This class consists of marine calcareous sponges with a skeleton composed of massive calcite or separate calcareous spicules, not divisible into megascleres (larger) and microscleres (smaller). They have an asconoid, syconoid or leuconoid construction. Many are dull coloured -- and some are, admittedly, just plain dull. However, brilliant red, yellow, and lavender species are also known. In size they are generally smaller than representatives of other classes, most are less than 10 cm in height. They have a world-wide distribution, mostly restricted to shallow coastal waters. Possible Calcarea are known as early as the Tommotian. Wood (1998).
classification according to Valid PMPD Orders (marine only)
classification according to Synopsis of the described taxa of the world
Permosphincta may be Demospongiae? (see Palaeontographica Canadiana No. 16 "Silurian Wenlock demosponges from the Avalanche Lake area of the Mackenzie Mountains southwestern District of Mackenzie Northwest Territories Canada."
In this large group the spicules form a closely packed mesh of different sized "tuning forks", giving a rigid skeleton. During the Jurassic these sponges formed large reefs
(includes the genera Stellispongia, Myrmecium, Elasmostoma, Corynella, Raphidonema, Peronidella, Porosphaera, Petrostoma, etc)
(includes the genus Barroisia.)
Calcarea - Curt Smecher's summary
Parker, Sybil P. (ed.), 1982: Synopsis and Classification of Living Organisms. New York: McGraw-Hill Book Co., 2 vols.
Invertebrate Zoology by Edward E. Ruppert, Robert D. Barnes
University of California Museum of Paleontology -- Calcarea