Description: Thin sheets, cushions, to massive-flanged, rarely branching-erect. More than one form can be detected in the intertidal and shallow sub-littoral. It is possible that these may eventually be recognized as including more than one distinct species.

(a) Thin sheets, fully exposed on lower shore up to mid-tide level. Gains some shelter by growing along crevices and fault-lines and lying at the base of right-angled rock. Protective cover (e.g. algal canopy) is usually non-existent, with adjacent surfaces clean and dry. The only protection the animal seems to have is derived from (?) symbiotic algae living in the surface layers, causing a discolouration of the surface to a dull greenish-orange (deeper layers of body are a typical bright orange). Surface is even, smooth to minutely tuberculate.

(b) Cushions, half-exposed at LW and in the sublittoral fringe, favouring angles in rock and Laminaria holdfasts. Conditions generally muddy with a layer of fine muddy silt smothering the animal. When brushed aside, the colour is seen to be a clear pinky-orange. Surface even but distinctly tuberculate.

(c) Massive-flanged forms sometimes seen on the lower shore and in sublittoral fringe where conditions are distinctly muddy (e.g. estuaries and harbours) with fast-flowing currents. The animal can be overlooked as it is buried in the mud with only the tips of the flanges or oscular chimneys showing. Underneath, the colour is seen to be a deep dirty orange to brick red. Surface uneven, wrinkled, irregularly folded, with well-developed tubercles.

(d) In the sublittoral, cushions are generally found which can form large, spreading pinky-orange patches on hard substrates (e.g. rock) in semi-fast current areas (?). "Yellow to orange to blood-red." Shore forms tend towards blood-red, whilst sublittoral forms tend to be pinkish-red? Note the colour changes on preservation - the sponge goes patchily dark brown-black in alcohol. The degree of blackening depends (?) on t "Firm, compact, compressible." "Oscules scattered, level with surface or at top of branching processes." Not conspicuous.

Distribution: "Arctic; British Isles; Belgium; France; Spain; Mediterranean etc." Recently known from Tiree; Loch Sween; Menai Straits; Strangford Lough; Lough Hyne, Saltee Sound, Co. Wexford; Sussex; Solent; Lundy; Dyfed; Dorset; Jersey. A common species on shore and in the sublittoral. Not found on the East coast of Britain?

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

iNaturalist: Hymeniacidon perlevis at iNaturalist World Species Observations database.

WoRMS: Hymeniacidon perlevis at World Register of Marine Species.