Obelia hyalina Clarke, 1879

Calder, Dale R., 2019, On a collection of hydroids (Cnidaria, Hydrozoa) from the southwest coast of Florida, USA, Zootaxa 4689 (1), pp. 1-141 : 61-63

Obelia hyalina Clarke, 1879

Fig. 17b , 18

Obelia hyalina Clarke, 1879: 241 , pl. 4, fig. 21.— Fraser, 1943: 89; 1944: 160.— Shier, 1965: 40, pl. 22.

Obelia dichotoma .— Wallace, 1909: 137 [not Obelia dichotoma ( Linnaeus, 1758) ].

Type locality. Mexico: “Ten miles (16 km) north of Zoblos Island” (= Isla Holbox ) ( Clarke 1879: 242) .

Material examined. Fort Myers Beach, on stranded shell with Idiellana pristis , 01 March 2013, one colony, 7 mm high, without gonophores, coll. D. Calder, ROMIZ B4358.— Fort Myers Beach , on dead sand dollars ( Mellita quinquiesperforata ) near low water, 19 January 2018, several colony fragments, up to 1.4 mm high, without gonothecae, coll. D. Calder, ROMIZ B4359 .— Captiva Island , Turner Beach, 26°28’57.3”N, 82°11’02.8”W, on jetty, rocks at low tide, 01 March 2018, several colony fragments, up to 9 mm high, without gonothecae, coll. D. Calder, ROMIZ B4360 .— Sanibel Island , beach at Lighthouse Point, 26°26’57”N, 82°01’06”W, on detached Thalassia at water’s edge, 13 March 2018, 20° C, 33.5‰, one colony, 6 mm high, without gonophores, coll. D. Calder, ROMIZ B4361 .

Remarks. Obelia hyalina was generally recognized as a valid species over the first half of the 20 th century. Thereafter, it was treated in most works as conspecific with the supposedly cosmopolitan O. dichotoma ( Linnaeus, 1758) . Once again, for reasons outlined in a previous study ( Calder 2013), O. hyalina is recognized as valid here. Separating records of the two species in accounts by authors who had combined them under one binomen is problematic. Reports of the boreal O. dichotoma from the Gulf of Mexico and Caribbean regions are taken here, and in distribution records below, to have been based on specimens of the tropical and warm-temperate O. hyalina . Morphologically, O. hyalina differs from O. dichotoma in a number of characters: (1) colonies are small (<2.5 cm high); (2) hydrocauli are little if at all branched, and are almost always monosiphonic; (3) hydrothecae lack distal longitudinal folds; (4) hydrothecal rims are entire rather than crenulate or slightly so.

Differences in cnidome have been found to exist in polyps of certain species of Obelia Péron & Lesueur, 1810 from Europe ( Östman 1982, 1987, 1999). In O. dichotoma , the nematocyst complement consists of so-called Atype b-rhabdoids (microbasic b-mastigophores), as well as curved and exceedingly slender I d - type isorhizas and curved but somewhat thicker I D - type isorhizas. The cnidome of specimens from southwest Florida identified as O. hyalina ( Fig. 18 ) comprises nematocysts like the first two types, with the third resembling I g - type isorhizas found in O. geniculata ( Linnaeus, 1758) ( Östman 1982, 1999). Most abundant in material examined here were A-type bmastigophores (5.3–5.8 long x 1.5–1.8 μm wide, undischarged, n=10, ROMIZ B4361), although I g - type isorhizas (7.1–8.2 long x 0.8–1.3 μm wide, n=10, undischarged, ROMIZ B4361) and I d - type isorhizas (6.2–7.3 long x 0.4–0.7 μm wide, undischarged, n=10, ROMIZ B4361) were also well-represented. The presence of isorhizas more closely resembling the I g - type rather than the I D - type in these specimens is taken as additional evidence that O. hyalina is distinct from O. dichotoma .

