Rhizorhagium antarcticum ( Hickson & Gravely, 1907 )

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 : 9-10

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.

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).