa
Clara, California, USA) Bioanalyzer high sensitivity
chip assay and combined into an equimolar pool.
Samples were run using the Ion Torrent 400 bp
sequencing kit and v314 chip according to the
manufacturer’s protocol, yielding 500,000 reads
passing filter. Reads were trimmed of primers and
clustered into groups using a 95% similarity threshold
using the software package Geneious v9 (Biomatters,
Auckland, New Zealand).
Consensus sequences were compared to Genbank
for any matches to COI sequences annotated as derived
from Hydrozoa. Candidate novel sequences were
aligned with hydroid sequences downloaded from
Genbank, aligned with MAFFT (Katoh and Standley
2013). Maximum likelihood trees were constructed
with FastTree (Price et al. 2010) from within Geneious.
Samples of individual hydroids collected from a
wide variety of JTMD objects (below) were also sub-
mitted for genetic analysis (by analytical techniques
as described in McCuller et al. 2018), but failed to
yield useful sequences.
To the 12 hydroid species previously identified on
JTMD and believed to originate from the Japanese
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
coast (based upon evidence reviewed in Calder et al.
2014, and further detailed in the Discussion below),
we now add an additional 16 species (Table S2). Two
of the 12 taxa reported earlier only to genus, Phialella
quadrata (Forbes, 1848) and Plumularia caliculata
Bale, 1888, are now resolved to species level based
upon the availability of additional material. Campanu-
lariid hydroids (sensu lato, here treated in the families
Campanulariidae, Clytiidae, and Obeliidae) are the
most diverse group in the JTMD hydroid fauna.
In addition to these species, Calder et al. (2014)
found two anthoathecate species (?Bougainvillia
muscus (Allman, 1863) and Stylactaria sp.); additional
athecate hydroids are in hand, and these will be
treated separately in a subsequent report.
Fourteen of the 28 species collected from JTMD
objects (50%) were detected only once (three species
reported earlier by Choong and Calder (2013) and
Calder et al. (2014), and 11 additional species newly
reported herein) (See Table S2). Forty-three percent
(six) of these unique species arrived in 2015, in concert
with a peak of detected overall JTMD diversity
(Carlton et al. 2017).
Of interest (and argued below as partial evidence
for the Western Pacific origin of the JTMD hydroid
fauna) is that total hydroid diversity per object declined
after 2013 (even as unique species continued to arrive
and peaked later). On four objects (BF-1, 8, 23, and 40)
arriving in Oregon and Washington between summer
2012 and spring 2013, hydroid diversity ranged from
four to eight species (excluding Obelia griffini
Calkins, 1899, as discussed below). Thus, eight
species (Amphisbetia furcata (Trask, 1857), Eutima
japonica Uchida, 1925, Halecium tenellum Hincks,
1861, Phialella quadrata, Plumularia caliculata,
Sertularella mutsuensis Stechow, 1931, Sertularella
sp., and Gonionemus vertens A. Agassiz, 1862) were
found on the Misawa dock (BF-1, noted above) that
landed in June 2012 in Oregon. Five and six species
were found on debris items arriving in Oregon in
February 2013 (BF-23) and in Washington in March
2013 (BF-40), respectively: on the former were
Hydrodendron gracile (Fraser, 1914), Orthopyxis
platycarpa Bale, 1914, Plumularia setacea (Linnaeus,
1758), Eutima japonica, and Stylactaria sp.; on the
latter were Phialella quadrata, Obelia longissima
(Pallas, 1766), Amphisbetia furcata, Plumularia
caliculata, Plumalecium plumularioides (Clark, 1877)
and Eutima japonica. Since spring 2013, most objects
arrived with one species, and no object was found
with more than two species.
Twenty-four species (89% of the JTMD hydroid
fauna) were already reported from Japan (Table S2);
two species, Hydrodendron gracile and Plumalecium
plumularioides represent new records for the country
(one reported earlier by Calder et al. 2014), and two,
not taken to species level, Clytia sp. and Antennella sp.
are of uncertain geographic distribution. In turn, 14
species (52%) already known from the North East
Pacific Ocean (Table S2), are held to be either naturally
amphi-Pacific in distribution or possible ship-borne
introductions. Twelve taxa are unknown from the
Pacific coast of North America. However, they are
not treated here as new records for the Eastern
Pacific because they are present only on intercepted
debris and are not yet known to have established
populations. Six hydroid species (Orthopyxis caliculata
(Hincks, 1853), Obelia dichotoma (Linnaeus, 1758),
Amphisbetia furcata, Plumularia setacea, and
Plumalecium plumularioides) were found on debris
arriving in the Hawaiian Islands; two of these (O.
dichotoma and P. setacea) were previously known
from Hawai‘i, recognized there as introduced and
cryptogenic, respectively (Carlton and Eldredge 2009).
Notably, species of Clytia Lamouroux, 1812 were
absent on JTMD arriving in 2012 and 2013, but began
to appear in 2014. Clytia sp., whose affinities are
discussed below, was found once (BF-363) on an
object landing in Washington during early 2015.
Clytia linearis (Thornely, 1900) was discovered on a
derelict vessel (BF-538) arriving in Oregon in spring
2016. Clytia hemisphaerica (Linnaeus, 1767) appeared
on six items in Oregon and Washington between
2014 and 2015. Clytia linearis is a distinctive warm-
water species, although Galea (2007) reported it from
colder waters of the Subantarctic in the fjords region
of southern Chile. Its later appearance on JTMD may
be due to a longer, more circuitous route through
lower latitudes before the rafted vessel became
caught up in ocean currents moving north and east.
Clytia sp., although currently unidentified, was
accompanied by a warm-water, southern species of
neustonic bryozoan, Jellyella eburnea (Hincks, 1891),
also indicating a longer route through lower latitudes
(McCuller and Carlton 2018). The six objects on
which C. hemisphaerica arrived, however, bore no
distinctive indication of their route after departure
from the Tōhoku coast in March 2011. Finally, the
most common hydroid in our samples was Obelia
griffini. We suggest below that it may be an element
of the open ocean neustonic fauna.
Details are provided below on identification,
taxonomy, and geographic distribution of 24 species
of neritic hydroids on JTMD, and of the putatively
pelagic hydroid Obelia griffini. Four additional JTMD
leptothecate species (Halecium tenellum, Hydrodendron
gracile, Sertularella mutsuensis, and Sertularella
sp.), not represented in the newer samples analyzed
here, are recorded in Calder et al. (2014).
H.H.C. Choong et al.
Table 1. Comparison between the trophosome in the hydroid stages of Opercularella lacerata, Opercularella rugosa, Phialella quadrata,
and JTMD specimen BF-382 (ROMIZ B4107).
Opercularella lacerata
(in Cornelius 1995a)
Opercularella rugosa
(from Nutting 1901)
Phialella quadrata
(in Cornelius 1995a)
(ROMIZ B4107)
Colony Erect, much branched,
branches angled at ca 60°
Erect; irregularly branched,
branches alternate,
Erect, branches tending all
to be directed upwards
Stolonal and erect,
branches directed
Hydrotheca height 300–400 µm Not given ca 250 µm 230–260 µm
Hydrotheca shape Widest in middle Widest distally (towards
aperture or in middle)
Widest distally (towards
Widest distally
(towards aperture)
Operculum 9–12 pointed flaps (cusps) 10–12 pointed flaps Pleated sheath, ca 10
pleats, not cusped
Pleated, < 10
pleats, not cusped
Pedicel Typically shorter than
hydrotheca Very short Often longer than
Often longer than
Stem Both spirally and
transversely grooved (ringed)
Transversely grooved
Transversely grooved
grooved (ringed)
Gonophores Fixed sporosacs Medusae Medusae unknown
North Atlantic Ocean, Baltic
Sea (Schuchert 2001); Indo-
Pacific (?) (Cornelius 1995a)
Alaska (Nutting 1901);
West Seattle, Washington
(Fraser 1946)
Sea of Japan (Naumov
1960); Atlantic and Indo-
Pacific (Cornelius 1995a)
Systematic Account
Order Leptothecata Cornelius, 1992
Family Phialellidae Russell, 1953
Phialella quadrata (Forbes, 1848)
Thaumantias quadrata Forbes 1848: 43, pl. 9, figures. 2a–e
[medusa stage].
Material.—Washington, on vessel, stolonal and
branching colony, bryozoan Scruparia ambigua
(d’Orbigny, 1841) epizoic, no gonothecae (JTMD-
BF-40), ROMIZ B4175; Washington, on basket,
branching colony, no gonothecae, S. ambigua epizoic
(JTMD-BF-343), RBCM 017-00011-003; California,
on the pelagic gooseneck barnacle Lepas on crate, no
gonothecae (JTMD-BF-382), ROMIZ B4107.
Description.—Colony with both stolonal and erect
parts. Stolon smooth, hydrocaulus annulated. Erect
hydrocauli flexuous, annulated throughout, branched
or unbranched. Branches, when present, angled
upwards. Annuli tranverse. Hydrotheca operculate,
long-conical, widest distally towards aperture, thin-
walled, operculum pleated, not demarcated basally by
crease line, pedicel ringed. Gonothecae not observed.
Remarks.—In our previous study (Calder et al. 2014)
we reported (as Phialella sp.) the occurrence of a
species, closely resembling P. quadrata, on a floating
dock (JTMD-BF-1) from Misawa, Japan. It was
compared as well with Opercularella rugosa (Nutting,
1901) and O. lacerata (Johnston, 1847). Specimens
in one of our present samples (JTMD-BF-382),
growing on young species of Lepas Linnaeus, 1758,
had both stolonal and erect stems. Stolonal colonies
of P. quadrata have been reported in other zooben-
thic communities (Voronkov et al. 2010). The JTMD
material most closely corresponds to P. quadrata in
the following ways: (1) branches are directed
upwards at a more acute angle than in O. lacerata
(see Cornelius 1995a, Table 1) (2) hydrothecal pedicels
are long (those of P. quadrata are often longer than
the hydrothecae, while those of O. lacerata and O.
rugosa are mostly shorter), and (3) hydrothecal size
and shape differ (in O. lacerata, hydrothecae are
300–400 µm high and widest in the middle; those of
P. quadrata are 230–260 µm high and widest below
their opercula). Comparisons with species having
similar characters are given in Table 1.
Distribution.—Sea of Japan (Naumov 1960). A well-
known European species (Bouillon et al. 2004, and
records summarized in Mendoza-Becerril et al. 2009),
held to be introduced to Australia (Hewitt et al. 2004)
through ship fouling, and thus perhaps to other
coasts of the southern hemisphere as well, including
New Zealand, Chile, and South Africa.
Family Eirenidae Haeckel, 1879
Eutima japonica Uchida, 1925
Eutima japonica Uchida 1925: 93, figure 17.
Remarks.—Calder et al. (2014) reported this
endocommensal hydroid in the mussel Mytilus
galloprovincialis Lamarck, 1819 from JTMD-BF-8.
Eutima japonica Uchida, 1925 has also been found
in M. galloprovincialis in samples from JTMD-BF-
1, 6, 23, 40, 43, and 168 (Table S1) (G. Ruiz and J.
Geller) based upon morphological and genetic analyses.
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
Figure 1. Campanularia volubilis:
(A) pedicel and hydrotheca. Scale
equals 500 µm. (B) detail of
hydrotheca. RBCM 017-00006-001.
Scale equals 100 µm. (C) gonotheca.
RBCM 017-00006-001. Scale equals
500 µm. Del. HHC Choong.
Family Campanulariidae Johnston, 1837
Campanularia volubilis (Linnaeus, 1758)
(Figure 1)
Sertularia volubilis Linnaeus 1758: 811.
Campanularia reduplicata Nutting 1901: 172, pl. 18, figure 1.
Campanularia urceolata.–Nutting 1915: 40, pl. 4, figures 4 and 5.
Campanularia groenlandica.–Hirohito 1995: 54, figure 16a–b
[not Campanularia groenlandica Levinsen 1893].
Material.—Oregon, on vessel, epizoic on Scruparia
ambigua, single pedicel with hydrotheca, with
gonothecae (JTMD-BF-201), RBCM 017-00006-001.
