Nemertesia ramosa Lamouroux 1816

Nemertesia ramosa Lamouroux, 1816

Fig. 43

Nemertesia ramosa Lamouroux, 1816: 164.— Jägerskiöld, 1971: 63.— Cornelius, 1995b: 156.

Antennularia ramosa.— Segerstedt, 1889: 20, 27.— Jäderholm, 1909: 105, pl. 12, fig. 2.

Antennularia (Nemertesia) ramosa.— Gislén, 1930: 310.

Type locality. “Océan Européen” (Lamouroux 1816: 164).

Museum material. Kosterhavet, 58°52.424’N, 11°06.178’E, 35– 11 m, 06.ix.2010, biological dredge, R / V Nereus, on a pebble and unattached, several colony fragments, up to 7 cm high, with gonothecae, ROMIZ B3884.

Remarks. Three species of the genus Nemertesia Lamouroux, 1812, N. antennina (Linnaeus, 1758), N. ramosa Lamouroux, 1816, and N. norvegica (G.O. Sars, 1874), have been reported from southern Scandinavia. The first two are known from western Sweden (see Checklist) and are widespread in European waters. The only record of N. norvegica from the Skagerrak-Kattegat area is that of G.O. Sars (1874), who described it from Stormeberget in the Oslofjord (Christiansen 1972). The species has been observed infrequently and is poorly known. Cornelius (1995b: 146) noted the possibility that it might be referable to Antennopsis Allman, 1877, if that genus were to be recognized as valid.

Nemertesia ramosa, collected here from the Kosterhavet, is easily distinguished from N. antennina (Linnaeus 1758) in having homomeric (with all or mostly all hydrocladial internodes hydrothecate) rather than heteromeric (with hydrocladial internodes alternately hydrothecate and non-hydrothecate) hydrocladia. Nemertesia norvegica is similar, but its stems are non-canaliculate, apparently unbranched, and have four or fewer longitudinal rows of hydrocladia (Cornelius 1995b). In addition, gonothecae of N. norvegica are described by Cornelius as being in the form of a “crescent-shaped sausage” rather than “curved ovoid.”

Although Nemertesia ramosa is known from southern Iceland (Schuchert 2001a), the Skagerrak presently appears to be its northern limit in continental Europe. In addition to its Atlantic distribution the species has been reported from the Indian Ocean, the Malay Archipelago, the South China Sea, and the western South Atlantic, but Ramil & Vervoort (1992) provided evidence that materal so identified from those areas was different. They concluded that N. ramosa, at least so far, is a “purely Atlantic” species, and discussed its synonymy. Other accounts of the taxonomy of the species are given in works such as those of Cornelius (1995b) and Calder & Vervoort (1998).

In waters of southwestern Scandinavia, Nemertesia ramosa has been reported from the west coast of Jutland in Denmark (Kramp 1935b), from the west coast of Sweden (Jäderholm 1909), and from the Oslofjord, Norway (Christiansen 1972).

Reported distribution. West coast of Sweden.—From the Säcken Reef area to Flatholmen (Jäderholm 1909; Jägerskiöld 1971).

Elsewhere.—Eastern Atlantic from southern Iceland and the Oslofjord, Norway, to South Africa (Christiansen 1972; Ramil & Vervoort 1992; Schuchert 2001a); Mid-Atlantic Ridge (Calder & Vervoort 1998).

FIGURE 45. Schizotricha frutescens: part of hydrocladium with hydrothecae and nematothecae, ROMIZ B3928. Scale equals 0.5 mm.