Obelia geniculata ( Linnaeus, 1758 )

Calder, Dale R., 2019, On a collection of hydroids (Cnidaria, Hydrozoa) from the southwest coast of Florida, USA, Zootaxa 4689 (1), pp. 1-141 : 57-58

Obelia geniculata ( Linnaeus, 1758)

Fig. 17a

Sertularia geniculata Linnaeus, 1758: 812 .

Obelia geniculata .— Joyce, 1961: 57, pl. 12, figs. 3, 4.— Bros, 1987: 503.

Type locality. UK: Dover (see Cornelius 1975a: 273) .

Material examined. Sanibel Island, beach at Lighthouse Point, 26°26’58”N, 82°01’04.5”W, on stranded Sargassum pteropleuron , 21 March 2018, 22° C, 34.5‰, two colonies, up to 4.5 mm high, without gonophores, coll. D. Calder, ROMIZ B4357.

Remarks. Of all the hydroids known to science, Obelia geniculata ( Linnaeus, 1758) is likely one of the most familiar. Along with species of Hydra Linnaeus, 1758 , it is often mentioned in science textbooks, studied in labo- ratories of introductory biology and invertebrate zoology, and used in experimental research. In being widespread in distribution, abundant over many parts of its range, easy to collect because of its occurrence in shallow waters, recognizable from its distinctive morphology, and addressed in many classic and influential early taxonomic works on hydroids (e.g., Johnston 1838, 1847; Hincks 1868 [1869], Nutting 1915; Fraser 1937, 1944), it has long been well-known. Long lists of references in publications such as those by Nutting (1915) and especially Medel & Vervoort (2000) attest to the volume of research undertaken on the species. While named early on by Linnaeus (1758: 812), as Sertularia geniculata , the synonymy of the species in that publication referred back even further in time to the “Knotted-thread Coralline” (“ Corallina minor repens caule nodoʃo, articulato & veʃiculis alternis inʃtructo ”) of Ellis (1755: 22, pl. 12, fig. b, B). Cornelius (1975a: 273) offered evidence that the account of this hydroid by Linnaeus was based solely on the illustration by Ellis, and that the type locality is likely to have been Dover, UK.

Distribution records of O. geniculata below suggest an essentially continuous range of the species on this coast from northern Hudson Bay and Hudson Strait ( Fraser 1944; Calder 1970), and the west coast of Greenland ( Kramp 1932: 66), to the southern Caribbean Sea ( Versluys 1899; Wedler 1975; Flórez González 1983; Bandel & Wedler 1987). The hydroid has also been reported in the western South Atlantic from Brazil, Argentina, the Falkland Islands, and South Georgia ( Oliveira et al. 2016). Hydroids identified as O. geniculata occur in the Pacific and Indian oceans ( Fraser 1938a, b; Millard 1975; Hirohito 1995) as well as in the Atlantic.

While O. geniculata has generally been regarded as essentially cosmopolitan in shallow neritic waters, misgivings have existed whether this can be so based on the exceptionally wide reported distribution of the species, morphological variations in populations from one location to another, and more recently on differences in DNA. Latitudinally, the hydroid is believed to occur from subpolar to tropical waters, exceptional for a marine species. In New Zealand, Ralph (1956) found that hydroids assigned to O. geniculata from the subantarctic were eight times taller than those from subtropical locations. She also documented a poleward increase in the extent of branching and in the size of both internodes and gonothecae. Observed differences were attributed by her to latitudinal and water temperature effects, and she assigned no taxonomic significance to them. Ralph nevertheless recognized three forms of O. geniculata : forma subtropica, forma intermedia , and forma subantarctica. In their monograph on New Zealand leptothecates, Vervoort & Watson (2003) considered these forms to be unwarranted. In the western North Atlantic, morphological differences between populations from boreal (Passamaquoddy Bay, New Brunswick, Atlantic Canada) and temperate (Chesapeake Bay, Virginia, USA) regions have been documented ( Calder 1971: 56, 57). While there was overlap in most characters considered, the cauline internodal perisarc of specimens from Virginia was always uniformly thin rather than being much thickened internally on the side beneath the hydrotheca, as in specimens from New Brunswick. Again, however, observed differences were interpreted as taxonomically unimportant. More significantly, and on a global scale, Govindarajan et al. (2005) detected considerable genetic differentiation and the possible existence of cryptic species in a study of hydroids assigned to O. geniculata from Canada (St. Andrews, New Brunswick), USA (Woods Hole, Massachusetts), France (Roscoff), Iceland (Garour/Sandgerdi), Japan (Misaki, Sagami Bay), and New Zealand (Wellington) based on comparisons of two mitochondrial markers in the populations. Three reciprocally monophyletic clades were detected, one from New Zealand, another from Japan, and a third from the North Atlantic (St. Andrews + Woods Hole + Garour/Sandgerdi + Roscoff). Govindarajan et al. suggested that these three clades may well represent different species. If the nominal species is eventually subdivided, the Atlantic population will retain the binomen O. geniculata , with that name having been applied originally to hydroids from northwest Europe. Low haplotype diversity within examined Atlantic populations was taken to be consistent with a more recent origin, perhaps by invasion from the North Pacific after the Bering Strait opened some 3.1–4.1 million years ago ( Govindarajan et al. 2005).

