However, the major works in this area published by Leonard Compagno , supplemented by a phylogenetic study by Shigeru Shirai , form the basis of the classification, and consequent identification, scheme employed herein. True jaws with teeth are present and well developed. Males have paired claspers behind the pelvic fins. Fertilization is internal. Subclass Holocephalii - chimeras and ratfishes, characterized by having a single pair of gill openings.
Males have an additional single clasper on the dorsal surface of head.
Body covered in placoid scales. Orders Chlamydoselachiformes, Hexanchiformes, Echinorhiniformes, Dalatiiformes, Centrophoriformes, Pristiophoriformes, Rajiformes, Squaliformes, and Squatiniformes. Superorder Galea - sharks that possess five pairs of gill slits, two dorsal fins, and a single anal fin. Orders - Carcharhiniformes, Heterodontiformes, Lamniformes, and Orectolobiformes Classification is a dynamic field, and the present use of one system does not negate the validity of another. It must be remembered that this guide is a key , not a classification.