"Sharks, Skates And Rays"

The elasmobranchs, the skates and rays, together with the chimaeras make up the cartilaginous fish (they have no calcified bones). Also, unlike the bony fish, elasmobrachs have no swim bladders. Again, unlike bony fish with one gill cleft, these fish have five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth lie in several series. The upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The eyes have a tapetum lucidum. The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm. These fish are widely distributed in tropical and temperate marine waters, a few occur in freshwaters. There are about 1000 species.