Acanthopolymastia acanthoxa (Koltun, 1964) (Fig. 2) Synonymy Atergia acanthoxa — Koltun 1964: 27, fig. 3. Acanthopolymastia acanthoxa— Kelly­Borges and Bergquist 1997: 396, fig. 27; Boury­Esnault 2002: 209, fig. 7. Not Atergia acanthoxa— Lévi 1993: 26, fig. 7C, pl. II (9–12). Material examined SMF 10539 (1 specimen): PS67/080­6. Description External morphology. Slightly damaged, cushion­shaped sponge measuring about 13x13 x 5.5 mm and removed from substrate (fig. 2A). The upper surface of the sponge is mainly hispid, where not damaged. Its colour is greyish due to sediment particles, which soil the hispidation. Bare areas of the surface are paler. The basal surface is rather damaged. The marginal spicule fringe is well preserved and measures about 6 mm in width. A single exhalant papilla is pale and measures approximately 1 mm in length and 2 mm in diameter. The cortex is semi­transparent, hardly detachable, moderately firm and somewhat fragile. The choanosome is soft, crumbly and whitish in colour. Skeleton. The main choanosomal skeleton consists of the radial tracts of principal spicules measuring in the basal choanosome 100–300 µm in thickness, penetrating the cortex and making up a surface hispidation of 650 µm in thickness (fig. 2B). The additional choanosomal skeleton is composed of free­scattered, abundant, acanthose, centrotylote microxeas (fig. 2C). The cortex, measuring 340–1140 µm in thickness, consists of two layers—the external palisade of small tylostyles and the internal unordered mass of centrotylote acanthoxeas. The marginal fringe is made of extremely long and thin spicules. Spicules. There are three main categories of spicules including acanthoxeas. We measured 20 spicules of each category. An additional category is constituted by the extra­long spicules of the marginal fringe. Very few of them were measured, because most were broken on the slides. Principal spicules vary from styles to tylostyles. They are straight, slender and slightly fusiform and measure: length 1525­2123 ­2693 ìm, maximal diameter 11­14.7­17 ìm. Small cortical tylostyles are straight and slender. They measure: length 257­369­549 ìm, maximal diameter 9­10.3­12 ìm. Acanthose, centrotylote microxeas measure: length 89­113­158 ìm, diameter of central tyle 5­5.9­8 ìm (fig. 2D). Extra­long spicules of the marginal fringe vary from styles to subtylostyles. They are slightly curved and slender. We estimate that their maximal length exceeds 5900 ìm, while the maximal diameter can be more than 30 ìm. Type locality: Antarctic: Northern Ross Sea, 3200–3400 m. Distribution (other than type locality): Antarctic: NE Weddell Sea, ca. 3000 m (present study). Remarks. This is the second finding of A. acanthoxa since Koltun (1964) described it from the northern Ross Sea. Both specimens have come from approximately 3000 m and demonstrate no sufficient difference in external morphology, skeletal arrangement, spicule shape and size. The comprehensive comparison of A. acanthoxa with its congeners has been completed by Kelly­Borges and Bergquist (1997).

Published as part of Plotkin, Alexander S. & Janussen, Dorte, 2008, Polymastiidae and Suberitidae (Porifera: Demospongiae: Hadromerida) of the deep Weddell Sea, Antarctic *, pp. 95-135 in Zootaxa 1866 on pages 98-99, DOI: 10.5281/zenodo.183878