Sertularella gigantea Hincks 1874

Sertularella gigantea Hincks, 1874

Fig. 21

Sertularella polyzonias var. gigantea Hincks, 1874: 151, pl. 7, figs. 11, 12.

Sertularia polyzonias.— Stimpson, 1853: 9.— Fuller, 1862a: 129; 1862b: 91 [not Sertularella polyzonias (Linnaeus, 1758)].

Cotulina polyzonias.— A. Agassiz, 1865: 146 [not Sertularella polyzonias (Linnaeus, 1758)].

Sertularella polyzonias.— Stafford 1912: 73.— Fraser 1918: 358.— Fraser 1944: 268.— Caddy, 1970: 12.— Linkletter et al. 1977: 8.— Fuller et al. 1998: 15, 23.— Henry 2003: 129.— Henry & Kenchington 2004a: 127.— Trott 2004a: 273 [not Sertularella polyzonias (Linnaeus, 1758)].

Type locality. Greenland: Frederickshaab (Paamiut). This hydroid, originally thought to have been from Iceland (Hincks 1874), was later reported to have been from Greenland (Hincks 1877).

Material examined. NS: off Digby, 119–123 m, scallop dredge, --. v.1966, several colony fragments, up to 2.1 cm high, with gonophores, coll. J.F. Caddy, ARC 8650161; ROMIZ B636.—NB: St. Croix River, at entrance of Oak Bay, 23.viii.1984, one colony, 3.2 cm high, without gonophores, coll. D. Calder, ROMIZ B656.—NB: St. Andrews, off Joe’s Point, 16 m, scallop dredge, 06.ix.1984, one young colony, 5 mm high, without gonophores, coll. D. Calder, ROMIZ B1989.—NB: St. Andrews, off Joe’s Point, 16 m, scallop dredge, 06.ix.1984, one young colony, 5 mm high, without gonophores, coll. D. Calder, ROMIZ B1993.—NB: St. Andrews, off Joe’s Point, 16 m, scallop dredge, 06.ix.1984, one young colony, 7 mm high, without gonophores, coll. D. Calder, ROMIZ B1995.— ME: Passamaquoddy Bay, off Frost Cove near Perry, 58 m, 27.viii.1988, 11°C, 33‰, one colony, 4 cm high, without gonophores, coll. D. Calder, ROMIZ B4134.—NB: St. Andrews, off Brandy Cove, 13 m, 27.viii.1988, 13°C, 32‰, scallop dredge, several colonies and colony fragments, up to 2.7 cm high, without gonophores, coll. D. Calder, ROMIZ B4138.—ME: Passamaquoddy Bay, American side opposite Northern Harbour, NB, 58 m, 28.viii.1988, one colony, 2 cm high, without gonophores, ROMIZ B4136.

Description. Hydroid colonies erect, up to 3.2 cm high, unbranched or sparingly and irregularly branched, with branches seldom rebranched; perisarc quite thick except in youngest parts of colony. Hydrocaulus monosiphonic, arising from a creeping hydrorhiza, with from one to several annulations at base, slightly to distinctly zigzag, divided into rather short, stout internodes by distinct nodes sloping alternately in opposite directions; internodes 925–1425 um long, 200–325 wide at nodes, often with an annulation or slight swelling at base, each one beyond basal region bearing a hydrotheca, internodal walls widening from proximal end to base of hydrotheca, then tapering again to distal node. Branches usually short, given off at a wide angle, resembling hydrocaulus in form, arising from internode immediately below base of a hydrotheca. Hydrothecae large, deep, in shape of a bent flask, curving slightly outwards, arranged alternately on opposite sides of hydrocaulus, walls smooth to somewhat undulating, adnate to internode for less than half their length, with axis oblique to that of hydrocaulus; hydrothecal walls widest near point of departure from hydrocaulus, narrowing basally, narrowing again towards margin before expanding again at rim, length abcauline wall 875–1125 um, length adcauline wall adnate 275–400 um, length adcauline wall free 750–1000 um, both adcauline and abcauline walls convex over much of their length, concave at distal end; hydrothecal base 200–350 um wide. Hydrothecal margin with four distinct, pointed, equally developed cusps, margin infrequently renovated from 1-3 times; hydrothecal orifice 375– 475 um wide, quadrate in shape; hydrothecal cavity enclosed by an operculum of four faintly striated triangular valves; submarginal cusps absent. Hydranths with an abcauline diverticulum.

Gonophores fixed sporosacs. Gonothecae 1.5–2.2 mm long, 0.9–1.3 mm maximum diameter, elongate-oval in lateral view, resembling a cocoon, nearly round in cross-section, each borne on a very short, stout pedicel arising from hydrocaulus opposite basal end of a hydrotheca, gonotheca arching upwards and inwards over adjacent hydrotheca and cauline internode; perisarc quite thick. Gonothecal walls with about 5–7 prominent spiral ribs that become less developed at proximal end; margin 0.4–0.5 mm wide, bearing four prominent, horn-shaped spines; each spine about 0.20–0.24 mm long. Sex undetermined.

