(Haeckel, 1870)
Species Overview
Sycon villosum (Haeckel, 1870) is a whitish ovate tube-shaped calcareous sponge. It is one of several Sycon species which can only reliably identified by microscopic examination. The characteristic feature of S . villosum are the long apical rays of the atrial tetractines filling up much of the internal cavity.
Taxonomic Description
Colour: White or grey.
Shape, size, surface and consistency: Small, ovate or cylindrical tubes with a short apical fringe surrounding the oscule. Size up to 2 cm high 0.7 cm in diameter, but normally not exceeding 1.2 x 0.5 cm. Surface minutely papillate-hispid. Consistency soft.
Spicules: (Sycon villosum spics) Calcareous. Triactines, regular or sagittal, in two forms: one (tubar triactines) with about equal sized paired rays and basal rays: 100-300 x 10-30 µm, and the other (choanosomal triactines) with thinner paired rays: 100-200 x 5-8 µm and longer and thinner basal rays: 100-400 x 5-8 µm.
Tetractines: with paired rays 100-200 x 5-8 µm, basal rays 100-400 x 5-8 µm and apical rays 500-1500 x 5-10 µm.
Oxeas: 1000-3000 x 10-30 µm.
Skeleton: Distal ends (cones are not clearly recognizable in this species) of radial tubes ornamented with oxeas; tubar skeleton made up of triactines and the basal rays of choanosomal triactines; choanosomal-atrial skeleton made up of the paired rays of choanosomal triactines and a tangential layer of triactines and tetractines. Atrial cavity is almost entirely filled by the apical rays—pointing upwards—of the tetractines.
Choanocyte chambers: Completely fused over their entire length.
Reproduction: August.
Ecology: On hard bottoms, in shallow depths down to 9 m.
Distribution: Scotland (E coast), Norway, Roscoff, Iles des Glénans.
Etymology: Villosus (Latin) = hairy.
Type specimen information: BMNH 1882.3.6.20-1, BMNH 1882.3.6.31-2, BMNH 1882.3.6.33 (dry).
Remarks
The microscopic features are well-established and make this an easily recognizable species. It has not been recorded very often.
Source: Arndt, 1935.