Animals, suborder earthworms. The body of an earthworm consists of annular segments, the number of segments can reach up to 320. When moving, earthworms rely on short bristles that are located on the body segments. When studying the structure of an earthworm, it is clear that, unlike the whipworm, its body looks like a long tube. Earthworms are distributed throughout the planet, except for Antarctica.

Appearance

Adult earthworms are 15 - 30 cm in length. In the south of Ukraine, it can reach and large sizes. The body of the worm is smooth, slippery, has a cylindrical shape and consists of piece rings - segments. This form of the body of the worm is explained by the way of its life, it facilitates movement in the soil. The number of segments can reach 200. The ventral side of the body is flat, the dorsal side is convex and darker than the ventral side. Approximately where the front of the body ends, the worm has a thickening called a girdle. It contains special glands that secrete a sticky liquid. During reproduction, an egg cocoon is formed from it, inside which the eggs of the worm develop.

Lifestyle

If you go out into the garden after rain, you can usually see small piles of earth thrown out by earthworms on the path. Often at the same time, the worms themselves crawl along the path. It is because they appear on the surface of the earth after rain that they are called rain. These worms crawl out to the surface of the earth also at night. The earthworm usually lives in humus-rich soil and is not common in sandy soils. He also does not live in swamps. Such features of its distribution are explained by the way of breathing. The earthworm breathes on the entire surface of the body, which is covered with mucous, moist skin. Too little air is dissolved in the water, and therefore the earthworm suffocates there. He dies even faster in dry soil: his skin dries up, and breathing stops. In warm and humid weather, earthworms stay closer to the surface of the earth. During a prolonged drought, as well as during a cold period, they crawl deep into the ground.

moving

The earthworm moves by crawling. At the same time, it first draws in the anterior end of the body and clings with the bristles located on the ventral side to the unevenness of the soil, and then, contracting the muscles, pulls up the posterior end of the body. Moving underground, the worm makes its own passages in the soil. At the same time, he pushes the earth apart with the pointed end of the body and squeezes between its particles.

Moving in dense soil, the worm swallows the earth and passes it through the intestines. The worm usually swallows the earth at a considerable depth, and throws it out through the anus at its mink. So on the surface of the earth long "laces" of earth and lumps are formed, which can be seen in the summer on garden paths.

This method of movement is possible only in the presence of well-developed muscles. Compared to the hydra, the earthworm has more complex musculature. She lies under his skin. Muscles together with the skin form a continuous musculocutaneous sac.

The muscles of the earthworm are arranged in two layers. Beneath the skin lies a layer of circular muscles, and beneath them is a thicker layer of longitudinal muscles. Muscles are made up of long contractile fibers. With the contraction of the longitudinal muscles, the body of the worm becomes shorter and thicker. When the circular muscles contract, on the contrary, the body becomes thinner and longer. Contracting alternately, both layers of muscles cause the movement of the worm. Muscle contraction occurs under the influence of the nervous system, branching out in muscle tissue. The movement of the worm is greatly facilitated by the fact that there are small bristles on its body from the ventral side. They can be felt by running a finger dipped in water along the sides and along the ventral side of the worm's body, from the rear end to the front. With the help of these bristles, the earthworm moves underground. With them, he lingers when he is pulled out of the ground. With the help of bristles, the worm descends and rises along its earthen passages.

Food

Earthworms feed mainly on half-decayed plant remains. They drag, usually at night, leaves, stems and other things into their minks. Earthworms also feed on humus-rich soil, passing it through their intestines.

Circulatory system

The earthworm has a circulatory system that the hydra does not have. This system consists of two longitudinal vessels - dorsal and abdominal - and branches that connect these vessels and carry blood. The muscular walls of the vessels, contracting, drive blood throughout the body of the worm.

The blood of the earthworm is red, it is very important for the worm, as well as for other animals. With the help of blood, the connection between the organs of the animal is established, metabolism occurs. Moving through the body, it carries nutrients from the digestive organs, as well as oxygen entering through the skin. At the same time, the blood carries carbon dioxide out of the tissues into the skin. Various unnecessary and harmful substances formed in all parts of the body, together with the blood, enter the excretory organs.

Irritation

The earthworm does not have special sense organs. He perceives external stimuli with the help of the nervous system. The earthworm has the most developed sense of touch. Sensitive tactile nerve cells are located all over the surface of his body. The sensitivity of the earthworm to various kinds of external irritation is quite high. The slightest vibrations of the soil make him quickly hide, crawling into a mink or into deeper layers of soil.

The value of sensitive skin cells is not limited to touch. It is known that earthworms, having no special organs of vision, still perceive light stimuli. If at night you suddenly illuminate the worm with a lantern, it quickly hides.

The response of an animal to stimulation, carried out with the help of the nervous system, is called a reflex. There are different types of reflexes. The contraction of the body of the worm from touch, its movement when suddenly illuminated by a lantern, has a protective value. This is a protective reflex. Grabbing food is a digestive reflex.

