Sponges of the Guyana Shelf Van, Rob W. M. Zootaxa 2017 1 1 225 [151,461,940,966] Demospongiae Desmacellidae Biemna Animalia Poecilosclerida 67 68 Porifera species rhabdotylostylota sp. nov.    Material examined. Holotype  RMNH9927, Suriname, ‘ Snellius O.C.P.S.’ GuyanaShelf Expedition, station G7, 7.28°N 56.7933°W, depth  64 m, bottom sand,  7 May 1966.   Description.( Fig. 44a) Sponge consolidating an irregularly curled mass of rubble, shell debris and sand, size about 10 cmlong and 2.5 wide and thick. Sponge recognized as a glassy, grayish, smooth tissue (in alcohol) cementing white and brown foreign objects.  Skeleton.( Fig. 44b) Not clearly differentiated, largely confused, with larger megascleres singly erect on pieces of calcareous matter, carrying a membrane charged with microscleres.  Spicules.( Figs 44c–j) Tylostyles, rhabdotylostyles, sigmas, dragmas of microxeas. Tylostyles ( Figs 44c–d), smooth, curved gently, especially in the proximal part below the tyle, tapering to thinner, but often bluntly rounded endings ( Fig. 44c1), in a large size range, not clearly divisible in two distinct sizes, larger ( Fig. 44c) 690–936 x 5.5–8.5 µm, smaller ( Fig. 44d) 237–456 x 2–5.5 µm), overall 237– 571–936 x 2–4.9–8.5 µm. Rhabdotylostyles ( Figs 44e–f), smooth, abruptly curved just below the tyle, gradually tapering to a sharp ending ( Fig. 44f1), in a large size range, not clearly divisible in two distinct sizes, larger ( Fig. 44e) 207–387 x 4–7.5 µm, smaller ( Fig. 44f) 78–189 x 1–5µm), overall 78– 181–387 x 1– 4.4–7.5 µm. Sigmas ( Figs 44g–h), small and thin, with faint roughening of the apices, divisible in two distinct size ranges, (1) larger ( Fig. 44g) 13– 15.3–18 µm, (2) smaller ( Fig. 44h) 6– 8.0–9 µm. Microxeas ( Figs 44i–j), smooth, straight, fusiform, arranged in tightly developed trichodragmas, in two distinct size categories, (1) long ( Figs 44i, i1) 198– 253–301 x 6– 10.4–17 µm, (2) short ( Figs 44j,j1) 24– 30.4– 36 x 6– 9.5–12 µm.   Distribution and ecology. GuyanaShelf, on sand bottom at 64 mdepth.   Etymology.The name reflects the shape of the smaller megascleres.   Remarks.The new species is assigned to the Biemnidaby its combination of microxeas in dragmata and sigmas with roughened apices. The megascleres are unique among Central WestAtlantic  Biemnaspecies by being a diverse combination of tylostyles and rhabdotylostyles. The known Central WestAtlantic 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. spinomicroxeaMothes, Campos, Lerner, Carraro & Van Soest, 2005have 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, 1961and 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.   FIGURE 44.  Biemna rhabdotylostylota  sp. nov.,a, habitus of holotype RMNH Por. 9927 (scale bar = 1 cm), b, light microscopic image of the skeleton showing the diversity of mega- and microscleres, c–j, SEM images of spicules, c, large tylostyle, c1, details of c, d, small tylostyle, e, large rhabdotylostyle, e1, details of e, f, small rhabdotylostyle, f1, details of f, g, large sigma, h, small sigma, i, long trichodragma, i1, detail of i showing individual long microxeas, j, short trichodragma, j1, detail of j showing individual short microxeas. The above described morphological characters of the present new species make it an atypical  Biemnaspecies. A future revision of the genus may result in assignment to a separate, so far undescribed, genus along with B. rhabdostyla. 1424726264 1966-05-07 RMNH Snellius O. C. P. S. Suriname 64 7.28 Suriname 555 -56.7933 67 68 RMNH 9927 1 holotype