Description.—Colony stolonal, pedicel arising from
creeping hydrorhiza. Pedicel approximately 3 times
length of hydrotheca, perisarc mostly smooth,
wrinkled at base, with irregular annulations towards
the distal end. Subhydrothecal spherule almost oval.
Perisarc slightly thickened. Hydrotheca deeply
campanulate, one side somewhat curved to resemble
the urceolate form, ca. 400 µm in length from hydro-
thecal margin to bottom of basal chamber, walls
narrowing slightly towards hydrothecal base. Basal
chamber 32 µm high. Hydrothecal margin with 11–12
well-demarcated, triangular but slightly rounded
cusps, 39 µm in length, separated by rounded
embayments. Margin reduplicated. Hydrothecal walls
thin to slightly thickened around basal chamber.
Gonothecae somewhat cylindrical, ca 725 µm in
length, ca 266 µm at widest part, truncated at distal
end, on very short pedicel with one spiral twist,
arising from stolon. Pedicel length ca 64 µm.
Remarks.—The specimen examined corresponds
most closely with accounts of Campanularia urceolata
Clark, 1877 and C. reduplicata Nutting, 1901, both
considered conspecific with C. volubilis (Calder and
Stephens 1997; Calder 2004). Campanularia volubilis
and C. urceolata were reported from Japan by
Yamada (1950). The gonotheca of our specimen
closely resembles that reported by Hirohito (1995) as
being C. groenlandica Levinsen, 1893, but we follow
Schuchert (2001) in not considering Campanularia
cf. C. groenlandica sensu Hirohito (1995) to be
conspecific with C. groenlandica Levinsen, 1893.
The gonotheca of our specimen, and that of Hirohito,
resembles that of C. urceolata figured by Nutting
(1915). Gonothecae in C. volubilis have no neck
when young (Cornelius 1995b). The shape of the
hydrotheca in Hirohito’s specimen appears to be
morphologically closer to C. volubilis than C.
groenlandica as shown by Naumov (1960), and by
Schuchert (2001). The pedicel in our specimen and
those of Hirohito are not as annulated as in most
descriptions of C. volubilis but Cornelius (1995b)
reported straight to spirally grooved pedicels in this
Distribution.—Japan (Fraser 1946; Yamada 1950).
Fraser (1946) characterized C. volubilis as a naturally
circumpolar species, widespread through the North
Atlantic and North Pacific Oceans, from the Bering
Sea to the Galapagos Islands in the Eastern Pacific
(Fraser 1937, 1946), although the conspecificity of warm-
temperate and tropical populations is improbable.
Orthopyxis caliculata (Hincks, 1853)
Campanularia caliculata Hincks 1853: 178, pl. 5, figure B.
Material.—Hawai‘i, on buoy, colony arising from
hydrorhiza, no gonothecae (JTMD-BF-90), ROMIZ
H.H.C. Choong et al.
Figure 2. Clytia sp.: (A) part of colony. ROMIZ B4156.
Scale equals 1000 µm. (B) detail of hydrotheca. ROMIZ
B4156. Scale equals 200 µm. Del. HHC Choong.
Remarks.—The occurrence of Orthopyxis caliculata
in JTMD material was reported in our previous study
(Calder et al. 2014), along with a detailed discussion
of the synonymy of O. caliculata into O. integra
(Macgillivray, 1842) by some workers (e.g. Kramp
1911; Cornelius 1995b; Vervoort and Watson 2003).
Following our earlier work, we retain O. caliculata
as a separate species from O. integra based upon
observed trophosomal characters, particularly the
presence of bilaterally symmetrical hydrothecae in
the former, rather than being radially symmetrical as
in the latter. The validity of O. caliculata as a species
has been corroborated through a re-evaluation of
morphological diagnostic characters, including diffe-
rential hydrothecal perisarc thickness resulting in
bilateral symmetry, together with molecular analyses
(Cunha et al. 2015). Our specimens correspond with
Japanese material considered by Hirohito (1995) as
O. caliculata (although referred by him to the genus
Campanularia Lamarck, 1816).
Distribution.—Japan (Hirohito 1995); northwest
Pacific (Korea, Russia) and northeast Pacific (Fraser
1937, 1946, and records reviewed in Calder et al.
2014); widely reported (often as Orthopyxis integra)
from the North Atlantic Ocean.
Orthopyxis platycarpa Bale, 1914
Orthopyxis platycarpa Bale 1914: 79, pl. 11, figure 3.
Campanularia platycarpa.–Hirohito 1995: 56, figure 16e–g.
Material.—Oregon, on float, several pedicels with
hydrothecae, without gonothecae (JTMD-BF-18),
ROMIZ B4232; Oregon, on vessel, colony with
epizoic bryozoan Scruparia ambigua, on Lepas sp.
stalk, without gonothecae (JTMD-BF-23), ROMIZ
Remarks.—We regard Orthopyxis platycarpa as
being distinct from O. integra based on differences
in the morphology of the hydrothecae and gono-
thecae, including the frequent occurrence of a convex
submarginal, basal band of thickened perisarc on the
hydrothecae in O. platycarpa and gonothecae that
are distinctly compressed compared to O. integra
(Bale 1914; Cunha et al. 2015). Comparisons of some
trophosomal characters of specimens of O. platycarpa,
O. integra, and O. caliculata from the collections of
the Royal Ontario Museum, together with infor-
mation on O. platycarpa from Naumov (1960, as
Campanularia platycarpa) are provided in Calder et
al. (2014).
Distribution.—Western Pacific Ocean (Japan, China,
Russia) (Calder et al. 2014).
Family Clytiidae Cockerell, 1911
Clytia sp.
(Figure 2)
Material.—Washington, on plastic bowl, section of
colony amongst fouling, without gonothecae
(JTMD-BF-363), ROMIZ B4156.
Description.—Colony bushy, partial colony section
about 17 mm high, stem and main branches fascicled.
Hydrothecal pedicels long, reaching over 2.8 mm,
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
Figure 3. Clytia hemisphaerica:
(A) detail of hydrotheca. RBCM 017-
00016-001. Scale equals 500 µm.
(B) proximal part of pedicel branches.
RBCM 017-00016-001. Scale equals
500 µm. (C) gonotheca. RBCM 017-
00016-001. Scale equals 500 µm. Del.
HHC Choong.
arising from main branch and branchlets, annulated
throughout or having smooth sections between basal
and distal parts. Hydrotheca large, deeply campanu-
late, up to 470 µm long and 252 µm wide at its widest
point, with 10–14 prominent, pointed-to-slightly-
rounded cusps about 25–30 µm tall. No gonothecae
Remarks.—We are unable to assign the limited
material in hand to a known Japanese species. In
many respects, our specimen corresponds to Clytia
universitatis Torrey, 1904 (see Fraser 1937), parti-
cularly in details of the trophosome and fascicled
stem. We compared the present material to Fraser’s
specimen of C. universitatis from Isla Partida, Gulf
of California, Mexico, in the holdings of the Royal
BC Museum (BCPM 976-395-1). Some hydrothecae
in our specimen are broader than those in Fraser’s
material and that illustrated by Torrey (1904), which
are uniformly deeply campanulate, and increase in
diameter very slightly from base to margin. Clytia
universitatis, however, is known largely from
southern California and Mexico (with reports as far
north as San Francisco Bay; Fraser 1946), and the
JTMD trajectories do not bring objects past these
lower latitudes along the North American coast toward
Washington. The absence of any other unique
Eastern Pacific species on BF-363 further argues
against recruitment in the eastern Pacific Ocean.
Clytia hemisphaerica (Linnaeus, 1767)
(Figure 3)
Medusa hemisphaerica Linnaeus 1767: 1098 [medusa stage].
Clytia minuta.–Nutting 1915: 61, pl. 14, figures 1–4.–Fraser
1937: 76, pl. 15, figure 74a–b.
Clytia edwardsi.–Hirohito 1995: 61, figure 17d–e.
Material.—Oregon, on lid, colony on Lepas sp.,
without gonothecae (JTMD-BF-136), ROMIZ B4099;
Oregon, on basket (JTMD-BF-252), ROMIZ B4102;
Washington, on basket, colony with gonothecae,
Scruparia ambigua epizoic (JTMD-BF-343), RBCM
017-00011-001; Washington, on tote, colony with
gonothecae (JTMD-BF-469), RBCM 017-00016-001;
Washington, on basket, colony with hydranths, with
gonothecae (JTMD-BF-470), RBCM 017-00016-005;
Washington, colony with hydranths, without gonothe-
cae, on tote (JTMD-BF-472), RBCM 017-00016-003.
Description.—Colony arising from creeping stolon,
pedicels usually very long, branching several times.
Colony height reaching 22 mm, branches reaching as
long as half of colony height. Secondary branches
may be shorter. Basal region of branch curves upward,
branches often aligned parallel with primary pedicel.
Main pedicel annulated basally and distally, central
portion smooth. Perisarc thin to very slightly thicke-
ned. Pedicellate form also present in same colony.
Hydrotheca thin-walled, campanulate, 643 µm high,
widest at margin, about 343 µm, narrowing slightly
to 305 µm at middle. Diaphragm 154 µm wide. Basal
chamber approximately 84 µm high. Margin with
10–12 prominent, triangular, slightly rounded teeth,
approximately 37 µm high, separated by rounded
embayments. Hydrothecal pedicels annulated basally
and distally or fully annulated. Gonothecae arising
from stolon or stem, on short, annulated pedicels;
approximately 901 µm high, broadly cylindrical,
slightly tumid in mid-section; wall with spiral ridges.
Remarks.—The occurrence of C. hemisphaerica in
JTMD samples is notable because of the presence of
morphologically variable colonies. In the material
examined, the colonies possess extremely long pedicels
and repeated branching, but also possess distinctly
annulated gonothecae, suggesting the possibility that
populations settling in coastal fouling communities
may change morphology as they drift for long
periods of time at sea. West and Renshaw (1970) found
that branching in Clytia sp. can vary in response to
food and temperature conditions.
H.H.C. Choong et al.
Figure 4. Clytia linearis: (A)
hydrotheca and part of pedicel.
RBCM 017-00022-001. Scale
equals 500 µm. B) portion of stem
showing apophyseal region and
fold of perisarc projecting inward
into internode lumen. RBCM 017-
00022-001. Scale equals 1000
µm. (C) part of colony showing
branching. RBCM 017-00022-
001. Scale equals 2000 µm. Del.
HHC Choong.
Clytia hemisphaerica, along with Obelia dichotoma
and O. geniculata (Linnaeus, 1758), which also occur
in the JTMD samples, have been found on a wide
variety of vertebrate, invertebrate and algal substrates,
which phoretic habitat may facilitate dispersal through
long-distance transoceanic transport (Cornelius 1982).
Our samples are found on various anthropogenic
substrates, overgrowing young Lepas sp., with
Scruparia ambigua epizoic.
Distribution.Clytia hemisphaerica was reported
from the Tōhoku region by Nishihira (1968) and
from Matsuyama by Yamada (1958). This species is
reported to be nearly cosmopolitan in coastal waters
(Schuchert 2001), and may thus involve a species
Clytia linearis (Thornely, 1900)
(Figure 4)
Obelia linearis Thornely 1900: 453, pl. 44, figure 6.
Clytia ? obliqua Clarke 1907: 9, pl. 5, figures 1–4.
Clytia carinadentata Fraser 1938: 28, pl. 7, figure 30.
Clytia linearis.–Lindner and Migotto 2002: 542, figure 2.
Material.—Oregon, on vessel, weathered colonies,
without gonothecae (JTMD-BF-538), RBCM 017-
Description.—Colony erect, stem flexuous, sym-
podially branched, stems up to 16.5 mm high.
Internode with smooth, upward-curved apophysis.
Apophyses alternate left-and-right of stem. Apo-
physeal region has fold of perisarc projecting inward
into internode lumen. Internode supports succeeding
internode or distal pedicel. Stem, branches and pedi-
cels with moderately thickened perisarc, variously
annulated, ranging from almost fully annulated to
alternating annulated and smooth sections. Distal
portion of pedicel supporting hydrotheca always annu-
lated. Hydrotheca large, cylindrical, 1065–1164 µm
long, 660–956 µm wide at margin. Hydrothecal
walls almost parallel, occasionally narrowing slightly
towards margin. Perisarc thin. Basal chamber 60–
114 µm high, diaphragm thin, 194–253 µm wide.
