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https://doi.org/10.11646/zootaxa.5085.1.1
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ZOOTAXA
ISSN 1175-5326 (print edition)
ISSN 1175-5334 (online edition)
Accepted by H. Galea: 18 Nov. 2021; published: 24 Dec. 2021
5085
ZOOTAXA
Magnolia Press
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Zootaxa 5085 (1): 001–073
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Copyright © 2021 Magnolia Press Monograph
Licensed under Creative Commons Attribution-N.C. 4.0 International https://creativecommons.org/licenses/by-nc/4.0/
Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise
to the Northwestern Hawaiian Islands
DALE R. CALDER1,2* & ANUSCHKA FAUCCI3
1Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario, Canada M5S 2C6
2Research Associate, Royal British Columbia Museum, 675 Belleville Street, Victoria, British Columbia, Canada V8W 9W2
3Math & Sciences Division, Leeward Community College, Pearl City, Hawaii, 96782, USA
�
anuschka@hawaii.edu; https://orcid.org/0000-0001-9002-8987
*Corresponding author.
�
dalec@rom.on.ca; https://orcid.org/0000-0002-7097-8763
CALDER & FAUCCI
2 · Zootaxa 5085 (1) © 2021 Magnolia Press
DALE R. CALDER & ANUSCHKA FAUCCI
Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern
Hawaiian Islands
(Zootaxa 5085)
73 pp.; 30 cm.
24 Dec. 2021
ISBN 978-1-77688-438-4 (paperback)
ISBN 978-1-77688-439-1 (Online edition)
FIRST PUBLISHED IN 2021 BY
Magnolia Press
P.O. Box 41-383
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New Zealand
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https://www.mapress.com/j/zt
© 2021 Magnolia Press
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purpose other than private research use.
ISSN 1175-5326 (Print edition)
ISSN 1175-5334 (Online edition)
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 3
Table of Contents
Abstract ...................................................................................................4
Introduction ................................................................................................5
Materials and methods .......................................................................................5
Systematic Account ..........................................................................................6
Phylum Cnidaria Verrill, 1865 .................................................................................6
Subphylum Medusozoa Petersen, 1979 ..........................................................................6
Class Hydrozoa Owen, 1843 ...................................................................................6
Subclass Hydroidolina Collins, 2000 ............................................................................6
Order Anthoathecata Cornelius, 1992 ............................................................................7
Clade Capitata Kühn, 1913, sensu stricto .........................................................................7
Family Pennariidae McCrady, 1859 .............................................................................7
Genus Pennaria Goldfuss, 1820. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Pennaria disticha Goldfuss, 1820 ........................................................................7
Family Sphaerocorynidae Prévot, 1959 ..........................................................................9
Genus Sphaerocoryne Pictet, 1893 .............................................................................9
Sphaerocoryne bedoti Pictet, 1893 .......................................................................9
Family Oceaniidae Eschscholtz, 1829 ...........................................................................9
Genus Turritopsis McCrady, 1857 ..............................................................................9
Turritopsis sp. .......................................................................................9
Family Eudendriidae L. Agassiz, 1862 ..........................................................................10
Genus Eudendrium Ehrenberg, 1834 ...........................................................................10
Eudendrium merulum Watson, 1985 ....................................................................10
Order Leptothecata Cornelius, 1992 ............................................................................11
Family Phialellidae Russell, 1953 ..............................................................................11
Phialellidae (undetermined) ..................................................................................11
Family Hebellidae Fraser, 1912 ...............................................................................12
Genus Hebella Allman, 1888 .................................................................................12
Hebella furax Millard, 1957 ...........................................................................12
Hebella sp. .........................................................................................13
Genus Hebellopsis Hadži, 1913 ...............................................................................15
Hebellopsis scandens (Bale, 1888) ......................................................................15
Hebellopsis sibogae Billard, 1942 .......................................................................15
Family Clytiidae Cockerell, 1911 ..............................................................................16
Genus Clytia Lamouroux, 1812 ...............................................................................16
Clytia brevithecata (Thornely, 1900) .....................................................................16
Clytia elsaeoswaldae Stechow, 1914 .....................................................................17
Clytia linearis (Thornely, 1900) .........................................................................19
Clytia cf. noliformis (McCrady, 1859) ....................................................................20
Family Haleciidae Hincks, 1869 ...............................................................................21
Genus Halecium Oken, 1815 .................................................................................21
Halecium sp. .......................................................................................21
Genus Nemalecium Bouillon, 1986 ............................................................................22
Nemalecium lighti (Hargitt, 1924) .......................................................................22
Family Sertularellidae Maronna, Miranda, Peña Cantero, Barbeitos & Marques, 2016 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Genus Sertularella Gray, 1848 ................................................................................23
Sertularella affinicostata, sp. nov. .......................................................................23
Sertularella angulosa Bale, 1894 .......................................................................26
Sertularella areyi Nutting, 1904 ........................................................................27
Family Sertulariidae Lamouroux, 1812 .........................................................................28
Genus Disertasia Neppi, 1917 ................................................................................28
Disertasia crisioides (Lamouroux, 1824), comb. nov. ........................................................28
Disertasia disticha (Bosc, 1802), comb. nov. ..............................................................30
Genus Pasya Stechow, 1922 ............................................................................31
Pasya heterodonta (Jarvis, 1922), comb. nov. ..............................................................31
Genus Salacia Lamouroux, 1816 ..............................................................................32
Salacia tetracythara Lamouroux, 1816 ...................................................................32
Genus Tridentata Stechow, 1920 ..............................................................................33
Tridentata loculosa (Busk, 1852) .......................................................................33
Tridentata orthogonalis (Gibbons & Ryland, 1989), comb. nov. ...............................................33
Tridentata rugosissima (Thornely, 1904) .................................................................35
Tridentata turbinata (Lamouroux, 1816) .................................................................36
Family Symplectoscyphidae Maronna, Miranda, Peña Cantero, Barbeitos & Marques, 2016 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
CALDER & FAUCCI
4 · Zootaxa 5085 (1) © 2021 Magnolia Press
Genus Bicaularia Song, Lyu, Ruthensteiner, Wang & Gravili, 2019 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Bicaularia tongensis (Stechow, 1919b) ...................................................................36
Family Plumulariidae McCrady, 1859 ..........................................................................37
Genus Monotheca Nutting, 1900 ..............................................................................37
Monotheca flexuosa (Bale, 1894) .......................................................................37
Monotheca gibbosa, sp. nov. ..........................................................................38
Genus Plumularia Lamarck, 1816 .............................................................................40
Plumularia floridana Nutting, 1900 .....................................................................40
Plumularia strictocarpa Pictet, 1893. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Family Kirchenpaueriidae Stechow, 1921 .......................................................................42
Genus Pycnotheca Stechow, 1919b ............................................................................42
Pycnotheca producta (Bale, 1881) ......................................................................42
Family Halopterididae Millard, 1962 ...........................................................................42
Genus Antennella Allman, 1877 ..............................................................................42
Antennella cf. secundaria (Gmelin, 1791) ................................................................42
Genus Halopteris Allman, 1877 ...............................................................................45
Halopteris alternata (Nutting, 1900) .....................................................................45
Halopteris longibrachia, nom. nov. ......................................................................45
Family Aglaopheniidae Marktanner-Turneretscher, 1890 ...........................................................46
Genus Aglaophenia Lamouroux, 1812 ..........................................................................46
Aglaophenia postdentata Billard, 1913 ...................................................................46
Aglaophenia suensonii Jäderholm, 1896. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Aglaophenia whiteleggei Bale, 1888 .....................................................................48
Genus Lytocarpia Kirchenpauer, 1872 ..........................................................................49
Lytocarpia flexuosa (Lamouroux, 1816) ..................................................................49
Lytocarpia phyteuma (Stechow, 1919b) ..................................................................51
Genus Macrorhynchia Kirchenpauer, 1872 ......................................................................52
Macrorhynchia philippina Kirchenpauer, 1872 ............................................................52
Macrorhynchia phoenicea (Busk, 1852). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Acknowledgements .........................................................................................55
References ...............................................................................................55
Abstract
Forty-two species of hydroids, excluding stylasterids, are reported in the present collection from the Northwestern
Hawaiian Islands. Of these, four are anthoathecates and 38 are leptothecates. Among the latter, Sertularella affinicostata
and Monotheca gibbosa are described as new species. The binomen Halopteris longibrachia is proposed as a new
replacement name for Plumularia polymorpha var. sibogae Billard, 1913, an invalid junior primary homonym of P.
sibogae Billard, 1911. Based largely on evidence from earlier molecular phylogenies, the genus Disertasia Neppi, 1917
is resurrected to accommodate species including Dynamena crisioides Lamouroux, 1824, Sertularia disticha Bosc, 1802,
and Sia. moluccana Pictet, 1893. Sertularella robusta Coughtrey, 1876 is an invalid junior primary homonym of Sla. gayi
var. robusta Allman, 1874a, and has been replaced here by the binomen Sla. quasiplana Trebilcock, 1928, originally
described as Sla. robusta var. quasiplana Trebilcock, 1928. Clytia hummelincki (Leloup, 1935) is referred to the synonymy
of its senior subjective synonym, C. brevithecata (Thornely, 1900). Following Reversal of Precedence provisions in
the International Code of Zoological Nomenclature to preserve prevailing usage of binomena, the familiar names Sia.
disticha Bosc, 1802 (also known as Dynamena disticha) and Lytocarpia phyteuma (Stechow, 1919b) are designated
nomena protecta and assigned precedence over their virtually unknown senior synonyms Hydra quinternana Bosc, 1797
and Aglaophenia clavicula Whitelegge, 1899, respectively, names now reduced to the status of nomena oblita. Twenty
species are reported for the first time from Hawaii [Eudendrium merulum Watson, 1985, Phialellidae (undetermined),
Hebella sp., Hebellopsis scandens (Bale, 1888), H. sibogae Billard, 1942, Clytia brevithecata, C. linearis (Thornely,
1900), C. cf. noliformis (McCrady, 1859), Halecium sp., Sla. affinicostata, Sla. angulosa Bale, 1894, Pasya heterodonta
(Jarvis, 1922), Tridentata orthogonalis (Gibbons & Ryland, 1989), Pycnotheca producta (Bale, 1881), Monotheca
gibbosa, H. longibrachia, A. postdentata Billard, 1913, A. suensonii Jäderholm, 1896, A. whiteleggei Bale, 1888, and
L. flexuosa (Lamouroux, 1816)]. Sertularia orthogonalis, reported for only the third time worldwide, is assigned to
the genus Tridentata Stechow, 1920. Hydroids of the NOWRAMP 2002 collection consisted largely of presumptive
widespread species, with over 75% of them having been reported elsewhere in the tropical Indo-west Pacific region.
Key words: Anthoathecata, Hydroidolina, Leptothecata, marine invertebrates, Medusozoa, Papahānaumokuākea Marine
National Monument, taxonomy, tropical Indo-west Pacific region, zoological nomenclature
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 5
Introduction
Located in the central Pacific, the oceanic islands of Hawaii are remote from all continents. Far to the west is the
so-called Coral Triangle of the tropical Indo-west Pacific, a region of unequalled marine species biodiversity (San-
ciangco et al. 2013) encompassing the Philippines, eastern Indonesia, Papua New Guinea, the Solomon Islands, and
East Timor (Veron et al. 2009). The biota of the isolated Hawaiian archipelago, by comparison, is much less diverse.
Amongst zooxanthellate corals, Veron et al. reported multiple times fewer species from the main Hawaiian Islands
(62) and the Northwestern Hawaiian Islands (47) than from locations such as the Celebes Sea (545), the Sulu Sea
(540), the southeast Philippines (533) and the north Philippines (510). A biogeographic parallel occurs in the Atlan-
tic, with the marine biota of isolated and subtropical Bermuda representing an attenuated outpost of a much richer
tropical one in the Caribbean Sea (Calder 1993). However, distant oceanic islands in both cases have been populated
over centuries by invasive species that crossed significant biogeographic barriers, likely in large part via rafting and
shipping. Nevertheless, only a fraction of those species inhabiting a centre of diversity are ever transported to and
successfully colonize such distant and physically dissimilar new territories. Even for those that survive long-range
transport to remote islands, environmental conditions there must be suitable for them to survive and become estab-
lished. In short, the Hawaiian archipelago neither duplicates the habitat diversity and size, nor the optimal physical
environment, of the Coral Triangle region, and its reduced species richness is axiomatic.
While hydroid species numbers are known to be much greater in the Coral Triangle than in Hawaii, with several
hundred recorded there to date (e.g., Billard 1913, 1925b; Hargitt 1924; Nutting 1927; Vervoort 1993; Schuchert
2003; Di Camillo et al. 2008; Galea 2016), the Hawaiian fauna is nevertheless moderately diverse. Some 117 spe-
cies, including those identified here, have been reported thus far from the archipelago. The first major inventory
of hydroids from the Hawaiian Islands was undertaken by Nutting (1905) after examination of a collection from
a cruise of the United States Bureau of Fisheries steamer Albatross in 1902. In it, he identified 49 species, mostly
from relatively deep waters, with 29 described as new. Before Nutting, Allman (1888) had described two species
from Oahu in collections from HMS Challenger, and Hartlaub (1901) had reported one from Laysan Island. Later,
surveys for invasive species (Coles et al. 1999a, b, 2002a, b, 2004, 2006, 2009; DeFelice et al. 2002; Menza &
Monaco 2009; See et al. 2009; Carlton & Eldredge 2009, 2015), and accounts of hydroids predominantly from in-
shore locations (Cooke 1977; Calder 2010, 2020), added dozens more species to the faunal list of the islands. Other
information exists in various reports on one or a few hydrozoans from the state (see Calder 2010: 5).
The hydroids of geographically isolated Hawaii consist largely of widespread species. Overall, affinities of the
fauna are closer to species assemblages of the Indo-west Pacific than with those of the west coast of the Americas,
as with most other groups of marine invertebrates in the state (Kay & Palumbi 1987). Meanwhile, previous reports
of hydroids from the Northwestern Hawaiian Islands are limited in number. Most such records are based on the work
of Nutting (1905) and more recently on studies of invasive species (DeFelice et al. 2002; Godwin et al. 2006; Menza
& Monaco 2009; See et al. 2009).
The objective of this study was to investigate hydroids collected during the NOWRAMP 2002 cruise to the
Northwestern Hawaiian Islands, contained within the Papahānaumokuākea Marine National Monument. The report
complements two earlier papers (Calder 2010, 2020) on hydroids of Hawaii, largely comprising species inhabiting
the main islands.
Materials and methods
Materials examined here were collected using SCUBA by one of us (AF) during the 2002 NOWRAMP (Northwest-
ern Hawaiian Islands Reef Assessment and Monitoring Program) cruise, aboard R/V Rapture, to the Northwestern
Hawaiian Islands (Fig. 1). Hydroids were present in collections from eight of the locations surveyed during the
cruise, with the maximum depth sampled at each location in parentheses: Nihoa (23 m), French Frigate Shoals (25
m), Gardner Pinnacles (17 m), Laysan Island (16 m), Lisianski Island (22 m), Pearl & Hermes Atoll (26 m), Mid-
way Atoll (19 m), and Kure Atoll (23 m). Initially preserved in formalin, these materials are now in 70% ethanol.
Voucher specimens have been deposited in collections at the Bernice Pauahi Bishop Museum, Honolulu, and the
Royal Ontario Museum, Toronto.
Accounts of each species include a synonymy list, information on type locality, data on examined material, re-
CALDER & FAUCCI
6 · Zootaxa 5085 (1) © 2021 Magnolia Press
marks on taxonomy and nomenclature, and a summary of distribution records. Synonymy lists are limited to a cita-
tion of the publication in which a given species name was first made nomenclaturally available, to works providing
original records of particular species in Hawaii, and to publications providing significant information on introduced
and cryptogenic marine species of hydroids from the state. In a Reported Distribution section, only original records
of a species from the Hawaiian archipelago are included. As well, a broad overview of records from other loca-
tions worldwide is provided. Line drawings were prepared with Koh-I-Noor Rapidograph pens and ink from pencil
sketches made using a camera lucida. Photomicrographs were taken using a Zeiss Axioscop microscope. Illustra-
tions of nematocysts, all to the same magnification, are from photomicrographs originally taken at ×1000.
FIGURE 1. Map of the Northwestern Hawaiian Islands, with island names in both English and Hawaiian. Figure courtesy of
Kaji Fujii, National Oceanographic and Atmospheric Administration.
Abbreviations used in this work refer to the following:
BPBM Bernice Pauahi Bishop Museum (Honolulu, HI, USA)
ICZN International Commission on Zoological Nomenclature; International Code of Zoological Nomen-
clature. Fourth Edition (International Commission on Zoological Nomenclature 1999)
NOWRAMP Northwestern Hawaiian Islands Reef Assessment and Monitoring Program
ROMIZ Royal Ontario Museum (Toronto, ON, Canada), Invertebrate Zoology collections
WoRMS World Register of Marine Species (http://www.marinespecies.org, with content on Hydrozoa from
the World Hydrozoa Database by Peter Schuchert (http://www.marinespecies.org/hydrozoa)
Systematic Account
Phylum Cnidaria Verrill, 1865
Subphylum Medusozoa Petersen, 1979
Class Hydrozoa Owen, 1843
Subclass Hydroidolina Collins, 2000
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 7
Order Anthoathecata Cornelius, 1992
Clade Capitata Kühn, 1913, sensu stricto
Family Pennariidae McCrady, 1859
Genus Pennaria Goldfuss, 1820
Pennaria disticha Goldfuss, 1820
Fig. 2a
Pennaria disticha Goldfuss, 1820: 89.—Hoover, 1998: 20, unnumbered figure; 2006: 20, unnumbered figure.—Coles et al.,
2002a: 318, 343; 2002b: 21, 25, 32; 2004: 22, 73; 2006: 489, 492, 494; 2009: 59, 69, 76, 82.—DeFelice et al., 2001: 15,
two unnumbered photographs; 2002: 25, 50.—Godwin et al. 2006: 27.—See et al., 2009: 276, 281.—Calder, 2010: 63, fig.
43.—Miglietta et al., 2015: 5; 2019: 86, 87.
Pennaria sp.—Edmondson, 1933: 23, figs 11, 12a; 1946: 24, figs 12, 13a.
Corydendrium splendidum Boone, 1938: 33, pl. 4.
Pennaria tiarella.—Edmondson & Ingram, 1939: 256.—Chu & Cutress, 1954: 9.—Josephson, 1961: 565.—Pardy & Lenhoff,
1968: 197, figs 1–3.—Banner, 1968: 21.—Mariscal & Lenhoff, 1969: 330.—Rees et al., 1970: 309, figs 1, 2.—Reed, 1971:
48.—Pardy, 1971: 84, figs 1–3.—Rees, 1971: 119, figs 1, 2.—Long, 1974: 27.
Halocordyle disticha.—Cooke, 1977: 80, fig. 8.—Coles et al., 1999a: 194, 205, 209; 1999b: 150.
Pennaria distachia.—Menza & Monaco, 2009: 1 [incorrect subsequent spelling].
Type locality. Italy: Gulf of Naples (see Calder 2013: 7).
Voucher material. Pearl & Hermes Atoll, 19.ix.2002, one colony fragment, 6 mm high, with a medusa bud,
coll. A. Faucci, ROMIZ B5404.—French Frigate Shoals, 11.ix.2002, four colonies or colony fragments, to 10 cm
high, with medusa buds, coll. A. Faucci, ROMIZ B5488.
Remarks. Pennaria disticha Goldfuss, 1820 has been reported numerous times from shallow tropical and tem-
perate waters worldwide, although cryptic species seem certain to exist under the name (Miglietta et al. 2015, 2019).
A taxonomic overview of the species in the Hawaiian Islands has been given earlier (Calder 2010).
The earliest record of P. disticha from Hawaii is based on Boone (1938, as Corydendrium splendidum), whose
material was collected in Kaneohe Bay during 1928. It is now the most frequently reported hydroid species across
the Hawaiian archipelago. DeFelice et al. (2001) noted that P. disticha is common as a fouling organism in har-
bours of the main islands, as well as in cracks, crevices, and protected areas of reefs. In the Northwestern Hawaiian
Islands, it has been reported to date from Necker Island, French Frigate Shoals, Gardner Pinnacles, Maro Reef,
Laysan Island, Lisianski Island, Pearl & Hermes Reef, Midway Atoll, and Kure Atoll (See et al. 2009). A record of
its occurrence at Midway Atoll (Carlton & Eldredge 2009), based on DeFelice et al. (1998), could not be confirmed,
although it has been reported from there by Godwin et al. (2006) and See et al. (2009).
Contemporary taxonomic accounts of Pennaria disticha are given in works by Calder (1988a, as Halocordyle
disticha, 2010, 2013, 2019) and Schuchert (2006). DeFelice et al. (2001) reported that hydroid populations of the
species in Hawaii are capable of inflicting a mild sting.
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay (Edmondson 1933, 1935, as Pennaria
tiarella; Boone 1938, as Corydendrium splendidum; Edmondson & Ingram 1939, as “probably Pennaria tiarella”;
Josephson 1961, as P. tiarella; Banner 1968, as P. tiarella; Pardy & Lenhoff 1968, as P. tiarella; Mariscal & Lenhoff
1969, as P. tiarella; Rees et al. 1970, as P. tiarella; Pardy 1971, as P. tiarella; Rees 1971, as P. tiarella; Reed 1971,
as P. tiarella; Coles et al. 2002a; Calder 2010; Miglietta et al. 2015, 2019); Pearl Harbor (Edmondson 1933, as Pen-
naria sp.; Long 1974, as P. tiarella; Cooke 1977, as Halocordyle disticha; Hoover 1998, 2006; Coles et al. 1999b, as
H. disticha; Coles et al. 2009; Calder 2010; Miglietta et al. 2015, 2019); Ala Wai Harbor (Cooke 1977, as H. disti-
cha; Coles et al. 1999a, as H. disticha; Calder 2010); Kewalo Basin (Cooke 1977, as H. disticha; Coles et al. 1999a,
as H. disticha; Calder 2010; Miglietta et al. 2015, 2019); Honolulu Harbor (Cooke 1977, as H. disticha; Coles et al.
1999a, as H. disticha, 2009; Calder 2010); Lanai Lookout (Hoover 1998, 2006); Pearl Harbor (Coles et al. 1999b;
Calder 2010; Miglietta et al. 2019); Waikiki (Coles et al. 2002b); Maunalua Bay (Coles et al. 2002b); Kuapâ Pond
(Coles et al. 2002b); Keehi Lagoon/Marina (Coles 2009; Miglietta et al. 2015, 2019); Haleiwa (Miglietta et al.
2015, 2019).—French Frigate Shoals (DeFelice et al. 2002; Godwin et al. 2006; See et al. 2009).—Kauai: Nawili-
CALDER & FAUCCI
8 · Zootaxa 5085 (1) © 2021 Magnolia Press
wili Harbor Pier 2 (Coles et al. 2004); Marriott Hotel Reef (Coles et al. 2004, 2006); Port Allen Harbor Main Pier
(Coles et al. 2004); Port Allen Reef (Coles et al. 2004); Port Allen Harbor (Coles et al. 2006); Hoai Bay (Coles et
al. 2006).—Molokai: Hale O Lono Harbor Dock (Coles et al. 2004); Kaunakakai Dock (Coles et al. 2004).—Maui:
Kahului Harbor Pier 1 (Coles et al. 2004); Kahului Harbor Pier 2 (Coles et al. 2004); Maalaea Small Boat Harbor
(Coles et al. 2004); Mala Wharf (Coles et al. 2006); Maui (Miglietta et al. 2015, 2019).—Island of Hawaii: Kawai-
hae Reef (Coles et al. 2004, 2006); Kawaihae Harbor Main Pier (Coles et al. 2004); Hilo Harbor Pier 1 (Coles et al.
2004).—All of the main islands (DeFelice et al. 2001; Carlton & Eldredge 2009).—Laysan Island (Godwin et al.
2006; See et al. 2009).—Lisianski Island (Godwin et al. 2006; See et al. 2009; Calder 2010; Miglietta et al. 2015,
2019).—Pearl & Hermes Atoll (Godwin et al. 2006; See et al. 2009; Calder 2010; Miglietta et al. 2015, 2019).—
Kure Atoll (Godwin et al. 2006; See et al. 2009).—Midway Atoll (Godwin et al. 2006; See et al. 2009).—Necker
Island (See et al. 2009).—Gardner Pinnacles (See et al. 2009).—Maro Reef (See et al. 2009).—Northwestern Ha-
waiian Islands (Menza & Monaco 2009, as Pennaria distachia).
