Rhizorhagium roseum M. Sars, 1874

Calder, Dale R., 2012, On a collection of hydroids (Cnidaria, Hydrozoa, Hydroidolina) from the west coast of Sweden, with a checklist of species from the region 3171, Zootaxa 3171 (1), pp. 1-77 : 14

Rhizorhagium roseum M. Sars , in G.O. Sars, 1874

Fig. 12

Rhizorhagium roseum M. Sars , in G.O. Sars, 1874: 129.— Rees & Rowe, 1969: 10.

Perigonimus roseus .— Lönnberg, 1902: 173.— Jäderholm, 1909: 46, pl. 3, fig. 7.— Jägerskiöld, 1971: 64.

Type locality. Norway: Mangerfjord , Bognestrømmen, 20 fm (37 m) ( Rees 1956b: 114) .

Museum material. Kosterhavet, 58°53.093’N, 11°05.668’E, 20–30 m, 09.ix.2010, biological dredge, R / V Nereus , two colonies, up to 5 mm high, on stems of Tubularia indivisa and Lafoea gracillima , without gonophores, ROMIZ B3909.

Remarks. Gonophores were lacking in studied material, but the trophosome of Rhizorhagium roseum M. Sars , in G.O. Sars, 1874, with its stolonal habit, long hydrocaulus, thin pseudohydrotheca, single tentacular whorl, and nipple-shaped hypostome, as well as its reddish to pinkish hydranths that bend over when disturbed, is distinctive among hydroids in the biogeographic region. A detailed account of this small species, from boreal and subarctic waters on both sides of the Atlantic Ocean, has recently been given by Schuchert (2007).

Rees (1956b) examined type material of Rhizorhagium roseum and concluded from the original label that it was from “Bongnestrømmen” (Bognestrømmen) in the Mangerfjord, Norway. In addition to its occurrence on the west coast of Sweden (e.g., Jäderholm 1909, as Perigonimus roseus ), R. roseum has been reported from the Oslofjord, Norway ( Christiansen 1972).

Reported distribution. West coast of Sweden.—Kosterfjord to Gullmarfjord ( Rees & Rowe 1969).

Elsewhere.—North Atlantic from the Barents and White seas to western Scotland in Europe ( Schuchert 2007), and from northern Foxe Basin in the Canadian Arctic to Buzzard’s Bay, Massachusetts, in eastern North America ( Calder 2004); eastern North Pacific from Alaska to southern Vancouver Island ( Fraser 1944, as Garveia groenlandica ; Brinckmann-Voss 1996).