Rhizorhagium antarcticum Hickson & Gravely 1907

Rhizorhagium antarcticum (Hickson & Gravely, 1907)

(Fig. 2 C)

Perigonimus antarcticus Hickson & Gravely, 1907: 4 –6, pl. 1 figs 1–3, pl. 4 fig. 32.

Atractylis antarcticus — Ritchie, 1913: 10, 11.

Gravelya antarctica — Totton, 1930: 139 –140, fig. 1a, b.

Rhizorhagium antarcticum— Peña Cantero et al., 2013: 735–736, figs 2c–d, 3a–b; Peña Cantero, 2015: 377–378, figs 1C, D, 2E, 3F (synonymy).

Material examined. Stn 25, a few polyps, with gonophores, on Schizotricha turqueti Billard, 1906, and numerous polyps on Staurotheca densa Peña Cantero & Vervoort, 2003 (NIWA 117473); Stn 53, a few stolonal, pedicelated polyps, on Staurotheca densa (MNCN 2.03/527); Stn 130, a few polyps on Staurotheca densa (NIWA 117474); Stn 198, one stolonal colony with four polyps on Schizotricha nana Peña Cantero, Svoboda & Vervoort, 1996 (MNCN 2.03/528).

Measurements (in µm). Cnidome: microbasic euryteles (seen discharged) [range 7.0–8.0 x 3.5–4.0, mean 7.4±0.3 x 3.8±0.2 (n=10); ratio, range 1.8–2.1, mean 1.9±0.1 (n=10)], desmonemes [range 4.5–5.0 x 3.0].

Ecology and distribution. Recently reviewed by Peña Cantero (2015). Shelf species found at depths from the tidal level (Hickson & Gravely 1907) to 450 m (Totton 1930); present material between 110 and 222 m, epibiotic on Schizotricha nana, S. turqueti and Staurotheca densa and with gonophores in February.

Probably Antarctic-Kerguelen distribution (Peña Cantero 2015). In the Ross Sea, already known from McMurdo Sound (Hickson & Gravely 1907; Ritchie 1913; Totton 1930), Cape Royds (Ritchie 1913), Cape Adare (Totton 1930) and Tethys Bay (Peña Cantero et al. 2013). Present material collected off Cape Adare, Adare Peninsula, Possession Islands and Cape Hallett.