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. 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.