As with other species of the genus Obelia , O. hyalina is known to have a metagenetic life cycle. Its newly liberated medusa stage was described by Vannucci (1955), based on specimens from Brazil. Medusae of Obelia , including those of O. hyalina , are reduced and morphologically unique. Unusual characters of note include: (1) presence of an umbrella that is flattened and disc-shaped, with thin and flexible mesoglea; (2) marginal tentacles that are solid, short, stiff, essentially inextensible, and with endodermal bases projecting into the mesoglea of the umbrella margin; (3) a velum that is rudimentary or absent. While Obelia medusae are thereby highly distinctive, those liberated by the various hydroid species of the genus are so alike in morphology that they have long been considered essentially indistinguishable ( Russell 1953: 297; Kramp 1959: 146). An overview of the medusoid characters of Obelia has been given by Cornelius (1975a, 1990, 1995b, 1999), and others.

In being a component of the biota associated with pelagic Sargassum , O. hyalina is transported wherever floating gulfweed is carried by ocean currents. Thus, it has been reported to the east of Nova Scotia in the Gulf Stream ( Fraser 1918), from mid-ocean (43.4°N, 31°W) in the North Atlantic Drift (Leloup 1935), and from across the Sargasso Sea ( Timmermann 1932), as well as from tropical and warm-temperate inshore waters. However, its normal range in the western North Atlantic appears to be from North Carolina ( Fraser 1912b; Wells et al. 1964; Cain 1972) to the southern Caribbean Sea (Leloup 1935; Wedler 1975, as Laomedea congdoni ), and from there southwards to Brazil in the western South Atlantic ( Vannucci 1955).

Among subjective synonyms of O. hyalina are O. congdoni Hargitt, 1909 , Laomedea sargassi Broch, 1913 , and Gonothyraea integra Fraser, 1940 , found on sunken Sargassum off Block Island, Rhode Island ( Calder & Choong 2018). Additional comments on the hydroid of O. hyalina are given elsewhere ( Calder 2013).

Reported distribution. Gulf coast of Florida. Dry Tortugas ( Wallace 1909: 137, as Obelia dichotoma ).—Key West ( Fraser 1943: 89).—SW of Key West, Eastern Dry Rocks, on reefs ( Fraser 1943: 89).—Key West ( Fraser 1944: 161).—Cape San Blas area, on Syringodium and Diplanthera (= Halodule ) ( Shier 1965: 119).