Hydrothecal margin with 12–16 pointed to slightly
rounded cusps, approximately 54 µm high. Hydro-
thecal cusps triangular, not narrow; pleated, pleats
extending from apex of cusp, occasionally reaching
into middle of hydrotheca. Gonothecae not observed.
Remarks.—Our material corresponds to the des-
criptions of Fraser (1938) and Lindner and Migotto
(2002), with the exception of the general shape of
the hydrothecal cusps, which resemble those of
Clytia ?obliqua Clarke, 1907 in being triangular
instead of long and narrow. Material with similar
cusps is described by Migotto (1996). Cornelius (1982)
did not consider the angle of slope of the hydrothecal
cusps to be significant, and assigned Clarke’s species
to C. linearis. The fold of the perisarc projecting
inward into the internode lumen in the apophyseal
region was also observed by Lindner and Migotto
(2002). Clytia linearis is widely reported in both
benthic habitats and in the open ocean on plankton,
where, if the same species, it facultatively rafts and
disperses as an epizooite on pteropods (Cornelius
1982, 1987).
Clytia linearis is one of two species represented
in the JTMD hydroid fauna apparently acquired by
tsunami objects south of the Boso Peninsula. While
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
Figure 5. Laomedea flexuosa:
(A) portion of stem with hydrothecae.
RBCM 017-00016-004. Scale equals 500 µm.
(B) basal chamber of hydrotheca. RBCM
017-00016-004. Scale equals 200 µm.
(C) gonotheca. RBCM 017-00016-004. Scale
equals 200 µm. Del. HHC Choong.
many of the other species considered here are regarded
as wide ranging from lower-latitude warm climates
to sub-boreal if not boreal waters, C. linearis is
considered a species of warmer waters (Kirkendale
and Calder 2003; Calder 2013). JTMD-BF-538, a
Japanese vessel washing ashore in spring 2016 in
southern Oregon, also had aboard warmer-water
western Pacific bivalves, in addition to a typical
colder-water fauna representative of the tsunami
strike zone of the Tōhoku coast. Many JTMD objects
were transported by coastal currents to southern
Japan and the South China Sea and acquired species
typical of warmer, southern waters, before being re-
engaged by ocean currents and being swept north
and east to North America (Carlton et al. 2017).
Similarly, Boero et al. (2005) recorded the possible
colonization and invasion of colder European waters
by C. linearis as an alien species.
Distribution.—Japan (Yamada 1959; Hirohito 1995).
Originally described from Papua New Guinea, it is
widely reported from subtropical and tropical waters
of the Atlantic, Pacific, and Indian Oceans (Kirkendale
and Calder 2003; Calder 2013), and may thus also
represent a species complex. Bouillon et al. (2004)
suggested that C. linearis is a Lessepsian migrant
into the Mediterranean through the Suez Canal.
Family Obeliidae Haeckel, 1879
Laomedea flexuosa Alder, 1857
(Figure 5)
Laomedea flexuosa Alder 1857: 122.–Cornelius 1982: 97, figure
19 a–d.–Schuchert 2001: 154, figure 134 a–c.
Material.—Washington, on basket, living colonies
with gonangia (JTMD-BF-465), RBCM 017-00016-004.
Description.—Colony erect, unbranched, approxi-
mately 2000 µm tall. Stems flexuose, internodes
characteristically curved, stem internodes annulated
proximally, 2–5 annulations. Perisarc of moderate
thickness. Hydrothecae arise out of annulated pedi-
cels given off from distal parts of internodes. Usually
one pedicel per internode, very infrequently two, 3–10
or more annuli per pedicel, tapering distally. Central
portion of pedicels sometimes smooth. Hydrothecae
bell-shaped, perisarc sometimes slightly thickened
asymmetrically. Hydrothecal rim entire. Diaphragm
thin, transverse or slightly oblique. Gonothecae arising
directly from stolon, internodes, or axils, carrot-shaped,
truncated distally (?), or apex slightly rounded.
Distribution.—Widely reported from the North
Atlantic, Arctic, and Europe, as well as from South
Africa and New Zealand (Cornelius 1982; Schuchert
2001). Fraser (1944) recorded it from the Gulf of St.
Lawrence. Very common intertidally in the Bay of
Fundy, on fucoids (Calder 2017). Chaplygina (1992)
reported the introduction of L. flexuosa to the Sea of
Obelia dichotoma (Linnaeus, 1758)
Sertularia dichotoma Linnaeus 1758: 812.
Obelia dichotoma.–Hincks 1868: 156, pl. 28, figure 1a–b.–Cornelius
1995b: 296, figure 69a–k.
Obelia alternata Fraser 1938: 35, pl. 8, figure 38a–b.
Material.—Oregon, on float, several pedicels with
hydrothecae, without gonothecae (JTMD-BF-18),
ROMIZ B4200; Oregon, on pallet, stem fragments,
with gonothecae (JTMD-BF-24), ROMIZ B4190;
Hawai‘i, on I-beam, stems arising from stolon, no
hydrothecae or gonothecae (JTMD-BF-72), ROMIZ
B4197; Washington, on post-and-beam wood, colony,
H.H.C. Choong et al.
Figure 6. Obelia geniculata: (A) portion of stem with
hydrothecae. ROMIZ B4181. Scale equals 500 µm.
(B) gonotheca. ROMIZ B4181. Scale equals 200 µm.
Del. HHC Choong.
no gonothecae (JTMD-BF-97), ROMIZ B4199;
Washington, on vessel, stems, no gonothecae (JTMD-
BF-131), ROMIZ B4185; Washington, on vessel, colo-
nies covered by fouling, with remnants of coenosarc,
without gonothecae (JTMD-BF-134), ROMIZ B4205;
Oregon, on vessel, colony fragments, without gono-
thecae, likely dried out at some point, bryozoans
Scruparia ambigua / Aetea Lamouroux, 1812 epizoic
(JTMD-BF-202), ROMIZ B4191; Hawai‘i, on vessel,
dense colonies, without gonothecae (JTMD-BF-209),
ROMIZ B4209; Washington, on tote, partially covered
by S. ambigua, juvenile Lepas sp. also present, no
gonothecae (JTMD-BF-464), RBCM 017-00016-002;
Washington, colony without gonothecae, on crate
(JTMD-BF-473) RBCM 017-00015-001; Japan,
Minami-sanriku, Motoyoshi District, Miyagi Prefec-
ture, Tōhoku Coast, August 2016, 3-month test panel,
several hydrocauli, without gonothecae (MS-1)
RBCM 017-00023-001.
Remarks.Obelia dichotoma remains a problematic
taxon due to a high degree of morphological variation
in the characters used to delimit the species
(Cornelius 1982, 1995b; Calder 2013). Nevertheless,
although the non-monophyly of O. dichotoma remains
problematic (Cunha et al. 2017), some widespread
populations appear to be identical based upon
nematocyst types and isoenzyme patterns (Ӧstman
1982) and hydranth characters (Cornelius 1987).
Despite intraspecific variability, branching pattern
and shape of the hydrothecal rim remain useful in
delimiting hydroids attributed to the O. dichotoma
species complex from its congeners such as O.
geniculata, O. longissima and O. griffini (Kubota
1981, 1999; Calder et al. 2014) from Japanese waters.
Specifically, we assigned our specimens to O. dicho-
toma based on the presence of hydrothecae with
polyhedral margins, and with walls that are poly-
gonal in cross-section, rather than round as in O.
griffini (Cornelius 1995b; Calder et al. 2014). Obelia
dichotoma is also less profusely branched than O.
griffini (Fraser, 1914). Specimens referable to O.
dichotoma also occurred on a test panel recovered
from the Tōhoku Coast in August 2016 (RBCM 017-
Distribution.—Japan, where it is the most widely
distributed species of Obelia (Kubota 1999). A likely
cosmopolitan species complex.
Obelia geniculata (Linnaeus, 1758)
(Figure 6)
Sertularia geniculata Linnaeus 1758: 812.
Obelia geniculata.–Fraser 1937: 87, pl. 17, figure 89a–b.–Cornelius
1975b: 272, figure 5a–b.–Hirohito 1995: 76, figure 22a–b.
Material.—Washington, Misawa 3 dock, hydrocauli
with coenosarc, with gonothecae (JTMD-BF-8),
ROMIZ B4181; Washington, Misawa 3 dock, stems
and colonies on Lepas sp., with gonothecae (JTMD-
BF-8 ), ROMIZ B4188.
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
Description.—Colony arising from stolon. Hydro-
caulus monosiphonic, flexuose, unbranched. Internodes
short, curved, usually one annulation basally. Perisarc
of internode greatly thickened on side where hydro-
thecal pedicel originates. Pedicels short, arising from
shelf-like lateral processes, 2–5 annulations. Hydro-
thecae campanulate-to-bell-shaped, margin entire.
Annular in apical view and hydrothecal perisarc
slightly thickened. Gonothecae arising from axils of
hydrothecae, on short pedicels, conical, tapering
basally, with distal short, prominent collar.
Remarks.—The samples examined correspond with
accounts of Obelia geniculata from Japan (Yamada
1958; Hirohito 1995; Kubota 1999) and elsewhere in
having thickened perisarc of the stem, only one
annulation between the internodes of the stem, and
the lack of branching. Our samples contain remnants
of coenosarc, but the gonothecae were empty, and
the hydrothecal margins showed some damage from
weathering the elements.
Distribution.—Japan (Hirohito 1995); nearly cosmo-
politan in temperate to cold waters (Cornelius 1975b;
Schuchert 2001).
Obelia griffini Calkins, 1899
Obelia griffini Calkins 1899: 357, pl. 4, figs. 18, 18A-C; pl. 6, fig.
Material.—Hawai‘i, fragments of stem and one
crushed hydrotheca, no gonothecae (JTMD-BF-21),
ROMIZ B4202; Oregon, on pallet, colonies with
gonophores (JTMD-BF-24), ROMIZ B4201; Oregon,
on pallet, colony with gonothecae (JTMD-BF-24),
ROMIZ B4203; Washington, on vessel, colony with
gonothecae, Scruparia ambigua epizoic (JTMD-BF-
40), ROMIZ B4173; Washington, on vessel, colony on
pelagic crab Plagusia Latreille, 1804, no gonothecae
(JTMD-BF-40), ROMIZ B4174; Washington, on
vessel, several colonies, no gonothecae (JTMD-BF-40),
ROMIZ B4176; Oregon, on vessel, colonies with gono-
phores (JTMD-BF-50), ROMIZ B4186; Washington,
several hydrocauli arising from hydrorhiza, with peri-
sarc, with gonotheca (JTMD-BF-97), ROMIZ B4198;
Washington, on vessel, stem fragments, without
gonothecae, S. ambigua epizoic (JTMD-BF-131),
ROMIZ B4184; Washington, amidst fouling on
vessel, fragments of hydrocauli with hydrothecae
arising from hydrorhiza, without gonothecae (JTMD-
BF-134), ROMIZ B4194; Washington, on vessel,
colonies with perisarc and gonangia (JTMD-BF-170),
ROMIZ B4189; Oregon, on buoy, colony with gono-
thecae (JTMD-BF-172), ROMIZ B4204; Washington,
on vessel, stems arising from hydrorhiza, without
hydrothecae or gonothecae, S. ambigua epizoic
(JTMD-BF-223), ROMIZ B4193; Oregon, on helmet,
colony fragments, with gonothecae, likely dried out
at some point (JTMD-BF-241), ROMIZ B4182;
Washington, on pallet, several colonies, largely devoid
of coenosarc, with gonothecae (JTMD-BF-338),
ROMIZ B4150; Washington, on basket, colony with
gonothecae, S. ambigua epizoic (JTMD-BF-343),
RBCM 017-00011-002; Washington, Long Beach, on
cap, weathered, empty colonies, stems and branches
only, hydrothecae missing, with gonothecae (JTMD-
BF-370), ROMIZ B4149; California, on crate, 2
colonies with gonothecae (JTMD-BF-382), ROMIZ
B4158; Washington, on vessel, hydrocauli arising from
hydrorhiza, with coenosarc, with gonophores, S.
ambigua epizoic (JTMD-BF-402), ROMIZ B4154.
