Chondrichthyes
Chondrichthyes or cartilaginous fishes are the sharks and their relatives. They have jaws and paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone. They are divided into two subclasses: Elasmobranchii (sharks, rays and skates) and Holocephali (chimaera, sometimes called ghost sharks).