Chondrichthyes, or cartilaginous fishes, are jawed fish with paired fins, paired nares, scales, a two-chambered heart, and skeletons made of cartilage rather than bone. The class is divided into two subclasses: Elasmobranchii (sharks, rays and skates) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class). The skeleton is cartilaginous. Chondrichthyes have toothlike scales called denticles or placoid scales. Denticles provide two functions, protection, and in most cases streamlining. Mucous glands exist in some species as well. All Chondrichthyes breathe through 5-7 gills, depending on the species. Fertilization is internal. Development is usually live birth (ovoviviparous species) but can be through eggs (oviparous). There is no parental care after birth; however, some Chondrichthyes do guard their eggs. Examples : - all sharks - ray - sawfish - skate - chimaera - rabbit-fish