Obelia oxydentata Stechow, 1914

Calder, Dale R., 2019, On a collection of hydroids (Cnidaria, Hydrozoa) from the southwest coast of Florida, USA, Zootaxa 4689 (1), pp. 1-141 : 65-66

Obelia oxydentata Stechow, 1914

Figs. 17 c–f

Obelia (?) oxydentata Stechow, 1914: 131 , fig. 7.

? Laomedea bicuspidata .— Leloup, 1937: 99, figs. 4A, B [not Obelia bicuspidata Clark, 1875 = O. bidentata Clark, 1875 ].

Obelia bicuspidata .— Fraser, 1944: 154.— Deevey, 1950: 343; 1954: 270 [not Obelia bicuspidata Clark, 1875 = O. bidentata Clark, 1875 ].

Obelia oxydentata .— Joyce, 1961: 56, pl. 12, figs. 1, 2.

Clytia longicyatha .— Shier, 1965: 39, pl. 21 [not Obelia longicyatha Allman, 1877 ].

Type locality. Virgin Islands of the United States: St. Thomas , Charlotte Amalie ( Stechow 1914: 131) .

Material examined. Caloosahatchee River at Fort Myers, 26°38.788’N, 81°52.356’W, on floating dock, less than 1 m, 25 March 2012, 25° C, 17‰, several colonies, up to 1.2 cm high, with gonophores, coll. D. Calder, ROMIZ B4362. — Caloosahatchee River at Fort Myers, 26°38.790’N, 81°52.354’W, on floating dock, less than 1 m, 18 July 2012, 7‰, several colonies, up to 10 mm high, with gonophores, coll. D. Calder, ROMIZ B4363 . — Sanibel Island , beach at Lighthouse Point, 26°26’57”N, 82°01’07”W, on a detached alga, in intertidal pool, 03 August 2014, one colony, 5 mm high, without gonophores, coll. D. Calder, ROMIZ B4364 .— Fort Myers Beach , on detached Thalassia testudinum , 30 October 2017, one colony, 5 mm high, without gonophores, coll. D. Calder, ROMIZ B4365 .— Fort Myers Beach , Salty Sam’s Marina, 26°27’21.7”N, 81°56’34.6”W, on floating dock on oyster shells, algae, and Calyptospadix cerulea , <0.1 m, 24 C, 22 February 2018, three colonies, up to 1 cm high, without gonophores, coll. D. Calder, ROMIZ B4366 .— 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, 4 mm high, without gonophores, coll. D. Calder, ROMIZ B4367 .— Caloosahatchee River at Fort Myers, 26°38.788’N, 81°52.356’W, on floating dock, less than 1 m, 29 March 2018, 22° C, 15‰, several colonies, up to 1 cm high, condition very good, without gonophores, coll. D. Calder, ROMIZ B4368 .

Remarks. Reasons for recognizing Obelia oxydentata Stechow, 1914 as distinct from O. bidentata Clark, 1875 have been discussed earlier ( Calder 2013, 2017; Calder et al. 2019). Supporting evidence exists from differences in colony morphology and geographic distribution, and most recently from the results of molecular studies. Hydroids of O. bidentata (type locality: Greenport, Long Island, New York) are large (commonly 5–10 cm but reaching as much as much as 35 cm high) and polysiphonic when fully developed, and they occur in temperate to cool-temperate regions. Those of O. oxydentata (type locality: U.S. Virgin Islands) are tiny (usually 1-2 cm high or less) and monosiphonic, even when fertile, and they inhabit tropical and warm-temperate waters. While evidence from molecular studies is thus far indirect (e.g., Govindarajan et al. 2006; Leclere et al. 2009), populations identified as O. bidentata from North Carolina (but probably referable to O. oxydentata ) appear to be genetically distinct from those collected in northwest Europe (likely identified correctly as O. bidentata ).

From the records below, O. oxydentata can be regarded primarily as a species of shallow and more or less sheltered inshore waters, including harbours, rivers, canals, bayous, lagoons, seagrass beds, and mangrove swamps. It has also been reported as part of the floating Sargassum fauna (e.g., Fraser 1944; Defenbaugh & Hopkins 1973; both as O. bicuspidata ). In the region studied here, no record of O. oxydentata was found below a depth of 18 m and most were much less. Obelia oxydentata also is a decidedly euryhaline species, having been collected during this study at salinities as low as 7‰. As a species forming part of the fouling community in harbours ( Calder et al. 2019), it has likely been transported widely by shipping.

