Class amphibians. Amphibian - what is it? General features and appearance of animals Who belongs to the amphibian group

Terrestrial, or amphibians(lat. Amphibia) - a class of vertebrate tetrapods, including newts, salamanders, frogs and worms - more than 6700 (according to other sources - about 5000) modern species, which makes this class relatively small in number. In Russia - 28 species, in Madagascar - 247 species.

The group of amphibians belongs to the most primitive terrestrial vertebrates, occupying an intermediate position between terrestrial and aquatic vertebrates: reproduction and development in most species occurs in the aquatic environment, and adults live on land.

general characteristics

Skin integument

All amphibians have smooth, thin skin, which is relatively easily permeable to liquids and gases. The structure of the skin is typical for vertebrates: a multilayer epidermis and the skin itself (corium) are distinguished. The skin is rich in mucus-secreting cutaneous glands. For some, mucus can be toxic or facilitate gas exchange. The skin is an additional organ of gas exchange and is equipped with a dense network of capillaries.

Horny formations are very rare, and ossification of the skin is also rare: Ephippiger aurantiacus and the horned toad species Ceratophrys dorsata there is a bone plate in the skin of the back, in legless amphibians - scales; in toads, lime is sometimes deposited in the skin under old age.

Skeleton

The body is divided into a head, torso, tail (in tailed beasts) and five-fingered limbs. The head is movably connected to the body. The skeleton is divided into sections:

• axial skeleton (spine);
• skeleton of the head (skull);
• the skeleton of paired limbs.

• pulmonary arteries (carry venous blood to the lungs and skin);
• carotid arteries (supply arterial blood to the organs of the head);
• the aortic arches carry mixed blood to the rest of the body.

Small circle - pulmonary, begins with the pulmonary arteries carrying blood to the respiratory organs (lungs and skin); from the lungs, oxygen-enriched blood is collected in paired pulmonary veins that flow into the left atrium.

The systemic circulation begins with aortic arches and carotid arteries, which branch out in organs and tissues. Venous blood through the paired anterior vena cava and the azygos posterior vena cava enters the right atrium. In addition, oxidized blood from the skin enters the anterior vena cava, and therefore the blood in the right atrium is mixed.

Due to the fact that the organs of the body are supplied with mixed blood, amphibians have a low level of metabolism, and therefore they are cold-blooded animals.

Digestive organs

All amphibians feed only on mobile prey. At the bottom of the oropharyngeal cavity is the tongue. In tailless, it attaches with its front end to the lower jaws, when catching insects, the tongue is thrown out of the mouth, prey sticks to it. The jaws have teeth that serve only to hold the prey. In frogs, they are located only on the upper jaw.

The ducts of the salivary glands open into the oropharyngeal cavity, the secret of which does not contain digestive enzymes. From the oropharyngeal cavity, food enters the stomach through the esophagus, from there into the duodenum. The ducts of the liver and pancreas open here. Digestion of food takes place in the stomach and in the duodenum. The small intestine passes into the rectum, which forms an extension - the cloaca.

Excretory organs

The brain consists of 5 sections:

• the forebrain is relatively large; divided into 2 hemispheres; has large olfactory lobes;
• the diencephalon is well developed;
• the cerebellum is poorly developed due to simple, monotonous movements;
• the medulla oblongata is the center of the respiratory, circulatory and digestive systems;
• the midbrain is relatively small, is the center of vision, skeletal muscle tone.

Sense organs

In the organ of hearing, a new section is the middle ear. The external auditory opening is closed by the eardrum, which is connected to the auditory bone - the stapes. The stripe rests against the oval window leading to the inner ear cavity, transmitting to it the vibrations of the eardrum. To equalize the pressure on both sides of the tympanic membrane, the middle ear cavity is connected to the oropharyngeal cavity by the auditory tube.

The organ of touch is the skin, which contains the tactile nerve endings. Aquatic representatives and tadpoles have lateral line organs.

Genitals

All amphibians are dioecious. In most amphibians, fertilization is external (in water).

Amphibians of some species take care of the offspring (toad, tree frogs).

Lifestyle

Most live in humid places, alternating between being on land and in water, but there are some purely aquatic species, as well as species that live exclusively on trees. Insufficient adaptation of amphibians to living in a terrestrial environment leads to drastic changes in their lifestyle in connection with seasonal changes in living conditions. Amphibians are capable of hibernating for a long time under unfavorable conditions (cold, drought, etc.). In some species, activity can change from night to day when temperatures drop at night. Amphibians are active only in warm conditions. At a temperature of +7 - +8 ° C, most species fall into a torpor, and at −1 ° C they die. But some amphibians are able to withstand prolonged freezing, drying out, and also regenerate significant lost parts of the body.

Some amphibians, such as the sea toad Bufo marinus can live in salt water. However, most amphibians are found only in fresh water. Therefore, they are absent on most oceanic islands, where conditions are in principle favorable for them, but which they cannot reach on their own.

Nutrition

All modern amphibians in the adult stage are predators, feed on small animals (mainly insects and invertebrates), and are prone to cannibalism. There are no herbivorous animals among amphibians due to extremely sluggish metabolism. The diet of aquatic species can include juvenile fish, and the largest ones can hunt chicks of waterfowl and small rodents that have fallen into the water.

The feeding habits of the larvae of tailed amphibians are practically similar to that of adult animals. Tailless larvae have a cardinal difference, feeding on plant food and detritus, passing to predation only at the end of the larval stage.

Reproduction

A common breeding feature of almost all amphibians is their attachment during this period to water, where they lay their eggs and where the larvae develop. Amphibians breed in small, well-heated areas of water bodies. On warm spring evenings, in late April and May, loud croaking sounds are heard from the ponds. These "concerts" are organized by male frogs to attract females. The reproductive organs in males are the testes, in females - the ovaries. Fertilization is external. Caviar sticks to aquatic plants or rocks.

