Earthworm belongs to the group of annelids. It does not have any special organs specifically designed for gas exchange, and gas exchange occurs by diffusion across 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 much oxygen.
However, in annelids there is a circulatory system (unlike some simpler animals and single-celled organisms), and the respiratory pigment hemoglobin is dissolved in their blood. Contractions of large blood vessels drive blood along with 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 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.
A. Tracheal system in locusts. B. The structure of the insect trachea.Respiratory system of insects - locusts.
Gas exchange in insects carried out through a system of tubes, the so-called trachea. This system allows oxygen to flow from the air directly to the tissues and there is no need for its transportation by blood. It's much more quick way, rather than the diffusion of dissolved oxygen through tissue; Such gas exchange creates conditions for high metabolic rate.
Spiracles- paired openings located on the second and third thoracic and on the first eight abdominal segments of the insect’s body lead to air cavities. Branched tubes - tracheas - extend from these cavities. Each trachea is lined by an epithelium that secretes a thin layer of chitinous material. Typically, this tough 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 body segment, the trachea branches 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 flight muscles, they end blindly inside individual cells. The degree of branching of tracheoles can vary depending on the metabolic needs of the tissues.
Tracheoles have chitinous lining absent. At rest they are filled with watery fluid; at this time, oxygen diffuses through them to the tissues (and CO 2 in the opposite direction) at a speed 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, under the influence of osmotic forces, is partially absorbed into the tissues, and more air enters the tracheoles, and therefore more oxygen, and this oxygen is supplied directly to the tissues just when they need it.
Conditions created in insect tissues at rest and in an active state (work of tracheoles).
The overall air flow passing through the insect's body is regulated by a mechanism closing the 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 insect’s body.
Increased activity leads to increased formation of CO 2. Chemoreceptors they catch this and the spiracles open. The same stimulus can also cause ventilation movements of the body, especially in large insects, such as locusts. The dorsoventral muscles, contracting, make the insect's body flatter, as a result of which the volume of the tracheal system decreases and air is pushed out of it (“exhalation”). Air absorption (“inhalation”) occurs passively when the body segments, due to their elasticity, return to their original shape.
Judging by some data, thoracic and abdominal spiracles open and close alternately, and this, combined with the ventilation movements of the body, creates a unidirectional flow of air that enters the insect's body 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 in most insects is determined exclusively by the diffusion of oxygen through the tissues of the insect. Diffusion, as is known, is effective only over short distances, and this imposes severe restrictions on the size that insects can reach. These small distances at which diffusion is quite effective do not exceed 1 cm; therefore, although there are insects up to 30 cm long, their body should not be more than 2 cm thick.
In the world of fauna is earthworm. He can rightfully be called an earth worker, since it is thanks to him that the soil on which we walk is completely saturated with oxygen and other minerals. By passing various sections of the ground lengthwise and crosswise, this worm makes them loose, which then makes it possible to plant cultivated plants there, as well as to do gardening.
General characteristics of the species
The earthworm belongs to the kingdom Animalia, to the subkingdom Multicellular. Its type is characterized as Ringed, and its class is Oligochaete. The organization of annelids is very high compared to other types. They have a secondary body cavity, which has its own digestive, circulatory and nervous systems. They are separated by a dense layer of mesoderm cells, which serve as a kind of airbag for the animal. Also, thanks to them, each individual segment of the worm’s body can exist autonomously and progress in development. The habitats of these earthly orderlies are wet soil, salty or fresh water.
External structure of an earthworm
The worm's body has round shape. The length of representatives of this species can be up to 30 centimeters, which can include from 100 to 180 segments. The front part of the worm's body has a small thickening in which the so-called genital organs are concentrated. Local cells are activated during the breeding season and perform the function of laying eggs. The lateral outer parts of the worm's body are equipped with short bristles, completely invisible to the human eye. They allow the animal to move in space and move through the ground. It is also worth noting that the earthworm’s tummy is always painted in a lighter tone than its back, which has a dark burgundy, almost brown color.
What is he like from the inside?