In spite of their stunted colony form compared with hydroids of the boreal Atlantic, and their existence under warmer water temperatures, specimens from southwest Florida are retained here in O. geniculata . Comparisons are nevertheless warranted between populations from the cold-temperate North Atlantic (especially from the type locality in the UK) and those considered in this work from tropical and subtropical regions of the Americas.

For more on the taxonomy and nomenclature of this species, see Cornelius (1975a, 1995b) and Medel & Vervoort (2000).

Reported distribution. Gulf coast of Florida. Seahorse Key, on Halodule ( Joyce 1961: 57) .— Tampa Bay , ca. 1.5 km W of Ben T. Davis beach, on glass settlement plates, 1.8 m ( Bros 1987: 503) .

Elsewhere in western North Atlantic. Canada: Quebec, Gulf of St. Lawrence, on seaweeds ( Dawson 1858: 408, as Laomedea geniculata ).— USA: Massachusetts, Nahant + Naushon, shallow water, on Laminaria and other seaweeds (L. Agassiz 1862: 322, 352, as Eucope diaphana ).— USA: Massachusetts, Nahant + Naushon, near low water, on Fucus vesiculosus (A. Agassiz 1865: 85, as Eucope diaphana ).— USA: Massachusetts, Nahant + Nantasket (A. Agassiz 1865: 86, as Eucope alternata ).— USA: Massachusetts, Nahant (A. Agassiz 1865: 87, as Eucope polygena ).— USA: Massachusetts, Nahant (A. Agassiz 1865: 87, as Eucope parasitica ).— USA: Massachusetts, Nahant (A. Agassiz 1865: 90, as Eucope fusiformis ).— USA: Maine, Casco Bay, off Cape Elizabeth, near East and West Cod ledges + Casco Bay, among the islands, 8–30 ftm (15–55 m) ( Verrill 1874a: 41, 44).— USA: Maine, Casco Bay, lower intertidal and tidepools + Casco Bay, Quahog Bay, low water ( Verrill 1874b: 133, 136).— USA: Maine, Casco Bay off Cape Elizabeth, near East and West Cod ledges ( Verrill 1874c: 359).— USA: Maine, Casco Bay, 8–30 ftm (15–55 m) + Casco Bay, rocky shores, intertidal + Casco Bay, Quahog Bay ( Verrill 1874c: 364, 370, 374).— USA: Vineyard Sound and vicinity, rocky shores + sandy bottoms + outer rocky shores ( Verrill 1874d: 327, 429, 489, as Obelia diaphana ).— USA: Vineyard Sound and vicinity, rocky shores + rocky bottoms + gravelly and shelly bottoms + outer rocky shores ( Verrill 1874d: 334, 411, 424, 489).— USA: Long Island Sound ( Verrill 1874d: 727, as Obelia diaphana and O. geniculata ).— USA: Massachusetts, Massachusetts Bay ( Verrill 1874d: 727, as Obelia diaphana ).— Canada: Labrador ( Verrill 1874d: 727).— USA: Connecticut, near New Haven, common + Thimble Islands ( Verrill 1874d: 727).— USA: Rhode Island, Watch Hill ( Verrill 1874d: 727).— USA: Massachusetts, Vineyard Sound, 4–15 ftm (7–27 m) + Massachusetts Bay ( Verrill 1874d: 727).— USA: Maine, Casco Bay ( Verrill 1874d: 727).— Canada / USA: Bay of Fundy ( Verrill 1874d: 727).— Canada: Gulf of St. Lawrence ( Whiteaves 1874: 185).— USA: Massachusetts, Vineyard Sound ( Verrill & Rathbun 1880: 229).— USA: Massachusetts, Provincetown, Long Point beach, inner shore, on floating Fucus ( Rathbun 1880: 132) .— USA: Massachusetts, Boston ( Marktanner-Turneretscher 1890: 207).— USA: New England ( Fewkes 1891: 87, as Obelia diaphana , O. geniculata and O. fusiformis ).