Hydroids identified as Clytia longicyatha ( Allman, 1877) by Shier (1965) from northern Florida appear to correspond with O. oxydentata as understood here, although they were said to be fascicled at the base. They reached a height of only 6–12 mm, yet gonothecae were observed on the colonies. Certain other reports of C. longicyatha from the warm western North Atlantic (distribution records listed in Fraser 1944) may also have been based on O. oxydentata . Clytia longicyatha , dredged off the Florida reef at a depth of 90 fathoms (165 m) ( Allman 1877), has incorrectly been considered a synonym of O. bidentata in some contemporary works (Calder 1991). The species, described by Allman as being about 2.5 cm high and with a fascicled stem, somewhat resembles both O. bidentata and O. oxydentata . In particular, marginal cusps of its hydrothecae are bimucronate. However, examination of two colonies or colony fragments of the species from deep water off Bermuda (2 km off Castle Roads, 329 m, on line of a crab trap, 04.iv.1992, coll. D. Calder) essentially confirms Allman’s brief account. The colony form is that of a species of Clytia Lamouroux, 1812 rather than Obelia Péron & Lesueur, 1810 , and its hydrothecae are much deeper than those of either O. bidentata or O. oxydentata . Clytia longicyatha is a valid, deep water species.

In the western North Atlantic, Obelia oxydentata is believed here to range from Chesapeake Bay ( Calder 1971, as Obelia bicuspidata ) to the tropics. The hydroid is widespread in the Caribbean region, and it occurs southwards at least to southern Brazil ( Oliveira et al. 2016, as O. bidentata ). Records of it from cold and deeper waters in southern South America are likely based on other species. It has also been reported in parts of the tropical eastern Pacific ( Stechow, 1914; Calder et al. 2019) and Indian Ocean ( Gravier-Bonnet 1999). As for the cool-temperate O. bidentata , it occurs from Minas Basin, Nova Scotia ( Calder 2017) at least to South Carolina ( Calder & Hester 1978: 90, as O. longicyatha ).

Reported distribution. Gulf coast of Florida.?Off Tampa Bay, 7–10 miles (11–16 km) offshore, 8–10 ftm (15–18 m) ( Leloup 1937: 99, as Laomedea bicuspidata ).—Tampa Bay ( Fraser 1944: 154, as Obelia bicuspidata ).— West coast of Florida ( Deevey 1950: 343, as Obelia bicuspidata ).— Florida Keys ( Deevey 1954: 270, as Obelia bicuspidata ).—Seahorse Key ( Joyce 1961: 56).— Cape San Blas area ( Shier 1965: 39, as Clytia longicyatha ).