The structure of the earthworm differs from all other relatives by the presence of real tissues that form its body. The outer part is covered with ectoderm, which is rich in mucous cells containing iron. This layer is followed by muscles, which are divided into two categories: circular and longitudinal. The former are located closer to the surface of the body and are more mobile. The latter are used as auxiliary during movement, and also allow internal organs to work more fully. The muscles of each individual segment of the worm's body can function autonomously. When moving, the earthworm alternately compresses each ring group of muscles, as a result of which its body either stretches or becomes shorter. This allows him to dig new tunnels and fully loosen the ground.
Digestive system
The structure of a worm is extremely simple and understandable. It originates from the mouth opening. Through it, food enters the pharynx and then passes through the esophagus. In this segment, products are purified from acids released by rotting products. The food then passes through the crop and into the stomach, which contains many small muscles. Here the products are literally ground up and then enter the intestines. The worm has one midgut, which goes into the posterior opening. In its cavity, all useful substances from food are absorbed into the walls, after which waste leaves the body through the anus. It is important to know that earthworm excrement is rich in potassium, phosphorus and nitrogen. They perfectly nourish the earth and saturate it with minerals.
Circulatory system
The circulatory system possessed by an earthworm can be divided into three segments: the abdominal vessel, the dorsal vessel and the annular vessel, which combines the previous two. The blood flow in the body is closed, or circular. The annular vessel, which is shaped like a spiral, unites two vital arteries for the worm in each segment. Capillaries also branch from it, which come close to the outer surface of the body. The walls of the entire annular vessel and its capillaries pulsate and contract, due to which blood is driven from the abdominal artery to the spinal artery. It is noteworthy that earthworms, like humans, have red blood. This is due to the presence of hemoglobin, which is regularly distributed throughout the body.
Breathing and the nervous system
The earthworm's breathing process occurs through the skin. Each cell of the outer surface is very sensitive to moisture, which is absorbed and processed. It is for this reason that worms do not live in dry sandy areas, but live where the soil is always filled with water or in the reservoirs themselves. The nervous system of this animal is much more interesting. The main “lump”, in which all neurons are concentrated in huge numbers, is located in the anterior segment of the body, but its analogues, smaller in size, are present in each of them. Therefore, each segment of the worm’s body can exist autonomously.
Reproduction
Let us immediately note that all earthworms are hermaphrodites, and in each organism the testes are located in front of the ovaries. These seals are located in the front part of the body, and during the mating period (and it is cross-breeding), the testes of one of the worms pass into the ovaries of the other. During the mating period, the worm secretes mucus, which is necessary for the formation of a cocoon, as well as a protein substance that will feed the embryo. As a result of these processes, a mucous membrane is formed in which embryos develop. Afterwards they leave it, back end first, and crawl into the ground to continue their lineage.
Earthworms, they are earthworms, this is not just one species, but a whole suborder of the class Oligochaete worms, belonging to the type Annelids. The earthworm is characterized by most of the structural features of its type and class.
Earthworms are ubiquitous. Our area is home to more than a dozen similar friends on another species (European earthworms), the body length of which 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 the edge of the hole with its rear end.
The body of an earthworm, as a representative of annelids, is divided into segments by ring constrictions. As in all oligochaetes, the parapodia are reduced, only tufts of bristles are 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 and 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 and also contains many mucous cells. Under the epithelium there are circular and longitudinal muscles. The body of an earthworm can contract and elongate. Circular muscles make the body of the worm thin and long, longitudinal muscles shorten and thicken. The longitudinal layer of muscles is more powerful. Alternate contraction of these muscles ensures movement. Each segment can change its shape separately.
The coelomic sacs of adjacent segments communicate with each other, thus the liquid in them mixes.
An earthworm often swallows soil, eating its way through. Nutrient particles are absorbed from the soil in the intestines. If the soil is soft, then it drills it with the front end. First, the front end is stretched and thinned, inserted between lumps of soil. Then the front end thickens, causing the soil to move apart. Next, the worm pulls up the back of the body.
They feed on rotting plant debris. In addition, they can drag fallen leaves from the surface. By dragging plant debris into the soil, worms contribute to their decomposition and the formation of fertile soil.
