(1) Claudiobranchia is spindle-shaped or disc-shaped. 5-7 pairs of gill holes, each open to the outer cover; The maxilla will not heal with the skull. Males only have flippers located in the ventral fins. ***2 heads.
1. Shark-shaped suborder is spindle-shaped and has lateral gill holes, so it is also called lateral foramen suborder. The fin does not heal with the cephalic side; Dorsal position of dorsal fin; A crooked tail.
(1) Hexagonidae: There are 3 genera and 3 species of Hexagonidae in China. The most common flat-headed Hana shark is distributed in the Yellow Sea and Bohai Sea, with a body length of 4-5 m and a weight of 200 kg-300 ㎏. There are seven gill holes. Benthic life, slow swimming, swallowing small fish and crustaceans. The oil content of viviparous liver is 65% ~ 70%, which can be used to make cod liver oil.
(2) Tiger shark: Blunt nose and mouth, protruding eye ridge and nasal groove; The front teeth are sharp and thin, while the back teeth are flat and grind. 2 dorsal fins, each with a fin thorn in front; There are anal fins.
2. The ray suborder is flat, and its ventral surface is in branchial foramen, also called inferior foramen; The front part of pectoral fin is connected with the head side; Dorsal fin is often located at the top; No anal fin; The caudal fin may or may not exist. There are about 430 species in 20 families of 4 orders in the world, and about 80 species in China.
(1) Sawfish: The kiss is long and narrow, flat, protruding like a sword, with a sharp kiss on the edge. This order only contains sawdust, which is distributed in tropical and subtropical coastal waters, and some species can also live in rivers. Sawfish with sharp teeth are found in the South China Sea and the East China Sea of China, and the fish body can be as long as 9 meters. They are often killed or stabbed by sword-shaped kiss saws.
(2) Ray: The snout is blunt or protruding, and there is no snout on the side edge. This kind of use mainly includes plough-shaped rays, circular fan-shaped rays of circular fan-shaped bodies and rays of rhombic bodies.
(2) Cephalopods have smooth surfaces or occasionally shield-like scales. The gill cavity is covered by a membranous gill cover, and there is a total gill hole at the rear edge. There are two dorsal fins. The first dorsal fin has a strong hard spine in front of it, which can stand or fall freely. In addition to the flippers inside the ventral fins, males also have flippers on the front abdomen and flippers on the front forehead. There are 1 order, 3 families and nearly 30 species in the world. There are five species in China, the most common one is silver striped mackerel, commonly known as sea rabbit. Its snout is conical, its body is silvery gray, its head and back are dark brown, and there are black longitudinal bands below the lateral line, which feed on invertebrates and small fish. Teleost fish include 2 subclasses.
(1) There are internal nostrils in the mouth of this subclass of fish; The lateral fin has a protofin, that is, the lateral fin has a developed fleshy base, the fin is supported by a segmented base fin bone, and the fin is covered with scales and is fleshy or whiplike, so it is also called fleshy fin subclass. There is a spiral valve in the intestine. * * * There are 2 orders. Cephalopods and lungfish.
(2) All fins of Actinidia are supported by dermal radial fins. Withered hard scales, round scales or combs or bare scales. No internal nostrils. There are many kinds, accounting for more than 90% of the total number of live fish, with 9 orders and 36 orders. Hard Scale Order, Herring Order, Eel Order, Cypriniformes Order, Silverfish Order, Salmonella Order, Perciformes Order, Bufo Order.