Elsewhere. Considered circumglobal in tropical and warm-temperate waters (Calder 2010), although cryptic
species likely exist (Miglietta et al. 2015, 2019).
FIGURE 2. Pennariidae, Oceaniidae, Eudendriidae, and Phialellidae. a, Pennaria disticha Goldfuss, 1820, hydranth with
a medusa bud and part of pedicel, Pearl & Hermes Atoll, ROMIZ B5404. Scale equals 0.2 mm. b, Turritopsis sp., hydrocaulus
with two hydranths, Midway Atoll, ROMIZ B5490. Scale equals 0.2 mm. c, Eudendrium merulum Watson, 1985, hydranth
and part of pedicel, Nihoa, ROMIZ B5405. Scale equals 0.1 mm. d, Eudendrium merulum Watson, 1985, hydrocaulus and
proximal ends of three branches, Nihoa, ROMIZ B5405. Scale equals 0.2 mm. e, Eudendrium merulum Watson, 1985, female
gonophores, Nihoa Island, ROMIZ B5405. Scale equals 0.1 mm. f. Phialellidae (undetermined), three hydrothecae, Gardner
Pinnacles, ROMIZ B5406. Scales equal 0.05 mm.
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 9
Family Sphaerocorynidae Prévot, 1959
Genus Sphaerocoryne Pictet, 1893
Sphaerocoryne bedoti Pictet, 1893
Sphaerocoryne bedoti Pictet, 1893: 10, pl. 1 figs 5, 6.—Calder, 2010: 67, figs 44, 45.
Type locality. Indonesia: Moluccas, Ambon (Pictet 1893).
Voucher material. Midway Atoll, on coral rubble, 20.ix.2002, one colony, up to 6 mm high, without medusa
buds, coll. A. Faucci, ROMIZ B3830.
Remarks. A hydroid identified as Sphaerocoryne bedoti was described and illustrated earlier from the Ha-
waiian archipelago (Calder 2010), based in part on a specimen from Midway Atoll examined again here (ROMIZ
B3830). Recent comments on the species exist in that account, in Schuchert (2010), and in Maggioni et al. (2021).
Of particular interest in the work of Maggioni et al. is discovery of species with hydroids much like those of S.
bedoti, including Kudacoryne diaphana Maggioni, in Maggioni et al., 2021 from the Red Sea, Saudi Arabia, and
Maldives, Euphysilla pyramidata Kramp, 1955, an essentially circumglobal species, and Euphysilla sp. from the
Caribbean Sea (Martinique and Panama). They noted that hydroids of S. bedoti were distinguishable in colouration
(hypostome white or yellowish, with a bright red band below it; gastric cavity with broadest part transparent or yel-
lowish, and whitish below) and in having medusa buds in large clusters. Also similar is the hydroid currently known
as Sphaerocoryne agassizii (McCrady, 1859), although it is distinguished by medusa buds with only two opposite,
prominently capitate tentacles.
Reported Distribution. Hawaiian archipelago. Midway Atoll (Calder 2010).
Elsewhere. Considered circumglobal in tropical and warm temperate waters (Calder 2010; Schuchert 2010).
Family Oceaniidae Eschscholtz, 1829
Genus Turritopsis McCrady, 1857
Turritopsis sp.
Fig. 2b
Turritopsis nutricula.—Cooke, 1977: 82, fig. 10.—Grovhoug & Rastetter, 1980: 252.—Coles et al., 2002a: 206, 31, 343.—
Carlton & Eldredge, 2009: 33.
Turritopsis cf. nutricula.—Calder, 2010: 16, fig. 6.
Voucher material. Midway Atoll, on calcareous rubble, 23.ix.2002, one colony, 1.75 mm high, without gono-
phores, coll. A. Faucci, ROMIZ B5490.
Remarks. While species of the genus Turritopsis McCrady, 1857 from Hawaii and elsewhere across the Indo-
Pacific region have earlier been commonly assigned to T. nutricula McCrady, 1857 (e.g., Kramp 1968; Millard &
Bouillon 1973, 1974; Millard 1975; Cooke 1977; Hirohito 1988; Park 1993; Bouillon 1995; Schuchert 1996; Wat-
son 1996; Kubota 2005; Calder 2010), molecular investigations contradict that identification. Such studies reveal
the existence of a species complex in T. nutricula (Miglietta et al. 2007, 2019; Miglietta & Lessios 2009). Instead
of being cosmopolitan in distribution, Miglietta et al. (2007) suggested that T. nutricula may be restricted to the
western Atlantic Ocean. Little progress has yet been made in resolving the nomenclature of cryptic species within
hydroids assigned to the species. As noted by Schuchert (2003), a likely valid species in the tropical Indo-west
Pacific region is T. chevalense (Thornely, 1904), but others are of probable existence as well. For now, the sterile
hydroid colony examined here is identified simply as Turritopsis sp.
Molecular phylogenetic studies also indicate that the family Oceaniidae Eschscholtz, 1829, as presently con-
stituted, is polyphyletic (Prudkovsky et al. 2016; Schuchert 2016; Maggioni et al. 2017). Nevertheless, the type
species of Turritopsis (T. nutricula) and that of Oceania Kölliker, 1853 (O. armata Kölliker, 1853), the type genus
of the family, cluster in close proximity to each other (Prudkovsky et al. 2016; Schuchert 2016). Relationships of
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two other genera usually included in the family, Rhizogeton L. Agassiz, 1862 and Turritopsoides Calder, 1988b,
appear to lie elsewhere. Species assigned to those genera, R. nudus Broch, 1910 and T. marhei Maggioni, Puce,
Galli, Seveso & Montano, 2017, occur in clades remote from O. armata (Prudkovsky et al. 2016; Maggioni et al.
2017). Although substantial data gaps still exist in molecular assessments of the family, Turritopsis can confidently
be included, with Oceania, in Oceaniidae.
Reported Distribution. Hawaiian archipelago. Oahu: Ala Wai Yacht Harbor, on stems of Pennaria (Cooke
1977, as Turritopsis nutricula).—Pearl Harbor, on test panels (Grovhoug & Rastetter 1980, as T. nutricula).—
Kaneohe Bay, on test panels (Grovhoug & Rastetter 1980, as T. nutricula).—Kaneohe Bay from BPBM-D-457
(“Kaneohe Bay”), Coconut Island, Hawaii Institute of Marine Biology Pier, Kaneohe Yacht Club dock, MCB Fuel
Dock, and SAG Harbor (Coles et al. 2002a, as T. nutricula).—Kaneohe Bay at Kaneohe Yacht Club dock, and Co-
conut Island and reef, shallow (Calder 2010, as T. cf. nutricula).
Elsewhere. The relationships and geographic distribution of the hydroid assigned to Turritopsis from Hawaii
needs to be established by barcoding studies.
Family Eudendriidae L. Agassiz, 1862
Genus Eudendrium Ehrenberg, 1834
Eudendrium merulum Watson, 1985
Figs 2c–e, 3
Eudendrium merulum Watson, 1985: 200, figs 53–58.
Type locality. Australia: Victoria, Bass Strait, 0.5 km S of Clonmel Island, 38°45’S, 146°43’E, from wreck of
streamer Blackbird, 6 m (Watson 1985).
Voucher material. Nihoa, 06.x.2002, three branched colonies or colony fragments, to 8 mm high, one with female
gonophores, coll. A. Faucci, ROMIZ B5405.—Kure Atoll, on algae and calcareous rubble, 25.ix.2002, two mostly
stolonal colonies, to 5 mm high, without gonophores, coll. A. Faucci, ROMIZ B5476.
Cnidome. Microbasic euryteles, small (Fig. 3a), (n=10): 6.4–7.0 µm long × 2.4–2.7 µm wide (undischarged)
Microbasic euryteles, large (Fig. 3b, c), (n=6): 19.0–20.8 µm long × 10.0–11.3 µm wide (undischarged)
Remarks. Approximately 80 species are currently recognized worldwide in the genus Eudendrium Ehrenberg,
1834. Hydroids of the group are easily distinguished in having monopodial growth, perisarc reaching to a groove at
the base of relatively large, naked, urn-shaped hydranths, a typically flared or knob-shaped hypostome, and solid,
filiform tentacles arranged more or less in a single whorl. Their gonophores are also distinctive, arising in a whorl
around bases of the hydranths. Those of the male usually comprise a linear series of oval to nearly round chambers,
while those of the female initially possess a spadix curving over a single ovum.
While hydroids of Eudendrium are distinctive, identification of species assigned to the genus can be particularly
troublesome. Within the last few decades, the nematocyst complement and morphology of the gonophores, particu-
larly those of the female, have been emphasized as characters of particular value in the morphological distinction of
species.
In terms of the cnidome, all known species of Eudendrium have small microbasic euryteles. Most, but not all,
of the others also have additional “complementary nematocysts”. While these often comprise nematocysts of an
entirely different category, they may simply be microbasic euryteles of a noticeably larger size. The locations of
the complementary nematocysts, and the shapes that aggregations of them sometimes create, are also of taxonomic
value.
Complementary nematocysts in hydroids examined here consisted solely of large microbasic euryteles (Fig.
3a–c). On hydranths, these were scattered around the base above the perisarc groove and around the rim of the hy-
postome. In this overall character, they align with some 20 of the known species of the genus (Calder 2017: 34–36),
and they conform with a so-called “Eudendrium ramosum (Linnaeus, 1758) group”.
Colonies from the present collection were small (up to 8 mm high) and stolonal to alternately branched. One
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 11
of the specimens nevertheless had female gonophores, indicative of a species having small colonies. Developing
female gonophores, with unbranched spadices, were observed on a nearly atrophied hydranth. Fully mature gono-
phores were present on a blastostyle, lacking tentacles and with expanded and wrinkled pedicel perisarc (Fig. 2e).
The perisarc of the hydrocaulus and branches was smooth, except for a few annulations basally and with occasional
irregular ones elsewhere. Although hydranths were mostly in poor condition, the best ones bore a single whorl of
about 20–23 tentacles.
FIGURE 3. Eudendriidae. Eudendrium merulum Watson, 1985, nematocysts, material from Nihoa, ROMIZ B5405. a, mi-
crobasic eurytele, small, undischarged. b, microbasic eurytele, large, undischarged. c, microbasic eurytele, large, discharged.
The characters of these hydroids, together with the presence of large euryteles as complementary nematocysts,
most closely resemble E. merulum Watson, 1985. While the trophosomes also resemble those of E. generale von
Lendenfeld, 1885, female gonophores occur on atrophied rather than fully developed hydranths, as in that species
(Watson 1985). In addition, complementary euryteles tend to be larger and their shafts are spinier in material ex-
amined here. Also similar in morphology are hydroids of E. pusillum var. amoyicum Hargitt, 1927 [=E. generale
amoyicum], and E. kirkpatricki Watson, 1985. Colonies of the first of these species appear to be more profusely
branched (Ling 1938; Xu et al. 2014a), while complementary nematocysts of the second are larger and possess a
longer, less spiny shaft (Watson 1985). Hydroids from Fiji having a similar colony form were identified as Euden-
drium sp. by Gibbons & Ryland (1989). Finally, stolonal colonies of this hydroid resemble E. breve Fraser, 1938a,
but the complementary microbasic euryteles were much larger than even the largest of those reported in that species
(13.0–14.6 × 5.8–6.8 µm) (Calder et al. 2021). While specimens from this collection have been assigned here to E.
merulum, DNA analyses are needed to sort out the taxonomy of this and related species (Schuchert 2008).
Hydroids of E. merulum may be restricted to the Pacific Ocean. Schuchert (2008) found that hydroids identified
as this species from the eastern Atlantic Ocean, Mediterranean Sea, and Black Sea all represented distinct genetic
lineages, and that they likely differ from the Australian population.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Australia (Watson 1985); Yemen (Marques et al. 2000). As noted above, records of the species from
the eastern Atlantic and adjacent seas are likely erroneous (Schuchert 2008).
Order Leptothecata Cornelius, 1992
Family Phialellidae Russell, 1953
Phialellidae (undetermined)
Fig. 2f
Voucher material. Gardner Pinnacles, on Halopteris longibrachia, nom. nov., 14.ix.2002, one colony, 0.35 mm
high, without gonothecae, coll. A. Faucci, ROMIZ B5406.
Remarks. The single, sterile, stolonal colony examined here occurred as a tiny epizoite on the hydroid Halop-
teris longibrachia, nom. nov. Although referable to the family Phialellidae Russell, 1953, and likely to either Oper-
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12 · Zootaxa 5085 (1) © 2021 Magnolia Press
cularella Hincks, 1869 or Phialella Browne, 1902, neither the specific nor generic identity of the hydroid could
be categorically established. Given a paucity of species-specific characters, and in the absence of gonophores,
distinguishing hydroids of these two genera is difficult. The specimen from Gardner Pinnacles has therefore been
identified here simply as Phialellidae (undetermined).
The trophosome of this hydroid resembles those of species such as ?Phialella quadrata (Forbes, 1848) from the
Seychelles (Millard & Bouillon 1973) and Opercularella sp. from the coast of Ecuador (Calder et al. 2021). Some
10 species are currently assigned to Phialella in WoRMS (Schuchert 2021b). Distinguished by characters of the me-
dusa stage, their trophosomes are likely all much alike. Notably, hydroids assigned to three species of Phialella from
California were found to be essentially indistinguishable (Boero 1987), and Watson (1994b) reported that colonies
of P. quadrata and P. fragilis (Uchida, 1938) were identical. A hydroid tentatively assigned by Galea et al. (2014) to
P. falklandica Browne, 1902, the type species of Phialella, resembles that of Opercularella lacerata Johnston, 1847,
but it differs in having gonothecae with rounded longitudinal ridges rather than smooth to wavy walls.
Morphologically similar to P. quadrata, P. falklandica, and related species are hydroids included in Opercu-
larella, with some four species recognized in WoRMS (Schuchert 2021a). Indeed, molecular data in Maronna et al.
(2016) indicate that P. quadrata is genetically close to Campanularia lacerata, the type species of Opercularella.
Even closer to P. quadrata in their phylogram is Opercularella pumila S.F. Clark, 1875, misassigned to Cam-
panulina Van Beneden, 1847 in that work and certain others (e.g., Cornelius 1995; Bouillon et al. 2006; Schuchert
2021a).
As presently defined, hydroids assigned to Opercularella are said to have fixed gonophores while those referred
to Phialella liberate a medusa (Cornelius 1995; Bouillon et al. 2006). Should the two genera prove to be identical,
the name Opercularella would have nomenclatural priority.
Reported Distribution. Hawaiian archipelago. First record.
Family Hebellidae Fraser, 1912
Genus Hebella Allman, 1888
Hebella furax Millard, 1957
Fig. 4a
Hebella furax Millard, 1957: 200, fig. 8A–C.
Anthohebella parasitica.—Coles et al., 2002a: 34, 318, 344; 2002b: 21, 25, 177 [not Lafoea parasitica Ciamician, 1880].
Hebella sp.—Calder, 2020: 205, fig. 1c.
Type locality. South Africa: False Bay, off Swartklip, 34°5.5ʹS, 18°39ʹE, 15–18 m (Millard 1957).
Voucher material. Midway Atoll, on Antennella secundaria, 23.ix.2002, one colony, 0.8 mm high, without
gonothecae, coll. A. Faucci, ROMIZ B5407.—Gardner Pinnacles, on Macrorhynchia phoenicea, 14.ix.2002, one
colony, 1.3 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5408.—Midway Atoll, on M. phoenicea and
Aglaophenia whiteleggei, 23.ix.2002, two colonies, to 1.0 mm high, without gonothecae, coll. A. Faucci, ROMIZ
B5409.
Remarks. These hydroids closely resembled Lafoea parasitica Ciamician, 1880 (type locality: Adriatic Sea),
Hebella dyssymetra Billard, 1933 (type locality: Gulf of Suez), and H. furax Millard, 1957 (type locality: South
Africa). All three species have been reported from warm-waters of the Pacific Ocean. Vervoort & Vasseur (1977)
noted that there was little to separate H. dyssymetra and H. furax, but both were upheld pending examination of
additional material. With trophosomes that are all much alike, these species are most reliably distinguished by
their gonosomes. Those of L. parasitica release “swimming gonophores” with gonads on the manubrium, those of
H. dyssymetra liberate medusoids with gonads on radial canals, and those of H. furax release immature medusae
(Boero et al. 1997). Based on the character of its gonophores, L. parasitica was referred by them to new genus,
Anthohebella Boero, Bouillon & Kubota, 1997.
During identification of material examined here, H. dyssymetra was dismissed because hydrothecae were not
markedly bent (Hirohito 1995), and hydrothecal pedicels were distinctly developed rather than being indistinct
(Boero et al. 1997). Unlike H. furax, with occasional colonies said to be parasitic, all colonies in the collection
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 13
were epizoites on plumularioid hydroids. Nevertheless, hydroids of the species are predominantly free-living, and
Boero et al. (1997) suspected that records of Anthohebella parasitica in the Pacific were based instead on H. furax.
Following their assumption, and considering the type locality and center of distribution of A. parasitica, specimens
from Midway Atoll and Gardner Pinnacles have been assigned to H. furax. Hydroids identified as Hebella sp. from
Hawaii by Calder (2020) are here considered conspecific.
The taxonomy of the family Hebellidae Fraser, 1912, and current concepts of genera assigned to it, remain
unsettled. For example, life cycle studies (Migotto & de Andrade 2000) reveal that the adult medusa of H. furax
shares characters with Toxorchis kellneri Mayer, 1910 [=Staurodiscus kellneri] (formerly in family Laodiceidae L.
Agassiz, 1862). Peña Cantero et al. (2010) pointed to an affinity between Anthohebella parasitica and Stegopoma
plicatile (M. Sars, 1863) (family Tiarannidae Russell, 1940). Marques et al. (2006) suggested that Hebella Allman,
1888 (type species: Hebella striata Allman, 1888) and Anthohebella (type species: Lafoea parasitica Ciamician,
1880) were either sister groups or congeneric. Investigations by Moura et al. (2012) and Maronna et al. (2016) in-
dicate that A. parasitica is close genetically to Hebella venusta (Allman, 1877). Their studies also establish that the
family Hebellidae as presently constituted is polyphyletic and in need of revision.
DNA barcoding of H. striata will be needed to better resolve the taxonomy of the genus Hebella, the family
based on it, and affinities of species assigned to it. A detailed morphological account of the species has been given
by Vervoort (1972). Also called for is a molecular analysis of Campanularia mutabilis Ritchie, 1907, type species
of Scandia Fraser, 1912, to establish its systematic relation with Hebella.
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay, Moku Manu Island (Coles et al. 2002a,
as Anthohebella parasitica; Calder 2020, as Hebella sp.); Waikiki, Ala Wai buoy (Coles et al. 2002b, as A. para-
sitica).
Elsewhere. ?Japan (Stechow 1913b, as Hebella parasitica; Hirohito 1995, as H. parasitica); ?Indochina (Daw-
ydoff 1952, as H. parasitica); South Africa (Millard 1957, and others); Seychelles (Millard & Bouillon 1973; Boero
et al. 1997); Australia (Watson 1975); Moorea, French Polynesia (Vervoort & Vasseur 1977, as H. parasitica);
Mediterranean Sea (Garcia Corrales et al. 1979, and others); Papua New Guinea (Boero et al. 1997); Indonesia (Di
Camillo et al. 2008); Brazil (Migotto and de Andrade 2000; Oliveira et al. 2016, and others); Maldives (Gravier-
Bonnet & Bourmaud 2012); St. Helena (Galea 2015).
Hebella sp.
Fig. 4b
Voucher material. Midway Atoll, on a hydroid stem, 23 ix.2002, one colony, with two hydrothecae, 1.3 mm high,
without gonothecae, ROMIZ B5493.
Remarks. This hydroid could not confidently be assigned to any known species of the family Hebellidae
Fraser, 1912. Its characters are closest to those of the hebellid genera Hebella Allman, 1888 (type species: Hebella
striata Allman, 1888) and Anthohebella Boero, Bouillon & Kubota, 1997 (type species: Lafoea parasitica Ciami-
cian, 1880), purportedly distinguished by the morphology of their liberated gonophores. Although gonophores of H.
striata are certainly medusoids or medusae (Hartlaub 1905), their anatomy after liberation has yet to be described.
Thus, the molecular phylogenetic relationship of H. striata and H. parasitica needs study to determine whether the
two nominal genera they nomenclaturally typify are indeed distinct. The species examined here has therefore been
provisionally assigned to Hebella. Given the absence of gonosomes, our specimen is best not dealt with as an unde-
scribed species. It is different from a hydroid reported earlier by Calder (2020) from Oahu as Hebella sp., identified
above as Hebella furax Millard, 1957, and the species it represents is new to Hawaii.
In having a distinct, annulated pedicel, a deeply campanulate to almost cylindrical hydrotheca, hydrothecal
walls with modest transverse annulations, a strongly flaring hydrothecal rim, and a ring of thickened perisarc at the
hydrothecal base, this species most closely resembles Hebella venusta (Allman, 1877). However, it differs in hav-
ing fewer and less distinct annulations on the hydrothecal wall. Moreover, its hydrothecae are larger (ca. 1000 µm
long × 400 µm wide) than those of H. venusta as measured by Calder (1991a: to 650 µm long × 300 µm wide) and
Galea (2010: 470–545 µm long × 265–315 µm wide). In terms of biogeography, H. venusta may be endemic to the
Atlantic Ocean; records of it from the Indian Ocean (Ritchie 1910, as Lafoea venusta) and the Red Sea (Mergner &
Wedler 1977) are regarded here as questionable.
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FIGURE 4. Hebellidae. a, Hebella furax Millard, 1957, hydrotheca, Midway Atoll, ROMIZ B5407. Scale equals 0.1 mm.
b. Hebella sp., hydrotheca, pedicel, and stolon, Midway Atoll, ROMIZ B5493. Scale equals 0.2 mm. c, Hebellopsis scandens
(Bale, 1888), hydrotheca and pedicel, Pearl & Hermes Atoll, ROMIZ B5413. Scale equals 0.1 mm. d, Hebellopsis sibogae
Billard, 1942, hydrotheca and pedicel, Pearl & Hermes Atoll, ROMIZ B5410. Scales equal 0.1 mm. e, Hebellopsis sibogae
Billard, 1942, hydrotheca and pedicel, Pearl & Hermes Atoll, ROMIZ B5411. Scale equal 0.1 mm. e,
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 15
In the molecular barcoding studies of Moura et al. (2012) and Maronna et al. (2016), H. venusta and A. para-
sitica have been shown to be very close. Gonothecae of the two also appear to be morphologically similar (Boero et
al. 1997; Galea 2010), although the medusoid or medusa stage of H. venusta is unfortunately still unknown.
Reported Distribution. Hawaiian archipelago. First record.
Genus Hebellopsis Hadži, 1913
Hebellopsis scandens (Bale, 1888)
Fig. 4c
Lafoea scandens Bale, 1888: 758, pl. 13 figs 16–19.
Type locality. Australia: Port Stephens; Port Jackson (Bale 1888, as Lafoea scandens).
Voucher material. Pearl & Hermes Atoll, on Pasya heterodonta, 28.ix.2002, three colonies, to 0.5 mm high,
without gonothecae, coll. A. Faucci, ROMIZ B5413.
Remarks. Hebellopsis scandens Bale, 1888 is common as an epizoite on other hydroids, especially sertulariids
and syntheciids. In typically curving from back to front of the substrate, its long, slender, and nearly cylindrical
hydrothecae tend to be variously contorted.
Taxonomic and nomenclatural accounts of this species have been given in works including Calder (1991a),
Boero et al. (1997, as Hebella scandens), and Vervoort & Watson (2003). In having a distinct diaphragm rather
than a variably developed annular perisarcal thickening at the base of the hydrotheca, the species is assigned here to
Hebellopsis Hadži, 1913 rather than to Hebella Allman, 1888. Meanwhile, confusion over the names H. scandens
and Hebella calcarata (A. Agassiz, in L. Agassiz, 1862), as applied to this species, has been addressed in the works
by Calder (1991a) and Boero et al. (1997).
Of the putative hebellids included in the molecular study of Maronna et al. (2016), H. scandens was closest
genetically to Staurodiscus gotoi (Uchida, 1927). By contrast, it was distant from Hebella venusta (Allman, 1877)
and H. parasitica (Ciamician, 1880). Similar results had been reported earlier by Moura et al. (2012).
