[1] Originally it was believed that this family was restricted to hollow, bladder-like, spherical, club-shaped, tubular, and cushion-shaped growth forms.

[2][3] This family now contains a diverse array of forms, including fistular (hollow), branching, massive and encrusting sponges.

It is usually irregularly pitted in non-fistular forms, but areolated (colour ringed) pore-fields are absent.

In the bladder-like fistular forms, the skeleton making up the choanosome (inner part of the sponge) is absent or reduced to a few wispy bundles.

These, however have low phylogenetic importance and are typically only used at the subgenus level in the larger genera.