The digestive system consists of the mouth, pharynx, esophagus, crop, gizzard, midgut and hindgut, anus. Swallowing food is done through the muscular pharynx. The stomach grinds food; in addition to the muscles of the walls, swallowed grains of sand are involved in this. On the dorsal side, the wall of the midgut forms an invagination, increasing the absorption surface. The midgut is lined with ciliated epithelium, in which there are many unicellular glands. Complex organic substances are broken down in it, and simpler substances are absorbed into the blood. In the walls of the earthworm's midgut there is a dense network of blood vessels. The hindgut is small and ends at the anus.
A special feature of earthworms are calcareous glands, whose ducts flow into the esophagus. The substances they release neutralize the acids contained in the soil.
Breathing occurs over 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 crawl to the surface due to lack of air in the soil.
The circulatory, nervous and excretory systems are similar to polychaetes. However, in the circulatory system there are so-called “hearts” - annular vessels capable of muscular contraction. Located in segments 7-13. In a number of species, ring vessels are present only in the anterior part of the body.
There are no metanephridia (excretory organs of annelids) in the anterior three segments.
Sense organs are poorly developed. The skin contains sensitive cells - organs of touch. There are also cells in the skin 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 testes are located in front of the ovaries.
Mutual cross fertilization. Each of the mating worms transfers sperm 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 muff. Unfertilized eggs are laid in it. After mating, spermatozoa enter from the seminal receptacles. Fertilization occurs. After this, the sleeve slides off the worm's body and turns into a cocoon. Small worms develop from the eggs.
Capable of regeneration. If a predator tears off part of the worm's body, the other half completes the missing part. If the worm is divided into two parts, the result is two individuals, which can be considered asexual reproduction. However, the earthworm itself does not reproduce this way.
Annelids, which include earthworms, do not have special organs responsible for respiration. Gas exchange occurs in them through diffusion throughout the body, that is, they “breathe through their skin.”
Instructions
Worms do not need respiratory organs, since the annular structure and cylindrical shape provides an optimal ratio of volume and surface area involved in obtaining oxygen. Considering that the worms move quite little, we can say that such breathing through the skin is quite enough for them.
However, worms have a circulatory system, unlike unicellular organisms and some types of insects; hemoglobin is dissolved in the blood of an earthworm, which is carried throughout the body by contraction of large vessels during the movement of the worm. This distributes oxygen throughout the body, helping to maintain diffusion. Large vessels are one vein and one artery, which is exactly how many vessels the worm has (except for the capillaries located under the cuticle).
In principle, the earthworm does not have skin as such, like mammals, but has a very thin covering - the cuticle. Such skin is moistened by epithelial secretions, and due to its minimal thickness allows the worm to breathe. However, such skin is not protected from drying out, so the worms must live in some kind of moist environment in order to protect the skin from drying out. Oxygen is first dissolved in the water that covers the body of the worm, and only then is absorbed into the blood through the capillaries. If the worm's skin dries out, it cannot receive environment oxygen dies.
Since the earthworm practically does not come to the surface, such a respiration system turns out to be extremely beneficial for it - it can take oxygen directly from the soil for gas exchange. There is enough oxygen between the earth particles to supply the worm. When it rains, worms crawl out of the ground to the surface, this is due to the fact that water glues the particles of the earth together, and there is no air between them. To get the oxygen they need, the worms must rise to the surface.
To test the breath of an earthworm, you can conduct a simple experiment: pour earth into a jar and place several worms on top. After a short time, the worms will burrow into the ground, but if you water the ground, they will rise to the surface. All annelids breathe in a similar way - using the skin, over the entire surface of the body.
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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 - the girdle (its cells function during the period of sexual reproduction and egg laying). On the sides of each segment there are two pairs of short elastic setae, 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
A characteristic feature of the internal structure is that earthworms have developed real tissues. The outside of 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 muscle, consisting of a layer of circular muscles and a more powerful layer of longitudinal muscles located under it. Powerful longitudinal and circular 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 crawling through the burrow, but also pushing the soil apart, expanding the movement.
Digestive system
The digestive system begins at the front end of the body with the mouth opening, from which food enters sequentially into the pharynx and 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 on which the animals feed). Then the food passes into the enlarged crop and a small muscular stomach (the muscles in its walls help grind the food).
