(Montagu, 1818)
Species Overview
Stelligera rigida (Montagu, 1818) are rather small and squat, branching to lamellate, pale yellow sponges with a strongly hispid surface. It may be confused with S . stuposa , but is more robust, lower and has more robust spicules. Axinella damicornis may also look similar, but that is more brightly yellow, less bristly, and has different spicules. It is a common species along the west coasts of the British Isles and France.
Taxonomic Description
Colour: Pale yellow to orange. Usually there is adhering detritus which has to be brushed aside to see the features.
Shape, size, surface and consistency: (Stelligera rigida V) Branching-erect to sub-lamellate (palm-like) with the branches webbed together along their length. Up to 5 cm high. The terminal branches are typically 5 mm in diameter, tending to be bulbous at their extremities in smaller specimens. Surface strongly villose (very bristly) with long projecting spicules (to 2 mm), which often trap quantities of silt. The oscules are small and inconspicuous, on the tops of branches. In situ they are apparent as 'clear' areas in the layer of silt. The oscules are not apparent when the sponge is preserved. The stalk is relatively short and thick. Some slime. Consistency firm. The strong axial skeleton gives a firm axial consistency. The peripheral tissue is soft and easily rubbed off but less so than Stelligera stuposa .
Spicules: (Stelligera rigida spics) The megascleres of the axial core are styles of variable length, possibly in size categories: 500-550 µm and 890-3000 µm long and, occasionally, strongyles of 775-1075 µm. In the extra-axial skeleton similar long styles are found, with slender oxeas to about 460-780 µm in the divergent brushes.
The microscleres are euasters: ca. 22 µm in diameter. Compared with Stelligera stuposa these asters have fewer rays which are more robust and conical in shape.
Skeleton: Plumose. An axial skeleton of longitudinally orientated megascleres forms a stiff core along the centre of each branch. There is a softer, extra-axial skeleton of often single, long megascleres which radiate out at right angles from the core and project through the surface. Slender megascleres scattered in the choanosomal skeleton also form divergent brushes around the projecting spicules at the surface. The microscleres (euasters) form a layer at the surface. There is a minimal amount of spongin.
Ecology: Usually in somewhat sheltered locations with some current, 10-20 m. Found in Strangford Lough on sides of boulders with a 2 knot current.
Distribution: British lsles, Channel coast of France. A fairly common species.
Etymology: Rigida (Latin)= stiff, referring to the stiffness of the branches.
Type specimen information: Type specimen probably lost. MCS Voucher BELUM Mc975, Carlingford Lough, N Ireland.
Remarks
More robust but smaller than Stelligera stuposa , with larger spicule categories. Some authorities consider these species to be synonymous. Descatoire (1969b: 18) considers S . stuposa and S . rigida two forms of the same species. The form may be similar to that of Axinella damicornis but the colour, robust bristles and slimness are characteristic.
Source: Ackers et al., 1992 (B.E. Picton, S.M. Stone, D. Moss).