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The register of global extinctions of marine invertebrates in historical time is updated. Three gastropod and one insect species are removed from the list of extinct marine species, while two gastropods, one echinoderm, and three parasites (a nematode, an amphipod, and a louse) are added. The nine extinct marine invertebrates now recognized likely represent a minute fraction of the actual number of invertebrates that have gone extinct. Urgently needed for evaluation are inventories of globally missing marine invertebrates across a wide range of phyla. Many such species are likely known to systematists, but are either rarely flagged, or if mentioned, are not presented as potentially extinct taxa.

Cirrholovenia tetranema Kramp, 1959 (Figure 5b) Cirrholovenia tetranema Kramp, 1959: 253, fig. 17a, b [medusa]. Egmundella amirantensis Millard and Bouillon, 1973: 40, fig. 5 [hydroid]. Type Locality: Solomon Islands: 9°25.416667° ʹ S, 160°E 29 m (Kramp 1959). Material examined Wafer Bay, 5.54535, −87.06185, 1 colony, on a hydroid stem, 0.25 mm high, without gonothecae, coll. G. Ashton, #240629. Remarks This hydroid has been widely reported across shallow tropical marine waters of the world, mostly as Lafoeina amirantensis (Millard and Bouillon, 1973). It was linked to the medusa Cirrholovenia tetranema Kramp, 1959 in life cycle studies by Migotto and Cabral (2005). Brinckmann (1965) had raised the polyp stage of the medusa even before the hydroid was described and named by Millard and Bouillon (1973). However, no nematothecae were observed on the hydrorhiza of her hydroids and she considered it to be referable to Cuspidella Hincks, 1866. Moreira (1975) also undertook life cycle studies on the species by rearing planulae from known medusae, but did not attempt an identification of the polyp stage. Cirrholovenia tetranema is a minute hydrozoan, with hydroids less than 0.5 mm high and medusae reaching 1.5 mm high and wide (Kramp 1961, 1968). Originally described from medusae collected in the Tropical Western Pacific (Solomon Islands, Strait of Malacca, Gulf of Thailand, the Philippines and Indonesia) (Kramp 1959), both stages of the species have now been reported from warm waters of the Atlantic, Pacific and Indian oceans (Migotto and Cabral 2005). In the Tropical Eastern Pacific, the hydroid has been reported from the Galápagos Islands and from the coast of mainland Ecuador (Calder et al. 2003, as L. amirantensis; 2019, 2021). Its range is extended here to Cocos Island, and it will likely be found elsewhere in the region. The medusa has yet to be reported from the Eastern Pacific. In concert with its status in the Galapagos Islands (Carlton et al. 2019), we treat C. tetranema as cryptogenic on Cocos Island. Reported distribution Cocos Island: first record. Elsewhere: considered essentially circumglobal, in tropical and warm-temperate waters (Migotto and Cabral 2005; Calder et al. 2019, 2021)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 579-581, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Kramp PL. 1959. Some new and little-known Indo-Pacific medusae. Videnskabelige Meddelelser fra Dansk Naturhistorisk Forening. 121: 223 - 259.","Millard NAH, Bouillon J. 1973. Hydroids from the Seychelles (Coelenterata). Annales du Musee Royal de l'Afrique Centrale, serie In- 8 ° Sciences Zoologiques. 206: 1 - 106.","Migotto AE, Cabral AS. 2005. Lafoeina amirantensis (Cnidaria: Hydrozoa, Campanulinoidea), the hydroid stage of the medusa Cirrholovenia tetranema (Cnidaria: hydrozoa, Lovenelloidea). Zootaxa. 919: 1 - 16. doi: 10.11646 / zootaxa. 919.1.1","Brinckmann A. 1965. The life cycle of the medusa Cirrholovenia tetranema Kramp 1959 (Leptomedusae, Lovenellidae) with a hydroid of the genus Cuspidella Hincks. Can J Zool. 43: 13 - 15. doi: 10.1139 / z 65 - 002","Hincks T. 1866. On new British Hydroida. Ann Mag Nat Hist Ser. 3 (18): 296 - 299. doi: 10.1080 / 00222936608679646","Moreira GS. 1975. Sobre duas Leptomedusae do litoral do estado de Sao Paulo. Ciencia e Cultura. 27: 556 - 558.","Kramp PL 1961. Synopsis of the medusae of the world. Journal of the Marine Biological Association of the United Kingdom. 40: 1 - 469. doi: 10.1017 / S 0025315400007347","Kramp PL. 1968. The hydromedusae of the Pacific and Indian oceans. Dana Rep. 72: 1 - 200.","Calder DR, Mallinson JJ, Collins K, Hickman CP. 2003. Additions to the hydroids (Cnidaria) of the Galapagos, with a list of species reported from the islands. J Nat Hist. 37: 1173 - 1218. doi: 10.1080 / 00222930110116039","Carlton JT, Keith I, Ruiz GM. 2019. Assessing marine bioinvasions in the Galapagos Islands: implications for conservation biology and marine protected areas. Aquat Invasions. 14: 1 - 20. doi: 10.3391 / ai. 2019.14.1.01","Calder DR, Carlton JT, Larson K, Mallinson JJ, Choong HHC, Keith I, Ruiz GM. 2019. Hydroids (Cnidaria, Hydrozoa) from marine fouling assemblages in the Galapagos Islands, Ecuador. Aquat Invasions. 14: 21 - 58. doi: 10.3391 / ai. 2019.14.1.02"]}

Macrorhynchia philippina Kirchenpauer, 1872 (Figure 7c) Macrorhynchia philippina Kirchenpauer, 1872: 19. Aglaophenia philippina Kirchenpauer, 1872: 45, text-fig. p. 17; pl. 1, fig. 26; pl. 2, fig. 26a, b; pl. 7, fig. 26. Type locality Philippines: Manila (Kirchenpauer 1872). Material examined Chatham Bay, dock 004, no coordinates, 1 colony, 3 cm high, without reproductive structures, coll. G. Ashton, #266335. Remarks The reported geographic distribution of Macrorhynchia philippina Kirchenpauer, 1872 in the eastern Pacific Ocean extends from Gull Island, southern California, USA, and the Gulf of California, Mexico, to southern Ecuador (Fraser 1947, 1948). It has been widely reported within that range, with collections from Mexico (White Friars, Morro de Petatlán, Tenacatita Point, islands off Navidad Head, Ildefonso Island, Tres Marias Island, San Lorenzo Channel, Guaymas Bay), Costa Rica (South Viradores Islands), Panama (Bahia Honda, Secas Islands), Colombia (Gorgona Island, Port Utria), coastal Ecuador (Santa Elena Bay, La Plata Island, San Francisco Bay, La Libertad), and the offshore Galápagos Islands (Isabela, Española, Santa Cruz, San Cristóbal, Marchena, Santiago) (Fraser 1938a, 1938b, 1938c, 1948; Calder et al. 2003). In the Galápagos, it is one of the most conspicuous hydroids in the upper 10 m on exposed coastal bottoms of the warmer eastern islands, usually occurring with Pennaria disticha Goldfuss, 1820 (D. Calder, personal observations, 16–22 June 2001). Its occurrence on Cocos Island thus coincides with the known distribution of the species across the Tropical Eastern Pacific Realm. Elsewhere, M. philippina is taken to be essentially circumglobal in shallow tropical to warm-temperate waters (Moura et al. 2018; Calder and Faucci 2021). As with Halopteris alternata (Nutting, 1900), hydroids of the species from the western Atlantic and eastern Pacific have been shown to share the same 16S haplotypes (Moura et al. 2019). Hydroids of M. philippina are venomous to humans (Kirchenpauer 1872, as Aglaophenia urens; Gravely 1927, as Lytocarpus philippinus; Halstead 1988, as L. philippinus; Rifkin et al. 1993, as L. philippinus; Santhanam 2020). The absence of a planktonic stage that would permit natural long-distance transoceanic dispersal, combined with genetically identical populations in the Atlantic and Pacific, suggests that ship-mediated transport has likely played an important role in the distribution of this species. We regard it as likely native to either the Atlantic or Indo-West Pacific theatres, and introduced into the Tropical Eastern Pacific. Reported distribution Cocos Island: first record. Elsewhere: circumglobal in shallow tropical, subtropical, and warm-temperate seas (Calder 1997; Ansín Agís et al. 2001; Schuchert 2003; Zhenzu et al. 2014; Moura et al. 2018, 2019; Chakraborty and Raghunathan 2020; Calder and Faucci 2021)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 593-594, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Kirchenpauer GH. 1872. Ueber die Hydroidenfamilie Plumularidae, einzelne Gruppen derselben und ihre Fruchtbehalter. I. Aglaophenia Lx. Abhandlungen aus dem Gebiete der Naturwissenschaften herausgegeben von dem Naturwissenschaftlichen Verein in Hamburg. 5 (3): 1 - 52.","Fraser CM. 1947. Distribution and relationship in American hydroids. Toronto: University of Toronto Press.","Fraser CM. 1948. Hydroids of the Allan Hancock Pacific Expeditions since March, 1938. Allan Hancock Pac Expeditions. 4 (5): 179 - 343.","Fraser CM. 1938 a. Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pac Expeditions. 4 (1): 1 - 105.","Fraser CM. 1938 b. Hydroids of the 1936 and 1937 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (2): 107 - 127.","Fraser CM. 1938 c. Hydroids of the 1932, 1933, 1935, and 1938 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (3): 129 - 153.","Calder DR, Mallinson JJ, Collins K, Hickman CP. 2003. Additions to the hydroids (Cnidaria) of the Galapagos, with a list of species reported from the islands. J Nat Hist. 37: 1173 - 1218. doi: 10.1080 / 00222930110116039","Goldfuss GA. 1820. Handbuch der Zoologie. I. Abtheilung. Nurnberg: Johann Leonhard Schrag.","Moura CJ, Lessios H, Cortes J, Nizinski MS, Reed J, Santos RS, Collins AG. 2018. Hundreds of genetic barcodes of the species-rich hydroid superfamily Plumularioidea (Cnidaria, Medusozoa) provide a guide toward more reliable taxonomy [including supplementary text]. Sci Rep. Article 17986, 8: 14. doi: 10.1038 / s 41598 - 018 - 35528 - 8","Calder DR, Faucci A. 2021. Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands. Zootaxa. 5085: 1 - 73.","Nutting CC. 1900. American hydroids. Part I. The Plumularidae. Smithsonian Inst U S Natl Mus Spec Bull. 4 (1): 1 - 285.","Moura CJ, Collins AG, Santos RS, Lessios H. 2019. Predominant east to west colonizations across major oceanic barriers: insights into the phylogeographic history of the hydroid superfamily Plumularioidea, suggested by a mitochondrial DNA barcoding marker. Ecol Evol. 9: 13001 - 13016. doi: 10.1002 / ece 3.5608","Gravely FH. 1927. Coelenterata. Class Hydrozoa. Orders Gymnoblastea and Calyptoblastea, and Gravely FH, editor. The littoral fauna of Krusadai Island in the Gulf of Manaar. Bulletin of the Madras Government Museum, new series, natural history section. Vol. 1. Madras, India; p. 7 - 20.","Halstead BW. 1988. Poisonous and venomous marine animals of the world. 