Class Amphibians, or Amphibians. Amphibians

Let amphibians be not the most attractive and cute creatures. Not kittens after all, to please everyone. But among them there are also the most interesting rare individuals that are able to conquer anyone with a truly extravagant appearance. Let's get acquainted with this strange class of animals (such as neither on earth nor on water - neither yours nor ours) and learn more about the most prominent representatives.

Signs of amphibians: duplicity as a gift

Amphibians, they are also amphibians (translated from Greek means "the one that lives a double life") - these are the groups of animals that can live both on land and in water. Therefore, against the background of all other living beings, they stand out and have a number of advantages.

The main external sign of an amphibian is "nudity" (they are devoid of wool or any other heat-insulating covers). It is believed that the progenitors of amphibians were lobe-finned fish. But they themselves gave life to reptiles.

Types of amphibians: with or without a tail?

Scientists distinguish three types of amphibians by the presence and development of the tail and paws.

Anurans

They have a short body, a poorly defined neck, developed legs (the hind legs are larger and more massive than the front ones: they serve to move by jumping), of course they do not have a tail. This species includes toads, frogs, tree frogs, spadefoot, toads, and others. This is the most numerous detachment, which has about five thousand different species.

Tailed amphibians

They have a long body, which ends with a strong developed tail, but their paws are short and weak (although there are exceptions). Among the representatives of this order, the most noticeable newts, salamanders. In total, the group has about five hundred species. And just some types of salamanders stand out against the general background - they can run fast and even jump.

Legless (they are worms)

They differ in that they have neither a tail nor paws - the animals are unlucky, they seem completely helpless! Moreover, they also look very unattractive - these amphibians look like nasty worms. And from a scientific point of view, they have the most primitive structure of their kind.

Not only hypocrites, but opportunists

Animals belonging to the class of amphibians are surprisingly tenacious - they live on all continents of the globe, except for Antarctica. They are still opportunists: very salty waters, arid territories and serious cold - they have nothing to do with any difficulties! You will climb into the Himalayas - you will meet an amphibian in the mountain heights.

And if you are brought into the desert or beyond the Arctic Circle (you never know what is fanciful for the sake of entertainment), then they are here too, just like underground.

True, these are rather exceptional options. The most fertile environment for amphibians is humid, warm and satisfying (where it is easy for amphibians to find edible prey) tropical countries.

Amphibious Animals: Immortal Snow Queen

One of the rarest amphibians is the Siberian salamander. It has a unique cold resistance, which allows this amphibian to exist, in principle, in conditions uncharacteristic of the class - in the harsh north of Russia (the territory from the Urals to Kamchatka). And these are temperatures reaching 30-35 degrees below zero, and permafrost ...

It is noteworthy that these creatures can survive even in ice for several years in a row. After such seemingly frozen individuals were found by geologists, they thawed, warmed up and returned to frisky life. How can one return to life after an icy death? The fact is that during frost, the water in the cells of this amphibian turns into glycerin, which protects them from certain death.

Rare amphibians: the frog that doesn't croak

But in the lowlands of the British mountains lives a kind of frog, called chicken. In addition to being one of the largest frog species in the world (reaching 21 centimeters), its meat also has an exceptional taste.

Actually, for this, a green amphibian of peculiar beauty was called that. True, only criminal wealthy gourmets can now afford such a delicacy, because it is under the protection of the country as a species on the verge of extinction.

The fish that walks

Either a fish or a reptile - a very strange creature! Another unique class of amphibians with awesome names is a water monster, a walking fish, and in science, an axolotl. He, too, can boast of unbanal beauty and strange qualities of survival.

The most remarkable of them is that these amphibians reach sexual maturity without passing into the adult stage, but remaining a larva, sometimes even for life. They, as befits amphibians, can live both on land and in water. But often they do not “work” on the development of the lungs, like other amphibians, but live in water spaces, but without the scales that fish rely on.

Take it, tell your friends!

general characteristics

Skin

All amphibians have smooth thin skin, relatively easily permeable to liquids and gases. The structure of the skin is characteristic of vertebrates: a multilayered epidermis and the skin itself (corium) stand out. The skin is rich in skin glands that secrete mucus. In some, the mucus may be poisonous or facilitate gas exchange. The skin is an additional organ for gas exchange and is supplied with a dense network of capillaries.

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

Skeleton

The body is divided into head, trunk, tail (for caudates) and five-fingered limbs. The head is movably connected to the body. The skeleton is divided into sections:

axial skeleton (spine);
head skeleton (skull);
paired limb skeleton.

skin-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 skin-pulmonary arteries that carry blood to the respiratory organs (lungs and skin); From the lungs, oxygenated blood is collected into the paired pulmonary veins that empty into the left atrium.

