EVERYDAY SCIENCE

Detailed explanation-1: -The calcareous sponges of class Calcarea are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made of calcium carbonate in the form of calcite or aragonite. While the spicules in most species have three points, in some species they have either two or four points.

Detailed explanation-2: -Class Calcarea contains sponges with calcium carbonate spicules of three or four rays.

Detailed explanation-3: -Calcarea is the only extant class that produce calcium carbonate spicules whereas the other three have silicium spicules. Demospongiae is the most speciose class, representing almost 85% of the phylum.

Detailed explanation-4: -calcareous sponge, any of a class (Calcarea) of sponges characterized by skeletons composed entirely of calcium carbonate spicules (needlelike structures). Calcareous sponges occur mainly on the rocky bottoms of the continental shelves in temperate, shallow waters; they are usually dull in colour.