2 nd revised ed. Princeton: Darwin Press.","Rifkin JF, Fenner PJ, Williamson JAH. 1993. First aid treatment of the sting from the hydroid Lytocarpus philippinus: the structure of, and in vitro discharge experiments with its nematocysts. J Wilderness Med. 4: 252 - 260. doi: 10.1580 / 0953 - 9859 - 4.3.252","Santhanam R. 2020. Biology and ecology of the venomous marine hydrozoans (Class Hydrozoa). In: Santhanam R, editor. Biology and ecology of venomous marine cnidarians. Singapore: Springer Nature; p. 29 - 73. doi: 10.1007 / 978 - 981 - 15 - 1603 - 0 _ 3","Calder DR. 1997. Shallow-water hydroids of Bermuda: superfamily Plumularioidea. Royal Ontario Museum. Life Sci Contrib. 161: 1 - 85.","Ansin Agis J, Ramil F, Vervoort W. 2001. Atlantic Leptolida (Hydrozoa, Cnidaria) of the families Aglaopheniidae, Halopterididae, Kirchenpaueriidae and Plumulariidae collected during the CANCAP and Mauritania-II expeditions of the National Museum of Natural History, Leiden, the Netherlands. Zool Verhandelingen. 333: 1 - 268.","Schuchert P. 2003. Hydroids (Cnidaria, Hydrozoa) of the Danish Expedition to the Kei Islands. Steenstrupia. 27: 137 - 256.","Zhenzu X, Huang J-Q, Lin M, Guo D-H, Wang C-G. 2014. The superclass Hydrozoa of the phylum Cnidaria in China. Beijing: China Ocean Press. Vol. II p. 459 - 945.","Chakraborty O, Raghunathan C. 2020. Notes on seven aglaopheniids (Cnidaria: Hydrozoa: Aglaopheniidae) from Andaman and Nicobar Islands with three new records to India. Zootaxa. 4790: 291 - 317. doi: 10.11646 / zootaxa. 4790.2.6"]}

Clytia obliqua (Clarke, 1907) (Figure 5g –j) Campanularia (?) obliqua Clarke, 1907: 9, pl. 5, figs 1–4. Type locality Panama: Perico Island, on the hydroid Disertasia crisioides (Lamouroux, 1824) (Clarke 1907). Material examined Chatham Bay, 5.55208, −87.0431, several colonies, to 4 mm high, with gonothecae, coll. I. Keith, #253541. – Chatham Bay, 5.55208, −87.04308, several colony fragments, to 6 mm high, with a gonotheca, coll. I. Keith, #253540. – Chatham Bay, 5.55208, −87.04308, several colony fragments, without gonothecae, coll. I. Keith, #253539. – Wafer Bay, 5.5456, −87.06235, 1 colony, on a barnacle, 3 mm high, without gonothecae, coll. G. Ashton, #240584. – Wafer Bay, 5.5456, −87.06235, 4 colonies on 4 barnacles, to 2 mm high, with gonothecae, coll. G. Ashton, #240585. – Wafer Bay, 5.54535, −87.06185, 1 colony, on a barnacle, 4 mm high, with a gonotheca, coll. G. Ashton, #240629. – Wafer Bay, 5.54535, −87.06185, 1 colony fragment, 2 mm high, without gonothecae, coll. G. Ashton, #240630. – Wafer Bay, 5.5456, −87.06235, 1 colony, on a barnacle, 3 mm high, with gonothecae, coll. G. Ashton, #240587. – Wafer Bay, 5.54618, −87.06318, 2 colony fragments, 2 mm high, without gonothecae, coll. I. Keith, #307706. – Chatham Bay, 5.55208, −87.04308, 2 colony fragments, to 2 mm high, without gonothecae, coll. I. Keith, #307715. – Chatham Bay, dock 004, no coordinates, 1 colony, on Macrorhynchia philippina, 2 mm high, without gonothecae, coll. G. Ashton, #266335. Remarks Clarke (1907) applied the binomen Campanularia (?) obliqua to a hydroid collected at Perico Island off the Pacific coast of Panama. Its prime distinguishing characters included (1) a small, creeping colony form, with pedicels 1.0– 1.5 mm high and with annulations at proximal and distal ends and sometimes in between; (2) hydrothecae having nearly cylindrical walls above the base; and (3) marginal cusps that are prominent and pointed at an oblique angle. Gonothecae were lacking in Clarke’s specimens, and the species was assigned by him, with uncertainty, to Campanularia Lamarck, 1816. Specimens listed above from Cocos Island, indistinguishable from Clarke’s (1907) brief description and illustrations of C. (?) obliqua, have been assigned to that species here. This hydroid was re-assigned from Campanularia to Clytia Lamouroux, 1812 by Fraser (1936), who found gonothecae in colonies from Japan that he identified as belonging to the species. Gonothecae were also observed in material from Japan by Hirohito (1969, 1995), although some uncertainty was expressed by him about their identification. Fertile specimens from Cocos Island (Figure 5i–j), with gonothecae arising from the hydrorhiza, confirm inclusion of the species in Clytia rather than Campanularia. The validity of C. obliqua has often been questioned. On examining presumed type material (syntype, USNM 29616) of the species, Cornelius (1982) concluded that it differed only in the slope of the hydrothecal cusps from C. gravieri Billard, 1904, now considered a synonym of C. linearis (Thornely, 1904). He therefore considered the two to be conspecific, a proposed synonymy that has been widely followed (e.g. Gibbons and Ryland 1989; Calder 1991; Watson 2000; Zhenzu et al. 2014; Wedler 2017; Choong et al. 2018). However, C. linearis clearly differs from the account of C. obliqua by Clarke (1907) in having colonies that are usually erect and sympodially branched, hydrothecae that are large and deep, and marginal cusps with distinctive inward-folding pleats that extend onto the distal wall of the hydrotheca (Lindner and Migotto 2002; Cunha et al. 2020). By contrast, illustrations of C. obliqua by Clarke depict hydroids with unbranched pedicels, hydrothecae that were not particularly tall, and hydrothecal cusps that had no keel-like infolded pleats. Gibbons and Ryland (1989, p. 400), in remarks on a hydroid identified as ‘ C. (?) gracilis (M. Sars) ’, also reported examining syntype material of C. obliqua. The types were described, in contradistinction to Clarke’s (1907) account of C. obliqua, as branched and with tall hydrothecae. Although no infolding pleats were observed on the hydrothecal cusps, Gibbons and Ryland concluded that C. obliqua was conspecific with C. linearis. Based on the account of Clarke (1907), however, characters of C. obliqua appear to have more in common with those of C. hemisphaerica (Linnaeus, 1767), C. gracilis and especially C. elsaeoswaldae Stechow, 1914 (Lindner et al. 2011) than with C. linearis. Thus, while C. obliqua is a poorly known species, it is considered a valid one here. Moreover, if it should prove to be conspecific with C. elsaeoswaldae, a putative species having many of the same characters, the name C. obliqua has priority. Clytia obliqua has been mentioned infrequently in studies on hydroids. Surprisingly, it was never included in accounts by Fraser (1938a, 1938b, 1938c) of species from the Tropical Eastern Pacific region. Meanwhile, a record by Fraser (1948) from southern California seems suspect on zoogeographic grounds. As noted above, reports of the species from Japan (Fraser 1936; Hirohito 1969, 1995) are open to question and this material should be re-examined. A record of it from the Mediterranean coast of France (Picard 1950) appears to have been based on another species and has been discounted (Picard 1958; Bouillon et al. 2000). Finally, C. obliqua was included in a paper by Calder et al. (2019) on hydroids from the Galápagos Islands. It was one of the most common species in the current collection from Cocos Island. Reported distribution Cocos Island: first record. Elsewhere: questionably from Point Fermin, California (Fraser 1948) to the Galápagos Islands (Calder et al. 2019), including the type locality of Perico Island, Panama (Clarke 1907); other questionable reports include those of Fraser (1936) and Hirohito (1969, 1995) from Sagami Bay, Japan., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 583-586, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Clarke SF. 1907. Reports on the scientific results of the expedition to the eastern tropical Pacific, in charge of Alexander Agassiz, by the U. S. Fish Commission Steamer \" Albatross \", from October, 1904, to March, 1905, Lieut. - Commander L. M. Garrett, U. S. N., commanding. VIII. The hydroids. Mem Mus Comp Zool Harvard Coll. 35 (1): 1 - 18.","Lamouroux JVF. 1824. Description des polypiers flexibles. In: Quoy JRC, Gaimard JP, editors. Zoologie. Voyage autour du monde, entrepris par ordre du Roi, execute sur les corvettes de S. M. l'Uranie et la Physicienne, pendant les annees 1817, 1818, 1819 et 1820; par M. Louis de Freycinet. Paris: Pillet Aine; p. 603 - 643.","de Lamarck JBPA. 1816. Histoire naturelle des animaux sans vertebres. Tome 2. Paris: Verdiere.","Lamouroux JVF. 1812. Extrait d'un memoire sur la classification des polypiers coralligenes non entierement pierreux. Nouveau Bulletin des Sciences, par la Societe Philomatique de Paris. 3: 181 - 188.","Fraser CM. 1936. Some Japanese hydroids, mostly new. Π Trans R Soc Canada Series 3, Section 5. 30: 49 - 54. Section 5, 30.","Hirohito, The Showa Emperor. 1969. Some hydrozoans of the Amakusa Islands. Tokyo: Biological Laboratory, Imperial Household.","Cornelius PFS. 1982. Hydroids and medusae of the family Campanulariidae recorded from the eastern North Atlantic, with a world synopsis of genera. Bull Br Mus (Nat Hist) Zool. 42: 37 - 148.","Billard A. 1904. Hydroides recoltes par M. Ch. Gravier dans le Golfe de Tadjourah. Bulletin du Museum d'Histoire Naturelle. 10: 480 - 485.","Thornely LR. 1904. Report on the Hydroida collected by Professor Herdman, at Ceylon, in 1902, and Herdman WA, editor. Report to the Government of Ceylon on the pearl oyster fisheries of the Gulf of Manaar, with supplementary reports upon the marine biology of Ceylon, by other naturalists, part 2. p. 107 - 126. London: The Royal Society.","Gibbons MJ, Ryland JS. 1989. Intertidal and shallow water hydroids from Fiji. I. Athecata to Sertulariidae. Mem Queensland Mus. 27: 377 - 432.","Calder DR. 1991. Shallow-water hydroids of Bermuda. The Thecatae, exclusive of Plumularioidea. Royal Ontario Museum. Life Sci Contrib. 