Sphaerotylus antarcticus Kirkpatrick, 1907

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 : 501-502

Sphaerotylus antarcticus Kirkpatrick, 1907

( Figure 24 )

Specimens. BELUM. Mc 2015.597 , BELUM. Mc 2015.606 , BELUM. Mc 2015.607 and BELUM. Mc 2015.613 Grotto Island , Verdansky Base (Site 1) (65°14.615’S, 64° 15.019’W), depth 14–24 m; collected by C. Goodwin and E. Priestley, 16/02/2015 ; BELUM. Mc 2015.620 Grotto Island , Verdansky Base (Site 2) (65°14.529’S, 64° 15.451’W), depth 6–18 m; collected by C. Goodwin and E. Priestley, 16/02/2015 ; BELUM. Mc 2015.635 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 2015.658; 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 2015.687 Rocks NW of Laktionov Island (65°45.536’S, 65° 47.319’W), depth 6–23 m; collected by C. Goodwin and E. Priestley, 22/02/2015 ; BELUM. Mc 2015.743 Rocks on west side of Pleneau Island (65°06.407’S, 64° 04.417’W), depth 8–12 m; collected by C. Goodwin and E. Priestley, 24/02/2015 ; BELUM. Mc 2015.812 and BELUM. Mc 2015.823; Nelson Island, South Shetland Islands (62°59.607’S, 60° 33.601’W), depth 7–18 m; collected by C. Goodwin and E. Priestley, 27/02/2015 .

External morphology. In situ appearance ( Figure 24A ): Low oval lobe with densely hispid brown surface. From the lobe transluscent conical papillae, up to 3 cm in length, arise. These are yellow in colour but some are tinged brown.

Preserved appearance. Pale brown sponge. Columns visible in interior. Cortical layer about 0.5–1 mm thick. Ectosomal projecting spicules very dense, giving a fur like appearance. Project up to 5 mm. Smooth papillae visible but shrunken. Alcohol is yellow.

Skeleton ( Figure 24C ): From BELUM.Mc2015.635.

Choanosome formed of thick radiating columns of over 20 styles with sphaerotyles nearer the surface. These cross the cortex and form a dense and thick surface hispidation. The cortex is formed of a sub-cortical tangential layer of smaller cortical styles and a dense palisade of tylostyles. Some sphaerotyles project through the surface, either individually or in tufts.

Spicules: Measurements from BELUM.Mc2015.635.

Cortical and choanosomal styles ( Figure 24D ): 407(694)1342 by 8.8(13.4)22.0 µm with very slightly tylote heads.

Sphaerotyles ( Figure 24B ):> 3000 µm long. Heads 20–23 µm diameter, shaft 7–14 µm diameter.

Small tylostyles of cortex and choanosome ( Figure 24E ): 116(135)155 by 5.0(6.4) 7.7 µm Spear shaped tylotes with pronounced rounded heads below a constricted neck.

Remarks. Our specimens correspond well to the form and size range of spicules given in Plotkin et al. (2017) taken from the lectoype and paralectotypes, although we have not divided the cortical and choanosomal styles into two categories (Styles 900–2900 by 20–41 µm; Subtylostyles 240–630 by 8–20 µm; Small tylostyles 100–150 by 5.5–7 µm; exotyles 1000–8000 by 20–30 µm). Morley et al. (2016) note that in overwintering specimens of S. antarcticus the papillae elongated and narrowed, and grew long filaments with asexual buds along their length.

Sphaerotylus antarcticus is very similar to S. borealis from the Northern hemisphere. This led Koltun (1976) to assume they were subspecies of a single bipolar species. However, they can be distinguished by the sabre-like shape of the small tylostyles in S. antarcticus ( Plotkin et al. 2017) .

Distribution. This is a widely distributed species in the Antarctic having been recorded from the Davis Sea, Adelie Land, Bellingshausen Sea, Weddell Sea (Sarà et al. 1992) and the South Shetland Islands 20–60m ( Desqueyroux-Faúndez 1989) in addition to the type locality Winter Quarters, McMurdo Sound, Ross Sea. It has been recorded from several shallow-water sites in the Bellinghausen Sea between 12–21m depth (New Rock and Cape Bellue near Palmer Base; Almirante Brown Base, Paradise Bay) and is locally very common in shallow depths on King George Island, South Shetlands ( Hajdu et al. 2016).

Figures

FIGURE 24. Sphaerotylus antarcticus Kirkpatrick, 1907. A. In situ appearance BELUM.Mc2015.606. B. Sphaerotyle, BE- LUM.Mc2015.812, scale bar 500 µm. C. Skeleton BELUM.Mc2015.635, scale bar 1000 µm. D. Large style, BELUM. Mc2015.635, scale bar 500 µm. E. Small tylostyle, BELUM.Mc2015.635, scale 200 µm.