Virulence

The most poisonous vertebrates on Earth belong to the order of amphibians - these are dart frogs. The poison, which is secreted by the skin glands of amphibians, contains substances that kill bacteria (bactericides). In the majority of amphibians in Russia, the poison is completely harmless to humans. However, many tropical frogs are not as safe.

The absolute "champion" of poisonousness among all vertebrates, including snakes, should be recognized as an inhabitant of the rainforests of Colombia - a tiny, only 2-3 cm in size, terrible leaf climber (locals call him "cocoi"). Her mucus contains batrachotoxin. The Indians prepare poison for arrows from the skin of the cocoa. One frog is enough to poison 50 arrows. 2 mg of purified poison is enough to kill a person. However, this frog has a natural enemy - a small snake Leimadophis epinephelus that feeds on young leaf climbers.

Amphibians and humans: an active life

Due to their vitality, amphibians are often used as laboratory animals.

Classification

Modern representatives are represented by three groups:

• Tailless (frogs, toads, tree frogs, etc.) - about 2100 species.
• Tailed (salamanders, newts, etc.) - about 280 species.
• Legless, the only family of worms - about 60 species.

Evolution

In evolutionary terms, amphibians descended from ancient cross-finned fishes and gave rise to representatives of the reptile class. The tailed beasts are considered the most primitive order of amphibians. Tailed amphibians are most similar to the oldest representatives of the class. More specialized groups are tailless amphibians and legless ones.

There is still debate about the origin of amphibians, and according to the latest data, amphibians descend from ancient cross-finned fish, specifically, from the order of ripidistia. By the structure of the limb and skull, these fish are close to the fossil amphibians (stegocephals), which are considered the ancestors of modern amphibians. The most archaic group is considered to be ichthyostegids, which retain a number of features characteristic of fish - the caudal fin, rudiments of gill covers, organs corresponding to the organs of the lateral line of fish.

Basic aromorphoses

1. The appearance of a five-toed limb.
2. Lung development.
3. The presence of a three-chambered heart.
4. Middle ear formation.
5. The appearance of two circles of blood circulation

see also

Notes (edit)

1. Amphibian Species of the World. Amphibian database. Darrel Frost and The American Museum of Natural History. Archived
2. Class Amphibians, or Amphibians: a general characteristic. Biology and Medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
3. Classis AMPHIBIA (L. Ya.Borkin, 1992). Archived from the original on June 22, 2012. Retrieved March 13, 2012.
4. // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.
5. Workshop on Vertebrate Zoology. Autopsy of an amphibian. Archived from the original on August 4, 2012. Retrieved July 16, 2012.
6. Nikitenko, 1969 The brain of amphibians. Biology and Medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
7. Why are they ... aquatic? ... Zoo club. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
8. Alexander Markov How Amphibians Learned to Transform (January 24, 2008). Archived from the original on June 22, 2012. Retrieved March 13, 2012.
9. Food for amphibians. Biologists and Medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
10. Digestive system of amphibians. Biology and Medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
11. Poisonous evolution. The magazine "Around the world". Archived from the original on June 22, 2012. Retrieved March 13, 2012.

Which consists of three modern orders: tailless (frogs and toads), legless (worms) and tailed (newts and salamanders). The ancestors of modern amphibians were the first animals to leave the water and adapt to life on land.

Amphibian larvae begin their life in water, usually fresh, and undergo a complex process of metamorphosis before transforming into an adult. Their skin is moist without scales, feathers or hair.

The life cycle of amphibians reflects their evolutionary history of transition from life in water to life on land. Most amphibians lay their eggs in fresh water, but there are species that prefer salt water or dry land. Surprisingly, some species carry eggs on their bodies. Although the life cycle of amphibians varies from species to species, they all have the following three main stages of development: egg → larva → adult.

Eggs (eggs) of amphibians without a waterproof shell. Instead, they are composed of a gelatinous shell that must remain moist for the larva to survive. The eggs have small holes through which tiny larvae get out, where they have to go through the path of metamorphosis into an adult.

Many amphibians are capable of absorbing oxygen directly into the bloodstream, as well as releasing carbon dioxide into the atmosphere through their skin. The skin of amphibians does not have scales and hair. It is smooth and often damp, making it sufficiently permeable to gases and water.

The permeability of the skin makes amphibians especially vulnerable to toxins in the air and water, such as herbicides, pesticides and other pollutants. For this reason, we are seeing a sharp decline or complete extinction of amphibian species in many areas around the world.

The first amphibians evolved from lobe-finned fish about 370 million years ago, during the Devonian period. Early amphibians included the following creatures: diplocaulus, ophiderpeton, adelospondylus, and pelodosotis. The world of the first amphibians was completely different from what we see it today. A world without birds, mammals and reptiles. Invertebrates and many of the prehistoric plants that colonized the Earth. It was a quiet place, devoid of birdsong and the growling of predators. The land was opened to amphibians, which began a new and important stage in the history of life on our planet. Some fish have developed lungs.

Scientists believe that the ancestors of amphibians were crossopterygians - a group of primitive cross-finned fish. They developed several key features: the musculoskeletal framework to support body weight on land, and the nostrils and leg bones.

Most amphibians never completely disconnect from their aquatic habitat. Some amphibians return to the water to reproduce, while some species remain in the water throughout their entire life cycle. Many amphibians go through a complex process of metamorphosis before becoming an adult.

Amphibians are a group of anamnias that partially passed to a terrestrial way of life, but retained the features of their aquatic ancestors.

Systematics. The world fauna numbers about 3400 species. Modern amphibians are divided into three groups.

