Rhizorhagium antarcticum Hickson & Gravely 1907

• Main Author: Peña Cantero, Álvaro L.
• Format: Other/Unknown Material
• Language: unknown
• Published: Zenodo 2015
• Subjects: Biodiversity; Taxonomy; Animalia; Cnidaria; Hydrozoa; Anthoathecata; Bougainvilliidae; Rhizorhagium; Rhizorhagium antarcticum; Antarc*; Antarctic; Antarctica; antarcticus; Ross Sea
• Online Access: https://doi.org/10.5281/zenodo.5671794; http://treatment.plazi.org/id/3D10878AFF92B44210905FB1FEE43BE5

Rhizorhagium antarcticum (Hickson & Gravely, 1907) (Figs 1 C, D, 2E, F, 3F) Perigonimus antarcticus Hickson & Gravely, 1907: 4 –6, pl. 1 figs 1–3, pl. 4 fig. 32; Rees, 1938: 7; 1956: 338, 347; Naumov & Stepanjants, 1972: 33, 35; Stepanjants, 1972: 56–57, fig. 1; 1979: 10, pl. 1 fig. 1. Atractylis antarctica — Vanhöffen, 1910: 283, fig. 8; Atractylis antarcticus — Ritchie, 1913: 10, 11. Gravelya antarctica — Totton, 1930: 139, fig. 1a, b. ? Gravelya antarcticum — Schuchert, 1996: 41 –42, fig. 21a–d. Rhizorhagium antarcticum — Stechow, 1919: 21; Rees, 1956: 338, 347; Rees & Thursfield, 1965: 55; Millard, 1971: 401, fig. 3; Branch & Williams, 1993: 8, fig.; Peña Cantero, 2004: 768; Bouillon et al ., 2006: 137, fig. 79I, J; Peña Cantero et al ., 2013: 735 –736, figs 2c–d, 3a–b. Material examined. Discovery Antarctic Expedition 1901-04: Type (NHM 1907.8.20.1), McMurdo Bay (Ross Sea), 1–20 fms, several stems, with gonophores, on Hydrodendron arboreum . Description. Usually stolonal (Fig. 1 C, D), but stems with up to three polyps present. Stems covered with perisarc (Figs 1 C, D, 2E, F), smoothly disappearing on hydranth body (Fig. 2 E, F). No distinct pseudohydrotheca present. Polyps 800–900 µm high and 250–300 µm in maximum diameter, with conical hypostome and a distal crown of nine to 12 filiform tentacles (Fig. 2 E, F). Gonophores c. 950 µm high and c. 680 µm in maximum diameter, on short pedicels, either on hydrorhizal stolon or at basal part of largest stems (Figs 1 C, D, 3F). “The colonies appear to be invariably dioecious. In both sexes the gonophore is a degenerate medusa. protected by a thin layer of perisarc. It is larger in the female than in the male (1.1 mm. x 0.9 mm. in the female, and 0.9 mm. x 0.7 mm. in the male). In the female gonophore there is a large sub-umbrella cavity (fig. 3, su.c), the manubrium is well developed and has a well-marked endoderm cavity. In the young gonophore there is a distinct endodermal layer of cells and mesoglea in the umbrella, but in the adult ...