Experiments also show that earthworms smell. The sense of smell helps the worm find food. Charles Darwin also established that earthworms can smell the leaves of the plants they feed on.

reproduction

Unlike the hydra, the earthworm reproduces exclusively sexually. It does not have asexual reproduction. Every earthworm has male organs- the testicles, in which the gums develop, and the female genital organs - the ovaries, in which the eggs are formed. The worm lays its eggs in a slimy cocoon. It is formed from a substance secreted by the girdle of the worm. In the form of a clutch, the cocoon slides off the worm and is pulled together at the ends. In this form, the cocoon remains in the earthen burrow until young worms emerge from it. The cocoon protects the eggs from moisture and other adverse effects. Each egg in the cocoon divides many times, as a result of which tissues and organs of the animal are gradually formed, and, finally, small worms similar to adults emerge from the cocoons.

Regeneration

Like hydras, earthworms are capable of regeneration, in which lost parts of the body are restored.

Type Annelids. Class Small-bristle worms - (answers)

Task 1. Perform laboratory work.

Topic: "The external structure of the earthworm, movement, irritability."

Objective: to study the external structure of the earthworm, observing its movement and reaction to irritations.

3. Draw an earthworm. Label the parts of the body.

4. Write down the results of observations and draw a conclusion.

Annelids evolved from primitive (lower) worms with an unsegmented body, similar to flat ciliary worms. In the process of evolution, they had a secondary body cavity, a circulatory system, and the body was divided into rings (segments).

Task 2. Fill in the diagram.

Task 3. Complete the laboratory work.

Topic: "The internal structure of the earthworm".

Objective: to study the internal structure of the earthworm on a wet preparation.

1. Make sure that the workplace has everything you need to complete the lab.

2. Using the instructions given in paragraph 19 of the textbook, complete the laboratory work.

3. Draw the internal structure of the earthworm and mark the organs.

Write down the results of observations and draw a conclusion.

Annelids are descended from lower worms with an undivided body, similar to flat ciliary worms. In the process of evolution, they had a secondary body cavity (as a whole), a circulatory system.

Task 4. Fill in the table by entering the required numbers from the information provided in the columns.

Task 5. In the most favorable conditions (most often this broadleaf forests) the number of earthworms reaches 500-800 per 1 sq.m. Calculate and write down how much soil earthworms process per day on an area of ​​20 hectares of land, if one earthworm can process about 0.5 g of soil during this time. Based on the data obtained, draw a conclusion about the role of earthworms in soil formation.

On one square meter on average (800 + 500) / 2 = 650 worms1 Ha = 10000m2 in 1 Ha - 650 * 10000 = 65 * 10^5 worms65 * 10^5 * 0.5 = 32.5 * 100 kg = 3250 kg of soil

Conclusion - worms process a huge amount of soil per day, without their participation the soil would be less fertile.

General characteristics. Earthworms and many other soil and water forms belong to this class. They are characterized by the absence of parapodia and a small number of setae, which usually sit in bundles on the sides of the segments (except for the anterior and posterior segments). The head part of the body is not isolated. There are no tentacles in most forms. Hermaphrodites. Development occurs without metamorphosis.

About 3 thousand species of this class are known. They live mainly in the soil and at the bottom of fresh water bodies.

Soil earthworms play an important role in soil formation (Fig. 109).

Structure and vital functions. The body of the oligochaete worms is strongly elongated, cylindrical and consists of different number externally similar segments. At the front end of the body is the mouth, at the back - the anus.

Body sizes range from a few millimeters to 3 m (in some tropical forms). The integument contains a large number of skin glands that secrete mucus. Each segment is equipped with bristles collected in bundles.

In soil forms, they play an important role in the movement of worms.

The body cavity is secondary, well developed, filled with coelomic fluid with cellular elements (lymphocytes, etc.). In most species, it is segmentally divided into separate chambers (Fig. PO, 111).

The nervous system is represented by the supraesophageal ganglion, peripharyngeal ring, suboesophageal ganglion, and abdominal nerve chain.

The sense organs are poorly developed. Eyes and tentacles are absent in most forms. There are sensory setae, olfactory pits, and statocytes.

Rice. 109. Earthworm:

/ - female genital opening;
2 - male genital opening;
3 -belt

Rice. 110. Anatomy of an earthworm:

/ rotoinya to deprive; 2 supraesophageal ganglion; And- throat; / - esophagus; 5. 13 — annular vessels; 6 dorsal vessel; 7 seed bags; H testes; 9 — seed funnels; 10 vas deferens; // partitions between segments; 12 - metapefridin; 14 ~ gut; 15
- stomach; 16 -: u6 \ 17 nicenode; /L' - egg funnels; til ovary;
20 seminal receptacles. Roman numerals for body segments

Digestive organs are usually large and adapted to the passage of large masses of soil and bottom soil, on which most worms feed. Per oral cavity followed by the pharynx, esophagus, gizzard and intestines.

All these organs lie along the body without forming bends.

The circulatory system. The main vessels of the dorsal and abdominal. In the integument there is a dense network of capillaries, from which oxidized blood is collected in the eubpeural vessel, which lies under the ventral nerve chain.

Respiratory system, with rare exceptions, none.

The skin of low-bristle worms is permeated with a network of capillaries that facilitate gas exchange through the integument (Fig. 112).

Sexual system. All small-brittle worms are hermaphrodites, they are characterized by cross-fertilization. The structure of the gonads differs in representatives of different groups.

Of the large number of oligochaete worms for agriculture, of particular interest are different kinds earthworms. Their body is slightly flattened and consists of 50-248 outwardly similar segments. On the border of the anterior and middle thirds of the body, a girdle of several thickened segments is clearly distinguished.