A juvenile medusa has been described in the life cycle of H. scandens (e.g., Altuna 1996; Boero et al. 1997),
but the identity of the adult stage is as yet unresolved. Thus, the nomenclature of this hydrozoan remains unsettled
at the rank of both species and genus.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Considered circumglobal, temperate to tropical waters: western Pacific (Xu et al. 2014b, as He-
bella scandens); central Pacific (Vervoort & Vasseur 1977, as H. scandens var. contorta; Coles et al. 2003); eastern
Pacific (Fraser 1948, as Hebella calcarata); western Atlantic (Calder 2013); eastern Atlantic (Altuna 1996, as H.
scandens); Indian Ocean (Millard 1975, as H. scandens).
Hebellopsis sibogae Billard, 1942
Fig. 4d, e
Hebellopsis sibogae Billard, 1942: 70, fig. 8.
Type locality. Indonesia: Siboga Expedition Sta. 129, Sulawesi, Karkaralong group, anchorage off Kawio and Kam-
boling, 04°40ʹ19″N, 125°24ʹ05″E (Billard 1942; van Soest 1976).
Voucher material. Pearl & Hermes Atoll, on Macrorhynchia philippina, 19.ix.2002, two hydrothecae and pedi-
cels, to 0.55 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5410.—Pearl & Hermes Atoll, on calcareous
rubble, 28.ix.2002, one colony, 0.55 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5411.—Kure Atoll,
on sponge, 25.ix.2002, one colony, 0.6 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5412.—Kure Atoll,
25.ix.2002, one colony, 1 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5482. Gardner Pinnacles, on
calcareous rubble, 14.ix.2002, one colony, 3.5 mm high, without gonophores, ROMIZ B5494.
Remarks. Hydroids examined here closely resemble those of Lafoea gigas Pieper, 1884 (type locality: Adriatic
Sea), Laomedea michaelsarsi Leloup, 1935 (type locality: Tortugas, Florida, USA), and Hebellopsis sibogae Bil-
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lard, 1942 (type locality: Indonesia). Morphological differences between the three are presently unclear. The first of
these, well-known in the Mediterranean Sea and vicinity, has been reported infrequently elsewhere (Peña Cantero
& García Carrascosa 2002; Galea 2008). The second has been reported from the western and eastern North Atlantic
(Leloup 1935; Vervoort 1959). The only record of either one in the Pacific Ocean is that of L. michaelsarsi from
Darwin Island, Galapagos Islands (Calder et al. 2003, as Hebellopsis michaelsarsi). Reports of Hebella pocillum
(Hincks, 1869) from the west coast of North America by Fraser (1937a, 1947) have occasionally been included with
question in the synonymy of L. gigas (e.g., Peña Cantero & García Carrascosa 2002, as Scandia gigas), but such
inclusion seems erroneous. The third species is known only from Indonesia, based on the original account of Billard
(1942). As for the first two, they may be conspecific (Galea 2008).
With reference to the generic assignment of these species, the well-known L. gigas has been referred at various
times to Lafoea Lamouroux, 1821, Hebella Allman, 1888, Scandia Fraser, 1912, Hebellopsis Hadži, 1913, and Cro-
atella Hadži, 1915. Its characters clearly differentiate it from Lafoea in having stolonal rather than erect colonies,
and isolated rather than aggregated gonophores. Unlike the hebellid genera Hebella, Scandia, and Anthohebella
Boero, Bouillon & Kubota, 1997, a well-developed hydrothecal diaphragm rather than a rounded annular thickening
is present at the base of the hydrotheca. This species has usually been misassigned in current literature to Scandia,
as S. gigas, but its gonosomal characters clearly differ from those of S. mutabilis (Ritchie, 1907), type species of
that genus. Female gonothecae are pumpkin-shaped (Peña Cantero & García Carrascosa 2002) to spherical (Gravili
et al. 2015) rather than sac-shaped, somewhat corrugated, and distally truncate (Fraser 1944), while those of the
male are fusiform (Peña Cantero & García Carrascosa 2002) rather than resembling hydrothecae in shape and size
(Fraser 1944). The species was assigned to Hebellopsis by Calder (2013) based on the character of its hydrothecal
diaphragm, but that too is taken here to be incorrect given its unusual gonothecae. It diverges from the putative he-
bellid genera Bedotella Stechow, 1913a in lacking nematophores and nematothecae, and from Halisiphonia Allman,
1888 in lacking laterally flattened and fan-shaped gonothecae. Hydroids of Staurodiscus Haeckel, 1879 are as yet
scarcely known.
In a molecular study by Maronna et al. (2016), “Scandia gigas” was considered a “rogue taxon” and included
as “Leptothecata incertae sedis” because of its unexpected and isolated placement in phylograms. Excluded from
Hebellidae in their analyses, it has been provisionally retained in the family here pending further study. In appearing
to be genetically remote from other known hebellids, however, and in having what appear to be morphologically
distinctive gonophores, we conclude that the species should be assigned at least to a different genus. It is therefore
returned here to Croatella, a taxon originally based primarily on L. gigas but also provisionally including Campanu-
laria corrugata Thornely, 1904 (Hadži 1915: 78). Hadži distinguished the genus largely by the morphology of its
diaphragm, which was said to be two-layered with a peripheral cleft.
Given all this, specimens from the Northwestern Hawaiian Islands have been assigned, largely on zoogeo-
graphic grounds, to the western tropical Pacific hydroid H. sibogae. This is only the second collection record of
the species. With no information yet available on either the gonosome or the molecular phylogeny of the species,
however, it is kept here in Hebellopsis rather than being assigned to Croatella. The holotype (Van Soest 1976), on
an alga (Billard 1942), is now at the Naturalis Biodiversity Center, Leiden, the Netherlands (ZMA.COEL.5224).
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Indonesia (Billard 1942).
Family Clytiidae Cockerell, 1911
Genus Clytia Lamouroux, 1812
Clytia brevithecata (Thornely, 1900)
Fig. 5a
Campanularia brevithecata Thornely, 1900: 454, pl. 44 figs 8, 8a, b.
Type locality. Papua New Guinea: New Britain, Blanche Bay (Thornely 1900, as Campanularia brevithecata).
Voucher material. Nihoa, on calcareous rubble, 06.x.2002, one colony, 1.25 mm high, without gonothecae,
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 17
coll. A. Faucci, ROMIZ B5414.—Pearl & Hermes Atoll, on Halimeda sp., 19.ix.2002, one colony, 3 mm high,
without gonothecae, ROMIZ B5480.
Remarks. The hydroid of Clytia brevithecata (Thornely, 1900), type locality Papua New Guinea, appears
indistinguishable morphologically from that of Clytia hummelincki (Leloup, 1935), type locality Bonaire, in the
Caribbean Sea. Both have very shallow, cup-shaped hydrothecae with an entire margin, a subhydrothecal spherule,
and unbranched pedicels with annulations at the base and occasionally elsewhere. Their gonothecae also seem in-
distinguishable. Connections between Indo-Pacific and Atlantic populations appear to exist, given Millard’s (1966a,
1975) record of C. hummelincki from Agulhas Bank at the southern tip of Africa. Based on morphology, the two are
taken here to be conspecific, with the name C. brevithecata having nomenclatural priority. Galea & Ferry (2015:
241) had suggested earlier that the two might be conspecific. Confirmation of their synonymy through DNA studies
of topotypic material of the two would be germane. Of note already, however, hydroids identified as C. hummelincki
from South Africa, Italy, and Belize are genetically close (Cunha et al. 2017). Synonyms or not, the name of the
Pacific species has been adopted for the specimen recorded here from Nihoa.
Hydroids identified as C. hummelincki have been shown to be genetically distant from certain other species as-
signed to Clytia Lamouroux, 1812. Cunha et al. (2017) debated the ambiguous inclusion of the species in Clytiidae,
but its medusa is typical of the group (Gravili et al. 2008) and it has been retained here in both the family Clytiidae
and the genus Clytia.
The hydrozoan assigned the binomen C. hummelincki has been considered a likely invasive species in the Medi-
terranean (Gravili et al. 2008). Invasive or not, its known distribution has expanded considerably since the mid-20th
century. From the original description of the species in the Caribbean Sea (Leloup 1935), its reported range now
extends to the Florida Keys, USA (Deevey 1954), Ghana, west Africa (Buchanan 1957, as Laomedea hummelincki),
Agulhas Bank, South Africa (Millard 1966a, 1975), Bermuda and adjacent banks (Calder 1991a, 2000), Brazil
(Migotto 1996; Oliveira et al. 2016), the Mediterranean Sea (Boero et al. 1997; Gravili et al. 2008, 2015), the Gala-
pagos Islands (Calder et al. 2003), Papua New Guinea (Boero & Bouillon, unpublished, cited in Gravili et al. 2008),
Guadeloupe, Martinique, and Panama, in the Caribbean Sea (Galea 2008, 2013; Miglietta et al. 2018), Indonesia
(Di Camillo et al. 2008), Cuba (Castellanos-Iglesias et al. 2009, 2018), Baa Atoll (Gravier-Bonnet & Bournaud
2012), and Belize (Cunha et al. 2017). A record from Pakistan (Moazzam & Moazzam 2006) was likely based on a
misidentification of C. edentula Gibbons & Ryland, 1989. Records of C. hummelincki from the Indo-Pacific region
(Calder et al. 2003; Di Camillo et al. 2008; Gravier-Bonnet & Bourmaud, 2012; Boero & Bouillon, unpublished)
are taken here to have been based on C. brevithecata.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Circumglobal in tropical and warm-temperate waters (see Remarks above).
Clytia elsaeoswaldae Stechow, 1914
Fig. 5b, c
Clytia elsae-oswaldae Stechow, 1914: 125, fig. 4.
Clytia cf. gracilis.—Coles et al., 2009: 59, 68, 72, 76, 82, 85 [not Clytia gracilis (M. Sars, 1850)].
Clytia elsaeoswaldae.—Calder, 2020: 208, fig. 2b, c.
Type locality. Virgin Islands of the United States: St. Thomas, port of Charlotte Amalie (Stechow 1914).
Voucher material. Midway Atoll, on algae, 23.ix.2002, one colony, 2 mm high, with a gonotheca, coll. A.
Faucci, ROMIZ B5415.
Remarks. Hydroids from our collections corresponded closely with original descriptions of two warm-water
species of the genus Clytia Lamouroux, 1812, C. obliqua (Clarke, 1907) and C. elsaeoswaldae Stechow, 1914.
Colonies of both appear to be stolonal or mostly so rather than erect and branched, hydrothecae are relatively broad
with rounded bases, and hydrothecal cusps slant to the right rather than being regularly triangular when viewed
laterally (Clarke 1907; Stechow 1914; Lindner et al. 2011; Cunha et al. 2020). Gonothecae were lacking in Clarke’s
(1907) specimens of C. obliqua, but those of C. elsaeoswaldae had smooth to slightly undulating walls, a constric-
tion below the truncated distal end, and they usually arose from the hydrorhiza (Lindner et al. 2011; Stechow 1914).
Such characters correspond with material examined here. From these descriptions the two species seem much alike
and, if conspecific, the binomen C. obliqua would have priority.
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FIGURE 5. Clytiidae. a, Clytia brevithecata (Thornely, 1900), hydrotheca and pedicel, Nihoa, ROMIZ B5414. Scale equals
0.2 mm. b, Clytia elsaeoswaldae Stechow, 1914, hydrotheca and pedicel, Midway Atoll, ROMIZ B5415. Scale equals 0.1 mm.
c, Clytia elsaeoswaldae Stechow, 1914, gonotheca, Midway Atoll, ROMIZ B5415. Scale equals 0.1 mm. d, Clytia linearis
(Thornely, 1900), hydrotheca and distal end of pedicel, Gardner Pinnacles, ROMIZ B5418. Scale equals 0.2 mm. e, Clytia
linearis (Thornely, 1900), gonotheca, Laysan Island, ROMIZ B5417. Scale equals 0.2 mm. f, Clytia cf. noliformis (McCrady,
1859), hydrotheca and pedicel, Pearl & Hermes Atoll, ROMIZ B5419. Scale equals 0.2 mm. g, Clytia cf. noliformis (McCrady,
1859), hydrotheca and distal end of pedicel, Pearl & Hermes Atoll, ROMIZ B5419. Scale equals 0.1 mm.
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 19
However, the identity of C. obliqua is uncertain based on subsequent accounts of the species. After examining
type material of the species, Cornelius (1982) concluded that it was conspecific with C. linearis (Thornely, 1900).
That synonymy was followed in several other works (e.g., Gibbons & Ryland 1989; Calder 1991a; Watson 2000; Xu
et al. 2014b; Wedler 2017; Choong et al. 2019). However, unlike material examined here, hydroids of C. linearis are
mostly erect and branched, and their hydrothecal cusps are slender and regularly triangular, with an internal keel-
like thickening of perisarc.
Meanwhile, Gibbons & Ryland (1989) discussed the identity of a hydroid from Fiji that closely resembled
Clarke’s (1907) illustration of C. obliqua (although hydrothecal cusps were shown with a slant to the left rather
than the right in their illustrations). They nevertheless followed Cornelius (1982) in concluding that C. obliqua was
conspecific with C. linearis, and identified their hydroids as C. ?gracilis instead. A syntype of C. obliqua (USNM
29616) examined during their deliberations was said to be branched, with tall hydrothecae. That seems at least
somewhat at variance with the original account of Clarke (1907), who described the species as “…a small creeping
form with peduncles from 1 mm to 1½ mm in height.” The specimens portrayed in Clarke’s illustrations were sto-
lonal, and hydrothecae were not particularly deep. Moreover, unlike in C. linearis, Gibbons & Ryland observed no
keel-like thickening on the inner edge of the cusps in the type. Given the conflicting accounts of C. obliqua, along
with the lack of gonophores in Clarke’s material, the species is regarded here as a species inquirenda. The type of C.
obliqua at the NMNH was unavailable for examination during this study because of the pandemic outbreak in 2019.
Hydroids examined here have therefore been assigned to C. elsaeoswaldae.
Clytia elsaeoswaldae is morphologically close to the much better-known C. gracilis (M. Sars, 1850), type lo-
cality Lofoten, Norway. Progress has been made in distinguishing the tropical to warm-temperate C. elsaeoswaldae
from the boreal C. gracilis based on characters noted above (Lindner et al. 2011; Cunha et al. 2020). Records of C.
gracilis from the tropical Pacific Ocean, including the Hawaiian Islands (Coles et al. 2009), are therefore believed
to have been based on misidentifications of the present species. Its is likely much more widespread than currently
recognized.
Reported Distribution. Hawaiian archipelago. Oahu: Pearl Harbor, West Loch entrance channel (Coles et al.
2009, as Clytia cf. gracilis; Calder 2020); Pearl Harbor, Hospital Point South (Coles et al. 2009, as C. cf. gracilis);
Pearl Harbor, Rainbow Bay Marina, floating buoys and docks (Coles et al. 2009, as C. cf. gracilis; Calder 2020);
Keehi Lagoon, marina docks (Coles et al. 2009, as C. cf. gracilis); Pearl Harbor, Rainbow Bay Marina, <1 m, on
dock (Calder 2020).
Elsewhere. Tropical and warm-temperate waters of the western Atlantic, including the Caribbean Sea (Stechow
1914; Lindner et al. 2011; Calder 2019) and the warm eastern Pacific (Bryant & Arehart 2019, medusa stage). If C.
obliqua is conspecific, the species has also been reported from Panama, Pacific coast (Clarke 1907), Japan (Fraser
1936; Hirohito 1969, 1995), California, USA (Fraser 1948), and Ecuador (Calder et al. 2019). A report of C. obliqua
from the Mediterranean coast of France (Picard 1950) seems questionable.
Clytia linearis (Thornely, 1900)
Fig. 5d, e
Obelia linearis Thornely, 1900: 453, pl. 44 fig. 6.
Type locality. Papua New Guinea: New Britain, Blanche Bay (Thornely 1900, as Obelia linearis).
Voucher material. Laysan Island, on coralline algae, 18.ix.2002, three colonies or colony fragments, to 7
mm high, without gonothecae, coll. A. Faucci, ROMIZ B5416.—Laysan Island, on Halimeda sp., 17.ix.2002, one
colony, 1.7 cm high, with gonothecae, coll. A. Faucci, ROMIZ B5417.—Gardner Pinnacles, 14.ix.2002, two colo-
nies or colony fragments, to 6 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5418.—Laysan Island, on
Halimeda sp., 17.ix.2002, one colony, 3 mm high, with gonothecae, coll. A. Faucci, ROMIZ B5423.
Remarks. These records of Clytia linearis (Thornely, 1900) constitute the first reports of the species from
the Hawaiian Islands. This well-known hydrozoan has been reported elsewhere from tropical and warm-temper-
ate waters across the Indian and Pacific oceans [Millard 1975, as Clytia gravieri (Billard, 1904); Mergner 1977,
as Campanularia (Clytia) gravieri; Mergner & Wedler 1977, as C. gravieri; Rees & Vervoort 1987; Gibbons &
Ryland 1989; Hirohito 1995; Watson 2000; Schuchert 2003; Xu et al. 2014b; Mendoza-Becerril et al. 2020]. It is
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widespread in the Atlantic Ocean as well (e.g., Calder 1991a, 2013; Altuna Prados 1994; Migotto 1996; Lindner &
Migotto 2002; Gravili et al. 2015; Oliveira et al. 2016).
Clytia linearis occurs in a clade linked to another that includes C. hemisphaerica (Linnaeus, 1767), taken to be
conspecific with C. johnstoni (Alder, 1856), the type species of Clytia Lamouroux, 1812 (e.g., Govindarajan et al.
2006; Leclère et al. 2009; Lindner et al. 2011; Zhou et al. 2013; He et al. 2015; Maronna et al. 2016; Cunha et al.
2017, 2020). These molecular studies also confirm the wide geographic distribution of the species, with specimen
vouchers from Brazil (São Sebastião), Italy (Torre Inserraglio) and the USA (Beaufort, North Carolina) being very
close genetically. Analyses of specimens from the Indo-Pacific region are needed to confirm the putative worldwide
distribution of the species.
The original date of publication of the work by Thornely, in which this binomen appeared (as Obelia linearis),
has commonly been cited as both 1899 and 1900. Rees & Vervoort (1987: 199) indicated that its publication date
was “v-1900”. That coincides with the date “May, 1900” on the Title Page of Willey, A., Zoological results based
on material from New Britain, New Guinea, Loyalty Islands and elsewhere. Part IV that included the paper by
Thornely. Her work has therefore been cited herein as “Thornely (1900)”. Another error in the literature warranting
attention has been the frequent misspelling of Thornely’s name as “Thorneley”. A synonymy list of C. linearis has
been given elsewhere (Calder 1991a).
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Circumglobal, tropical to warm-temperate waters (Lindner & Migotto 2002).
Clytia cf. noliformis (McCrady, 1859)
Fig. 5f, g
Campanularia noliformis McCrady, 1859: 194, pl. 11 fig. 4.
Type locality. Bermuda: Castle Harbour, on a dead octocoral (based on a neotype; Opinion 1986, International
Commission on Zoological Nomenclature 2002).
Voucher material. Pearl & Hermes Atoll, on Aglaophenia whiteleggei and adhering algae, 28.ix.2002, one
colony, 2.8 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5419.—Laysan Island, on Halimeda sp. and
Tridentata orthogonalis, 17.ix.2002, two colonies, to 3 mm high, without gonothecae, coll. A. Faucci, ROMIZ
B5420.
Remarks. These hydroids resemble Clytia noliformis (McCrady, 1859), and are provisionally assigned to that
species here. Hydrothecae appear to be slightly longer, and embayments separating hydrothecal cusps somewhat
deeper, than usual in C. noliformis (e.g., Nutting 1915; Calder 1991a, 2013). As such, they are essentially identical
to specimens identified as C. noliformis from the tropical eastern Pacific by Calder et al. (2021). While hydroids
from both locations also resemble Orthopyxis crenata (Hartlaub, 1901) in hydrothecal outline, they differ from that
species in having thinner hydrothecal walls, deeper cusps, and regularly annulated rather than sinuous pedicels.
When present, gonosomes readily distinguish the two as well, with C. noliformis liberating a free medusa and O.
crenata releasing a medusoid. However, our material was sterile.
Lindner & Migotto (2001) discovered an unusual category of nematocysts in C. noliformis, the merotrichous
isorhiza. Nematocysts resembling them in shape and size were present in specimens examined here, but all were
undischarged and their identity could not be determined with certainty.
Characters of both hydroid and medusa stages, as well as DNA barcoding (e.g., Maronna et al. 2016), support
the inclusion of C. noliformis in the genus Clytia Lamouroux, 1812. To date, no genetic comparisons have been
undertaken of hydroids assigned to the species from the Atlantic and Pacific or Indian oceans. Past uncertainty over
the specific identity of C. noliformis has been resolved by the designation of a neotype (International Commission
on Zoological Nomenclature 2002). The type locality of the species is Bermuda.
Clytia noliformis is a widely distributed species in warm waters of the Atlantic Ocean (e.g., Nutting 1915; Fra-
ser 1944; Lindner & Migotto 2002; Calder 2013; Galea 2013; Gravili et al. 2015; Oliveira et al. 2016), and it is a
major epibiont there on pelagic Sargassum (Ryland 1974; Calder 1991a; 1995; Mendoza Becerril et al. 2020). The
species has been recorded earlier in the Pacific from the coast of Ecuador (Fraser 1948; Calder et al. 2021), from
Guam (Kirkendale & Calder 2003), the Korea Strait (Lee et al. 2018, 18S rDNA sequences of plankton) and from
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 21
Tahiti (Pearman et al. 2020, metabarcoding of plankton). A record of it from Chile by Leloup (1974) was discounted
by Galea and Schories (2012) as an unidentified species of Clytia. In the Indian Ocean, records of it exist from
India (Leloup 1932; Panikkar & Aiyar 1937; Mammen 1965; Sarma 1974, 1975; Pati et al. 2014, 2015), the Anda-
man and Nicobar Islands (Leloup 1932; Deepa et al. 2015); Myanmar (Leloup 1932), Madagascar (Gravier 1970,
Gravier-Bonnet 1999), La Réunion (Bourmaud 2003) and Pakistan (Moazzam & Moazzam 2006). Collections from
the Northwestern Hawaiian Islands constitute the first records of C. noliformis, or of a species resembling it, in the
central North Pacific Ocean.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Considered circumglobal in warm-temperate to tropical waters: western Pacific (Kirkendale &
Calder 2003); eastern Pacific (Fraser 1948; Calder et al. 2021), western Atlantic (Calder 2013; Oliveira et al. 2016);
eastern Atlantic (Faucci & Boero 2000); Indian Ocean (Mammen 1965; Bourmaud 2003).
Family Haleciidae Hincks, 1869
Genus Halecium Oken, 1815
Halecium sp.
Fig. 6a, b
Voucher material. Pearl & Hermes Atoll, on calcareous rubble, 28.ix.2002, two colonies or colony fragments, to
4 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5421.—Nihoa, on calcareous rubble, 06.x.2002, one
colony, 9 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5422.
FIGURE 6. Haleciidae. a, Halecium sp., part of colony with two hydrothecae, Pearl & Hermes Atoll, ROMIZ B5421. Scale
equals 0.1 mm. b, Halecium sp., part of colony with five hydrothecae, Pearl & Hermes Atoll, ROMIZ B5421. Scale equals
0.1 mm. c, Nemalecium lighti (Hargitt, 1924), part of hydrocaulus, with four hydrothecae, Kure Atoll, ROMIZ B5424. Scale
equals 0.1 mm.
Remarks. In overall colony form, hydroids examined here resemble those identified as Halecium sp. 2 from
Fiji by Gibbons & Ryland (1989). Their colonies, collected from both the Suva barrier reef and the Great Astrolabe
reef, were rarely more than 5 mm high. Ours were also small, attaining a maximum height of 9 mm. Likewise of
similar morphology are hydroids identified as Halecium lankesterii (Bourne, 1890) from locations including the
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tropical west coast of Africa (Vervoort 1959) and South Africa (Millard 1975). However, hydranths of that species
may contain zooxanthellae (Schuchert 2005), unlike those examined here. Moreover, that species, originally de-
scribed from Plymouth, UK, seems unlikely to occur in the tropical central Pacific. Another allied species is H. pli-
catum Galea, in Galea & Ferry, 2015 from Martinique in the Caribbean Sea. Unlike in that species, no internal pegs
of perisarc were present in the hydrorhiza. Nemalecium lighti (Hargitt, 1924), common in Hawaii, was discounted
as a possibility because both nematodactyls and large pseudostenotele nematocysts were absent. Given the absence
of gonophores, and especially those of the female, these hydroids could not be positively identified.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. ?Fiji (Gibbons & Ryland 1989, as Halecium sp. 2).
