And the suborder of earthworms (Haplotaxida). Its body consists of ring-shaped segments, the number of which can reach 320! These animals are widespread in all corners of our planet. They are not found only in Antarctica. Very often children are interested in how they move earthworms. In our article, we will analyze this issue in detail, and at the same time learn about their appearance, lifestyle and method of reproduction.

Lifestyle of earthworms

If in the morning or after rain you walk through the garden, then, as a rule, you can see small piles of soil thrown out by worms on the ground, and you can see them in the puddles. Due to the fact that these individuals crawl out to the surface of the earth after rain, such a name was assigned to them. (the photo above shows this invertebrate animal) also creeps out to the earth's surface at night. As a rule, it prefers humus-rich soil, so it is rarely found in sandstones. Dislikes earthworm and swampy soils. These features are explained physiological features Lumbricidae. The fact is that worms breathe the entire surface of their body, covered with a mucous epidermis. Too little air is dissolved in moisture-saturated soil. As a result, the earthworm suffocates there. By the way, this explains his behavior during the rain. Dry soil is also detrimental to representatives of Haplotaxida: their skin dries up and breathing stops. in wet and warm weather earthworms (the photo below shows the Lumbricidae in all their "glory") stay close to the surface of the earth. With a decrease in temperature, as well as with the onset of a dry period, they crawl into the deep layers of the soil.

earthworms

Adults reach 30 centimeters in length, although there are individual specimens of larger sizes. Body earthworm slippery, smooth, has a cylindrical shape, consists of segments - piece rings. Such a constitution is explained by the way of life of Lumbricidae: such a structure facilitates the process of movement in the soil. The number of piece rings reaches two hundred. The surface of the body, which could conditionally be called the back, is convex, the ventral surface is flat and lighter. On the body of the earthworm, where its front end ends, there is a thickening, which is called the girdle. It contains special glands that secrete a sticky liquid. During reproduction, an egg cocoon is formed from the girdle, eggs develop in it.

How do earthworms move?

Representatives of Haplotaxida crawl. First, they stretch the front end of their body and cling to bumps with special bristles, which are located on the ventral side of the rings. earth's surface. After this, muscle contraction occurs, and the back is pulled forward. The movement of the worm in the ground is characterized by the fact that it makes passages in the soil. At the same time, with the pointed end of the body, he pushes the earth apart, and then squeezes between its particles. It is also interesting how earthworms move in more dense layers. In the process of movement, they swallow the earth and pass it through the intestines. As a rule, worms swallow the soil at a considerable depth, and throw it out through the anus already at the top, near their own mink. It can often be observed in the summer on the surface of the earth in the form of lumps and elongated "laces".

Earthworm and its biology

Worms have well-developed muscles, thanks to which such a method of movement became possible. Their muscles are located under the epidermis, in fact, together with the skin, they form a kind of skin-muscle bag. Musculature is located in two layers. Directly under the epidermis are the circular muscles, and below them is a second, thicker longitudinal layer (consists of contractile long fibers). When the longitudinal muscles are compressed, the body of the earthworm becomes thicker and shorter. With a contraction of the circular muscles, on the contrary, it is long and thin. Alternate contraction of both layers of muscles, carried out under the influence of the nervous system branching in the muscle tissue, determines the movement of Lumbricidae.

The movement of worms is greatly facilitated by the presence of small bristles on the lower part of the body. You can feel them if you run a wet finger along the abdomen of the worm from the back to the front end. Thanks to these bristles, earthworms not only move in the soil, but also “grab” the ground when they are pulled out. They also help to rise and fall along the already made earthen passages. At this point, we will finish dealing with the question of how earthworms move, and move on to at least interesting facts about the life of the Lumbricidae.

Circulatory system

It consists of two longitudinal vessels - the abdominal and dorsal, as well as the branches connecting them. Due to muscle contraction of the walls, blood moves throughout the body. The blood of earthworms is scarlet. With its help, a connection is established between the internal organs, and metabolism is also carried out. As the blood circulates, it carries nutrients from digestive organs, as well as oxygen from the skin. At the same time, carbon dioxide is removed from the tissues. In addition, the blood removes unnecessary and harmful compounds into the excretory organs.

Earthworm nutrition

The basis of nutrition of representatives of Haplotaxida is half-decayed remains of plants. As a rule, at night, earthworms drag leaves, stems, etc. into their holes. In addition, they can pass humus-rich soil through their intestines.

