Schmidt, 1862
Species Overview
Stelletta grubii Schmidt, 1862 is an inconspicous whitish mass overgrown with epibionts (other sponges, hydroids, etc.). The sponge surface is rough and the consistency is firm and incompressible. A southern species (Mediterranean) which occurs fairly rarely along the coasts of France and the British Isles.
Taxonomic Description
Colour: Pale grey, off-white or "cream tinged with grey or brown" when clean, but usually discoloured by silt. The interior is somewhat creamier in colour.
Shape, size, surface and consistency: (Stelletta grubii 2) Massive lobose, rounded or irregular in outline, to 30 cms across. Often heavily overgrown with other sponges (including Antho , Haliclona spp, Clathrina coriacea ), tunicates like Dendrodoa , miscellaneous hydroids and bryozoans, and consequently not obvious to the eye when seen in situ. Surface even or conulose, hispid. Rough to the touch, like sandpaper, because of penetrating heads of large oxeas and triaenes (visible at 40x with stereomicroscope). Oscules not obvious, small when seen. Consistency very firm, but somewhat compressible. Contraction not noticeable. It has a characteristic slightly sharp smell.
Spicules: (S. grubii spics V) Megasleres are oxeas: 1000-2000 µm, and long-shafted orthotriaenes of a similar but somewhat smaller size.
Microscleres are euasters of three types: tylasters to strongylasters with microspined rays: 6-12 µm diameter in the cortex, and oxyasters of two types, one with multispined tips: 12 µm, and the other with few rays: 40 µm diameter, both in the choanosome. The large oxyasters may be reduced to one or two rays, so that they look like short tylostyles or centrotylote oxeas.
Skeleton: (S. grubii skeleton) Radiate, with a well developed cortex, and densely packed, radially arranged tracts of oxeas and triaenes. Microscleres are scattered in the choanosome and form a layer in the cortex. This hard 'rind', which is up to 2 or 3 mm thick, almost peels away from the interior. The choanosome has a slightly softer texture and consists mainly of oxeas with relatively fewer triaenes.
Ecology: Usually found on dark vertical or overhung rock faces, caves, etc., maybe in presence of some silt. Seems to avoid the light. Littoral to 135 m on rocks. Maybe locally common in shallow water (below 2m), where moderately exposed to, or sheltered from, wave action.
Distribution: England (Anglesey), Ireland (Mulroy Bay, N. Donegal, Rathlin Island, Northern Ireland), France, Spain; Mediterranean.
Etymology: Named after Grubi.
Type specimen information: Two specimens are extant (cf. Desqeyroux-Faúndez and Stone, 1992), both originally in the Graz Museum (LMJG 15702, and LMJG 15272), now in the Geneva Museum, from Quarnero, Adriatic. One slide in BMNH 1867.3.11.20 (Schmidt slide). MCS voucher: BELUM Mc94, Mulroy, NW Ireland.
Remarks
Overgrown appearance and division into rind and creamier interior gives an initial tentative identification, but microscopic examination is necessary to be certain. There is a possibility of confusion with other species of Stelletta and with Stryphnus ponderosus (Bowerbank, 1866: 56), which may only be resolved by careful comparison of spicules. Stryphnus has short-shafted triaenes (i.e. dichotriaenes or orthotriaenes), and does not possess such a well developed rind. Stelletta dorsigera Schmidt (1864) is similar in spiculation but has only a single category of oxyasters (and has a characteristic surface). Stelletta lactea Carter (1871: 9) has long-shafted dichotriaenes in addition to the orthotriaenes of S . grubii , and there are bundles of raphides in the body of the sponge.
Source: Ackers et al., 1985, 1992 (D. Moss, S.M. Stone, B. Picton).