Genus with filamentous spongin threads filling the choanosome,
which make the sponges extremely tough and difficult to tear; reticulated
sand pattern on surface.
Typical form (f. felix) of species crustose, with raised oscula, or massive, with 1-2mm conules on surface. Forma fistularis with simple erect holoow branches and terminal oscula; f. acuta conical or massive, with elevated oscula, with large (2-4 mm) conuli. All forms grayish to chestnut-brown, up to 25 cm. With a very distinctive odour when exposed to the air.
On protected sediment and rock bottoms (f.
felixf. fistularis) and on the reefs (f. felixf. acuta)
0.5 to 5 meters; very common.