Form: Cushion to massive-lobose, filling crevices in vertical rock faces. Appearance as of a black membrane stretched across the back of crevices.

Colour: Black to dark grey-brown externally. Usually a greyish-yellow internally.

Smell: None.

Consistency: Moderately firm but compressible and spongy when in situ.

Surface: Smooth but often has ridges looking like stretch-marks. The surface is usually concave.

Apertures:

• Oscules are flush with the surface, variable in size and usually collected into groups towards the centre of the sponge.

Contraction:

• Not noticeable.

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Internal characters

Skeleton: Main skeleton confused, of randomly arranged calthrops, with microxea and toxa near the surface. There are many pigment cells with black inclusions evident in sections.

Spicules: Megascleres are large calthrops (a) with rays 250-300 μm, often with axial canals seen clearly running through the rays. Microscleres are microspined or microtuberculate microxea (b) ca. 25 μm and toxa (c) 55-80 μm.

Identity: 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)!

Distribution Map from NBN: Dercitus bucklandi at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Dercitus bucklandi at iNaturalist World Species Observations database.

WoRMS: Dercitus bucklandi at World Register of Marine Species. Accepted name: Dercitus (Dercitus) bucklandi (Bowerbank, 1858). AphiaID: 555677.

Classification: Biota; Animalia; Porifera; Demospongiae; Heteroscleromorpha; Tetractinellida; Astrophorina; Ancorinidae; Dercitus

Voucher: BELUM : Mc458. St John's Pt, Donegal.

Editors: D. Guiterman, D. Moss, B.E. Picton.