Irritation of earthworms

Special earthworms do not have. They perceive external stimuli through the nervous system. Worms have a highly developed sense of touch. The nerve cells responsible for this are located over the entire surface of the skin. The sensitivity of earthworms is so great that the slightest fluctuations in the soil cause them to possible speed hide in burrows or in deeper layers of the earth. However, the significance of sensitive nerve endings is not limited to the function of touch. Scientists have found that with the help of these cells, earthworms are able to sense the rays of light. So, if a beam of a flashlight is directed at a worm at night, then it will hide in a safe place with great speed.

The response of animals to any irritation, carried out thanks to the nervous system, is called a reflex. It is customary to distinguish between different kinds of reflexes. Thus, contraction of the body of an earthworm from touching it, as well as its movement in sudden illumination, is a protective function. This is the defensive reflex. Experiments of scientists have shown that earthworms can smell. They use their sense of smell to find food.

reproduction

Earthworms reproduce sexually, although protostomes are generally hermaphrodites. Each representative of Haplotaxida has male organs, which are called testes (they develop spermatozoa), as well as female organs called ovaries (they produce eggs). The earthworm lays its eggs in a slimy cocoon. It is formed from a substance that is released through the girdle. Further, the cocoon in the form of a clutch slides off the body and is pulled together at the ends. It remains in the ground until the young worms come out of it. The cocoon serves to protect the eggs from moisture and other adverse effects.

What are worms for?

This section will be useful for those who think that earthworms are needed only for fishing. Of course, a fisherman without them has nothing to do without them on the river, but this is not the whole benefit of representatives of Lumbricidae. The role of the earthworm in nature is so great that it is impossible to overestimate it. They contribute to the decomposition of organic matter in the soil. In addition, earthworms enrich the earth with the most valuable fertilizer - humus. They are also a kind of indicator: if the soil contains a lot of worms, then it is fertile.

A complete understanding of the role of Haplotaxida has come to mankind relatively recently. However, even now, many farmers prefer to use chemical fertilizers, despite the fact that they kill all living things. Today, chemicals have found an alternative - vermicompost and biohumus. Essentially, this Magic wand for the earth, because they contain a large number of phosphorus, potassium, nitrogen, that is, precisely those substances that are vital for plants for their full growth.

Conclusion

Earthworms are the most important link in soil formation. Let's look at the process. In autumn, leaves fall from the trees and cover the entire surface of the earth. Immediately after that, they get down to business and decompose the leaves to the compost stage. And then the baton is picked up by worms, which process the foliage to the stage of vermicompost. Thus, the most valuable fertilizers get into the soil.

earthworms, they are earthworms, this is far from one species, but a whole suborder of the class Small-bristle worms, belonging to the type Annelids. The earthworm is characterized by most of the structural features of its type and class.

Earthworms are ubiquitous. More than a dozen live in our area. similar friend on another species (European earthworms), whose body length is 10-20 cm, the number of segments is 100-180. At the same time, the Australian earthworm can reach a length of 3 meters.

During the day, earthworms crawl in the soil. At night and after rain they can come to the surface. With the onset of cold weather, they go underground, to a depth of 2 m. The back of the body is slightly flattened. When crawling out of the soil, the worm holds on to the edge of the mink with its hind end.

The body of an earthworm, as a representative of annelids, is divided into segments by annular constrictions. As in all oligochaetes, the parapodia are reduced, only tufts of setae have been preserved from them, which allow the worm to cling, rest against the ground and facilitate pushing the body forward. In other words, the bristles provide adhesion to the substrate.

The surface of the body is moist, covered with mucus, which facilitates movement in the soil, and also facilitates the penetration of oxygen into the body.

The epithelium secretes a layer of transparent cuticle, it also contains many mucous cells. Under the epithelium are circular and longitudinal muscles. The body of an earthworm can contract and lengthen. The circular muscles make the body of the worm thin and long, the longitudinal muscles shorten and thicken. The longitudinal layer of muscles is more powerful. Alternate contraction of these muscles provides locomotion. Each segment can change its shape separately.

The coelomic sacs of neighboring segments communicate with each other, thus, the liquid in them is mixed.

An earthworm often swallows the soil, eating its own way. Nutrient particles are absorbed from the soil in the intestines. If the soil is soft, then it drills with its front end. First, the front end is stretched and thinned, pushed between the lumps of soil. After the front end thickens, as a result, the soil moves apart. Next, the worm pulls up the back of the body.

