Phorbas glaberrimus ( Topsent, 1917 )

Goodwin, Claire E., Berman, Jade & Hendry, Katharine R., 2019, Demosponges from the sublittoral and shallow-circalittoral (<24 m depth) Antarctic Peninsula with a description of four new species and notes on in situ identification characteristics, Zootaxa 4658 (3), pp. 461-508 : 483-484

Phorbas glaberrimus ( Topsent, 1917)

( Figure 11 )

Synonomy: Anchinoe glaberrima ( Topsent, 1917) ; Clathrissa glaberrima Topsent, 1917 .

Specimens. BELUM. Mc 2015.643 Rocks near San Martin Islands (65°41.297’S, 65° 20.091’W), depth 6–21 m; collected by C. Goodwin and E. Priestley, 17/02/2015 . BELUM. Mc 2015.664 Detaille Island (Site 1) (66°52.373’S, 66° 46.967’W), depth 6–24 m; collected by C. Goodwin and E. Priestley, 18/02/2015 . BELUM. Mc 2015.698 Vieugue Island (65°38.758’S, 65° 12.540’W), depth 10–22 m; collected by C. Goodwin and E. Priestley, 23/02/2015 . BE- LUM. Mc 2015.752 Paradise Bay Wall (64°53.841’S, 62° 52.391’W), depth 14–21 m; collected by C. Goodwin and E. Priestley, 24/02/2015 . BELUM. Mc 2015.774 Paradise Bay Wall (64°53.841’S, 62° 52.391’W), depth 10–24 m; collected by C. Goodwin and E. Priestley, 25/02/2015 . BELUM. Mc 2015.830 and BELUM. Mc 2015.838 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 11A, B ): Very large thickly encrusting specimens, some over 30 cm in diameter and over 15 cm thick. The sponge is cream but the surface layer is often brown (potentially from algae) so the densely packed pore sieves, which remain cream, are very distinct.

Preserved appearance. Firm, grey, mass. Skeletal columns clearly distinguishable and spaces visible between them.

Skeleton ( Figure 11C ): Choanosomal skeleton composed of a basal layer of acanthostyles from which thick ascending columns of up to 20 oxea ascend. Acanthostyles echinate the lower parts of these columns. In the ectosome the ends of the columns of oxea fan out to form a continuous surface layer. Chelae are very abundant and scattered throughout tissue.

Spicules: Measurements from BELUM.Mc2015.698.

Oxeas ( Figure 11D ): 429(484)528 by 12(15) 20 µm. Fusiform with abrupt points.

Acanthostyles: 202(268)403 by 14(20) 27 µm. Parallel sided with an abrupt point. Head not tylote. Strongly spined along whole length.

Chelae ( Figure 11E ): 22(24) 28 µm.

Remarks. Phorbas glaberrimus ( Topsent, 1917) was originally described from 297 m in the Antarctic and ap- pears to be a good match for these specimens, although Topsent reports slightly larger oxeas (530–600 by 20–22 μm). Rios (2006) and Goodwin et al. (2012) report smaller oxeas of 420–590 μm and 365–476 μm respectively, more similar to the range in our specimens, and Koltun (1964) also gives a wider size range (382–600 μm). Rios (2006) reports two categories of acanthostyles but this division is not apparent in our specimens.

Distribution. This species is widely distributed in the Antarctic: Alexander I land ( Topsent 1917), Wilheim II coast, Banzare coast, Wilkes Land, Victoria Land, Princess Astrid Coast ( Koltun 1964), MacRobertson Coast (Kol- tun 1976), Weddell Sea ( Barthel et al. 1990; Gutt & Koltun 1995), Ross Sea ( Pansini et al. 1994), South Trinidad Island and Bransfield Strait ( Rios 2006), and South Georgia ( Goodwin et al. 2012) from depths 10–1370m. Burton (1929) also erroneously reported it as a synonym of Pyloderma latrunculioides ( Ridley and Dendy, 1886) from the Antarctic but it is not clear which of his specimens are this species.

Figures

FIGURE 11. Phorbas glaberrimus (Topsent, 1917). A. In situ appearance BELUM.Mc2015.698. B. In situ appearance, close up of sponge surface, BELUM.Mc2015.698. C. Skeleton BELUM.Mc2015.664, scale bar 1000 µm. D. Spicules BELUM. Mc2015.698, scale bar 200 µm. E. Chelae BELUM.Mc2015.698, scale bar 10µm.