Earthworms prefer to live in a moderately moist night rich in humus. They avoid acidic and saline soils. They usually spend the winter in the ground at a depth of 2-3 m (under conditions temperate zone). They feed on organic matter contained in the soil, as well as dead parts of plants.

Rice. 111, Cross section of the body of an earthworm:

/ - metahiefridium; 2 - funnel metanephrine; 3 - ganglia of the abdominal nerve chain; 4 - skin epithelium; 5 - non-river muscles; 6
- longitudinal muscles; 7 - bristles; 8 - dorsal fold of the intestine; 9, 10 - dorsal and abdominal blood vessels; // - subneural vessel

They reproduce by cross fertilization. Hermaph-born genitals of earthworms are distinguished by the complexity of their structure. One pair of ovaries. Near them, a funnel trimmed with cilia, short oviducts begin, the other end opening outward in the next segment. They are found inside large seminal sacs in which seminal fluid accumulates. The funnels of the seminal ducts adjoin the testes, opening outwards behind the openings of the oviducts. Usually in the 9th-10th segments there are two pairs of small sacs - seminal receptacles, which open outwards with short ducts. When mating, two earthworms attach with their ventral sides. At the same time, their heads are turned in opposite directions, and the openings of the sperm ducts of one individual are adjacent to the sperm receptacle of the other. After this, there is a mutual exchange of seminal fluid. The mated worms then disperse.

When the eggs ripen, a mucous ring is released on the girdle of the worm. The worm drops the ring through the anterior part of the body; when it passes by the openings of the oviducts and seminal receptacles, in

Rice. 112. Cross section of the wall of the skin-muscular sac of rain black;

/ - skin epithelium; 2 - a layer of circular muscles; 3 - a layer of longitudinal muscles; 4 - blood vessels and capillaries

113. Soil oligochaete annelids (enchytreids) at the time of mating

Rice. 114. Freshwater small-bristle worm Tubifex (Tubifex)

it receives eggs and sperm and fertilization of the eggs occurs. The discarded ring with eggs enclosed in it hardens, turning into a cocoon. It is in it that the initial development of young worms takes place, which proceeds without metamorphosis.

earthworms play huge role in soil-forming processes.

The passages of the worms contribute to the penetration of water and air into the soil, which achieves uniform moistening and ventilation of the soil, which is important for the successful growth of plants. Worms loosen the soil and fertilize it, dragging it into minks plant remains that contribute to the formation of humus.

The number of earthworms in the soil is sometimes huge, reaching 5 million individuals per 1 ha, which is about 1 thousand kg in weight. If 50-100 earthworms live in the soil on an area of ​​1 m2, then they throw out on the surface of 1 ha from 10 to 30 tons of earth that has passed through their intestines in a year. Hence, the great importance of earthworms for creating soil fertility is obvious.

Small oligochaete worms from the family Enchy— treidae(Fig. 113). Their length usually does not exceed 1 cm, and their thickness is 1 mm. Quite often, tens of thousands of different representatives of this family can be found in the soil layer on an area of ​​1 m2. There are especially many of them near the decaying remains of plants and animals. Many enchitreids live at the bottom of fresh and brackish water bodies. Their life here takes place in silt, in an almost anoxic environment. During freezes, they fall into suspended animation.

Small oligochaete worms common in lakes and ponds pipe makers(sem. Tibificidae) (Fig. 114). Worms, having buried their rear end in the silt, make oscillatory movements with their bodies. It has been noticed that the less oxygen in the water, the more they stretch the body and more often make oscillatory movements, increasing gas exchange through the covers.

In a number of aquatic oligochaete worms, asexual reproduction budding. Sometimes whole chains of budding worms are formed. Aquatic oligochaete worms serve as an important food for fish. They contribute to the acceleration of the circulation of substances in the soil of reservoirs.

Type annelids (Annelida)

4.8.3. Class Oligochaeta (little bristles)

An earthworm (himbricus) is an animal with a long cylindrical body, reaching 12-18 cm. Its anterior end is cone-shaped, and the posterior end is flattened in the dorsoventral direction. And although he lives only on land, he could not fully adapt to the terrestrial way of life. The worm spends most of the day underground, burrowing into moist soil, thus saving itself from drying out. He leaves his hole only at night, going in search of food or a sexual partner. Differences in the structure of the body of the Nereis and the earthworm can be explained by the adaptation of the latter to a terrestrial lifestyle.

The body of the earthworm has a streamlined shape and is devoid of any outgrowths, since the outgrowths can prevent the worm from moving freely in the soil. The prostomium is small and rounded, there are no sensitive appendages. All segments, with the exception of the first and last ones, each have four pairs of setae: two ventral and two ventrolateral. The bristles emerge from the bristle sacs located in the wall of the body. Special muscles (retractors) can retract the bristle inward or, on the contrary, expose it outward (protractors) (Fig. 4.29). Setae of oligochaetes are involved in locomotor activity. Long setae located on segments 10-15, 26, and 32-37 play an important role in the process of copulation. Another structure used in the process of copulation is − belt, which is located on segments 32-37 (Fig. 4.30). The epithelium of the girdle contains many glandular cells, forming a noticeable thickening resembling a saddle on the dorsal and lateral surfaces. The girdle is involved in copulation and cocoon formation.

