Vertebrates are the highest class in the animal kingdom. Although the number of vertebrates is far less than that of invertebrates, there are only about 40 thousand species, but they have a broader living space, and the sea, land and sky are their living places.

First of all, fish

Fish is the oldest vertebrate. They have existed for more than 470 million years and are the largest group of vertebrates, with about 22,000 species.

Fish have some common characteristics, that is, most of them live in water, breathe through gills, have scales all over their bodies, swim with fins, and have swim bladders in their bodies.

When we observe a fish, we will find that its mouth is constantly opening and closing. In fact, this is the fish breathing. When the fish absorbs water, the gill cover is covered to prevent the absorbed water from losing; Then close the fish mouth, discharge the inhaled water pressure to the gill cover, and be filtered by the gills and transported to the whole body, and then open the fish mouth for the next round of breathing.

Just as fish are very different, different fish have scales of different shapes. However, not all fish have scales. Instead, they have a particularly rough skin or hard shell, such as the hippocampus.

Fish can move forward in the water, or they can stay still, relying entirely on the swing of fins. Swing the tail fin to generate thrust, and the fish will move forward; The function of pectoral fin and ventral fin is to make the fish change direction accurately and stop quickly. The shape of fins reflects the life habits of fish. Fast-moving pelagic fish with blade-like fins and deeply forked tail fins; Slow-moving fish are good at controlling their own direction. Their fins are wide and their tail fins are flat and square.

1, hippocampus

Hippocampus is a very interesting fish, named after its head looks like a horse, but its length is far from that of a horse, only about 10 cm. The hippocampus is gentle and slow, and walks upright in the water.

Hippocampus is a model of advocating "equality between men and women" in fish, because both "pregnancy" and "childbirth" of hippocampus are completed by male hippocampus. The caudal fin of the male hippocampus ends in a pouch. The fertilized egg stays in the pouch for 20 to 30 days before it matures, and then it is produced by the male hippocampus through a painful process.

2. sharks

Sharks are famous for their ferocity, and people will shudder at the mention of sharks. In fact, only a few concentrated sharks can really kill people. Great white sharks and great blue sharks are the most terrible man-eating sharks. Why do they attack humans? That's because their food is mainly seals and dolphins, but when they meet people swimming and diving in hunting waters, they will attack people because they can't see the difference in size and outline between people and seals. Others, such as whale sharks, are harmless despite their huge size and fierce appearance. Whale sharks only feed on plankton.

Sharks have different shapes. The largest shark in the world is whale shark, which is18m long and weighs 40 tons, while the smallest shark is less than15cm.

Step 3: Ray

Rays are close relatives of sharks, but their appearance is not much similar to that of sharks. Rays have a flat diamond-shaped body with a strange and elegant appearance. At present, there are more than 300 species of rays in the world.

Rays mainly live in temperate waters and generally stay at the bottom of the sea. Raccoon has five pairs of gill holes, which grow at the upper end of the abdomen. Rays' whole pectoral fins are like a pair of big wings, and when they swim in the water, they are like flying in the water. Rays usually feed on small fish, shellfish, marine worms and various benthic organisms.

Most rays are harmless, but some rays, such as stingrays, have a thorn on their dorsal fin that can release venom.

Another very famous torpedo with offensive power is the power generation expert of the torpedo family. When attacking the enemy, it first wraps the enemy with pectoral fins, and then releases 200 volts from the special muscles on the side of the head to subdue the enemy. Currently, there are about 35 kinds of torpedoes in the world.

Second, amphibians

Amphibians originated 360 million years ago, evolved from ancient fish, and were also the ancestors of terrestrial animals. Among vertebrates, amphibians are few in number and have a narrow distribution range. So far, only about 3000 amphibians have been found.

Frogs, toads, pythons and salamanders make up amphibians. They are all carnivores and share the same life experience: the mother breeds in the water, the larvae develop in the water, and through gill breathing, the larvae develop into adults through complex metamorphosis. Adults live on land, or they can live in water and breathe with their lungs. Some adults of cushion animals breathe entirely through their skin. They are not warm-blooded animals and hibernate when the ambient temperature is below 7℃.

1, frog

There are many kinds of frogs. They have different postures and temperaments. Frog is a greedy and beautiful frog in the frog family. They are good friends of mankind. Frog has a smooth and graceful figure, its body color is grass green, and the two big eyes on its head look very gentle. Frog is an expert in preying on pests and is the natural enemy of mosquitoes, flies, snails, grasshoppers and other pests. Frogs are good at jumping, with a special tongue, with the root of the tongue in front and the tip of the tongue backward. This structure helps frogs to prey quickly.

In sharp contrast to frogs, horned frogs. The horned frog has a bright skin color and a horn-shaped protrusion on its head. It looks ferocious and terrible, and its temperament is very cruel. It is the devil among frogs. In addition to preying on insects, birds and so on. It also feeds on its own kind, and many gentle frogs are usually in their mouths. Horn frogs were cruel when they were children. They prey on the young frogs of other frogs.

