Luecosolenia, Courtesy of The University of Glasgow

Calcarea is the only class within Porifera which is made of spicules composed of calcium carbonate, a mineralized substance. Unlike Demosponges, Calcarean spicules lack hollow canals, making calcareans stronger, in general, than demosponges. Calcareans are found predominantly in shallow, tropical water near a shore, but some species can live in marine environments at a depth of 4000 feet

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