The systemic circulation begins with the aortic arches and carotid arteries, which branch in organs and tissues. Venous blood flows through the paired anterior vena cava and unpaired posterior vena cava into 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 metabolic rate, and therefore they are cold-blooded animals.

Digestive organs

All amphibians feed only on moving prey. At the bottom of the oropharyngeal cavity is the tongue. In anurans, it is attached to the lower jaws with its front end, when catching insects, the tongue is thrown out of the mouth, prey sticks to it. The jaws have teeth that serve only to hold 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 occurs 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;
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 department is the middle ear. The external auditory opening is closed by the tympanic membrane, connected to the auditory bone - the stirrup. The stirrup rests against the oval window leading to the cavity of the inner ear, transmitting to it the vibrations of the tympanic membrane. To equalize 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 tactile nerve endings. Aquatic representatives and tadpoles have lateral line organs.

Sex organs

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

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

Lifestyle

Most spend their lives in humid places, alternating between land and water, but there are some purely aquatic species, as well as species that spend their lives exclusively on trees. Insufficient adaptability of amphibians to living in a terrestrial environment causes drastic changes in their lifestyle due to seasonal changes in living conditions. Amphibians are able to hibernate for a long time under adverse conditions (cold, drought, etc.). In some species, activity can change from nocturnal to diurnal as temperatures drop at night. Amphibians are active only in warm conditions. At a temperature of +7 - +8 ° C, most species fall into a stupor, and at -1 ° C they die. But some amphibians are able to endure 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 favorable for them in principle, but which they cannot reach on their own.

Food

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 may include juvenile fish, and the largest may prey on chicks of waterfowl and small rodents that have fallen into the water.

The nature of the nutrition of the larvae of tailed amphibians is almost similar to the nutrition of adult animals. Tailless larvae have a fundamental difference, feeding on plant food and detritus, turning to predation only at the end of the larval stage.

reproduction

A common feature of the reproduction of almost all amphibians is their attachment during this period to the water, where they lay their eggs and where the larvae develop. Amphibians breed in shallow, well-warmed areas of water bodies. On warm spring evenings, at the end of April and in May, loud croaking sounds are heard from the ponds. These "concerts" are arranged 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. Poison, which is secreted by the skin glands of amphibians, contains substances that kill bacteria (bactericides). In most amphibians in Russia, the poison is completely harmless to humans. However, many tropical frogs are not so safe.

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

Amphibians and people: 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 caecilians - about 60 species.

Evolution

In evolutionary terms, amphibians descended from ancient lobe-finned fish and gave rise to representatives of the reptile class. The most primitive order of amphibians are caudate. Tailed amphibians are most similar to the most ancient representatives of the class. More specialized groups are the anurans and the legless.

There is still debate about the origin of amphibians, and according to the latest data, amphibians descend from ancient lobe-finned fish, specifically, from the order of ripidistia. In terms of the structure of the limbs and skull, these fish are close to fossil amphibians (stegocephals), which are considered the ancestors of modern amphibians. Ichthyostegids are considered the most archaic group, 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

The appearance of a five-fingered limb.
Lung development.
The presence of a three-chambered heart.
Formation of the middle ear.
The appearance of two circles of blood circulation

Notes

Amphibian Species of the World. Amphibian database. Darrel Frost and The American Museum of Natural History. archived
Class Amphibians, or Amphibians: general characteristics. Biology and medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
Classis AMPHIBIA (L. Ya. Borkin, 1992) . Archived from the original on June 22, 2012. Retrieved March 13, 2012.
// Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
Workshop on vertebrate zoology. An autopsy of an amphibian. Archived from the original on August 4, 2012. Retrieved 16 July 2012.
Nikitenko, 1969 The brain of amphibians. Biology and medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
Why are they ... water? . Zooclub. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
Alexander Markov How Amphibians Learned to Transform (January 24, 2008). Archived from the original on June 22, 2012. Retrieved March 13, 2012.
Amphibian nutrition. Biologists and medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
Digestive system of amphibians. Biology and medicine. Archived from the original on June 22, 2012. Retrieved March 13, 2012.
Poisonous evolution. Magazine "Around the World". Archived from the original on June 22, 2012. Retrieved March 13, 2012.

Amphibians, or Amphibians, are the first group of vertebrates that have mastered the terrestrial environment, but retained a close relationship with the aquatic one.

