Myxilla (Burtonanchora) ponceti Goodwin & Brickle 2012, sp. nov.

Myxilla (Burtonanchora) ponceti sp. nov.

(Figure 13)

Type material: Holotype: BELUM Mc 7572. Sample in 95% ethanol, tissue section and spicule preparation on slides; Floating Dock, Grytviken, South Georgia (54º 16.937´S, 36º 30.475´W); depth range: 0–6.6m; collected by C. Goodwin and S. Cartwright, 18 th November 2010.

Paratypes: Samples in 95% ethanol, tissue section and spicule preparation on slides. BELUM Mc 7573. Floating Dock, Grytviken, South Georgia (54º 16.937´S, 36º 30.475´W); depth range: 0–6.6m; collected by C. Goodwin and S. Cartwright, 18 th November 2010. BELUM Mc 7600. Prion Island Site 2, South Georgia (54°001.862’S, 37° 15.032’W); depth 18m; collected by C. Goodwin, D. Poncet, and P. Brewin, 19 th November 2010. BELUM Mc 7655. Prince Olav Harbour, South Georgia (54°03.579’S, 37° 08.203’W); depth 18m; collected by C. Goodwin, D. Poncet, and S. Brown, 23 rd November 2010.

Etymology: Named for Dion Poncet, member of the expedition dive team, who alerted us to this ‘probable sponge’ under Grytviken jetty, and whose knowledge of South Georgia was invaluable to this survey.

External morphology: In situ appearance: Specimens are large (10–20cm maximum dimension), smooth surfaced, lobed sponges, carrot orange in colour, bearing large terminal oscules on the ends of the lobes. The two largest specimens are fan shaped and bear the oscules in a line along the edge of the fan. They are attached by the base of the specimen to the substrate; the attachment point is quite broad in some specimens but in the fan shaped specimens is smaller and might be considered a stalk (Fig. 13a).

Preserved appearance: Tissue firm but compressible. Ectosome is a dark brown, choanosome a paler brown.

Skeleton: Choanosomal skeleton consists of ascending fibres of 4–10 styles joined by smaller, shorter, fibres of 1–3 styles. There is an ectosomal palisade of tylotes. Chelae scattered throughout skeleton and not forming rosettes (Fig. 13b).

Spicules: Measurements from Mc7572.

Choanosomal subtylostyles: 281(325)369 by 12.2(14.3)18.7µm. Smooth styles, often slightly curved. Some have a faint swelling at the head (Fig. 13c).

Ectosomal tylotes: 197(276)324 by 6.9(10.3)14.5µm. Anisotylotes in which one or both ends are swollen. In some one end has a mucronate point (Fig. 13d).

Chelae: In two categories 31(40)49 and 57(66)72µm (Fig. 13e).

Remarks: Myxilla (Burtonanchora) is defined by possession of smooth rather than spined choanosomal styles. There are several species of Antarctic Myxilla (Burtonanchora) species (Table 7). However, all of these can be distinguished by having much larger choanosomal styles or the presence of sigmata. Myxilla (Burtonanchora) pistillaris Topsent, 1916 is most similar but has larger styles (480–500µm) and possesses raphides which are not present in this species.