Remarks. This species was first recognized and identified by M. Sars (1857) as a robust northern form of Sertularella polyzonias (Linnaeus, 1758). It was described and named later by Hincks (1874), as S. polyzonias var. gigantea. Hincks initially believed that material examined by him was from Iceland, as reported in the title of his paper, but discovered later that it was from Frederickshaab, Greenland (Hincks 1877). Considered by Hincks to be a northern variety of S. polyzonias, the hydroid was said to be marked by its “robust habit and gigantic calycles (hydrothecae).” Mereschkowsky (1878) was first to regard it as a distinct species, “ Sertularella gigantea Mihi ” from the White Sea region. The binomen he thereby created is invalid as both a junior homonym and a junior subjective synonym of S. gigantea Hincks, 1874 (ICZN Arts. 45.6.4; 46.1).

Authors including Kirchenpauer (1884), Broch (1918), and Bedot (1925) remained unconvinced that Sertularella gigantea was a distinct species. With some exceptions (e.g., Nutting 1904; Jäderholm, E. 1909; Fraser 1944; Naumov 1960), the concept that it was simply a variety of S. polyzonias persisted throughout the twentieth century. Recent accounts (e.g., Antsulevich 2015; Choong 2015) provide evidence for recognizing S. gigantea as distinct. After comparing specimens in this study with those of S. polyzonias from northwestern Europe (Calder 2012), I agree. Morphological characters distinguishing trophosomes and gonosomes of the two species have been summarized by Choong (2015: 399), and partial synonymies of S. polyzonias and S. gigantea are given by Antsulevich (2015). Because of earlier misconceptions that the two were conspecific, it is difficult to establish accurate collection records and geographic distributions of both S. polyzonias and S. gigantea. However, it is clear that S. gigantea occurs at higher latitudes (Antsulevich 2015) and in colder waters than S. polyzonias.

Fraser (1944) recognized Sertularella gigantea as distinct, yet his description and illustrations of S. polyzonias from the northwestern North Atlantic were almost certainly based on the former species as well. The same error exists in Fraser’s (1937) account of the species from Alaska and the Pacific coast of Canada (Choong 2015; Antsulevich 2015). Likewise, my records of S. polyzonias from the Canadian north (Calder 1970), from Cape Cod Bay (Calder 1975), and from Northumberland Strait (Calder 2004) were based instead on S. gigantea. No specimens corresponding with S. polyzonias were observed during this study in collections from the Bay of Fundy, whereas hydroids of S. gigantea were frequent. As reflected in the synonymy list above, earlier records of S. polyzonias from the bay are believed here to have been based on misidentifications. Indeed, if S. polyzonias exists in the boreal Northwest Atlantic, confirmation is needed.

Mereschkowsky (1878), with Nutting (1904) and Fraser (1944) following him, emphasized that hydrothecal margins of Sertularella gigantea in fully mature colonies from the White Sea were always repeatedly renovated. That character is not mentioned in more recent descriptions of Russian material by Naumov (1960) and Antsulevich (2015). Only a small percentage of hydranths examined during this study had renovated margins, and in no case was the renovation particularly conspicuous.

Although Sertularella gigantea has been reported over a bathymetric range from 5–4820 m (Naumov 1960; Antsulevich 2015), it is most frequently encountered at depths between 20 – 200 m. In studies on the Russian hydroid fauna, Naumov noted that it is often abundant in the upper 100 m. A circumpolar species extending southwards into boreal waters, it is common in the lower Bay of Fundy. The only material with gonothecae in the present collection was dredged during May 1966 at a depth of 119–123 m off Digby, NS (ARC 8650161; ROMIZ B636). While no water temperature data exist for this collection, it is certain to have been below 10° C given the location, depth, and time of year (Petrie & Jordan 1993).

Recorded distribution. Bay of Fundy: recorded for the first time as Sertularella gigantea. Grand Manan, NB (Stimpson 1853, as Sertularia polyzonias); Treat’s Island, near Eastport, ME (Fuller 1862a; 1862b; both as S. polyzonias); Eastport, ME (A. Agassiz 1865, as Cotulina polyzonias); St. Andrews, NB (Stafford 1912, as Sertularella polyzonias); Passamaquoddy Bay area (Fraser 1918, as S. polyzonias); Grand Manan, NB, off Cherry Island, NB, Eastport, ME (Fraser 1944, as S. polyzonias); Bay of Fundy (Linkletter et al. 1977; Henry 2003; Henry & Kenchington 2004a, all as S. polyzonias); Lower Bay of Fundy, commercial scallop grounds (Fuller et al. 1998, as S. polyzonias); Cobscook Bay, ME (Trott 2004a, as S. polyzonias).

Eastern North America: Greenland (Hincks 1874, as Sertularella polyzonias var. gigantea); Northern Foxe Basin (Calder 1970, as S. polyzonias) to Nantucket, Massachusetts (Fraser 1944).

Elsewhere: Spitzbergen, Chukchi Sea, Bering Sea, Kuril Islands, Sea of Okhotsk, Sea of Japan, Alaska to Vancouver Island (Kramp 1911; Naumov 1960; Antsulevich 2015; Choong 2015).