154: 1 - 140.","Watson JE. 2000. Hydroids (Hydrozoa: Leptothecatae) from the Beagle Gulf and Darwin Harbour, northern Australia. Beagle. 16: 1 - 82. doi: 10.5962 / p. 254535","Zhenzu X, Huang J-Q, Lin M, Guo D-H, Wang C-G. 2014. The superclass Hydrozoa of the phylum Cnidaria in China. Beijing: China Ocean Press. Vol. II p. 459 - 945.","Wedler E. 2017. Hidroides del Mar Caribe con enfasis en la region de Santa Marta, Colombia. Instituto de Investigaciones Marinas y Costeras - INVEMAR. Santa Marta (Colombia): Serie de Publicaciones Generales del INVEMAR ; p. 94.","Choong HHC, Calder DR, Chapman JW, Miller JA, Geller JB, Carlton JT. 2018. Hydroids (Cnidaria: Hydrozoa: Leptothecata and Limnomedusae) on 2011 Japanese tsunami marine debris landing in North America and Hawaii, with revisory notes on Hydrodendron Hincks, 1874 and a diagnosis of Plumaleciidae, new family. Aquat Invasions. 13: 43 - 70. doi: 10.3391 / ai. 2018.13.1.05","Lindner A, Migotto AE. 2002. The life cycle of Clytia linearis and Clytia noliformis: metagenic campanulariids (Cnidaria: Hydrozoa) with contrasting polyp and medusa stages. J Mar Biol Assoc U K. 82: 541 - 553. doi: 10.1017 / S 0025315402005866","Cunha AF, Collins AG, Marques AC. 2020. When morphometry meets taxonomy: morphological variation and species boundaries in Proboscoida (Cnidaria: Hydrozoa). Zool J Linn Soc. 190: 417 - 447. doi: 10.1093 / zoolinnean / zlz 166","Linnaeus C. 1767. Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Pars II. Editio duodecima, reformata. Holmiae: Laurentii Salvii. p. 533 - 1317. doi: 10.5962 / bhl. title. 156772","Stechow E. 1914. Zur Kenntnis neuer oder seltener Hydroidpolypen, meist Campanulariden, aus Amerika und Norwegen. Zool Anz. 45: 120 - 136.","Lindner A, Govindarajan AF, Migotto AE. 2011. Cryptic species, life cycles, and the phylogeny of Clytia (Cnidaria: Hydrozoa: Campanulariidae). Zootaxa. 2980: 23 - 36. doi: 10.11646 / zootaxa. 2980.1.2","Fraser CM. 1938 a. Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pac Expeditions. 4 (1): 1 - 105.","Fraser CM. 1938 b. Hydroids of the 1936 and 1937 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (2): 107 - 127.","Fraser CM. 1938 c. Hydroids of the 1932, 1933, 1935, and 1938 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (3): 129 - 153.","Fraser CM. 1948. Hydroids of the Allan Hancock Pacific Expeditions since March, 1938. Allan Hancock Pac Expeditions. 4 (5): 179 - 343.","Picard J. 1950. Observations sur les hydraires recoltes aux Martigues dans le canal de Caronte. Vie et Milieu. 1: 51 - 52.","Picard J. 1958. Origines et affinites de la faune d'hydropolypes (gymnoblastes et calyptoblastes) et d'hydromeduses (anthomeduses et leptomeduses) de la Mediterranee. Rapport et Proces-Verbaux des Reunions, Commission Internationale pour l'Exploration Scientifique de la Mer Mediterranee. 14: 187 - 199.","Bouillon J, Medel MD, Pages F, Gili JM, Boero F, Gravili C. 2000. Fauna of the Mediterranean Hydrozoa. Sci Mar. 68 (Suppl 2): 1 - 449. doi: 10.3989 / scimar. 2004.68 s 25","Calder DR, Carlton JT, Larson K, Mallinson JJ, Choong HHC, Keith I, Ruiz GM. 2019. Hydroids (Cnidaria, Hydrozoa) from marine fouling assemblages in the Galapagos Islands, Ecuador. Aquat Invasions. 14: 21 - 58. doi: 10.3391 / ai. 2019.14.1.02"]}

Phialellidae (undetermined) (Figure 5a) Material examined Wafer Bay, 5.54618, −87.06318, 2 colonies, on two barnacles, to 0.4 mm high, without gonothecae, coll. I. Keith, #240600. – Chatham Bay, 5.55271, −87.03826, numerous hydrothecae, to 2 mm high, without gonothecae, coll. I. Keith, #240565. Remarks Nothing morphologically similar to these hydroids has been reported before from the Tropical Eastern Pacific region. The closest to them is a specimen identified by Calder et al. (2021) as Opercularella sp. from La Libertad, Ecuador, but it differs in lacking a hydrothecal diaphragm and in having tapered rather than nearly cylindrical hydrothecae. Instead, they more closely resemble specimens identified as? Phialella quadrata (Forbes, 1848) from the Seychelles by Millard and Bouillon (1973), and especially ‘ Phialellidae undetermined’ from Gardner Pinnacles in the Northwestern Hawaiian Islands by Calder and Faucci (2021). While likely referable to either Opercularella Hincks, 1869 or Phialella Browne, 1902, in the family Phialellidae, the generic identity of our Cocos material could not be reliably determined in the absence of gonophores. These genera are distinguished largely on characters of the gonosome, with species of Opercularella said to have fixed sporosacs and Phialella a medusa stage (Bouillon et al. 2006). As with the hydroid from Hawaii, specimens examined here have been identified simply as Phialellidae (undetermined). Reported distribution Cocos Island: first record. Elsewhere: possibly from Gardner Pinnacles in the Northwestern Hawaiian Islands (Calder and Faucci 2021)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 578-579, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Forbes E. 1848. A monograph of the British naked-eyed medusae: with figures of all the species. London: Ray Society. doi: 10.5962 / bhl. title. 54122","Millard NAH, Bouillon J. 1973. Hydroids from the Seychelles (Coelenterata). Annales du Musee Royal de l'Afrique Centrale, serie In- 8 ° Sciences Zoologiques. 206: 1 - 106.","Calder DR, Faucci A. 2021. Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands. Zootaxa. 5085: 1 - 73.","Hincks T. 1869. A history of the British hydroid zoophytes. London: John van Voorst. [Dating of this two-volume work follows Williams (2018), who presented evidence that it was published in March 1869 and not 1868 as per the title-pages].","Browne ET. 1902. A preliminary report on hydromedusae from the Falkland Islands. Ann Mag Nat Hist Ser. 7 (9): 272 - 284. doi: 10.1080 / 00222930208678586","Bouillon J, Gravili C, Pages F, Gili J-M, Boero F. 2006. An introduction to Hydrozoa. Memoires du Museum National d'Histoire Naturelle. 194: 1 - 591."]}

Clytia brevithecata (Thornely, 1904) (Figure 5c, d) Campanularia brevithecata Thornely, 1900: 454, pl. 44, figs 8a, b. Type locality Papua New Guinea: New Britain, Blanche Bay (Thornely 1904, as Campanularia brevithecata). Material examined Wafer Bay, 5.54618, −87.06318, 2 colonies, on two barnacles, to 3 mm high, without gonothecae, coll. I. Keith, #240600. Remarks Hydroids of Clytia brevithecata (Thornely, 1904) have unusually shallow, cup-shaped hydrothecae with an entire hydrothecal rim and a subhydrothecal spherule. A whorl of about 20 filiform tentacles is borne on the hydranths. Pedicels are long and unbranched, with annulations at the base and occasionally elsewhere. Gonothecae, clavate with smooth walls and a truncated distal end, arise on short pedicels from the hydrorhiza (Thornely 1904). In describing the species, Thornely commented on the remarkably large, trumpet-shaped hypostomes of its hydranths, reminiscent of those in species of Eudendrium Ehrenberg, 1834. The species was originally described from Papua New Guinea, based on specimens overgrowing the barnacle Lepas, ropes and fish baskets. Other than this record from Cocos Island, hydroids assigned to C. brevithecata have been reported only once since the original description, from the Northwestern Hawaiian Islands (Calder and Faucci 2021). Clytia hummelincki (Leloup, 1935), originally described from the Caribbean Sea (type locality: Bonaire, the Netherlands), is essentially identical in morphology to C. brevithecata. The two have recently been taken to be conspecific, with the senior name C. brevithecata having priority (Calder and Faucci 2021). Galea and Ferry (2015, p. 241) had noted earlier that they might be identical. Although a connection appears to exist between Indo-Pacific and Atlantic populations given the record of C. hummelincki from a buoy on Agulhas Bank at the southern tip of Africa (Millard 1966, 1975), molecular comparisons are needed to confirm synonymy of the two names. Of its two synonyms, the species is much more widely recorded and better known under the name C. hummelincki. As such, it has been reported more than a dozen times across the Atlantic region and at least four times in the Indo-Pacific (Calder and Faucci 2021). In the Tropical Eastern Pacific, it has been reported from Isla San Cristóbal and Isla Wolf in the Galápagos Islands (Calder et al. 2003). The generic affinities of C. hummelincki (= C. brevithecata) appear unsettled on the basis of recent molecular studies. The species has been shown to be genetically distant from other included species of Clytia (Govindarajan et al. 2006; Leclère et al. 2009; Maronna et al. 2016), and its assignment to Clytia and the family Clytiidae has been debated (Cunha et al. 2017). However, in having a medusa stage that conforms with that of the genus (Gravili et al. 2008, as C. hummelincki; Gravili et al. 2015, as C. hummelincki), the species is maintained here in both the family Clytiidae and the genus Clytia. A recent overview of C. brevithecata has been given by Calder and Faucci (2021). In concert with its status in the Galapagos Islands (Carlton et al. 2019), we treat C. brevithecata as introduced on Cocos Island, and native to either the Western Atlantic Ocean or the Indo-West Pacific. Reported distribution Cocos Island: first record. Elsewhere: currently taken to be circumglobal in tropical and warm-temperate waters (Calder and Faucci 2021)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 581-582, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Thornely LR. 1904. Report on the Hydroida collected by Professor Herdman, at Ceylon, in 1902, and Herdman WA, editor. Report to the Government of Ceylon on the pearl oyster fisheries of the Gulf of Manaar, with supplementary reports upon the marine biology of Ceylon, by other naturalists, part 2. p. 107 - 126. London: The Royal Society.","Thornely LR. 1900. The hydroid zoophytes collected by Dr. Willey in the southern seas. In: Willey A, editor. Zoological results based on material from New Britain, New Guinea, Loyalty Islands and elsewhere. Part IV. Cambridge: Cambridge University Press; p. 451 - 457.","Ehrenberg CG. 1834. Beitrage zur physiologischen Kenntniss der Corallenthiere im allgemeinen, und besonders des rothen Meeres, nebst einem Versuche zur physiologischen Systematik derselben. Vol. 1. Berlin: Abhandlung der Koniglichen Akademie der Wissenschaften; p. 225 - 380.","Calder DR, Faucci A. 2021. Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands. Zootaxa. 5085: 1 - 73.","Leloup E. 1935. Hydraires calyptoblastiques des Indes Occidentales. Memoires du Musee Royal d'Histoire Naturelle de Belgique, 2 me Serie. 2: 1 - 73.","Galea HR, Ferry R. 2015. Notes on some hydroids (Cnidaria) from Martinique, with descriptions of five new species. Rev Suisse Zool. 122: 213 - 246.","Millard NAH. 1966. The Hydrozoa of the south and west coasts of South Africa. Part III. The Gymnoblastea and small families of Calyptoblastea. Ann S Afr Mus. 48: 427 - 487.","Millard NAH. 1975. Monograph on the Hydroida of Southern Africa. Ann S Afr Mus. 68: 1 - 513.","Calder DR, Mallinson JJ, Collins K, Hickman CP. 2003. Additions to the hydroids (Cnidaria) of the Galapagos, with a list of species reported from the islands. J Nat Hist. 37: 1173 - 1218. doi: 10.1080 / 00222930110116039","Govindarajan AF, Boero F, Halanych KM. 2006. Phylogenetic analysis with multiple markers indicates repeated loss of the adult medusa stage in Campanulariidae (Hydrozoa, Cnidaria). Mol Phylogenet Evol. 38: 820 - 834. doi: 10.1016 / j. ympev. 2005.11.012","Leclere L, Schuchert P, Cruaud C, Couloux A, Manuel M. 2009. Molecular phylogenetics of Thecata (Hydrozoa, Cnidaria) reveals long-term maintenance of life history traits despite high frequency of recent character changes. Syst Biol. 58: 509 - 526. doi: 10.1093 / sysbio / syp 044","Maronna MM, Miranda TP, Cantero AL P, Barbeitos MS, Marques AC. 2016. Towards a phylogenetic classification of Leptothecata (Cnidaria, Hydrozoa). Sci Rep. 6: 18075. doi: 10.1038 / srep 18075","Cunha AF, Collins AG, Marques AC. 2017. Phylogenetic relationships of Proboscoida Broch, 1910 (Cnidaria, Hydrozoa): are traditional morphological diagnostic characters relevant for the delimitation of lineages at the species, genus, and family levels? Mol Phylogenet Evol. 106: 118 - 135. doi: 10.1016 / j. ympev. 2016.09.012","Gravili C, D'Ambrosio P, Di Camillo C, Renna G, Bouillon J, Boero F. 2008. Clytia hummelincki (Hydroidomedusae: Leptomedusae) in the Mediterranean Sea. J Mar Biol Assoc U K. 88: 1547 - 1553. doi: 10.1017 / S 0025315408001975","Gravili C, De Vito D, Di Camillo CG, Martell L, Piraino S, Boero F. 2015. The non-siphonophoran Hydrozoa (Cnidaria) of Salento, Italy with notes on their life-cycles: an illustrated guide. Zootaxa. 3908 (1): 1 - 187. doi: 10.11646 / zootaxa. 3908.1.1","Carlton JT, Keith I, Ruiz GM. 2019. Assessing marine bioinvasions in the Galapagos Islands: implications for conservation biology and marine protected areas. Aquat Invasions. 14: 1 - 20. doi: 10.3391 / ai. 2019.14.1.01"]}

Corydendrium flabellatum Fraser, 1938a (Figures 2b, 3) ? Corydendrium flabellatum Fraser, 1938a: 11, pl. 1, fig. 2a, b. Type locality Panama: Secas Islands, 7,965278°N, 82.00833°W, 46 m (lectotype, Calder et al. 2009). Material examined Chatham Bay, dock 004, 1 colony, 3.2 cm high, without gonophores, coll. G. Ashton, #179822. –Chatham Bay, dock 004, 2 colonies, to 3 cm high, without gonophores, coll. G. Ashton, #266340. Cnidome Nematocysts of hydranth (Figure 3a–c): desmonemes (n = 10): 4.7–5.2 μm long × 3.2–3.4 μm wide; heterotrichous microbasic euryteles (n = 10): 8.3–9.0 μm long × 3.8–4.1 μm wide. Remarks The original description of Corydendrium flabellatum Fraser, 1938a was based on sterile material from the Tropical Eastern Pacific. Uncertainty was expressed at the time about its generic affinities (Fraser 1938a). Hydroids of Corydendrium are defined as oceaniids having colonies that are either erect, polysiphonic and irregularly branched, or exceptionally stolonal, perisarc tubes of hydrocaulus and branches that are adnate over all or a considerable part of their lengths and that terminate near the hydranth bases, hydranths that are elongate and cylindrical, with scattered filiform tentacles, and gonophores that are elongate, fixed and either located within perisarc tubes beneath the hydranths or appearing as external outgrowths of the stem and branches (Calder 1988; Schuchert 2004; Bouillon et al. 2006). Fraser’s (1938a) account of C. flabellatum corresponds with these characters except for the gonophores, which were, and remain, undescribed. Corydendrium flabellatum has been considered a synonym of the circumglobal C. parasiticum Linnaeus, 1767 (Vervoort, 1946; Calder 1988), although it is retained as a distinct species by Schuchert (2004). There appears to be little in terms of morphology to distinguish C. flabellatum from C. parasiticum. The cnidome of C. flabellatum was not described by Fraser (1938a), and was previously unknown. That of material examined here, comprising desmonemes and euryteles, is identical to that of C. parasiticum Linnaeus, 1767 from Bermuda (Calder 1988). Sizes of the two categories in C. parasiticum and in Cocos material are close, particularly those of the euryteles. Desmonemes of C. parasiticum from Bermuda were slightly larger than those in hydroids from the present collection. The essentially identical morphology and cnidome might thus suggest that C. flabellatum represents introduced populations of C. parasiticum, which is considered introduced in the Hawaiian Islands (Carlton and Eldredge 2015). Alternatively, C. flabellatum may represent an endemic Tropical Eastern Pacific clade of the globally distributed hydroid referred to as C. parasiticum (a likely species complex). With C. parasiticum having originally been described from the Mediterranean Sea, its type locality is geographically remote from that of C. flabellatum, located on the Pacific coast of Panama. Moreover, the type localities of the two species are separated by the Central American Isthmus, a major biogeographic barrier. Few hydroid species are known to have naturally crossed that barrier (Moura et al. 2019). For now, we recognise C. flabellatum as valid, pending genetic comparisons, and tentatively native to the Eastern Pacific. Further complicating this species’ status is, as we note above, a lack of knowledge of the gonophores; additional study may suggest that the species should eventually be treated as a species inquirenda. Within the suborder Filifera Kühn, 1913, four separate clades were recognised by Cartwright et al. (2008). Utilising grey nomenclature (Minelli 2017), they assigned the family Oceaniidae Eschscholtz 1829 (inclusive of Corydendrium and C. flabellatum) to ‘ Filifera IV’. According to the phylogenetic analyses of Bentlage and Collins (2021), components of Filifera III and Filifera IV have a closer relationship to siphonophores than to Capitata Kühn, 1913, Filifera I, Filifera II and Leptothecata Cornelius, 1992. In terms of classification, C. flabellatum might thus have been discussed at the end of this work rather than near the beginning. For now, however, it has been placed between Pennaria disticha (Capitata) and Eudendrium cf. certicaule (‘ Filifera I’) as in traditional taxonomic accounts. Corydendrium flabellatum has been reported from the Pacific coasts of Panama (Secas Islands, 07°57 ʹ 55″N, 82°00 ʹ 30″W) and Mexico (east of islands off Navidad Head, 19°12 ʹ 50″ N, 104°49 ʹ 48″W; off Isabel Island, 21°51 ʹ 35″N, 105°54 ʹ 30″W) (Fraser 1938a, 1943). Reported distribution Cocos Island: first record. Elsewhere: Pacific coasts of Panama and Mexico (Fraser 1938a; Calder et al. 2009)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 573-576, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Fraser CM. 1938 a. Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pac Expeditions. 4 (1): 1 - 105.","Calder DR, Vervoort W, Hochberg FG. 2009. Lectotype designations of new species of hydroids (Cnidaria, Hydrozoa), described by C. M. Fraser, from Allan Hancock Pacific and Caribbean Sea Expeditions. Zool Mededelingen. 83: 919 - 1058.","Calder DR. 1988. Shallow-water hydroids of Bermuda: the Athecatae. Royal Ontario Museum. Life Sci Contrib. 148: 1 - 107. doi: 10.5962 / bhl. title. 52225","Schuchert P. 2004. Revision of the European athecate hydroids and their medusae (Hydrozoa, Cnidaria): families Oceanidae and Pachycordylidae. Rev Suisse Zool. 111: 315 - 369. doi: 10.5962 / bhl. part. 80242","Bouillon J, Gravili C, Pages F, Gili J-M, Boero F. 2006. An introduction to Hydrozoa. Memoires du Museum National d'Histoire Naturelle. 194: 1 - 591.","Linnaeus C. 1767. Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Pars II. Editio duodecima, reformata. Holmiae: Laurentii Salvii. p. 533 - 1317. doi: 10.5962 / bhl. title. 156772","Vervoort W. 1946. Exotic hydroids in the collections of the Rijksmuseum van Natuurlijke Historie and the Zoological Museum at Amsterdam. Zool Mededelingen. 26: 287 - 351.","Carlton JT, Eldredge LG 2015. Update and revision of the marine bioinvasions of Hawaii: the introduced and cryptogenic marine and estuarine animals and plants of the Hawaiian Archipelago. In: Evenhuis NL, Carlton JT, Lucius G, editors. Eldredge III memorial volume: tribute to a polymath. Bishop Museum Bulletin Zoology. Vol. 9. Honolulu, Hawaii: Bishop Museum Press; p. 25 - 47.","Moura CJ, Collins AG, Santos RS, Lessios H. 2019. Predominant east to west colonizations across major oceanic barriers: insights into the phylogeographic history of the hydroid superfamily Plumularioidea, suggested by a mitochondrial DNA barcoding marker. Ecol Evol. 9: 13001 - 13016. doi: 10.1002 / ece 3.5608","Kuhn A. 1913. Entwicklungsgeschichte und Verwandtschaftsbeziehungen der Hydrozoen. I. Teil: Die Hydroiden. Ergebnisse und Fortschritte der Zoologie. 4: 1 - 284.","Cartwright P, Evans NM, Dunn CW, Marques AC, Miglietta MP, Schuchert P, Collins AG. 2008. Phylogenetics of Hydroidolina (Hydrozoa: Cnidaria). J Mar Biol Assoc U K. 88: 1663 - 1672. doi: 10.1017 / S 0025315408002257","Minelli A. 2017. Grey nomenclature needs rules. Ecol Montenegrina. 7: 654 - 666. doi: 10.37828 / em. 2016.7.31","Eschscholtz F. 1829. System der Acalephen. Eine ausfurliche Beschreibung aller medusenartigen Strahltiere. Berlin: Ferdinand Dummler. doi: 10.5962 / bhl. title. 10139","Bentlage B, Collins AG. 2021. Tackling the phylogenetic conundrum of Hydroidolina (Cnidaria: Medusozoa: Hydrozoa) by assessing competing tree topologies with targeted high-throughput sequencing. PeerJ. 9: e 12104. doi: 10.7717 / peerj. 12104","Cornelius PFS. 1992. Medusa loss in leptolid Hydrozoa (Cnidaria), hydroid rafting, and abbreviated life-cycles among their remote-island faunae: an interim review. Sci Mar. 56: 245 - 261.","Fraser CM. 1943. A ten-year list of the Velero III collecting stations. General account of the scientific work of the Velero III in the eastern Pacific. Part III. Allan Hancock Pac Expeditions. 1 (3): 259 - 432."]}

