Thuiaria articulata (Pallas, 1766)

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 : 41-42

Thuiaria articulata (Pallas, 1766)

Fig. 41

Sertularia articulata Pallas, 1766: 137 .

Salacia lonchitis .— Rees & Rowe, 1969: 20.

Thuiaria lonchitis .— Segerstedt, 1889: 19, 27.— Jäderholm, 1909: 89, pl. 9, fig. 3.— Kramp, 1935b: 197, fig. 81C.— Jägerskiöld, 1971: 64.

Type locality. UK: England, Lancashire, off Lytham (53°44’N, 02°58’W), based on a neotype ( Cornelius 1979: 276) .

Museum material. Kosterhavet, 58°52.536’N, 11°06.229’E, 6–30 m, 07.ix.2010, SCUBA , one colony, 7 cm high, without gonophores, coll. B.E. Picton, ROMIZ B3902 .

Remarks. The troubled synonymy of Thuiaria articulata (Pallas, 1766) has been resolved to a considerable extent by Cornelius (1979, 1995b). Syntypes of Sertularia lichenastrum Linnaeus, 1758 , sometimes considered its senior synonym, are much more like Thuiaria alternitheca Levinsen, 1893b than T. articulata ( Cornelius 1979: Fig. 18a –c). Cornelius also concluded that T. lonchitis ( Ellis & Solander, 1786) , a name often applied to this species, is an objective synonym of T. articulata , both having been based on a species of hydroid described by Ellis (1755). Supposed differences in branching, whether alternate or opposite, are inconsequential because the arrangement can vary even within a given colony ( Schuchert 2001a).

Thuiaria thuja ( Linnaeus, 1758) , present in southern Scandinavian waters and elsewhere in northwest Europe ( Cornelius 1995b), differs in having branched hydrocladia that arise in a spiral around the stem. Hydrocladia of T. articulata are unbranched and pinnately arranged.

Two species somewhat resembling T. articulata occur at higher latitudes of the North Atlantic. Schuchert (2001a) employed a ratio of the length of the free part of the adcauline wall of the hydrotheca to the diameter of the hydrothecal orifice to distinguish T. carica Levinsen, 1893c . The ratio was consistently above 1 in T. carica , but mostly below 0.8 in T. articulata . In T. laxa Allman, 1874a , hydrocladia of older colonies are branched instead of simple, and hydrothecae are entirely or almost entirely immersed in the hydrocladia, instead of being partly free.

Thuiaria kolaensis Jäderholm, 1907 , originally described from the Kola Peninsula, was included in the synonymy of T. lonchitis by Vervoort (1946). A detailed synonymy of T. articulata is given in Cornelius (1979). Meanwhile, however, molecular studies suggest there may be crypsis within this species ( Moura et al. 2011).

Thuiaria articulata has been reported frequently in southern Scandinavia (e.g., Jäderholm 1909, as T. lonchitis ; Kramp 1935b, as T. lonchitis ; Rees & Rowe 1969, as Salacia lonchitis ; Jägerskiöld 1971, as T. lonchitis ; Christiansen 1972).

Reported distribution. West coast of Sweden.—From the border with Norway to near Anholt in the Kattegat ( Jägerskiöld 1971, as Thuiaria lonchitis ).

Elsewhere.—Circumpolar, from the Arctic Ocean to Britain and Brittany in the eastern Atlantic ( Cornelius 1979, 1995b), to Nantucket, Massachusetts ( Fraser 1944) in the western Atlantic, to the Queen Charlotte Islands in the eastern Pacific ( Fraser 1937, as Thuiaria lonchitis ) to Japan in the western Pacific ( Yamada 1959).