Origin of amphibians

In the middle of the Devonian period (about 385 million years ago), conditions favorable for the mass development of land by vertebrates formed on Earth:

warm and humid climate;
the presence of a sufficient food base (formed abundant fauna of terrestrial invertebrates);
a decrease in the oxygen content in water (it was spent on the oxidation of a large amount of organic matter in water bodies): the appearance in fish of adaptations for breathing atmospheric air.

Basic aromorphoses:

five-fingered limbs for movement on land;
pulmonary respiration.

The ancestors of ancient amphibians, most likely, were the ancient, now extinct lobe-finned fish (ripidistia).

One of the most "advanced" lobe-finned fish was tiktaalik ("fishfoot"), which had a number of transitional features that bring it closer to amphibians:

shortened skull;
relatively mobile head;
the presence of the elbow and shoulder joints.

Tiktaalik breathed through holes located at the end of a flat "crocodile" muzzle.

Ichthyostegidae- the first amphibians that appeared in fresh water at the end of the Devonian. They were real transitional forms between lobe-finned fish and amphibians:

vestiges of gill cover;
fish tail;
fish scales;
paired five-fingered limbs of terrestrial vertebrates.

Ichthyostegids lived not only in water, but also on land. It can be assumed that they not only reproduced, but also fed in the water, systematically crawling out onto land.

Stegocephalians (shell-headed) appeared during the dry Devonian period. They had a solid shell of skin bones that covered the cranium from above and from the sides. The shell protected them from drying out, but prevented skin respiration and made it difficult to move on land.

Stegocephalians survived until the beginning of the Mesozoic. Modern detachments of amphibians are formed only at the end of the Mesozoic.

General characteristics of the class Amphibians

They are ubiquitous, but most widely found in regions with a warm and humid climate.

They live near water bodies: they breed in water.

The body is divided into the head, trunk and two pairs of five-fingered limbs. A small group of amphibians have a tail.

The skin is thin, naked, moist, rich in mucous glands.

amphibian skeleton

The head is movably connected to the body.

The skeleton is divided into sections: axial skeleton (spine); head skeleton (skull); paired limb skeleton.

There are 4 sections in the spine: cervical, trunk, sacral and caudal. The number of vertebrae varies from 7 in anurans to 200 in legless amphibians.

In all amphibians, a single cervical vertebra is movably attached to the occipital region of the skull, which provides some head mobility.

Short ribs are attached to the trunk vertebrae (except for anurans, in which they are absent).

There is no chest.

The only sacral vertebra is connected to the pelvic girdle.

In anurans, the vertebrae of the caudal region fuse into one bone - urostyle.

The flat and wide skull protects the brain and is connected to the spine by the occipital bones.

The limb skeleton is formed by the skeleton of the limb girdle and the skeleton of the free limbs. Shoulder girdle: paired shoulder blades, clavicles and crow bones connected to the sternum.

Skeleton of the forelimbs: shoulder (humerus), forearm (radius and ulna) and hand (carpus, metacarpus and phalanges of the fingers).

Pelvic girdle: fused paired iliac, ischial and pubic bones.

Skeleton of the hind limbs: thigh, lower leg (tibia and fibula) and foot (tarsus, metatarsus and phalanges). In anurans, the bones of the forearm and lower leg merge, all the bones of the hind limb are greatly elongated, forming powerful levers for jumping.

frog skeleton

The internal structure of amphibians

Nervous system: the forebrain of amphibians is more developed than that of fish, and is divided into two hemispheres. The cerebellum is developed worse due to low mobility.
Sense organs. The eyes of amphibians are protected from drying out and clogging by movable upper and lower eyelids and a nictitating membrane. The cornea has acquired a convex shape, and the lens - lenticular. Amphibians see mostly moving objects.
The middle ear with one auditory ossicle (stapes) appeared in the organ of hearing. The middle ear cavity is separated from the environment by the tympanic membrane and connected to the oral cavity through a narrow canal - eustachian tube, due to which the internal and external pressure on the eardrum is balanced. The appearance of the middle ear is caused by the need to amplify the perceived sound vibrations, since the density of the air medium is less than that of water.
The nostrils of amphibians, unlike fish, are through and lined with sensitive epithelium that perceives odors.
Circulatory system: closed. Two circles of blood circulation: large (trunk) and small (pulmonary). Three-chambered heart: two atria, one ventricle. Mixed blood flows through the arteries of the systemic circulation, and only the brain is supplied with arterial blood. cold-blooded (poikilothermic). The larvae have one circle of blood circulation and a two-chambered heart (like fish).

