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(2001) argued that calcareans were more closely related to Eumetazoa (non-sponge animals) than to other sponges. This would also render Porifera (the sponge phylum) paraphyletic. Some molecular analyses suggest the class Calcarea is not exclusively related to other sponges, and should thus be designated as a phylum. Calcareans reached their greatest diversity during the Cretaceous period. Calcareans are probably descended from ' heteractinid' sponges, which first appeared in the early Cambrian. The oldest putative calcarean genus is Gravestockia, from the ' Atdabanian' (Cambrian Stage 3) of Australia. Some older studies applied the name Calcispongiae to the class, though 'Calcarea' is much more common in modern nomenclature.Ĭalcarean sponges likely first appeared during the Cambrian Period. Of the approximately 15,000 living species of Porifera, only around 400 are calcareans. Some extinct species were hypercalcified, meaning that the spicule-based skeleton is cemented together by solid calcite. The skeleton has either a mesh or honeycomb structure of interlocking spicules. However, a few brightly coloured species are also known.Ĭalcareous sponges vary from radially symmetrical vase-shaped body types to colonies made up of a meshwork of thin tubes, or irregular massive forms. Typically, calcareous sponges are small, measuring less than 10 cm (3.9 in) in height, and drab in colour. Like nearly all other sponges, they are sedentary filter feeders.Īll three sponge body plans ( asconoid, syconoid, and leuconoid) can be found within the class Calcarea. Biology Īll sponges in this class are strictly marine, and, while they are distributed worldwide, most are found in shallow tropical waters. In addition, their spicules develop from the outside-in, mineralizing within a hollow organic sheath. Unlike other sponges, calcareans lack microscleres, tiny spicules which reinforce the flesh. While the spicules in most species are triradiate (with three points in a single plane), some species may possess two- or four-pointed spicules.

They are characterized by spicules made of calcium carbonate, in the form of high- magnesium calcite or aragonite. The calcareous sponges ( class Calcarea) are members of the animal phylum Porifera, the cellular sponges. 'Calcispongiae' from Ernst Haeckel's Kunstformen der Natur, 1904

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