Homaxinella balfourensis (Ridley & Dendy, 1886)

(Figure 22)

Synonomy: Axinella balfourensis Ridley & Dendy, 1886, Axinella supratumescens Topsent, 1907, Homaxinella supratumescens (Topsent, 1907) .

Specimens. BELUM. Mc 2015.541 and BELUM. Mc 2015.546 Gøuvernoren Wreck, Enterprise Island (64°32.407’S, 61°59.884’W),depth 8–18 m; collected by C. Goodwin and E. Priestley, 13/02/2015 . BELUM. Mc 2015.559 , BELUM. Mc 2015.565 , BELUM. Mc 2015.568 , BELUM. Mc 2015.569 , BELUM. Mc 2015.575 Port Lockroy (64°49.572’S, 63° 29.390’W), depth 12–17 m; collected by C. Goodwin and E. Priestley, 14/02/2015 . BELUM. Mc 2015.681— Jenny Island (67°43.325’S, 68° 20.590’W), depth 6–16 m; collected by C. Goodwin and E. Priestley, 21/02/2015 . BE- LUM. Mc 2015.742 Rocks on west side of Pleneau Island (65°06.407’S, 64° 04.417’W), depth 8–12 m; collected by C. Goodwin and E. Priestley, 24/02/2015 . BELUM. Mc 2015.827 Diomedea Island (62°12.185’S, 58° 56.760’W), depth 10–18 m; collected by C. Goodwin and E. Priestley, 01/03/2015 .

External morphology. In situ appearance (Figure 22A): Yellow branching sponge with branches ~ 0.5 cm in diameter. Specimens can be over 20 cm in height. Branches come abruptly to a sharp point. Some individuals have many branches, some only a few, and sometimes an individual may consist of a single branch. Branches may be undivided or divided. Dividing is sometimes dichotomous but can be very untidy and give the sponge a straggly appearance.

Preserved appearance. Fairly soft pale cream branch with smooth surface. Alcohol stained pale yellow.

Skeleton (Figure 22B): Choanosomal ascending columns of styles, up to 10 spicules thick, are joined by brush- es of ectosomal styles at the surface.

Spicules (Figure 22C): Measurements from BELUM.Mc2015.742.

Styles: 341(472)576 by 7.5(10.9) 14 µm. Thin styles, often slightly curved, heads not tylote.

Remarks. The type locality of Axinella balfourensis Ridley & Dendy, 1886 is Kerguelen Island in 37– 110 m. Axinella supratumescens Topsent, 1907 was described from Ile Wiencke in 2–30 m and Booth Island, dead specimen on shore. Both are now placed in Homaxinella (Topsent 1916) and considered synonyms (Van Soest 2002c). The species has been shown to be heavily impacted by anchor ice, with up to 87% being lost in a two year period (Dayton 1989). Overwintering specimens may develop thinner branches and have a twiggy rather than bushy appearance (Jade Berman pers. obs.).

Distribution. This species is widely distributed in the Antarctic and sub-Antarctic, in depths of between 0 and 500 m (Koltun 1964; Brueggeman 1998). Published records include the Ross Sea (Burton 1929, 1934; Dayton 1989), South Georgia (Burton 1932), Kerguelen (Ridley & Dendy 1886), the Antarctic Peninsula (Topsent 1907), and the South Shetland Islands (Hajdu et al. 2016).