Genus Nemalecium Bouillon, 1986
Nemalecium lighti (Hargitt, 1924)
Fig. 6c, pl. 4, fig. 13
Halecium lighti Hargitt, 1924: 489, pl. 4 fig. 13.
Halecium (beani?).—De Oreo, 1946: 645, figs 7–9 [not Halecium beanii (Johnston, 1838)].
Halecium beani.—Chu & Cutress, 1954: 9 [not Halecium beanii (Johnston, 1838)].
?Halecium beani.—Cooke, 1977: 87, fig. 15.—Coles et al., 1999a: 120, 194, 209 [not Halecium beanii (Johnston, 1838)].
Halecium sp.—Coles et al., 2002a: 206, 318; 2004: 73; 2009: 59, 76.
Halecium beanii.—Carlton & Eldredge, 2009: 35 [not Halecium beanii (Johnston, 1838)].
Nemalecium lighti.—Calder, 2010: 53; 2020: 214, fig. 4g, h.
Type locality. Philippines: Oriental Mindoro, Puerto Galera (Hargitt 1924, as Halecium lighti).
Voucher material. Kure Atoll, on algae and detached, 25.ix.2002, three colonies or colony fragments, to 1.6
cm high, without gonothecae, coll. A. Faucci, ROMIZ B5424.
Remarks. Nemalecium Bouillon, 1986 is a remarkable genus of hydroids. Its species are readily distinguished
by having 1–2 curved, finger-like nematodactyls (Bouillon 1986) in addition to typical tentacles in the tentacular
whorl of the hydranth. Immense pseudostenotele nematocysts (>25 µm long) are borne on these nematodactyls. To
date, two species, N. lighti (Hargitt, 1924) and N. gracile Galea, Ferry & Bertot, 2012, have been described and
assigned the genus. Of these, only N. lighti has been reported to date from the Pacific and Indian oceans, although
undescribed species are believed to occur there (Gravier-Bonnet & Migotto 2000; Gravier-Bonnet & Bourmaud
2006, 2012; Di Camillo et al. 2008; Galea et al. 2012; Boissin et al. 2018). Records of N. gracile to date are re-
stricted to the Atlantic Ocean, while N. lighti is taken to be circumglobal in shallow, warm waters. In Hawaii, the
species is well-represented in nearshore habitats (Calder 2020). It was misidentified in early records from the islands
as Halecium beanii (Johnston, 1838), a species inhabiting cool to cold rather than tropical waters (Fraser 1947;
Cornelius 1995a, Schuchert 2005; Antsulevich 2015). Moreover, those first Hawaiian reports were of a species that
was venomous (De Oreo 1946; Chu & Cutress 1954). Nemalecium lighti is known to sting humans (Marques et al.
2002; Santhanam 2020), while H. beanii is likely innocuous.
Taxonomically, Maronna et al. (2016) disputed the inclusion of Nemalecium in Haleciidae Hincks, 1869 based
on molecular data, referring it instead to the order Plumupheniida Maronna et al., 2016. Until its family-group af-
finities are resolved, however, we continue to assign it to Haleciidae Hincks, 1869 given its haleciid-like morpho-
logical characters.
Recent reviews of N. lighti have been given elsewhere (Calder 2019; Calder et al. 2019).
Reported Distribution. Hawaiian archipelago. Oahu: near Honolulu, human envenomations (De Oreo 1946, as
Halecium (beani?)); Maunalua Bay, on rubble (Cooke 1977, as H. beani); Barbers Point Harbor, barge pier (Coles et
al. 1999, as Halecium sp.); Honolulu Harbor, wood block, coll. 1945, Bishop Museum, BPBM-D-260 (Coles et al.
1999, as Halecium sp.; Carlton & Eldredge 2009, as H. beanii); Kaneohe Bay, coll. 1963, Bishop Museum, BPBM-
D-349 (Coles et al. 2002a, as Halecium sp.); Kaneohe Bay, Sag Harbor (Coles et al. 2002a, as Halecium sp.); Pearl
Harbor, entrance channel (Coles et al. 2009, as Halecium sp.); Pearl Harbor, West Loch entrance channel (Coles et
al. 2009, as Halecium sp.); Pearl Harbor, Hospital Point south (Coles et al. 2009, as Halecium sp.); Pearl Harbor,
Utah Memorial (Coles et al. 2009, as Halecium sp.); Pearl Harbor, Hawaiian Electric Company discharge (Coles
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et al. 2009, as Halecium sp.); Honolulu Harbor, Piers 40–41 (Coles et al. 2009, as Halecium sp.); Keehi Lagoon,
marina docks (Coles et al. 2009, as Halecium sp.); Keehi Lagoon, barge wreck (Coles et al. 2009, as Halecium
sp.); Keehi Lagoon, stream mouth (Coles et al. 2009, as Halecium sp.); north shore, in alphaeid crevices on corals
(Calder 2010).—Hawaiian Islands: no specific location (Chu & Cutress 1954, as H. beani).—Kauai: Nawiliwili
Harbor (Coles et al. 2004, as Halecium sp.).—Molokai: Kaunakakai main dock (Coles et al. 2004, as Halecium
sp.).—Maui: Kahului Harbor Pier 1 (Coles et al. 2004, as Halecium sp.).
Elsewhere. Atlantic, Pacific, and Indian oceans; warm waters (Calder et al. 2019).
Family Sertularellidae Maronna, Miranda, Peña Cantero, Barbeitos & Marques, 2016
Genus Sertularella Gray, 1848
Sertularella affinicostata, sp. nov.
Figs 7a–e, 8
Sertularella costata.—Calder et al., 2003: 1190, fig. 14a, b [not Sertularella costata Leloup, 1940].
Type locality. Ecuador: Galapagos Islands, Darwin Island, within SCUBA depth, on barnacle cluster (Calder et al.
2003, as Sertularella costata).
Etymology. The specific name is derived from the Latin adjective affinis (akin to) and the name costata, given
its resemblance to Sertularella costata.
Voucher material. HOLOTYPE: Ecuador: Galapagos Islands, Isla Darwin, SCUBA depth, on barnacle cluster,
26 January 1999, one colony, 1.5 mm high, with gonothecae, coll. K. Collins, ROMIZ B3339.
PARATYPES: Ecuador: Galapagos Islands, Cousin Rock, 10 m, on sponge, 17 June 2001, one colony, 5.2
mm high, without gonothecae, coll. D. Calder, ROMIZ B3409.—Ecuador: Galapagos Islands, Marchena Island,
Punta Espejo, ca. 8 m, 18 June 2001, four colonies, to 5 mm high, without gonothecae, coll. L. Garske, ROMIZ
B3418.—French Frigate Shoals, on calcareous rubble, 13.ix.2002, one colony, 2 mm high, without gonothecae, coll.
A. Faucci, ROMIZ B5486.
OTHER MATERIAL: Ecuador: Galapagos Islands, Wolf Island, 6 m, on algae, November 1992, two colonies,
to 0.55 mm high, without gonothecae, coll. P. Humann, ROMIZ B3315.—Ecuador: Galapagos Islands, Wolf Island,
on stolon of Aglaophenia sp., 25 January 1999, one colony, 1.1 mm high, without gonothecae, coll. J. Mallinson,
ROMIZ B3318.
Description. Holotype colony unbranched, diminutive, with cauli reaching 1.5 mm high, arising from a hydro-
rhiza overgrowing cluster of small barnacles. Paratype colonies unbranched to occasionally with a branch or two,
with cauli reaching 5.2 mm high, overgrowing a sponge. Basal stolons without internal pegs, diameter 59–83 µm;
cauli mostly erect, caulus bearing a maximum of three hydrothecae in holotype, occasionally with a single hydrothe-
ca borne on a short internode in parts of colony, paratypes with as many as 13 cauline hydrothecae (ROMIZ B3418).
Hydrocaulus monosiphonic, nearly straight to irregular, length of first internode from insertion with hydrorhiza to
base of first hydrotheca 0.14–0.35 mm, smooth to slightly wrinkled but without regular annulations, expanding
gradually in circumference distally, hydrocaulus beyond first hydrotheca divided into typically short internodes,
with first of these growing out directly from base of hydrotheca without nodes or annulations, more distal inter-
nodes separated by oblique nodes sloping alternately in opposite directions; internodes 322–423 µm long, 73–88
µm wide at nodes, 128–151 µm wide at base of hydrotheca, often with an annulation or slight swelling at proximal
end, mostly smooth elsewhere, widening gradually from proximal end to base of hydrotheca, then tapering again to
distal node, every internode bearing a hydrotheca; perisarc of moderate thickness. Hydrothecae sessile, alternate,
typically biseriate but sometimes given off in multiple planes, quite deep, barrel-shaped, extending upwards and
outwards, arranged alternately on opposite sides of hydrocaulus, adnate to internode for 1/3 or less of their length,
with axis oblique to that of hydrocaulus; hydrothecal walls with about 10–14 sharp-edged horizontal ridges, widest
near mid-point, tapering towards proximal and distal ends, narrowest at base, slightly constricted just below margin,
then expanding to rim, length abcauline wall 338–377 µm, length adcauline wall adnate 72–99 µm, length adcauline
wall free 279–310 µm, maximum diameter 189–218 µm, both adcauline and abcauline walls convex over much of
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their length, slightly concave at distal end; hydrothecal base 90–118 µm wide. Hydrothecal rim quadrangular, with
four distinct, pointed, equally developed cusps separated by shallow embayments, no evidence of renovations in
present material; hydrothecal orifice 150–183 µm wide; hydrothecal cavity enclosed by an operculum of four trian-
gular valves; submarginal cusps three, one being abcauline and two latero-adcauline. Hydranths with an abcauline
diverticulum.
Gonophores fixed sporosacs. Gonothecae of holotype colony male, containing spermatocytes, borne on a short,
smooth pedicel arising from hydrorhiza or from base of hydrocaulus adjacent to a hydrotheca, nearly circular in
cross-section, elongate-oval in lateral view, with rounded base and distal taper to a narrow neck, 0.8–1.0 mm long
from base to orifice, maximum diameter 0.45–0.60 mm; margin entire, 0.15–0.18 mm wide, orifice round or nearly
so. Gonothecal walls with seven to eight transverse, rounded ridges, those at distal end prominently developed,
those at proximal end flattened, less pronounced; perisarc quite thick.
Remarks. Of the many described species of Sertularella Gray, 1848, these hydroids resemble several in a group
bearing numerous sharp-edged horizontal ridges around walls of the hydrothecae. Amongst them, it appears closest
to S. costata Leloup, 1940, originally described from Sagami Bay, Japan. The hydroid examined here is neverthe-
less readily distinguished from that species in having fewer ridges, with ca. 10–14 instead of ca. 20 (Leloup, 1940;
Hirohito 1983, 1995). Its hydrothecae also differ in being barrel-shaped rather than distinctly tapered distally, and
a smooth part just below the rim is more elongated. Moreover, the basal-most internode of the hydrocaulus is typi-
cally short rather than forming a long, slender, smooth peduncle as in S. costata, and cauline internodes are shorter
and thicker. Given these differences, the hydroid is considered distinct from S. costata, as described by Leloup
(1940) and Hirohito (1983, 1995), and from other known species of Sertularella. It has therefore been described
here as new, under the binomen S. affinicostata. Of note, specimens from French Frigate Shoals are morphologically
indistinguishable from colonies identified as S. costata from the Galapagos Islands by Calder et al. (2003). Those
specimens, like the colony examined here, differ from S. costata in the characters noted above, and are taken here
to have been misidentified. All are taken to be referable to the same species, S. affinicostata.
In being sterile, the single colony from French Frigate Shoals has been designated as a paratype (ROMIZ
B5486). Selected as the holotype (ROMIZ B3339) is a fertile colony of the species from Darwin Island, Galapagos
Islands, erroneously assigned to S. costata by Calder et al. (2003). Additional paratypes include previously unre-
corded specimens from the Galapagos (ROMIZ B3409, ROMIZ B3418) in collections at the ROM. Cauli of these
colonies are noteworthy in being taller (to 5.2 mm vs. 2 mm high), and they bear more hydrothecae (as many as
13 vs. 5) than those from either Darwin Island (ROMIZ B3339) or French Frigate Shoals (ROMIZ B5486). Other
specimens from the Galapagos Islands (ROMIZ B3315, ROMIZ B3318), assigned to S. costata by Calder et al.
(2003) but here considered conspecific with S. affinicostata, are too miniscule to be considered adequate type mate-
rial.
Similar hydrothecal ornamentation appears on the hydrothecal walls of several other species of Sertularella, in-
cluding S. mirabilis Jäderholm, 1896 and S. sinensis Jäderholm, 1896. Hydroids of those species differ in morphol-
ogy from S. affinicostata, with colonies of S. mirabilis forming three-dimensional lattices and resembling sponges,
and those of S. sinensis being bushy (Jâderholm 1896; Vervoort 1993; Hirohito 1995; Schuchert 2015). Stems of
both species diverge from those of the hydroids described here in being repeatedly branched, and their colonies are
larger (to 5 cm or more high). Sertularella crenulata Nutting 1905, a species originally described from Hawaii, dif-
fers in having finer and more numerous hydrothecal ridges (>30). Its colonies are also significantly larger (to 7.5
cm high) and more robust, with basally polysiphonic cauli (Nutting 1905, Vervoort 1993). Two tropical western
Pacific species, S. paucicostata Vervoort, 1993 and S. pseudocostata Vervoort, 1993, are immediately distinguish-
able from S. affinicostata in lacking intrathecal cusps. Their hydrothecae are also considerably larger, with a total
depth × maximum diameter of 715–825 µm × 305–390 µm in S. paucicostata, and 1105–1300 µm × 540–585 µm
in S. pseudocostata. Others of the genus with similar hydrothecal ornamentation include S. patagonica (d’Orbigny,
1842), with 6–8 transverse ridges, S. peculiaris Leloup, 1935, with about five ridges, S. helenae Vervoort, 1993,
with 8–9 ridges encircling cylindrical hydrothecae, and S. fraseri Galea, 2010, with 5–6 ridges.
Sertularella affinicostata is unusual in being a species from the Hawaiian Archipelago that is currently known
elsewhere only from the eastern Pacific rather than the Indo-west Pacific region. Both poorly known and easily
overlooked, it undoubtedly occurs elsewhere in the tropical Pacific Ocean.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Galapagos Islands, Wolf and Darwin islands (Calder et al. 2003, as Sertularella costata).
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 25
FIGURE 7. Sertularellidae. a, Sertularella affinicostata, sp. nov., holotype, hydrocaulus with two hydrothecae, Darwin Is-
land, Galapagos Islands, Ecuador, ROMIZ B3339. Scale equals 0.1 mm. b, Sertularella affinicostata, sp. nov., holotype,
hydrocaulus with male gonotheca and a hydrotheca, Darwin Island, Galapagos Islands, Ecuador, ROMIZ B3339. Scale equals
0.1 mm. c, Sertularella affinicostata, sp. nov., paratype, hydrocaulus with three hydrothecae, French Frigate Shoals, ROMIZ
B5486. Scale equals 0.1 mm. d, Sertularella affinicostata, sp. nov., paratype, hydrocaulus with two hydrothecae, French Frig-
ate Shoals, ROMIZ B5486. Scale equals 0.1 mm. e, Sertularella affinicostata, sp. nov., paratype, hydrocaulus with a single hy-
drotheca, French Frigate Shoals, ROMIZ B5486. Scale equals 0.1 mm. f, Sertularella angulosa Bale, 1894, part of hydrocaulus
with four hydrothecae, French Frigate Shoals, ROMIZ B5477. Scale equals 0.2 mm. g, Sertularella angulosa Bale, 1894, part
of hydrocaulus with four hydrothecae, Kure Atoll, ROMIZ B5425. Scale equals 0.1 mm. h, Sertularella angulosa Bale, 1894,
part of hydrocaulus with two hydrothecae, Kure Atoll, ROMIZ B5425. Scale equals 0.1 mm. i, Sertularella areyi Nutting, 1904,
part of hydrocaulus with three hydrothecae, Nihoa, ROMIZ B5478. Scale equals 0.2 mm.
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FIGURE 8. Sertularellidae. Sertularella affinicostata, sp. nov., holotype, Isla Darwin, Galapagos Islands, Ecuador, ROMIZ
B3339. a, hydrocaulus and hydrorhiza, with two hydrothecae. b, a single hydrotheca, darkfield illumination. c, hydrocaulus
and hydrorhiza, with a male gonotheca and a hydrotheca, darkfield illumination. d, hydrocaulus and hydrorhiza, with a male
gonotheca and a hydrotheca.
Sertularella angulosa Bale, 1894
Fig. 7f–h
Sertularella angulosa Bale, 1894: 102, pl. 4 fig. 6.
Type locality. Unknown, but likely Australia (Bale 1894).
Voucher material. Kure Atoll, on algae and a bryozoan, 26.ix.2002, two colonies, to 5 mm high, without gono-
thecae, coll. A. Faucci, ROMIZ B5425.—French Frigate Shoals, on hydroid stem, 12.ix.2002, one colony, 7 mm
high, without gonothecae, coll. A. Faucci, ROMIZ B5477.
Remarks. These small hydroid colonies appear closest in morphology to accounts of Sertularella angulosa
Bale, 1894 from Indonesia by Billard (1925b) and Vervoort & Vasseur (1977), the latter in a discussion of S. ro-
busta Coughtrey, 1876 from Moorea, French Polynesia. Indeed, the two have generally been considered conspecific
(Hodgson 1950; Vervoort & Vasseur 1977; Hirohito 1995; Vervoort & Watson 2003). However, specimens exam-
ined here have been excluded from S. robusta, the putative senior synonym, largely on zoogeographic grounds.
Originally described from Foveaux Strait at the southern tip of New Zealand (Coughtrey 1876), and with a centre of
distribution in cold waters elsewhere in the Southern Hemisphere (Leloup 1960, 1974; Blanco 1968; Vervoort 1972;
Vervoort & Watson 2003; Galea 2007; Galea et al. 2009; El Beshbeeshy 2011; Galea & Schories 2012; Oliveira
et al. 2016; Galea et al. 2017), it seems improbable that S. robusta extends into tropical and warm-temperate parts
of the Pacific and Indian oceans. Hydroids assigned to it from such areas (Pennycuik 1959; Vervoort & Vasseur
1977; Hirohito 1983, 1995; Gravier-Bonnet & Bourmaud 2012) are likely to have been misidentified. Thus, S.
angulosa has been taken here to be valid, and populations inhabiting lower latitudes in the Pacific, including Kure
Atoll, are more likely referable to it than to S. robusta. In addition to the original account of S. angulosa by Bale
(1894), thorough accounts of its trophosome and gonosome have been given by Billard (1925b) and by Vervoort
& Vasseur (1977, partly under the binomen S. robusta). Uncertainties nevertheless remain over the identity of the
species. Bale’s (1894) type material of S. angulosa was sterile, and while his collections were almost certainly from
Australia, the exact type locality and original habitat of the species are unknown.
Also included in the synonymy of S. robusta by Vervoort & Vasseur (1977) was S. microgona von Lendenfeld,
1885. From accounts of it by Billard (1925b) and Vervoort & Vasseur (1977, as S. robusta, in part), the species dif-
fers from S. angulosa in having hydrothecae that are more slender and more tapered towards the distal end. Vervoort
& Vasseur also compared the type of S. inconstans Billard, 1925b with their S. robusta. Differences between them
were said to include the larger colony size, smaller submarginal cusps, and remarkably thick stem perisarc of S.
inconstans. Finally, hydrothecae of the similar S. keiensis Billard, 1925b are slenderer at the distal end, and four
submarginal cusps are present (Billard 1925b; Hirohito 1995; Xu et al. 2014b) rather than three, as in S. microgona,
S. angulosa, and S. robusta.
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As for S. robusta Coughtrey, 1876, its binomen is a permanently invalid junior primary homonym of S. gayi
var. robusta Allman, 1874a (ICZN 1999, Art. 57.2), originally described from the Faroe-Shetland Trough in the
North Atlantic Ocean. It is nomenclaturally inconsequential that Allman’s name was introduced as a variety (ICZN
1999, Art. 45.6.4). Moreover, Reversal of Precedence provisions cannot be applied (ICZN 1999, Art. 23.9.1.1) to
validate the junior homonym as a nomen protectum because its senior homonym has been used as a valid name
after 1899, including in certain recent works (e.g., Nutting 1904: 79; Billard 1906a: 331; 1906b: 185; Bedot 1925:
370; Vervoort 1972: 118; Ramil & Vervoort 1992: 223; Calder & Vervoort 1998: 39, with a synonymy list; Henry
et al. 2008: 794; Gil & Ramil 2017: 428). The junior homonym S. robusta Coughtrey, 1876 is replaced here by the
binomen S. quasiplana Trebilcock, 1928, originally described as S. robusta var. quasiplana Trebilcock, 1928. The
name of that variety qualifies as a replacement (ICZN 1999, Art. 60.2) in being considered a synonym of S. robusta
by Vervoort & Watson (2003). As with the S. robusta of Coughtrey, it was originally described from New Zealand
(Island Bay). Also described as a variety of the same species by Trebilcock (1928) was S. robusta var. flucticulata.
Although sharing the same general type locality (Bluff, in Foveaux Strait, New Zealand) with S. robusta, it was
excluded from consideration as a replacement name because it has been included in the synonymy of S. integra All-
man, 1876 (Vervoort & Watson 2003). With respect to authorship and date of the Atlantic species, now regarded in
some works as distinct from S. gayi (Lamouroux, 1821) (Moura et al. 2011), it should be credited to Allman (1874a)
and not Coughtrey (1876).
The name Sertularella polyzonias var. robusta as utilized by Verrill (1873a:10) was not accompanied by a de-
scription, illustration, or indication, and is a nomen nudum. The trinomen S. polyzonias f. robusta appeared again
in Kirchenpauer (1884) for hydroids “…mit viel dickeren Stämmen und Zweigen und grösseren Hydrotheken…”
from the Cape of Good Hope, South Africa. That hydroid was briefly mentioned in the work of Hartlaub (1901),
and an illustration of it was provided, but its nomenclature was left unsettled. The name S. polyzonias var. robusta
was listed by Bedot (1916, 1918, 1925), but in reference to the hydroid of Verrill (1873a), not Kirchenpauer (1884).
The nomenclature of Kirchenpauer’s junior homonym was finally settled by Millard (1964). She recognized it as
distinct from S. polyzonias (Linnaeus, 1758), and linked it instead to S. megista Stechow, 1923b. Finally, another
junior homonym of both S. gayi var. robusta Allman, 1874a and S. robusta Coughtrey, 1876 is S. robusta Clark,
1877. That binomen has been replaced by the name S. albida Kirchenpauer, 1884.
Material assigned to S. angulosa by Billard (1925b) was collected at depths between 59 m and 90 m at several
locations in Indonesia. Billard believed that hydroids identified by Jäderholm (1905) as S. tenella (Alder, 1856),
from Tierra del Fuego, were conspecific. Given the cold Southern Hemisphere collection locale of Jäderholm’s
material, however, it is more likely referable to S. robusta (=S. quasiplana), as indicated by Galea et al. (2017).
Vervoort & Vasseur (1977) found S. angulosa (as S. robusta) to be the most common hydroid on the entire Tia-
hura barrier reef at Moorea. It extended from the reef flat, at 1 m, to the spur and groove zone at 20 m, and reached
peak abundance in cavities on the reef flat.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Indian Ocean (Millard & Bouillon 1973, as Sertularella robusta; Gravier-Bonnet & Bourmaud
2012, as S. robusta), western Pacific Ocean (Pennycuik 1959, as S. robusta; Vervoort & Vasseur 1977, as S. robusta;
Hirohito 1983, 1995, as S. robusta).
Sertularella areyi Nutting, 1904
Fig. 7i
Sertularella areyi Nutting, 1904: 83, pl. 17 fig. 6.—Coles et al., 2002a: 318; 2002b: 177.—Carlton & Eldredge, 2009: 38.—
Calder, 2020: 216, fig. 5a.
Type locality. Cuba: near Havana, 100–200 fm (183–366 m) (Nutting 1904).
Material examined. Nihoa, on algae, 06.ix.2002, 2 colonies or colony fragments, to 5 mm high, without gono-
thecae, coll. A. Faucci, ROMIZ B5478.
