Diphasia fallax ( Johnston, 1847 )

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 : 34

Diphasia fallax ( Johnston, 1847)

Fig. 33

Sertularia fallax Johnston, 1847: 73 , pl. 11, figs. 2, 5, 6.

Diphasia fallax .— Segerstedt, 1889: 17, 26.— Jäderholm, 1909: 83, pl. 8, figs. 7, 8.— Rees & Rowe, 1969: 18.— Jägerskiöld, 1971: 61.

Type locality. UK: NE coast of Britain, between Scarborough and Aberdeen ( Cornelius 1979: 260) .

Museum material. Kosterhavet, 58°53.093’N, 11°05.668’E, 20–30 m, 09.ix.2010, biological dredge, R / V Nereus , five fragments of colonies, up to 2 cm high, on Nemertesia rugosa and unattached, without gonophores, ROMIZ B3911.

Remarks. Of the various species of Diphasia L. Agassiz, 1862 occurring in waters of southern Scandinavia, D. fallax ( Johnston, 1847) appears to be the most common ( Jäderholm 1909; Kramp 1935b; Jägerskiöld 1971; Christiansen 1972). It is readily distinguished by having smooth-walled and gradually outward-curved hydrothecae that are adnate to stem and branches for about 2/3 of their length. Details on the taxonomy of this boreal, amphi- Atlantic species have been given by Cornelius (1979; 1995b).

Reported distribution. West coast of Sweden.—From the border with Norway to the middle Kattegat ( Jägerskiöld 1971).

Elsewhere.—North Atlantic from the Barents and White seas, and Spitzbergen, to northern Britain ( Cornelius 1995b) in the east, and from Northumberland Strait to Block Island Sound ( Calder 2004) in the west. A record of the species from bathyal waters off Charleston, South Carolina, by Fraser (1944) needs confirmation.