Obelia microtheca Fraser, 1938a (Figure 6a–c) Obelia microtheca Fraser, 1938a: 37, pl. 9, fig. 40a–d. Type locality Ecuador: off Santa Elena Bay, 02°08 ʹ 20″S, 81°00 ʹ 15″W, 15–18 m (Calder et al. 2009). Material examined Wafer Bay, 5.54556, −87.06221, 23 colony fragments, to 1 cm high, with gonothecae, coll. G. Ashton, #240607. – Wafer Bay, 5.54556, −87.06221, 5 colony fragments, to 6 mm high, with a gonotheca, coll. G. Ashton, #240611. – Wafer Bay, 5.54556, −87.06221, 9 colony fragments, to 8 mm high, with gonothecae, coll. G. Ashton, #240605. – Chatham Bay, 5.55271, −87.03826, 2 colony fragments, to 7 mm high, with a gonotheca, coll. I. Keith, #307695. Remarks Material examined here has been identified as Obelia microtheca Fraser, 1938a by virtue of having the following combination of characters: (1) colonies small (1 cm high or less), erect, unbranched or mostly so, with sympodial growth; (2) hydrocaulus monosiphonic and only slightly geniculate, divided into internodes; (3) cauline internodes annulated proximally and with alternate apophyses distally; (4) hydrothecal pedicels exceptionally long, annulated either proximally and distally or throughout; (5) hydrothecae small (ca. 0.2 mm deep), funnel-shaped, with depth and diameter at margin essentially equal, walls nearly straight, margin entire; and (6) gonothecae cone-shaped with a terminal collar, axillary in position, arising from proximal ends of hydrothecal pedicels, walls smooth. Hydrothecal pedicels in present material were exceptionally long (Figure 6a, b), but otherwise specimens corresponded with the brief original description of O. microtheca by Fraser (1938a). While considered conspecific with O. dichotoma (Linnaeus, 1758) in some earlier works (Cornelius 1975, 1982; Calder 1991), the species was recognised as valid by Calder et al. (2021) and earlier provisionally so by Calder et al. (2009). Hydroids from Cocos Island were largely indistinguishable from the lectotype colony of O . microtheca (British Columbia Provincial Museum 976–00437-002) from Santa Elena Bay, Ecuador, and from specimens identified as the species from the same region by Calder et al. (2021). While hydrothecal pedicels reached a greater length in material examined here, the difference is not considered taxonomically significant. Obelia microtheca is a little-known species, originally described from Santa Elena Bay, Ecuador (Fraser 1938a). Subsequent records of it have come from Independencia Bay, Peru, La Libertad, Ecuador, and the Pacific coast of Panama (Fraser 1938c), and it was one of the commonest species of hydroids in a study of fouling organisms from coastal Ecuador by Calder et al. (2021). It was not found in samples from the Galápagos Islands as part of the same study. Ecologically, hydroids of O. microtheca have been reported over a depth range from the shore (Fraser 1938c) to 18 m (Fraser 1938a; Calder et al. 2009). A substrate generalist, the species has been reported from a rock, large shells, octocorals, bryozoans, algae, a barnacle, a sponge and a hydroid (Calder et al. 2009, 2021). Colony size has been reported to reach 1 cm high, although the lectotype specimen at only 3 mm high was fertile (Calder et al. 2009). The species is largely known from the Tropical Eastern Pacific, but its range reportedly extends to southern Peru in the Warm Temperate Southeastern Pacific (Fraser 1938c). Reported distribution Cocos Island: first record. Elsewhere: Panama (Pacific coast) to Independencia Bay, Peru (Fraser 1938a, 1938c)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 586-587, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Fraser CM. 1938 a. Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pac Expeditions. 4 (1): 1 - 105.","Calder DR, Vervoort W, Hochberg FG. 2009. Lectotype designations of new species of hydroids (Cnidaria, Hydrozoa), described by C. M. Fraser, from Allan Hancock Pacific and Caribbean Sea Expeditions. Zool Mededelingen. 83: 919 - 1058.","Linnaeus C. 1758. Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Editio decima, reformata. Holmiae: Laurentii Salvii. doi: 10.5962 / bhl. title. 542","Cornelius PFS. 1975. The hydroid species of Obelia (Coelenterata, Hydrozoa: Campanulariidae), with notes on the medusa stage. Bull Br Mus (Nat Hist) Zool. 28: 249 - 293. doi: 10.5962 / p. 314143","Cornelius PFS. 1982. Hydroids and medusae of the family Campanulariidae recorded from the eastern North Atlantic, with a world synopsis of genera. Bull Br Mus (Nat Hist) Zool. 42: 37 - 148.","Calder DR. 1991. Shallow-water hydroids of Bermuda. The Thecatae, exclusive of Plumularioidea. Royal Ontario Museum. Life Sci Contrib. 154: 1 - 140.","Fraser CM. 1938 c. Hydroids of the 1932, 1933, 1935, and 1938 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (3): 129 - 153."]}

Family SERTULARELLIDAE Maronna, Miranda, Peña Cantero, Barbeitos and Marques, 2016, Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on page 588, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486

Eudendrium cf. certicaule Fraser, 1938a (Figures 2 c–f, 4) Type locality Ecuador: Galápagos Islands, Albemarle Island (= Isla Isabela), off Tagus Cove, 0.2791667°S, 91.3811°W, 50–60 fathoms (91–110 m) (Fraser 1938a; Calder et al. 2009). Material examined Chatham Bay, 5.55271, −87.03826, several colony fragments, to 5 mm high, without gonothecae, coll. I. Keith, #240566. – Wafer Bay, 5.54556, −87.06221, several colony fragments, to 4 mm high, without gonothecae, coll. G. Ashton, #240611. – Wafer Bay, 5.54535, −87.06185, several colony fragments, to 7 mm high, with ♀ gonophores, coll. G. Ashton, #240634. – Wafer Bay, 5.54535, −87.06185, ca. 20 colony fragments, to 9 mm high, with ♂ gonophores, coll. G. Ashton, #240636. – Wafer Bay, 5.54535, −87.06185, 2 colony fragments, to 4 mm high, with ♂ gonophores, coll. G. Ashton, #240637. – Wafer Bay, 5.54535, −87.06185, 1 colony fragment, 7 mm high, with a ♂ gonophore, coll. G. Ashton, #240630. Cnidome Nematocysts of hydranths (Figure 4a–f): Abundant Heterotrichous microbasic euryteles, small (n = 10): 5.0–5.6 μm long × 2.3–2.8 μm wide; Heterotrichous microbasic euryteles, medium (n = 10): 7.0–8.0 μm long × 3.4–3.9 μm wide. Rare ?Microbasic mastigophores (n = 5): 10.0–12.0 μm long × 3.0–4.1 μm wide;?undetermined heteronemes (n = 10): 8.8–12.7 μm long × 4.6–7.7 μm wide. Remarks Of some 70+ species of Eudendrium Ehrenberg, 1834 recognised worldwide (Schuchert and Collins 2021), these hydroids appear closest in colony morphology to E. certicaule Fraser, 1938a, originally described from the Galápagos Islands. Its cnidome, now recognised as being of considerable importance in the identification of species in the genus, has yet to be described. In common with the original description of E. certicaule by Fraser (1938a), colonies examined here were monosiphonic and quite straight, branches made wide angles with the stem, stems and branches bore about two annulations basally with few or none elsewhere, and hydranths bore about 12–15 tentacles. Hydranths with gonophores were not fully aborted, and their pedicels were smooth throughout. Gonophores of the male were arranged in a whorl around the hydranth base, with each gonophore comprising a single chamber. Female gonophores were also arranged in a basal whorl around the hydranth, with an unbranched spadix curving over each egg. In contrast to the original description of E. certicaule, colonies examined here were smaller (4–9 mm high vs 14– 34 mm high) and consisted of both stolonal and erect components. Finally, hydroids from Cocos Island were collected at snorkelling depth, whereas the types of E. certicaule came from depths of 91–128 m (Calder et al. 2009). In light of all this, we have identified our specimens as E. cf. certicaule. The nematocyst complement of specimens from Cocos Island included abundant small microbasic euryteles (Figure 4a, b), resembling those found in all species of Eudendrium, and somewhat less abundant larger microbasic euryteles (Figure 4c). Also observed in these hydroids were two other kinds of nematocysts, but it is uncertain whether they are kleptocnidae or part of the cnidome. A banana-shaped type (Figure 4d), possibly a microbasic mastigophore, was observed five times in colonies from three different collections (#240634, #240636, #240637). A pear-shaped type (Figure 4e, f), considered an undetermined heteroneme, was observed more than 10 times, but in only one slide preparation from a single collection (#240566). Discharged threads were seen in neither of these two nematocyst categories, and their identity remains uncertain. Eudendrium certicaule is currently known only from warm waters of the eastern Pacific. It has been identified in collections from three locations in the Galápagos Islands (between Narborough (= Fernandina) and Albemarle (= Isabela) islands; James Bay on James Island (Santiago); between Charles (= Floreana) and Indefatigable (= Santa Cruz) islands) (Fraser 1938a) and one location off Baja California, Mexico (off Cedros Island) (Fraser 1948). No description or illustration was provided to accompany the report from Cedros Island. Reported distribution Cocos Island: first record. Elsewhere: Galápagos Islands, Ecuador (Fraser 1938a); off Baja California, Mexico (Fraser 1948)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 576-578, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Fraser CM. 1938 a. Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pac Expeditions. 4 (1): 1 - 105.","Calder DR, Vervoort W, Hochberg FG. 2009. Lectotype designations of new species of hydroids (Cnidaria, Hydrozoa), described by C. M. Fraser, from Allan Hancock Pacific and Caribbean Sea Expeditions. Zool Mededelingen. 83: 919 - 1058.","Ehrenberg CG. 1834. Beitrage zur physiologischen Kenntniss der Corallenthiere im allgemeinen, und besonders des rothen Meeres, nebst einem Versuche zur physiologischen Systematik derselben. Vol. 1. Berlin: Abhandlung der Koniglichen Akademie der Wissenschaften; p. 225 - 380.","Schuchert P, Collins R. 2021. Hydromedusae observed during night dives in the Gulf Stream. Rev Suisse Zool. 128: 237 - 356. doi: 10.35929 / RSZ. 0049","Fraser CM. 1948. Hydroids of the Allan Hancock Pacific Expeditions since March, 1938. Allan Hancock Pac Expeditions. 4 (5): 179 - 343."]}