They feed on decaying plant debris. In addition, fallen leaves can be dragged from the surface. By dragging plant residues into the soil, worms contribute to their decomposition and the formation of fertile soil.

The digestive system consists of the mouth, pharynx, esophagus, goiter, muscular stomach, middle and hindgut, anus. Swallowing food is produced by the muscular pharynx. The stomach grinds food, in addition to the muscles of the walls, swallowed grains of sand participate in this. From the side of the back, the wall of the middle intestine forms an invagination that increases the suction surface. The midgut is lined with ciliated epithelium, in which there are many unicellular glands. It breaks down complex organic substances, absorbs more simple substances. In the walls of the midgut of the earthworm there is a dense network of blood vessels. The hindgut is small, ending in the anus.

A feature of earthworms are calcareous glands, whose ducts empty into the esophagus. Substances released by them neutralize the acids contained in the soil.

Breathing is carried out by the entire surface of the skin. In the superficial layers of the body wall there is a dense network of blood vessels. When it rains, earthworms come to the surface due to lack of air in the soil.

The circulatory, nervous, and excretory systems are similar to polychaete. However, in the circulatory system there are so-called "hearts" - annular vessels capable of muscular contraction. Located in 7-13 segments. A number of species have annular vessels only in the anterior part of the body.

In the anterior three segments, there are no metanephridia (organs of excretion of annelids).

The sense organs are poorly developed. In the skin there are sensitive cells - organs of touch. Also in the skin there are cells that perceive the degree of illumination.

Earthworms are hermaphrodites. The reproductive system is located in several segments of the anterior part of the body. The testicles are in front of the ovaries.

Fertilization is mutual cross. Each of the mating worms transfers spermatozoa to the partner's seminal receptacle.

In the first third of the body of earthworms there is a special belt, its glandular cells secrete mucus, which, when dried, forms a clutch. Unfertilized eggs are laid in it. After mating, spermatozoa enter here from the spermatozoa. Fertilization takes place. After that, the clutch slips off the body of the worm and turns into a cocoon. The eggs develop into small worms.

Capable of regeneration. If a predator tears off part of the worm's body, then the other half completes the missing part. If the worm is divided into two parts, then two individuals will be obtained, which can be considered asexual reproduction. However, the earthworm itself does not reproduce in this way.

Earthworm belongs to the group of annelids. It does not have any special organs designed specifically for gas exchange, and gas exchange occurs by diffusion through the entire surface of the body. In essence, they do not need specialized organs, since, due to the cylindrical shape of the body, their surface area to volume ratio is large, and with their relatively low activity, they do not consume so much oxygen.

However, in annelids available circulatory system(unlike some simpler animals and unicellular organisms), and the respiratory pigment hemoglobin is dissolved in their blood. Contractions of large blood vessels drive the blood along with the gases dissolved in it throughout the body; this also contributes to the maintenance of steep diffusion gradients.

Thin skin of an earthworm(cuticle) is constantly moistened by the secretion of the glands located in the epithelium. Capillaries are located in the epithelium directly under the cuticle. The distance between the blood vessels and the surface of the body is small and this ensures the rapid diffusion of oxygen into the blood. Earthworms are practically not protected from drying out and therefore try to stay only in a humid environment.

Respiratory system of insects - locusts.

In insects, gas exchange carried out through a system of tubes, the so-called trachea. Such a system allows oxygen to flow from the air directly to the tissues and there is no need to transport it through the blood. It's much more fast way than the diffusion of dissolved oxygen through tissues; such gas exchange creates conditions for a high metabolic rate.

spiracles- paired openings on the second and third thoracic and on the first eight abdominal segments of the insect's body lead to the air cavities. Branched tubes - tracheas - depart from these cavities. Each trachea is lined with epithelium secreting a thin layer of chitinous material. Usually this rigid layer is further reinforced by spiral and annular thickenings, due to which the airways remain open, even if the pressure in the lumen of the trachea is negative (compare with the cartilaginous rings in the human trachea and bronchi). In each segment of the body, the tracheae branch into numerous smaller tubes called tracheoles; tracheoles also branch, penetrating the tissues of the insect, and in the most active tissues, for example, in the flying muscles, they end blindly inside individual cells. The degree of branching of the tracheoles can vary depending on the metabolic needs of the tissues.

chitin lining in tracheoles absent. At rest, they are filled with a watery fluid; at this time, oxygen diffuses through them to the tissues (and CO 2 - in the opposite direction) at a rate that is quite sufficient to satisfy the needs of the insect. In the active state, increased metabolic activity of the muscles leads to the accumulation of certain metabolites, in particular lactic acid, and the osmotic pressure in the tissues increases accordingly. When this happens, the fluid from the tracheoles is partially absorbed into the tissues by osmotic forces, and more air enters the tracheoles, and therefore more oxygen, and this oxygen is supplied directly to the tissues just when they need it.

