Hydractinia

ÁLVARO L. PEÑA CANTERO, 2017, Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa, Zootaxa 4293 (1), pp. 1-65 : 16-17

Hydractinia sp.

( Fig. 2 D)

Material examined. Stn 139, one colony fragment, 5 mm long, with a few polyps, basibiont of Campanularia hicksoni Totton, 1930 (NIWA 117481).

Description. Gastrozooids 200–400 µm high and 100–200 µm in maximum diameter, with conical hypostome and distal crown of 5–8 filiform tentacles ( Fig. 2 D). Each polyp usually within its own calyx delimited by perisarc ridges. No dactylozooids observed.

Cnidome consisting of microbasic euryteles (10–11 x 4 µm), microbasic mastigophores (9 x 3 µm) and desmonemes (6–6.5 x 3.5 µm).

Remarks. The material examined is morphologically close to H. dendritica Hickson & Gravely, 1907 by the distal position of the whorl of tentacles, the presence of perisarc ridges and spines, and the cnidome. However, H. dendritica has dactylozooids, which are not present here, although this could be related to the small colony fragment available. Peña Cantero (2015) only observed three dactylozooids in the abundant type material of H. dendritica . The infertile condition of the material also prevents me from giving a definitive identification.

Ecology and distribution. The colony was collected at a depth of 236 m off Cape Hallet. Basibiont of Campanularia hicksoni .

Figures

FIGURE 2. Bimeria corynopsis Vanhöffen, 1910: A, polyp with swollen tentacle ends; B, nematocysts (microbasic euryteles and desmonemes). Rhizorhagium antarcticum (Hickson & Gravely, 1907): C, discharged microbasic eurytele. Hydractinia sp.: D, polyp. (A, D from Stn 139; B from Stn 140; C from Stn 130). Scale bar: 200 µm (A, D), 10 µm (B – C).