The midgut stretches from the stomach almost to the posterior end of the body, in which, under the action of enzymes, food is digested and absorbed. Undigested remains enter the short hindgut and are thrown out through the anus. Earthworms feed on half-rotted plant remains, which they swallow along with the soil. As it passes 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 regular soil.
Circulatory system
The circulatory system is closed and consists of blood vessels. The dorsal vessel stretches along the entire body above the intestines, and below it is the abdominal vessel.
In each segment they are united by a ring vessel. In the anterior segments, some annular vessels are thickened, their walls contract and pulsate rhythmically, thanks to which blood is driven 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 - nutrients dissolved in the blood are distributed throughout the body.
Breath
Most annelids, including earthworms, are characterized by cutaneous respiration; almost all gas exchange is provided by the surface of the body, therefore the worms are very sensitive to moist soil and are not found in dry soil. sandy soils, where their skin soon dries out, and after rains, when there is a lot of water in the soil, they crawl to the surface.
Nervous system
In the anterior segment of the worm there is a peripharyngeal ring - the largest accumulation of nerve cells. The abdominal nerve cord with nodes of nerve cells in each segment begins with it.
This nodular type nervous system was formed by the fusion of nerve cords on the right and left sides of the body. It ensures the independence of the joints and the coordinated functioning 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 outside. New, simpler funnel-shaped excretory organs - metanephridia - remove harmful substances into the external environment as they accumulate.
Reproduction and development
Reproduction occurs only sexually. Earthworms are hermaphrodites. Their reproductive system is located in several segments of the anterior part. The testes lie in front of the ovaries. When mating, the sperm of each of the two worms is transferred to the seminal receptacles (special cavities) of the other. Cross fertilization of worms.
During copulation (mating) and oviposition, girdle cells on the 32-37 segment secrete mucus, which serves to form an egg cocoon, and a protein liquid to nourish the developing embryo. The secretions of the girdle form a kind of mucous coupling (1).
The worm crawls out of it with its back end first, laying eggs in the mucus. The edges of the coupling stick together and a cocoon is formed, which remains in the earthen hole (2). Embryonic development of eggs occurs in a cocoon, from which young worms emerge (3).
Sense organs
The sense organs are very poorly developed. The earthworm does not have real organs of vision; their role is played 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 restore the back part).
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 early in 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 subsequently preserved in all higher animals, and they are formed from the same three germ layers. Thus, higher animals in their development repeat the evolutionary development of their ancestors.
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There are no special respiratory organs: they breathe over the entire surface of the body. The thin cuticle and tenderness of the skin, the rich network of skin blood vessels provide the ability to absorb oxygen from the environment. The cuticle is well wetted by water, and oxygen first dissolves in water. This entails the need to keep the skin moist.
Earthworms (lat. Lumbricidae) are a family of worms from the class Oligochaeta, a type of annelids (Annelida). This family includes rather large worms (from 10 to 30 cm in length) with thick skin, red blood and no eyes; in each ring two pairs of small hooked bristles protrude from each side.
The genera and species of this family differ in the shape of the head (the so-called upper lip), in the position of the girdle and in the number of rings; In Russia there are several species of earthworms from the genera: Lumbricus, Dendrobaena and Allolobophora.
Earthworms live in the ground, in which they dig long tubular tunnels; at night they come to the surface of the earth; they drag various organic remains into their passages - particles of leaves and other plant parts. They feed on decaying organic matter. The feces of earthworms, containing a lot of crushed earth particles, are deposited on the surface of the earth. By doing this, earthworms help increase the arable layer of the soil, while with their burrows they loosen the soil, and by pulling out plant residues they increase its content with organic parts.
The importance of earthworms in the process of soil formation was first indicated by Darwin.
Fertilization occurs at night, on the surface of the earth, and is mutual; both individuals fit tightly to each other, turning with opposite ends, and the seed of one individual flows into the seed receptacles of the other; in this case, both individuals are connected to each other by a ring formed by the secretion of special glands of the so-called girdle; At the end of the act, the ring is reset.
Earthworms are used as bait for fishing.
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There are no special respiratory organs: they breathe over the entire surface of the body.
