Biemna variantia (Bowerbank, 1858)


Family : Desmacellidae

Form: Encrusting, becoming a thick cushion (e.g. 1-1.5cm thick by 7cm diameter; thickest at the centre and tapering to the edge). "It can grow into cuplike or lamellate forms when mature" (?).

Colour: Beige, occasionally yellow.

Smell: None.

Consistency: Very soft and friable.

Surface: Uneven with conulose projections, due to the ends of spicule fibres supporting the surface, rather like Dysidea. Larger specimens may have a distinctly 'lumpy' or shaggy appearance due to development of surface projections.

Apertures: Several oscules, scattered across the upper surface of the sponge, seen as dark holes in surface. Inhalent pore areas are obvious between conulose projections when seen alive.

Contraction: Slight.

Internal characters

Skeleton: Plumose. Stout multispicular fibres (of styles), branching and anastomosing, ascend through the sponge and support the surface. Tissue is packed with abundant microscleres. Minimal amounts of spongin are present.

Spicules: Megascleres are styles (a) 360-(580)-700m abruptly bent near the rounded end. Microscleres are sigmata (b) of two size categories, ca. 50-70m and ca. 10-20m; raphides (c), ca.165m, gathered loosely into trichodragmata, and commata, 63m, which are like small, straight, fusiform oxea. These microscleres are very numerous and are easily lost from the sponge and so may contaminate samples of other species if put together into the same container.

Habitat: On vertical surfaces with moderately strong water movement. At Hake Island, Sherkin Island, on underside of boulders; "on mud, gravel, stones". Tolerant of brackish conditions in Daucleddau estuary, Milford Haven.

Distribution: "Arctic-boreal south to ca. 40N. Mostly recorded from deep water, although type locality (Tenby) was intertidal." Known recently from Strangford Lough; Lough Hyne; Sherkin Island; Blaskets; Skomer; Milford Haven; Guernsey.

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

Identity: The appearance is quite characteristic but a check of the spicules is necessary for confirmation.

Voucher: BELUM : Mc319. 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