Description: Variable, depending on microhabitat, but typically from spreading cushions with mamillate oscular chimneys, to massive lobose forms with tall, rugose, volcano-like oscular chimneys. These oscular chimneys tend to be arranged in irregular rows in cushion forms. The rows can become ill-defined ridges, caused by the oscular chimneys anastomosing for up to 3/4 of their height. In large forms the oscular projections can be mammiform, or chimneys, which become bulbous for the first 2/3 of their height, narrowing more sharply in the upper 1/3. The oscular rows may appear as tassels, or as repent branches (see van Soest, 1980, p.9). More information is required on growth forms, and their relationships with habitat types. Specimens may be large, with a spread of up to 30cm, and height to 5cm. Typically purple, but can verge to pink or brown in some specimens. The colour is normally deeper on the higher portions of the sponge (i.e. oscular chimneys), becoming a washed-out fawn/grey away from the extremities. The depth of colour probably reduces Firm, compressible, friable. The oscules are formed on chimneys, as described under 'Form'. The openings are large, up to 1cm in diameter, and remain open after collection and preservation. Inhalant pores show through the surface, and are closely packed and conspicuous.

Habitat: This sponge is typically found from the upper circalittoral downwards, but less well developed specimens occur in shallower water and on the shore. It mainly occurs on vertical rock faces, in silt free areas of considerable water movement, e.g. gullies and/or areas exposed to wave action and tidal currents.

Distribution: Recently known from W. coast of Ireland; Northern Ireland (Antrim; Strangford Lough); W. coast of Scotland (Mull; Coll; Tiree; Oban; Lewis); S.W. Britain (Salcombe, Devon, Eddystone, Hard Deeps; Scilly Isles; Lundy).

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

iNaturalist: Haliclona viscosa at iNaturalist World Species Observations database.