Oceans make up about 71% of the Earth's area and have an average depth of about 3,795 meters. The ocean contains more than 1.35 billion cubic kilometers of water, accounting for about 97% of the total water volume on the earth has a huge living space, in this space, human beings can not normally move, but there are many mysterious spirits - fish live in this wonderful space, some of them are strange shapes, some are beautiful and moving, fish are the most closely related to people's lives, they are also one of the main inhabitants of the ocean, swimming freely in the blue sea, bringing infinite vitality to the sea. Let me introduce you to these underwater elves:
1. Sharks (cartilage): Sharks belong to the vertebrate phylum Cartilaginous plate gill subclass, 80% of the species of sharks have a total length of less than 1.6 m, about 225 species of sharks, all carnivores, about 27 species are considered to be dangerous to humans. They have two rows of large, sharp teeth, comb-shaped, used to tear and prey on fish smaller than them, and the vast majority of sharks are small fish. A small number of species enter the freshwater, for a group of fast swimming medium and large marine fish, in the last century humans began to kill sharks in large quantities, has led to their population has decreased, so it is necessary to protect them.
shark
2. Rays (cartilage): a common name for a group of plate gills with a larger gill in the gill foramen and a coarse tail. The body is flattened and round or diamond-shaped. The mouth and nostrils are in the abdominal position. 5 gill holes. Spray hole back. The dorsal fins are 1 to 2 or none, mostly located at the tail; the fins disappear; the pectoral fins are well developed and connected to the head side of the adult disc, sometimes there is a hair generator between the head side and the pectoral fins; the ventral fins sometimes differentiate into toe-like structures. The inner bone is made up entirely of cartilage. It inhabits the seafloor and eats small fish, shrimp and shellfish. It is widely divided into the sea areas of the three oceans and is also found along the coast of China. There are about 380 species worldwide.
ray
3. Stingray (Hong Chondroitsylidae) The body is flat, slightly round or diamond-shaped, the cartilage is scaleless, the pectoral fin is developed, such as butterfly wings, the tail is whip-like, and the spines are poisonous. It lives on the ocean floor. There are many species, common ones are sharp-billed stingray, red stingray, swallow stingray and so on.
stingray
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