Halecium arboreum — Hickson & Gravely, 1907: 27, pl. 4 figs 27–29; Dayton et al., 1970: 247, 254.
Ophiodes arboreus — Ritchie, 1913: 15, figs 2, 3.
Ophiodissa arborea — Totton, 1930: 142, fig. 2a.
Hydrodendron arboreum — Peña Cantero & Ramil, 2006: 952 –953, fig. 2C (synonymy); Peña Cantero & Gili, 2006: 766; Peña Cantero, 2008: 456; 2009: 1747; 2014a: 1720; Peña Cantero et al. 2013: 747, fig. 9a –c.
Material examined. Stn 21, three fragments up to 7 mm long (MNCN 2.03/655); Stn 112, a few stems and fragments, up to 45 mm long, some on pebbles, basibiont of Symplectoscyphus naumovi (NIWA 117603); Stn 134, at least one fragmented colony (largest fragment 230 mm long) (NIWA 117604); Stn 139, fragmented colony (largest fragment 70 mm long) (MNCN 2.03/656); Stn 140, several stem fragments up to 25 mm long, and complete stem 33 mm high, basibiont of Bimeria corynopsis (NIWA 117605); Stn 150, a few tiny stems, with just 2–3 polyps (NIWA 117606).
Ecology and distribution. Eurybathic species found at depths from 18 (Hickson & Gravely 1907) to 1370 m (Peña Cantero & Ramil 2006); present material between 60 and 480 m, epilithic on pebbles and basibiont for colonies of Bimeria corynopsis and Symplectoscyphus naumovi.
Pan-Antarctic distribution (Peña Cantero & Ramil 2006). Recently reported from off Bouvet Island (Peña Cantero & Gili 2006) and Livingston Island (Peña Cantero 2008), in West Antarctica, and from the Balleny Islands (Peña Cantero 2009) and off Queen Mary Coast (Peña Cantero 2014a), in East Antarctica. See Peña Cantero & Ramil (2006) for previous records. In the Ross Sea, already known from McMurdo (Hickson & Gravely 1907; Ritchie 1913; Totton 1930; Dayton et al. 1970), Cape Royds (Ritchie 1913) and Tethys Bay (Peña Cantero et al. 2013). Present material collected in Robertson Bay and off Cape Adare, Possession Islands and Moubray Bay.