blood circulation of amphibians

The pulmonary circulation begins in the ventricle, includes the vessels of the lungs and ends in the left atrium. A large circle also begins in the ventricle. Blood, having passed through the vessels of the whole body, returns to the right atrium. Thus, arterial blood from the lungs enters the left atrium, and venous blood from the whole body enters the right atrium. Arterial blood flowing from the skin also enters the right atrium. So, thanks to the appearance of the pulmonary circulation, arterial blood also enters the heart of amphibians. Despite the fact that arterial and venous blood enters the ventricle, complete mixing of the blood does not occur due to the presence of pockets and incomplete septa. Thanks to them, when leaving the ventricle, arterial blood flows through the carotid arteries to the head section, venous blood to the lungs and skin, and mixed blood to all other organs of the body. Thus, in amphibians there is no complete division of blood in the ventricle, therefore the intensity of life processes is low, and the body temperature is unstable.
The respiratory organs of adult animals are skin and lungs, in larvae - gills.
amphibian breathing

The lungs are paired hollow sacs with a cellular inner surface penetrated by a network of blood capillaries, where gas exchange occurs.
The mechanism of respiration in amphibians is imperfect, of the forced type. The animal draws air into the oropharyngeal cavity, for which it lowers the bottom of the oral cavity and opens the nostrils. Then the nostrils are closed with valves, the floor of the mouth rises, and air is forced into the lungs. The removal of air from the lungs occurs due to the contraction of the pectoral muscles. The surface of the lungs in amphibians is small, less than the surface of the skin. Therefore, oxygenation of the blood occurs not only through the lungs, but also through the skin. So, the pond frog receives 51% of oxygen through the skin. While under water, amphibians breathe exclusively through their skin. In order for the skin to function as a respiratory organ in terrestrial conditions, it must be moist.
Digestive system. Amphibians are predators.
The appearance of a real tongue in the oral cavity, the main organ of food extraction, is associated with the terrestrial way of life. In frogs, it is attached to the anterior part of the bottom of the oral cavity and is able to quickly move forward, gluing prey.
Salivary glands appear (absent in fish), the secret of which moisturizes the oral cavity, tongue and food.
The last section of the alimentary canal - an expanded cloaca - is common to the digestive, excretory and reproductive systems.

Rice. The internal structure of a frog
Excretory system: paired trunk kidneys. Urine flows through the two ureters into the cloaca, and from it into the bladder. The excreted end product of nitrogen metabolism is urea. After filling the bladder, its muscular walls contract, urine is excreted into the cloaca and thrown out. Losses of water from the body of amphibians with urine, as well as in fish, are replenished by its intake through the skin.
Reproductive system: dioecious.
Sex glands are paired. In females: paired ovaries and paired oviducts flowing into the cloaca. In males: paired testes and paired vas deferens that empty into the ureters.
Fertilization is external, in water.
Reproduction: Amphibians, like fish, lay eggs. Amphibian eggs do not have shells that protect them from drying out, and are able to develop only in water.
Development with incomplete metamorphosis, with the stage of a fish-like larva - tadpole. The tadpole is a typical aquatic animal: it breathes with gills, has a two-chambered heart, one circle of blood circulation and a lateral line organ, swims with a tail bordered by a membrane. During metamorphosis, larval organs are replaced by organs of an adult animal.

Rice. Frog metamorphosis

Some species, such as ambistoma, remain in the larval state all their lives, in which they reproduce.

Neoteny- the ability to reproduce at the larval stage of development.

Diversity of amphibians and their importance

Class Amphibians, or Amphibians

Order Tailless amphibians

Representatives: toads, spadeworts, krestovki, toads, tree frogs and frogs.

Anurans have a wide tailless body with a very short neck, short forelimbs and long hind limbs.

Order Tailed amphibians

Representatives: salamanders, newts, salamanders, frogtooths, ambistomes, proteas.

Tailed have an elongated body with a rather long tail, a small head and four approximately identical long limbs. In some tailed amphibians, the limbs are disproportionately small or so reduced that they lose their supporting function.

Order Legless amphibians

Representatives: worms.

Legless amphibians are characterized by a legless serpentine body, usually with transverse intercepts resembling worm segments.

The head has a pair of nostrils for breathing. There are eyes, they can be protected by eyelids. There is a mouth. The skin is bare, moistened with mucus. Amphibians can breathe with their lungs as well as with their 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 stupor. Meet in nature and poisonous individuals.

Amphibians reproduce like fish by laying eggs. The eggs are not protected by shells or skin, so amphibians usually breed in water. From the eggs of amphibians, a larva emerges, which looks very similar to a fish. Further development 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 their tail. Then they grow limbs and go to land in the form of an adult animal.

