Biemna rhabdotylostylota sp. nov.

Figures 44 a–j

Material examined. Holotype RMNH 9927, Suriname, ‘ Snellius O.C.P.S. ’ Guyana Shelf Expedition, station G7, 7.28°N 56.7933°W, depth 64 m, bottom sand, 7 May 1966 .

Description. (Fig. 44 a) Sponge consolidating an irregularly curled mass of rubble, shell debris and sand, size about 10 cm long and 2.5 wide and thick. Sponge recognized as a glassy, grayish, smooth tissue (in alcohol) cementing white and brown foreign objects.

Skeleton. (Fig. 44 b) Not clearly differentiated, largely confused, with larger megascleres singly erect on pieces of calcareous matter, carrying a membrane charged with microscleres.

Spicules. (Figs 44 c–j) Tylostyles, rhabdotylostyles, sigmas, dragmas of microxeas.

Tylostyles (Figs 44 c–d), smooth, curved gently, especially in the proximal part below the tyle, tapering to thinner, but often bluntly rounded endings (Fig. 44 c1), in a large size range, not clearly divisible in two distinct sizes, larger (Fig. 44 c) 690–936 x 5.5–8.5 µm, smaller (Fig. 44 d) 237–456 x 2 –5.5 µm), overall 237– 571 –936 x 2 –4.9–8.5 µm.

Rhabdotylostyles (Figs 44 e–f), smooth, abruptly curved just below the tyle, gradually tapering to a sharp ending (Fig. 44 f1), in a large size range, not clearly divisible in two distinct sizes, larger (Fig. 44 e) 207–387 x 4 –7.5 µm, smaller (Fig. 44 f) 78–189 x 1–5 µm), overall 78– 181 –387 x 1 – 4.4 –7.5 µm.

Sigmas (Figs 44 g–h), small and thin, with faint roughening of the apices, divisible in two distinct size ranges, (1) larger (Fig. 44 g) 13– 15.3 –18 µm, (2) smaller (Fig. 44 h) 6– 8.0 –9 µm.

Microxeas (Figs 44 i–j), smooth, straight, fusiform, arranged in tightly developed trichodragmas, in two distinct size categories, (1) long (Figs 44 i, i1) 198– 253 –301 x 6 – 10.4 –17 µm, (2) short (Figs 44 j,j1) 24– 30.4 – 36 x 6 – 9.5 –12 µm.

Distribution and ecology. Guyana Shelf, on sand bottom at 64 m depth.

Etymology. The name reflects the shape of the smaller megascleres.

Remarks. The new species is assigned to the Biemnida by its combination of microxeas in dragmata and sigmas with roughened apices. The megascleres are unique among Central West Atlantic Biemna species by being a diverse combination of tylostyles and rhabdotylostyles. The known Central West Atlantic species Biemna caribea Pulitzer-Finali, 1986, B. microacanthosigma Mothes, Hajdu, Lerner & Van Soest, 2004, B. microstyla De Laubenfels, 1950, and B. trisigmata Mothes & Campos, 2004, all have styles as megascleres, while B. cribraria (Alcolado & Gotera, 1986) and B. spinomicroxea Mothes, Campos, Lerner, Carraro & Van Soest, 2005 have oxeas or strongyles as megascleres. The megascleres are all in a single category, not differentiated in shape and size as in the new species.

Rhabdose megascleres are found in New Zealand Biemna rhabderemioides Bergquist, 1961 and in Namibian B. rhabdostyla Uriz, 1988 . In both species, the megascleres are styles, not tylostyles. The Namibian species is closest to the new species in having a diverse megasclere complement of longer styles (up to 1200 µm) and smaller rhabdostyles (up to 215 µm). Apart from lacking tylostyles it differs also in having three categories of sigmas, the largest of which are up to 112 µm.

The above described morphological characters of the present new species make it an atypical Biemna species. A future revision of the genus may result in assignment to a separate, so far undescribed, genus along with B. rhabdostyla .