Squad Legless- about 170 species of worms leading an underground lifestyle. All are tropical dwellers.

Tailed squad- about 350 species, distributed mostly in the northern hemisphere. These include newts, salamanders, salamanders, axolotls. There are about 12 species in the CIS.

Tailless squad- about 2900 species of frogs and toads, common on all continents. The fauna of the CIS includes about 25 species.

Body measurements... The smallest amphibians reach a length of 1-2 cm, and the largest - gigantic salamanders - exceed 1 m in length.

External structure. Amphibians have a naked, mucus-covered body. The head is movably connected to the only cervical vertebra by two condyles. Have tailed amphibians the body is elongated, there are four limbs of approximately the same length and a long tail. The limbs can be more or less reduced. There are also completely legless forms (worms). Have tailless amphibians the body is short and wide. The hind limbs are leaping and significantly exceed the length of the front ones.

Veils. The skin is devoid of horny formations and is very rich in mucus-secreting multicellular glands. There are large lymphatic sacs under the skin, so that the skin is attached to the body only in certain places. The skin is richly supplied with blood vessels and takes an active part in gas exchange (respiratory function). The covers also perform a protective function. Many species have bumps and warts on the skin that secrete a poisonous secret. Many poisonous species are brightly colored (salamanders, poison dart frogs), but in general the color of amphibians is patronizing.

Skeleton. The skull is mostly cartilaginous. The spine consists of several sections: cervical (one vertebra), trunk (several vertebrae), sacral (one vertebra) and caudal. In tailless amphibians, the rudiments of the caudal vertebrae grow together into a process - urostyle... There are no ribs on the spine.

The skeleton of the forelimb consists of the humerus, two bones of the forearm (radius and ulna), and numerous bones of the hand (wrist, metacarpus, phalanges of the fingers). The forelimb girdle consists of the scapula, coracoid, and clavicle. The sternum is connected to the girdle of the forelimbs.

The hind limb, respectively, consists of one thigh bone, two lower leg bones (tibia and tibia), and foot bones (tarsus, metatarsus and phalanges of the fingers). The hind limb includes the pelvic bones (iliac, sciatic, and pubic).

In the general case, the limbs are five-toed, however, many amphibians, especially on the forelimbs, have four toes.

Muscular system more differentiated than in fish. The muscles of the limbs are especially developed. In some places, there is a distinct segmentation of the muscles.

Digestive system in amphibians it is well developed. There are small teeth on the jaw bones. The ducts of the salivary glands open into the oral cavity. Saliva contains no digestive enzymes and only moistens food. In the mouth is the tongue, which has its own muscles. In frogs, it is attached to the front of the lower jaw. The eyeballs protrude strongly into the oral cavity and take part in pushing food further into the pharynx. The pharynx leads into a relatively short esophagus; the stomach is not sharply separated. The intestine is clearly differentiated into a thin and thick section. The ducts of the liver and pancreas open into the small intestine. The hindgut flows into the cloaca.

Respiratory system. At the end of the muzzle of amphibians there are nostrils, which are equipped with valves and open into the oropharyngeal cavity by the choanas. In the same cavity, the larynx opens, consisting of cartilages, of which the most developed pair of arytenoid, forming a laryngeal gap. Actually, the respiratory organs in amphibians are paired saccular cellular lungs with sufficiently elastic walls. The lungs are either suspended from the lower part of the laryngeal chamber (in tailless), or are connected to it by a long tube - the trachea, in the wall of which there are cartilaginous elements that prevent the tube from collapsing (in caudates). The trachea only opens into the lungs with an opening, but does not branch into them.

The act of breathing due to the absence of a chest occurs in a very peculiar way. The animal opens the valves of the nostrils and lowers the mouth floor: air fills the oral cavity. After that, the valves close and the bottom of the mouth rises: air through the laryngeal gap is pushed into the lungs, which are somewhat stretched. Then the animal opens the valves of the nostrils: the elastic walls of the lungs collapse and air is pushed out of them.

An equally important respiratory organ is, as already mentioned, the skin. For example, in a grass frog, about 30% of oxygen enters through the skin, and in a pond frog, up to 56%. Most of carbon dioxide (up to 90%) is removed through the skin.

In amphibian larvae, the respiratory organs are external or internal gills. For the most part, they subsequently disappear, but in some species (proteus, axolotl) they can persist throughout their life.

Circulatory system. Changes in the circulatory system are also associated with the development of cutaneous-pulmonary respiration. The three-chambered heart consists of two isolated atria and one ventricle. The arterial cone departs from the ventricle, from which three pairs of vessels originate: two carotid arteries carrying arterial blood to the head; two aortic arches with mixed blood, which release the vessels into the forelimbs and then merge into the unpaired dorsal aorta; two cutaneous-pulmonary arteries that carry venous blood to the lungs and to the skin for oxidation. This separation of blood flows is ensured by the presence of special pockets in the ventricle itself, as well as by the work of the muscles of the arterial cone.

The blood returns back to the heart through the veins: one posterior and two anterior vena cava with venous blood flow into the right atrium, while cutaneous veins with arterial blood also flow into the anterior vena cava. In the left atrium, arterial blood from the lungs flows through the pulmonary veins. Blood from the atria is pushed into the ventricle, where it does not mix completely.

Thus, amphibians form small, pulmonary circle circulation, which is not yet completely separated from the large circle. Erythrocytes in amphibians are oval in shape and contain a nucleus.

Body temperature. Amphibians are poikilothermic animals, since they are not able to maintain a constant body temperature and are highly dependent on the ambient temperature.