Elsewhere in western North Atlantic. USA: North Carolina, Beaufort + Bogue Sound, 10 ft (3 m) + North Riv- er, 8–10 ft (2–3 m) ( Fraser 1912b: 362, as Obelia bicuspidata ).— Virgin Islands of the United States: St. Thomas, Charlotte Amalie ( Stechow 1914: 131; 1919: 50; Ruthensteiner et al. 2008: 19).—? Bonaire: Kralendijk, 0.2–0.3 m + northern lagoon (“lagune septentrionale”), 0.2–0.5 m + lagoon, southern coast (“Lagoen, cote meridionale”), 0.3 m ( Leloup 1935a: 26, as Laomedea spinulosa var. minor ).—? Aruba: Boca Prins, on stranded Sargassum ( Leloup 1935a: 26, as Laomedea spinulosa var. minor ).— USA: Louisiana, Grand Isle + Bayou Pass + Bayou de Gettes + Hog island + Barataria Bay ( Fraser 1944: 154, as Obelia bicuspidata ; Behre 1950: 7, as Obelia bicuspidata ).— USA: Florida, Biscayne Bay ( Weiss 1948: 158).— USA: Florida, east coast ( Deevey 1950: 343, as Obelia bicuspidata ).— Bahamas ( Deevey 1950: 343, as Obelia bicuspidata ).— Panama ( Deevey 1950: 343, as Obelia bicuspidata ).—Unstated location: on buoys ( Woods Hole Oceanographic Institution 1952: 187).— USA: Mississippi, Mississippi Sound ( Fincher 1955: 92).— French Guiana: Cayenne + W of Grand Cermérable ( Leloup 1960, as Laomedea bicuspidata ).— USA: Mississippi, Horn Island ( Richmond 1962: 69).— Venezuela: Lake Maracaibo, Isla de Zapara, north coast, shore ( Rodriguez 1963: 214).— USA: Virginia, Norfolk, Norfolk Naval Base Pier 12, on fouling panels, 5 m ( Calder & Brehmer 1967: 153, as Obelia bicuspidata ).— Venezuela: La Guaira ( Vervoort 1968: 19, as Laomedea (Obelia) bicuspidata ).— Guatemala: Puerto Barrios ( Vervoort 1968: 19, as Laomedea (Obelia) bicuspidata ).—? Panama: Colón ( Vervoort 1968: 19, as Laomedea (Obelia) longicyatha ).— USA: Virginia, York River at VEPCO (electric power plant) outfall + Hampton Roads, Norfolk Naval Base Pier 12 ( Calder 1971: 53, as Obelia bicuspidata ).— USA: Texas, Galveston ( Defenbaugh 1972: 387; Defenbaugh & Hopkins 1973: 84; both as Obelia bicuspidata ).— Colombia: Ciénaga Grande de Santa Marta, entrance ( Wedler 1973: 34, as Laomedea bicuspidata ).— Colombia: Santa Marta ( Wedler 1975: 340, as Laomedea bicuspidata ).— USA: Florida, Bache Shoal ( Mergner 1977: 122, as Laomedea (Obelia) bicuspidata ; 1987: 187, as Laomedea (Obelia) bicuspidata ).— USA: South Carolina, estuaries, widespread ( Calder & Hester 1978: 90, as Obelia bidentata ).— Colombia: Ciénaga Grande de Santa Marta ( Palacios 1979: 114).— Colombia: Bahía de Cartagena region ( Flórez González 1983: 123, as Obelia bicuspidata ).— USA: South Carolina, Murrells Inlet, Capt. Dick’s Marina, floating docks + Charleston area + Folly River area, Oak Island, oyster reefs + Folly River, pilings + Isle of Palms, marina, on floating docks + Beaufort River, oyster reefs + Beaufort area, pilings and seawalls ( Fox & Ruppert 1985: 104, 141, 152, 162, 177, 211, 219, as Obelia bidentata ).— Bermuda: Ferry Reach at Bermuda Biological Station, 0.5 m + Castle Harbour, cave entrance near Tucker’s Town Bay, 2 m + Flatts Inlet, 1.5 m (Calder 1990 [1991a]: 71, as Obelia bidentata ).— Belize: Twin Cays ( Calder 1991b: 223, as Obelia bidentata ).— Panama: Buoy #6, Atlantic side, Canal Zone + Mole Buoy, Atlantic entrance to canal + Colón, Fort Sherman dock, 09°22’12”N, 79°56’59”W, 0–2 m + Colón, bridge near Fort Sherman, 09°17’33”N, 79°55’22”W, 0–2 m + Colón, Fort Sherman dock, marina, 09°20’57”N, 79°54’10”W, 0–2 m + Colón, Club Nautico, steel pilings, 09°21’51”N, 79°53’39”W, 0–1 m + Colón, Isla Margareta, Fort Randolph, shore, 09°23’15”N, 79°53’11”W, 0–1 m + Portobelo Harbor, dock, 09°33’14”N, 79°39’34”W, 0–1 m ( Calder & Kirkendale 2005: 487, as Obelia bidentata ).— Cuba: Playa Baracoa, 2 m ( Varela et al. 2005: 178, as Obelia bidentata ).— USA: North Carolina, Beaufort ( Govindarajan et al. 2006: 823, as Obelia bidentata ).—French Lesser Antilles: Guadeloupe, Grande-Terre, mangrove, Petit Canal, 16°21.891’N, 61°30.137’W, 0.5 m ( Galea 2010: 9, as Obelia bidentata ).— USA: Florida, Fort Pierce, ship canal at Link Port, 27°32’05”N, 80°20’50”W, 0.1 m ( Calder 2013: 59).—French Lesser Antilles: Martinique ( Galea 2013: 49, as Obelia bidentata ).—Caribbean Sea ( Wedler 2017b: 94, figs. 85A, B, 86A–C, as Obelia bidentata ).— Panama: Bocas del Toro area, San Cristóbal + vicinity of Manuguar Cay ( Miglietta et al. 2018b: 108, as Obelia bidentata ).

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.