Description: This is a massive, encrusting sponge which is inconspicuous due to the fact that it is often covered by other sponges, Parazoanthus anguicomus anemones, etc. If the Stryphnus tissue is visible it may consist of a pale grey porous surface or a dark grey patch. Cutting into the sponge reveals a thin harder exterior and a pale interior.

Habitat: Vertical walls, overhangs and caves, usually out of the light. Likes some strong water movement, surge or tidal streams.

Distribution: Found all round the British Isles.

Similar Species: Stelletta grubii can look very like this species in situ, the best distinguishing feature seems to be the thickness of the surface spicule rich layer.

Key Identification Features:

• Massive sponge with rough surface

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

iNaturalist: Stryphnus ponderosus at iNaturalist World Species Observations database.

WoRMS: Stryphnus ponderosus at World Register of Marine Species. Accepted name: Stryphnus ponderosus (Bowerbank, 1866). AphiaID: 133991.

Classification: Biota; Animalia; Porifera; Demospongiae; Heteroscleromorpha; Tetractinellida; Astrophorina; Ancorinidae; Stryphnus