Halopteris alternata (Nutting, 1900) (Figure 7a, b) Plumularia alternata Nutting, 1900: 62, pl. 4, figs 1, 2. Type locality Commonwealth of the Bahamas: Barracuda Rocks (Nutting 1900, p. 62, as Plumularia alternata). Material examined Chatham Bay, 5.55318, −87.03996, 1 colony fragment in poor condition, 2.5 mm high, without gonothecae, coll. G. Ashton, #240556. – Chatham Bay, 5.55318, −87.03996, 3 colony fragments, to 9 mm high, without gonothecae, coll. G. Ashton, #179805. – Chatham Bay, 5.55318, −87.03996, 7 colony fragments, to 8 mm high, without gonothecae, coll. I. Keith, #307699. – Chatham Bay, 5.55318, −87.03996, 11 colony fragments, to 1.2 cm high, without gonothecae, coll. G. Ashton, #240555. Remarks Hydroids from Cocos Island correspond with accounts of Halopteris alternata (Nutting, 1900), originally described from the Bahamas. The species is widespread in shallow waters of the warm western Atlantic Ocean (Oliveira et al. 2016; Calder 2019), although it was long included in the synonymy of the predominantly European H. diaphana (Heller, 1868). Schuchert (1997) distinguished the two on the basis of morphological characters, and their separation as distinct species has been confirmed by DNA barcoding (Galea et al. 2018; Moura et al. 2018). Differences distinguishing H. alternata from related species of the genus Halopteris Allman, 1877) have been reviewed by Schuchert (1997) and Calder et al. (2019). While separated geographically by a significant biogeographic barrier, hydroids identified as H. cf. alternata lineage 5 (one of five lineages recognised under the name) from both Atlantic and Pacific sides of Central America were found by Moura et al. (2019) to have corresponding 16S haplotypes. Occurrence of the species in the Tropical Eastern Pacific has thereby been confirmed. In concert with its introduced status on the Galapagos Islands (Carlton et al. 2019), we recognised it here as introduced on Cocos Island. Halopteris alternata has been reported from the region by Fraser (1938a, as Plumularia alternata) from Mexico (Revillagegedo Islands; east of islands off Navidad Head; Isabel Island), Ecuador (Galápagos Islands; Santa Elena Bay), Colombia (Port Utria) and Panama (Jicarita Island; Pacora Island); by Fraser (1938c, as P. alternata) from Panama (Secas Islands) and Mexico (Isabel Island); by Moura et al. (2018) from Panama (Coiba); and by Calder et al. (2019, 2021) from mainland Ecuador (Salinas) and the Galápagos Islands. Elsewhere in the Pacific it occurs in Hawaii (Cooke 1977, as H. diaphana), including the Northwestern Hawaiian Islands (Calder and Faucci 2021). As for Fraser’s reports of the species from the eastern Pacific, at least some appear to have been based on misidentifications (Schuchert 1997). An illustration in Fraser (1938a, pl. 14, fig. 71b) shows a colony with cornucopia-shaped rather than spindle-shaped gonothecae as in H. alternata; no indication was given of its collection location. Records from the Indian Ocean (Jarvis 1922, as P. alternata; Gravely 1927, as P. sp. nr. alternata) need confirmation. The known range of H. alternata in the Tropical Eastern Pacific extends from Isabel Island, Mexico, southwards to Salinas, Ecuador (Fraser 1938a, 1938c; Calder et al. 2021). The species was found in four of the samples examined here from Cocos Island. All of the examined specimens were sterile. Reported distribution Cocos Island: first record. Elsewhere: Western Atlantic (Oliveira et al. 2016; Calder 2019); eastern Atlantic (Ansín Agís et al. 2001); eastern Pacific (Calder et al. 2019, 2021); central Pacific (Cooke 1977, as Halopteris diaphana; Calder and Faucci 2021); possibly Indian Ocean (Jarvis 1922, as Plumularia alternata; Gravely 1927, as Plumularia sp. nr. alternata)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 592-593, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Nutting CC. 1900. American hydroids. Part I. The Plumularidae. Smithsonian Inst U S Natl Mus Spec Bull. 4 (1): 1 - 285.","Oliveira OMP, Miranda TP, Araujo EM, Ayon P, Cedeno-Posso CM, Cepeda-Mercado AA, Cordova P, Cunha AF, Genzano GN, Haddad MA, et al. 2016. Census of Cnidaria (Medusozoa) and Ctenophora from South American marine waters. Zootaxa. 4194 (1): 1 - 256. doi: 10.11646 / zootaxa. 4194.1.1","Schuchert P. 1997. Review of the family Halopterididae (Hydrozoa, Cnidaria). Zool Verhandelingen. 309: 1 - 162.","Galea HR, Di Camillo DG, Maggioni D, Montano D, Schuchert P 2018. A reassessment of Halopteris polymorpha (Billard, 1913 (Cnidaria: Hydrozoa), with descriptions of three new species. Revue Suisse de Zoologie. 125: 21 - 59.","Moura CJ, Lessios H, Cortes J, Nizinski MS, Reed J, Santos RS, Collins AG. 2018. Hundreds of genetic barcodes of the species-rich hydroid superfamily Plumularioidea (Cnidaria, Medusozoa) provide a guide toward more reliable taxonomy [including supplementary text]. Sci Rep. Article 17986, 8: 14. doi: 10.1038 / s 41598 - 018 - 35528 - 8","Allman GJ. 1877. Report on the Hydroida collected during the exploration of the Gulf Stream by L. F. de Pourtales, assistant United States Coast Survey. Mem Mus Comp Zool Harvard Coll. 5 (2): 1 - 66. doi: 10.5962 / bhl. title. 15852","Calder DR, Carlton JT, Larson K, Mallinson JJ, Choong HHC, Keith I, Ruiz GM. 2019. Hydroids (Cnidaria, Hydrozoa) from marine fouling assemblages in the Galapagos Islands, Ecuador. Aquat Invasions. 14: 21 - 58. doi: 10.3391 / ai. 2019.14.1.02","Moura CJ, Collins AG, Santos RS, Lessios H. 2019. Predominant east to west colonizations across major oceanic barriers: insights into the phylogeographic history of the hydroid superfamily Plumularioidea, suggested by a mitochondrial DNA barcoding marker. Ecol Evol. 9: 13001 - 13016. doi: 10.1002 / ece 3.5608","Carlton JT, Keith I, Ruiz GM. 2019. Assessing marine bioinvasions in the Galapagos Islands: implications for conservation biology and marine protected areas. Aquat Invasions. 14: 1 - 20. doi: 10.3391 / ai. 2019.14.1.01","Fraser CM. 1938 a. Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pac Expeditions. 4 (1): 1 - 105.","Fraser CM. 1938 c. Hydroids of the 1932, 1933, 1935, and 1938 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (3): 129 - 153.","Cooke WJ 1977. Order Hydroida. Devaney DM, Eldredge LG, editors. Reef and shore fauna of Hawaii. Section 1: protozoa through Ctenophora. Honolulu, Hawaii: Bernice P. Bishop Museum, Special Publication. Vol. 64 (1); 71 - 104","Calder DR, Faucci A. 2021. Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands. Zootaxa. 5085: 1 - 73.","Jarvis FE. 1922. The hydroids from the Chagos, Seychelles and other islands and from the coasts of British East Africa and Zanzibar. Trans Linn Soc London Zool. 18: 331 - 360. doi: 10.1111 / j. 1096 - 3642.1922. tb 00553. x","Gravely FH. 1927. Coelenterata. Class Hydrozoa. Orders Gymnoblastea and Calyptoblastea, and Gravely FH, editor. The littoral fauna of Krusadai Island in the Gulf of Manaar. Bulletin of the Madras Government Museum, new series, natural history section. Vol. 1. Madras, India; p. 7 - 20.","Ansin Agis J, Ramil F, Vervoort W. 2001. Atlantic Leptolida (Hydrozoa, Cnidaria) of the families Aglaopheniidae, Halopterididae, Kirchenpaueriidae and Plumulariidae collected during the CANCAP and Mauritania-II expeditions of the National Museum of Natural History, Leiden, the Netherlands. Zool Verhandelingen. 333: 1 - 268."]}

Sertularella affinicostata Calder and Faucci, 2021 (Figure 6e, f) Sertularella affinicostata Calder and Faucci, 2021: 23, figs 7a–e, 8 Type locality Ecuador: Galápagos Islands, Isla Darwin (Calder and Faucci 2021). Material examined Chatham Bay, 5.56126, −87.04516, 1 colony, 2 mm high, without gonothecae, coll. I. Keith, #253534. –Chatham Bay, 5.56216, −87.04516, 9 colony fragments, to 6 mm high, without gonothecae, coll. I. Keith, #240612. –Wafer Bay, 5.5456, −87.06235, 9 colony fragments, to 2 mm high, without gonothecae, coll. G. Ashton, #240597. –Wafer Bay, 5.5456, −87.06235, 2 colonies, on two barnacles, to 2 mm high, without gonothecae, coll. G. Ashton, #240591. –Wafer Bay, 5.5456, −87.06235, 6 colony fragments, to 3 mm high, without gonothecae, coll. G. Ashton, #240592. –Wafer Bay, 5.54535, −87.06185, 4 colony fragments, to 2.5 mm high, without gonothecae, coll. G. Ashton, #240636. –Wafer Bay, 5.54535, −87.06185, 1 colony, on a barnacle, 4 mm high, without gonothecae, coll. G. Ashton, #240629. –Wafer Bay, 5.54535, −87.06185, 1 colony fragment, 4 mm high, without gonothecae, coll. G. Ashton, #240630. –Chatham Bay, 5.56126, −87.04516, 2 colony fragments, to 5 mm high, without gonothecae, coll. I. Keith, #307712. –Chatham Bay, 5.56126, −87.04516, 1 colony fragment, 3 mm high, without gonothecae, coll. I. Keith, #307711. –Chatham Bay, dock 004, no coordinates, 1 colony fragment, 2 mm high, without gonothecae, coll. G. Ashton, #266336. Remarks Sertularella affinicostata Calder and Faucci, 2021 was first reported, as S. costata Leloup, 1940, from the two northernmost and warmest of the Galápagos Islands, Wolf and Darwin (Calder et al. 2003). It was discovered a second time in a collection from French Frigate Shoals in the Northwestern Hawaiian Islands (Calder