Stegopoma plicatile

Stegopoma plicatile (M. Sars, 1863)

Fig. 20

Lafoea plicatilis M. Sars, 1863: 31.

Stegopoma plicatile.— Kramp, 1935b: 131.— Rees & Rowe, 1969: 14.— Jägerskiöld, 1971: 64.— Cornelius, 1995a: 115, fig. 25B, 117, figs. 25C–F.

Type locality. Norway: “…ved Manger, Bejan, Tromsø og Vadsø…” (M. Sars 1863: 32).

Museum material. Kosterhavet, 58°53.093’N, 11°05.668’E, 20–30 m, 09.ix.2010, biological dredge, R / V Nereus, one colony, up to 2.3 cm high, on stem of tubularioid hydroid, without gonophores, ROMIZ B3913.

Remarks. Schuchert (2000) demonstrated that a free medusa occurs in the life cycle of Stegopoma plicatile (M. Sars, 1863), as in the related Modeeria rotunda (Quoy & Gaimard, 1827), and assigned the species to family Tiarannidae Russell, 1940. Stepanjants (1989) assigned this species to the genus Modeeria Forbes, 1848, as M. plicatile, while Schuchert suggested it might be the hydroid of Chromatonema rotunda (intending it for C. rubrum Fewkes, 1882). Other contemporary taxonomic accounts of this hydroid include those of Vervoort (1972), Edwards (1973a), Cornelius (1995a), and Schuchert (2001a).

Molecular studies by Peña Cantero et al. (2010) indicate a close relationship between S. plicatile (family Tiarannidae) and Anthohebella parasitica (Ciamician, 1880) (family Hebellidae Fraser, 1912). The link between Tiarannidae (superfamily Laodiceoidea L. Agassiz, 1862), generally considered an “operculate” taxon, and Hebellidae (usually assigned to superfamily Lafoeoidea A. Agassiz, 1865), traditionally classified amongst “non-operculate” families, had been noted earlier from the morphology of their medusa stages (Migotto & Andrade 2000; Bouillon et al. 2006). Indeed, a relationship between laodiceoids and supposed lafoeoids had been proposed in the nineteenth century by A. Agassiz (1865), who linked a laodiceid medusa to a hydroid he supposed to be a lafoeid, but the discovery had long been discounted (see Calder, 1991: 31, 32).

In southwestern Scandinavia, Christiansen (1972) reported finding Stegopoma plicatile throughout the year in the Oslofjord, with most records at depths below 100 m. It extends southwards along the west coast of Sweden to the Kosterfjord and Gullmarfjord (Rees & Rowe 1969; Jägerskiöld 1971). In Denmark, it is known only from deep waters of the Skagerrak off Hirtshals and Skagen (Kramp 1935b).

Gonophores of S. plicatile were observed during January in the Oslofjord by Christiansen (1972). Existence of gonophores has not been recorded in reports of the species from Sweden and Denmark.

Reported distribution. West coast of Sweden.—From Säcken Reef (Rees & Rowe 1969) to the Gullmarfjord (Kramp 1935b; Rees & Rowe 1969; Cornelius 1995a).

Elsewhere.—North Atlantic from Svalbard (Ronowicz 2007) and northern seas of the Russian Federation (Stepanjants 1989, as Modeeria plicatile) to the west coast of Sweden (Rees & Rowe 1969; Cornelius 1995a; Schuchert 2001a) in the east, and from Baffin Island (Calder 1970) and Greenland (Schuchert 2001a) to slope waters off northern Florida (Henry et al. 2008) in the west. This species has also been reported from the eastern and western Pacific, and from the Antarctic (Vervoort 1972; Schuchert 2001a).