Elsewhere in western North Atlantic. Mexico: 10 miles (16 km) N of “ Zoblos Island ” (= Isla Holbox) ( Clarke 1879: 242).— USA: Gulf Stream, unstated location off the southeastern US, on gulfweed ( Nutting 1895: 30).— Cuba: near Havana, off Morro Castle, “ Pentacrinus Grounds ”, on floating seaweed ( Nutting 1895: plate after p. 88, as Obella hyalina ).—Sargasso Sea: SE of Bermuda, 30°N, 70°W, on floating Sargassum ( Versluys 1899: 30) .— Bermuda: shallow water areas, on sponges, algae, large hydroids ( Congdon 1907: 468).— USA: Massachusetts, Woods Hole, on floating gulfweed ( Hargitt 1909: 375, as Obelia congdoni ).— USA: Louisiana, abundant on stranded gulfweed and floating wood in spring ( Cary & Spaulding 1909: 6, as Obelia dichotoma ).— USA: North Carolina, Beaufort area, off Bogue Bank, on Sargassum + Marshallberg, pilings, on ascidians + dredged offshore, on sponge ( Fraser 1912b: 363).— Cuba: Havana Harbor, on a buoy and a mussel ( Stechow 1914: 130, as Obelia dichotoma ).— USA: North Carolina, Beaufort ( Nutting 1915: 76).— Canada: E of Nova Scotia in the Gulf Stream, on Sargassum ( Fraser 1918: 350) .— Bermuda: on floating Sargassum + Agar’s Island, on a fish-car ( Bennitt 1922: 249).—Sargasso Sea, on Sargassum ( Hentschel 1922: 4, as Laomedea sargassi ).—Sargasso Sea: numerous stations (23), on Sargassum ( Timmermann 1932: 297–303).— Bonaire: Plaja Flambaai, on stranded algae (Leloup 1935: 24, as Laomedea sargassi ).— Aruba: Boca Prins, on stranded Sargassum (Leloup 1935: 24, as Laomedea sargassi ).—Sargasso Sea: 29°N, 44°W, on Sargassum + 30°N, 54°W, on Sargassum (Leloup 1935: 24, as Laomedea sargassi ).— North Atlantic Drift: 43.4°N, 31°W, on Sargassum (Leloup 1935: 24, as Laomedea sargassi ).—Sargasso Sea: E of Florida, 29°50’N, 74°W, on floating Sargassum + SE of Bermuda, 30°11’N, 71°08’W, on floating Sargassum + W of Bermuda, 32°07’N, 66°35’W, on floating Sargassum ( Leloup 1937: 101, as Laomedea sargassi ).— USA: Texas, Corpus Christi Bay ( Cross & Parks 1937: 9, as Obelia dichotoma ).—Gulf Stream, on pelagic Sargassum + Sargasso Sea, on pelagic Sargassum (Burkenroad, in Parr 1939: 24, as Obelia ).— USA: Rhode Island, Block Island, 1.25 miles (2 km) from North Light, on sunken Sargassum , 13 ftm (24 m) ( Fraser 1940: 577, as Gonothyraea integra ).—Gulf Stream: seaward of continental shelf E of Delaware, 130–167 miles (209–269 km) S of Nantucket (Massachusetts), surface, on gulfweed + 100 miles (161 km) E of Cape Hatteras, on Sargassum ( Fraser 1943: 89) .—? USA: New Jersey, on crustaceans parasitic in mouth of the shark Odontaspis ( Fraser 1943: 89) .— Haiti: Jérémie, on gulfweed ( Fraser 1943: 89).— Canada: Nova Scotia, S of Cape Sable, 41°43’N, 65°21’50”W, 1309 ftm (2394 m) (on sunken Sargassum ?) ( Fraser 1944: 161).— USA: Massachusetts, S of Marthas Vineyard, 39°57’30”N, 70°51’15”W, 150 ftm (274 m), (on sunken Sargassum ?) ( Fraser 1944: 161).— USA: Massachusetts, S of Nantucket, 38°59’N, 70°07’W, 1544 ftm (2824 m) (?on sunken Sargassum ?) ( Fraser 1944: 161).— USA: Massachusetts, off Marthas Vineyard, 38°25’N, 72°40’W, on floating Sargassum ( Fraser 1944: 161) .— USA: Florida, Florida Straits, on Sargassum ( Fraser 1944: 161) .— Cuba: off Havana, on Sargassum ( Fraser 1944: 161) .—? USA: Louisiana coast ( Fraser 1944: 157, as Obelia equilateralis ).—Sargasso Sea: on Sargassum ( Vervoort 1946: 346, as Laomedea sargassi ).—? Panama: Caledonia Bay (Puerto Escoces), on hand line on rocky reef ( Fraser 1947b: 7, as Obelia equilateralis ).— USA: Florida, Biscayne Bay, on boat slips ( Weiss 1948: 158).