The pectoral fin is developed and connected with the head side into a disc shape, and sometimes there is a generator between the head side and the pectoral fin; The ventral fins sometimes differentiate into toe-like structures. The endoskeleton consists entirely of cartilage. Habitat at the bottom of the sea, eat small fish, shrimp and shellfish. The body is flat, the dorsal fin and caudal fin are degenerated, and the tail is elongated or whiplike. The pectoral fin is developed, connected with the head side, forming a rhombic body disk with the body and ventral fin, and the lateral ventral fin has toe differentiation. Five pairs of branchial fissures are located on the ventral surface, and the mouth is open on the ventral surface of the head, showing a transverse fissure shape. The teeth are numerous and firm, and they are flat and flat, like a stone shop. There are often rows of thorns on the tail and back. Some species have a pair of round or long generators between the pectoral fin or the cephalad or caudal side. Rays are near-bottom fish, often lying on the bottom of the sea or buried in sand and mud. Sometimes they crawl on the bottom of the sea or swim by the sea. Swimming mainly depends on the pectoral fin fluctuating back and forth, moving slowly, lurking during the day and foraging at night. They mainly feed on small crustaceans, polychaetes, mollusks, small fish and cephalopods. Laying eggs, the eggs are covered with a layer of horny shells with four corners, which can be attached to attachments through the protrusions of the four corners for development. Usually spawn in batches every few days, with 2 eggs each time. Generally inhabit coastal sandy bottom water, and fish are often half buried in sand. Latent during the day and active at night, so night fishing in coastal areas is better. During the day, it can be caught at the edge of rocks and the bottom of sandy soil, occasionally.