Form: Massive-lobose, rounded or irregular in outline, to 30 cms or more across. Many specimens develop a circular depression in the upper surface. Often heavily overgrown with other sponges (including Antho involvens, Haliclona spp., Clathrina coriacea), Dendrodoa, miscellaneous hydroids and bryozoans, and consequently not obvious to the eye when seen in situ.
Colour: Pale grey, off white or cream tinged with red-brown at edges when clean, but usually discoloured by silt. In section living material has a pale grey-white rind and the interior is strikingly different in colour, ochre or cream-coloured.
Smell: A characteristic slightly sharp smell.
Consistency: Very firm but somewhat compressible.
Surface: Even or conulose, hispid. Rough to the touch, like sandpaper, because of penetrating heads of large oxea and trianes (visible at 40x with stereo microscope).
Apertures: Oscules not obvious, "small when seen".
Contraction: Not noticeable.
Skeleton: Choristid, with a well developed cortex, and densely packed, radially arranged tracts of oxea and trianes. Microscleres are scattered in the choanosome and form a layer in the cortex. This hard 'rind', which is up to 2 or 3mm thick, almost peels away from the interior. The choanosome has a slightly softer texture and consists mainly of oxea with relatively fewer triaenes.
Spicules: Megascleres are oxea (a), average length 1000-(1035)-1500Ám "average (2000Ám)", and long shafted orthotriaenes (b) 875-(975)-1175Ám. Microscleres are euasters of three types: tylasters to strongylasters (c) with microspined rays (6-(10)-12Ám diameter) in the cortex, and oxyasters of two types, 12Ám with multi-spined tips (d) and 40Ám with few rays (e) in the choanosome. The large oxyasters may be reduced to one or two rays, so that they look like short tylostyles or centrotylote oxea.
Habitat: Usually found on dark vertical or overhung rock faces, caves, etc., usually in the presence of some silt. Seems to avoid the light. "Littoral to 135m on rock". May be locally common in shallow water (below CD - 2m), where moderately exposed to, or sheltered from, wave action.
Distribution: In UK known recently from Raven's Point, Anglesey; Mulroy Bay & St John's Point, Co. Donegal; Rathlin Is, Co. Antrim. Arndt says "Shetlands (?); Atlantic coast of Great Britain; France; Spain: Mediterranean".
Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.
Identity: 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 especially with Stryphnus ponderosus, (Bowerbank, 1866), (q.v.) which may only be resolved by careful comparison of spicules. Stryphnus has short-shafted triaenes (i.e. dichotriaenes, sometimes modified to orthotriaenes), and does not possess such a well developed rind. This is a good field character, if a small piece of the sponge is cut off. Stelletta lactea Carter, 1871:9 has long-shafted dichotriaenes in addition to the orthotriaenes of Stelletta grubii, and there are bundles of raphides in the body of that sponge.
Voucher: BELUM : Mc94. Mulroy Bay, Co Donegal.
Editors: D. Moss, B.E. Picton.
|Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland |
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