Sharks are Chondrichthyes, elasmobranch fish, usually living in the sea, a few can enter fresh water. These fish swim fast, bones are all cartilage, but often calcified, but there is no real bone, and teeth can be regenerated and replaced. It has more than 130 species and is divided into 8 orders, namely Hexanchiformes, Lamnidales, Heterodontiformes, Carcharhiniformes, Squalidales, Squalidales, Carcharhiniformes and Cyprinodontiformes.
Chondrichthyes holocephala ray superorder is divided into four categories, namely, sawfish, ray, skates, electric rays, which ray and skates are collectively referred to as rays, this kind of fish's body is flat, the whole is rhombic, pectoral fins are very large, like a pair of wings, when swimming in the sea is like flying. And it has prominent eyes and two slits in its head, where seawater enters and exits through the gill slits, so that it can complete its breathing.
Chimaeras are synthetic fish of the class Chondrichthyes, order Chimaerae, also known as hairtail sharks or sea rabbits. Its body is very long, spindle-shaped, tail is very small, but the head is relatively large. Interestingly, although it is a cartilaginous fish, it also has some characteristics of bony fish, such as a pair of gill openings, an operculum, and a separate anus and mouth.
Sawfish is a Chondrichthyes holocephalous sawfish order fish, its body length up to 9 meters, the upper lip lengthened, left and right sides have snout teeth, like a saw. As a warm-water demersal fish, it has a fierce temperament, usually using a snout saw to find shellfish and mollusks on the bottom, or rushing into schools of fish to attack prey and then eat them.