Rice. 4.29. The structure of the body wall of the earthworm (Lumbhcus terrestris). Cross section through the bristle region

Rice. 4.30. Anterior end of the body of an earthworm (Lumbricus terresths). Bottom view

The structure of the body wall of the earthworm (Fig. 4.29) is similar to the structure of the body wall of the Nereis. The mouth and anus are located at different ends of the body. Food is swallowed as a result of contraction of the muscles of the motionless pharynx. The intestine is straight. Tiflozol(longitudinal fold on the dorsal side of the intestine, protruding into the intestinal lumen) increases the surface area involved in the digestion of food and absorption. The worm feeds on detritus; he swallows the earth and digests the organic residues contained in it. Nutrients, absorbed, enter the capillaries surrounding the intestinal wall. The main part of the soil passes through the intestines of the worm and is excreted in the form of coprolites.

The thin cuticle of oligochaetes is moistened by the coelomic fluid and mucus secreted by the glandular cells of the epithelium, constantly secreted through the dorsal pores. It is through the cuticle that gas exchange occurs by diffusion, and an extensive network of capillaries located in the epithelium ensures this process.

All segments, with the exception of the first three and one last, each have a pair of nephridia, which perform the functions of excretion and osmoregulation. The nephridia open on the surface of the body with special foramens located somewhat anterior to the ventrolateral setae. Surrounding the gut chloragogenic cells are also involved in the extraction process.

Blood from individual segments is collected in a pulsating dorsal vessel. Five pairs of muscular lateral "hearts", located in segments 7-11, it is pushed into the median abdominal vessel. In the "hearts" and the spinal vessel there are valves that prevent the reverse flow of blood. Lateral branches depart from the abdominal vessel, supplying blood to all segments of the body. In earthworms, there is no noticeable concentration of sensitive structures at the anterior end of the body. They have separate photosensitive cells, as well as cells that respond to chemicals and light; all these cells are scattered in the epithelium. Central nervous system the earthworm is similar to the nervous system of the Nereis. In the abdominal nerve chain they have giant nerve fibers, which, in response to any strong irritation, cause a contraction of the entire musculature of the worm, although general organization of the nervous system can ensure the coordinated work of the muscular layers associated with the burrowing or locomotor activity of the animal.

In an earthworm, the reproductive organ system is very complex, and the behavioral responses associated with reproduction are also complex. Perhaps this is due to the terrestrial way of life and the need to protect gametes and fertilized eggs from drying out. Earthworms are hermaphrodites (Fig. 4.31). This can be seen as an adaptation to the relatively settled way life. With this lifestyle, meetings of earthworms with each other are very rare, but if this happens, then any representative of the same species can arrange an earthworm as a sexual partner, since both of them are hermaphrodites. In the process of copulation, mutual fertilization occurs, that is, the exchange of male gametes.

Rice. 4.31. The reproductive system of the earthworm. Side view

The sex organs of earthworms are concentrated at the anterior end of the body. The location of the reproductive organ system is shown in fig. 4.31. A rather complex mating process and the subsequent laying of fertilized eggs in cocoon occur in the following way.

During spring and summer, on warm, humid nights, the earthworm emerges from its burrow, rarely leaving it completely, and mates with its neighbor. They are in contact with the abdominal surfaces so that the head of one of them is directed towards the tail end of the other. In this case, the 9th-11th body segments are located opposite the partner's girdle. In the region of the girdle, as well as on the 10-15th and 26th segments, there are long setae that the worms pierce into each other in order to ensure closer contact during copulation.

The epithelium of both worms secretes mucous sleeve around segments 11-31. These muffs separate the partners' sperm during copulation; a special closed groove appears in it for the passage of sperm.

In the region of the bands around the partners, a common tube is secreted, which also holds the oligochaetes together.

In both partners, the sperm from the seminal vesicle through the vas deferens, which opens outwards on the 15th segment, is brought out and moves along the abdominal seminal groove towards the posterior end. The movement of sperm along the groove is provided by contractions of the arcuate muscles located in the 15th-32nd segments in the layer of longitudinal muscles. Having reached the 9th and 10th segments of the partner's body, the sperm enters his seminal receptacles.

After the sperm exchange is completed, the partners disperse (the process takes 3-4 hours). And after two days, a cocoon begins to form.

Around each worm, a dense chitinous tube is secreted by the epithelial glands; she becomes the shell of a cocoon. Girdle cells secrete into a cocoon albumen which the embryos will subsequently feed on. As a result of the expansion of the segments located behind the cocoon, it is pushed forward. At this time, through the opening of the oviduct, located on the 14th segment, 10-12 eggs are laid in the cocoon. When the cocoon moves past the 9th and 10th segments, sperm enters it from the seed receptacles and fertilization occurs. Finally, the cocoon slips off the worm. The edges of the cocoon quickly close, which prevents the contents from drying out. The cocoon is yellow at first, but darkens as it dries.

Cocoons are formed every 3-4 days until all the sperm is used up. Cocoon formation can continue throughout the year without additional mating.

Development in annelids is direct, i.e. they do not have free-floating larval stages. Usually only one embryo develops in a cocoon. Young worms hatch 2-12 weeks after cocoon laying, depending on environmental conditions.