Remarks.—Following our previous study, we retain
O. griffini as distinct from generally considered
conspecific species such as O. dichotoma. Obelia
surcularis Calkins, 1899 and O. gracilis Calkins, 1899
are simultaneous synonyms, with nomenclatural
priority having been assigned to the binomen O. griffini
(see Calder et al. 2014 for discussion and description).
Obelia griffini was found on three of four stranded
objects sampled in our previous study (Calder et al.
2014). It is also the most common Obelia species
found in the present study, and the most abundant
hydroid in the JTMD material.
Distribution.—North Pacific Ocean (see discussion,
Obelia longissima (Pallas, 1766)
Sertularia longissima Pallas 1766: 119.
Material.—Oregon, on pallet, stem fragments, one
hydrotheca (flattened), without gonothecae (JTMD-
BF-24), ROMIZ B4187; Washington, on vessel,
Scruparia ambigua epizoic, no gonothecae (JTMD-
BF-40), ROMIZ B4177; Oregon, on vessel, colonies
with gonothecae, S. ambigua epizoic (JTMD-BF-43),
ROMIZ B4207; Oregon, on vessel, colony fragment,
without gonothecae (JTMD-BF-58), ROMIZ B4183;
Washington, on tote, dried stems and branches, no
gonothecae (JTMD-BF-374), ROMIZ B4169;
Washington, on tote, dried stems and branches
(JTMD-BF-380), ROMIZ B4171; California, on crate,
on mussel Mytilus galloprovincialis, with remnants
of coenosarc, with gonothecae (JTMD-BF-382),
ROMIZ B4161; Washington, on basket, stems with
few hydrothecae, no gonothecae, likely dried out pre-
viously (JTMD-BF-405), ROMIZ B4159; Washington,
weathered colony, primarily stems, with few hydro-
thecae, likely dried out, no gonothecae (JTMD-BF-
406), ROMIZ B4172.
Remarks.—Our samples correspond morphologi-
cally with Obelia longissima, previously reported as
originating from Japan (Calder et al. 2014). As in the
H.H.C. Choong et al.
Figure 7. (A) Halecium delicatulum:
ortion of stem and hydrothecae.
ROMIZ B4104. Scale equals 500 µm.
(B) Abietinaria inconstans: section of
hydrocaulus and side-branches.
ROMIZ B4106. Scale equals 1000
µm. Del. HHC Choong.
previous study, the colonies are also weathered and
contain empty gonothecae, indicating that the colonies
had persisted on the debris for extended periods.
Distribution.Obelia longissima is a cosmopolitan
species, and although more widespread in the Atlantic
(Vervoort 1972; Cornelius 1995b; Schuchert 2001),
is amphi-Pacific in distribution (Fraser 1937; Calder
1970; Park 1990). Hydromedusae of O. longissima
have been reported from the northwest Sea of Japan
(Dautova and Petrova 2010).
Family Haleciidae Hincks, 1868
Halecium delicatulum Coughtrey, 1876
(Figure 7A)
Halecium delicatula Coughtrey 1876: 299.
Halecium flexile var. japonica Leloup 1938: 4, figure 1.
Halecium delicatulum.–Ralph 1958: 334, figure 11e, h–n.–
Hirohito 1995: 20, figure 5a–c.
Material.—Washington, on vessel, monosiphonic
colony, no gonothecae, Scruparia ambigua epizoic
(JTMD-BF-339), ROMIZ B4104.
Description.—Colony monosiphonic, stolon tubular,
creeping, tangled. Hydrocaulus cylindrical, erect,
somewhat flexuous, branched. Internodes corrugated,
1–2 oblique twists basally, 1–2 corrugations above
each node. Alternate nodes twisted obliquely in
opposite directions. Perisarc moderately thickened.
Primary hydrophores alternate, length variable, not
constricted or delimited by node. Up to four
hydrophores in linear series, length of hydrophores
as in primary one or longer. Hydrothecae gradually
widening, rim everted or rolled, no reduplication,
ring of desmocytes below rim, diaphragm distinct.
Occasionally thickening of perisarc below diaphragm,
especially on adcauline side, forming pseudodia-
phragm. Gonothecae not present.
Remarks.—Although gonothecae are absent, the
trophosomes in our material correspond most closely
with accounts of Halecium delicatulum from Japan
(Hirohito 1995) and elsewhere in having erect mono-
siphonic stems, irregular branching, oblique nodes
twisted in opposite directions on successive internodes,
and hydrothecal margins everted. Additionally, in
our material, the primary hydrophore is short or
almost sessile, with the hydrothecal rim very close to
touching the internode supported by the apophysis of
the hydrophore-bearing internode. Although variable,
the length of the primary hydrophores and the
strongly everted hydrothecal rim primarily charac-
terize H. delicatulum (Vervoort and Watson 2003).
A pseudodiaphragm was observed in several hydro-
thecae (Leloup 1938, as Halecium flexile var. japonica;
Ralph 1958; Hirohito 1995). Hirohito (1995) repor-
ted both monosiphonic and polysiphonic colonies
from Japan.
The vessel on which H. delicatulum was found
also bore a southern species of open ocean, neustonic
bryozoan, Jellyella eburnea, indicating that this raft
passed through lower latitude waters in the North
Pacific before arriving in Washington (McCuller and
Carlton 2018).
Distribution.—Japan (Hirohito 1995); considered
circumglobal in tropical, subtropical and boreal
waters (Vervoort and Watson 2003). Described ori-
ginally from Dunedin harbor, New Zealand, it may
be introduced to the southwest Pacific (Hewitt et al.
2004), or may represent a global species complex
(Schuchert 2005; Galea et al. 2014).
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
Figure 8. Submarginal intrathecal
rojection in hydrotheca of Abietinaria
spp.: (A) A. inconstans. ROMIZ B4106.
Scale equals 100 µm. (B) A. abietina.
BCPM 976-515-1. Scale equals 200 µm.
(C) A. anguina. BCPM 976-520-1. Scale
equals 100 µm. (D) A. inconstans.
BCPM 976-530-1. Scale equals 100 µm.
(E) A. amphora. BCPM 976-519-1.
Scale equals 100 µm. (F) A. costata.
BCPM 976-521-1. Scale equals 100 µm.
Photomicrographs by HHC Choong.
Family Sertulariidae Lamouroux, 1812
Abietinaria inconstans (Clark, 1877)
(Figure 7B, 8A)
Sertularia inconstans Clark 1877: 222, pl. 15, figures 51–52.
Thuiaria costata Nutting 1901: 187, pl. 26, figures 4–9.
Abietinaria inconstans.–Nutting 1904: 116, pl. 33, figures 1–2.–
Fraser 1937: 133, pl. 29, figure 153a–c.
Material.—Washington, on buoy, section of hydro-
caulus with hydrocladia, without gonothecae,
Symplectoscyphus tricuspidatus (Alder, 1856) epizoic
(JTMD-BF-342), ROMIZ B4106.
Description.—Colony imperfectly pinnate, main stem
straight. Basal-most portion of stem deeply annu-
lated. Main branches secondarily unbranched, alternate,
coplanar, pointing laterally and upwards at angles
between 45–75 degrees, Wide angles proximally,
more acute distally, one or two internodes between
successive branches, 3–4 hydrothecae between
branches on same side of stem. Perisarc of stem
thickened. Base of branches with 1–2 spiral twists.
Internode length variable. Cauline nodes with single
constriction. Perisarc of branches slightly thickened.
Axillary hydrothecae present. Hydrothecae flask-
shaped, 1/3–1/2 adnate, swollen basally, perisarc of
adaxial wall of basal part of hydrothecae forming
chitinous projection downwards at junction with
hydrothecal base. Distal portion of hydrothecae
gradually narrowing towards aperture, flattening
somewhat on adcauline side, forming pronounced
neck. Aperture oval, facing upwards, occasionally
forming indistinct gutter on adaxial side. Submarginal
intrathecal projection occasionally present on adaxial
side of hydrothecae. Gonothecae not present.
Remarks.—We follow Ansulevich’s concept of the
species, and include A. amphora and A. costata in
the synonymy of A. inconstans. Antsulevich (1987)
considered A. inconstans to be identical to A. costata
Nutting (= Thuiaria costata Nutting, 1901), and A.
amphora Nutting, 1904 based upon similarities in
colony form, structure of the hydrothecae and gono-
thecae, as well as geographical distribution. Nutting
noted similarities between the hydrothecae of A.
inconstans and A. costata, including the presence of
an abcauline, sub-marginal intrathecal projection in
A. inconstans (Nutting 1901, 1904), but kept the two
species separate based on trophosomal differences
(A. inconstans being less robust), and the gonosome
(greater variation in A. inconstans, although he did
not examine the gonothecae). Antsulevich (1987)
H.H.C. Choong et al.
provided a diagnosis for the gonothecae of A. costata
and its congeners: gonothecae oval, short neck, small
pedicel; aperture circular, without cusps or internal
projections; gonothecal wall wavy, 4–6 longitudinal
ribs; gonothecae may be irregular due to deformation,
without the neck, and underdeveloped or curved ribs.
According to Antsulevich, the variability in the
gonosome of A. inconstans is due to deformation when
the gonothecae are densely packed.
Neither Nutting (1904) nor Fraser (1937) noted the
presence of an adcauline, sub-marginal intrathecal
projection in A. amphora, but it is present in Fraser’s
specimen of A. amphora (BCPM976-519-1) examined
by one of us (HHCC). This submarginal projection is
also present in specimens of A. abietina (Linnaeus,
1758) (BCPM 976-515-1) and A. anguina (Trask,
1857) (BCPM 976-520-1) examined here, as well as
A. pacifica Stechow, 1923. However, the shape of the
projection differs in being long and narrow in A.
abietina (Figure 8B), and rounded in A. anguina
(Figure 8C) while it is more triangular in our
specimen (ROMIZ B4106) (Figure 8A), and Fraser’s
other specimens of A. inconstans (BCPM 976-530-1)
(Figure 8D), A. amphora (BCPM 976-519-1) (Figure
8E), and A. costata (BCPM 976-521-1) (Figure 8F).
Stechow (1923) and Fraser (1937) did not illustrate
the adcauline submarginal projection in A. pacifica.
Distribution.—Reported by Kostina and Tsurpalo
(2016) from the South Kurile Islands bordering
northern Japan, and by Stepanjants (2013) in Japanese
waters. Widespread along the North American coast
from Alaska to Mexico (Mills et al. 2007).
Amphisbetia furcata (Trask, 1857)
Sertularia furcata Trask 1857: 101, pl. 5, figure 2a–e.–Fraser 1937:
162, pl. 37, figure 195a–e.
Material.—Washington, on vessel, two fragments
of stems arising from stolon, without gonothecae
(JTMD-BF-40), ROMIZ B4094; Washington, on
tray, hydrocauli, with gonothecae (JTMD-BF-328),
ROMIZ B4140; Hawai‘i, on vessel, colony on Lepas
sp., with gonothecae (JTMD-BF-329), ROMIZ B4103;
Washington, on buoy, colonies on young Lepas sp.,
with gonothecae (JTMD-BF-386), ROMIZ B4108;
Washington, on float, scraped from colony growing
on mussel Mytilus galloprovincialis shell, fragments
of hydrocauli arising from stolon, no gonothecae
(JTMD-BF-609), RBCM017-00017-001.
Remarks.—The occurrence of Amphisbetia furcata
originating in Japan was discussed in our previous
study (Calder et al. 2014). We follow Antsulevich
(1987) in regarding A. furcata originally described
from San Francisco Bay, California, and A. pacifica
Stechow, 1931, type locality Mutsu Bay, Japan, as
conspecific. Yamada (1959) distinguished A. pacifica
from A. furcata by the presence of two distinct spiral
constrictions at the base of the stem, and in having
gonothecae which are not globular but elongated-
oval with indistinct shoulders. However, illustrations
of A. furcata from California by Torrey (1902) and
of A. pacifica from Japan by Hirohito (1995) show
that the gonothecae of both putative species to be
very similar, and correspond to those present in our
material. The spiral twists at the base of the stem
described by Yamada are clearly visible in Fraser’s
specimen of A. furcata (BCPM 976-652-1) (Fraser
1937 as Sertularia furcata) examined by one of us
(HHCC) as well as in our material.
