Halecium tubatum Watson 2008

Halecium tubatum Watson, 2008

(Fig. 14 d–g)

Material examined. ANT XV/3: 48-276, several polyps, on Sc. nana; ANT XXI/2: PS65/278, several polyps, on Sy. weddelli and sponge; PS65/280, few polyps, on undetermined anthoathecata.

Remarks. Halecium tubatum was considered as species inquirenda by Peña Cantero (2014b), who pointed out that the species could correspond to incipient stems of other haleciids such as H. interpolatum. However, the analysis of the cnidome has contributed to a better characterization of the species (see below), proving to be different from other congenerics previously documented in Antarctic waters (cf. Peña Cantero 2014b). The species is considered here as valid, although mature specimens have not been found yet. We consider the two-three basal rings followed by a wavy internode (Fig. 14e), the absence of diaphragm (Fig. 14f), the presence of desmocytes (Fig. 14f), and the greatly recurved hydrotheca (Fig. 14 f–g), coupled with the size of the nematocysts, as unequivocal diagnostic characters of the species.

Cnidome composed of microbasic euryteles? [range 17.0–19.5 x 6.0–8.0 µm, mean 18.7±0.6 x 7.2±0.6 µm (n=19)] and microbasic mastigophores [range 8.0–8.5 x 1.5–2.0 µm, mean 8.2±0.2 x 1.6±0.2 µm (n=17)].

Ecology and distribution. Valid records of the species are restricted to the holotype, which was collected off Wilkes Land (East Antarctica) at a depth of 163 m (Watson 2008). Material examined here was found between 119 and 417 m depth. Present finding constitutes the first evidence of the species from both the Weddell Sea and West Antarctica, pointing to a circum-Antarctic distribution.