The economic importance of earthworms

The burrowing activity of earthworms improves soil aeration and its drainage properties. Dug passages facilitate the growth of roots in the soil. Earthworms bring earth particles containing inorganic components to the surface from deeper layers. Thus, they participate in mixing the soil.

Lumps larger than 2 mm in diameter cannot be swallowed by worms, therefore the soil they bring to the surface does not contain pebbles and good conditions for seed germination.

Thanks to the activity of earthworms, seeds can be under a layer of soil, which contributes to their successful maturation.

Earthworms drag leaves into holes, partially using them as food. The remains of leaves, as well as excrement, secretions and corpses of worms, enrich the soil with organic components.

Emissions earthworms have a pH of about 7, so they prevent alkalization or acidification of the soil.

Annelids have the highest organization compared to other types of worms; for the first time they have a secondary body cavity, a circulatory system, a more highly organized nervous system. In annelids, another, secondary cavity was formed inside the primary cavity with its own elastic walls from mesoderm cells. It can be compared to airbags, a pair in each segment of the body. They "swollen", filled the space between the organs and support them. Now each segment has received its own support from the bags of the secondary cavity filled with liquid, and the primary cavity has lost this function.

They live in soil, fresh and sea water.

External structure

The earthworm has an almost round body in cross section, up to 30 cm long; have 100-180 segments, or segments.

In the anterior third of the body there is a thickening - a girdle (its cells function during the period of sexual reproduction and oviposition). On the sides of each segment, two pairs of short elastic bristles are developed, which help the animal when moving in the soil. The body is reddish-brown in color, lighter on the flat ventral side and darker on the convex dorsal side.

Internal structure

characteristic feature internal structure is that earthworms have developed true tissues. Outside, the body is covered with a layer of ectoderm, the cells of which form the integumentary tissue. The skin epithelium is rich in mucous glandular cells.

muscles

Under the cells of the skin epithelium there is a well-developed musculature, consisting of a layer of annular and a more powerful layer of longitudinal muscles located under it. Powerful longitudinal and annular muscles change the shape of each segment separately.

The earthworm alternately compresses and lengthens them, then expands and shortens them. Wave-like contractions of the body allow not only to crawl along the mink, but also to push the soil apart, expanding the course.

Digestive system

The digestive system begins at the front end of the body with a mouth opening, from which food enters sequentially into the pharynx, esophagus (in earthworms, three pairs of calcareous glands flow into it, the lime coming from them into the esophagus serves to neutralize the acids of rotting leaves that animals feed on). Then the food passes into an enlarged goiter and a small muscular stomach (the muscles in its walls contribute to the grinding of food).

From the stomach almost to the rear end of the body stretches the middle intestine, in which, under the action of enzymes, food is digested and absorbed. Undigested residues enter the short hindgut and are thrown out through the anus. Earthworms feed on half-decayed plant remains, which they swallow along with the earth. When passing through the intestines, the soil mixes well with organic matter. Earthworm excrement contains five times more nitrogen, seven times more phosphorus and eleven times more potassium than ordinary soil.

Circulatory system

Circulatory system closed, consists of blood vessels. The dorsal vessel stretches along the entire body above the intestines, and under it the abdominal vessel.

In each segment, they are united by an annular vessel. In the anterior segments, some annular vessels are thickened, their walls contract and pulsate rhythmically, due to which blood is distilled from the dorsal vessel to the abdominal one.

The red color of blood is due to the presence of hemoglobin in the plasma. It plays the same role as in humans - the nutrients dissolved in the blood are carried throughout the body.

Breath

Most annelids, including earthworms, are characterized by skin respiration, almost all gas exchange is provided by the surface of the body, so the worms are very sensitive to wet soil and are not found in dry sandy soils, where their skin dries out quickly, and after rains, when in the soil a lot of water, crawl to the surface.

Nervous system

In the anterior segment of the worm there is a peripharyngeal ring - the largest accumulation of nerve cells. From it begins the abdominal nerve chain with nodes of nerve cells in each segment.

Such a nervous system of a knotty type was formed by the fusion of the nerve cords of the right and left sides of the body. It ensures the independence of the segments and the coordinated work of all organs.

excretory organs

The excretory organs look like thin loop-shaped curved tubes, which open at one end into the body cavity, and at the other outward. New, simpler funnel-shaped excretory organs - metanephridia remove harmful substances into external environment as they accumulate.

Reproduction and development

Reproduction occurs only sexually. Earthworms are hermaphrodites. reproductive system they are located in several segments of the anterior part. The testicles lie in front of the ovaries. When mating, the spermatozoa of each of the two worms are transferred to the spermatozoa (special cavities) of the other. Worms are cross fertilized.

During copulation (mating) and oviposition, the cells of the girdle on the 32-37th segment secrete mucus, which serves to form an egg cocoon, and a protein liquid to feed the developing embryo. The secretions of the girdle form a kind of mucous sleeve (1).