and Faucci 2021) and recognised therein as an undescribed species. Calder and Faucci (2021) also provide records of previously unreported material from Cousin Rock and Marchena Island in the Galápagos. The present record from Cocos Island constitutes the third record of this tiny but morphologically striking hydroid species. Hydroids of S. affinicostata are noteworthy in having a series of sharp-edged horizontal ridges that ring walls of its hydrothecae. Trophosomes of the species differ in part from those of S. costata, originally described from Sagami Bay, Japan, in having fewer (10–14) ridges instead of about 20 (Leloup 1940; Hirohito 1983, 1995). Hydrothecae also differ in being barrel-shaped rather than distinctly tapered distally, and a neck region lacking ridges below the rim is noticeably longer. The proximal end of the hydrocaulus is typically short rather than extending as a long, slender peduncle as in S. costata, and internodes of the hydrocaulus are shorter and thicker. The original account of S. affinicostata in Calder and Faucci (2021) was based on specimens from both the Galápagos Islands and the Northwestern Hawaiian Island. The holotype, from Darwin Island in the Galápagos archipelago, was selected as being the only fertile colony in the two collections. The species was well represented in our Cocos samples. It was present in 11 of the 42 samples (26%) of hydroids in the collection, although all of the specimens were sterile. Hydroids of S. affinicostata are minute, with colonies from Cocos Island ranging between 2 and 6 mm in height. Indeed, the holotype was merely 1.5 mm high. A substrate generalist, the species has been reported from barnacles, a sponge, calcareous rubble, algae and a hydroid stem (Calder and Faucci 2021). Specimens examined here were removed from fouling panels exposed at Chatham Bay and Wafer Bay. While S. affinicostata is certainly a species of shallow waters, its overall bathymetric range is not yet well known. Specimens from the Galápagos were collected at depths of 6 m off Wolf Island (Calder et al. 2003), and from 10 m off Cousin Rock and 8 m off Marchena Island (Calder and Faucci 2021). Collections from Cocos Island were on panels exposed at depths of 0.5– 3 m. A description and additional comments on S. affinicostata are provided by Calder and Faucci (2021). We treat S. affinicostata as cryptogenic in the Cocos, Galapagos and Hawaiian Islands. While potentially a member of a naturally transpacific fauna, its occurrence in shallow water, and particularly on biofouling panels in Cocos, do not exclude it from shipmediated transport. As we discuss below, an increasing number of invasions are recognised from open-ocean environments (such as in the Galapagos and the French Frigate Shoals), thus not excluding this species from being potentially introduced, even if its home port remains unknown at this time. Reported distribution Cocos Island: first record. Elsewhere: Galápagos Islands (Calder et al. 2003, as Sertularella costata); Northwestern Hawaiian Islands (Calder and Faucci 2021)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 588-590, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Calder DR, Faucci A. 2021. Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands. Zootaxa. 5085: 1 - 73.","Leloup E. 1940. Quelques hydropolypes de la Baie de Sagami, Japon. (2 e note). Bulletin du Musee Royal d'Histoire Naturelle de Belgique. 16 (19): 1 - 13.","Calder DR, Mallinson JJ, Collins K, Hickman CP. 2003. Additions to the hydroids (Cnidaria) of the Galapagos, with a list of species reported from the islands. J Nat Hist. 37: 1173 - 1218. doi: 10.1080 / 00222930110116039","Hirohito, The Showa Emperor. 1983. Hydroids from Izu Oshima and Niijima. Tokyo: Biological Laboratory, Imperial Household."]}

Tridentata borneensis Billard, 1925a (Figure 6g –i) Sertularia borneensis Billard, 1925a: 649, fig. 1D. Type locality Indonesia: Borneo, Borneo Bank, 02°25 ʹ S, 117°43 ʹ E, 34 m, on fine coral sand (Billard 1925 a, 1925b; Van Soest 1976; Vervoort and Vasseur 1977). Material examined Wafer Bay, 5.54535, −87.06185, 5 colony fragments, to 7 mm high, without gonothecae, coll. G. Ashton, #240634. – Wafer Bay, 5.54535, −87.06185, 1 colony, with 1 gonotheca, coll. G. Ashton, #240636. – Wafer Bay, 5.54535, −87.06185, 1 colony, on a barnacle, 3 mm high, without gonothecae, coll. G. Ashton, #240629. – Wafer Bay, 5.54535, −87.06185, 3 colony fragments, to 5 mm high, without gonothecae, coll. G. Ashton, #240637. – Wafer Bay, 5.54535, −87.06185, 6 colony fragments, to 7 mm high, without gonothecae, coll. G. Ashton, #240630. – Chatham Bay, 5.55318, −87.03996, 1 colony fragment, 6 mm high, without gonothecae, coll. I. Keith, #240556. – Chatham Bay, 5.55318, −87.03996, 2 colony fragments, to 5 mm high, without gonothecae, coll. G. Ashton, #179806. – Chatham Bay, dock 004, no coordinates, 1 colony fragment, 1 cm high, with gonothecae, coll. G. Ashton, #266336. – Chatham Bay, dock 004, no coordinates, 3 colony fragments, to 9 mm high, without gonothecae, coll. G. Ashton, #266335. Remarks These specimens from Cocos Island conform with accounts of the trophosomes and gonosomes of Sertularia borneensis Billard, 1925a by Billard (1925 a, 1925b), Gibbons and Ryland (1989), Schuchert (2003), and Preker and Lawn (2010, 2010), and they are referred to that species here. The nomenclature of the species is nevertheless unsettled, as the relationship between hydroids assigned the names S. tumida Allman, 1877, S. maldivensis Borradaile, 1905, S. tongensis Stechow, 1919, and S. borneensis is unclear. They all appear much alike in terms of trophosomal morphology; gonosomes have been described to date only in S. borneensis. All of these binomena predate that of S. borneensis, and the names of any found conspecific with it would have priority. In several works, S. borneensis has already been included in the synonymy of S. tumida (Leloup 1960; Calder 1991; Vervoort and Watson 2003; Zhenzu et al. 2014; Song 2019). Characters of both trophosome and gonosome of S. borneensis are very much as in the type species of the genus Tridentata Stechow, 1920, T. perpusilla (Stechow, 1919), and quite unlike those of S. argentea Linnaeus, 1758, type species of Sertularia Linnaeus, 1758. Other species now assigned to Tridentata besides its type include T. turbinata, T. marginata (Kirchenpauer, 1864), T. tumida (Allman, 1877), T. rugosissima (Thornely, 1904) and T. orthogonalis (Gibbons and Ryland, 1989). Included in the synonymy of T. borneensis by Schuchert (2003, as S. borneensis) were the records of S. westindica Stechow, 1920 from India by Mammen (1965) and from Eniwetak Atoll by Cooke (1975). As for the Atlantic species S. westindica, it has been considered conspecific with T. tumida by Leloup (1960), Calder (1991), Zhenzu et al. (2014), and Song (2019). However, records of it from the Indo-Pacific are taken here to have been based on T. borneensis. Vervoort and Vasseur examined and illustrated the holotype of S. borneensis, referring it in error to the synonymy of S. turbinata (Lamouroux, 1816) (= Tridentata turbinata). Most importantly, the species always lacks the distinctive intrathecal ridge of perisarc extending around the abcauline wall of the hydrotheca in T. turbinata. The two are therefore recognised as distinct species. The trophosome of T. borneensis resembles that of S. longa Millard, 1958, but gonothecae of the two species are fundamentally different in shape. Those of T. borneensis are horizontally ribbed, with two horns flanking a wide distal aperture (Figure 6g), while those of S. longa are smooth-walled, with a distal collar and narrower aperture (Millard 1975). The report of S. longa from the Galápagos Islands by Calder et al. (2003, as T. longa), based on sterile specimens, is believed here to have been based on T. borneensis instead. Given the morphology of its gonothecae, as described by Millard, S. longa cannot be assigned to either Tridentata or Sertularia. Its generic affinities are presently unclear. In accounts on hydroids obtained during the Allan Hancock Pacific Expedition, Fraser (1938a, 1938b, 1938c, 1948) did not report T. borneensis from the eastern Pacific. The closest of his species to it appears to be S. dispar Fraser, 1938a. However, hydrothecal walls of that species are marked by very fine striations (Calder et al. 2009) rather than being smooth as in T. borneensis, and the two are considered specifically distinct. In a study of stylasterids, Cairns (1991) considered that species of both Cocos Island and the Galápagos Islands had been derived from the western Pacific, and that they had no affinity with the eastern Pacific shelf and slope fauna of continental North and South America. In being known in the eastern Pacific only from those same oceanic islands, T. borneensis appears to have had a similar geographic origin. While possibly hailing from the Indo-West Pacific, we conservatively treat T. borneensis as cryptogenic in both the Eastern and Central Pacific. Reported distribution Cocos Island: first record. Elsewhere: shallow tropical waters from the east coast of India to the Galápagos Islands (Billard 1925a; 1925b, as Sertularia borneensis; Mammen 1965, as S. west-indica; Pennycuik 1959, as S. borneensis; Cooke 1975, as S. westindica; Van Soest 1976, as S. borneensis; Vervoort and Vasseur 1977, as S. turbinata and S. borneensis; Gibbons and Ryland 1989, as S. borneensis; Schuchert 2003, as S. borneensis; Tang, 1991, as S. westindica; Calder et al. 2003, as Tridentata longa; Kirkendale and Calder 2003; Vervoort and Watson 2003, as S. tumida; Preker and Lawn 2008, 2010, as S. borneensis)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 590-592, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Billard A. 1925 a. Note sur quelques especes la plupart nouvelles de synthecides et de sertularides du Siboga. Bulletin de la Societe Zoologique de France. 49: 646 - 652.","Billard A. 1925 b. Les hydroides de l'Expedition du Siboga. II. Synthecidae et Sertularidae. Siboga- Expeditie, Monographie. 