Form: Thin sheets covering extensive areas, typically 3mm thick by up to 30cm diameter. In the literature it has been reported as a cushion, but this may be the result of the sponge growing over a saddle oyster (BEP). Typically looks like a patch of red paint.
Colour: Bright red, scarlet or blood red. The blood-red sublittoral form is described here, and may be a distinct species from the scarlet one which seems to occur both in the littoral and sublittoral.
Consistency: Difficult to determine because of thinness of sheet but fairly soft; difficult to scrape off - it crumbles and tears.
Surface: With little structure - conforms closely to the underlying substrate. Excurrent channels are clearly visible as dark branching lines converging on the oscules. Slightly velvety appearance; minutely porous. "Tuberculate, hispid; often creviced" according to LÚvi (1960).
Apertures: Oscules have slightly raised transparent rims, apparent mainly because of converging excurrent channels. These oscules are "numerous and regularly spaced over the surface".
Contraction: Difficult to determine.
Skeleton: In the littoral form (juvenile) the skeleton is usually 'Hymedesmoid', with both the principal spicules of the main skeleton (usually styles) and also the auxiliary spicules (acanthostyles) standing up from a basal sheet of spongin, the bases of the spicules being implanted in the spongin and the points directed towards the surface. Slender accessory spicules (subtylostyles) are scattered throughout. In thicker sublittoral specimens (adult form) the skeleton becomes 'plumose'. The main skeleton then consists of plumose columns of spicules incorporating spongin 'raised' from the basal layer of the juvenile form. These are in turn echinated by smaller spicules (acanthostyles). Slender ectosomal spicules are present.
Spicules: Principal spicules of the main skeleton are subtylostyles (a) (rarely sparingly spined at the base) which measure 220-(250)-280Ám long x 10Ám thick and 110-(130)-145Ám; (note however that LÚvi (1960) gives a size range of 110-375Ám. Auxiliary megascleres are entirely-spined acanthostyles (b), 80-(90)-135Ám. Slender accessory subtylostyles (c) measure 225-(260)-355Ám and have microspined heads. The microscleres comprise palmate isochelae (d) 8.5-12Ám, and smooth tipped toxa (e), which may be numerous, 100-125Ám and 18-40Ám.
Habitat: Vertical surfaces of rock or wrecks. Boulders in brackish conditions. Encrusting pebbles in areas of strong current (Menai Straits) in the Littoral zone.
Distribution: "Atlantic coasts of Europe (from Shetlands southwards), Mediterranean etc." Known recently from Strangford Lough; Rathlin Island; Menai Straits; Daucleddau, Milford Haven. Littoral or shallow sublittoral.
Distribution Map from NBN: Grid map (fast) : Interactive map (slower, requires login to view records) : National Biodiversity Network mapping facility, data for UK.
Identity: Microciona species and other Clathriids often form thin reddish sheets. The dendritic branching of the excurrent channels of this species may be characteristic but the spicules should always be checked for a positive identification. Superficially it may be confused with Ophlitaspongia seriata (q.v.), but note the regular arrangement of oscules in the latter species which is not so apparent in M. atrasanguinea.
Voucher: BELUM : Mc821. Strangford Lough, Down.
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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