April to July is the breeding season of frogs every year, and it is also the busiest season in rural areas and rivers. At night, most male frogs frequently make pleasant calls to attract female frogs to lay eggs. Usually, a female frog can lay about 10000 eggs at a time, but because some eggs will be eaten by other animals, not many eggs are hatched. Frog eggs develop into adults through metamorphosis. Frog eggs first become tadpoles. Tadpoles drag their long tails. After a month and a half, tadpoles grow hind legs, and after half a month, gill holes also grow on their front legs. Interestingly, their legs first grow in the body and then suddenly stick out of the body. Finally, the tadpoles' gills and tails disappeared and they developed into frogs.

Some frogs will use their bright body colors to warn their enemies-they are highly toxic and don't go near them!

The poison dart frog is one of the most poisonous frogs. The venom of a poison dart frog is enough to kill 20 thousand mice! This frog is mostly distributed in South America. The local Indians used its venom to make poison arrows, hence the name poison dart frog. A poison dart frog can kill 30 people.

2. Toads

Compared with frogs, its hind legs are short and it can't jump. Toads live in the grass behind the flat land and dry fields in mountainous areas, and can only get close to the water source when laying eggs. They are "Nightcrawler". They hide during the day and come out to look for food at night.

Toads have warts (lumps) on the surface of their skin and mucus on their skin. Toads have a similar diet to frogs, but toads are not afraid of snakes. For frogs, snakes are their natural enemies, but for toads, those little snakes are delicious food. Poison is hidden in the ear gland behind toad's eyes. When he meets the enemy, he will spray venom on the enemy. This venom can make cats and other animals spit foam out of their mouths and make them miserable. However, Venenum Bufonis extracted from venom is an extremely precious Chinese herbal medicine.

3.giant salamander

Giant salamander is the largest and most precious amphibian in the world. It cries like a baby's cry, so it is also called giant salamander. The largest giant salamander can be as long as 180 cm and weigh 65 kg. Giant salamander's flat body, wide flat head and two small mung bean eyes on its head look childish. It has a big mouth, a long flat tail and four short fat legs. The whole body is covered with brown and black skin, smooth and moist.

Giant salamanders like to live in cool streams, fast-flowing mountain streams and porous rocks. Most of them live alone and go out at night. The giant salamander is a carnivorous animal, which mainly preys on frogs, crabs, fish, shrimps, snakes and aquatic insects. The teeth in the giant salamander's mouth are sharp and dense, so it is difficult for its prey to escape.

The metamorphosis process of giant salamander larvae is basically the same as that of tadpoles, but unlike tadpoles, the tail of giant salamander still exists after the larvae develop into adults.

Third, reptiles

Reptiles appeared 300 million years ago. They were the first completely terrestrial vertebrates. There are about 6000 species of reptiles in existence, mainly living in tropical and some temperate regions.

The respiratory organs of reptiles are lungs, and some breathe through the skin. Their skin is covered with scales. They belong to temperature-changing animals and can't control the temperature in their bodies, so they can't find reptiles in cold areas and hibernate in winter.

Reptiles fall into three categories: turtles, crocodiles, snakes and lizards.

1, turtle

There are about 330 kinds of reptiles. Their bodies are short and wide, and their soft bodies are hidden in thick and hard shells. They have no teeth, but their jawbones are very hard and can cut off food.

Tortoise's sense of smell and touch is quite developed, but its hearing and vision are not keen. Most turtles are gentle and not aggressive. When they are hurt by the enemy, they all shrink back and hide in turtle shells. Looking at a shell as hard as a stone, the enemy is often at a loss. It is with this special skill that turtles have lived on the earth for 200 million years and will continue to live happily. The life span of turtles is very long, generally around 70 years old, and most turtles can live to 100 years old.

Turtles breed by laying eggs, which are very secretive. During the annual breeding season, female turtles quietly climb to the beach under the cover of night, and choose a sunny and moderate temperature place as the spawning ground. Before laying eggs, turtles urinate on the sand to make the soil moist and soft, and then dig a hole with their hind feet. When the hole is dug to a depth above 10 cm, the tortoise begins to lay eggs in the hole. The turtle egg is about the size of a ping-pong ball, with a hard calcium shell outside. This shell is the protective layer of the egg, but it is an obstacle for the young turtle that is about to rise. Fortunately, there is a hard protrusion between the baby turtle's mouth and nose. With this "shell breaker", the young turtle struggled to drill, grind and struggle, finally drilled a small hole, tried his best to break the eggshell with his head, and the young turtle began to breathe for the first time. With the rise of the young turtle, the night of its survival crisis came. Young turtles are a delicacy for seabirds, lizards, dogs and snakes. Young turtles are often eaten on the way to the seaside or river ponds. Of the 65,438+000 baby turtles, only a few can survive.

Turtles are the biggest turtles. The length of their nails is generally around 100 cm. In addition to laying eggs or basking in the sun, turtles have been living in the sea, and their feet have become fins, so that turtles can swim freely in the water.

Turtles have three eating habits. Turtles are mostly herbivores, feeding on straw and plant leaves. Turtles are mostly carnivores. They prey on mollusks, shrimps and crabs. Freshwater turtles are mostly omnivorous turtles. They eat vegetarian food such as aquatic plants, as well as river shrimp, frogs and fish.

There are about 32 known species of soft-shelled turtle. They live in fresh water. Turtles often dive into the sediment at the bottom of the water, so their shells become flat and flat. The web between the toes of the tortoise is very developed, and it moves quickly in the water and swims very fast. Turtles are natural divers. Its neck and nose are very long, which enables it to lie on the bottom of the water and breathe through its nose.