Distribution.—Kurile Islands to the Sea of Japan,
Japan, and Yellow Sea (Antsulevich 2011); in north-
east Pacific from British Columbia to Ecuador
(Fraser 1937, 1946).
Family Symplectoscyphidae Maronna et al., 2016
Symplectoscyphus tricuspidatus (Alder, 1856)
Sertularia tricuspidata Alder 1856: 356, pl. 13, figures 1–2.
Sertularella tricuspidata.–Fraser 1937: 159, pl. 36, figure 191a–c.
Material.—Washington, on buoy, fragment of colony
epizoic on hydrocaulus and branch of Abietinaria
inconstans, without gonothecae (JTMD-BF-342),
ROMIZ B4106.
Description.—Stolon creeping, hydrocaulus arising
from stolon, bearing two hydrothecae, two trans-
verse annuli on basal part of hydrocaulus. Second
hydrotheca arising on transverse plane to first hydro-
theca on oblique annulation. Stolon tubular, robust,
perisarc slightly thickened. One end of stolon
branched dichotomously, bearing solitary, deformed
hydrothecae arising directly from each branch.
Hydrothecae on hydrocaulus tubular, slightly tumid
at base, smooth walled, 2–3 times longer than wide.
Abcauline side of hydrothecae forming continuous
curve with hydrocaulus. Hydrothecal aperture with
three prominent, equal-sized cusps, deeply emargi-
nated between cusps. Margin of aperture flared,
single renovation visible on one hydrotheca. Hydro-
thecal perisarc very slightly thickened. Gonothecae
not present.
Remarks.—Our sample is an epizoan with creeping
stolon on Abietinaria inconstans. Second-level epizoic
hydroids are facultative epizoites, and have been
observed as creeping colonies with solitary zooids in
contrast to their usual erect colony structure (Orlov
1997). Although the colonial structure exhibits great
plasticity, the hydrothecae observed in our material
correspond with accounts of Symplectoscyphus
tricuspidatus by Fraser (1937), Cornelius (1979), and
Hirohito (1995).
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
Distribution.—Circumpolar in distribution in Arctic
to northern boreal waters (Broch 1918; Naumov 1960;
Cornelius 1979). Northeast Pacific from Alaska to
San Diego (Fraser, 1937 as Sertularella tricuspidata)
and Japan (Yamada 1950; Hirohito 1995).
Family Aglaopheniidae Lamouroux, 1812
Aglaophenia aff. pluma (Linnaeus, 1758)
(Figure 9A, 10A, 10B)
Aglaophenia pluma.–Fraser 1937: 179, pl. 41, figure 217 a–c.–
Svoboda and Cornelius 1991: 30, figures 10–24.
Material.—Washington, on vessel, plumes with
corbulae (JTMD-BF-532), RBCM 017-00019-001;
Washington, on vessel, colonies with corbulae (JTMD-
BF-532), RBCM 017-00019-002; Hawai‘i, on rope
and buoy mass, colonies with corbulae (JTMD-BF-
667), ROMIZ B4233.
Description.—Colony unbranched, reaching 41 mm
tall. Two cauline nematothecae and one abortive
hydrotheca on each stem internode. Hydrotheca cup-
shaped, 9 cusps of varied length, outermost longest.
Median cusp sharp, straight or recurved, angled
towards adaxial side. Intrathecal ridge present but
not developed into intrathecal septum dividing
hydrotheca. Supracalycine nematothecae extending
past hydrothecal margin, covering adaxial-most cusps
in side-view. Hydrothecal length/breadth ratio 1.7–1.9.
Mesial nematotheca large, adaxial wall arising from
upper third of hydrotheca, not reaching its margin.
Free part approximately 88 µm, gutter-shaped, not
tubular, foramen to hydrotheca visible. Corbula three
times longer than height, with one basal hydrotheca,
9–15 pairs of unfused ribs, with narrow openings in
Remarks.—Identification of Aglaophenia aff. pluma
is difficult due to the lack of specific diagnostic cha-
racters (Cornelius 1995a), and 16S rRNA analyses
of north-east Atlantic and west Mediterranean speci-
mens strongly suggests that A. pluma is likely a
species complex including A. pluma, A. tubiformis
Marktanner-Turneretscher, 1890, and A. octodonta
Heller, 1868 (Leclère et al. 2009; Moura et al. 2012).
These three species show extremely low levels of
16S sequence divergence, and probably reflect intra-
specific variation, with the name A. pluma having
priority (Moura et al. 2008). Aglaophenia tubiformis
was recorded in the eastern Atlantic and the
Mediterranean Sea and A. octodonta from the
Mediterranean and adjacent Atlantic (Svoboda and
Cornelius 1991). Assessment of the true distribution
is difficult (Cornelius 1995b). Our material closely
corresponds with Fraser’s specimen from England
(BCPM 976-797-1) and the descriptions of A. pluma
by Cornelius (1995b), Fraser (1937), and Svoboda and
Figure 9. (A) Aglaophenia aff. pluma: portion of cladium
showing three cormidia. RBCM 017-00019-002. Scale equals 200
µm. (B) Antennella sp.: section of stem. ROMIZ B4105. Scale
equals 200 µm. Del. HHC Choong.
Cornelius (1991). The number of leaves reported in
the corbulae of A. pluma is quite varied, ranging
from nine in Fraser (1937) to 5–10 (or more) by
Svoboda and Cornelius (1991). Corbulae in our
samples varied in length within a colony, from 9–15
leaves (Figure 10).
Distribution.Aglaophenia pluma was reported from
Japan as A. pluma var. dichotoma M. Sars, 1857
(Rees and Thurfield 1965); the variety was included
in A. pluma by Svoboda and Cornelius (1991). Fraser
(1946) noted records from Vancouver Island and
Mexico, both of which would require confirmation.
The true distribution of this European boreal species
remains unclear, as reliable records from elsewhere
have yet to be confirmed (Svoboda and Cornelius 1991).
Family Halopterididae Millard, 1962
Antennella sp.
(Figure 9B)
Material.—Oregon, on vessel, colony arising from
hydrorhiza, without gonothecae (JTMD-BF-210),
RBCM 017-00007-001; Washington, on buoy, colony
arising from hydrorhiza, without gonothecae (JTMD-
BF-341), ROMIZ B4105.
Description.—Unbranched, erect, monosiphonic stem
arising directly from anastomosing hydrorhiza,
individual hydrocauli < 10 mm long. Segmentation
heteromerous; alternating transverse and oblique nodes.
Basal part of stem divided into segments (two or more)
divided by transverse nodes, distal-most segment with
H.H.C. Choong et al.
Figure 10. (A) Aglaophenia aff. pluma: corbula. RBCM 017-00019-002. Scale equals 1000 µm. (B) another corbula from same colony.
RBCM 017-00019-002. Scale equals 1000 µm. Photomicrographs by HHC Choong.
oblique node. Hydrothecate and ahydrothecate
internodes present. Hydrothecae confined to middle
part of internodes, cup-shaped, abcauline wall
straight in side view, rim even, hydrothecal opening
approximately 50° with main axis, adcauline side
adnate for approximately 1/3 its length. Hydrotheca
surrounded by three nematothecae: one median
inferior, conical with rim of upper chamber lowered
adaxially, outer side often reaching or exceeding
hydrothecal base; and two laterals, placed on short
apophyses, one on each side of hydrothecal aperture,
not fused to hydrotheca, not reaching hydrothecal
margin, two-chambered, conical with inner side
lowered. No axillar nematothecae. Ahydrothecate
internodes with one median nematotheca. Gono-
thecae not present.
Remarks.—In having no axillar nematothecae behind
the free adcauline wall of the hydrothecae, our
species differs from other Japanese species such as
A. quadriaurita Ritchie, 1909 (= A. variabilis Fraser,
1936 from Japan, which also has two pairs of lateral
nematothecae); A. varians (Billard, 1911), with two
pairs of lateral nematothecae and regular absence of
median inferior nematothecae; or A. secundaria
(Gmelin, 1791), with median nematothecae on the
upper part of the oblique node. Antennella avalonia
Torrey, 1902 reported from the west coast of North
America by Fraser (1946) is likely conspecific with
A. secundaria (Calder 1997; Schuchert 1997), although
it is currently accepted as valid in WoRMS. Our
samples were mostly devoid of coenosarc and appeared
Halopteris aff. campanula (Busk, 1852)
(Figure 11)
Material.—Washington, on vessel, sections of bran-
ched hydrocauli with hydrocladia, and fragments of
hydrocauli, with gonothecae (JTMD-BF-449), RBCM
Figure 11. Halopteris aff. campanula: (A) section of hydrocladium.
RBCM 017-00008-001. Scale equals 200 µm. (B) gonotheca.
RBCM 017-00008-001. Scale equals 200 µm. Del. HHC Choong.
Description.—Cormoids pinnate. Hydrocladia homo-
merously segmented. Internodes with hydrocladia
alternate left and right. Perisarc of hydrocaulus and
hydrocladia slightly thickened, particularly around
nodes. Each internode with one hydrotheca and its
3–4 nematothecae: one median inferior, not reaching
hydrotheca, two laterals placed on short apophyses,
one on each side of the hydrothecal aperture, short,
two-chambered, adaxial wall of upper chamber
reduced, not reaching hydrothecal margin; occa-
sionally one superior nematotheca on separate
intersegment in distal part of caulus. Apophysis of
hydrocladial insertion indistinct, without nematothe-
cae. First node of hydrocladium without hydrotheca
but with one nematotheca, proximal node transverse,
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
distal node oblique. Hydrotheca cup-shaped, rim
even, slightly flaring, reaching much higher than
lateral nematothecae, adaxial and abaxial walls
straight in side view, 1/3–1/2 of adaxial wall adnate.
Perisarc of abaxial wall slightly thickened. Hydro-
thecal aperture approximately 50° with main axis.
Gonothecae pear-shaped, approximately 500 µm long
(?), flattened laterally, arising from base of hydro-
thecae, two nematothecae on basal part, on pedicel
with two sometimes, quadrangular segments separated
by somewhat oblique nodes.
Remarks.—Due to the fragmentary nature of the
sample, we consider our identification as tentative,
pending further analysis. The available trophosome
and gonothecae of this hydroid generally correspond
in morphology with accounts of Halopteris campanula
by Hirohito (1995) and Schuchert (1997) in the number
and position of the nematothecae, shape and position
of the gonothecae and associated pedicel, hydro-
thecal shape and thickening of the abaxial wall of the
hydrotheca. However, it differs in the following
respects: the outer wall of the lateral nematothecae
lacks the distinct emargination over half its height
(spanner-type) as described in Schuchert (1997), i.e.,
the apical chamber is conical, not globular; the
gonothecae are slightly smaller in our material than
in Schuchert (1997) at 900 µm. We are unable to
determine if the branched colony is polysiphonic
from the available material.
Distribution.—Japan: Sagami Bay south to Kagoshima
Prefecture (Hirohito 1995); widespread through the
Indo-West Pacific to the Red Sea, as well as
Australia and New Zealand (Schuchert 1997). As
JTMD-BF-449 did not have otherwise a clear signa-
ture of warmer-water, southern species, this vessel
may have proceeded along slightly south of the Boso
Peninsula in order to acquire this hydroid, which has
not yet been reported from the Tōhoku coast.
Family Plumulariidae McCrady, 1859
Plumularia caliculata Bale, 1888
Plumularia caliculata Bale 1888: 780, pl. 20, figures 9, 10.–
Hirohito 1995: 271, figure 92a–e.
Plumularia sp. Calder et al. 2014: 434, figures 5e–f.