— Colombia: Bahía Honda, 5 m, on algae ( Versluys 1899: 30).— USA: Massachusetts and north Atlantic coast, common, on Fucus and Laminaria ( Hargitt 1901b: 382) .— USA: Massachusetts, Woods Hole region, on docks, floating seaweed, etc., one of commonest species ( Nutting 1901: 351).— USA: North Carolina, Beaufort, U.S. Bureau of Fisheries wharf (Fraser 1912: 362).— Canada: Quebec, Gaspé ( Stafford 1912a: 59; 1912b: 72).— Canada: New Brunswick, St. Andrews ( Stafford 1912b: 72).— Canada: Nova Scotia, Canso ( Stafford 1912b: 72).— Canada: Quebec, Seven Islands (Sept-Îles) ( Stafford 1912b: 72).— USA: Massachusetts, Vineyard Sound + Buzzards Bay, 1–16 ftm (2–29 m), on Laminaria , other seaweeds, pilings, floating timbers (Sumner et al. 2013: 569, as Obelia geniculata , in part).— Canada: Nova Scotia, Canso, low water, on Laminaria , seaweeds, pilings + Barrington Passage, 3 ftm (5 m) ( Fraser 1913: 167).— USA: Massachusetts, Woods Hole ( Nutting 1915: 76).— USA: Massachusetts, Georges Bank, on floating Zostera ( Fraser 1915: 311) .— Canada: New Brunswick, Bay of Fundy, Grand Manan Island (High Duck Island; Horse Island; Whale Cove off Swallowtail light) + The Wolves + north of Green Island + Bliss Island + Deer Island + St. Andrews, off Joe’s Point ( Fraser 1918: 350).— USA: Massachusetts, Woods Hole ( Root 1922: 77; Hyman & Bellamy 1922: 330).— USA: Massachusetts, Woods Hole region, on eelgrass, rocks and rockweed, pilings ( Allee 1923: 175).— Canada: New Brunswick, Miramichi River estuary, outside Portage and Fox islands,> 15 m ( Fraser 1926: 210).— Canada: Nova Scotia, Cape Breton, Eastern Harbour, along shore ( Fraser 1927: 326).— Canada: Nova Scotia, Cape Breton, Aspy Bay, 20 m ( Fraser 1927: 326).— Canada: Quebec, Magdalen Islands, Pleasant Bay (Baie de Plaisance), 15 m ( Fraser 1927: 326).— Canada: Nova Scotia, Gulf of St. Lawrence, Cape Breton, Pleasant Bay (Grand Anse), 20-25 m ( Fraser 1927: 326).— Canada: Quebec, St. Lawrence River near Trois Pistoles, on laminarians ( Préfontaine 1932: 214).— Greenland: Fylla Bank (=Fyllas Bank, off Nuuk), abt. 64°N, 50 m, on Laminaria ( Kramp 1932: 66, as Laomedea geniculata ).— USA: Maine, Mount Desert region, attached to algae, shore to 60 feet (18 m) ( Procter 1933: 120).— USA: New York, Montauk Point, on Laminaria ( Conard 1935: 446) .— USA: Connecticut, between Milford and New Haven ( Leloup 1938: 1, 2, as Laomedea geniculata ).— USA: Massachusetts, Nahant ( Fraser 1943: 88).— USA: South Carolina, Charleston ( Fraser 1943: 88).— Trinidad and Tobago, Trinidad, Maguaripe Bay (=Macqueripe Bay) ( Fraser 1943: 88).— Canada: Nunavut, Hudson Strait, 3 miles (5 km) from Southhampton light ( Fraser 1944: 160).— Canada: Nova Scotia, Minas Basin + Scots Bay + Cobequid Bay ( Fraser 1944: 160).— Canada: Quebec, Matamek + Trois Pistoles, laminarian zone ( Fraser 1944: 160).— Canada: Nova Scotia, near Halifax, Outer Halibut Island + White Island ( Fraser 1944: 160).— USA: Maine, Eastport ( Fraser 1944: 160).— USA: Maine, Casco Bay, 8–30 ftm (15–55 m) ( Fraser 1944: 160).— USA: Maine, Quahog Bay, low water ( Fraser 1944: 160).— USA: Massachusetts, Monomoy Point, from bird’s stomach ( Fraser 1944: 160).