Family Acarnidae Dendy, 1922

Abstract

Acarnidae Dendy (Demospongiae, Poecilosclerida, Microcionina) contains 37 nominal genera of which 13 are considered here to be valid, and probably several hundreds of species. Acarnids are distributed worldwide, although several genera are predominant in colder temperate waters, and several have very restricted (apparently endemic) geographic ranges. Major morphological characters diagnostic for the family include massive, burrowing, excavating or encrusting growth forms with fistules, as well as non-fistulose genera with digi- tate, flabellate, massive or encrusting growth forms; ectosomal skeleton with tangentially arranged tylotes with spined bases; choanoso- mal skeleton reticulate (in massive) or plumose (in encrusting growth forms), with or without echinating spicules; megascleres include styles; and microscleres are palmate isochelae and toxas, sometimes lost or sometimes with other microscleres such as bipocillae, modi- fied anisochelae, microrhabds and raphides.