The worm crawls out of it with its rear end forward, laying eggs in the mucus. The edges of the muff stick together and a cocoon is formed, which remains in the earthen burrow (2). Embryonic development eggs occur in a cocoon, young worms emerge from it (3).

sense organs

The sense organs are very poorly developed. The earthworm does not have real organs of vision, their role is performed by individual light-sensitive cells located in the skin. The receptors for touch, taste, and smell are also located there. Earthworms are capable of regeneration (easily restores the back).

germ layers

The germ layers are the basis of all organs. In annelids, the ectoderm (outer layer of cells), endoderm (inner layer of cells) and mesoderm (intermediate layer of cells) appear at the beginning of development as three germ layers. They give rise to all major organ systems, including the secondary cavity and the circulatory system.

These same organ systems are preserved in the future in all higher animals, and they are formed from the same three germ layers. Thus the higher animals in their development repeat evolutionary development ancestors.

Earthworms are one of the most ancient inhabitants of the planet Earth. They live almost everywhere, with the exception of the permafrost of Antarctica. Thanks to this boneless creature, the soil becomes fertile. It is their vital activity that is a fundamental factor for the formation of a fertile layer.

General characteristics and living conditions

The body shape of an earthworm, color, size are the unique characteristics of an invertebrate. Let's consider in more detail.

The body of the worm is a set of annular segments. In some individuals, their number reaches 320. Worms move with the help of short bristles located on these segments. Outwardly, the body of individuals resembles a long tube.

For their normal life, the humidity level should be at the level of 75%. Worms die if the earth dries up and the humidity drops to 35% or less. This is due to the fact that they breathe through the skin. Therefore, they simply cannot live in dry soil and in water.

The most optimum temperature for their comfortable life - from 18 to 24 degrees above zero. If it starts to get colder, then the worms begin to sink deeper, where it is warmer and more humid. If a atmospheric temperature does not increase, then they hibernate. If this indicator rises above 42 degrees, then the worms die. The same thing happens if the temperature is too low. And worms crawl out after rain due to lack of oxygen in the soil.

An interesting fact: it was the ability to fall into a state of suspended animation that allowed the worms to survive in the Ice Age.

The benefits of worms

It is thanks to worms that the soil all over the planet is in constant motion. The lower layers rise to the top and are saturated with carbon dioxide, humic acids. Thanks to these invertebrates, potassium and phosphorus enter.

Worms, better than any human hands and technology, prepare the soil for the growth of plants. Thanks to these creatures, even large stones and objects eventually sink deep into the ground. And small pebbles are gradually ground in the stomach of worms and turn into sand. However, the excessive use of chemicals by humans in agriculture inevitably leads to a reduction in their population. To date, the Red Book of Russia already contains 11 species of earthworms.

Color

The color of the earthworm is directly dependent on skin pigments. But this characteristic is relevant only for living individuals.

If the worm does not have skin pigments, then it has a pink or red color throughout its life. In the presence of this component, the color of the earthworm can be brown, blue, yellow or brown.

For example, the worm Allophora chlorotica has a yellowish or greenish color. A Lumbricus rubellus - earthworms - have a brown-red or purple color with a mother-of-pearl tint.

body length

The average size of all individuals is from 5 to 20 centimeters, with a thickness of 2 to 12 mm. However, in tropical forests there are invertebrates up to 3 meters long. Naturally, with such sizes of annular segments, there can be more than 3 thousand.

Types of worms

Invertebrates live in all layers of the soil, hence the species that feed on the surface of the earth are distinguished:

Surface feeders		Soil feeders
Litter	Individuals under no circumstances fall below 10 centimeters into the ground		Living in deep soil layers
Soil-litter	They live at a depth of 10 to 20 centimeters.		Constantly form new passages, but feed in the humus layer
	They constantly make deep passages, but only the upper end of the body can go outside, for food consumption and mating

Litter and burrowing individuals are characteristic of waterlogged soils. In other words, they live near water bodies, swamps and in regions with a humid subtropical climate.

The tundra is characterized by soil-litter and litter worms. In the steppes, only soil species can be found.

Worms nutrition and digestive organs

Regardless of the type and color of the earthworm, they are all omnivores. By swallowing huge amounts of earth, they absorb half-rotten leaves. From this mixture they get useful substances. They do not use only leaves with an unpleasant odor, but they love fresh ones.

Ch. Darwin wrote about the omnivorous nature of worms. He made many experiments by hanging pieces of various foods, including the remains of dead worms, over a pot of animals, and most of this food was eaten.

After digesting the soil, the worm rises out and throws it out. Excrement, saturated with intestinal secretions, is viscous, and after drying in air, it hardens. There is no randomness in their actions; first, waste is dumped from one side, then from the other. As a result, a characteristic entrance to the mink is formed, similar to a turret.

Worms not only feed on leaves, plant stems, and tufts of wool, they use them to plug burrow entrances.

In all, regardless of body shape and color, earthworms have a mouth located at the front end of the body. The process of swallowing occurs due to the muscular pharynx. After that, food - earth with leaves - enters the intestines. If some part of the food has not been digested, then it is thrown away along with the processed food. Emission occurs through the anus located at the posterior end of the body.

reproductive system

All earthworms are hermaphrodites. Before laying eggs, two different individuals exchange seminal fluid, with a light touch. After that, each worm from the "belt" located on the front of the body secretes mucus, into which the eggs enter. After some time, the lump with them practically slides off the body and turns into a cocoon. After maturation, young individuals emerge from it.

and sense organs

Absolutely all individuals, regardless of the color of the earthworm, do not have sensory organs. The tactile sense works best for them. Similar cells are located throughout the body, and even a slight vibration of the ground causes the worm to hide and sink into deeper layers of the soil. These elements are also responsible for the perception of light. After all, such individuals do not have eyes. But if you illuminate them at night with a lantern, they will quickly hide.