Remarks. Discovery of Sertularella areyi Nutting, 1904 from inshore waters of Hawaii in the central Pacific
(Calder 2019, 2020), and from diving depths at Nihoa in this study, is surprising given the type locality of the spe-
cies. The hydroid was originally described by Nutting (1904) from outer neritic and upper bathyal waters (100–200
ftm = 182–364 m) off Cuba, in the western North Atlantic. Records of it from the Atlantic to date have mainly been
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at intermediate depths, although the species appears to be quite eurybathic. Sertularella areyi has been most widely
reported in the western Pacific, with records from Japan (Yamada 1959; Hirohito 1995), Korea (Rho & Chang
1974), the Philippines (Vervoort 1993), New Caledonia (Vervoort 1993), the Loyalty Islands (Vervoort 1993), New
Zealand (Vervoort & Watson 2003), and China (Xu et al. 2014b; Song 2019). When subjective synonyms of the
species are included, its range also includes Australia (Sertularella annulaventricosa Mulder & Trebilcock, 1915,
from Queenscliff, Victoria), Tasmania (Sertularia undulata Bale, 1915, from South Cape), Indonesia (Sertularella
tricincta Billard, 1939, from the Kei Islands), and South Africa (Sertularella capensis delicata Millard, 1964, from
Natal). Molecular comparisons of populations across its reported distribution will therefore be enlightening. In the
western Atlantic Ocean, its putative range extends from Plantagenet Bank near Bermuda (Calder 2000) and from
shelf waters off South Carolina (Wenner et al. 1984) in the north to Brazil (Oliveira et al. 2016) in the south.
Type material of S. areyi was collected off Cuba during the Bahama Expedition of 1893, led by Charles Cleve-
land Nutting (1858–1927) of the State University of Iowa (now the University of Iowa). Nutting (1904) named the
species in honour of Melvin Franklin Arey (1844–1931), Professor of Natural Sciences at the Iowa State Normal
School (now the University of Northern Iowa), a participant in the expedition, and a veteran of the American Civil
War (https://scua.library.uni.edu/university-archives/historical-information-and-essays/lincoln-civil-war-and-uni).
An engaging narrative of the Bahama Expedition appears in Nutting (1895).
Detailed accounts of S. areyi from the western Pacific Ocean appear in the major works of Vervoort (1993) and
Vervoort & Watson (2003).
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay, Moku Manu Island (Coles et al. 2002a;
Calder 2020); Waikiki, Kapua Channel (Coles et al. 2002b).
Elsewhere. Atlantic, Pacific, and Indian oceans, mostly at lower latitudes (Vervoort & Watson 2003).
Family Sertulariidae Lamouroux, 1812
Genus Disertasia Neppi, 1917
Disertasia crisioides (Lamouroux, 1824), comb. nov.
Fig. 9a, b
Dynamena crisioides Lamouroux, 1824: 613, pl. 90 figs 11, 12.—Cooke, 1977: 93, fig. 20.—Coles et al., 2002a: 318; 2006:
492.—Carlton & Eldredge, 2009: 38.—Calder, 2020: 218, fig. 5e, f.
Dynamena crisiodes.—Coles et al., 1999a: 194 [incorrect subsequent spelling].
Type locality. Indonesia: Moluccas (Lamouroux 1824).
Voucher material. Lisianski Island, 01.x.2002, one young colony, 2 cm high, without gonothecae, coll. A.
Faucci, ROMIZ B5426.—Gardner Pinnacles, on calcareous rubble, 14.ix.2002, two colonies or colony fragments,
2.8 cm high, one with gonothecae, coll. A. Faucci, ROMIZ B5427.
Remarks. This hydroid, widely known as Dynamena crisioides Lamouroux, 1824, is a common and relatively
well-known shallow-water hydroid with a worldwide distribution in tropical and subtropical waters. It has been re-
ported several times earlier from the Hawaiian Islands (Cooke 1977; Coles et al. 1999a; Coles et al. 2002a; Carlton
& Eldredge 2009; Calder 2020).
Based on molecular data, D. crisioides must unfortunately be removed from the polyphyletic genus Dynamena
Lamouroux, 1812 and assigned elsewhere. In the phylogenetic analyses of Moura et al. (2011), Maronna et al.
(2016), and Song (2019), the species appears closest to Dy. disticha (Bosc, 1802) and Dy. moluccana (Pictet, 1893),
with all three being genetically distant from Dy. pumila (Linnaeus, 1758), the type species of Dynamena. They are
here referred instead to a resurrected genus Disertasia Neppi, 1917, type species Disertasia cavolini Neppi, 1917.
Inclusion of D. crisioides in the genus, as Disertasia crisioides, comb. nov., warrants further assessment, however,
as it is slightly separated from its two known congeners. Further comments on Disertasia are included in the Re-
marks section of Di. disticha immediately below. As for the specific name of its type species, Di. cavolini, it was
formed as a noun in apposition and is the correct original spelling. Such formation of specific names is nevertheless
discouraged by the code (ICZN 1999, Recommendation 31A).
For taxonomic and biological information on this species, see Millard (1975), Vervoort & Vasseur (1977), Gib-
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 29
bons & Ryland (1989), Calder (1991a, b, 2013), and Schuchert (2003), all under the binomen Dynamena crisioi-
des.
Reported Distribution. Hawaiian archipelago. Oahu: Kewalo Basin (Cooke 1977, as Dynamena crisioides);
Honolulu Harbor (Cooke 1977, as Dy. crisioides); Honolulu Harbor, Pier 29 (Coles et al. 1999a, as Dy. crisiodes,
sic); Honolulu Harbor, Snug Harbor (Coles et al. 1999a, as Dy. crisiodes, sic); Honolulu Harbor, Sand Island Coast
Guard Station (Coles et al. 1999a, as Dy. crisiodes, sic); Honolulu Harbor, Sand Island Park (Coles et al. 1999a, as
Dy. crisiodes, sic); Keehi Lagoon, Airport Rescue Dock (Coles et al. 1999a, as Dy. crisiodes, sic); Kewalo Basin,
Fisherman’s Wharf (Coles et al. 1999a, as Dy. crisiodes, sic); Barbers Point, coal pier (Coles et al. 1999a, as Dy.
crisiodes, sic); Kaneohe Bay, Sag Harbor (Coles et al. 2002a, as Dy. crisioides; Calder 2020, as Dy. crisioides);
Honolulu Harbor, in collections at the Bishop Museum (Carlton & Eldredge 2009, as Dy. crisioides).—Kauai: Port
Allen Harbor (Coles et al. 2006, as Dy. crisioides).
Elsewhere. Circumglobal, shallow tropical and subtropical waters (Calder 2013, as Dy. crisioides).
FIGURE 9. Sertulariidae. a, Disertasia crisioides (Lamouroux, 1824), part of hydrocladium with three hydrothecal pairs,
Gardner Pinnacles, ROMIZ B5427. Scale equals 0.2 mm. b, Disertasia crisioides (Lamouroux, 1824), gonotheca, Gardner
Pinnacles, ROMIZ B5427. Scale equals 0.2 mm. c, Disertasia disticha (Bosc, 1802), part of hydrocaulus with three hydrothecal
pairs, Pearl & Hermes Atoll, ROMIZ B5428. Scale equals 0.2 mm. d, Pasya heterodonta (Jarvis, 1922), proximal end of hydro-
caulus, with three hydrothecal pairs, Pearl & Hermes Atoll, ROMIZ B5436. Scale equals 0.2 mm. e, Pasya heterodonta (Jarvis,
1922), distal end of hydrocaulus, with three hydrothecal pairs, two pairs being stacked, Kure Atoll, ROMIZ B5491. Scale equals
0.2 mm. f, Pasya heterodonta (Jarvis, 1922), distal end of hydrocaulus, with three stacked hydrothecal pairs, Pearl & Hermes
Atoll, ROMIZ B5485. Scale equals 0.2 mm. g, Pasya heterodonta Jarvis, 1922), gonotheca, Kure Atoll, ROMIZ B5491. Scale
equals 0.1 mm. h, Salacia tetracythara Lamouroux, 1816, part of hydrocladium with three hydrothecal pairs, Lisianski Island,
ROMIZ B5429. Scale equals 0.2 mm. i, Salacia tetracythara Lamouroux, 1816, gonotheca from same colony, Lisianski Island,
ROMIZ B5429. Scale equals 0.2 mm.
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Disertasia disticha (Bosc, 1802), comb. nov.
Fig. 9c
Sertularia disticha Bosc, 1802: 101, pl. 29 fig. 2.
Dynamena cornicina.—Cooke, 1977: 95, fig. 21.—Coles et al., 2002a: 207; 2004: 73.—Carlton & Eldredge, 2009: 38.
Type locality. Atlantic Ocean: “...sur le fucus natans (Sargassum natans) dans la haute mer…” (Bosc 1802: 101, as
Sertularia disticha).
Voucher material. Pearl & Hermes Atoll, on algae, 28.ix.2002, one colony, 9 mm high, without gonothecae,
coll. A. Faucci, ROMIZ B5428.
Remarks. This hydroid conforms with traditional taxonomic accounts of Dynamena disticha (Bosc, 1802), and
it has been provisionally assigned to that species here. However, evidence from both morphology and DNA barcod-
ing (Moura et al. 2011) indicates the likely existence of a species complex under that name. The hydroid from Pearl
& Hermes Atoll may be specifically distinct from that of Bosc, and changes in nomenclature might be expected.
The species of Bosc (1802) was described from material collected on pelagic Sargassum in the open Atlantic
Ocean. Colonies from that substrate are small (1 cm high or less), gracile, and unbranched (Calder 1991a). Another
morphotype from a variety of substrates along the shallow Atlantic coast are larger in size (up to 5 cm high), more
robust, and an essentially perpendicular branch may infrequently be present (Fraser 1944, as Sertularia cornicina;
Calder 1971, as Dynamena cornicina). The overall morphology of their trophosomes and gonosomes are otherwise
much alike, and the colour of both is bright yellow. Comparisons of them are warranted to establish if observed dif-
ferences are attributable to genetics or environment.
Molecular studies by Moura et al. (2011), Maronna et al. (2016), and Song (2019) confirm that Dynamena
Lamouroux, 1812 is polyphyletic. Indeed, Dy. disticha has been shown by them in all phylograms to be geneti-
cally distant from Sertularia pumila Linnaeus, 1758, type species of the genus. The species also appears too remote
from Tridentata Stechow, 1920, type species Sertularia perpusilla Stechow, 1919b, to be assigned there. Instead,
as noted above, the genus Disertasia Neppi, 1917 has been resurrected here from the synonymy of Dynamena to
accommodate this and closely related species. Of particular note, the type species of Disertasia by monotypy, Di.
cavolini Neppi, 1917, is taken to be conspecific with Dy. disticha (Picard 1958; Calder 1991a; Medel & Vervoort
1998; Gravili et al. 2015). The present species is thus assigned the binomen Disertasia disticha, comb. nov. Also
assigned here to Disertasia, based on their proximity in molecular phylograms to Di. disticha, are Dy. moluccana
(Pictet, 1893) and, with somewhat less certainty, Dy. crisioides Lamouroux, 1824. Meanwhile, it is unclear if any of
the sampled populations of Di. disticha included in molecular analyses were from pelagic Sargassum, as with the
original account of the species by Bosc (1802).
In an obscure paper on hydroid epibionts from pelagic Sargassum in the North Atlantic, Bosc (1797) described,
as Hydra quinternana, a small yellow sertulariid likely to have been identical with Disertasia disticha. It therefore
constitutes a nomenclatural threat to the now widely used species name Dy. disticha (=Sertularia disticha Bosc,
1802). In the interests of nomenclatural stability, Reversal of Precedence provisions in the code (ICZN 1999, Art.
23.9) are followed here to designate Di. disticha (Bosc, 1802) as valid and a nomen protectum, and to relegate H.
quinternana Bosc, 1797 to a nomen oblitum. Reversal of Precedence is applicable in this case because the binomen
H. quinternana has not been used as a valid name in zoology after 1899, while Dy. disticha has appeared in more
than 25 publications by numerous authors (>10) in the past 50 years (e.g., Boero 1981; Calder 1991a, 1995, 2013,
2019; Cornelius 1992; Migotto 1996; Grohmann et al. 1997; Medel & Vervoort 1998; Faucci & Boero 2000; Peña
Cantero & García Carrascosa 2002; Kirkendale & Calder 2003; Schuchert 2003; Calder & Kirkendale 2005; Bouil-
lon et al. 2006; Vervoort 2006; Gravier-Bonnet 2007; Galea 2008, 2010; Cunha & Jacobucci 2010; Moura et al.
2011; Xu et al. 2014b; Galea & Ferry 2015; Gravili et al. 2015; Oliveira et al. 2016; Maronna et al. 2016; Mendoza-
Becerril et al. 2018; Miglietta et al. 2018).
For much of the 20th century, this species was assigned to Dynamena cornicina (=Sertularia cornicina Mc-
Crady, 1859). The actual identity of Dy. cornicina is ambiguous at present, however, and its binomen is now taken
to be a nomen dubium. McCrady’s (1859) original description of the species, from Charleston Harbor, South Caro-
lina, USA, was lacking in detail, no illustrations of it were provided, and no types are known to exist. His account
applies equally to two abundant species in the Charleston area (Calder 1991a), Di. disticha and Amphisbetia distans
(=Dynamena distans Lamouroux, 1816). As for hydroids assigned to Dy. cornicina auct. during the period, most are
taken to have been identical with Di. disticha rather than A. distans. Specimens identified as Sertularia cornicina
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 31
from Charleston exist in collections at the MCZ (MCZ IZ 175, MCZ IZ 176), but they were collected by Louis
Agassiz rather than John McCrady (Adam Baldinger, personal communication, 15 April 2021). The identity of S.
cornicina may therefore be suspected, but not unequivocally proven, from those collections.
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay, Coconut Point (Cooke 1977, as Dyna-
mena cornicina).—Kauai: Nawiliwili main dock, concrete pier pilings; Port Allen main dock, concrete pier pilings
(Coles et al. 2004, as Dy. cornicina).—Molokai: Kaunakakai Harbor main dock, main pier, concrete pier pilings
(Coles et al. 2004, as Dy. cornicina).—Maui: Kahului Harbor, Pier 1, concrete pilings (Coles et al. 2004, as Dy.
cornicina).
Elsewhere. Reported to be circumglobal in shallow waters, from tropical to temperate zones (Calder 2013).
Genus Pasya Stechow, 1922
Pasya heterodonta (Jarvis, 1922), comb. nov.
Fig. 9d–g
Pasythea heterodonta Jarvis, 1922: 344, pl. 24 figs 11A–B, 12.
Type locality. Republic of Mauritius: Cargados (=Cargados Carajas Shoals), 24 fm (44 m) (Jarvis 1922).
Voucher material. Pearl & Hermes Atoll, on calcareous rubble, 28.ix.2002, three colonies, to 9 mm high, with-
out gonothecae, coll. A. Faucci, ROMIZ B5436.—Midway Atoll, on Halimeda sp., 20.ix.2002, one colony, 8 mm
high, without gonothecae, coll. A. Faucci, ROMIZ B5437.—Pearl & Hermes Atoll, 19.ix.2002, three colony frag-
ments, 8.5 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5438.—Pearl & Hermes Atoll, on calcareous
rubble, 19.ix.2002, one colony, 8 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5485.—Kure Atoll, on
calcareous rubble, 25.ix.2002, five colonies or colony fragments, to 9 mm high, with gonothecae, ROMIZ B5491.
Remarks. Pasya heterodonta (Jarvis, 1922) resembles the much better-known P. quadridentata (Ellis & Solan-
der, 1786) in having stacked hydrothecal pairs on the stems (Fig. 9e, f). It differs, however, in having stacked pairs
only at the extreme distal ends the cauli. Indeed, such groups are sometimes entirely lacking in present material,
likely occurring in younger and earlier developmental stages of a given caulus. While gonothecae of the two species
are fundamentally alike, suggestive of a close relationship, those of P. heterodonta appear to have fewer and less
pronounced ridges. Grouping of hydrothecal pairs may occasionally occur as well in P. obliqua (Lamouroux, 1816),
but hydrothecae of that species are more swollen and internodes are much shorter and stouter.
In reporting P. heterodonta from Moorea, French Polynesia, Vervoort & Vasseur (1977, as Dynamena heter-
odonta) provided a description and illustrations of type material of the species. Unlike in P. quadridentata, hydrothe-
cae were said to have a longer free portion that curved away from the internode, the operculum was more acute,
and intrathecal cusps were well-developed. Similar differences in hydrothecal morphology had convinced Billard
(1925) earlier to recognize P. heterodonta as distinct from P. quadridentata. Gibbons & Ryland (1989) acknowl-
edged the distinct appearance of two equivalent morphotypes from Fiji, but nevertheless questioned the validity P.
heterodonta. They suggested that perceived differences might not exceed the range of morphological variability
within P. quadridentata. Given its distinct morphology, including the relative paucity of contiguous hydrothecal
groups and their limitation to the distal end of the stems, P. heterodonta is taken here to be a species of the tropical
Indo-Pacific, distinct from P. quadridentata (type locality: “...coast of Africa, not far from the island of Ascension”).
Pasya heterodonta has also been recognized recently as valid by Galea (2016, as Dynamena heterodonta) in mate-
rial from Indonesia.
Cauli of P. heterodonta lacking stacked pairs of hydrothecae closely resemble those of both Thuiaria maldiv-
ensis Borradaile, 1905 and Sertularia borneensis Billard, 1925. Given their similarity, Schuchert (2003) suspected
that the latter two might be conspecific. While gonothecae of T. maldivensis are still undescribed, Gibbons & Ryland
(1989) and Schuchert (2003) provided descriptions and illustrations of gonothecae of S. borneensis based on speci-
mens from Verde Island, the Philippines, and the Kei Islands, Indonesia, respectively. They differ from those of P.
heterodonta in being strongly ridged. Moreover, Gibbons and Ryland noted the existence of two lateral horns that
arose from a distal gonothecal collar, as in species assigned to Tridentata Stechow, 1920 (type species S. perpusilla
Stechow, 1919b).
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As for Pasya Stechow, 1922, the genus has recently been resurrected as valid (Calder 2013) given the genetic
distance of its type species, Sertularia quadridentata (Ellis & Solander, 1786), from that of Sertularia pumila
Linnaeus, 1758, type species of a currently polyphyletic genus Dynamena Lamouroux, 1816. The extent of their
separation is apparent in phylograms such as those of Moura et al. (2011) and Song (2019). Pasya was proposed by
Stechow (1922) as a replacement name for use in Hydrozoa of Pasythea Lamouroux, 1812 (type species: Cellaria
tulipifera Ellis & Solander, 1786), now restricted to Bryozoa. Tuliparia de Blainville, 1830 has the same type spe-
cies (Stechow 1922) and is a junior objective synonym of Pasythea.
Development of the intrathecal cusps varied considerably within colonies of P. heterodonta examined here (Fig.
9d–f). Disparities in their development were noted earlier by Billard (1925) and are apparent in illustrations of the
species by Galea (2016: fig. 1L, N). Only slight variations in cusp development were noted by Vervoort & Vasseur
(1977).
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. French Polynesia: Tuamotu Archipelago, Gambier Island (Billard 1905, as Sertularia gracilis).—
Indonesia: Makassar Strait, 2°25ʹS, 117°43ʹE; E of Sumbawa, 34–36 m, Billard 1925, as Dynamena heterodonta).—
New Caledonia: Ile des Pins (Redier 1966, as D. heterodonta; Gravier Bonnet 2007, as D. heterodonta).—South
Africa (Millard 1975, as Dynamena quadridentata, in part, Fig. 87H).—Moorea (Vervoort & Vasseur 1977, as
D. heterodonta).—Fiji (Gibbons & Ryland 1989, as D. quadridentata, type B).—Indonesia: Arafura Sea (Galea
2016).
Genus Salacia Lamouroux, 1816
Salacia tetracythara Lamouroux, 1816
Fig. 9h, i
Salacia tetracythara Lamouroux, 1816: 214, pl. 6 fig. 3a, B, C [correct original spelling].
Salacia tetracyttara Lamouroux, 1816: 553 [incorrect original spelling].
Thuiaria fenestrata.—Nutting, 1905: 950.
Type locality. Australasia? (Lamouroux 1816).
Voucher material. Lisianski Island, 01.x.2002, two colonies, to 3.4 cm high, one with gonothecae, coll. A. Faucci,
ROMIZ B5429.—Pearl & Hermes Atoll, 28.ix.2002, three colonies, to 5.5 cm high, without gonothecae, coll. A.
Faucci, ROMIZ B5430.—Laysan Island, 18.ix.2002, one colony, 1.5 cm high, without gonothecae, coll. A. Faucci,
ROMIZ B5431.—Kure Atoll, detached, 25.ix.2002, one colony, 2.3 cm high, without gonothecae, coll. A. Faucci,
ROMIZ B5432.—Laysan Island, 17.ix.2002, two colonies, to 5.2 cm high, without gonothecae, coll. A. Faucci,
ROMIZ B5433.
Remarks. As shown in the synonymy list above, the specific name of this species was spelled two different
ways (as tetracythara and tetracyttara) in the original work by Lamouroux (1816). Rees & Vervoort (1987: 103),
Acting as First Revisers (ICZN 1999, Art. 24.2.3), selected tetracythara as correct. Cornelius (1975: 381) noted that
Salacia tetracythara Lamouroux, 1816 is the type species, by monotypy, of the genus Salacia Lamouroux, 1816.
He provided a historical account of the synonymy of the genus and species, and noted that its type was destroyed
during World War II. Billard (1909b) had earlier examined the type and found that it corresponded well with Thui-
aria fenestrata Bale, 1884 from Australia. The two are now widely considered conspecific, and the account of Bale
(1884) facilitates identification of the species. Also taken to be a synonym is Calyptothujaria opposita von Campen-
hausen, 1896 from Ternate, Indonesia.
Salacia and Thuiaria Fleming, 1828 have at times been regarded as congeners (Stechow 1922, 1923c; Rees
& Thursfield 1965; Cornelius 1979), although they are currently held to be distinct (Cornelius 1995b; Hirohito
1995; Bouillon et al. 2006; Song 2019). A key difference in terms of morphology is the presence of an abcauline
diverticulum or caecum (Millard 1975, fig. 81A) in Thuiaria and its absence in Salacia. A molecular analysis of
S. tetracythara, needed to clarify relationships of Salacia, have yet to be undertaken. Sertularia desmoides Torrey
1902, subjectively assigned at present to the same genus, has been shown to be genetically distant from Thuiaria
thuja (Moura et al. 2011; Maronna et al. 2016; Song 2019), the type species of Thuiaria.
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 33
Salacia tetracythara is widely distributed across the tropical and subtropical Indo-Pacific region (Rees & Ver-
voort 1987), and it has recently been reported from Brazil in the Atlantic Ocean (Mendonça et al. 2021). The hy-
dranth and modified tentacles of this hydroid were studied and described by Gravier-Bonnet (2008).
Reported Distribution. Hawaiian archipelago. Laysan Island: north of the island, 20 fathoms (37 m) (Nutting
1905, as Thuiaria fenestrata).—Maui: NE of the island, 14 fathoms (26 m) (Nutting 1905, as T. fenestrata).
Elsewhere. Tropical and subtropical Indo-Pacific, from the Mozambique Channel and the Gulf of Aden to Ha-
waii (Lamouroux 1816; Billard 1909b, as Thuiaria tetracythara; Pennycuik 1959; Mammen 1965; Rees & Vervoort
1987; Gibbons & Ryland 1989; Hirohito 1995; Watson 2000; Schuchert 2003; Gravier-Bonnet 2007, 2008; Di Ca-
millo et al. 2008; Gravier-Bonnet & Bourmaud 2012; Preker & Lawn 2012; Song 2019).—Atlantic Ocean, Brazil
(Mendonça et al. 2021).
Genus Tridentata Stechow, 1920
Tridentata loculosa (Busk, 1852)
Fig. 10a, b
Sertularia loculosa Busk, 1852: 393.
Sertularia ligulata.—Cooke, 1977: 97, fig. 24.—Coles et al., 2002a: 318.
Tridentata ligulata.—Coles et al., 2002b: 177.
Tridentata loculosa.—Carlton & Eldredge, 2009: 39.—Calder, 2020: 221, fig. 6f.
Type locality. Australia: Bass Strait, 45 fm (82 m) (Busk 1852, as Sertularia loculosa).
