The calcareous sponges of class Calcarea are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made out of calcium carbonate.
|"Calcispongiae" from Ernst Haeckel's Kunstformen der Natur, 1904|
Typically, the Calcarea are very small, measuring about 7-10 cm (3-4 inches) in height. Of the 15,000 or so species of Porifera that exist, only 400 of those are Calcareans.
|Wikispecies has information on: Calcarea.|