— USA: Texas, off Sabine Pass, on buoys + Galveston Bay, on buoy + Sabine Bank, on buoys + off Freeport, on buoys + Matagorda Island, on buoys + Port Aransas, on driftwood, blue crab, oysters, Sargassum , tar + Port Aransas, on south jetty ( Deevey 1950: 343, as Obelia dichotoma ).— USA: Texas, Port Aransas, jetties ( Hedgpeth 1950: 73, as Obelia dichotoma ).— USA: Louisiana, Grand Isle, on Sargassum ( Behre 1950: 7) .—Unstated location: on buoys ( Woods Hole Oceanographic Institution 1952: 187).— USA: Mississippi, Mississippi Sound ( Fincher 1955: 92, as Obelia gracilis ).— USA: North Carolina, Core Banks, on Aequipecten gibbus , 17–20 ftm (31–37 m) ( Wells et al. 1964: 566).— Venezuela: “La Guaria” (= La Guaira) ( Vervoort 1968: 23, as Laomedea (Obelia) congdoni ).— USA: North Carolina, Lithothamnion reef S of Cape Lookout ( Cain 1972: 80).— USA: Texas, Galveston, on wooden pilings, submerged debris, Sargassum , blue crabs, Thais , hydroids ( Defenbaugh & Hopkins 1973: 86, as Obelia dichotoma ).— USA: Texas, West Flower Garden Bank, on glass float, float cable, floating Sargassum ( Defenbaugh 1974: 99, as Obelia dichotoma ).—Sargasso Sea + Gulf Stream, several stations between Florida and New Jersey, on Sargassum natans I, S. natans IX, S. fluitans III, S. fluitans , S. ramifolium , S. filipendula , S. polyceratium , S. pteropleuron , S. bermudense , Sargassum sp. ( Rackley 1974: 32).— Colombia: Santa Marta area, rocky littoral ( Wedler 1975: 340, as Laomedea congdoni ; Bandel & Wedler 1986: 41, as Obelia dichotoma ).— Colombia: north coast ( Mergner 1977: 122, as Laomedea (Obelia) congdoni ; 1987: 187, as Laomedea (Obelia) congdoni ).— USA: Florida, southeast coast ( Mergner 1977: 122, as Laomedea (Obelia) congdoni ; 1987: 187, as Laomedea (Obelia) congdoni ).— USA: South Carolina, estuaries, unstated locations ( Calder & Hester 1978: 90).— USA: Texas, Buccaneer oil field, on oil platform ( Fotheringham 1981: 194).— Belize: Carrie Bow Cay area, on Thalassia , mangrove roots, floating Sargassum , dead corals and gorgonians ( Spracklin 1982: 249, as Obelia dichotoma ).— USA: continental shelf off South Carolina and Georgia ( Wenner et al. 1983, as Obelia dichotoma ).— USA: South Carolina, inner (17–18 m), middle (32–36 m) and outer (46–69 m) continental shelf, + Georgia, inner (17–22 m), middle (23–29 m) and outer (59–67 m) continental shelf ( Wenner et al. 1984: 20, 39, as Obelia dichotoma ).— Colombia: Bahía de Cartagena region ( Flórez González 1983: 123, as Obelia dichotoma ).— USA: South Carolina, North Inlet area, Town Creek and tributaries + North Inlet, Baruch Plantation, oyster landing + North Inlet, pilings + Murrells Inlet, jetties + Murrells Inlet, Capt. Dick’s marina, floating docks + Charleston area + Breach Inlet, jetties + Isle of Palms, marina, floating docks + Hunting Island, seawalls and rubble + Beaufort area, floating docks ( Fox & Ruppert 1985: 61, 76, 84, 93, 104, 141, 167, 177, 226, 232, as Obelia dichotoma ).— Bermuda: shallow inshore waters, buoy chains ( Calder 1986: 136, as Obelia dichotoma ).—Sargasso Sea: on Sargassum natans ( Niermann 1986: 347, as Obelia dichotoma ).— USA: Louisiana, on coastal petroleum platforms ( Lewbel et al. 1987: 214, as Obelia dichotoma ).— USA: South Carolina, continental shelf, fouling plates ( Van Dolah et al. 1988: 684, as Obelia dichotoma ).— USA: South Carolina and Georgia, inner continental shelf, on artificial reefs ( Wendt et al. 1989: 1112, as Obelia dichotoma ).— USA: South Carolina, coastal areas, in stomachs of Atlantic spadefish ( Hayse 1990: 81, as Obelia dichotoma ).