Voucher material. Midway Atoll, 23.ix.2002, five colony fragments, to 1.3 cm high, with gonothecae, coll.
A. Faucci, ROMIZ B5434.—Gardner Pinnacles, on calcareous rubble, 14.ix.2002, one colony, 4 mm high, without
gonothecae, coll. A. Faucci, ROMIZ B5435.
Remarks. DNA sequences are as yet unavailable for Tridentata loculosa (Busk, 1852), and its genetic affinities
remain uncertain. Following previous work (Calder 2013, 2020), it has been assigned temporarily here to Tridentata
Stechow, 1920 given the general resemblance of its trophosome and gonosome to species of that genus (including
its type species, Sertularia perpusilla Stechow, 1919b). Its indistinct marginal cusps, markedly dissimilar upper and
lower opercular valves, and presence of a ligula (an intrathecal modification of the mantle, resembling a nemato-
phore), set it apart from them. In particular, the taxonomic significance of the ligula is uncertain. Given its unusual
characters, Hirohito (1974) suggested that a new genus might be warranted for the species, but later (Hirohito 1995)
retained it in Sertularia Linnaeus, 1758 following Vervoort & Vasseur (1977). With respect to its generic name, this
species bears little morphological resemblance to Sertularia argentea Linnaeus, 1758, type species of Sertularia.
Thus, it can certainly be excluded from that genus (Calder 2013, 2020), where it has usually been assigned.
Taxonomic reviews of T. loculosa were provided by Migotto (1996, as Sertularia loculosa) and Calder (2013).
Of note, Sertularia ligulata Thornely, 1904 was shown by Billard (1927) to be conspecific with S. loculosa. Al-
though widely distributed and possibly circumglobal in tropical and subtropical waters, this species has not been
recorded to date in the eastern Pacific Ocean. Colonies examined here from Midway Atoll (ROMIZ B5434), col-
lected during September 2002, bore gonothecae.
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay, 2 m, on Porites lobata (Cooke 1977,
as Sertularia ligulata); Kaneohe Bay, Waiahole Reef (Coles et al. 2002a, as S. ligulata; Calder 2020); Waikiki,
Aquarium Outside Reef, 3 m (Coles et al. 2002b, as Tridentata ligulata); Waikiki, Atlantis wreck, 20–30 m (Coles
et al. 2002b, as T. ligulata).
Elsewhere. Warm waters of the Indian Ocean (Millard 1975, as S. ligulata), western and central Pacific (Hiro-
hito 1995, as S. ligulata; Schuchert 2003, as S. ligulata; Calder 2020), and western and eastern Atlantic (Vervoort
1959, as S. ligulata; Calder 2013).
Tridentata orthogonalis (Gibbons & Ryland, 1989), comb. nov.
Fig. 10c
Sertularia orthogonalis Gibbons & Ryland, 1989: 423, fig. 38A–D.
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Type locality. Fiji: Viti Levu, Pacific Harbor, Ndeumba Island, Ndeumba fringing reef (Gibbons & Ryland 1989,
as Sertularia orthogonalis).
Voucher material. Laysan Island, 18.ix.2002, one colony, 6 mm high, without gonothecae, coll. A. Faucci,
ROMIZ B5439.—Laysan Island, on Halimeda sp. and unattached, 17.ix.2002, four colonies or colony fragments,
6–14 mm high, with gonothecae, coll. A. Faucci, ROMIZ B5440.
Remarks. Tridentata orthogonalis (Gibbons & Ryland, 1989), comb. nov., originally described from Fiji, is
a morphologically striking but little-known species. To date, the only other published records of it are those Coles
et al. (2003, as Sertularella orthogonalis) from American Samoa and Hewitt & Campbell (2010, as Sertularia or-
thogonalis) from Australia.
FIGURE 10. Sertulariidae and Symplectoscyphidae. a, Tridentata loculosa (Bale, 1852), part of hydrocaulus with two
hydrothecal pairs, Midway Atoll, ROMIZ B5434. Scale equals 0.2 mm. b, Tridentata loculosa (Bale, 1852), gonotheca, Mid-
way Atoll, ROMIZ B5434. Scale equals 0.2 mm. c, Tridentata orthogonalis (Gibbons & Ryland, 1989), part of hydrocaulus
with two hydrothecal pairs, Laysan Island, ROMIZ B5440. Scale equals 0.2 mm. d, Tridentata rugosissima (Thornely, 1904),
part of hydrocaulus with one hydrothecal pair, Laysan Island, ROMIZ B5489. Scale equals 0.1 mm. e, Tridentata turbinata
(Lamouroux, 1816), part of hydrocaulus with two hydrothecal pairs, Pearl & Hermes Atoll, ROMIZ B5444. Scale equals 0.1
mm. f, Tridentata turbinata (Lamouroux, 1816), gonotheca, Pearl & Hermes Atoll, ROMIZ B5444. Scale equals 0.2 mm. g,
Bicaularia tongensis (Stechow, 1919b), part of hydrocaulus with two hydrothecae, Midway Atoll, ROMIZ B5445. Scale equals
0.1 mm.
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Gibbons & Ryland (1989) noted the general resemblance of their hydroid to Sertularia tongensis Stechow,
1919b from Tonga. They distinguished it from that species in that each hydrotheca has an abcauline intrathecal
ridge and three distinct intrathecal cusps. Colonies from Laysan Island conform well with the original account of S.
orthogonalis and have been identified as such here. Based on characters of both the trophosome and gonosome of
the species, it has been transferred in this work from Sertularia Linnaeus, 1758 to Tridentata Stechow, 1920.
As for S. tongensis, it somewhat resembles S. borneensis Billard, 1925a, and was considered a questionable
synonym of that species by Schuchert (2003). In turn, S. borneensis was considered conspecific with Tridentata
maldivensis (Borradaile, 1905) by Calder (2010), although it now seems better to maintain them as separate spe-
cies until their gonosomes can be compared and their genetic affinities determined. Galea (2010) assigned the
replacement name Sertularia ephemera to S. tongensis, considering it referable to the same genus as Sertularella
tongensis Stechow, 1919b, a different species. However, the latter hydroid is now assigned to Bicaularia Song, Lyu,
Ruthensteiner, Wang & Gravili, 2019, and homonymy between Sertularella tongensis (=Bicaularia tongensis) and
Sertularia tongensis (=Tridentata tongensis) no longer exists.
This report extends the known distribution of T. orthogonalis to the central North Pacific Ocean.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Fiji (Gibbons & Ryland 1989, as Sertularia orthogonalis); American Samoa (Coles et al. 2003, as
Sertularella orthogonalis); Australia (Hewitt & Campbell 2010, as Sertularia orthogonalis).
Tridentata rugosissima (Thornely, 1904)
Fig. 10d
Sertularia rugosissima Thornely, 1904: 118, pl. 2 fig. 4.
Sertularia subtilis.—Cooke, 1977: 97, fig. 25.—Carlton & Eldredge, 2009: 39.
Tridentata humpferi.—Coles et al., 2002a: 318; 2002b: 177, 234 [incorrect subsequent spelling].
Tridentata hupferi.—Carlton & Eldredge, 2009: 39.
Tridentata rugosissima.—Calder, 2020: 222, fig. 6g.
Type locality. Sri Lanka: “Gulf of Manaar” (=Gulf of Mannar), on algae (Thornely 1904, as Sertularia rugosissima).
Material examined. Laysan Island, on Halimeda sp., 17 ix.2002, one colony, 4.5 mm high, without gonothe-
cae, coll. A. Faucci, ROMIZ B5489.
Remarks. An account of Tridentata rugosissima (Thornely, 1904) from Hawaiian waters has been provided
earlier (Calder 2020). The species has been reported there several times from locations around the island of Oahu
(Cooke 1977, as Sertularia subtilis; Coles et al. 2002a, as Tridentata humpferi; Coles et al. 2002b, as T. humpferi;
Calder 2020).
Hydroids of T. rugosissima are morphologically distinctive in having hydrothecal walls ringed by about 12 or
more transverse ridges. Also present are distinct abcauline and less distinct adcauline intrathecal cusps. Subjective
synonyms of the species, based on studies by Migotto (1996), include Sertularia hupferi Broch, 1914 from Ghana,
S. subtilis Fraser, 1937b from Puerto Rico, and Geminella subtilis Vannucci Mendes, 1946 from Brazil.
While reported from the Indo-Pacific, central Pacific, and both eastern and western Atlantic, genetic compari-
sons of widely separated populations of hydroids assigned to T. rugosissima are warranted. Also needed is confir-
mation of the generic identity of the species, based to date only on morphology (Stechow 1923c; Calder & Choong
2018; Calder 2020). Assigning it to Sertularia Linnaeus, 1758, as in most works to date (including WoRMS), is
clearly incorrect because T. rugosissima is morphologically remote from Sertularia argentea Linnaeus, 1758, type
species of that genus. It has been referred here to Tridentata Stechow, 1920 based on characters of both the tropho-
some and the gonothecae, which generally conform with those of the type species of the genus, Sertularia perpusilla
Stechow, 1919b. Vannucci Mendes (1946, as Geminella subtilis) appears to have been first in describing the gono-
theca of T. rugosissima.
Reported Distribution. Hawaiian archipelago. Oahu: Kahe Point reef, 2 m, on coral rubble (Cooke 1977, as
Sertularia subtilis); Kaneohe Bay, Pristine Reef (Coles et al. 2002a, as Tridentata humpferi; Calder 2020); Waikiki,
Canoes (Coles et al. 2002b, as T. humpferi); Waikiki, Kapua Channel, 5 m (Coles et al. 2002b, as T. humpferi);
Waikiki, Kaiser’s Channel (Coles et al. 2002b, as T. humpferi); Hawaii Kai, Channel Marker 1, Maunalua Bay, 4 m
(Coles et al. 2002b, as T. humpferi).
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Elsewhere. Indian Ocean (Thornely 1904, 1916, as Sertularia rugosissima; Millard & Bouillon 1973, as S. hup-
feri); western Pacific (Jäderholm 1919, as S. rugosissima; Cooke 1975, as S. subtilis; Yamada & Kubota 1987, as S.
rugosissima; Gibbons & Ryland 1989, as S. hupferi); western Atlantic (Fraser 1937b, as S. subtilis; Migotto 1996,
as S. rugosissima; Calder & Kirkendale 2005, as Tridentata. subtilis; Galea 2008, as S. rugosissima; Oliveira et al.
2016, as S. rugosissima; Miglietta et al. 2018, as S. rugosissima); eastern Atlantic (Broch 1914, as S. hupferi).
Tridentata turbinata (Lamouroux, 1816)
Fig. 10e, f
Dynamena turbinata Lamouroux, 1816: 180.
Tridentata turbinata.—Coles et al., 2002b: 177.—Carlton & Eldredge, 2009: 39.—Calder, 2020: 224, fig. 6h, i.
Type locality. Australasia: on “Fucus” (Lamouroux 1816, as Dynamena turbinata).
Voucher material. Laysan Island, on Halimeda sp., 18.ix.2002, two colonies or colony fragments, to 6 mm
high, without gonothecae, coll. A. Faucci, ROMIZ B5441.—Laysan Island, on Halimeda sp., 17.ix.2002, one col-
ony, 5 mm high, with gonothecae, coll. A. Faucci, ROMIZ B5442.—Laysan Island, on Halimeda sp., 17.ix.2002,
three colonies or colony fragments, to 3.5 mm high, with gonothecae, coll. A. Faucci, ROMIZ B5443.—Pearl &
Hermes Atoll, on Macrorhynchia philippina, 19.ix.2002, one colony, 6 mm high, with gonothecae, coll. A. Faucci,
ROMIZ B5444.
Remarks. The hydroid Tridentata turbinata (Lamouroux, 1816) is widespread and relatively well-known in
shallow, tropical to subtropical waters. Worldwide, it has been reported from the Pacific, Atlantic, and Indian oceans
(Redier 1971, as Sertularia turbinata; Millard 1975, as S. turbinata; Rees & Vervoort 1987, as S. turbinata; Gibbons
& Ryland 1989, as S. turbinata; Calder 1991a, 2020; Hirohito 1995, as S. turbinata; Migotto 1996, as S. turbinata;
Medel & Vervoort 1998, as S. turbinata; Schuchert 2003, as S. turbinata; Humara-Gil & Cruz-Gómez 2018).
In terms of relationships, the molecular phylogenies of Maronna et al. (2016), Song (2019), and Galea & Mag-
gioni (2021) combine T. turbinata in a clade with T. marginata (Kirchenpauer, 1864), T. tumida (Allman, 1877), and
T. perpusilla (Stechow, 1919b), with the last of these being the type species of the genus Tridentata Stechow, 1920.
Added to that clade by Galea & Maggioni was Sertularia trigonostoma Busk, 1852. In another clade relatively close
to them are species here assigned to Disertasia Neppi, 2017, including Dynamena crisioides Lamouroux, 1824,
Sertularia disticha Bosc, 1802 and S. moluccana Pictet, 1893. In a series of clades more distant from them in the
phylograms are Sertularia pumila Linnaeus, 1758, type species of Dynamena Lamouroux, 1812, S. operculata Lin-
naeus, 1758, type species of Amphisbetia L. Agassiz, 1862, and Sertularia argentea Linnaeus, 1758, type species of
Sertularia Linnaeus, 1758.
Discussion of the hydroid T. turbinata in Hawaiian waters has been given elsewhere (Calder 2020). In being a
predominantly shallow-water species, it was not reported by Nutting (1905) in collections from mostly deep waters
of the state by the United States Bureau of Fisheries steamer Albatross.
Reported Distribution. Hawaiian archipelago. Oahu: Waikiki, Outside Pop’s, 6 m (Coles et al. 2002b); Waiki-
ki, Atlantis Submarine site, 20 m (Coles et al. 2002b); Waikiki, Ala Wai buoy (Coles et al. 2002b); Waikiki, Kapua
Channel, 5 m (Coles et al. 2002b).—Maui: Molokini outer rim (Calder 2020).
Elsewhere. Circumglobal in shallow, tropical and subtropical waters (Calder 2019, 2020).
Family Symplectoscyphidae Maronna, Miranda, Peña Cantero, Barbeitos & Marques, 2016
Genus Bicaularia Song, Lyu, Ruthensteiner, Wang & Gravili, 2019
Bicaularia tongensis (Stechow, 1919b)
Fig. 10g
Sertularella tongensis Stechow, 1919b: 89, figs F1, G1.—Coles et al., 2002a: 318.—Carlton & Eldredge, 2009: 38.
Bicaularia tongensis.—Calder, 2020: 217, fig. 5c, d.
Type locality. Kingdom of Tonga: Tonga Islands (Stechow 1919b).
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 37
Voucher material. Midway Atoll, on a bryozoan, 23.ix.2002, one colony, 3.5 mm high, without gonothecae,
coll. A. Faucci, ROMIZ B5445.—Laysan Island, on Halimeda sp., 17.ix.2002, one colony, 5 mm high, with gono-
thecae, coll. A. Faucci, ROMIZ B5446.
Remarks. A taxonomic account of Bicaularia tongensis (Stechow, 1919b) in Hawaii has been given earlier
(Calder 2020). New records of the species from the region are added here from Midway Atoll and Laysan Island.
A thorough account of this species, accompanied by a synonymy list, has been provided by Song (2019) and
Song et al. (2019).
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay, Moku Manu Island (Coles et al. 2002a, as
Sertularella tongensis; Calder 2020).
Elsewhere. Indo-Pacific; Caribbean Sea; Mediterranean Sea (Song et al. 2019). If Sertularella exilis Fraser,
1938 is conspecific, the species also occurs in the eastern Pacific (Fraser 1938, 1948).
Family Plumulariidae McCrady, 1859
Genus Monotheca Nutting, 1900
Monotheca flexuosa (Bale, 1894)
Fig. 11a
Plumularia flexuosa Bale, 1894: 115, pl. 5 figs 6–10.
Monotheca flexuosa.—Calder, 2020: 225, fig. 7d–f.
Type locality. Australia: Victoria, “mouth of Snowy River and Cape Lefebvre” (Bale 1894, as Plumularia flex-
uosa).
Voucher material. Kure Atoll, on algae, 26.ix.2002, one colony, 2.5 mm high, without gonothecae, coll. A.
Faucci, ROMIZ B5447.
Remarks. Originally described from Australia, Monotheca flexuosa (Bale, 1894) was recently reported in the
central North Pacific from the main Hawaiian Islands of Oahu and Maui (Calder 2020). While its overall distribu-
tion is still uncertain, Watson (2011a) suspected that the species might be cosmopolitan.
In having slender colonies and cup-shaped hydrothecae with essentially straight margins, M. flexuosa resembles
M. margaretta Nutting, 1900, the type species of Monotheca Nutting, 1900. Unlike in M. margaretta, however, its
stems are more flexuous, lateral nematothecae appear sessile rather than pedicellate, and hydrothecae lack a median
adaxial notch. Another similar species is M. pulchella (Bale, 1881), but its stem is robust with stronger perisarcal
ridges, and hydrocladia arise midway along much shorter cauline internodes (Bale 1894; Watson 2011a). As for M.
obliqua (Johnston, 1847), its margin is more sinuous, and female gonothecae appear to be smooth (Cornelius 1995b)
rather than transversally ridged, as in M. margaretta (Calder 1997), or smooth to faintly undulated, as in M. flexuosa
(Watson 2011a).
Evidence for recognition of Monotheca as distinct from Plumularia Lamarck, 1816 has been made elsewhere
on the basis of both morphology (Calder 1997) and genetics (Moura et al. 2018). Species currently assigned to the
genus are small and often epiphytic, although M. obliqua, M. flexuosa, M. margaretta, and M. bergstadi Gil & Ra-
mil, 2021 are or appear to be substrate generalists (Watson 2011a; Gravili et al. 2015; Calder 2019; Gil & Ramil,
2021).
Reported Distribution. Hawaiian archipelago. Oahu: Palea Point, just outside Hanauma Bay, 8 m (Calder
2020).—Maui: Kanaio, 12 m (Calder 2020).
Elsewhere. Australia (Watson 2011a); Japan (Hirohito 1974, as Monotheca flexiosa); New Zealand (Vervoort &
Watson 2003, as M. pulchella); ?South Africa (Stechow 1925; Millard 1975, as M. pulchella); ?Strait of Gibraltar
(Medel & Vervoort 1995, as M. pulchella); ?Vema Seamount (Millard 1966b, as M. pulchella).
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FIGURE 11. Plumulariidae. a, Monotheca flexuosa (Bale, 1894), part of hydrocaulus with two hydrocladia, each with a
hydrotheca, Kure Atoll, ROMIZ B5447. Scale equals 0.1 mm. b, Monotheca gibbosa, sp. nov., holotype, part of hydrocaulus
with hydrocladia and three hydrothecae, Laysan Island, ROMIZ B5448. Scale equals 0.1 mm. c, Monotheca gibbosa, sp. nov.,
holotype, part of hydrocaulus, and a hydrocladium with one hydrotheca, Laysan Island, ROMIZ B5448. Scale equals 0.05 mm.
d, Plumularia floridana (Nutting 1900), part of hydrocaulus with bases of two hydrocladia, one with two hydrothecae, Gard-
ner Pinnacles, ROMIZ B5449. Scale equals 0.1 mm. e, Plumularia strictocarpa Pictet, 1893, part of hydrocaulus with bases
of two hydrocladia, one with two hydrothecae, Kure Atoll, ROMIZ B5453. Scale equals 0.1 mm. f, Plumularia strictocarpa
Pictet, 1893, part of hydrorhiza, and proximal end of hydrocaulus with a gonotheca, Kure Atoll, ROMIZ B5453. Scale equals
0.2 mm.
Monotheca gibbosa, sp. nov.
Figs 11b, c, 12
Plumularia margaretta.—Cooke, 1977: 100, fig. 27 (not Monotheca margaretta Nutting, 1900).
Type locality. USA: Hawaii, Laysan Island, at SCUBA depth, on calcareous rubble.
Etymology. The specific name is derived from the Latin adjective gibbus, meaning “bulging”, “protuberant”,
or “hunpbacked”, in allusion to the prominent hump at the base of the hydrotheca.
Voucher material. HOLOTYPE: Laysan Island, on a small piece of calcareous rubble, 18.ix.2002, three frag-
ments of a colony, to 2 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5448.
PARATYPE: Laysan Island, on algae, 18.ix.2002. two colonies or colony fragments, to 2 mm high, without gono-
thecae, coll. A. Faucci, ROMIZ B5492.
Description. Colonies minuscule, inconspicuous, with erect cormoids reaching 2 mm high, arising from a
creeping hydrorhiza having occasional internal perisarcal spurs in its lumen. Hydrocaulus monosiphonic, strongly
geniculate distal to a straight pedicellate base of varied length, unbranched, divided at regular intervals into long,
slender, ahydrothecate internodes by distinct, transverse nodes; cauline internodes relatively straight, 180–230 µm
long beyond basal region, 19–25 µm wide at nodes, with firm perisarc and internal perisarcal ridges at proximal and
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 39
distal ends, each internode with one nematotheca in axil of a distal apophysis and one about midway on internode on
side opposite apophysis. Apophyses with a mamelon and a distal perisarcal ridge, given off alternately from oppo-
site sides of hydrocaulus, bearing short, unbranched hydrocladia each with a single distal hydrotheca. Hydrocladia
140–190 µm long, with one proximal athecate internode and a longer distal thecate internode; nodes nearly straight;
athecate internodes short, lacking nematothecae, 35–40 µm long, narrowest proximally, widest distally, with a dis-
tal perisarcal ridge; thecate internodes 120–150 µm long, saddle-shaped in lateral view, each with a hydrotheca, a
median inferior nematotheca, two lateral nematothecae, and usually with three internal perisarcal ridges beneath
hydrotheca, terminating in a blunt and short central point between lateral nematothecae, ending proximal to adaxial
wall of hydrothecal orifice. Nematothecae bithalamic, movable, conical; cauline nematothecae 45 µm long; median
nematothecae 30–40 µm long, not reaching base of hydrotheca, rim sloping only slightly downwards from abaxial
to adaxial wall; lateral nematothecae 35–45 µm long, arising from slight lateral bulges at distal end of internode, not
reaching hydrothecal orifice. Hydrothecae prostrate, with base elevated on raised subhydrothecal chamber of inter-
node, creating a prominent basal hump, proportionately deep, with maximum depth 125–145 µm, slender and cy-
lindrical but with a pronounced U-shaped bend, perisarc firm relative to thecal size; adaxial wall concave, adnate to
internode except free at distal end; abaxial wall strongly convex except becoming strongly concave below margin;
rim nearly circular, entire, facing obliquely upwards, aperture diameter 65–67 µm; base with a ring of desmocytes;
intrathecal ridge lacking.
Gonothecae not seen.
FIGURE 12. Plumulariidae. Monotheca gibbosa, sp. nov., holotype, Laysan Island, ROMIZ B5448. a, part of colony, with
hydrorhiza, hydrocaulus, six hydrocladia, and six hydrothecae. b, distal end of hydrocaulus, with four hydrocladia and four
hydrothecae. c, distal end of hydrocaulus, with hydrocladium and a hydrotheca.
Remarks. Monotheca gibbosa, sp. nov., is immediately distinguishable from all other species currently as-
signed to Monotheca Nutting, 1900 in the distinctive shape of its hydrothecae. These are proportionately elongate,
slender, and bent in the shape of a curved cylinder, with the abaxial wall having a prominent basal hump. In this,
they somewhat resemble an inchworm (caterpillar of a geometrid moth) in motion. By contrast, hydrothecae in
other species of the genus, namely M. obliqua (Johnston, 1847), M. australis (Kirchenpauer, 1876), M. hyalina
(Bale, 1881), M. pulchella (Bale, 1881), M. spinulosa (Bale, 1881), M. flexuosa (Bale, 1894), M. margaretta Nut-
ting, 1900, M. posidoniae Picard, 1951, M. togata Watson, 1973, M. amphibola Watson, 2011a, M. bergstadi Gil
& Ramil, 2021, are shaped like a cup, bowl, scoop, cowl, or bonnet. Also differing in the same way are other spe-
cies that have been assigned at times to Monotheca, including Plumularia excavata (Mulder & Trebilcock, 1911),
P. crateriformis (Mulder & Trebilcock, 1911), P. vervoorti (Leloup, 1971), P. epibracteolosa Watson 1973, and P.
meretricia Watson, 1973. More closely resembling hydrothecae of M. gibbosa are those of Plumularia goldsteini
Bale, 1881. However, each hydrocladium in that species bears 3–4 hydrothecae rather than one, and the aperture of
the hydrotheca is vertical rather than oblique in orientation.