The total flow of air passing through the body of an insect is regulated by a mechanism closing spiracles. The opening of each spiracle is equipped with a system of valves controlled by very small muscles. The edges of this opening are covered with hairs, which prevent foreign particles from entering the spiracles and prevent excessive loss of moisture. The size of the hole is adjusted depending on the amount of CO 2 in the body of the insect.

Increased activity leads to increased formation of CO 2 . Chemoreceptors catch it and the spiracles open. The same stimulus can also cause ventilation movements of the body, especially in large insects such as locusts. Dorsoventral muscles, contracting, make the body of the insect flatter, as a result of which the volume of the tracheal system decreases and air is pushed out of it (“exhalation”). The suction of air (“inhalation”) occurs passively, when the segments of the body, due to their elasticity, take their original shape.

According to some data, thoracic and abdominal spiracles open and close alternately, and this, combined with the ventilation movements of the body, creates a unidirectional airflow that enters the body of the insect through the thoracic region and exits through the abdominal region.

Tracheal system, of course, is very effective in terms of gas exchange, however, it should be borne in mind that gas exchange is determined in most insects solely by the diffusion of oxygen through the tissues of the insect. Diffusion, on the other hand, is known to be effective only at short distances, and this imposes severe limits on the size that insects can reach. These small distances, at which diffusion is sufficiently effective, do not exceed 1 cm; therefore, although insects up to 30 cm long are found, their body should not be more than 2 cm thick.

Earthworm – Lumbricus terrestris(type Annelids, class Small-bristle worms, Lumbricidae family) lives in moist, humus-rich soil. It feeds on organic matter, passing earth with plant debris through the intestines. Even C. Darwin noted the beneficial effect of earthworms on soil fertility. Dragging the remains of plants into the mink, they enrich it with humus. Laying passages in the soil, they contribute to the penetration of air and water to the roots of plants.

Earthworms are active in the warm season. In winter they hibernate. Freezing kills worms instantly, so they must burrow deeper into the ground where low temperatures do not penetrate. In the spring, when the temperature reaches a suitable value and the ground is saturated with rainwater, they have a mating season. They reproduce very quickly, producing about a hundred young worms a year. In summer, the worms are not so active. Food - dying plant residues - is very scarce at this time, and the soil is devoid of moisture, which can cause the death of worms. autumn period again characterized by worm activity. At this time, the reproduction of offspring begins again, which lasts until the onset of winter.

Earthworms live relatively long lives. Some manage to live for about ten years if they do not become victims of birds and moles. Another threat to their lives is the pesticides so widely used in horticulture today.

So, the Earthworm has an elongated, cylindrical body from 10 to 30 cm long. dorsal side more rounded, it is darker, a dorsal blood vessel shines through its skin. Abdominal side somewhat flattened and lighter colored. The anterior end of the body is thicker and darker colored. The body is made up of rings segments. In an adult worm, their number reaches 200. In the area of ​​\u200b\u200b32-37 body segments there is belt rich in mucous glands. External segmentation corresponds to the division of the body cavity by partitions into separate chambers and the segment-by-segment (i.e., in each segment) arrangement of the row internal organs. On each segment 8 bristles(they are easy to detect if you run your finger along the body of the worm in the direction from the rear end of the body to the front). The setae are arranged in four pairs on the lateral sides of the segments. Clinging to the unevenness of the soil with them, the worm moves forward with the help of the muscles of the skin-muscular sac.

Covers. The body of an earthworm is covered skin-muscle sac. He is educated cuticle, single layer epithelium and two layers of muscles - external ring and internal longitudinal. The skin epithelium of the worm is rich mucous glands that produce slime covering the entire body of the worm and protecting it from drying out. The mucus also makes it easier to crawl in burrows by reducing friction on the soil.