Nervous system... The brain of amphibians differs in a number of ways from the brain of fish. The main ones are the complete division of the forebrain into hemispheres and a very weak development of the cerebellum. The latter is associated with low mobility and monotony of animal movements. In the forebrain, the roof (vault) contains nerve matter, but there are no nerve cells on the surface of the brain. The olfactory lobes are poorly differentiated. This formation is called the primary cerebral vault ( archipallium). Of the peripheral nervous system, the nerves of the hind limbs are especially developed.

Sense organs in connection with landfall, they acquire a more complex structure than that of fish.

Organs of vision... The eyes are well developed. The lens has the appearance of a biconvex lens, in contrast to the spherical lens of fish. The cornea is also convex. Accommodation is achieved by changing the distance from the lens to the retina. The eyes are protected by movable eyelids. Some species are devoid of eyes (proteas).

Organs of hearing... In addition to the inner ear, developed in fish, amphibians have a middle ear delimited from the external environment by the tympanic membrane. This membrane is connected to the inner ear by the auditory bone - stapes(column), which transmits vibrations of air, conducting sound much worse than water. The middle ear cavity is connected to the oral cavity by the Eustachian tubes, which equalize internal and external pressure, preventing the eardrum from rupture.

Organ of balance connected with the inner ear and represented by a sac and three semicircular canals.

Smell organs located in the nasal passages of amphibians. Unlike fish, the olfactory surface is increased by folding.

Lateral line organ, characteristic of fish, is present in amphibians exclusively in the larval phase. In the process of development, it disappears.

Organs of touch represented by numerous nerve endings in the skin.

Excretory system amphibians perform the function of removing excess fluid from the body, which flows not only through the mouth, but also through the entire surface of the skin. Amphibians have two large trunk ( mesonephric) kidneys. From them, the ureters depart, flowing into the posterior part of the intestine - the cloaca. It also opens the bladder, in which urine accumulates before being removed from the body.

Reproductive system amphibians are very similar to the reproductive organs of fish.

Have male on the front of the kidneys there are paired testes, from which numerous vas deferens branch off, flowing into the ureters. There are seminal vesicles where sperm are stored.

Have females sex glands - ovaries - large, granular. Their size depends on the season. During the breeding season, they occupy most of the body cavity. Mature eggs fall into the body cavity, from where they are excreted through the oviducts into the cloaca, and then outside.

Nutritional biology. Amphibians respond only to mobile food. All amphibians, without exception, feed on invertebrates - arthropods, molluscs and worms. Large tropical frogs are also capable of eating small rodents. They all swallow their prey whole.

Reproduction biology... The breeding season usually occurs in the spring. Mating is preceded by various courtship rituals. During this period, males may change color, and a crest may appear (in newts). In tailless amphibians, fertilization is external, as in fish: the female spawns into the water, and the male immediately fertilizes the laid eggs. In a number of species of tailed amphibians, the male lays the so-called spermatophore- a gelatinous lump containing sperm and attaches it to underwater objects. The female later captures these formations with the edges of the cloaca and places them in the spermatheca. Fertilization takes place inside the female's body.

Development... In the vast majority of amphibians, eggs are deposited in water. Each egg is covered with a gelatinous membrane, which contains substances that suppress the development of microorganisms. Fertilized eggs, poor in yolk, undergo complete uneven crushing... Gastrulation occurs by intussusception and at the same time epiboly... In the end, a tadpole larva is formed from the egg. This larva is in many ways similar to fish: a two-chambered heart, one circle of blood circulation, gills, lateral line organ. In the process of metamorphosis, the disappearance or change of larval organs and the formation of an adult animal occur. External gills gradually turn into internal ones, and with the appearance of pulmonary respiration, they can disappear altogether. The tail and the lateral line are reduced, the hind limbs appear first, and then the forelimbs. A septum appears in the atrium, and the heart becomes three-chambered.

In this way, in the process of individual development (ontogenesis) of amphibians, a repetition of the historical development of this group (phylogenesis) is clearly visible.

In some species, fertilized eggs attach to the hind limbs of the male (midwife toad) or to the dorsal part of the female (pipa toad). Sometimes fertilized eggs are swallowed by males, and further development of eggs and the formation of tadpoles and frogs takes place in his stomach. In some species, viviparity takes place.

Neoteny. In some tailed amphibians, the final transformation of the larva into an adult animal does not occur. Such larvae have acquired the ability to reproduce sexually. This phenomenon is called neoteny. Especially well studied neoteny on the example of axolotls - neotenic ambist larvae. Under artificial conditions, through the action of hormones, it is possible to obtain adult forms that do not have external gills.

Life span amphibians are usually estimated at several years. However, individual specimens lived in captivity for 10-30 years. Some Siberian species, such as salamanders living in the permafrost zone, are capable of falling into a stupor for 80-100 years.

Origin... The ancestral form of amphibians is considered to be ancient cross-finned fish, which probably had pulmonary respiration. Their paired fins gradually developed into a five-fingered limb. This happened, as is assumed, in the Devonian period (at least 300 million years ago). Among the paleontological remains of that time, imprints of the most primitive amphibians - stegocephals and labyrinthodonts - were found, which had many features in common with ancient cross-finned fish.

It has been proven that lungfish separated from the common trunk much earlier than cross-finned and could not be among the ancestors of amphibians.

Spreading... The abundance and species diversity of amphibians is especially great in the tropics, where it is constantly warm and humid. Naturally, towards the poles the number of amphibian species will decrease.

Lifestyle. Amphibians can be divided into two groups according to the nature of their habitat.

The first group includes terrestrial species... They mainly live on land and return to the water only for the breeding season. These include toads, tree frogs and other tree tailless, as well as burrowing species - garlic and all legless (worms).

The second group includes aquatic species... If they leave the reservoirs, then not for long. These include most of the tailed amphibians (salamanders, proteas) and some tailless (lake frog, pipa).

