Vacelet, Jean Centre d'Océanologie de Marseille, Aix-Marseille Université, Marseille, France.
Hartman, Willard D. Peabody Museum of Natural History, Yale University, New Haven, Connecticut.
Finks, Robert M. Department of Geology, Union College, Schenectedy, New York.
Last reviewed:June 2019
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A class of the phylum Porifera, including exclusively marine sponges with a skeleton composed of spicules of calcium carbonate to which can be added a solid basal calcitic skeleton. The sponges that constitute the phylum Porifera are assigned to four classes—Calcarea, Hexactinellida, Demospongiae, and Homoscleromorpha. Members of the class Calcarea are commonly called calcareous sponges (Fig. 1). They vary from radially symmetrical vase-shaped species, to aggregates made up of a reticulum of thin tubes, to irregular massive forms. Calcareous sponges are mostly small and inhabit the shallow waters of all seas, from tidal areas to depths of 200 m (656 ft), with a few species extending down to at least 4000 m (13,120 ft). See also: Calcite; Demospongiae; Hexactinellida; Porifera; Skeletal system
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