— Bermuda: Flatts Inlet, 0.5–2 m, on rock, algae, Thyroscyphus marginatus , barnacle + Whalebone Bay, on pelagic Sargassum + Ferry Reach, 3 m, on float line + Atlantic Ocean, 2 km SE of Castle Roads, 0–10 m, on pelagic Sargassum and polypropylene trap lines + Green Bay Cave, 40 m inside, 5–6 m depth, on Eudendrium sp. + Natural Arches Beach, on stranded Sargassum (Calder 1990 [1991a]: 73–74, as Obelia dichotoma ).— Belize: Twin Cays ( Calder 1991b: 223, as Obelia dichotoma ).— Belize: South Water Cay, South Water Cut, on Thalassia ( Kaehler & Hughes 1992: 331, as Obelia dichotoma ).— USA: Florida, off Vero Beach, on artificial reef ( Nelson et al. 1994: 1306).— Bermuda: various locations, on Sargassum natans , S. fluitans ( Calder 1995: as Obelia dichotoma ).— Cuba: north coast ( Ortiz Rosado 2000: 87, as Obelia dichotoma ).— Bermuda: Argus (=Plantagenet) Bank + Challenger Bank ( Calder 2000: 1134, as Obelia dichotoma ).— Cuba: Ciudad de La Habana province, Cojimar, on Sargassum ( Ortiz 2001a: 64, as Campanularia cf. angulata ).— Panama: Canal Zone, Atlantic side, Buoy #6 + Colón, Fort Sherman dock, wood, 09°22’12”N, 79°56’59”W, 0-2 m + Colón, Club Nautico, steel pilings, 09°21’51”N, 79°53’39”W, 0-1 m + Bocas del Toro area, Crawl Cay, 09°15.261’N, 82°07.787’W, 2–4 m + Bocas del Toro area, Swan’s Key, 09°27’12.2”N, 82°18’01.8”W, 1-4 m + Bocas del Toro area, Bastimentos (north), 09°20.898’N, 82°09.959’W, 1–4 m + Bocas del Toro area, Drago 2, 1– 2 m + Bocas del Toro area, Drago 2, 2– 4 m ( Calder & Kirkendale 2005: 487, as Obelia dichotoma ).— USA: Florida, Canaveral National Seashore, on Caretta caretta ( Pfaller et al. 2008: 1097, as Obelia dichotoma ; Reich et al. 2010: 117, as Obelia dichotoma ).—French Lesser Antilles: Guadeloupe, Grande-Terre, L’Oeil, 16°26.782’N, 61°32.405’W, 12–15 m, on gorgonian + Grande-Terre, Pointe d’Antigues, 16°26.251’N, 61°32.523’W, 10 m, on gorgonian + Grande-Terre, Passe à Colas, 16°21.269’N, 61°34.193’W, 10–15 m, on sponge ( Galea 2010: 9, as Obelia dichotoma ).— USA: Florida, Fort Pierce, Fort Pierce Inlet State Park, 27°28’29.5”N, 80°17’25.8”W, on stranded Sargassum fluitans ( Calder 2013: 58) .—French Lesser Antilles: Martinique ( Galea 2013: 49, as Obelia dichotoma ).—Caribbean Sea ( Wedler 2017b: 96, figs. 87A, B, 88, 89, as Obelia dichotoma ).— Mexico: Alacranes Reef, on algae, sponges, hydroids, soft corals, ascidians, rock, artificial reef ( Mendoza-Becerril et al. 2018b: 131, as Obelia dichotoma ).— Cuba: Havana, coral reef system west of the city (Castellanos et al. 2018: 572, Supplementary Table S2, as Obelia dichotoma ).— Panama: Bocas del Toro area, Punta Hospital + Crawl Cay ( Miglietta et al. 2018b: 108).

Figures

FIGURE 17. a, Obelia geniculata: basal part of hydrocaulus with two hydrothecae, Sanibel Island, ROMIZ B4357. Scale equals 0.2 mm. b, Obelia hyalina: part of hydrocaulus with a hydrotheca, Fort Myers Beach, ROMIZ B4358. Scale equals 0.1 mm. c, Obelia oxydentata: part of hydrocaulus with a hydrotheca, Sanibel Island, ROMIZ B4364. Scale equals 0.1 mm. d, Obelia oxydentata: part of hydrocaulus with a hydrotheca, Caloosahatchee River at Fort Myers, ROMIZ B4362. Scale equals 0.1 mm. e, Obelia oxydentata: gonotheca, Caloosahatchee River at Fort Myers, ROMIZ B4362. Scale equals 0.1 mm. f, Obelia oxydentata: colony undergoing stolonization from the hydrocaulus, Caloosahatchee River at Fort Myers, ROMIZ B4362. Scale equals 0.1 mm.

FIGURE 18. Obelia hyalina: nematocysts, ROMIZ B4361. a, A-type b-mastigophores. b, A-type b-mastigophores (?). c, Ig- type isorhiza. d, Id-type isorhiza.