Calcareous sponge

Class of marine sponges of the phylum Porifera which have spicules of calcium carbonate

The calcareous sponges or calcereans are sponges that make up the class Calcarea, characterized by spicules made of calcium carbonate in the form of high-magnesium calcite or aragonite. While the spicules in most species are triradiate (with three points in a single plane), some species may possess two- or four-pointed spicules. Unlike the far more common siliceous sponges, calcareans lack microscleres, tiny spicules which reinforce the flesh.

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