Calcarea (Calcispongea; phylum Porifera) A class of marine sponges that have a skeleton of calcareous spicules. Forms displaying leucon structure are common, and sycon and ascon forms also occur. Individuals vary in shape from tube colonies to massive forms. They first appeared in the Cambrian.

Calcarea (Calcispongea; phylum Porifera) A class of sponge, ranging from Cambrian to Recent, in which the skeleton is made entirely of calcareous spicules which are commonly of a tuning-fork shape. The sponges are sometimes associated with reefs in the Jurassic, or they may form widespread sponge beds.