In the world there are about 4500 species of amphibians.They live literally on every continent except Antarctica - the Arctic Circle and in arid regions at high altitudes and in salt waters.But most of them can be found in the tropics.
Modern reptiles or amphibians are divided into 3 group.The first includes about 5000 species of animals called Anura.It's good to see frogs, toads and spadefoot toad, frog, fire-bellied toads a
nd other. Animals of this group have a well-developed limbs, and tail is much longer than the front and are designed to move the jumps;short trunk, the tail is missing.Next
squad - tailed - comprises about 500 species of amphibians.These include salamanders, newts, sirens, etc. All the salamanders have an elongated body, turning into a tail, short limbs and weaknesses.An important feature of this type of organism amphibians is a high degree of regeneration - not uncommon for a full and quick recovery of the animals that have lost almost half of his body.Last
squad - caecilians or legless amphibians.It is the most primitive of all the amphibians, have neither tail nor limbs.Externally, they resemble earthworms.
Features of development and functioning of amphibians
amphibians lay eggs in water.Fertilization is external.The eggs do not have a hard protective shells.In water they swell, and this prevents them from drying.From the eggs develop into larvae, unlike the adult animals adapted to life only in the aquatic environment.They have a two-chambered heart, a circle of blood circulation, breathing through gills, limbs missing.The movement occurs by means of the tail.
During development, a second circulation, becomes a three-chambered heart, there are five-fingered limbs, gill breathing is replaced by air.The structure of the brain and throughout the nervous system is complicated.Adult amphibians are terrestrial life, actively hunting for insects and invertebrates and occasionally returning to the water.
Another feature of the amphibian body - they breathe not only oxygen in air.In the water, amphibians breathe through their skin, and when it turns on land, connects the pulmonary respiratory system and mucous membranes of the mouth.But even in this case, they can get through the skin of half the body needs oxygen and excrete through it up to 70% of carbon dioxide.All this is possible only if the animal's skin moist.Some inhabit the land salamanders have no lungs and gills and all the necessary breathing oxygen get through the skin and oral mucosa.
Amphibians no ribs or diaphragm, not muscle, makes it easy to shrink and crack down, providing breathing.As a pump pumping air into the lungs, performs mouth.
amphibians - cold-blooded animals, the body temperature depends on the environment.Well known for their ability to survive at low temperatures.For example, Siberian saber - newt living in the Arctic Circle - to freely transfer temperature of about -20 °, and sometimes below -30 ° C.Some tailless amphibians also have this remarkable property.Their body is released into the blood substances that act like "antifreeze", whereby the cells of the animal is not killed by freezing.For example, the common frog may spend the winter months, vmerznuv ice.In the spring she thaws and warms safely continues to live on.
Interesting features have a family tree frog amphibian called fillomeduzami.This tree frogs that live in Central and South America.They have a prehensile foot type - the first finger is opposed to all the others.Fillomeduzy can neither jump nor swim, but good climb trees.The eggs they lay on the broad leaves, somewhere over the water.Leaf turns kulechkom animal glues and sticky shells of eggs.When the tadpoles hatch, leaf unfolding, and they fall into the water, where it is further developed.