7: 115 - 232. Publication date December l 925, following Vervoort (1995).","Van Soest RWM. 1976. A catalogue of the coelenterate type specimens of the Zoological Museum of Amsterdam. II. Benthic Hydrozoa. Beaufortia. 25 (323): 79 - 95.","Vervoort W, Vasseur P. 1977. Hydroids from French Polynesia with notes on distribution and ecology. Zool Verhandelingen. 159: 1 - 98.","Gibbons MJ, Ryland JS. 1989. Intertidal and shallow water hydroids from Fiji. I. Athecata to Sertulariidae. Mem Queensland Mus. 27: 377 - 432.","Schuchert P. 2003. Hydroids (Cnidaria, Hydrozoa) of the Danish Expedition to the Kei Islands. Steenstrupia. 27: 137 - 256.","Preker M, Lawn ID 2010. Hydroids (Cnidaria: Hydrozoa: Leptolida) from Moreton Bay, Queensland, and adjacent regions: a preliminary survey. In: Davie PJF, Phillips JA, editors. Proceedings of the Thirteenth International Marine Biological Workshop, The Marine Fauna and Flora of Moreton Bay, Queensland, Australia. Memoirs of the Queensland Museum - Nature. Vol. 54 (3): 109 - 149.","Allman GJ. 1877. Report on the Hydroida collected during the exploration of the Gulf Stream by L. F. de Pourtales, assistant United States Coast Survey. Mem Mus Comp Zool Harvard Coll. 5 (2): 1 - 66. doi: 10.5962 / bhl. title. 15852","Borradaile LA. 1905. Hydroids. In: Gardner JS, editor. The fauna and geography of the Maldive and Laccadive Archipelagoes. Being the account of the work carried on and of the collections made by an expedition during the years 1899 and 1900. Vol. 2 (4). Cambridge: Cambridge University Press; p. 836 - 845.","Stechow E. 1919. Zur Kenntnis der Hydroidenfauna des Mittelmeeres, Amerikas und anderer Gebiete, nebst Angaben uber einige Kirchenpauer'sche Typen von Plumulariden. Zool Jahrbucher, Abteilung fur Systematik, Geographie und Biologie der Tiere. 42: 1 - 172.","Leloup E. 1960. Hydropolypes du Museum National d'Histoire Naturelle de Paris. Memoires du Museum National d'Histoire Naturelle de Paris, Nouvelle Serie, Serie A, Zoologie. 17: 217 - 241.","Calder DR. 1991. Shallow-water hydroids of Bermuda. The Thecatae, exclusive of Plumularioidea. Royal Ontario Museum. Life Sci Contrib. 154: 1 - 140.","Vervoort W, Watson JE. 2003. The marine fauna of New Zealand: leptothecata (Cnidaria: Hydrozoa) (Thecate hydroids). Natl Inst Water Atmos Res Biodivers Mem. 119: 1 - 538.","Zhenzu X, Huang J-Q, Lin M, Guo D-H, Wang C-G. 2014. The superclass Hydrozoa of the phylum Cnidaria in China. Beijing: China Ocean Press. Vol. II p. 459 - 945.","Song X 2019. Biodiversity of Sertulariidae Lamouroux, 1812 (Cnidaria; Hydrozoa) in Chinese seas, with records from Chinese National Arctic and Antarctic research expeditions. Beijing: Science Press.","Stechow E. 1920. Neue Ergebnisse auf dem Gebiete der Hydroidenforschung. Sitzungsberichte der Gesellschaft fur Morphologie und Physiologie in Munchen. 31: 9 - 45.","Linnaeus C. 1758. Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Editio decima, reformata. Holmiae: Laurentii Salvii. doi: 10.5962 / bhl. title. 542","Kirchenpauer GH. 1864. Neue Sertulariden aus verschiedenen Hamburgischen Sammlungen, nebst allgemeinen Bemerkungen uber Lamouroux's Gattung Dynamena. Verhandlungen der Kaiserlichen Leopoldino-Carolinischen Deutschen Akademie der Naturforscher. 31 (3): 1 - 16.","Thornely LR. 1904. Report on the Hydroida collected by Professor Herdman, at Ceylon, in 1902, and Herdman WA, editor. Report to the Government of Ceylon on the pearl oyster fisheries of the Gulf of Manaar, with supplementary reports upon the marine biology of Ceylon, by other naturalists, part 2. p. 107 - 126. London: The Royal Society.","Mammen TA. 1965. On a collection of hydroids from south India. II. Suborder Thecata (excluding family Plumulariidae). J Mar Biol Assoc India. 7: 1 - 57.","Cooke WJ. 1975. Shallow water hydroids from Enewetak Atoll, Marshall Islands. Micronesica. 11: 85 - 108.","Lamouroux JVF. 1816. Histoire des polypiers coralligenes flexibles, vulgairement nommes zoophytes. Caen: F. Poisson. doi: 10.5962 / bhl. title. 11172","Millard NAH. 1958. Hydrozoa from the coasts of Natal and Portuguese East Africa. Part I. Calyptoblastea. Ann S Afr Mus. 44: 165 - 226.","Millard NAH. 1975. Monograph on the Hydroida of Southern Africa. Ann S Afr Mus. 68: 1 - 513.","Calder DR, Mallinson JJ, Collins K, Hickman CP. 2003. Additions to the hydroids (Cnidaria) of the Galapagos, with a list of species reported from the islands. J Nat Hist. 37: 1173 - 1218. doi: 10.1080 / 00222930110116039","Fraser CM. 1938 a. Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pac Expeditions. 4 (1): 1 - 105.","Fraser CM. 1938 b. Hydroids of the 1936 and 1937 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (2): 107 - 127.","Fraser CM. 1938 c. Hydroids of the 1932, 1933, 1935, and 1938 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (3): 129 - 153.","Fraser CM. 1948. Hydroids of the Allan Hancock Pacific Expeditions since March, 1938. Allan Hancock Pac Expeditions. 4 (5): 179 - 343.","Calder DR, Vervoort W, Hochberg FG. 2009. Lectotype designations of new species of hydroids (Cnidaria, Hydrozoa), described by C. M. Fraser, from Allan Hancock Pacific and Caribbean Sea Expeditions. Zool Mededelingen. 83: 919 - 1058.","Cairns SD. 1991. New records of Stylasteridae (Hydrozoa: Hydroida) from the Galapagos and Cocos Islands. Proc Biol Soc Wash. 104 (2): 209 - 228.","Pennycuik PR. 1959. Faunistic records from Queensland. Part V - Marine and brackish water hydroids. Pap Department Zool Univ Queensland. 1: 141 - 210.","Tang Z-C. 1991. On a collection of Hydroida from the Nansha Islands, Hainan province, China. Contrib Study Mar Biol Nansha Islands Neighbouring Waters. 1: 25 - 36. In Chinese.","Kirkendale L, Calder DR. 2003. Hydroids (Cnidaria: Hydrozoa) from Guam and the Commonwealth of the Northern Marianas Islands (CNMI). Micronesica. 35 - 36: 159 - 188."]}

Pennaria disticha Goldfuss, 1820 (Figure 2a) Pennaria disticha Goldfuss, 1820: 89. Type locality Italy: Gulf of Naples (see Calder 2013, p. 7). Material examined Chatham Bay, dock 004, 1 colony, 2.8 cm high, without gonophores, coll. G. Ashton, #266339. Remarks The hydroid of Pennaria disticha Goldfuss, 1820 has in the past been considered essentially cosmopolitan in tropical to temperate waters. While the species is known to be invasive, barcoding studies reveal the existence of cryptic species within the binomen (Miglietta et al. 2015, 2019). In the analysis of Miglietta et al. (2019), specimens from the Pacific coast of Panama, in the Tropical Eastern Pacific, occurred in both a clade (1A) with other populations from Brazil, Florida, Hawaii, China Sea, and Mayotte in the Western Indian Ocean, and in another clade (2D) with specimens from North Carolina, the Caribbean, Atlantic Panama, Hawaii, Chuuk, Guam, American Samoa, and the Red Sea. Specimens from Italy (the type locality of the species) and elsewhere in the Mediterranean occurred in a separate clade (‘Clade 2C’), along with material from the Azores and the Gulf of Mexico. Taxonomic and nomenclatural issues arising from these results have yet to be resolved, however, and the name P. disticha has been retained for specimens examined here. In the eastern Pacific, Pennaria disticha has been reported from San Francisco Bay, California, to Santa Elena Bay, Ecuador (Fraser 1937, 1938a, 1938c, 1947, 1948, as Pennaria tiarella). On the Pacific coast of Costa Rica, it has been reported from Port Culebra (Fraser (1938a) and Bahía Huevos at 10.64444°N, 85.69167°W (Kelmo and Vargas 2002). In the Galápagos Islands P. disticha is one of the most common and conspicuous species of hydroids on exposed coasts at depths ranging from the surface to 10 m, except on the westernmost Isla Fernandina (D. Calder, personal observations, 16–22 June 2001). A species of many habitats, we regard P. disticha as cryptogenic in the Tropical Eastern Pacific (including in Cocos and the Galapagos Islands), pending further resolution of the taxonomy and geography of the multiple genetic clades detected to date. Reported distribution Cocos Island: first record. Elsewhere: reported to be circumglobal in tropical and warm-temperate waters, although cryptic species appear to exist (Calder 2010; Miglietta et al. 2015, 2019)., Published as part of Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, pp. 565-606 in Journal of Natural History 56 (9 - 12) on pages 572-573, DOI: 10.1080/00222933.2022.2068387, http://zenodo.org/record/7012486, {"references":["Goldfuss GA. 1820. Handbuch der Zoologie. I. Abtheilung. Nurnberg: Johann Leonhard Schrag.","Calder DR. 2013. Some shallow-water hydroids (Cnidaria: Hydrozoa) from the central east coast of Florida, USA. Zootaxa. 3648: 1 - 72. doi: 10.11646 / zootaxa. 3648.1.1","Miglietta MP, Odegard D, Faure B, Faucci A. 2015. Barcoding techniques help tracking the evolutionary history of the introduced species Pennaria disticha (Hydrozoa, Cnidaria). PLoS ONE. 10 (12): e 0144762. doi: 10.1371 / journal. pone. 0144762","Miglietta MP, Maggioni D, Matsumoto Y. 2019. Phylogenetics and species delimitation of two hydrozoa (phylum Cnidaria): Turritopsis (McCrady, 1857) and Pennaria (Goldfuss, 1820). Mar Biodivers. 49: 1085 - 1100. doi: 10.1007 / s 12526 - 018 - 0891 - 8","Fraser CM. 1937. Hydroids of the Pacific coast of Canada and the United States. Toronto: University of Toronto Press. doi: 10.3138 / 9781487595548","Fraser CM. 1938 a. Hydroids of the 1934 Allan Hancock Pacific Expedition. Allan Hancock Pac Expeditions. 4 (1): 1 - 105.","Fraser CM. 1938 c. Hydroids of the 1932, 1933, 1935, and 1938 Allan Hancock Pacific Expeditions. Allan Hancock Pac Expeditions. 4 (3): 129 - 153.","Fraser CM. 1947. Distribution and relationship in American hydroids. Toronto: University of Toronto Press.","Fraser CM. 1948. Hydroids of the Allan Hancock Pacific Expeditions since March, 1938. Allan Hancock Pac Expeditions. 4 (5): 179 - 343.","Kelmo F, Vargas R. 2002. Anthoathecatae and Leptothecatae hydroids from Costa Rica (Cnidaria: Hydrozoa). Rev Biol Trop. 50: 599 - 627.","Calder DR. 2010. Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago. Zootaxa. 2590: 1 - 91. doi: 10.11646 / zootaxa. 2590.1.1"]}