— USA: Massachusetts, Gloucester, near Eastern Point light, 45 ftm (82 m) ( Fraser 1944: 160).— USA: Massachusetts, Little Stellwagen Basin N of Provincetown, 42°09’N, 70°13’W, 30 ftm (55 m) + Stellwagen Bank + Provincetown, Long Point + Provincetown, on stranded Fucus ( Fraser 1944: 160) .— USA: Maine, Casco Bay, East and West Cod ledges ( Fraser 1944: 160).— USA: Massachusetts, Nantucket Shoal, 15 ftm (27 m) ( Fraser 1944: 160).—Atlantic Ocean: E of New Jersey, 40°00’45”N, 70°54’15”W, surface ( Fraser 1944: 160).— USA: Massachusetts, Vineyard Sound, 10 ftm (18) ( Fraser 1944: 160).— USA: Rhode Island, Narragansett Bay, near Fort Dumpling + off Newport, 11.25 ftm (21 m) + Block Island, off North light, 13 ftm (24 m) ( Fraser 1944: 160).— USA: Connecticut, Long Island Sound, Noank ( Fraser 1944: 160).— USA: New York, Long Island, Greenport, piles + Gardners Bay ( Fraser 1944: 160).— USA: Delaware, offshore waters, surface, 38°29’N, 73°21’W ( Fraser 1944: 160).—Antilles ( Fraser 1944: 160).— USA: Maine, Boothbay Harbor, on Laminaria , producing gonangial buds ( Berrill 1948: 94).— USA: Maine, Boothbay Harbor ( Berrill 1950: 2).— USA: Texas, Sabine Pass, on buoy ( Deevey 1950: 345).—Location unspecified: on buoys ( Woods Hole Oceanographic Institution 1952: 187).— Canada: Nova Scotia, Minas Basin + Bass River, intertidal + Scots Bay, intertidal ( Bousfield & Leim 1960: 14).— Canada: Quebec, Baie de Trois-Pistoles, on rocks and algae ( Préfontaine & Brunel 1962: 246).— USA: Massachusetts, Woods Hole area, on floats, piles, Laminaria ( Petersen 1964: 18) .— USA: Massachusetts, Woods Hole area, studies on bioluminescence ( Morin et al. 1968: 429; Morin & Reynolds 1969: 410; 1970: 430; 1974: 398; Morin & Cooke 1971a: 690; 1971b: 708; 1971c: 723; Morin & Hastings 1971: 305).— Canada: Nunavut, Hudson Bay, Coats Island, 62°57.5’N, 82°43’W, 18 m ( Calder 1970: 1522).— USA: Virginia, York River (Tue Marsh Light; Guinea Neck; Perrin; Gloucester Point), on Zostera + Chesapeake Bay (New Point Comfort; Cape Charles), on Zostera ( Calder 1971: 55) .— Canada: New Brunswick, Passamaquoddy Bay ( Calder 1971: 57).— USA: Texas, Galveston, on detached Sargassum ( Defenbaugh & Hopkins 1973: 88) .— USA: Texas, West Flower Garden Bank, on floating Sargassum ( Defenbaugh 1974: 100) .— USA: Connecticut, Noank, on Laminaria and Zostera ( Clark 1975: 34, 40).— USA: Massachusetts, Cape Cod Bay, 2–33 m, 1.5° C–17° C, 30.16‰–32.49‰ ( Calder 1975: 303).— Colombia: Santa Marta area, rocky littoral, on algae, Zostera , other hydroids ( Wedler 1975: 340, as Laomedea geniculata ).— USA: Rhode Island, Newport, on wood, 25 m ( Cornelius 1975a: 276).— USA: Maine, South Harpswell, Potts Point, on Fucus ( Cornelius 1975a: 276) .— USA: Massachusetts, Vineyard Sound, on Laminaria ( Cornelius 1975a: 276) .— USA: Massachusetts, Nonamesset Island, Sheep Pen Harbor, 41°31’N, 70°40’40”W, on slate settling panels ( Osman 1977: 48; 1978: 398).— Canada: New Brunswick, Bay of Fundy ( Linkletter et al. 1977: 7; Henry 2003: 129; Henry & Kenchington 2004: 127).— USA: Massachusetts, Woods Hole ( Harrigan & Alkon 1978: 433).