Stellitethya incrustans, Samaai & Pillay & Janson, 2019

Samaai, Toufiek, Pillay, Ruwen & Janson, Liesl, 2019, Shallow-water Demospongiae (Porifera) from Sodwana Bay, iSimangaliso Wetland Park, South Africa, Zootaxa 4587 (1), pp. 1-85 : 23

Stellitethya incrustans sp. nov.

( Fig. 8 A–F)

Material examined. Holotype . SAMC–A24734 (cross-reference Ts 948 & Saf 03-Sod 103), Seven Mile reef, Sodwana Bay (27.4580°S, 32.7141°E), South Africa, 0 7 November 2003, collected by T. Samaai, depth 24 m.

Type locality. Seven Mile reef, Sodwana Bay, east coast of South Africa .

Description. Thinly encrusting sponge measuring 9 cm in length, 6 cm in width and 1 cm in height ( Fig. 8A ). The surface is fuzzy and no oscules are visible. The texture is tough and firm. Colour in situ dull orange, in preservative beige.

Skeleton ( Fig. 8B, C ). Choanosomal skeleton radial, consisting of subtylostyle tracks Interstitial subtylostyles found between these tracts. Large and small oxyspherasters are common throughout the choanosome. The ectosomal skeleton is a dense mass of oxyspherasters and tylasters. Subtylostyles protrude through the surface.

Spicules. Megascleres ( Fig. 8F ). Subtylostyles, smooth, straight and distal end fusiform, sometimes hastate, in two size classes: I) 2154 (1984–2645) × 64 (64) µm, n = 10; II) 697 (631–722) × 9 (9) µm, n = 10. Microscleres ( Fig. 8D, E ). Oxyspherasters either smooth or spined, in two size classes: I) 139 (109–240) µm, n = 10; II), 13 (9– 16) µm, n = 10. Tylasters terminally spined: 15 (10–18) µm, n = 10.

Substratum, depth range and ecology. The sponge is found attached to a rocky ledge and fed on by hawksbill turtles at a depth of 23 m.

Etymology. Named for the thinly encrusting shape of the sponge.

Remarks. Stellitethya contains three known species described from south Arabia and southwestern Australia ( Sarà 2002; Sarà & Sarà 2003). These are S. murrayi Sarà & Bavestrello, 1996 , S. extensa ( Hentschel, 1909) and S. ingens Sarà & Sarà, 2003 .

This is the first record of the genus in South Africa. All Stellitethya are described from the Indo-Pacific region with records from the Arabian coast and western Australia ( Sarà & Sarà 2003). Stellitethya ingens is irregularly massive whereas S. extensa and S. murrayi are thickly encrusting (or cushion shaped) similar in external morphology to S. incrustans sp. nov. Stellitethya murrayi and S. ingens have giant oxyasters, 500 µm in diameter, whereas S. incrustans sp. nov. have smaller oxyasters, 240 µm in diameter. Other distinguishing characters are the shape and size of the micrasters. Stellitethya incrustans sp. nov. have tylasters similar in shape to S. murrayi , but larger in size, 10–18 µm, instead of 8–12 µm (see Sarà & Bavestrello 1996). The micrasters in S. ingens are strongylasters and not tylasters as in S. incrustans sp. nov. Stellitethya incrustans sp. nov. have smaller subtylostyles on average ( S. incrustans sp. nov. primary subtylostyles 2154 µm, S. extensa 3250 µm; S. murrayi 3100 µm; S. ingens 3800 µm).

Key diagnostic characters.

• Sponge thinly encrusting and often fed on by hawksbill turtles.

• Small oxyspherasters, either smooth or spined.

• Tylasters terminally spined.

Figures

FIGURE 8. Stellitethya incrustans sp. nov. A. Preserved sample; B & C. Skeletal architecture (B, x5; C, x10). Spicule compliment, D & E. Oxyspherasters; F. Strongyloxea.