Amphibia - is that? General features and appearance of animals

Amphibians are the direct descendants of brush blooded fishes. They appeared 380 million years ago and subsequently gave rise to a class of reptiles. What do the amphibians look like? What is different from other animals and what way of life do they lead?

Amphibia - what is it?

According to the widespread version, brush-fish were the first inhabitants of water bodies, which managed to reach the dry land. Mastering the new space and adapting to other conditions, they gradually began to change, giving rise to new creatures - amphibians.

"Amphibian" is an ancient Greek word that translates as "two kinds of life". In biology, it means animals living on land and in water. In Russian terminology, it is increasingly clear, since amphibians are amphibians.

Earlier the concept also implied seals and otters, but later it only included four-legged vertebrates that did not belong to amniotes. The modern class of amphibians covers only salamanders, worms, newts and frogs. In total there are 5 to 6,7 thousand species.

Brief characteristics of the class

Amphibians are vertebrates, which in the animal kingdom occupy an intermediate position between fish and reptiles. Many representatives alternate periods of life in water and on land. Reproduction and initial development in the majority occurs in water, and growing, they lead a terrestrial way of life. Some species live only in water.

Most amphibians do not tolerate cold weather, prefer warm and humid places, but can live in arid terrain. At the onset of unfavorable conditions, you can fall asleep or change the activity time, for example, from night to daytime. However, some species settled far in the north, for example, the Siberian angler.

Amphibians live near fresh water bodies, and larvae sometimes lay even in deep puddles. Only a few species live in sea water. Development, as a rule, is accompanied by four stages: an egg (caviar), a larva, a metamorphosis and an adult. The Newts also have live births.

At all representatives of a class a weak metabolism, therefore it is not under force to assimilate vegetative food. Amphibians are predators and feed on insects, small invertebrates, and sometimes their fellow humans. Large individuals eat young fish, chicks and rodents. Plants feed on only the larvae of the order of the tailless.

How do they look?

The external structure of amphibians is very different. The group of tailed, which includes newts and salamanders, resembles lizards in appearance. They grow up to 20 centimeters. Their body is stretched and ends with a long tail. Neck, hind and forelegs short.

Frogs refer to tailless amphibians. They have a wide, slightly flattened trunk and short neck. The tail is only at the tadpole stage. Their limbs are elongated and bent, straightened at the time of jumping and swimming (the main ways of moving). The fingers of frogs and salamanders are connected by a skin membrane.

Worms are the amphibians of the detachment "legless." Outwardly they look like worms or snakes. Their sizes range from ten centimeters to one meter. The worms have no limbs, and the tail is shortened. Their body is covered with calcareous scales and colored in dark black or brown tones, sometimes with spots or stripes.

Features of the structure

The skin of these vertebrates is multilayer, but rather thin. It contains glands that secrete mucus that covers the entire body. Through it is partially carried out breathing. The lungs help the amphibians breathe on the surface, and the species that live predominantly in the water have gills.

The heart of amphibians is three-chambered, two chambers are observed only in salamanders. Circles of blood circulation two: small and large. Body temperature is unstable and depends on the environment.

The brain of amphibians is larger than in fish, and ranges from 0.30% (in the tailed) to 0.73% (in tailless) from body weight. Their vision is able to distinguish colors. Eyes cover the transparent lower and leathery upper eyelids. They discern a taste badly and can only define salty and bitter.

Skin is the main organ of touch and contains many nerve endings. Tadpoles and aquatic species from fish have preserved the lateral line, which is responsible for orientation in space.

A number of tailless slime on the skin contains poison. In most cases, it is not harmful to humans and serves to disinfect the surface. However, the poison of some tropical species can be dangerous. So, the little yellow frog (see photo above) the terrible leaf-eye is one of the most poisonous creatures in the world.