— Canada: Nova Scotia, Minas Basin ( Bromley 1979: 520; Bromley & Bleakney 1985: 22; both as Laomedea geniculata ).— Canada: Quebec, Gulf of St. Lawrence, north shore and lower north shore, on navigation buoys ( Fradette & Bourget 1980: 985; 1981: 139).— Colombia: Bahía de Cartagena region, 0.2–2.5 m, on the coast, some areas exposed to the sea ( Flórez González 1983: 123).— USA: South Carolina, Murrells Inlet, jetties ( Fox & Ruppert 1985: 93).— Colombia: Santa Marta area, rocky littoral, surf zone, on Sargassum vulgare , rocks ( Bandel & Wedler 1987: 41).— USA: South Carolina, coastal areas, in stomachs of Atlantic spadefish ( Hayse 1990: 81).— USA: Maine, York, Cape Neddick, ca. 43°10’N, 70°36’W, on Laminaria , with nudibranch predators ( Lambert 1991: 36; 1993: 116; Berman et al. 1992: 437; Lambert et al. 1992: 304).— Canada: Quebec, St. Lawrence River estuary + Gaspé + Anticosti Island (Île d’Anticosti) + Gulf of St. Lawrence, north shore, all on navigation buoys ( Ardisson & Bourget 1992: 24).— USA: Georgia, St. Catherines Island, Northwest Marsh ( Prezant et al. 2002: 8).— USA: New Hampshire, Portsmouth, Coast Guard Station pilings ( Frick 2003: 369).— USA: Massachusetts, Woods Hole ( Naranjo et al. 1994: 1300).— Canada: Northumberland Strait, 5–32 m, 6.2° to 16.2° C ( Calder 2004a: 559).— USA: Maine, Cobscook Bay ( Trott 2004: 272).— USA: Maine, Eastport ( Sisson 2005: 1725).— Canada: New Brunswick, St. Andrews ( Govindarajan et al. 2005: 214).— USA: Massachusetts, Woods Hole ( Govindarajan et al. 2005: 214).— Canada: Nova Scotia, Western Bank ( Henry et al. 2006: 68).— USA: Rhode Island, Point Judith Pond, 41°23’N, 71°31’W ( Maranda et al. 2007: 627).— USA: Virginia, Yorktown, on experimental substrates ( Bullard et al. 2010: 589).— Cuba: “Oriente”, but without precise location, on Emerita talpoida ( Varela 2012: 6) .— USA: Florida, off Fort Pierce, between Capron Shoal and the beach, on Thyroscyphus ramosus + Hutchinson Island, Walton Rocks area, 27°20’19”N, 80°13’59”W, on algae + Fort Pierce Inlet, north jetty, 27°28’24.2”N, 80°17’20.3”W, on Thyroscyphus ramosus , 0.1 m + Sebastian Inlet, 27°51’43”N, 80°26’47”W, on stranded Sargassum ( Calder 2013: 57, 58).— USA: Maine, South Freeport ( Cunha et al. 2017: 121).— USA: New Hampshire, New Castle ( Cunha et al. 2017: 121).— Canada: New Brunswick, Deer Island, Fairhaven, <1 m, on kelp ( Calder 2017: 81).— Canada: Nova Scotia, Digby Neck, Sandy Cove, intertidal ( Calder 2017: 81).— Canada: Nova Scotia, Black Rock, Canada Creek, in tidepool, on algae ( Calder 2017: 81).— Canada: Nova Scotia, Petit Passage, south of East Ferry, extreme low tide ( Calder 2017: 81).— Canada: New Brunswick, St. Andrews, on pontoon slip of wharf at Atlantic Biological Station, <1 m ( Calder 2017: 81).— Canada: Nova Scotia, Brier Island, Westport, on kelp on floating dock, <1 m ( Calder 2017: 81).—Can- ada: New Brunswick, Deer Island, Richardson, on pontoon slip of wharf, <1 m, on Agarum cribrosum ( Calder 2017: 81) .— USA: Maine, Eastport, Harris Point, on Ascophyllum nodosum and Laminaria sp., <1 m ( Calder 2017: 81).— Caribbean Sea ( Wedler 2017b: 98, figs. 90, 90A–C).

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.