Earthworm movement. When the worm crawls, waves of muscle contractions run through its body, and both the length and thickness of individual sections of its body are constantly changing. The movements produced by each part of the body consist in the fact that the segments that make it up are sometimes stretched and at the same time become thinner, then they contract and become thicker. As a result of such alternating extensions and contractions, the worm gradually moves forward: first, its head end is pulled forward, and then the posterior segments of the body are gradually pulled towards it; after that, the rear end of the body remains in place, and the head end sticks out even further forward, and thus the further advancement of the worm continues (it is convenient to observe it by letting the worm crawl along the paper spread out on the table).

body cavity. Inside the skin-muscular sac in annelids is located secondary body cavity, or in general. This body cavity is not limited by muscles, as in roundworms, but has its own epithelial(coelomic) pavement, i.e. inner side longitudinal muscles is lined with epithelium of mesodermal origin, and there is also an epithelial lining on the side of the intestine lying in the body cavity. Due to the coelomic epithelium, internal two-layer transverse partitions are formed between the segments - dissipations. The secondary cavity is divided into chambers, each segment contains a pair of coelomic sacs. The coelomic fluid is under pressure and plays a role hydroskeleton, so the worm is elastic to the touch.

Digestive system comprises front, middle And hindgut. Mouth located on the second segment on the ventral side of the body. anus

type Annelids Earthworm

At the posterior end of the body, it looks like a small gap. Due to the nutrition of rotting plant remains and humus, the digestive system has a number of features. Its anterior section is differentiated into a muscular throat, esophagus, goiter and muscular stomach. To increase the suction surface, a fold has formed on the upper part of the intestine typhlosol(typhlozolis). Please note: differentiated parts of the foregut - pharynx, esophagus, goiter, stomach - were absent in previous types of worms.

Breath. An earthworm breathes over the entire surface of its body due to the presence of a dense subcutaneous network of capillary blood vessels. Therefore, it is important that the integuments of the worm's body do not dry out, but excessive moisture (for example, very wet soil after rain) is just as detrimental to them.

Circulatory system closed, that is, the blood moves through the vessels without spilling into the body cavity. The movement of blood is determined by the pulsation of large vessels, mainly encircling the esophagus. These are kind of hearts. Blood supplies all organs and tissues nutrients, transporting them from the intestines, and oxygen entering the capillaries of the skin from external environment. By dorsal vessel blood moves from the back end of the body to the front, and along abdominal vessel- in the opposite direction. The blood of an earthworm is red. An iron-containing protein, close to vertebrate hemoglobin and transporting oxygen, is contained in a dissolved state in the blood plasma, and erythrocytes are absent.

Nervous system more complex than that of flat and roundworms. It consists of nerve parapharyngeal ring with ganglia and abdominal nerve chain. This so-called nervous system ladder type. supraesophageal paired ganglion performs the functions of the brain and is more developed than subesophageal. The nerve chain originates from the subpharyngeal node and is a segment-by-segment pairs of nerve nodes, connected to each other by transverse and longitudinal commissures. From the ganglia, nerves depart to various organs. The sense organs of the earthworm are poorly developed: eyes and tentacles are absent, but numerous sensory cells and nerve endings are embedded in their skin.

excretory organs are presented segment by segment (i.e., in each segment) by located paired metanephridia. They look like convoluted tubules, begin in the body cavity with a funnel with cilia. A channel departs from the funnel, which penetrates the transverse partition, passes into the cavity of the next segment. The final department of metanephridium has an extension - bladder , which opens outward on the lateral side of the body of the worm (i.e., each segment has a pair of very small excretory openings). In addition to metanephridia, the excretion involves chloragogenic cells covering the intestinal surface with a thin brown-yellow coating. Chlorogenic cells accumulate excretion products. Filled with metabolic products, these cells die, and their contents enter the body cavity, from where they are removed by metanephridia.

Reproduction. earthworms hermaphrodites. The reproductive organs and the girdle can only be seen during the breeding season - in the spring. To male

type Annelids Earthworm

reproductive system include two pairs of testicles located in segments 10 and 11, four vas deferens, which merge in pairs and open outward paired male genital opening located in segment 15. The female reproductive system includes pair of ovaries located in segment 13, oviducts, which open outward in segment 14 a pair of female genital openings. There are two pairs in segments 9 and 10 seminal receptacles, each of which opens outwards with an independent opening.

Earthworms reproduce sexually. Cross fertilization, in a cocoon. Two worms meet, wrap their bodies tightly around each other, attach themselves to each other with their ventral sides and exchange sperm, which enters the spermatic receptacles. After that, the worms disperse. Further, the girdle forms a mucous sleeve, eggs are laid in it. When the clutch is advanced through the segments containing the seed receptacles, the eggs are fertilized by sperm belonging to another individual. The clutch is dropped through the front end of the body, compacted and turns into an egg cocoon, where young worms develop.

