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(Bowerbank, 1858)

Species Overview

Dercitus bucklandi (Bowerbank, 1858) is a thin blackish crust filling up crevices in rocks. Surface is a bit uneven, ridged. It is not rare along the coasts of France and the Bristish Isles, but not often recorded because of its inconspicuous and cryptic habit.

Taxonomic Description

Colour: Black to dark grey-brown externally. Usually a greyish-yellow internally.
Shape, size, surface and consistency: Cushion-shaped to massive-lobose, filling crevices in vertical rock faces. Appearance as of a black membrane stretched across the back of crevices (Dercitus bucklandi larger). Surface smooth but often has ridges looking like stretch-marks. The surface is usually concave. Oscules are flush with the surface, variable in size and usually collected into groups towards the centre of the sponge. Contraction not noticeable. Consistency moderately firm but compressible and spongy when in situ. No smell.
Spicules: (Dercitus bucklandi spics) Megascleres are large calthropses, often with axial canals seen clearly running through the rays, length of rays: 250-300 µm. Microscleres are microspined or microtuberculate microrhabds: ca. 25 µm and smooth toxiform microxeas: 55-80 µm.
Skeleton: Main skeleton confused, of randomly arranged calthropses, with microrhabds and toxas near the surface. There are many pigment cells with black inclusions evident in sections.
Ecology: In crevices in vertical rock faces in clean water. Particularly common on limestone substrata. From ELWS to a few metres subtidally in rock pools and caves.
Distribution: British Isles and France (Roscoff, Iles de Glénan). Distribution poorly known—it has not often been dredged up because of its habitat. Recorded recently from: west coast British Isles; common in the southwest; W. Sussex. Not on east coast of UK?
Etymology: Named after Mrs. Buckland of Guernsey, who collected the type specimen (in fact the species should probably have been named "bucklandae" since the named person is female).
Type specimen information: The type is in the Natural History Museum, London: BMNH 1877.5.21.142 (wet). MCS voucher BELUM Mc458. St John's Pt., Donegal, NW Ireland.

Remarks

The black colour and the habit of bridging crevices makes it unlikely to be confused with anything else. Other black sponges do exist so it is necessary to check spicule categories for a positive identification. Bowerbank's 1874 figure "is a magnificent portrait of a piece of rock from cliffs around Torbay, with small portions of sponge suspected to be present on its edges" (Burton)!
Sources: Topsent, 1896; Hiscock et al., 1983 [1984]; Ackers et al., 1992 (D. Guiterman, S.M. Stone, B.E. Picton, D. Moss).

Dercitus bucklandi