Material.—Washington, on vessel, colony fragment,
remnants of coenosarc in hydrothecae and nemato-
thecae, no gonothecae (JTMD-BF-40), ROMIZ B4234;
Oregon, on vessel, several broken plumes attached to
hydrorhiza, without gonangia (JTMD-BF-533), RBCM
Remarks.—This material corresponds in morpho-
logy to the specimen examined previously (Calder et
al. 2014: 434, figures 5e–f) through its hydrothecae
with a convex abaxial wall, which distinguishes it
from P. setacea (Linnaeus, 1758). In P. setacea the
abcauline wall is straight or occasionally curved
inward in the middle, never curved outwards
(Schuchert 2013). Although the previous specimen
could not be differentiated with certainty from
Plumularia lagenifera Allman, 1885 due to its con-
dition and the lack of gonothecae, the substrate and
collection date of that sample (the floating dock
from Misawa, Honshu, Japan, JTMD-BF-1, 05 June
2012) pointed to P. caliculata of Japanese origin.
The present material also supports the identification
of this species as P. caliculata; in the cauline inter-
nodes in our samples we observed two nematothecae
associated with the apophysis bearing the hydro-
cladium. While apophyses with two nematothecae
were observed occasionally in northeastern Pacific
and Atlantic P. setacea, this character seems to be
invariable in P. lagenifera in the northeastern Pacific
(one nematotheca only) (Schuchert 2013). As our
specimens possess hydrothecae with inwardly curved
abaxial wall and two apophyseal nematothecae were
observed, we assign them to P. caliculata.
Distribution.—Australia, its type locality; Japan,
and likely Korea (Calder et al. 2014).
Plumularia setacea (Linnaeus, 1758)
Sertularia setacea Linnaeus 1758: 813.
Material.—Hawai‘i, on buoy, remnants of hydro-
rhiza, several cormoids with hydrocauli and several
hydrocladia, without gonothecae (JTMD-BF-144),
ROMIZ B4100; Oregon, on vessel, several plumes,
with gonangia, Scruparia ambigua epizoic (JTMD-
BF-356), RBCM 017-00012-001; Oregon, on vessel,
several plumes, with coenosarc and gonangia, partially
covered by S. ambigua (JTMD-BF-356), RBCM
017-00020-001; Washington, on float, several plumes,
with male and female gonangia (JTMD-BF-462),
RBCM 017-00009-001; Oregon, on buoy, several
plumes, with gonangia (JTMD-BF-531), RBCM 017-
00018-001; Oregon, on vessel, several weathered
and broken plumes, without gonangia, (JTMD-BF-
533), RBCM017-00021-001.
Remarks.—In our previous study (Calder et al. 2014)
we reported Plumularia setacea from JTMD. The
present material also corresponds morphologically to
other accounts of P. setacea in having a straight
outer wall of the hydrotheca, one nematotheca
associated with the apophysis bearing the hydro-
cladium, and a nematotheca on the ahydrothecate
internode of the hydrocladia, as well as nemato-
thecae on the internodes of the hydrocaulus (Calder
1997; Schuchert 2013). Gonothecae were observed
arising from apophyses via short pedicels, fusiform
in shape. Both male and female gonothecae are
present. Our material was in good condition, with
H.H.C. Choong et al.
a significant amount of coenosarc present, partially
overgrown by the bryozoan Scruparia ambigua.
Distribution.—Japan (Hirohito 1995); Pacific coast
of North America from Alaska to southern California
(Fraser 1937), and reported from all oceans; almost
certainly a species complex (Mills et al. 2007;
Schuchert 2014).
Family Phylactothecidae Stechow, 1921
Diagnosis (emended) and Systematic Discussion.
Colonies stolonal or erect, arising from creeping
hydrorhiza; hydrocauli monosiphonic or polysipho-
nic; hydrothecae shallow to bell-shaped, sessile or
pedicellate, basal region with delicate diaphragm,
with or without desmocytes; hydranths usually much
larger than hydrothecae, with or without an inter-
tentacular web. Nematophores present, with variably
reduced nematothecae. Gonophores fixed sporosacs;
gonothecae solitary or aggregated to form a glomulus.
Watson (1969) noted the need for revision of
nominal genera of nematophore-bearing hydroids in
Haleciidae, which was reiterated by Cornelius (1975a)
who recognized the arbitrary nature of the limits of
these genera. The inclusion of the genus Hydrodendron
Hincks, 1874 within the family Haleciidae is indeed
problematic, as shown by phylogenetic analysis using
16S as well as combined 16S, 18S, and 28S rRNA
data; Hydrodendron shows a marked divergence
from the Halecium species studied (Moura et al.
2008; Leclère et al. 2009; Maronna et al. 2016).
Rees and Vervoort (1987) had previously noted the
usefulness of gonosomal characters in separating
Hydrodendron from Halecium. Hydrodendron mirabile
shares the presence of nematophores and nemato-
thecae with Plumularioidea. Maronna et al. (2016)
proposed the taxon Plumupheniida (which includes
the families within Plumularioidea) to accommodate
H. mirabile. There is some support for the inclusion
of Hydrodendron within Plumularioidea, suggesting
that the presence of nematothecae in Plumularioidea
and Hydrodendron is not due to convergence, and
that defensive polyps (dactylozoids) were acquired
only once within Macrocolonia in the ancestor of
Plumularioidea (Leclère et al. 2009). Nematophore-
bearing haleciid species were included under Hydro-
dendron, Ophiodissa Stechow, 1919 and Phylactotheca
Stechow, 1913 (the latter two currently included as
synonyms of Hydrodendron) to accommodate forms
having shallow to deeply campanulate hydrophores
(Watson 1969). We propose that Phylactothecinae
Stechow, 1921 be elevated to full family rank, and
that Hydrodendron mirabile and its congeners are
included in the family Phylactothecidae Stechow,
1921 within the superfamily Plumularioidea.
While the family name Hydrodendriidae (see
Nutting 1905) exists, it is based on the genus Hydro-
dendrium Nutting, 1905. Phylactotheca is the type
genus of the subfamily Phylactothecinae. The name
is currently included as a synonym of Haleciidae, but
from the evidence in Maronna et al. (2016), outlined
above, this synonymy is incorrect. Although its type
genus (Phylactotheca) is a junior subjective synonym
of Hydrodendron, the name is not thereby invalidated
under the code (ICZN Art. 40.1). Under the Principle
of Coordination in nomenclature, Stechow (1921) is
credited as author of the family name as well as the
subfamily name. Further analysis which includes the
other species of Hydrodendron, and especially its
type species H. gorgonoide (G.O. Sars, 1874), is
required to clarify the taxonomic position of H.
mirabile and its congeners, but clearly Hydrodendron
is shown to be remote from Haleciidae and merits
assignment to its own family.
Hydrodendron mirabile (Hincks, 1866)
(Figure 12)
Ophiodes mirabilis Hincks 1866: 422, pl. 14, figures. 1–5.
Material.—Washington, colony with some coenosarc
remaining, amidst fouling, without gonothecae
(JTMD-BF-402), ROMIZ B4110; Washington, no
gonothecae, Scruparia ambigua epizoic (JTMD-BF-
402), ROMIZ B4109; Washington, on vessel, colony
with remnants of hydranths and coenosarc present,
amidst fouling, without gonothecae (JTMD-BF-402),
ROMIZ B4155; Washington, colony with some
coenosarc remaining, amidst bryozoan Aetea sp.,
amphipod Jassa marmorata Holmes, 1905, and algal
colonies, without gonothecae (JTMD-BF-402), ROMIZ
B4170; Washington, hydrocauli arising from hydro-
rhiza, with coenosarc, without gonothecae, S. ambigua
epizoic (JTMD-BF-402), ROMIZ B4235.
Description.—Hydrorhiza stolonal, irregularly branched.
Stolon wrinkled, perisarc moderately thickened,
occasionally projecting internally. Stem segmented,
monosiphonic or loosely fascicled at base, irregularly
branched; perisarc of stem and branches thickened.
Internodes smooth or with one basal wrinkle. Hydro-
theca borne on long internode process, shallow,
widening moderately towards hydrothecal opening.
Occasionally secondary hydrophores present.
Hydrothecal rim entire, often everted, no redupli-
cation; perisarc slightly thickened, but not as thick as
in stems and branches. Desmocytes large, refringent,
about middle of hydrotheca. Nematothecae sessile,
dispersed, often on node processes, occasionally on
stolon, large, cone-shaped, margin flared; conspi-
cuous, irregular refringent ring of desmocytes on upper
third. Nematophore long, filiform. No gonothecae.
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
Figure 12. Hydrodendron mirabile: (A) part of
colony. ROMIZ B4155. Scale equals 500 µm.
(B) hydrothecae. ROMIZ B4155. Scale equals
200 µm. Del. HHC Choong.
Table 2. Trophosomal dimensions of Hydrodendron mirabile compared to JTMD specimen BF-402 (ROMIZ B4155).
Hydrodendron mirabile
(in Cornelius 1995b)
mirabile (in Preker
and Lawn 2010)
Hydrodendron mirabile
(in Hirohito 1995)
Hydrodendron mirabile
(in Millard 1975, as
H. caciniformis)
(ROMIZ B4155)
Colony height
20–50 mm (small
colonies stolonal, large
colonies polysiphonic
5.1 mm (small
colonies, stolonal
or erect)
> 10 mm (stolonal,
larger colonies
polysiphonic basally)
> 10 mm
~ 10 mm
Hydrotheca height 40–120 µm 95–130 µm 160–320 µm 50–120 µm 104–125 µm
Hydrothecal width
at rim 150–250 µm 220–240 µm 190–220 µm 140–200 µm 199–234 µm
Hydrothecal width
at base 90–230 µm Not provided Not provided Not provided 120–150 µm
length 20–200 µm 128–136 µm 120–170 µm Not provided 142–149 µm
width (at rim
unless stated
60–90 µm (maximum
width only; width at
rim not given)
40–120 µm 60–100 µm
(given as width) Not provided 69–100 µm
Internode length 370–750 µm 480–760 µm Not given Not given 253–694 µm
Remarks.—The trophosome of our material agrees
with accounts of Hydrodendron mirabile by Cornelius
(1995b), Hirohito (1995), and Preker and Lawn (2010).
The adcauline peridermal thickening or pseudo-
diaphragm, sometimes present near the base of the
hydrophore in H. caciniformis (Hincks, 1866) (now
reduced to a synonym of the present species; see
Cornelius 1975a) observed by Millard (1975) and
Vervoort (1959), was not mentioned by Hirohito
(1995) in H. mirabile from Japan, nor was it observed
in our samples. Cornelius (1975a, 1995b) considered
larger colonies (in growth length) of H. caciniformis
(= O. caciniformis) to be due to intra-specific popu-
lation variation. Size comparisons of some characters
of H. mirabile given in various accounts are
summarized in Table 2. Our material corresponds to
that of Hirohito (1995) in general dimensions, and in
the occasional presence of secondary hydrophores.
No gonothecae were seen in our material.
Distribution.—Japan (Hirohito 1995). Hydrodendron
mirabile has been reported circumglobally from
tropical, subtropical, and temperate waters (Kirkendale
and Calder 2003; Preker and Lawn 2010), including
the oceanic islands of Guam, Bermuda, the Azores,
and the Cape Verdes (Calder 2000; Medel and
Vervoort 2000; Kirkendale and Calder 2003).
Reported in South Africa (as H. caciniformis) by
Millard (1975).
Family Plumaleciidae Choong and Calder, fam. nov.
Diagnosis.—Colonies erect, arising from a stolonal
hydrorhiza; hydrocauli unbranched, divided into
internodes, giving rise to hydrocladia from alternate
H.H.C. Choong et al.
or mostly alternate apophyses, cauline hydrothecae
absent; hydrocladia dichotomously or irregularly
branched, or unbranched, divided into internodes,
often with terminal hydrothecae; hydrothecae uni-
seriate, sessile, small, cup-shaped, relatively shallow,
free of hydrothecial internode or not completely
adnate; radially symmetrical; margin entire; opercu-
lum absent. Nematophores and nematothecae absent.
Gonophores presumably fixed sporosacs; gono-
thecae solitary, conical, without nematothecae, arising
from apophyses of hydrocaulus; phylactocarps absent.
Plumalecium plumularioides (Clark, 1877)
(Figure 13)
Halecium (?) plumularioides Clark 1877: 217, pl. 10, figures. 16, 17.