Regeneration. Earthworms are characterized by a high ability to regenerate, i.e. from each piece of the torn body of an earthworm, a whole worm is restored.

Questions for self-control

Name aromorphoses of the type Annelids.

Name the classification of the type Annelids.

What is the systematic position of the earthworm?

Where do earthworms live?

What body shape do earthworms have?

What is the body of an earthworm covered with?

What body cavity is characteristic of an earthworm?

What is the structure of the worm's digestive system?

What is the structure of the circulatory system of the worm?

How does an earthworm breathe?

What structure does excretory system worm?

What is the structure of the worm's nervous system?

What structure does reproductive system earthworm?

How does an earthworm reproduce?

What is the significance of the earthworm?

type Annelids Earthworm

Rice. Earthworm, its moves in the ground and movement.

Rice. The internal structure of the earthworm.

1, 16 - gut; 2 - partitions; 3 - epithelial lining of the secondary body cavity; 4 - dorsal (back) blood vessel; 5 - annular blood vessel; 6 - skin-muscular sac; 7 - cuticle; 8 - skin epithelium; 9 - whole; 10 - metanephridium; 11 - eggs; 12 - circular muscles; 13 - longitudinal muscles; 14 - ventral (abdominal) blood vessel; 15 - abdominal nerve chain.

type Annelids Earthworm

Rice. The structure of the anterior end of the body of an earthworm.

The prostomium is a protrusion of the upper part of the first segment that covers the mouth. The peristomium is the name of the first segment of the body.

type Annelids Earthworm

Rice. The structure of the earthworm.

A - head end; B - internal structure; B - nervous system.

1 - mouth opening; 2 - male genital opening; 3 - female genital opening; 4 - belt; 5 - pharynx; 6 - esophagus; 7 - goiter; 8 - stomach; 9 - intestines; 10 - dorsal blood vessel; 11 - annular blood vessels; 12 - abdominal blood vessel; 13 - metanephridia; 14 - ovaries; 15 - testes; 16 - seed bags; 17 - seed receptacles; 18 - peripharyngeal ganglion; 19 - peripharyngeal nerve ring; 20 - abdominal nerve chain; 21 - nerves.

type Annelids Earthworm

Rice. Longitudinal section of the body of an earthworm.

1 - mouth; 2 - throat; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - gut; 7 - peripharyngeal ring; 8 - abdominal nerve chain; 9 - "hearts"; 10 - dorsal blood vessel; 11 - abdominal blood vessel.

annelids have the following aromorphoses: 1. The body was divided into segments (metamers) with repeating sets of internal organs. 2. A secondary cavity appeared - the whole, which has its own mesodermal lining. 3. There was a further complication of the nervous system: the concentration of nerve cells on the ventral side in each segment (the ventral nerve chain was formed), a significant increase in the brain ganglia (nodes) (supraoesophageal, suboesophageal nerve ganglia, peripharyngeal ring). 4. A closed circulatory system arose, which ensured the rapid transport of substances throughout the body. 5. Appeared respiratory system, which increased the respiratory surface and the intensity of gas exchange. 6. The digestive system became more complicated: the midgut was differentiated into sections, which led to a gradual process of digestion. 7. Parapodia formed - limbs for movement. 8. There was a further complication of the excretory organs: a metanephridial multicellular excretory system was formed.

• Earthworm

Earthworm – Lumbricus terrestris(type Annelids, class Small-bristle worms, Lumbricidae family) lives in moist, humus-rich soil. It feeds on organic matter, passing earth with plant debris through the intestines. Even C. Darwin noted the beneficial effect of earthworms on soil fertility. Dragging the remains of plants into the mink, they enrich it with humus. Laying passages in the soil, they contribute to the penetration of air and water to the roots of plants.

Earthworms are active in the warm season. In winter they hibernate. Freezing temperatures kill the worms instantly, so they must burrow deeper into the ground, where low temperatures do not penetrate. In the spring, when the temperature reaches a suitable value and the ground is saturated with rainwater, they have a mating season. They reproduce very quickly, producing about a hundred young worms a year. In summer, the worms are not so active. Food - dying plant residues - is very scarce at this time, and the soil is devoid of moisture, which can cause the death of worms. The autumn period is again characterized by the activity of worms. At this time, the reproduction of offspring begins again, which lasts until the onset of winter.

Earthworms live relatively long lives. Some manage to live for about ten years if they do not become victims of birds and moles. Another threat to their lives is the pesticides so widely used in horticulture today.