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Other noteworthy characters also set M. gibbosa apart from its congeners. For example, there are no abaxial and
adaxial flanges on the hydrothecae, as in M. amphibola. Thecate internodes of the species end in an inconspicuous
point, while those of M. spinulosa terminate in a prominent spine (Bale 1881; Watson 2011a). Hydrothecae lack
an intrathecal ridge, such as that present in both M. australis and M. spinulosa. Nematothecae are not adaxially
excavated like those in M. spinulosa and M. togata, and median nematothecae are neither adaxially excavated nor
immovable as in M. australis and M. amphibola (Watson 2011a). The hydrothecal rim is entire rather than being
indented by a median adaxial notch as in M. margaretta. Characters of the gonothecae are also of value in distin-
guishing species of Monotheca, but those of M. gibbosa are as yet unknown.
Although described here as a new species, this is the second report of M. gibbosa from Hawaii. Cooke (1977)
reported it, as Plumularia margaretta, from red algae (Amansia sp.) on the Kahe Point Reef, Oahu. As noted above,
the Atlantic M. margaretta differs in having hydrothecae that are cup-shaped and shallow rather than being elongate
and in the form of a curved cylinder.
Hydroid colonies of M gibbosa are exceptionally minuscule and inconspicuous. Of all the species in a genus
having diminutive cormoids, it is perhaps the smallest. Colonies described here were only 2 mm in height, and spec-
imens reported from Kahe Point Reef, Oahi, by Cooke (1977, as M. margaretta) were likewise 1–2 mm high. Other
species of Monotheca with colonies less than 5 mm high include M. togata and M. amphibola (Watson 2011a). The
largest colonies of the genus appear to be those of M. obliqua, which can reach 4 cm high (Gravili et al. 2015).
Although most species of Monotheca are believed to be epiphytic (Watson 2011a), hydroids of M. gibbosa
examined here occurred on a fragment of calcareous rubble as well as on algae. Of 11 species recognized in the
genus in this work (M. obliqua, M. australis, M. hyalina, M. spinulosa, M. pulchella, M. flexuosa, M. margaretta,
M. posidoniae, M. togata, M. amphibola, and M. bergstadi), only four appear to be substrate generalists. The pre-
dominantly European M. obliqua has been reported from algae, sponges, hydroids, bryozoans, cirripedes, and rocks
(Cornelius 1995b; Gravili et al. 2015). In the Pacific, M. flexuosa has been found on red and green algae, mussels,
ascidians, and polychaete tubes (Watson 2011a). The common Atlantic hydroid M. margaretta has most often been
observed on algae (e.g., Sargassum, Turbinaria) and seagrasses (Thalassia), but it also occurs on invertebrates and
inanimate substrates (Galea 2010, as Plumularia margaretta; Mendoza-Becerril et al. 2018; Calder 2019). The re-
cently described M. bergstadi was found on algae and a bryozoan (Gil & Ramil 2021).
Reported Distribution. Hawaiian archipelago. Oahu: Kahe Point Reef (Cooke 1977, as Plumularia margaretta).
Genus Plumularia Lamarck, 1816
Plumularia floridana Nutting, 1900
Fig. 11d
Plumularia floridana Nutting, 1900: 59, pl. 2 figs 4, 5.—Coles et al., 2002a: 318; 2004: 73; 2006: 492.—Carlton & Eldredge,
2009: 36.—Calder, 2020: 226, fig. 7g.
Plumularian hydroid.—Edmondson, 1946: 26, fig. 13d.
Type locality. USA: Florida, 3.2 km west of Cape Romano (Nutting 1900).
Voucher material. Gardner Pinnacles, on rubble, 14.ix.2002, one colony, 4.5 mm high, without gonothecae,
coll. A. Faucci, ROMIZ B5449.
Remarks. Plumularia floridana Nutting, 1900 was originally described from the Atlantic Ocean off the south-
west coast of Florida (Nutting 1900). From identifications based on morphology, the species has subsequently been
reported worldwide in shallow tropical to temperate waters, including Hawaii (Calder 2020). Cryptic diversity likely
exists in hydroids assigned that binomen. With molecular work needed to sort out the taxonomy of this morphotype,
current usage of the name P. floridana has been maintained for the colony from Gardner Pinnacles examined here.
Information on hydroids identified as P. floridana are provided in works such as those by Calder (1997, 2019,
2020), Ansín Agís et al. (2001), and Calder et al. (2021).
Reported Distribution. Hawaiian archipelago. Oahu: Waikiki Reef, underside of stones (Edmondson 1946,
as “plumularian hydroid”); Kaneohe Bay, Hakipuu Reef Flat (Coles et al. 2002a); Kaneohe Bay, Waiahole Reef
(Calder 2020).—Island of Hawaii, Kawaihae Reef, just seaward of Kawaihae Harbor (Coles et al. 2004, 2006); Red
Hill (Coles et al. 2006).
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 41
Elsewhere. Circumglobal in the neritic zone of tropical, subtropical, and temperate waters (Ansín Agís et al.
2001; Calder 2020).
Plumularia strictocarpa Pictet, 1893
Fig. 11e, f
Plumularia strictocarpa Pictet, 1893: 55, pl. 3 figs 47–49.—Coles et al., 2002a: 318; 2002b: 177, 234; 2004: 73; 2006: 492.—
Carlton & Eldredge, 2009: 36.—Calder, 2020: 228, fig. 7h–j.
Plumularia setacea.—Cooke, 1977: 101, fig. 28.—Bailey-Brock, 1989: 591.—Carlton & Eldredge, 2009: 36 [not Plumularia
setacea (Linnaeus, 1758)].
Type locality. Indonesia: Ambon Bay; shallow water (Pictet 1893).
Voucher material. Midway Atoll, on rubble, 23.ix.2002, three colonies or colony fragments, to 1.3 cm high,
with developing gonothecae, coll. A. Faucci, ROMIZ B5450.—Laysan Island, 18.ix.2002, four colonies or colony
fragments, to 2.5 cm high, without gonothecae, coll. A. Faucci, ROMIZ B5451.—Laysan Island, on Halimeda sp.,
17.ix.2002, one colony, 2.5 cm high, without gonothecae, coll. A. Faucci, ROMIZ B5452.—Kure Atoll, on Halim-
eda sp., 25.ix.2002, three colonies or colony fragments, to 6 mm high, with gonothecae, coll. A. Faucci, ROMIZ
B5453.
Remarks. In terms of morphology, Plumularia strictocarpa Pictet, 1893 can be difficult to separate from P.
setacea (Linnaeus, 1758), with the latter being taxonomically important as the type species of Plumularia Lamarck,
1816 (International Commission on Zoological Nomenclature 1998, Opinion 1886). While colonies of P. stricto-
carpa are typically smaller and finer, the two species are most readily distinguished by their gonosomes. Fertile
colonies from Kure and Midway atolls were therefore helpful in establishing identifications, with gonothecae of
specimens examined here conforming with those of P. strictocarpa. Thus, they were typical of the species in being
cocoon-shaped with spirally annulated walls (Fig. 11f), instead of being fusiform with a tubular neck and smooth
walls, as in P. setacea. They also differed from gonothecae of the similar P. warreni Stechow, 1919b, which lack
annulated walls (Millard 1975). Notably, these three species fall within the same clade in DNA barcoding studies
(Moura et al. 2018), but were considered “likely good biological species” by Schuchert (2014).
Originally described from Ambon Bay, Indonesia (Pictet 1893), P. strictocarpa has been widely reported across
the tropical and subtropical Pacific Ocean. The species has been reported to be circumglobal in distribution (Calder
2020), although evidence of genetic diversity now exists (Schuchert 2014; Moura et al. 2018). Schuchert identi-
fied at least two and possibly three distinct lineages in specimens from locations in the Indian (Mayotte, Maldives),
Pacific (French Polynesia), and Atlantic (Brazil) oceans. Moura et al. concluded that these constitute three putative
species.
Identifications from this study confirm the occurrence of P. strictocarpa in the Hawaiian region, and it is likely
common in occurrence there. As implied earlier (Calder 2020), reports of the temperate P. setacea from Hawaii have
probably been based on misidentifications of P. strictocarpa.
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay, on a variety of substrates (Cooke 1977,
as Plumularia setacea); 2.4 km off SE coast, 20 m, on PVC settlement plates (Bailey-Brock 1989, as P. setacea);
Kaneohe Bay, North Channel (Coles et al. 2002a); Kaneohe Bay, Pristine Reef (Coles et al. 2002a); Kaneohe Bay,
“Floating City” (Coles et al. 2002a); Kaneohe Bay, Moku Manu Island (Coles et al. 2002a); Waikiki, Canoes, 3.5
m (Coles et al. 2002b); Waikiki, Ala Wai buoy (Coles et al. 2002b); Waikiki, Kaiser’s Channel (Coles et al. 2002b);
Hawaii Kai, Maunalua Bay, Channel Marker 1 (Coles et al. 2002b); Hawaii Kai, Maunalua Bay, Koko Marina
nearshore, 1.5 m (Coles et al. 2002b); Palea Point, just outside Hanauma Bay, 8 m (Calder 2020).—Maui, Maalaea
Reef, near Maalaea Harbor (Coles et al. 2004).—Island of Hawaii, Red Hill (Coles et al. 2006).
Elsewhere. Reportedly circumglobal, tropical and subtropical waters (Pictet 1893; Millard & Bouillon 1973;
Hirohito 1974, 1995; Millard 1975; Ryland & Gibbons 1991; Migotto 1996; Calder 1997, 2013, 2020; Calder et al.
2003; Kirkendale & Calder 2003; Coles et al. 2003; Calder & Kirkendale 2005; Galea & Ferry 2015; Oliveira et al.
2016).
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Family Kirchenpaueriidae Stechow, 1921
Genus Pycnotheca Stechow, 1919b
Pycnotheca producta (Bale, 1881)
Fig. 13a
Plumularia producta Bale, 1881: 39, pl. 15 fig. 3.
Type locality. Australia: Victoria, Queenscliff (Bale 1881).
Voucher material. Laysan Island, on algae, 13.ix.2002, four colonies or colony fragments, to 6 mm high, with-
out gonothecae, coll. A. Faucci, ROMIZ B5481.
Remarks. The generic name Pycnotheca Stechow, 1919b was proposed as a replacement name for Diplochei-
lus Allman, 1883, an invalid junior homonym of Diplocheilus van Hasselt & Temminck, 1823 (Pisces). The type
species of the genus, by subsequent designation by Stechow (1923c: 215), is Diplocheilus mirabilis Allman, 1883.
Molecular phylogenetic studies (Maronna et al. 2016; Moura et al. 2018) confirm the close phylogenetic relation-
ship of Pycnotheca to kirchenpaueriid genera including Kirchenpaueria Jickeli, 1883 and Oswaldella Stechow,
1919a.
Watson (1990) provided a review of characters useful in distinguishing the three currently recognized species
of Pycnotheca. Pycnotheca mirabilis (Allman, 1883) differs from P. producta (Bale, 1881) and P. biseptata (Black-
burn, 1938) in having stems that are longer (up to 35 mm rather than to 10–15 mm), hydrocladia that arise at a more
acute angle and are both long and flexuous rather than short and stiffer, hydrothecae that are decidedly scoop-shaped
rather than jug- or bowl- shaped, and gonothecae that are large and usually erect rather than small and typically
adherent to the hydrorhiza or substrate. In life, hydranths of P. producta were said by Watson to be a luminescent
bluish–white in colour. Pycnotheca biseptata differs from both P. mirabilis and P. producta in having a rudimentary
septal ridge passing from the hydrocladial internode into the adcauline wall of the hydrotheca. Watson also provided
measurements of major morphological characters of each species. In terms of substrate preferences, P. mirabilis was
reported by Vervoort & Watson (2003) to be predominantly an epizoite and P. producta an epiphyte. Nonetheless,
Vervoort & Watson noted that differences between P. producta and P. mirabilis were not clearly resolved. If the two
should prove conspecific, the name P. producta was described first and would have nomenclatural priority. Based
on Watson’s (1990) characterization of the three species, specimens from Laysan most closely correspond with P.
producta and have been assigned to that species here.
The geographic distribution of P. producta is uncertain because it and P. mirabilis may have been confused in
some works (Watson 1990). To date, the species has been reported from locations in both the western and eastern
Pacific, although the report of it from California by Torrey (1902, as Halicornaria producta) needs confirmation.
If P. mirabilis is conspecific, the range of the species is extended to many locations across the Indo-west Pacific
(Ansín Agís et al. 2014), as well as to False Bay, South Africa (Millard 1957), Vema Seamount (Millard 1966b), and
Brazil (Oliveira et al. 2016) in the Atlantic.
The publication of Bale (1881) in which P. producta was first described is usually dated as 1882. Evidence ex-
ists that it appeared as a separate in 1881 (see comment in References section).
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Australia (Bale 1881, as Plumularia producta; Watson 1990, 1997); Japan (Inaba 1892, as P. pro-
ducta); ? California, USA (Torrey 1902, Halicornaria producta).
Family Halopterididae Millard, 1962
Genus Antennella Allman, 1877
Antennella cf. secundaria (Gmelin, 1791)
Fig. 13b–d
Sertularia secundaria Gmelin, 1791: 3854.
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 43
Antennella secundaria.—Coles et al., 2002a: 318; 2002b: 177; 2004: 73.—Carlton & Eldredge, 2009: 36.
Monostaechas quadridens.—Calder, 2020: 230, fig. 8h, i [not Monostaechas quadridens (McCrady, 1859)].
Type locality. “Habitat in mari mediterraneo” (Gmelin 1791, as Sertularia secundaria).
Voucher material. Midway Atoll, on algae, 23.ix.2002, one unbranched colony, 3 mm high, without gono-
thecae, coll. A. Faucci, ROMIZ B5454.—Midway Atoll, 23.ix.2002, one branched colony, 6.5 mm high, without
gonothecae, coll. A. Faucci, ROMIZ B5455.—Kure Atoll, on algae, 25.ix.2002, one unbranched colony, 4 mm high,
without gonothecae, coll. A. Faucci, ROMIZ B5456.—Nihoa, 06.x.2002, two branched colonies or colony frag-
ments, to 6 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5457.
Remarks. Originally described from the Mediterranean Sea, Antennella secundaria (Gmelin, 1791) has now
been reported numerous times from tropical to temperate waters worldwide (Cornelius 1995b). This is reflected in
the extensive distribution records and lengthy synonymy list of the species provided by Ansín Agís et al. (2001). It
nevertheless appears certain now that cryptic species exist in hydroids assigned to A. secundaria, with multiple lin-
eages having been distinguished through barcoding sequences (Moura et al. 2018, 2019). Indeed, Cornelius (1995b)
had suspected, based on observed morphological differences, that more than one species was represented under the
name. Given their wide separation geographically, hydroids from the Hawaiian Islands may well be distinct from
those of the Mediterranean. However, with the current taxonomy of A. secundaria being unsettled, traditional no-
menclature has been maintained here.
Of multiple cryptic species identified by Moura et al. (2018) within the A. secundaria complex, one lineage,
conjointly with A. confusa Ansín Agís, Ramil & Vervoort, 2001, clustered with the genus Monostaechas Allman,
1877. Differences between Antennella Allman, 1877 and Monostaechas therefore need to be explored, and if valid
the two genera may need to be redefined. If congeneric, precedence would have to be established according to the
First Reviser Principle in nomenclature (ICZN 1999, Art. 24.2) inasmuch as they were described in the same work
by Allman (1877). As for the species A. secundaria and Monostaechas quadridens, little doubt exists that they are
distinct.
While hydroids of A. secundaria are usually unbranched and arise directly from the hydrorhiza, occasional
colonies of the species are branched in the form of a helicoid sympodium. Accounts of the branched form have
been given in various works including those of Billard (1913), Van Gemerden-Hoogeveen (1965), Millard & Bouil-
lon (1973), Millard (1975), Vervoort & Vasseur (1977), Ryland & Gibbons (1991), Calder (1997), and Schuchert
(2003). Both unbranched (ROMIZ B5454; ROMIZ B5456) and branched (ROMIZ B5455; ROMIZ B5457) colo-
nies were represented in the present collection.
In a previous paper on hydroids from the main islands of Hawaii (Calder 2020), branched colonies of A. se-
cundaria were misidentified as M. quadridens. Indeed, several records of M. quadridens in the Pacific and Indian
oceans may likewise have been based on such misidentifications. Accounts of M. quadridens from the vicinity of its
type locality near Charleston, South Carolina, USA, indicate that branching in the species is extensive and differs in
typically being truly dichotomous. In it, the basal hydrocaulus usually gives rise to a pair of opposite and upward-
directed branches, with the continuation of the main stem often similarly re-branched (Nutting 1900; Calder 1983).
Branches are then re-branched in the form of a helicoid sympodium. Colonies of the species attain a height of as
much as 15 cm (Nutting 1900; Fraser 1944) and are light mahogany in colour. By contrast, the number of branches
in colonies of A. secundaria, if there are any at all, are almost always limited to four or fewer (Ryland & Gibbons
1991), colonies seldom reach 5 cm high, and the colour is greenish-yellow to red (Cornelius 1995b; Gravili et al.
2015).
Nomenclaturally, the type species of Antennella Allman, 1877, by monotypy, is A. gracilis Allman, 1877. It, in
turn, has been considered a junior subjective synonym of A. secundaria. That putative synonymy may need reas-
sessment in light of the genetic diversity discovered in this morphospecies.
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay, North Channel (Coles et al. 2002a); Pris-
tine Reef (Coles et al. 2002a; Calder 2020, as Monostaechas quadridens); Waikiki, Outside Pop’s, scoured reef, 6
m (Coles et al. 2002b); Waikiki, Atlantis submarine artificial reef, 20 m (Coles et al. 2002b); Waikiki, Ala Wai buoy
(Coles et al. 2002b); Waikiki, Kapua Channel, 5 m (Coles et al. 2002b).—Molokai: Kaunakakai Harbor main dock
(Coles et al. 2004).
Elsewhere. Considered cosmopolitan in temperate to tropical waters (Millard 1975; Ansín Agís et al. 2001), but
this is likely subject to revision.
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FIGURE 13. Kirchenpaueriidae and Halopterididae. a, Pycnotheca producta (Bale, 1881), part of a hydrocladium with two
hydrothecae, Laysan Island, ROMIZ B5481. Scale equals 0.1 mm. b, Antennella secundaria (Gmelin, 1791), part of hydro-
caulus with two hydrothecae, Midway Atoll, ROMIZ B5454. Scale equals 0.1 mm. c, Antennella secundaria (Gmelin, 1791),
part of a colony to show branching, Midway Atoll, ROMIZ B5455. Scale equals 0.5 mm. d, Antennella secundaria (Gmelin,
1791), part of hydrocaulus, and base of a hydrocladium with a hydrotheca, Midway Atoll, ROMIZ B5455. Scale equals 0.1 mm.
e, Halopteris alternata (Nutting, 1900), part of a hydrocladium with two hydrothecae, Laysan Island, ROMIZ B5458. Scale
equals 0.1 mm. f, Halopteris alternata (Nutting, 1900), part of hydrocaulus, with a cauline hydrotheca and proximal end of a
hydrocladium, Laysan Island, ROMIZ B5458. Scale equals 0.1 mm g, Halopteris longibrachia, nom. nov., part of a hydrocla-
dium with two hydrothecae, Gardner Pinnacles, ROMIZ B5459. Scale equals 0.1 mm. h, Halopteris longibrachia, nom. nov.,
female gonotheca, Pearl & Hermes Atoll, ROMIZ B5461. Scale equals 0.1 mm. i, Halopteris longibrachia, nom. nov., part of
hydrocaulus with a male gonotheca, Gardner Pinnacles, ROMIZ B5459. Scale equals 0.1 mm.
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 45
Genus Halopteris Allman, 1877
Halopteris alternata (Nutting, 1900)
Fig. 13e, f
Plumularia alternata Nutting, 1900: 62, pl. 4 figs 1, 2.
Halopteris diaphana.—Cooke, 1977: 99, fig. 26.—Carlton & Eldredge, 2009: 36 [not Halopteris diaphana (Heller, 1868)].
Halopteris diaphena.—Coles et al., 2004: 73 [incorrect subsequent spelling; not Halopteris diaphana (Heller, 1868)].
Type locality. Bahamas: Barracuda Rocks (Nutting 1900: 62, as Plumularia alternata).
Voucher material. Laysan Island, on hydroid stem, 18.ix.2002, two colonies or colony fragments, to 8 mm
high, without gonothecae, coll. A. Faucci, ROMIZ B5458.
Remarks. Hydroids examined here were referable to Halopteris Allman, 1877, and to the “H. diaphana” species
group recognized within that genus by Schuchert (1997). Included in the group by him were H. diaphana (Heller,
1868), H. tenella (Verrill, 1873b), H. alternata (Nutting, 1900), H. billardi (Vannucci, 1951), and H. platygonotheca
Schuchert, 1997. Halopteris violae Calder et al. 2003 has subsequently been assigned to the same group. Within that
assemblage, specimens examined here from Laysan Island are closest to H. alternata. Characters distinguishing the
species from others in the cluster have been reviewed by Schuchert (1997) and Calder et al. (2019).
For much of the 20th century, H. alternata was included in the synonymy of H. diaphana. Confusion over the
status of two species was addressed and resolved by Schuchert (1997). He resurrected H. alternata as valid based
on its distinctive trophosomal and gonosomal characters. DNA barcoding has confirmed that the two are distinct
species (Moura et al. 2018; Galea et al. 2018). In H. alternata, an axillar nematotheca is usually present behind each
cauline hydrotheca, one nematotheca rather than two or three is present on the athecate hydrocladial internodes, and
female gonothecae are fusiform and mostly straight rather than cornucopia-shaped. Additional characters distin-
guishing the two were noted by Ansín Agís et al. (2001). In H. alternata, colonies were often found to be geniculate
rather than straight, especially in younger parts. Also, they found segmentation of the hydrocaulus to be homomer-
ous in basal parts but heteromerous in younger and apical parts, rather than being completely heteromerous as in
H. diaphana. Halopteris vervoorti Galea, 2008, another similar species, differs from H. alternata in having paired
rather than single cauline axillar nematothecae (Galea 2008; Galea et al. 2018; Calder 2020).
Halopteris alternata is widely distributed in warm parts of the western North Atlantic (Oliveira et al. 2016;
Calder 2019), and it has been reported as well from the eastern Atlantic (Ansín Agís et al. 2001). In the Pacific,
records of the species exist from Ecuador (Calder et al. 2019, 2021), and hydroids from Hawaii that have been iden-
tified earlier as the mostly European H. diaphana are taken here to have been based instead on H. alternata.
Obvious cryptic diversity has been identified within the H. alternata complex by Moura et al. (2018).
Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay (Cooke 1977, as Halopteris diaphana).—
Maui: Kahului Harbor, Pier 1 (Coles et al. 2004, as H. diaphena sic); Kahului Harbor, Pier 2 (Coles et al. 2004, as
H. diaphena sic).
Elsewhere. Western Atlantic (Oliveira et al. 2016; Calder 2019); eastern Atlantic (Ansín Agís et al. 2001); east-
ern Pacific (Calder et al. 2019, 2021); central Pacific (Cooke 1977, as Halopteris diaphana); possibly Indian Ocean
(Jarvis 1922, as Plumularia alternata; Gravely 1927, as Plumularia sp. nr. alternata).
Halopteris longibrachia, nom. nov.
Fig. 13g–i
Plumularia polymorpha var. sibogae Billard, 1913: 25, fig. 16.
Type locality. Indonesia: Raja Ampat, 1°42.5’S, 130°47.5’E, 32 m (Billard 1913).
Voucher material. Gardner Pinnacles, on rubble, 14.ix.2002, two colonies or colony fragments, to 1.5 cm high,
with gonothecae, coll. A. Faucci, ROMIZ B5459.—Gardner Pinnacles, on Macrorhynchia phoenicea, 14.ix.2002,
two colonies, to 7 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5460.—Pearl & Hermes Atoll, 19.ix.2002,
four colonies or colony fragments, to 1.7 cm high, one colony with female gonothecae, coll. A. Faucci, ROMIZ
B5461.
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Etymology. The replacement specific name longibrachia is derived from the Latin words longus, meaning
long, and brachium, meaning arm, in reference to the exceptionally long, arm-like lateral nematothecae that distin-
guish this species.
