Rossella nuda Topsent 1901

Rossella nuda Topsent, 1901

(Figure 22)

Material: Samples in 95% ethanol, tissue section and spicule preparation on slides. BELUM Mc 7650. 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.

Comparative material examined: BMNH Rossella nuda (Topsent) Discovery Antarctic Collection 1926 - 27.Dried specimens RN CLVI II, R.N. CKVI I

External morphology: In situ appearance: Large (maximum diameter> 100cm) vase shaped white sponge with lobose surface (Fig. 22a).

Preserved appearance: Small slide of edge of sponge. Tough with a very hispid surface like a mat of hairs.

Skeleton: Skeleton composed of free diactines with hypodermal diactines and pentactines, outer dermal spicules spined pentatines and hexactines.

Spicules: Hypodermal diactines: (not measured, Barthel and Tendal (1994) report 2500–3500µm)

Spined hexactine (Fig. 22b).

Calycocome: very rare, one measured: 211µm in diameter (Fig. 22c).

Oxyhexaster: diameter 101(181)247µm (Fig. 22d).

Microdiscohexaster: diameter 30(32)35µm (Fig. 22e).

Remarks: In the original description Topsent lists the microscleres as oxyhexasters 120µm in diameter, calcycocomes of a uniform diameter (250µm), microdiscohexasters 40–50µm in diameter, and larger discohexasters 100µm in diameter. The latter were only noted in small quantities and we didn’t find them in our specimen.

Distribution: This specimen was situated in a small cave at 8m, attached to bedrock. Rossella nuda has been recorded on the Victoria Land coast from the eastern Weddell Sea to the Ross Sea, including McMurdo Sound, and the Bellingshausen Sea (Topsent 1901; Kirkpatrick 1907; Burton 1929; Koltun 1976; Barthel and Tendal, 1994; Janussen and Reiswig 2009); South Georgia (Burton 1940 but no details given, Barnes et al. 2006b) and the Falkland Islands (Burton 1940 but no details given) and the coast of Argentina (Burton 1940); from depths of 18–1579m. Burton (1929) recognised five species of Rossella including R. nuda but Koltun (1976) only recognised R. antarctica and R. racovitzae one of which he regarded as a ‘ highly polymorphic species’, many species have since been reinstated by Barthel and Tendal (1994). Barnes et al. (2006b) recorded specimens of Rossella nuda from Morraine Fjord on South Georgia at 18m, which were the shallowest known records for R. nuda at that time.