So, the Earthworm has an elongated, cylindrical body from 10 to 30 cm long. dorsal side more rounded, it is darker, a dorsal blood vessel shines through its skin. Abdominal side somewhat flattened and lighter colored. The anterior end of the body is thicker and darker colored. The body is made up of rings segments. In an adult worm, their number reaches 200. In the area of ​​\u200b\u200b32-37 body segments there is belt rich in mucous glands. External segmentation corresponds to the division of the body cavity by partitions into separate chambers and the segment-by-segment (i.e., in each segment) arrangement of a number of internal organs. On each segment 8 bristles(they are easy to detect if you run your finger along the body of the worm in the direction from the rear end of the body to the front). The setae are arranged in four pairs on the lateral sides of the segments. Clinging to the unevenness of the soil with them, the worm moves forward with the help of the muscles of the skin-muscular sac.

Covers. The body of an earthworm is covered skin-muscle sac. He is educated cuticle, single layer epithelium and two layers of muscles - external ring and internal longitudinal. The skin epithelium of the worm is rich mucous pieces of iron that produce slime covering the entire body of the worm and protecting it from drying out. The mucus also makes it easier to crawl in burrows by reducing friction on the soil.

Earthworm movement. When the worm crawls, waves of muscle contractions run through its body, and both the length and thickness of individual sections of its body are constantly changing. The movements produced by each part of the body consist in the fact that the segments that make it up are sometimes stretched and at the same time become thinner, then they contract and become thicker. As a result of such alternating extensions and contractions, the worm gradually moves forward: first, its head end is pulled forward, and then the posterior segments of the body are gradually pulled towards it; after that, the rear end of the body remains in place, and the head end sticks out even further forward, and thus the further advancement of the worm continues (it is convenient to observe it by letting the worm crawl along the paper spread out on the table).

• body cavity. Inside the skin-muscular sac in annelids is located secondary cavity body, or in general. This body cavity is not limited by muscles, as in roundworms, but has its own epithelial(coelomic) pavement, i.e. the inner side of the longitudinal muscles is lined with epithelium of mesodermal origin, and there is also an epithelial lining on the side of the intestine lying in the body cavity. Due to the coelomic epithelium, internal two-layer transverse partitions are formed between the segments - dissipations. The secondary cavity is divided into chambers, each segment contains a pair of coelomic sacs. The coelomic fluid is under pressure and plays a role hydroskeleton, so the worm is elastic to the touch.

Digestive system comprises front, middle And rear guts. Mouth located on the second segment on the ventral side of the body. anal hole

type Annelids Earthworm

At the posterior end of the body, it looks like a small gap. Due to the nutrition of rotting plant remains and humus, the digestive system has a number of features. Its anterior section is differentiated into a muscular throat, esophagus, goiter and muscular stomach. To increase the suction surface, a fold has formed on the upper part of the intestine typhlosol(typhlozolis). Please note: differentiated parts of the foregut - pharynx, esophagus, goiter, stomach - were absent in previous types of worms.

Breath. An earthworm breathes over the entire surface of its body due to the presence of a dense subcutaneous network of capillary blood vessels. Therefore, it is important that the integuments of the worm's body do not dry out, but excessive moisture (for example, very wet soil after rain) is just as detrimental to them.

Circulatory system closed, that is, the blood moves through the vessels without spilling into the body cavity. The movement of blood is determined by the pulsation of large vessels, mainly encircling the esophagus. These are kind of hearts. Blood supplies all organs and tissues with nutrients, transporting them from the intestines, and oxygen entering the capillaries of the skin from the external environment. By dorsal vessel blood moves from the back end of the body to the front, and along abdominal vessel- in the opposite direction. The blood of an earthworm is red. An iron-containing protein, close to vertebrate hemoglobin and transporting oxygen, is contained in a dissolved state in the blood plasma, and erythrocytes are absent.