In the temperate climatic zone, amphibians hibernate. Newts and toads hibernate in underground shelters (rodent burrows, basements and cellars). Frogs most often hibernate in water.

Proteins inhabiting cave reservoirs, where the temperature does not change, remain active throughout the year.

Some amphibians, despite their moisture-loving nature, can sometimes even live in deserts, where they are active only during the rainy season. The rest of the time (about 10 months) they spend in hibernation, buried in the ground.

Meaning. Amphibians make up a significant proportion of the vertebrate population in most landscapes. They eat a huge number of invertebrates. This is even more important if we consider that birds are the main competitors of amphibians for food, most of them sleep at night, and amphibians are mainly night hunters. At the same time, amphibians themselves serve as food for a huge number of animals. This is especially true for tadpoles and young animals, the density of which reaches hundreds, and sometimes thousands of specimens per square meter!

In practical terms, amphibians are useful as exterminators of harmful invertebrates (slugs, Colorado beetles), which other animals most often do not eat. Lake frogs sometimes kill fish fry, but the harm they do is very small. Several amphibian species have become classic experimental animals. A number of species are eaten. Many countries have adopted laws on the protection of amphibians.

Class Reptiles or Reptiles.

Reptiles are real terrestrial animals of the amniote group with variable body temperature (poikilothermic).

Systematics. The modern fauna of reptiles numbers about 8000 species belonging to several orders.

Turtle squad- about 250 species, in the CIS - 7 species.

Squad scaly- about 7000 species. In the CIS there are about 80 species of lizards and about 60 species of snakes.

Beak-headed squad- 1 species (tuatara)

Squad crocodiles- 26 types.

External structure. The body of reptiles is usually elongated. The head is connected to the body by a well-defined cervical region and carries various sensory organs. Most reptiles have two pairs of originally five-toed limbs on the sides of the body. However, in a number of groups, the limbs were completely or partially reduced. The tail section is well developed.

Body measurements reptiles vary widely. The smallest representatives (geckos) can be only a few centimeters in length. The largest are considered to be anacondas snakes, the length of which sometimes reaches 10-11 m.

Veils. Reptiles are covered with dry skin that lacks glands. The skin is tightly attached to the body and often fuses with the skull on the head. The whole body is covered with horny scales (lizards, snakes) or horny scutes (crocodiles). In snakes, the eyes are covered with transparent shields that replace the eyelids. The body of turtles is enclosed in a shell, covered with scutes from the outside. All reptiles shed periodically - shedding old skin. At the same time, in turtles, old shields are erased from the shell or peeled off; in lizards, the old skin flakes off in large pieces, and in snakes it slides off in a stocking.

Skeleton quite ossified. The skull is connected to the first cervical vertebra ( atlant) with only one condyle, and the atlas, in turn, is "put on" on the process of the second cervical vertebra ( epistrophy); thus, the head is connected to the body in a very flexible way. The teeth are located at the jaw ends. The spine is divided into several sections: cervical, thoracic, lumbar, sacral and caudal. Ribs are attached to the thoracic vertebrae, which, connecting with the sternum, form the rib cage. The ribs of the lumbar and posterior thoracic vertebrae are not connected to the sternum. In snakes, ribs are part of the function of movement. In turtles, a number of sections of the spine and ribs fuse with the shell. The skeleton of the fore and hind limbs consists of the same bones and sections as in other terrestrial vertebrates.

In flying dragon lizards, elongated false ribs support the lateral folds of the skin. Thanks to this, the animals have developed the ability to glide.

Muscle... The musculature reaches even greater development in comparison with amphibians. Of the features, it should be noted the appearance of intercostal muscles, as well as underdeveloped subcutaneous muscles. The muscles of some snakes are very strong.

Digestive system. The salivary glands enter the oral cavity. Poisonous snakes have special glands that produce toxins. The ducts of these glands open into the so-called poisonous teeth... Snake venoms are complex complexes of biologically active compounds. According to the effect on warm-blooded animals, poisons are divided into two groups: neurotoxic and hemotoxic.

Neurotoxic poison affects the central nervous system, causing flaccid paralysis of the respiratory and motor muscles. At the same time, pain and swelling at the site of the bite, as a rule, are not very pronounced. The poison of this group is possessed by asps, cobras and sea snakes.

Hemotoxic poison contains proteolytic enzymes that destroy tissues and increase vascular permeability. At the same time, against the background of general intoxication at the site of the bite, severe edema develops, accompanied by pain. These poisons can cause disseminated intravascular coagulation. The poisons of this group are characteristic of viper and pit viper snakes (vipers, efa, gyurza, shitomordnik, rattlesnake).

In addition to snakes, poison is also contained in the saliva of a large Mexican lizard - the gila-toothed lizard.

The muscular tongue is well developed. In chameleons, the tongue is able to stretch strongly, and serves to catch insects.

The esophagus is usually highly distended, especially in snakes that swallow whole prey. The esophagus leads to a well-developed stomach. The intestine is divided into a thin and a thick section. The ducts of the liver and pancreas flow into the beginning of the small intestine. The large intestine ends with an expansion - a cloaca, into which the ureters and ducts of the reproductive system flow.

Respiratory system. Gas exchange through the skin is completely absent in reptiles, in contrast to amphibians. On the front of the head in reptiles there are paired nostrils that open with choans into the oral cavity. In crocodiles, the choans are pushed far back and open into the pharynx, so that they can breathe while grabbing food. From the choanas, air enters the larynx, consisting of cricoid and two arytenoid cartilages, and from there into trachea... The trachea is a long tube made up of cartilaginous half rings that prevent it from collapsing. In the lower part, the trachea divides into two bronchi, which connect to the lungs, but do not branch into them. The lungs are bags with a cellular structure on the inner surface. Breathing is carried out by changing the volume of the chest due to the work of the intercostal muscles. Such a mechanism is not possible in turtles; they breathe like amphibians, swallowing air.

