Spirastrella erylicola sp. nov.

Figures 107 a–c

Material examined. Holotype RMNH Por 10535, French Guyana, ‘Luymes’ Guyana Shelf Expedition, station 14, 6.7333°N 52.75°W, depth 76 m, bottom muddy calcareous sand, 26 August 1970.

Description. (Fig. 107 a) Thinly encrusting (<1 mm) on the holotype of Erylus rhabdocoronatus sp. nov. (RMNH Por. 9339). Microhispid. Lateral size about 1 cm 2. Color in alcohol orange-beige. No apparent openings.

Skeleton. Single erect tylostyles, heads embedded in the sponge surface it encrusts, protruding through a thick crust of microscleres.

Spicules. (Figs 107 b–c) Tylostyles, spirasters.

Tylostyles (Figs 107 b,b1), curved, with prominent heads and sharply pointed apices, 570– 744 –882 x 6 – 9.3 –13 µm (heads 9– 12.8 –18 µm).

Spirasters (Figs 107 c,c1,c2), in the form of singly curved asters, spines conical, compound; smaller forms are few, supposedly juvenile stages, including thinly spined forms, overall diameters 13– 18.6 –23 µm.

Distribution and ecology. Guyana Shelf, encrusting another sponge, in muddy sand environment at 76 m.

Etymology. The name means ‘living on Erylus ’, referring to the fact the holotype encrusts a specimen of Erylus.

Remarks. The new species differs from the two common Central West Atlantic species of Spirastrella, S. coccinea (Duchassaing & Michelotti, 1864) (as Thalysias) and S. mollis Verrill, 1907 (which was recently extensively described in Rützler et al. 2014), in having very small compact spirasters only. The first of these, S. coccinea, has spirasters up to 61 µm, the second, S. mollis, up to 50 µm. Both show a clear division of large and small spirasters (types 1 and 2 in Rützler et al. 2014) with, in the larger spirasters, 2 spiral turns, whereas the microscleres in the new species described here have a more continuous variation, and are generally more compact showing 1–1.5 (rarely 2) spiral turns only. Detailed shapes are also clearly different among all three species. Tylostyles in the present new species exceed these of the other two in length (up to 822 µm vs. 680 and 520 respectively).