(Bowerbank, 1858)
Species Overview
Biemna variantia (Bowerbank, 1858) is a thickly to massively encrusting beige sponge with a rough, uneven surface and soft, friable consistency. Several flush oscules may be seen scattered across the surface. It is widespread in the British Isles, along the NW coast of France, and to the north, especially in deeper habitats, although it may occasionally occur intertidally under boulders.
Taxonomic Description
Colour: Beige, occasionally yellow.
Shape, size, surface and consistency: Encrusting, becoming a thick cushion (e.g. 1-1.5 cm thick by 7 cm diameter; thickest at the centre and tapering to the edge). It can grow into cup-like or lamellate forms when mature. Surface uneven (Biemna variantia MCS2) 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 (Desmacidon peachii Bwbk) due to development of surface projections. Several oscules, scattered across the upper surface of the sponge, seen as dark holes in surface. Inhalant pore areas are obvious between conulose projections when seen alive. Consistency very soft and friable. Smell none.
Spicules:(# Biemna variantia spics) (Hymeniacidon variantia spics) Megascleres are styles: 360-(580)-700 µm, abruptly bent near the rounded end.
Microscleres are sigmas of two size categories: ca. 50-70 µm and ca. 10-20 µm; microxeas and raphides, grading into each other: ca. 63-165 µm, gathered loosely into trichodragmata; commas: 10-20 µm, which are like small, halved sigmas. 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.
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.
Ecology: On vertical surfaces with moderately strong water movement. At Hake Island, Sherkin Island, SW Ireland, on underside of boulders; on mud, gravel, stones. Tolerant of brackish conditions in Daucleddau estuary, Milford Haven, W Scotland.
Distribution: Arctic-boreal, south to ca. 40°N. Mostly recorded from deep water (down to 1608 m), although type locality (Tenby) was intertidal. Recorded recently from Strangford Lough, Lough Hyne, Sherkin Island, Blaskets (Ireland), Skomer(Wales), Milford Haven (Scotland), Guernsey. If synonymy is correct then it occurs also off the coast of East Greenland, down to 250 m.
Etymology: The name refers to the varied spicule complement.
Type material: The type is in the Natural History Museum, London. MCS voucher BELUM: Mc319, Strangford Lough, N Ireland.
Remarks
The appearance is quite characteristic but a check of the spicules is necessary for confirmation. In the present concept of the species inclusion of high arctic specimens which tend to have styles up to 1500 µm long is tentatively accepted (various "species" of Lundbeck, 1902 are thus considered synonyms). This species has had a chequered taxonomic history and a revision may decide that its name has been too severely compromised and has to be changed.
Source: Ackers et al., 1992 (Editors B.E. Picton, D. Moss, S.M. Stone).