Circulatory system... The heart of reptiles is generally three-chambered. However, in the ventricle there is incomplete septum, which partly separates the flow of venous and arterial blood in the heart. In the ventricle of crocodiles full partition... Thus, their heart becomes four-chambered, and the venous and arterial blood in the heart is completely separated. Two aortic arches depart from the heart: one with arterial, the other with mixed (in crocodiles - with venous) blood. Behind the heart, these vessels merge into a common dorsal aorta. From the arc with arterial blood, the carotid arteries, which carry blood to the head, and the subclavian arteries, which supply blood to the forelimbs, depart. A pulmonary artery also departs from the heart, carrying venous blood to the lungs. Oxidized blood returns to the left atrium through the pulmonary vein. Venous blood from the whole body is collected in the right atrium through two anterior and one posterior vena cava.

Nervous system... The brain is relatively larger than that of amphibians. The roof of a well-developed forebrain contains bodies of nerve cells, in contrast to amphibians, in which the cerebral vault contains only processes of nerve cells. The olfactory lobes are differentiated. The medulla oblongata forms a sharp bend, characteristic of all amniotes. The cerebellum is well developed. Parietal organ, associated with the diencephalon, is extremely well developed and has an eye structure.

Sense organs in reptiles they are diverse and well developed.

Organs of vision- eyes - differ in structure from the eyes of amphibians by the presence of striated muscles, which, when accommodated, not only moves the lens, but also changes its curvature. Reptile eyes are surrounded by centuries. There is also a third eyelid - the nictitating membrane. The exceptions are snakes and some lizards, whose eyes are covered with transparent shields. The parietal organ is covered with a transparent shield and also functions as a light-sensitive organ.

Olfactory organ located in the paired nasal cavity leading through the choanae into the oral cavity or pharynx. In lizards and snakes, the so-called Jacobson organ opens into the oral cavity. This is a chemical analyzer that receives information from the tip of the tongue, from time to time protruding from the open mouth of reptiles.

Organ of hearing represented by the inner and middle ear, in which the only auditory bone is located - the stapes. The inner ear, like all terrestrial vertebrates, is also associated with a paired organ of balance represented by a sac and three semicircular canals.

Organs of touch represented by nerve endings in the skin. However, due to the development of the stratum corneum, the skin sense of touch is rather poorly developed.

Organs of taste located in the oral cavity.

Thermosensitive organ located in snakes on the front of the head in the form of small fossae. With the help of this organ, reptiles can detect prey (small warm-blooded animals) by heat radiation.

Excretory system reptiles are represented by a pair of compact metanephric buds adjacent to the dorsal side in the pelvic region. From them, the ureters depart, flowing into the cloaca from the dorsal side. From the ventral side, the bladder flows into the cloaca. Snakes and crocodiles do not have a bladder.

Reproductive system... Reptiles are dioecious animals. For many, sexual dimorphism is characteristic. Usually males are somewhat larger than females and are more brightly colored.

In males, paired oval testes lie on the sides of the lumbar spine. Numerous tubules extend from each testicle, which unite in the vas deferens, which flows into the ureter of the corresponding side. Paired copulatory organs of a peculiar structure depart from the posterior part of the cloaca.

In females, paired lumpy ovaries also lie in the lumbar region. Paired thin-walled wide oviducts open at one end into the anterior part of the body cavity, and at the other end into the cloaca.

Autotomy. Some lizards are capable of throwing their tail in danger. At this moment, the muscles of the tail in a certain place are sharply contracted and, as a result, the vertebra breaks. The detached tail remains mobile for some time. There is practically no blood at the site of injury. After 4-7 weeks, the tail will regenerate.

Nutritional biology. Reptiles are primarily carnivores that feed on vertebrates and invertebrates. Small species mainly catch insects, and large ones also cope with large ungulates. This group includes both ambush species (chameleons, crocodiles) and active hunters (snakes, monitor lizards). Some reptiles swallow food whole (snakes), others can tear prey to pieces (crocodiles, monitor lizards). The diet of some groups of lizards (iguanas) and turtles is dominated by plant foods. There are also fish-eating species.

Reproduction biology. Mating is sometimes preceded by peculiar tournaments between males for the possession of a female. Fertilization is internal. Most reptiles lay eggs rich in yolk and covered with leathery shells. These eggs are usually placed in a substrate - heaps of humus, sun-warmed sand, where incubation takes place. Some reptiles, such as crocodiles, build special nests, which are then guarded. And the boas even "incubate" their clutch. Already formed animals emerge from the eggs. Thus, development in reptiles is direct, without metamorphosis.

Some species are ovoviviparous. These include vipers, viviparous lizards, and spindles. In this case, eggs develop in the mother's body until the formation of young animals, which are then born in the egg membranes. Those cubs that could not get out of the shells are often eaten by the mother. Ovoviviparity is characteristic of reptiles living in northern latitudes, where the sun's heat is not enough for the incubation of offspring in any substrate. Therefore, for example, a viviparous lizard gives birth to young in our region, and in central Russia and in the Jurassic it lays eggs.

Reptile fertility is limited to a few dozen eggs or cubs. Crocodiles, some snakes and lizards take care of the offspring.

Reptile lifestyle. Due to the fact that reptiles are poikilothermic animals (with variable body temperature), most of them are thermophilic. For different species, the optimum ambient temperature ranges from 12 to 45 ° C. Therefore, reptiles of the temperate zone are usually active during the day or at dusk, and in tropical climates there are many nocturnal species.