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

The most ancient and survived to our times due to their underground lifestyle 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 naked, equipped with mucous poisonous glands. There are transverse rings, like earthworms. Animals do not have limbs or a tail. Their head is strong, small, imperceptibly passes into the body. With it, the worms lay their dungeons in the damp earth. In connection with the burrowing lifestyle, the eyes were under their skin. Amphibians find food using their sense of smell and touch. They eat snails, worms, larvae, insects. They lead a very hidden lifestyle, do not like sunlight. The most famous is the ringed worm (Fig. 2).

Rice. 2. Ringed worm ()

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

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

Rice. 3. Fish snake ()

The Central American worm does not lay eggs, it immediately gives birth to live cubs.

Science knows about 350 species tailed amphibians. These animals look like lizards, only the skin is soft and completely devoid of scales. Tailed amphibians include newts, salamanders. These animals have an elongated spindle-shaped body, which imperceptibly passes into a long tail. Curving 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 fingers may be webbed and devoid of 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 diverse. There are small teeth. Many caudates have the ability to grow a new one if they lose a tail or leg. Amphibians do not know how to chew, they swallow food whole. Amphibians grab everything that moves and do not take completely edible motionless food. Tailless amphibians feed on insects, grabbing them in motion with a long sticky tongue. Tailed birds feed on worms and arthropods.

Legless amphibians find food by touch or use the sense of 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 triton (Fig. 6). They look like little dragons. Tritons 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 species of them. This is the most famous group of people. These include toads, frogs, tree frogs, toads, and spadefoot. Their body is short and squat. The head is wide, without a neck, passes into the body. There is no tail. The skin is bare, moisturized with secrets. On the head are a pair of movable eyes. Amphibians use their eyesight to find prey. There are a pair of nostrils. The forelimbs are shorter than the hind ones. They have membranes that help them 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 bullfrog 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 Surinam pipa is famous for carrying tadpoles in cells on its back (Fig. 10). Adult frogs emerge from them.

Rice. 10. Surinam pipa ()

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

Rice. 11. Hairy frog ()

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

Rice. 12. Colombian frog ()

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

Rice. 13. Flying frogs ()

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

Bibliography

Samkova V.A., Romanova N.I. The world around 1. - M .: Russian word.
Pleshakov A.A., Novitskaya M.Yu. The world around 1. - M .: Education.
Gin A.A., Faer S.A., Andrzheevskaya I.Yu. The world around 1. - M .: VITA-PRESS.

Worldofnature.ru ().
Floranimal.ru ().
Zoodrug.ru ().

Homework

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

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

Amphibian - what is it?

According to a common version, the lobe-finned fish were the first inhabitants of the reservoirs who 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 refers to animals that live both on land and in water. In Russian terminology, everything is more clear, since amphibians are amphibians.

Previously, the concept also included seals and otters, but later it began to include only four-legged vertebrates, which do not belong to amniotes. The modern class of amphibians includes only salamanders, caecilians, 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 in most occurs in the water, and growing up, they lead a terrestrial lifestyle. Some species live only in water.

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

Amphibians settle near fresh water bodies, and sometimes the larvae are laid even in deep puddles. Only a few species live in sea water. Development, as a rule, is accompanied by four stages: egg (caviar), larva, metamorphosis and adult. Salamanders also have live birth.

All representatives 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 own brethren. Large individuals eat young fish, chicks and rodents. Plants feed only on the larvae of the anurans order.

How do they look?

The external structure of amphibians is very different. The caudate group, which includes newts and salamanders, resembles lizards in appearance. They grow up to 20 centimeters. Their body is elongated and ends with a long tail. The neck, hind and forelimbs are short.

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

Worms are amphibians of the "legless" order. Outwardly, they look like worms or snakes. Their sizes range from ten centimeters to a meter. Worms have no limbs, and the tail is shortened. Their body is covered with calcareous scales and is colored 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. Through it, breathing is partially carried out. On the surface, amphibians use lungs to breathe, while species that live primarily in water have gills.

The heart of amphibians is three-chambered, two chambers are observed only in salamanders. There are two circulation circles: small and large. Body temperature is not constant and depends on the external environment.

The brain of amphibians is larger than that of fish, and ranges from 0.30% (in caudates) to 0.73% (in anurans) of body weight. Their vision is able to distinguish colors. The eyes are covered with a transparent lower and leathery upper eyelids. They distinguish taste poorly and can only determine 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 anurans, the mucus 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, a small yellow frog (see photo above) terrible leaf-eye is one of