Plumularia plumularioides.–Nutting 1900: 62, pl. 4, figure. 3.–
Cairns et al. 1991: 28.
not Plumularia plumularoides.–Torrey 1902: 78, pl. 11, figures.
103, 104.–Fraser 1911: 84; 1918: 136, pl. 2, figures. 5A–C; 1937:
190, pl. 44, figures. 230a–c; 1947: 92, 363. [Incorrect subsequent
not Plumularia plumularioides.–Torrey 1904: 38.–Fraser 1935: 145.
Plumalecium plumularioides.–Antsulevich 1982: 71, figures, A,
B; 2015: 561, figure 282a–b.
Halecium plumularioides.–Antsulevich 1987: 112, figures, 31A, B.
not Kirchenpaueria plumularoides.–Brinckmann-Voss 1996: 96.
[Incorrect subsequent spelling]
Kirchenpaueria plumularioides.–Cairns et al. 2002: 20, 55.–
Calder and Stephens 1997: 31.
Ventromma plumularioides Bouillon et al. 2006: 335.
not Kirchenpaueria plumularioides.–Marques et al. 2007: 131, pl.
45, figure. C.–Mills et al. 2007: 161.
Material.—Washington, on vessel, colonies with
gonothecae (JTMD-BF-40), ROMIZ B4095;
Washington, on vessel, section of hydrocaulus with
perisarc, no gonothecae (JTMD-BF-40), ROMIZ
B4178; Washington, on vessel colonies with gono-
thecae (JTMD-BF-40), ROMIZ B4192; Washington,
on vessel, colonies without gonothecae (JTMD-BF-40),
ROMIZ B4193; Washington, on vessel, section of
hydrocaulus with hydrothecae, without gonothecae
(JTMD-BF-40), ROMIZ B4237; Oregon, on vessel,
dense colonies, overgrowing Lepas sp. without gono-
thecae (JTMD-BF-50), ROMIZ B4196; Hawai‘i, on
vessel, found live, scraped off Mytilus galloprovin-
cialis shell, without gonothecae (JTMD-BF-87),
ROMIZ B4097; Washington, amidst fouling on
vessel, fragment of stem with several hydrothecae,
with remnants of coenosarc, without gonothecae
(JTMD-BF-134), from ROMIZ B4236; Oregon, on
buoy, colony arising from hydrorhiza, with remnants
of perisarc, overgrowing gooseneck barnacle Lepas
sp., without gonothecae (JTMD-BF-207), ROMIZ
B4101; Washington, on vessel, colonies growing on
styrofoam, with gonothecae, Lepas sp. also present
(JTMD-BF-352), RBCM 017-00010-001; Japan:
Miyako, Iwate Prefecture, Tōhoku Coast, November
2015, 3-month test panel, colony arising from stolon,
without gonothecae (M12) RBCM 017-00014-001;
Japan: Miyako, Iwate Prefecture, Tōhoku Coast,
September 2015, 1-month test panel, colony arising
from stolon, with gonothecae (M19) RBCM 017-
Description.—Colony up to 12 mm high, arising from
stolon. Hydrocaulus monosiphonic, erect, usually
straight but occasionally slightly geniculate, 1–3
transverse annulations at base, divided into regular
internodes, each segment bearing one hydrocladial
apophysis distally, hydrocladia alternate. Perisarc
moderately thickened. Hydrothecae uniseriate, 1–3
or more per hydrocladium, cup-shaped, tapering
slightly to base, margin entire. Gonothecae solitary,
conical, with rounded apices, borne on axils of
hydrocladial apophyses.
Remarks.—Our material is referable to Plumalecium
plumularioides, based on trophosomal and gonosomal
characters. This species was well-represented on
JTMD that stranded on the coasts of Washington,
Oregon, and Oahu, Hawai‘i. It was found as well on
test panels immersed at Miyako, Iwate Prefecture,
Tōhoku region, Japan. The only reliable previous
records of P. plumularioides are those of Clark
(1877) from the type locality (Alaska, Nunivak
Island, 15–18 m) and Antsulevich (1982) from the
Kurile Islands, Russian Federation (near Kunashir
Island, 6 m). As noted by Antsulevich (2015), several
records of P. plumularioides from the west coast of
North America have been based on misidentified
hydroids possessing mesial nematothecae (Torrey
1902, as Plumularia plumularoides (sic); Fraser
1918, as Plumularia plumularoides (sic), 1935, as
Plumularia plumularioides; Brinckmann-Voss 1996,
as Kirchenpaueria plumularoides (sic); Mills et al.
2007, as Kirchenpaueria plumularioides). The species
in all of these reports is likely a bona fide kirchen-
paueriid and not P. plumularioides. This is the first
record of its presence in Japan (from test panels
recovered from the coast of Tōhoku). While
infrequently reported, it is possible that hydroids of
P. plumularioides from the North Pacific have at
various times been misidentified as one or more
species of Halecium.
Distribution.—Japan (new record, herein). Kurile
Islands (Antsulevich 2015) and Bering Sea (Clark
Systematic discussion.—Clark (1877) first described
this species, as Halecium (?) plumularioides, from
Cape Etolin, Nunivak Island, Alaska. The uniserial
arrangement of the hydrothecae, and absence of
gonothecae, left him uncertain how it should be
classified. He noted the resemblance of its trophosome
to that of plumulariid hydroids, but provisionally
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
Figure 13. Plumalecium plumularioides:
(A) section of hydrocaulus and hydrocladia.
ROMIZ B4101. Scale equals 500 µm.
(B) gonothecae. ROMIZ B4095. Scale
equals 500 µm. Del. HHC Choong.
assigned it instead to the genus Halecium Oken,
1815 because colonies lacked nematophores, although
also absent is the ring of desmocytes consistent with
diagnoses of the taxon. Nutting (1900) saw no new
material but referred the species instead to Plumularia
Lamarck, 1816, and to the family Plumulariidae
McCrady, 1859, concluding that the absence of
nematophores was merely accidental or temporary,
notwithstanding the fact that nematophores with
well-developed nematothecae are essential character
states in that family. Studies by Antsulevich (1982,
1987, 2015), based on specimens from the Kurile
Islands, Russian Federation, discounted Nutting’s
conclusion about the existence of nematophores (and
nematothecae) in the species. As originally described
by Clark (1877), and later by Antsulevich (1982,
1987, 2015), they are indeed lacking. Our specimens
fully correspond with theirs in this character. Given the
distinctive morphology of its trophosome, Antsulevich
(1982) established Plumalecium as a new genus to
accommodate the species. While he abandoned the
genus shortly after (Antsulevich 1987), including it
in the synonymy of Halecium, Plumalecium was
recognized as valid again by him in a later work
(Antsulevich 2015). We likewise recognize the validity
of the genus, and include the species here under the
binomen Plumalecium plumularioides.
Clark’s species has been included as Plumularia
plumularioides in Cairns et al. (1991), as Kirchen-
paueria plumularioides in Cairns et al. (2002) and in
the World Register of Marine Species (http://www.,
and as Ventromma plumularioides in Bouillon et al.
(2006). Classification of this species at the rank of
family has also been unsettled. Authors including
Cairns et al. (2002), Bouillon et al. (2006), and
Antsulevich (2015) referred P. plumularioides to
Kirchenpaueriidae Stechow, 1921. While kirchen-
paueriids lack paired lateral nematothecae, mesial
nematophores (either naked or with reduced nemato-
thecae) occur below each hydrotheca (Leclère et al.
2007; Maronna et al. 2016). Such nematothecae are
lacking in P. plumularioides.
Plumalecium Antsulevich, 1982 (type species:
Halecium plumularioides Clark, 1877) appears
referable to superfamily Plumularioidea based on
trophosomal characters, notwithstanding the lack of
nematothecae. We propose that the diagnosis of
Plumularioidea be amended to accommodate this
species lacking nematothecae. In that character it
differs from all known families of plumularioids, as
defined in works such as those of Cornelius (1995b),
Calder (1997), Bouillon et al. (2006), Leclère et al.
(2007), and Maronna et al. (2016). A new family,
Plumaleciidae, is thus proposed herein to accommodate
the genus. Plumalecium is currently monotypic, with
P. plumularioides as its only known species.
Halecium linkoi Antsulevich, 1980 resembles P.
plumularioides, but it seems to differ (Antsulevich
2015: 366) in having hydrocladia that are repeatedly
and consistently branched rather than being bran-
ched or unbranched, with hydrothecae in the latter
case being arranged in a straight series.
Order Limnomedusae Kramp, 1938
Family Olindiidae Haeckel, 1879
Gonionemus vertens A. Agassiz, 1862
Gonionemus vertens A. Agassiz 1862: 350
Material.—BF1: A community metabarcode sequence
with 98.4% pairwise identity to Genbank sequences
(over 311 bp) from Japan (KY43780, Okirai Bay)
and Russia (KY437948 and KY437951, from Amur
Bay and Vostok Bay, respectively) as well as to
introduced populations in New England (for example,
KY437814, KY437864, and KY437898), as studied
and deposited by Govindarajan et al. (2017).
H.H.C. Choong et al.
Remarks.—No additional specimens of Gonionemus
were recovered from the Misawa fisheries dock
(JTMD-BF-1) that landed in June 2012 in central
Oregon. However “Misawa 1” supported vast bio-
fouling communities (exceeding 75 square meters),
only a small portion of which was sampled, and it is
thus not surprising that the small polyps of this
species were not recovered. Our material aligns with
the toxic clade of Gonionemus vertens from the
Northwest Pacific Ocean, which is distinct from the
non-toxic clade of G. vertens known from the
Northeast Pacific Ocean (Govindarajan et al. 2017).
The toxic Western Pacific clade was recently intro-
duced to New England (Govindarajan et al. 2017).
Biogeographic sources of JTMD hydroid fauna
We suggest that all of the species reported here, with
the exception of Obelia griffini (discussed in detail
below), originate from the coast of Japan (or, in the
case of Clytia linearis discussed earlier, slightly
farther south). In concert with the findings of Elvin
et al. (2018) and Cordell (2018), reporting on JTMD
sponges and copepods, respectively, we also found
that diversity per object declined over time. As
suggested by Elvin et al. (2018) and Cordell (2018),
if species were being regularly acquired by JTMD
after entering the coastal zone of North America or
Hawai‘i, there would be no reason for diversity to
decline over time. Rather, this decline suggests a
steady attrition of species richness per object raft
originating from Japan, as would be expected from
the challenges of long-term survival by coastal
species rafting for years in an oceanic environment.
It is possible that survival in many species may have
been prolonged through resting stages (menonts).
However, we also observed (in the present study and
in Calder et al. 2014) large, weathered colonies with
empty gonothecae in some species such as Obelia
longissima, suggesting persistence of these colonies
on the debris for extended periods. In addition, a
number of JTMD species arriving in North America,
including Orthopyxis caliculata, O. dichotoma,
Amphisbetia furcata, Aglaophenia aff. pluma, and
Plumalecium plumularioides, were found on debris
arriving in Hawai‘i. As none of these species are
known from Hawai‘i, their only source is the
Western Pacific Ocean.
Finally, as noted by Calder et al. (2014), Carlton
et al. (2017), and Elvin et al. (2018), if JTMD objects
were being typically colonized after arrival in the
Eastern Pacific, it would be highly unlikely that the
only species to do so would also be those occurring
in Japanese or other Western Pacific waters. We
documented no hydroid species believed to be unique
to North America or the Hawaiian Islands on JTMD.
Obelia griffini as a potential member of the North
Pacific Oceanic Fauna
We propose that the abundant hydroid Obelia
griffini may be a member of the poorly known North
Pacific open ocean neustonic fauna. Obelia griffini
was described from either Bremerton or Port Townsend,
Washington, without habitat data, by Calkins (1899).
Two species described in the same paper are now
held to be synonyms of O. griffini: Obelia gracilis,
“on grasses” from Scow Bay, Port Townsend Harbor,
and Obelia surcularis, on “water grasses” from the
same location. O. griffini was first synonymized
with Obelia dichotoma by Cornelius (1975b), but we
regard it as a distinct species, as noted earlier, based
upon morphological criteria (Calder et al. 2014).