In addition, in the tropics there is no sharp change of seasons, so there are no rest periods for reptiles. And in the temperate zone, reptiles are forced to hibernate. Reptiles overwinter most often in underground shelters. Lizards and turtles usually hibernate singly or in small groups. Vipers sometimes congregate in dozens in suitable places, and ordinary snakes even in hundreds. Wintering of reptiles in our region depends on the weather and begins on average from mid-September and lasts until April-May.

In some species, for example, in the Central Asian tortoise, summer hibernation is also observed. In late May - early June, when vegetation begins to burn out in the deserts, turtles dig holes and fall into a daze. In places where vegetation does not dry out, turtles are active all summer.

Among reptiles, ecological groups can be distinguished according to their habitats.

living on solid ground (real lizards, monitor lizards, snakes, land turtles).

living in loose sands (round-headed lizards, slender boa constrictors, ephas).

underground and burrowing species (skinks, blind people).

tree and shrub species (chameleons, iguanas, geckos, snake arrows, keffiyees).

aquatic species (crocodiles, anacondas, sea and freshwater turtles, sea iguanas)

Distribution of reptiles. The species diversity and population density of certain species regularly increases from north to south. In our latitudes, there are 8 species of reptiles with a density of 1-2 to several dozen individuals per hectare. In more southern regions, these same species have a density of up to several hundred individuals per hectare.

The origin and history of reptiles. The ancestors of reptiles were primitive amphibians - stegocephals. The most primitive forms of reptiles are Seimuria and Cotylosaurus, whose fossils were found in layers dating back to the Carboniferous and Permian periods of the Paleozoic era (300-350 million years ago). The era of reptiles began 225 million years ago - in the Mesozoic era, when they reigned on land, in the sea and in the air. Among them, dinosaurs were the most diverse and numerous group. Their sizes ranged from 30-60 cm to 20-30 m, and the weight of the giants reached 50 tons. In parallel with them, the ancestors of modern groups developed. In total, there are about hundreds of thousands of extinct species. However, 65 million years ago, the era of reptiles ended, and most of their species became extinct. The causes of extinction are called planetary disasters, gradual climate change and others.

Skeletons and imprints of extinct reptiles are relatively well preserved in sedimentary rocks, thanks to which science makes it possible to restore the appearance and, in part, the biology of ancient lizards.

Meaning. Reptiles play an essential role in the biotic circulation of substances as consumers of various trophic levels. At the same time, they are mostly fed by harmful invertebrates, and in some cases even rodents. Reptiles are also a source of raw materials for the leather industry (crocodiles). Snake venom is used in medicine. A number of species are used for food. Many species are protected.

Reptiles can also be harmful in places. For example, water snakes can kill large numbers of fry. Reptiles often host nymphs and adult ixodid ticks and thus can be a reservoir of human and animal diseases (tick-borne typhus, etc.). In some countries, poisonous snakes cause serious harm, which kill thousands of people every year.

Amphibians are direct descendants of cross-finned fish. They appeared 380 million years ago and subsequently gave rise to the class of reptiles. What do amphibians look like? How do they differ from other animals and what kind of life do they lead?

Amphibian - what is it?

According to the widespread version, cross-finned fish were the first inhabitants of reservoirs that managed to go to land. Mastering a 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 denotes animals that live both on land and in water. In Russian terminology, everything is more understandable, since amphibians are amphibians.

Previously, the concept also included seals and otters, but later it began to include only four-legged vertebrates that do not belong to amniotes. The modern class of amphibians includes only salamanders, worms, newts and frogs. In total, there are from 5 to 6.7 thousand species.

Brief description of the class

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

Most amphibians do not tolerate cold weather, prefer warm and humid places, but they can also live in arid areas. When unfavorable conditions occur, they can hibernate or change the time of activity, for example, from night to day. However, some species have settled far to the north, for example, the Siberian salamander.

Amphibians settle near fresh water bodies, and the larvae sometimes lay even in deep puddles. Only a few species live in seawater. Development is usually accompanied by four stages: egg (eggs), larva, metamorphosis and adult. Salamanders also have viviparity.

All members of the class have a weak metabolism, so they cannot absorb plant foods. Amphibians are predators and feed on insects, small invertebrates, and sometimes their cousins. Large individuals eat young fish, chicks and rodents. Only the larvae of the tailless order feed on plants.

How do they look?

The external structure of amphibians is very different. The group of tailed beasts, which includes newts and salamanders, looks like lizards. They grow up to 20 centimeters. Their body is elongated and ends with a long tail. The neck, hind and forelegs are short.

Frogs are tailless amphibians. They have a wide, slightly flattened body and a short neck. The tail is present only at the tadpole stage. Their limbs are elongated and bent, straighten at the moment of jumping and swimming (the main methods of movement). The toes of frogs and salamanders are connected by a skin membrane.

Worms are amphibians of the legless squad. 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 painted in dark black or brown tones, sometimes with spots or stripes.

Structural features

The skin of these vertebrates is multi-layered, but rather thin. It contains glands that secrete mucus that covers the entire body. Breathing is partially carried out through it. On the surface, the lungs help amphibians breathe, and species that live mainly in water have gills.

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

The brain of amphibians is larger than that of fish, and ranges from 0.30% (in tailed beasts) to 0.73% (in tailless) of body weight. Their eyesight is capable of distinguishing colors. The eyes cover the transparent lower and leathery upper eyelids. They distinguish taste poorly and can only identify salty and bitter.

The skin is the main organ of touch and contains many nerve endings. In tadpoles and aquatic species, a lateral line has been preserved from fish, which is responsible for orientation in space.

In a number of tailless, the mucus on the skin contains poison. In most cases, it is not harmful to humans and serves to disinfect the surface. However, the venom of some tropical species can be dangerous. So, a small yellow frog (see photo above), a terrible leaf-eye is one of the

A pair of nostrils for breathing are located on the head. There are eyes, they can be protected for centuries. There is a mouth. The skin is bare, moist with mucus. Amphibians can breathe with their lungs and skin. Some species have gills.

