Clathria (Clathria) stromnessa Goodwin & Brickle 2012, sp. nov.

Clathria (Clathria) stromnessa sp. nov.

(Figure 6)

Type material: Holotype: BELUM Mc 7690. Sample in 95% ethanol, tissue section and spicule preparation on slides; Green Island, Stromness, Site 2, South Georgia (54°09.381’S, 36° 39.852’W); depth 17.4m; collected by C. Goodwin, J. Brown, and S. Brown, 28 th November 2010.

Paratype: BELUM Mc 7674. Sample in 95% ethanol, tissue section and spicule preparation on slides, Green Island, Stromness, Site 1, South Georgia (54°09.448’S, 36° 39.752’W); depth 17.4m; collected by C. Goodwin, P. Brickle and S. Cartwright, 27 th November 2010.

Etymology: Named after the type locality, Stromness, South Georgia

External morphology: In situ appearance: Lobed massive (type specimen maximum diameter 20cm) rust orange sponge with large oscules on top of lobes (Fig. 6a).

Preserved appearance: Grey, firm, with a slightly hispid surface.

Skeleton: The choanosomal skeleton is an irregular reticulation of bundles of 4–6 smooth styles (Fig. 6b), there is no differentiation between axial and extra-axial regions. The ectosome is formed of brushes of styles. Toxa and chelae microscleres are present throughout the tissue.

Spicules: Measurements from Mc7690.

Choanosomal styles: 424(495)563 by 17(26)31µm. Fat smooth styles, the majority are gently curved (Fig. 6c). Ectosomal styles: 232(292)414 by 3(6)7µm. Thin styles, the heads are microspined, bearing several short blunt spines (Fig. 6d, e).

Chelae: 10(12)14µm. Typical clathriid palmate isochelae (Fig. 6f).

Toxa: 45(150)477µm, thin smooth toxas, very wide ranging in size. Some of the smallest have a pronounced central flexion and upturned points (Fig. 6g).

Remarks: We have assigned this species to Clathria (Clathria) rather than one of the other seven sub-genera on the basis of the lack of differentiation between the axial and extra-axial regions of the choanosome and the presence of a reticulate skeleton and only a single category of auxillary style (Hooper 2002). This species is unusual in not possessing any echinating acanthostyles, however these can be secondarily lost in this subgenus (Hooper 2002). The subgenus Clathria (Isociella) lacks echinating acanthostyles but has a regular renieroid reticulate skeleton with plumose multispicular tracts connected by paucispicular ones (Hooper 2002), whereas the skeleton of our species is irregularly reticulate. From the South Atlantic and Antarctic C. papillosa Thiele, 1905 and C. paucispicula (Burton, 1932) are the only species in Clathria (Clathria), which do not possess any echinating spicules. However, the former has strongylote ectosomal spicules and bipocoelles and should probably be reassigned to Iophon, and the latter lacks any microscleres. The large size of the toxa is also unusual; C. toxipraedita Topsent, 1913 (type locality Burdwood Bank to the south of Falkland Islands and north west of South Georgia) has toxa up to 1750µm but possesses echinating acanthostyles.