Sponges in this class are typified by skeletal spicules composed of calcium carbonate. The spicules often protrude through the epipinecodermal covering of the body wall, giving the organism a rough texture. Calcareous sponges are small, usually only a few inches high, and are generally dull in appearance, although several species are brightly colored. Members of this class are among the simplest sponges, and all three morphological types—asconoid, syconoid, and leuconoid—are represented. There are approximately 150 known species, exclusively marine and shallow-water dwellers.