Calcarea is a class of the animal phylum Porifera, consisting of calcareous sponges, characterized by 2-4 spicules made of calcium carbonate in the form of calcite or aragonite. There are about 400 species of sponges in the Calcarea group, exclusively marine, found throughout the oceans, but mainly in temperate areas.
Calcarea sponges are usually found in shallower, sheltered waters less than 1000 m, and in tropical regions they are associated with coral reefs. Thought to be the most primitive group of sponges, it is the only class with asconoid and syconoid construction, and has sponges with leuconoid construction as well. The Hexactinellida and Demospongiae groups have only leuconoid forms. Calcarea is divided into two groups, Calcinea and Calcaronea, differentiated by the larvae and location of the nuclei in the choanocytes. Calcinea is further divided to two orders and nine families, and Calcaronea has two orders and ten families. Taxonomic resolution is still being revised.