What is a flat fish that looks like a thin tail behind a fan?

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1, Introduction:

Rays, belonging to the order Rays and Rays of Chondrichthyes, are the general name of many kinds of flat cartilage fishes. Distributed in most waters of the world, including 2 suborders, ***8 families, about 49 genera, 3 15 species. There are 28 species in China, belonging to 6 families and 8 genera. Different regions in China have different common names. Zhoushan fishermen call stingrays yellow tigers, manta rays swallow flowers, black tiger fish and two-headed flowers, Herzog ray catfish, and Jiaodong fishermen call them Laozi fish and Laoban fish. Rays vary in size, ranging from 50 cm long to 8 m long. Rays are harmless and live on the bottom of the sea, usually partially buried in underwater sand.

2. Appearance characteristics

X-ray endoskeleton is completely composed of cartilage, and some parts have a certain hardness after calcification, but it is different from the hard bone tissue formed by ossification. The body surface is covered with tarsal scales and is formed by ectoderm and mesoderm. The scales and teeth of ferns are homologous structures. The position of the mouth is not in the snout, but on the ventral surface, which is transverse (so it is called transverse mouth); The lateral fin is in a horizontal position; The tail fin is crooked. The differentiation of the stomach is obvious, the pancreas is independent and the liver is developed. There is a spiral valve in the intestine. No swimming. The branchial septum is very long, extending to the body surface and connected with the skin, so the branchial fissure opens directly to the body surface. The heart has an arterial cone. The male reproductive tube is borrowed from the middle renal tube. A single cloaca opens outward. Males have mating organs called flippers. Oviposition, viviparous or pseudoviviparous, in vivo fertilization, in vitro development or in vivo development. Fewer eggs are laid, but the survival rate is high. The brain is developed and more advanced than bony fish. The brain is very big, and there are nerve substances at the top of the brain.

Rays are round or diamond-shaped, with broad pectoral fins extending from the snout to the slender tail root; Some species have sharp snouts, flat bodies and slender tails, and some species of rays have one or several spines with jagged edge on their tails. Rays' eyes and blowholes grow on the top of the head, at the bottom of the mouth and nose, and are formed by coracoid cartilage protruding from the skull. The body is monochromatic or patterned, most kinds of ridges have spines or thorns, and some tail parts have power generation organs, so the power generation ability is weak. As far as we know, all rays are laid eggs, and their eggs are also called "mermaids' wallets", which are common on the beach and are rectangular and protected by shells.

65,438+008,000 years ago, rays were similar to sharks, but in order to adapt to underwater life, they hid their bodies in the seabed sand for a long time and gradually evolved into this appearance. Rays have a circle of fan-shaped pectoral fins around their bodies, and their caudal fins degenerate like a long thin whip, moving forward by the wave-like movement of pectoral fins. Rays usually hide in the sand. When two shells, crabs and shrimps approach, they will suddenly attack. Their teeth are like stone mortar, which can grind hard things, and there is a poisonous red thorn on their back, which will kill people. Features: Ray's head and body are directly connected, and there is no neck.