The body temperature of these animals depends on the ambient temperature, so they are active only in warm weather. When the temperature drops, they immediately fall into a daze. Poisonous individuals are also found in nature.

Amphibians breed, like fish, laying eggs. Eggs are not protected by shells or skin, so amphibians usually breed in water. A larva emerges from the eggs of amphibians, which outwardly is very similar to a fish. Development further takes place in water with transformation - metamorphoses. Metamorphosis- This is a deep transformation of the structure of the body, transformation. Then, future amphibians lose their gills, some individuals even lose their tail. Then they grow limbs and go out onto land in the form of an adult animal.

Amphibians feed exclusively on mobile live food. They destroy a huge number of insects and their larvae. They are found everywhere, excluding only too cold or sultry zones of the Earth.

The most ancient and surviving to our times due to their underground way of life are legless amphibians. There are about 150 species of them in nature. These include all tropical and very many aquatic worms. These amphibians are distinguished by their unusual body structure. These amphibians have a worm-like cylindrical body. The skin is bare, supplied with mucous poisonous glands. There are transverse rings, like earthworms. Animals have no limbs and no tail. Their head is strong, small, imperceptibly passes into the body. With it, the worms are laying dungeons in the moist earth. Due to their burrowing lifestyle, their eyes were under their skin. Amphibians find food by smell and touch. They eat snails, worms, larvae, insects. They lead a very hidden lifestyle, they do not like sunlight. The most famous is the annelid worm (Fig. 2).

Rice. 2. Ringed worm ()

Unlike other amphibians, they lay eggs on land. The female curls up around a clutch of eggs and moistens it with her mucus, incubates.

The fish snake has small invisible bony scales in the skin (Fig. 3).

Rice. 3. Fish snake ()

The Central American worm does not lay eggs; live cubs are born immediately.

Science knows about 350 species tailed amphibians. These animals look like lizards, only the skin is soft and completely devoid of scales. Tritons and salamanders are tailed amphibians. These animals have an elongated, fusiform body, which imperceptibly turns into a long tail. Curling the tail to the right and left helps to move in the water. On land, amphibians move with the help of two pairs of underdeveloped limbs. The toes may be webbed and lack claws.

Sirens have only forelimbs (Fig. 4).

Amphibians, constantly living in water, breathe with gills. There is a tongue in the mouth, its shape is varied. There are small teeth. Many tailed beasts have the ability to regrow a new one when a tail or leg is lost. Amphibians cannot chew, they swallow food whole. Amphibians seize everything that moves, and do not take stationary food that is completely suitable for food. Tailless amphibians feed on insects, grabbing them in motion with a long sticky tongue. The tailed beasts feed on worms and arthropods.

Legless amphibians find food by touch or smell. They feed on insect larvae and worms.

The Siberian salamander is one of the few amphibians that is not afraid to live in permafrost conditions (Fig. 5).

Rice. 5. Siberian salamander ()

The most well-known tailed amphibian is the newt (Fig. 6). They look like little dragons. Newts love to hunt at night.

The fire salamander is famous for its bright color (fig. 7). It is interesting that the shape, size, pattern on the body of salamanders is unique for each individual.

Rice. 7. Salamander ()

The axolotl looks like an adult larva (Fig. 8).

Rice. 8. Axolotl ()

In nature, there is the most numerous detachment of amphibians - these are tailless amphibians. There are about 3 thousand of them. This is the squad most known to man. These include toads, frogs, tree frogs, toads, and garlic. Their body is short, squat. The head is wide, without a neck, passing into the body. There is no tail. The skin is bare, moisturized with secretions. There are a pair of movable eyes on the head. With the help of sight, amphibians look for prey. There is a pair of nostrils. The front legs are shorter than the hind legs. They have webbing to help you swim. On the ground, amphibians jump, they lead an active lifestyle. Small teeth and a sticky tongue that folds in the mouth help them catch prey.

The bull frog is a predator (fig. 9). She even attacks chickens and eats young ducklings. Her cry resembles the roar of a bull.

Rice. 9. Bullfrog ()

The Surinamese pipa is famous for carrying tadpoles in cells on its back (Fig. 10). From them already adult frogs appear.

Rice. 10. Surinamese pipa ()

The hairy frog defends itself with sharp claws, like a cat's (Fig. 11).

Rice. 11. Hairy frog ()

A tiny Colombian frog (Fig. 12) fits in a teaspoon, and its poison is the most powerful of all animal poisons.

Rice. 12. Colombian frog ()

Flying frogs deftly jump from trees, straightening their membranes (Fig. 13). This helps keep them in the air.

Rice. 13. Flying frogs ()

Amphibians play a big role in human life... They destroy a huge number of insects, thereby benefiting agriculture. They also eat insects, which are carriers of diseases. Also, amphibians are used in medical laboratory research. Man even breeds amphibians as a pet. In some countries, they are even eaten.

Bibliography

1. Samkova V.A., Romanova N.I. The world around us 1. - M .: Russian word.
2. Pleshakov A.A., Novitskaya M.Yu. The world around us 1. - M .: Enlightenment.
3. Gin A.A., Fire S.A., Andrzheevskaya I.Yu. The world around us 1. - M .: VITA-PRESS.

1. Worldofnature.ru ().
2. Floranimal.ru ().
3. Zoodrug.ru ().

Homework

1. Who are amphibians?
2. How do amphibians breed?
3. What three orders of amphibians are distinguished? Describe each order of amphibians.
4. * Prepare a story about the most unusual and interesting, in your opinion, representative of the Amphibian class.