Nervous system more complex than that of flat and roundworms. It consists of nerve parapharyngeal ring with ganglia and abdominal nervous chains. This is the so-called nervous system ladder type. supraesophageal double ganglion performs the functions of the brain and is more developed than subesophageal. The nerve chain originates from the subpharyngeal node and is a segment-by-segment pairs of nerve nodes, connected to each other by transverse and longitudinal commissures. From the ganglia, nerves depart to various organs. The sense organs of the earthworm are poorly developed: eyes and tentacles are absent, but numerous sensory cells and nerve endings are embedded in their skin.

excretory organs are presented segment by segment (i.e., in each segment) by located paired metanephridia. They look like convoluted tubules, begin in the body cavity with a funnel with cilia. A channel departs from the funnel, which penetrates the transverse partition, passes into the cavity of the next segment. The final department of metanephridium has an extension - uric bubble, which opens outward on the lateral side of the body of the worm (i.e., each segment has a pair of very small excretory openings). In addition to metanephridia, the excretion involves chloragogenic cells covering the intestinal surface with a thin brown-yellow coating. Chlorogenic cells accumulate excretion products. Filled with metabolic products, these cells die, and their contents enter the body cavity, from where they are removed by metanephridia.

Reproduction. earthworms hermaphrodites. The reproductive organs and the girdle can only be seen during the breeding season - in the spring. To male

type Annelids Earthworm

reproductive system include two pairs of testicles located in segments 10 and 11, four vas deferens, which merge in pairs and open outward doubles male sexual hole located in segment 15. The female reproductive system includes pair ovaries located in segment 13, oviducts, which open outward in segment 14 couple women's genital holes. There are two pairs in segments 9 and 10 seminal receptacles, each of which opens outwards with an independent opening.

Earthworms reproduce sexually. Cross fertilization, in a cocoon. Two worms meet, wrap their bodies tightly around each other, attach themselves to each other with their ventral sides and exchange sperm, which enters the spermatic receptacles. After that, the worms disperse. Further, the girdle forms a mucous sleeve, eggs are laid in it. When the clutch is advanced through the segments containing the seed receptacles, the eggs are fertilized by sperm belonging to another individual. The clutch is dropped through the front end of the body, compacted and turns into an egg cocoon, where young worms develop.

Regeneration. Earthworms are characterized by a high ability to regenerate, i.e. from each piece of the torn body of an earthworm, a whole worm is restored.

Questions for self-control

Name aromorphoses of the type Annelids.

Name the classification of the type Annelids.

What is the systematic position of the earthworm?

Where do earthworms live?

What body shape do earthworms have?

What is the body of an earthworm covered with?

What body cavity is characteristic of an earthworm?

What is the structure of the worm's digestive system?

What is the structure of the circulatory system of the worm?

How does an earthworm breathe?

What is the structure of the excretory system of the worm?

What is the structure of the worm's nervous system?

What is the structure of the reproductive system of an earthworm?

How does an earthworm reproduce?

What is the significance of the earthworm?

type Annelids Earthworm

Rice. Earthworm, its moves in the ground and movement.

Rice. The internal structure of the earthworm.

1, 16 - gut; 2 - partitions; 3 - epithelial lining of the secondary body cavity; 4 - dorsal (back) blood vessel; 5 - annular blood vessel; 6 - skin-muscular sac; 7 - cuticle; 8 - skin epithelium; 9 - whole; 10 - metanephridium; 11 - eggs; 12 - circular muscles; 13 - longitudinal muscles; 14 - ventral (abdominal) blood vessel; 15 - abdominal nerve chain.

type Annelids Earthworm

Rice. The structure of the anterior end of the body of an earthworm.

The prostomium is a protrusion of the upper part of the first segment that covers the mouth. The peristomium is the name of the first segment of the body.

type Annelids Earthworm

Rice. The structure of the earthworm.

A - head end; B - internal structure; B - nervous system.

1 - mouth opening; 2 - male genital opening; 3 - female genital opening; 4 - belt; 5 - pharynx; 6 - esophagus; 7 - goiter; 8 - stomach; 9 - intestines; 10 - dorsal blood vessel; 11 - annular blood vessels; 12 - abdominal blood vessel; 13 - metanephridia; 14 - ovaries; 15 - testes; 16 - seed bags; 17 - seed receptacles; 18 - peripharyngeal ganglion; 19 - peripharyngeal nerve ring; 20 - abdominal nerve chain; 21 - nerves.

type Annelids Earthworm

Rice. Longitudinal section of the body of an earthworm.

1 - mouth; 2 - throat; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - gut; 7 - peripharyngeal ring; 8 - abdominal nerve chain; 9 - "hearts"; 10 - dorsal blood vessel; 11 - abdominal blood vessel.

Rice. Reproduction of the earthworm.

1 - mucous sleeve; 2 - cocoon; 3 - exit of young worms from the cocoon.

type annelids

Rice. Structure polychaete worm Nereids.

type annelids

Rice. Appearance of a medical leech.