Remarks. Originally described as Plumularia polymorpha var. sibogae Billard, 1913, this species was recently
elevated to species rank by Galea et al. (2018), as Halopteris sibogae (Billard, 1913). The species is a morphologi-
cally striking one in having unusually long lateral nematothecae that extend well beyond the rim of the hydrothecae.
Other morphological differences setting it apart from H. polymorpha Billard, 1913 include an interesting colour
difference in living specimens (Galea et al. 2018). While hydranths of H. polymorpha are yellow everywhere, those
of the so-called H. sibogae are mostly yellow on the stems but white on the cladia. The distinctness of the species
has been further confirmed by 16S DNA sequences (Galea et al. 2018). It occurs in a clade well-separated from H.
polymorpha and close to H. vervoorti Galea, 2008.
Nomenclaturally, however, Plumularia polymorpha var. sibogae (=Plumularia sibogae; Halopteris sibogae)
is a permanently invalid junior primary homonym of Plumularia sibogae Billard, 1911, a different species now
assigned to Antennella Allman, 1877 (ICZN, 1999, Art. 57.2). With no available and potentially valid synonyms in
existence for the rejected junior primary homonym Plumularia sibogae, Halopteris longibrachia is proposed here
as a new replacement name for it.
Other halopteridids with exceptionally long lateral nematothecae and nematothecal apophyses include Corhiza
valdiviae (Stechow, 1925), assigned to the new genus Thamnopteros by Galea, in Galea & Maggioni, 2020, and
T. uniserius Galea, in Galea & Maggioni, 2020. However, colonies of the latter two differ greatly from those of H.
longibrachia in being much larger (to 40 cm in T. valdiviae; to 17.2 cm in T. uniserius; to 2.5 cm high in H. longibra-
chia) and in having polysiphonic stems (Stechow 1925; Millard 1975; Schuchert 1997, Galea, in Galea & Maggioni
2020). Other characters distinguishing T. valdiviae, reported from South Africa and Mozambique, are provided by
Stechow (1925), Millard (1975), and Schuchert (1997). Characters distinguishing T. uniserius, described from New
Caledonia, have been summarized by Galea, in Galea & Maggioni (2020). Halopteris infundibulum Vervoort, 1966
also has a pair of long lateral nematothecae, but adjacent to each one, at the base of the same apophysis, is a smaller,
much shorter nematotheca. Its hydrocladia differ in appearing essentially unsegmented. The species is known from
bathyal depths off New Zealand, the Chatham Islands, and New Caledonia (Vervoort 1966; Vervoort & Watson
2003; Ansín Agís et al. 2009).
Although H. longibrachia ranges at least from the Seychelles (Millard & Bouillon, 1973, as H. polymorpha var.
sibogae) to the Hawaiian Archipelago (this report), it has been reported infrequently. The type material of Billard
(1913, as Plumularia polymorpha var. sibogae) consisted of two colonies from Raja Ampat, Indonesia, collected
during the Siboga Expedition. Schuchert (1997, as H. polymorpha var. sibogae) examined those types, along with
specimens from the Seychelles reported by Millard & Bouillon. Horia Galea collected numerous fertile colonies
from two shipwrecks at Bali, Indonesia (Galea et al. 2018, as H. sibogae). Others examined in the same report were
found on a reef north of Hoga Island in the Tukang Besi Archipelago, Indonesia, by G. Allard. A record from Japan
by Hirohito (1983, as H. polymorpha var. sibogae) has been viewed with uncertainty (Galea et al. 2018). Specimens
examined here from the Northwestern Hawaiian Islands were found at Gardner Pinnacles and Pearl & Hermes
Atoll.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Western Pacific (Galea et al. 2018, as Halopteris sibogae); Indian Ocean (Millard & Bouillon 1973,
as H. polymorpha var. sibogae).
Family Aglaopheniidae Marktanner-Turneretscher, 1890
Genus Aglaophenia Lamouroux, 1812
Aglaophenia postdentata Billard, 1913
Fig. 14a
Aglaophenia postdentata Billard, 1913: 100, fig. 89A–C.
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 47
Type locality. Indonesia: Makassar and vicinity; Baie de Wunoh, NW de l’Île Waigeu (=Wunoh Bay, NW of Waigeo
Island) (Billard 1913).
Voucher material. Gardner Pinnacles, on Halimeda sp., 14.ix.2002, one colony, 2.6 mm high, without corbu-
lae, coll. A. Faucci, ROMIZ B5462.—Gardner Pinnacles, on Halimeda sp., 14.ix.2002, one colony, 2.0 mm high,
without corbulae, coll. A. Faucci, ROMIZ B5487.
Remarks. The hydroid of Aglaophenia postdentata Billard, 1913 is delicate, diminutive, and inconspicuous,
with the single sterile colony observed here reaching a height of only 2.6 mm. Colonies of the species are commonly
reported to be 5.0–8.5 mm high (Billard 1913; Jäderholm 1920; Vervoort 1941; Redier 1966; Millard & Bouillon
1973; Ryland & Gibbons 1991; Watson 2005; Moura 2020), although they are said to attain a height of about 1 cm
(Watson 1994b; Galea 2010).
Morphological accounts of this species include those of Billard (1913), Jäderholm (1920), Vervoort (1941),
Redier (1966), Millard & Bouillon (1973), Ryland & Gibbons (1991), Watson (1994b, 2005), Galea (2010), and
Moura (2020). The open corbula of the species has been described by Millard & Bouillon (1973), Watson (1994b),
and Moura (2020). Hydroid specimens examined by Watson (1994b) were yellow in life, with pink gonophores.
The hydrotheca of A. postdentata is small, with its distalmost adaxial quarter free from the internode. An
intrathecal ridge extends from the adaxial to the abaxial wall, and the ridge continues partway into the adjoining
internode in the examined specimen. Ten quite sharp cusps occur on the rim, comprising single abaxial and adaxial
cusps together with four laterals on each side. The adaxial cusp is prominent, unlike the shallow, broad equivalent
sometimes seen in the similar A. pluma var. sibogae Billard, 1913 (Schuchert 2003).
The center of distribution of this infrequently reported little species appears to be the tropical Indo-west Pacific
region. However, it is now known to be widely distributed (Moura et al. 2018, 2019). In addition to its discovery
in the central Pacific Ocean (this study), it has recently been reported from various locations in the Caribbean Sea
(Galea 2010; Moura et al. 2018, 2019), the Gulf of Guinea in the eastern Atlantic Ocean (Moura et al. 2018), and
from Brazil (Moura 2020). Of note, the molecular phylogenies of Moura et al. indicate that populations of the spe-
cies across its range are genetically quite close. However, such studies also reveal that A. postdentata is distant from
Sertularia pluma Linnaeus, 1758 (=Aglaophenia pluma), the type species of Aglaophenia Lamouroux, 1812. Based
on evidence from molecular phylogenetic studies, its inclusion in the genus has been justifiably questioned by Post-
aire et al. (2016b).
The reported depth distribution of the species is from 3 m (Moura et al. 2018) to 102 m (Moura 2020). In studies
undertaken at Juan de Nova Island, Gravier-Bonnet & Bourmaud (2006) found it to be a species of the reef platform
(< 20 m).
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Indo-west Pacific (Billard 1913; Jäderholm 1920; Vervoort 1941; Redier 1966; Millard & Bouillon
1973; Ryland & Gibbons 1991; Watson 1994b, 1996, 2005; Gravier-Bonnet & Bourmaud 2006, 2012; Moura et al.
2018); western Atlantic (Galea 2010; Moura et al. 2018; Moura 2020); eastern Atlantic (Moura et al. 2018).
Aglaophenia suensonii Jäderholm, 1896
Fig. 14b, c
Aglaophenia suensonii Jäderholm, 1896: 18, pl. 2 fig. 9.
Type locality. Japan: Hirudostrasse (=Hirado Strait), 33°10ʹN, 129°16ʹE (Jäderholm 1896).
Voucher material. Laysan Island, detached, 17.ix.2002, three unbranched, monosiphonic cormoids, to 2.4 cm
high, one with a corbula, coll. A. Faucci, ROMIZ B5463.
Remarks. Trophosomes of these hydroids conform most closely with accounts of Aglaophenia suensonii Jäder-
holm, 1896 by authors including Jäderholm (1896), Stechow (1909, 1913b, 1923c), Rho (1967), Hirohito (1995),
and Xu et al. (2014b). Corbulae resemble those in type material of the species in being moderately long, with about
11 pairs of fused corbulacostae. Jäderholm did not include an illustration of the corbula in describing A. suensonii,
but one was provided later by Stechow (1909: 91, fig. 6) based on an examination of the type. It was elongate, with
about 16 pairs of fused corbulacostae that lacked basal hydrothecae. Some subsequent illustrations of corbulae at-
tributed to the species have been shorter, with about 5–8 pairs of ribs (Stechow 1913; Rho 1967; Hirohito 1995).
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Aglaophenia suensonii somewhat resembles the temperate to boreal A. pluma (Linnaeus, 1758) of Europe and
possibly elsewhere (Svoboda & Cornelius 1991; Cornelius 1995b). It is distinguished by corbulae that reach to a
greater length (Stechow, 1923c), and by the shape of the marginal cusps of the hydrothecae. Unlike in A. pluma, the
median abaxial hydrothecal cusp in A. suensonii is turned sharply inwards and is partly hidden in lateral view by a
pair of large, arrowhead-shaped lateral cusps flanking it. In this, it approaches A. parvula Bale, 1881, but differs in
having nine rather than 10 marginal cusps. Moreover, the four pairs of lateral cusps are regularly wavy in shape and
are mostly similar in size, rather than being irregular in both shape and size as in A. parvula. As for A. pluma, it has
been considered a species complex based on 16S rRNA sequences by Moura et al. (2012, 2018, 2019).
Aglaophenia suensonii is a little-known species, reported elsewhere from warm waters of the western Pacific.
The specific name has been spelled suensoni in some works, but suensonii is the original and correct spelling (ICZN
1999, Art. 32.2).
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Southern Japan (Hirohito 1995); southern South Korea (Park 1995); East China Sea (Xu et al.
2014).
Aglaophenia whiteleggei Bale, 1888
Fig. 14d
Aglaophenia (?) whiteleggei Bale, 1888: 794, pl. 21 fig. 8.
Type locality. Unknown (Bale 1888); possibly Australia.
Voucher material. Pearl & Hermes Atoll, 28.ix.2002, two colonies, to 3.5 cm high, without corbulae, coll.
A. Faucci, ROMIZ B5464.—Midway Atoll, 23.ix.2002, one colony, 2 cm high, without corbulae, coll. A. Fau-
cci, ROMIZ B5465.—Kure Atoll, 25.ix.2002, one colony, 8 mm high, without corbulae, coll. A. Faucci, ROMIZ
B5466.—Laysan Island, detached, 17.ix.2002, one branched colony, 1.8 cm high, without corbulae, coll. A. Faucci,
ROMIZ B5467.
Remarks. The identity of Aglaophenia whiteleggei Bale, 1888 is somewhat in doubt. In describing this hy-
droid, Bale (1888) noted that the single, incomplete colony available to him was sterile, and its collection location
was unknown (“Hab.—?”). Subsequent reports of the species have been from Japan (Stechow 1913b, 1923a; Jäder-
holm 1919; Stechow & Uchida 1931; Uchida 1958; Hirohito 1969; 1983; 1995), China (Hargitt 1927, as Lytocarpus
nuttingi; Ling 1938, as L. nuttingi; Wei 1959; Huang 1988; Xu et al. 2014b), South Korea (Rho 1969; Rho & Park
1986), and Australia (Watson 1994a, 2011b). As for Lytocarpus nuttingi Hargitt, 1927, it has been included in the
synonymy of A. whiteleggei by Huang (1988), Vervoort & Watson (2003), and Xu et al. (2014). Concurrently, it is
accepted as a valid species (Macrorhynchia nuttingi) in WoRMS (Schuchert 2021c).
Ensuing descriptions of the reproductive structures of A. whiteleggei differ significantly. For example, Ste-
chow (1913b), Hargitt (1927, as Lytocarpus nuttingi), Rho (1969) and Hirohito (1995) described them as forming
an open corbula, as in certain species of Aglaophenia Lamouroux, 1812. By contrast, Watson (2011b) considered
them to be phylactogonia in her material, and she transferred the species to Macrorhynchia Kirchenpauer, 1872. In
her account, Watson neither cited records of the species from locations outside Australia nor mentioned any of the
earlier accounts of the reproductive structures of A. whiteleggei. She thus considered her description to be the first
account of them. Given material differences in these accounts, it appears certain that two different species have been
reported under the binomen A. whiteleggei. To establish the likely identity of the species, and of specimens from the
Northwestern Hawaiian Islands, accounts of the species by the various authors were compared here with the original
description of Bale (1888).
In terms of cormidial structure, specimens from the Northwestern Hawaiian Islands corresponded quite closely
with the accounts of Stechow (1913b), Ling (1938, as L. nuttingi), Hirohito (1995), and particularly Jäderholm
(1919). These all appear more like those described and illustrated by Bale (1888) than those of Watson (2011b), and
are taken here to represent A. whiteleggei. As with those multiple accounts, the outline of the hydrothecal margin
beyond the first pair of cusps is wavy to slightly crooked rather than distinctly cuspate, and the mesial nematotheca
diverges at an angle from the axial line of the hydrotheca over its distal third rather than following it. Marginal cusps
illustrated by Rho (1969) were as distinct as those in figures by Watson, but they differ in being pointed rather than
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blunt. While cormidia illustrated by Huang (1988) are close in morphology to those described here, the first pair of
cusps were low, with the largest pair being located midway along the lateral sides of the rim. Mesial nematothecae
were similar in shape, but were less divergent from the hydrothecae. The perisarc of the cormidia was illustrated
as being more thickened, but the overall pattern of the internodal ridges was essentially identical. As with material
examined here, the intrathecal ridge is shown to be incomplete by Bale (1888), Stechow (1913), Jäderholm (1919),
Rho (1969), Huang (1988), and Hirohito (1995), but complete in Ling (1938), Wei (1959), and Watson (2011).
However, that character may vary depending upon the age of the colony part examined. Otherwise, our cormidia
are much as described by Bale, Stechow, Jäderholm, Ling, Wei, Huang, and Hirohito. Specimens examined here
have therefore been assigned to A. whiteleggei. Nevertheless, the identity of the species warrants additional consid-
eration.
Watson (1911) concluded from collection records in the Australian Museum, Sydney, and Museum Victoria,
Melbourne, that the type material of Bale (1888) came from Port Jackson, Australia. Stranks (1993) had concluded
that different material from an unknown locality might be the type. We simply follow Bale (1888) in concluding that
the collection locality of A. whiteleggei is unknown.
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. Unknown location, possibly Australia (Bale 1888); South Korea (Rho 1969); Okinawa (Yamada &
Kubota 1987); Japan (Hirohito 1995); China (Huang 1988; Xu et al. 2014).
Genus Lytocarpia Kirchenpauer, 1872
Lytocarpia flexuosa (Lamouroux, 1816)
Fig. 14e
Aglaophenia flexuosa Lamouroux, 1816: 167.
Type Locality. “Indes Orientales” (Lamouroux 1816).
Voucher material. Pearl & Hermes Atoll, unattached, 19.ix.2002, two colonies, to 4.4 cm high, without corbu-
lae, coll. A. Faucci, ROMIZ B5479.
Remarks. Most records of Lytocarpia flexuosa (Lamouroux, 1816) to date have been from locations in the
western Indian Ocean (e.g., Billard 1907, as Thecocarpus giardi; Millard 1975, as T. flexuosus flexuosus; Gravier-
Bonnet 1979, as T. flexuosus; Rees & Vervoort 1987; Gravier-Bonnet & Bourmaud 2006). Rees & Vervoort (1987)
considered reports of the species from the East Indies by Lamouroux (1916, as Aglaophenia flexuosa) and from
Australia by Kirchenpauer (1872, as A. flexuosa) to be dubious inasmuch as it has not been recorded again from the
Tropical Western Pacific. Its discovery far to the east at Pearl & Hermes Atoll in this study may reduce some of the
doubt. The reported range of the species now extends from South Africa (Millard 1975) and the Red Sea (Mergner
& Wedler 1977) to the Northwestern Hawaiian Islands.
Considerable variation in colony form and hydrothecal morphology has been described in hydroids assigned to
L. flexuosa (Millard 1958, as T. giardi, 1962, as T. flexuosus, 1975, as T. flexuosus). In particular, branching of the
colony may be in the form of a spiral or an umbel. Hinge joints vary in location, and hydrocladia may be short or
long. The abcauline marginal cusp may be solid or hollow, and it may be simple or bifurcated. One pair or more of
the lateral cusps are usually bifid, but not always. The existence of intermediate forms led Millard (1962, 1975) to
regard the variants as subspecies of L. flexuosa.
Rees & Vervoort (1987: 175) provided a synonymy list for L. flexuosa. Included in it was Thecocarpus giardi
Billard, 1907 and, with question, Aglaophenia bifida Stechow, 1923b. They suspected that none of the various sub-
species of L. flexuosa recognized by Millard (1962, 1975), including T. flexuosus plumiferus (Kirchenpauer, 1872),
T. flexuosus solidus (Millard, 1958), and T. flexuosus umbellatus Millard 1962, would prove to be valid. Their ma-
terial most closely resembled that of the nominotypical subspecies, T. flexuosus flexuosus (Lamouroux, 1816). So,
too, do specimens examined here from Pearl & Hermes Atoll.
As for T. flexuosus plumiferus, Kirchenpauer (1872) spelled its original species-group name two ways, as
Aglaophenia plumifera in the text and as A. plumulifera in the figure captions. Under the Principle of the First
Reviser (ICZN 1999, Art. 24.2) in nomenclature, Bedot (1912: 252) cited the two names together and selected A.
plumifera as the correct original spelling.
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FIGURE 14. Aglaopheniidae. a, Aglaophenia postdentata Billard, 1913, part of a cladium with two hydrothecae, Gardner
Pinnacles, ROMIZ B5462. Scale equals 0.1 mm. b, Aglaophenia suensonii Jäderholm, 1896, part of a cladium with three hy-
drothecae, Laysan Island, ROMIZ B5463. Scale equals 0.1 mm. c, Aglaophenia suensonii Jäderholm, 1896, corbula, Laysan
Island, ROMIZ B5463. Scale equals 0.2 mm. d, Aglaophenia whiteleggei Bale, 1888, part of a cladium with two hydrothecae,
Pearl & Hermes Atoll, ROMIZ B5464. Scale equals 0.1 mm. e, Lytocarpia flexuosa (Lamouroux, 1816), part of a cladium with
three hydrothecae, Pearl & Hermes Atoll, ROMIZ B5479. Scale equals 0.1 mm. f, Lytocarpia phyteuma (Stechow, 1919b),
part of a cladium with two hydrothecae, Pearl & Hermes Atoll, ROMIZ B5468. Scale equals 0.1 mm. g, Macrorhynchia philip-
pina Kirchenpauer, 1872, part of a cladium with two hydrothecae, Midway Atoll, ROMIZ B5470. Scale equals 0.1 mm. h,
Macrorhynchia phoenicea (Busk, 1852), part of a cladium with three hydrothecae, Gardner Pinnacles, ROMIZ B5475. Scale
equals 0.1 mm. i, Macrorhynchia phoenicea (Busk, 1852), one phylactocarp, without gonothecae, Gardner Pinnacles, ROMIZ
B5475. Scale equals 0.2 mm.
HYDROIDS OF THE NW HAWAIIAN ISLANDS Zootaxa 5085 (1) © 2021 Magnolia Press · 51
In a study of hydroids on reefs at Juan de Nova Island, Gravier-Bonnet & Bourmaud (2006) found L. flexuosa
only on the outer slope at 30 m. While the substrate of that biotope comprised a large amount of dead stony corals, it
supported a diverse hydroid fauna of some 58 species. Specimens collected there occurred on hard substrates, algae,
and sessile benthic invertebrates. Aglaopheniids, with 16 species, were well-represented, as were solanderiids.
Hydroids of L. flexuosa were described by Lamouroux (1816) as having a shiny fawn colour (“couleur fauve
brillant”).
Reported Distribution. Hawaiian archipelago. First record.
Elsewhere. “East Indies” (Lamouroux 1816, as Aglaophenia flexuosa); Australia (Kirchenpauer, 1872, as A.
flexuosa); Madagascar (Billard 1907, as Thecocarpus giardi; Gravier-Bonnet 1979, as T. flexuosus); South Africa
(Millard 1975, as T. flexuosus flexuosus), including Agulhas Bank (Stechow 1923b, as Aglaophenia (?) bifida; Mil-
lard 1975, as T. flexuosus solidus); Mozambique (Millard 1975, as T. flexuosus flexuosus); Red Sea (Mergner &
Wedler 1977, as T. flexuosus var. flexuosus); Gulf of Aden (Rees & Vervoort 1987); Oman (Rees & Vervoort 1987);
Juan de Nova Island (Gravier-Bonnet & Bourmaud 2006).
Lytocarpia phyteuma (Stechow, 1919b)
Fig. 14f
Aglaophenia phyteuma Kirchenpauer, 1876: 23, 33 [nomen nudum].
Thecocarpus phyteuma Stechow, 1919b: 139, figs C2, D2.
Lytocarpia phyteuma.—Coles et al., 2002b: 90, 177.—Carlton & Eldredge, 1009: 36.
Type locality. Tonga (Stechow 1919b, as Thecocarpus phyteuma).
Voucher material. Pearl & Hermes Atoll, 19.ix.2002, one colony, 2.4 cm high, without gonophores, coll. A.
Faucci, ROMIZ B5468.—Pearl & Hermes Atoll, 19.ix.2002, two colonies or colony fragments, to 3.5 cm high, one
with a developing corbula, coll. A. Faucci, ROMIZ B5483.—Pearl & Hermes Atoll, 19.ix.2002, four colonies or
colony fragments, to 4.8 cm high, with corbulae, coll. A. Faucci, ROMIZ B5484.
Remarks. The hydroid examined here from Pearl & Hermes Atoll is essentially indistinguishable from ac-
counts of Lytocarpia phyteuma (Stechow, 1919b) by Stechow (1919b), Millard & Bouillon (1973), Watson (2000),
and Di Camillo et al. (2011). It also resembles the original descriptions of Thecocarpus leopoldi Leloup, 1930a
from West Papua, Indonesia, and especially Aglaophenia clavicula Whitelegge, 1899, from Funafuti, Tuvalu, both
now regarded as conspecific with L. phyteuma (Pennycuik 1959; Vervoort & Vasseur 1977; Watson 2000; Schuchert
2003; Vervoort & Watson 2003; Di Camillo et al. 2011). Watson (2000) and Di Camillo (2011) questioned the iden-
tity of hydroids from Moorea assigned to this species by Vervoort & Vasseur (1977) given their longer hydrothecae
and downward angle of the lateral nematothecae. In those characters they are also unlike the specimen examined
here.
The specific name of this species first appeared, as Aglaophenia (Calathophora) phyteuma, in a work by Kirch-
enpauer (1876: 23, 33). It is therefore almost universally credited to him in current literature on hydroids. No-
menclaturally, however, Kirchenpauer provided neither a description, nor an illustration, nor an “indication” to
accompany the name (Calder & Brinckmann-Voss 2011), rendering it a nomen nudum (ICZN, 1999, Art. 12.1),
indistinguishable from a group of 12 other associated species in his work. The name was first made available by
Stechow (1919b), as Thecocarpus phyteuma, in an examination of Kirchenpauer’s material. Both the trophosome
and the corbula of the species were described and illustrated in that work by Stechow. In having a hydrotheca at the
base of each rib, this species is referable under current hydrozoan classification to Lytocarpia Kirchenpauer, 1872.
Thecocarpus Nutting, 1900, a name utilized by Stechow and by many others long after, is an objective junior syn-
onym of Lytocarpia in that the type species of both genera is Sertularia myriophyllum Linnaeus, 1758. Lytocarpus,
another name often encountered in older literature, is an unjustified emendation of Lytocarpia introduced by Allman
(1883). It was accompanied by a redefinition that created taxonomic confusion by altering the concept of the genus
(Calder 1997).
In not having been made nomenclaturally available until the work of Stechow (1919b), the familiar binomen
Aglaophenia phyteuma is threatened by Aglaophenia clavicula Whitelegge, 1899, a little-known senior subjective
synonym. In the interests of nomenclatural stability, Reversal of Precedence provisions under the code (ICZN 1999,
Art. 23.9) have been applied here to preserve current usage. Thus, while the senior synonym (A. clavicula) has been