Researchers claim that worms have a nervous system. This is confirmed by the fact that they have elementary reflexes: when touching the body, it instantly contracts, protecting the worm from touch.

Even Darwin noticed that such creatures are distinguished by smell. If the worms do not like the aroma of food, then he will refuse such a dinner.

Animal Enemies

It doesn’t matter at all what body color an earthworm has, what kind it has and where it lives, all individuals have natural enemies. The most terrible of them is the mole. This mammal animal not only eats worms, but also stocks them for the future. The mole has a paralyzing substance in its saliva that acts specifically on invertebrates. This is how he catches the worms.

Frogs and shrews will not disdain to taste them. Many birds eat earthworms - these are thrushes, domestic chicken, starlings and woodcocks. Many arthropods do not disdain worms - these are arachnids, different types insects and centipedes.

Vermiculture

AT recent times the topic of organic vegetable growing has become relevant. The question may arise as to what the worms have to do with it. Everything is very simple. The basis of vermiculture is the cultivation of earthworms. At the same time, it does not matter at all what color the earthworm has, the most important thing is the production of biohumus. Recent trends suggest that soon vermiculture will completely replace harmful chemical fertilizers from agriculture.

Target: To study the external structure of the earthworm.

Equipment: live earthworms, Petri dishes (disposable cups), tweezers, filter paper, magnifiers, onion pieces.

Progress

The multimedia board reproduces the stages of laboratory work that students do and write down at their workplaces.

1. Examine the body of an earthworm.

Determine the size of the worm's body (length and thickness) using a ruler (bio_2007_053_p,:1.1, 1.2)

The body length of an adult earthworm is usually 15–20 cm.

Determine the segmentation of the body. Find out the same segmentation of the body throughout the body of the worm (BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.: hint)

the same segments.

Determine the shape of the body, find out how the dorsal side of the body differs from the abdominal.

Convex (dorsal) and flat (abdominal)

Determine body color. Find out how the dorsal side of the body differs from the ventral side.

Find the anterior (more pointed, closer to the girdle - thickening at the anterior end of the body) (bio_2007_053_p,:1.3; BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.1) and the posterior (more blunt) ends of the body (bio_2007_053_p,:1.4),

The anterior end of the body of the worm with a mouth opening. A small movable blade in front of the mouth is located on the ventral side of the body. In an earthworm, it has neither eyes nor tentacles.

The posterior end of the body of the worm with an anus. belt. Determine on which segments of the body the girdle is located. (bio_2007_053_p,:1.5; BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.2)

Glandular thickening of the integument. During reproduction, the cells of the girdle secrete the substance of a cocoon into which fertilized eggs are placed. Pay attention to the thinnest layer of the cuticle, which is distinguished by the skin epithelium and covers the entire body.

2. Pay attention to the skin of the worm. Determine if it is dry or wet?

3. Gently touch a piece of filter paper to the skin of the worm(bio_2007_053_p,:1.6).

The skin epithelium of earthworms is rich in mucous glands. Therefore, their skin is constantly moisturized. It has great importance in breathing, which occurs through the integument of the body when moving in the soil

4. Gently run your finger along the ventral or lateral side of the worm's body from the back to the front end(you will feel the touch of the bristles). Use a magnifying glass to examine the location of the bristles on the body of the worm (BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.3).

Each segment of the body, except for the head lobe, bears 8 setae arranged in pairs, so that 4 double rows of setae extend along the body. The earthworm moves with the help of body contractions. When moving in the soil, an important role is played by the alternating extension and expansion of the front end of the body, causing the separation of soil particles. The bristles with which the worm clings to the substrate also play a significant role in the process of locomotion.

5. What do you think is the significance of such skin and such bristles for the life of a worm in the soil?

6. Watch a worm crawl on paper(listen if he rustles bristles) (bio_2007_053_p,:2.1).

When the worm moves along rough paper, the bristles rustle against the paper. The worm clings to the substrate with bristles.

7. Watch a worm crawling on glass soaked in water. How does he move(bio_2007_053_p,:2.2)?

When moving on glass (smooth surface), the rustling of bristles is not audible: the worm does not cling to a smooth substrate with bristles. The body of the worm is strongly elongated, alternate muscle contractions are observed along the entire length of the body.

8. Touch different parts of the earthworm's body with the tip of a pencil. What are you watching?

9. Bring a piece of onion to the front end of the worm's body. What are you watching?

Irritability, defensive reflex.

10. Draw a conclusion about the features of the structure and movement of the earthworm in connection with the habitat.

Small bristle worms have an elongated segmented body. The surface of the body is constantly moistened due to the secretion of mucus by the glands of the skin epithelium. This is of great importance for breathing. The movement of oligochaetes occurs due to muscle contractions. But the bristles with which the worm clings to the substrate also play a significant role in the movement of oligochaetes. The nervous system is developed: they have irritability, protective reflexes.

Homework paragraph 13

Presence earthworm in the soil is the ultimate dream of any farmer. They are excellent helpers in agriculture. In order to make their way, they have to move a lot underground.

