Description: Cushions to massive-lobose, with a tendency to throw out occasional, or many, fistulae and tassel-like extensions. These vary in length from short (usually fistulae), which give a warty appearance, to long (tassels), up to 4cm. The latter can anastomose with other tassels. The growth of the fistulae can be either vertical or lateral, and they are easily broken on collection. Narrow fistulae end 'blind', whereas wider ones possess terminal oscules. These may be borne on fistulae of any length (up to about 2cm), or can be flush with the surface of the main body, or possess rims. Oscules tend to be sparse. Specimens tend to remain compact, with a typical diameter of about 7cm, and height 2.5cm. The ectosome is translucent white; the interior tissue is brownish- orange or greyish-orange. The two in combination can cause specimens to appear to be off-white, greyish, or pinkish. The fistulae normally consist solely of ectosomal tissue, and so are t The ectosomal surface is brittle, crisp and quite hard, requiring high pressure before it 'gives'. The subdermal tissue is friable. As a whole the sponge is moderately to very firm. See under 'Form' for a description of the oscules. They are of varying diameter, up to about 0.75cm, and remain open on collection and preservation. They may be sparse, or even apparently absent in some specimens.

Distribution: Known recently from Strangford Lough, Down; Arranmore Island, Mulroy Bay, Donegal; Newquay, Galway; W. coast of Scotland; Ravens Pt., Anglesey; Lundy; Scilly Isles; E. Channel (Pullar Bank, Outer Mulberry, Shelly Rocks, Sussex).

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

iNaturalist: Haliclona fistulosa at iNaturalist World Species Observations database.

WoRMS: Haliclona fistulosa at World Register of Marine Species.