Chrondricthyes includes almost 1050 (mostly-marine) existing species of cartilaginous fishes which can be divided between two monophyletic subclasses. The first subclass, Elasmobranchii, includes various skates, rays, and sharks while the second subclass, Holocephali, includes chimaeras. Chrondricthyes commonly have skeletons made of calcified cartilage instead of bone, coverings of placoid scales, and calcified/true teeth.