Polymastia invaginata Kirkpatrick 1907

Polymastia invaginata Kirkpatrick, 1907

(Figure 3)

Synonymy: Polymastia invaginata Kirkpatrick, 1907.

Polymastia invaginata var. gaussi Hentschel, 1914 is regarded as a synonym by Plotkin and Janussen (2008).

Material: All samples in 95% ethanol, tissue section and spicule preparation on slides. BELUM Mc 7610. Rosita Harbour Site 2, South Georgia (54°00.649’S, 37° 25.618’W); depth 11.5m; collected by C. Goodwin, J. Brown, and S. Brown, 20 th November 2010. BELUM Mc 7618 and BELUM Mc 7620. Right Whale Bay, South Georgia (54°00.173’S, 37° 40.856’W); depth 18m; collected by C. Goodwin, J. Brown and S. Brown, 21 st November 2010. BELUM Mc 7648. Jagged Point, Possession Bay, South Georgia (54°04.514’S, 37° 07.188’W); depth 10.4m; collected by C. Goodwin, D. Poncet and P. Brewin, 23 rd November 2010. BELUM Mc 7660. Husvik, South Georgia (54°10.285’S, 36° 40.412’W); depth 18m; collected by C. Goodwin, D. Poncet and P. Brewin, 26 th November 2010.

Comparative material examined: BMNH 03.2.5.78 Polymastia invaginata. Discovery Antarctic Expedition McMurdo Bay ~20fms. W.Q.28.2.02. Specimen in alcohol. This specimen is the figured half specimen in PL XIV Fig. 5 of the description.

External morphology: In situ appearance: Brown hispid mound attached to bedrock bearing single, lemon yellow, smooth surfaced, large papillae with large terminal oscule. Individuals up to 20cm in height (Fig. 3a). Often occur in clusters of several individuals.

Preserved appearance: Transverse slice of basal mound of specimen. Tissue very tough. Choanosome grey, cortical layer white and 2–3mm thick. A fringe of dark grey hairs ~ 5mm long present on the surface.

Skeleton: Radiate skeleton of bundles of large styles, these penetrate the ectosome and form the thick surface pile (Fig. 3b). Stellate groups of small tylostyles are present between the fibres (Fig. 3c). The ectosome is formed of a dense tylostyles, positioned vertically with their points towards the surface. This layer forms a fibrous cortex to the sponge, easily visible on slides, around 0.5–1cm thick.

Spicules (Fig. 3d): Styles: 1825 (2462) 3076 by 22.1 (26.9) 42.1µm—although many broken and difficult to measure so longer spicules may be present.

Tylostyles: 119 (307) 625 by 6.3 (10.1) 13.6µm. Fusiform tylostyles with a neat swelling at their head. Some forming stellate clusters between the fibres but these do not seem to represent a seperate size category.

Remarks: Our specimens are a good match with the type description and specimens and correspond to the external form and spiculation of other specimens assigned to this species (Brueggeman, 1998; Hentschel 1914; Koltun 1964; Plotkin and Janussen, 2008). However, like previous authors, we did not record the sceptre-like spicules noted by Plotkin and Janussen (2008) in the cortical palisade and our styles are of a larger size than those noted by Boury-Esnault and van Beveren (1982). Polymastia invaginata can be distinguished from other Antarctic and Southern Atlantic species of Polymastia by its single inhalant papillae, densely hispid surface and single spicule layer in the cortex (Plotkin and Janussen, 2008).

Kirkpatrick (1907) noted that the papillae in all of his specimens was ‘invaginated’, flush with the surface of the basal mound, this is presumably the origination of the species name. He was studying preserved material and this may have been an artifact of preservation, in all our living specimens the papillae stood proud.

Distribution: Originally recorded from Winter Quarters (18–55m depth) and from off Mount Erebus (914m depth). Widespread in the Antarctic and sub-Antarctic: records from Kerguelen and Heard Islands (Boury-Esnault and Van Beveren 1982) McMurdo Sound (Burton 1929), South Georgia, South Orkneys and South Shetlands (Burton 1932) in depths of 18–1080m. Polymastia invaginata var. gaussi Hentschel, 1914 was regarded as a synonym by Burton (1932) but this is a much smaller sponge (maximum 8mm high) and has smaller spicules (styles up to 1792µm, tylostyles 120–600µm) so is a distinct species.