Sertularia tenera G.O. 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 : 39-40

Sertularia tenera G.O. Sars, 1874

Fig. 39

Sertularia tenera G.O. Sars, 1874: 108 , pl. 4, figs. 1–4.— Segerstedt, 1889: 18, 27.— Jägerskiöld, 1971: 64.

Thuiaria tenera .— Jäderholm, 1909: 93.

not Sertularia tenera .— Cornelius, 1979: 299, figs. 27a, b [= Sertularia spitzbergensis Jäderholm, 1909 ].

Type locality. Norway: Skudesnaes , in open ocean (G.O. Sars 1874: 109) .

Museum material. Väderöarna, 58°35.005’N, 11°04.983’E, 121– 50 m, 13.ix.2010, biological dredge, R / V Nereus , on a rock, 11 plumes, 3.7 cm high, with one developing gonotheca, ROMIZ B3927 .

Remarks. Sertularia tenera G.O. Sars, 1874 was originally described from the open coast off southwestern Norway. Material from western Sweden, collected here, corresponded closely with the original account of the species. These small and fine hydroids were initially thought to be juveniles of either Sertularia cupressina Linnaeus, 1758 or S. argentea Linnaeus, 1758 , or even Hydrallmania falcata ( Linnaeus, 1758) . However, presence of a developing gonotheca on one of the plumes provided evidence that these were fully developed colonies. Indeed, they corresponded with an account and illustration of S. tenera from Karlsö, northern Norway, by Jäderholm (1909). His material, of a similar size and slenderness, bore fully developed gonothecae. Sertularia arctica Allman, 1874b from Spitzbergen and S. birulae Schydlowsky, 1902 , from the White Sea, appear very similar morphologically.

Hydroids of S. tenera observed here, and those described by authors including G.O. Sars (1874), Winther (1880b), Jäderholm (1909, as Thuiaria tenera ), Ritchie (1911, as T. tenera ), Kudelin (1914), and Kramp (1935b), differ significantly in morphology from many other accounts of the species. A distinctive morphotype identified as Sertularia tenera by Thompson (1887), Marktanner-Turneretscher (1895), Broch (1910, 1918), Calder (1970), Cornelius (1979), and Schuchert (2001a), as Thuiaria arctica forma siberica and T. arctica forma spitzbergensis by Jäderholm (1909), as Sertularia tenera arctica by Kudelin (1914), and as Thuiaria tenera by Fraser (1944), is regarded here as a different species. Unlike S. tenera , hydrothecae are almost strictly alternate rather than being subopposite, and their shape is relatively thick and close to triangular instead of decidedly slender and curved. Its hydrocladia are sometimes arranged in a spiral distally instead of being in one plane throughout, and its colonies tend to be larger and more robust. Finally, its gonothecae have longitudinal ridges and are polygonal in cross-section instead of being smooth and oval in cross section. This form appears to be more characteristically Arctic or subarctic in distribution than S. tenera .

This misidentified morphotype is not considered conspecific with Sertularia arctica Allman, 1874b , a species more like the true S. tenera . The oldest available names for it appear to be the simultaneous synonyms Thuiaria arctica forma sibirica and T. arctica forma spitzbergensis of Jäderholm (1909), with the names of the two forms being taken here as subspecific (International Code of Zoological Nomenclature, Art. 45.6.4). Acting as First Reviser, I assign priority to the name spitzbergensis over siberica for the species, the binomen being Sertularia spitzbergensis ( Jäderholm, 1909) . The name spitzbergensis , elevated in rank from subspecific to specific, was chosen because the species it represents is presently better known from the northern North Atlantic and adjacent Arctic than from the far-eastern seas of the Russian Federation, as implied by the other eligible name.

Other records of S. tenera are numerous (e.g., Hincks 1874b; Thompson 1887; Marktanner-Turneretscher 1890, 1895; Levinsen 1893a, b; Vanhöffen 1897; Bonnevie 1899; Nutting 1899, 1904; Saemundsson 1902; Broch 1908; Hartlaub & Scheuring 1915; Jäderholm 1919; Kramp 1932a, b, 1938, 1942, 1943; Yamada 1950; Naumov 1960; Antsulevich 1987; Węsławski et al. 1997; Henry & Kenchington 2004; Henry et al. 2006: 68), but the identity of hydroids assigned to the species is uncertain in nearly all of these works. In some, hydroids differ from both S. tenera and S. spitzbergensis .

Given the confusion over the identity of S. tenera , its actual distribution is in considerable doubt. Based on records that appear sound, the currently known range of S. tenera is taken here to be from northern Scandinavia to northern Britain in the eastern North Atlantic.

Reported distribution. West coast of Sweden.—From Säcken area to near Anholt in the Kattegat, 23–85 m ( Jägerskiöld 1971: 64).

Elsewhere.—North Atlantic: Norway ( Jäderholm 1909) to Scotland ( Ritchie 1911).