As reviewed by Calder et al. (2014), O. griffini
has also been reported (as O. gracilis) from benthic
habitats in China and the South Kurile Islands. In
contrast, we find O. griffini to be not only the most
common hydroid on tsunami debris, but also to be
the only species (or in sole company with the native
oceanic gooseneck barnacle Lepas spp.) often on
marine debris (JTMD as well as non-Japanese
tsunami debris). Of interest in this regard is
Cornwall’s (1927) report that hydroids on the whale
barnacle Coronula diadema (Linnaeus, 1767) (taken
from a humpback whale off Vancouver Island) were
identified by Charles H. O’Donoghue as O. griffini.
The populations of O. griffini on JTMD are typically
too expansive to have been acquired in the nearshore
Eastern Pacific by debris in the brief time most of
this debris field is believed to have rafted along the
coast prior to landing, especially considering (as
discussed above) that no uniquely Eastern Pacific
hydroid species were found on any of these objects.
Further, O. griffini is found on JTMD arriving in the
Hawaiian Islands, where no members of this species-
group are known to occur, thus making it unlikely
that the populations were acquired there.
Finally, neither O. griffini, O. gracilis, nor O.
surcularis have been reported from the Japanese
hydroid fauna. While it may be that since 1976
populations matching the morphology of these
species have been assigned by Japanese workers to
O. dichotoma following Cornelius (1975b, but not
issued until November 1975), O. griffini and O. gracilis
were in regular use prior to that date, O. gracilis in
particular having been identified in other Asian
hydroid studies, and with other workers in the
Western Pacific continuing to recognize O. griffini
Hydroids on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i
after 1975 as well (for example, Antsulevich 1992).
While we report here and in Calder et al. (2014)
other less common hydroid species that we interpret
as new records for Japan, the abundance and
ubiquity of O. griffini on JTMD make it difficult to
imagine that it has been overlooked in the Japanese
coastal fauna. Rather, we suggest that JTMD acquired
O. griffini during the North Pacific transit, and that
this is a native high-seas species.
This said, the presence of oceanic, neustonic species—
such as Obelia griffini, as well as the gooseneck
barnacle Lepas, the crabs Planes spp. and Plagusia
spp., the nudibranch Fiona pinnata (Eschscholtz,
1831) and the polychaete worm Amphinome rostrata
(Pallas, 1766), all of which have been found on
JTMD (Carlton et al. 2017)—in benthic habitats in
China, Russia, or the Pacific Northwest would be
highly anomalous. While all of these oceanic species
may be found on occasion washed ashore, they are
not regular members of coastal benthic communities.
Thus, Obelia griffini may represent a cryptic species
complex, with apparently morphologically identical
benthic and pelagic clades. Molecular genetic studies
are called for to clarify the status of purported
oceanic and shore populations. If the pelagic taxon
were to be found to represent a distinct taxon, it
would likely require a new name.
A number of species of hydroids are regarded as
naturally occurring in both benthic and pelagic
habitats (such as Clytia hemisphaerica and Clytia
linearis, both treated herein; see also Calder 1995,
for species from the Sargasso Sea, many of which
are also reported from nearshore benthic commu-
nities). While all or most of these species likely
represent species complexes as well, in the case of
O. griffini, we underscore the observation that this
abundant species is not known from the Tōhoku
source region of JTMD, thus making its high seas
acquisition en route through the Pacific Ocean more
probable. While hydroids have been previously
reported on debris drifting in the North Pacific
Ocean (Calder et al. 2014; Goldstein et al. 2014),
they have not been regarded as part of the naturally
occurring neustonic fauna.
There is some evidence in our material for direct
settlement of Obelia griffini larvae on Lepas or other
substrates in the open ocean (that is, sexually produ-
ced colonies as opposed to clonally produced colonies
or stolonal extension of colonies growing originally
on Japanese substrates). For example, runner-like
hyperplastic stolons exhibiting directional growth
were observed on an O. griffini colony on the pelagic
crab Plagusia sp. (ROMIZ B4174), which colony is
small and relatively sparse, indicating that larval
recruitment is probable. Production of hyperplastic
stolons exhibiting directional growth have been
observed in sexually produced colonies of Hydractinia
symbiolongicarpus Buss and Yund, 1989 (Van Winkle
and Blackstone 2002). The presence of these colonies,
in addition to tightly packed “sheets” indicating later
development of stolonal mats (also present in our
material) supports the argument for open larval
recruitment and persistence of these colonies. It is
possible that the availability of planulae of O. griffini,
as well as those species such as Amphisbetia furcata,
which is probably not part of the oceanic neustonic
fauna sensu stricto, may be mediated by the release
of mature medusae which do not need to feed or by
release of larval stages from fixed gonophores. This
life cycle plasticity has been observed in Clytia
linearis, Obelia sp., and A. operculata (Lindner and
Migotto 2002; Genzano et al. 2008).
Conclusions: JTMD hydroid diversity and
transoceanic dispersal
Campanularioid hydroids in the genera Campa-
nularia, Orthopyxis, Clytia, Laomedea, and Obelia,
are frequent and well-known members of ship
fouling (Hutchins 1952; Zvyagintsev 2003, 2005),
harbor fouling (Karlson and Osman 2012), and, often,
rafting (Thiel and Gutow 2005; Farrapeira 2011)
communities. Not surprisingly, 10 species in these
genera comprise the most diverse group of JTMD
hydroids. Thiel and Gutow (2005) summarized
records of hydroids reported in the literature as
rafting species. Other than taxa associated with the
drifting brown alga Sargassum in the North
Atlantic’s Sargasso Sea (Calder 1995), they noted
five species whose association with rafting was
based only upon circumstantial evidence or distri-
butional inference, rather than direct observation,
and an additional four species reported from local or
regional coastal debris. Goldstein et al. (2014) reported
three species, Clytia gregaria (Agassiz, 1862), Obelia
sp., and Plumularia setacea from marine debris
collected floating in the North Pacific. The present
report represents the first documentation of the 28
species reported here and earlier (Choong and Calder
2013; Calder et al. 2014) as rafting from one conti-
nental margin to another.
That half of the species found in our collections
occurred only once speaks to the strong probability
that JTMD hydroid diversity is far greater than
reported here. Only a small fraction of Japanese
tsunami marine debris was sampled (Carlton et al.
2017), suggesting that the many thousands of objects
not intercepted and studied may have transported
many more hydroid species to the Central and
Eastern Pacific.
H.H.C. Choong et al.
We are indebted to (in Oregon) Steven Rumrill, Fawn Custer, and
Matthew Hunter, (in Washington) Allen Pleus, Dustin Court, Marcus
Reeves, and Russell Lewis, and (in Hawai‘i) Sonia Gorgula, Scott
Godwin, and Jonathan Blodgett, amongst many other collectors, all
of whom secured samples from newly landed JTMD objects. We
thank L. Best and K. Sendall of the Royal British Columbia Museum
(RBCM) for their support of JTMD research and collections. Thanks
are due also to M. Zubowski, Royal Ontario Museum, and H.
Gartner, RBCM, for providing collections management assistance.
We thank Melinda Wheelock and Tracy Campbell for laboratory
assistance. Finally, we thank H.R. Galea and two anonymous
reviewers for their valuable comments and thorough review of the
manuscript. Support for field sampling and laboratory processing
was provided by Oregon Sea Grant, the National Science Foundation
(Division of Ocean Science, Biological Oceanography), NSF-OCE-
1266417, 1266234, 1266397, 1266406, and the Ministry of the
Environment of Japan through the North Pacific Marine Science
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Journal of Marine Biology 29: S10–S21,
Zvyagintsev AY (2005) Marine fouling in the north-west part of the
Pacific Ocean. Vladivostok, Dalnauka, 432 pp
Supplementary material
The following supplementary material is available for this article:
Table S1. JTMD Objects: BF numbers, landing site locations, dates and object types, and prefecture and city origins if known.
Table S2. Summary of North Pacific distribution of hydroids originating from the Japanese coast and found on tsunami marine
debris between 2012 and 2016.
This material is available as part of online article from:
... Thus, while the medusa occasionally swim out of the eelgrass meadows, natural or anthropogenic medusa dispersal, while possible, may not be the primary mechanism for its spread. Gonionemus sp. has a complex life history that includes minute benthic asexual stages (Perkins, 1903;Kakinuma, 1971;Uchida, 1976) that may be amenable to human-mediated transport on ship hulls (Tambs-Lyche, 1964), shellfish (Edwards, 1976), and debris (Choong et al., 2018). ...
... includes minute polyp and cyst stages (Perkins, 1903;Kakinuma, 1971;Uchida, 1976) that could have easily arrived unnoticed. In a genetic survey of epifauna, Gonionemus sp. was recently identified from the North American Pacific coast on tsunami debris originating from Japan (Choong et al., 2018). This suggests that polyp, frustule, and or cyst stages are capable of long-distance transport on anthropogenic surfaces. ...
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The clinging jellyfish Gonionemus sp. is a small hydromedusa species known historically from the Swedish west coast but not reported in recent times. This species is thought to be native to the northwest Pacific where it is notorious for causing severe stings in humans and is considered invasive or cryptogenic elsewhere. This year, unlike in the past, severe stings in swimmers making contact with Gonionemus sp. medusae occurred in Swedish waters from a sheltered eelgrass bed in the inner Skagerrak archipelago. To the best of our knowledge, this is only the second sting record of Gonionemus sp. from the Northeast Atlantic—with the first record occurring off the Belgian coast in the 1970s. Stinging Gonionemus sp. medusae have also been recently reported from the northwestern Atlantic coast, where, like on the Swedish coast, stings were not reported in the past. We analyzed sea surface temperature data from the past 30 years and show that 2018 had an exceptionally cold spring followed by an exceptionally hot summer. It is suggested that the 2018 temperature anomalies contributed to the Swedish outbreak. An analysis of mitochondrial COI sequences showed that Swedish medusae belong to the same clade as those from toxic populations in the Sea of Japan and northwest Atlantic. Gonionemus sp. is particularly prone to human-mediated dispersal and we suggest that it is possible that this year’s outbreak is the result of anthropogenic factors either through a climate-driven northward range shift or an introduction via shipping activity. We examined medusa growth rates and details of medusa morphology including nematocysts. Two types of penetrating nematocysts: euryteles and b-mastigophores were observed, suggesting that Gonionemus sp. medusae are able to feed on hard-bodied organisms like copepods and cladocerans. Given the now-regular occurrence and regional spread of Gonionemus sp. in the northwest Atlantic, it seems likely that outbreaks in Sweden will continue. More information on its life cycle, dispersal mechanisms, and ecology are thus desirable.
... He therefore considered the two to be conspecific, a proposed synonymy that has been widely followed (e.g. Gibbons and Ryland 1989;Calder 1991;Watson 2000;Zhenzu et al. 2014;Wedler 2017;Choong et al. 2018). However, C. linearis clearly differs from the account of C. obliqua by Clarke (1907) in having colonies that are usually erect and sympodially branched, hydrothecae that are large and deep, and marginal cusps with distinctive inward-folding pleats that extend onto the distal wall of the hydrotheca (Lindner and Migotto 2002;Cunha et al. 2020). ...
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The hydroids of Cocos Island (Isla del Coco), Costa Rica, have received scant attention and are poorly known. Only 11 species have been reported from there previously, with five of them being stylasterids. Hydroids examined here were collected during 2019 in a search for invasive species, as part of a fouling survey. Fourteen species – three anthoathecates and 11 leptothecates – were identified in the collection. All represent new records for Cocos Island, elevating its number of reported species to 25. The most abundant species in the collection were Clytia obliqua (Clarke, 1907) and Sertularella affinicostata Calder and Faucci, 2021, found in 11 of 42 samples (26%), and Tridentata borneensis Billard, 1925a, present in nine (21%) of them. Nematocysts of Corydendrium flabellatum Fraser, 1938a and Eudendrium cf. certicaule Fraser, 1938a are newly identified, measured and illustrated. Three species (Clytia brevithecata (Thornely, 1900), Halopteris alternata (Nutting, 1900) and Macrorhynchia philippina Kirchenpauer, 1872), are introduced, with the rest assigned to a native or cryptogenic status.