Acarnidae
Acarnidae is a family of sponges belonging to the order Poecilosclerida. It has a global distribution, although several genera occur primarily in colder temperate waters, and several have very restricted ranges. It is estimated that there are several hundred species.
Description
Species form encrusting, massive, fan-shaped or digitate growth forms that may burrow into the substrate. The species of many genera produce fistules.The outer skeleton is made of tylotes which may be modified to have a spined base as well as strongyles. These form tangential and/or paratangential tracts, often with an irregular or halichondroid arrangement.
The inner skeleton is made of styles or modified styles. These form massive networks to create isodictyal, isotropic, anisotropic or more irregular skeletons. In encrusting forms they form plumose or hymedesmioid skeletons instead.
Spined spicules may be present or absent. When present, they take the form of acanthostyles and/or unique cladotylotes. Spined microscleres include palmate isochelaes and various toxas. Both may, however, be lost in some species. Some genera also have other microscleres such as modified anisochelae such as the bipocillae, microrhabd-like spicules and diamond-shaped microxeas.