Their over millions of years has made the earth much more fertile. On rainy days, they can be observed on the ground, but it is not easy to catch them. They have a muscular enough body to easily hide from a person underground.

They occupy the main place in the structure of the soil, enriching it with humus and many important components, making the yield much higher. This is work of earthworms. Where did such a name come from? During rain, underground rain burrows are filled with water, because of this they have to crawl out to the outside.

How to characterize biohumus? This is an amazing substance that regulates soil moisture well. When the soil lacks water, it stands out from the humus, and vice versa, with its excess, biohumus easily absorbs it.

In order to understand how these spineless creatures can produce such valuable material, it is enough to understand how and what they eat. Their favorite delicacy is half-rotted leftovers. flora used by these creatures simultaneously with the soil.

The soil is mixed with natural additives while moving inside. In the waste products of these creatures, the amount of important elements necessary for plants exceeds many times over.

Features and habitat of earthworms

These creatures are considered oligochaetes. earthworm body has the most different length. It stretches from 2 cm to 3 m. There are from 80 to 300 segments. The structure of the earthworm unique and interesting.

They move with the help of short bristles. They are on every segment. The only exceptions are the anterior ones, which have no setae. The number of bristles is also not unambiguous, there are eight or more of them, the figure reaches several tens. A greater number of bristles from the tropics.

As for the circulatory system of earthworms, it is closed and well developed in them. Their blood color is red. These creatures breathe thanks to the sensitivity of their skin cells.

On the skin, in turn, there is a special protective mucus. Their sensitive recipes are absolutely not developed. They don't have eyes at all. Instead of them, there are skin special cells that respond to light.

In the same places are taste buds, smell and touch. The ability to regenerate is well developed. They can easily recover from damage to their back of the body.

In a large family of worms, which are now discussed, there are about 200 species. earthworms are of two types. They have distinctive features. It all depends on lifestyle and biological features. The first category includes earthworms that find food for themselves in the ground. The second ones get their own food on it.

Worms that get their own food underground are called litter and are under the soil no deeper than 10 cm and do not deepen even under conditions of soil freezing or drying. Soil worms are another category of worms. These creatures can sink a little deeper than the previous ones, 20 cm.

For burrowing worms feeding under the soil, the maximum depth starts from 1 meter and deeper. Burrowing worms are generally difficult to notice on the surface. They almost never show up there. Even during mating or feeding, they do not fully protrude from their holes.

Life of an earthworm digging completely from beginning to end goes deep underground in agricultural work. Earthworms can be found everywhere except in cold arctic places. Burrowing and bedding worms are comfortable in waterlogged soils.

They are found on the banks of water bodies, in marshy places and in subtropical zones with humid climate. Taiga and tundra are loved by litter and soil litter worms. And soil is best in steppe chernozems.

In all places they can adapt, but they feel most comfortable earthworms in the soil coniferous-deciduous forests. AT summer time year they live closer to the surface of the earth, and in winter time sink deeper.

The nature and lifestyle of the earthworm

Most of the life of these spineless passes underground. Why earthworms most often found there? This provides them with security. Networks of corridors at various depths are dug underground by these creatures.

They have a whole underground kingdom there. Mucus helps them to move even in the hardest soils. They cannot be under the sun for a long time, for them it is like death because they have a very thin layer of skin. Ultraviolet represents a real danger for them, therefore, to a greater extent, worms are underground and only in rainy cloudy weather crawl to the surface.

Worms prefer to be nocturnal. It is at night that you can find a large number of them on the surface of the earth. Initially earthworms in the soil they leave part of their body in order to scout the situation, and only after the surrounding space did not frighten them, they gradually go outside in order to get their own food.

Their body is able to stretch perfectly. A large number of the bristles of the worm curve back, which protects it from external factors. It is practically impossible to pull out a whole worm without tearing it, because in order to protect itself, it clings to the walls of the mink with its bristles.

Earthworms sometimes reach quite large sizes.

It has already been said that the role of earthworms for people is just incredible. They not only ennoble the soil and fill it useful substances, and also loosen it, and this contributes to the saturation of the soil with oxygen. In winter, in order to survive in the cold, they have to go deeper so as not to experience frost and fall into hibernation.

They feel the arrival of spring by warmed soil and rainwater, which begin to circulate in their burrows. With the coming of spring earthworm crawling out and begins his labor agrotechnical activity.

Earthworm food

It is a spineless omnivore. earthworm organs designed so that they can swallow a huge amount of soil. Along with this, rotten leaves are used, all but hard and unpleasantly smelling for the worm, as well as fresh plants.

The figure shows the structure of an earthworm

They drag all these foodstuffs underground and begin to eat there. They do not like the veins of the leaves, the worms use only the soft part of the leaf. Earthworms are known to be thrifty creatures.

They keep the leaves in their burrows in reserve, neatly stacking them. Moreover, they may have a special hole dug to store provisions. They fill the hole with food and cover it with a clod of earth. Do not visit their storage until it is required.

Reproduction and life span of the earthworm

These spineless hermaphrodites. They are attracted to the scent. They mate, unite with their mucous membranes and, cross-fertilizing, exchange spermatozoa.

The embryo of the worm is stored in a strong cocoon on the parent's belt. It is not exposed to even the most difficult external factors. Most often, one worm is born. They live 6-7 years.