Fig. 48
Medusa hemisphaerica Linnaeus, 1767: 1098 [medusa stage].
Clytia johnstoni.— Segerstedt, 1889: 11, 25.— Jäderholm, 1909: 61, pl. 5, fig. 12.
Clytia hemisphaerica.— Rees & Rowe, 1969: 16.— Cornelius, 1982: 75, fig. 9k.— Östman, 1999: 17.
Campanularia johnstoni.— Jägerskiöld, 1971: 61.
Clytia hemisphaerica form (or forma) johnstoni.— Östman, 1979a: 5; 1979b: 127, figs. 1, 2, 4, 5; 1982a: 156; 1983: 6.
Type locality. “ Habitat in Oceano Belgico ” (Linnaeus 1767: 1098).
Museum material. Kosterhavet, 58°50.278’N, 11°02.680’E, 13 m, 07.ix.2010, biological dredge, R / V Nereus, on algae, one stolonal colony, without gonophores, ROMIZ B3894.— Kosterhavet, 58°53.093’N, 11°05.668’E, 20– 30 m, 09.ix.2010, biological dredge, R / V Nereus, on algae, one stolonal colony, with gonophores, ROMIZ B3907.— Saltö naturreservat, outer ledge, 58°52’40”N, 11°06’53”E, <1 m, 11.ix.2010, collected manually, on red algae, two stolonal colonies, with gonophores, ROMIZ B3923.— Väderöarna, 58°34.931’N, 11°04.931’E, 121– 50 m, 13.ix.2010, biological dredge, R / V Nereus, on antenna of a decapod crustacean, one colony, with a few branched pedicels, up to 9 mm high, with gonophores, ROMIZ B3930.
Remarks. A comprehensive taxonomic overview of Clytia hemisphaerica (Linnaeus, 1767) was given by Cornelius (1982), and additional details were provided by Calder (1991). The sympatric C. gracilis (M. Sars, 1850) is similar, but its gonothecae have smooth rather than spirally ribbed walls. Nematocysts of the two species also differ (Östman 1979a). Östman added that colonies of C. gracilis are often branched, and hydrothecal cusps are sharppointed, whereas colonies of C. hemsphaerica are usually unbranched, and hydrothecal cusps are broad and symmetrical. Comments on C. gigantea (Hincks, 1866), sometimes included as a synonym, are given above. Although C. hemisphaerica is generally reported to be virtually cosmopolitan, Cornelius (1995b: 254) is probably correct that “nearly all” records of species of the taxonomically difficult genus Clytia Lamouroux, 1812 are suspect.
Clytia hemisphaerica has been reported numerous times along the west coast of Sweden (see Checklist). Hydroids of the species die back during winter in nearby waters of Denmark (Kramp 1935b: 100, as Campanularia johnstoni Alder, 1856) and the Oslofjord, Norway (Christiansen 1972: 293–294, as Clytia johnstoni).
Reported distribution. West coast of Sweden.—From the border with Norway to southern Kattegat (Jägerskiöld 1971).
Elsewhere.—North Atlantic from Svalbard and Finnmark to the Mediterranean Sea in Europe (Christiansen 1972; Cornelius 1982), and from Labrador to Florida in North America (Calder 2004). Reported to be circumglobal (Calder 1991).