1058;thin cuticle and tenderness of the skin, a rich network of skin blood vessels provide the ability to absorb oxygen from the environment. The cuticle is well wetted by water, and oxygen first dissolves in water.
1069;this entails the need to keep the skin moist.
09mog.ru
Features and habitat
Earthworm , he is also a ringed one - a well-known resident on any personal plot. And it would seem an absolutely invisible creature that no one needs.
However, any person who is at least somehow connected with the land will be very happy to have such inhabitants of his garden. IN Russian Federation There are no more than a hundred species of earthworm. But all over the world there are one and a half thousand varieties of them.
It belongs to the family of annelids, the oligochaete class. Its entire long body consists of many rings. There may be seventy of them, or maybe all three hundred. Since it grows more than twenty-five centimeters in length.
But there are also the smallest ones, two or three centimeters. The Australian earthworms reach two and a half meters in size. Its color is literally gray-brown - crimson.
Also, on each ring, or it is also called a segment, there are bristles. Our ordinary garden worms, as a rule, grow eight bristles. They are classified as oligochaetes.
However, there are also tropical, polychaete species of worms in which the villi grow in dozens. The bristles help the worms crawl, absolutely over all soil tubercles or burrow into holes.
You can find them by holding the worm in your hands and running your finger from back to front. But since it is difficult for an inexperienced person to determine where his butt is, you can simply run your hand lightly along the body and back. You can feel it right away. In one direction the worm will be absolutely smooth, and in the opposite direction it will be rough.
Anyone who has ever picked up a worm knows that it is covered with not very pleasant mucus, which is vital for it. Firstly, mucus helps the invertebrate move freely in the ground. Secondly, since the worm does not have lungs, it breathes through the skin. And thanks to the moisture found on the mucus, the body is saturated with oxygen.
Self earthworm body consists of two groups of muscle tissue. They are longitudinal and transverse. The transverse muscles are located under the protective top layer of the worm's skin.
With their help, the worm becomes as long as possible. And the stronger muscles are longitudinal. They cut and make the body smaller. This is how the animal moves, sometimes lengthening, sometimes shortening.
The earthworm belongs to the secondary cavity animals. Consequently, he has a complete closed circulatory system. Because their life activity is active.
The muscles contract many times more often than in protocavitary worms. To do this, they need blood to provide the worm with all the nutrients and oxygen.
IN the structure of an earthworm There are a pair of blood vessels, one of them is called dorsal, the second is abdominal. Ring vessels connect them to each other. Blood flows through them from back to front, and vice versa.
Each ring, or segment as it is also called, has a pair of tubes. The funnels at their ends open and feces are discharged through the bottom. earthworm. This is the principle of operation of the excretory system.
As for the nervous system, it is nodal. Its components are the ventral nerve cord and the peripharyngeal nerve ring. These endings consist of fibers, and they, in turn, respond to the urges of the contracted muscles of the worm. Thanks to them, the worm can eat, move purposefully, reproduce, and develop.
In the building earthworm organs Those responsible for smell, touch, vision, and sensation are absent. But there are certain cells, they are located along the entire body of the invertebrate. With their help, the worm navigates in the dark and impassable ground.
Character and lifestyle
Charles Darwin also suggested the presence of intelligence in earthworms. Watching them, he noticed that when dragging a dry leaf into his home, it was turned with the narrow side. This makes it easier for a leaf to pass through a dense, earthy burrow. But on the contrary, he takes spruce needles by the base so that they do not fork.
All day, all life of rain worm scheduled by the minute. Every now and then he climbs in the ground, makes moves, swallowing it. The worm digs holes in two ways. He or, as already mentioned, swallows the earth, gradually moving forward.
In case the ground is too hard. And then leaving behind their biological waste. Or, he pushes it with his delicate end in different directions, and makes moves for himself. The passages are obliquely vertical.
Same rain worm, subsistence in the soil, drags into its holes, for insulation, various leaves, veins from leaves, thin pieces of paper and even scraps of wool. Its burrows are up to one meter deep. And the worms larger in size, and all ten meters. The worm works mainly at night.
A why earthworms crawl to the surface in huge quantities. This means he can't breathe. This usually happens after heavy rains. The earth is clogged with moisture, and there is no oxygen for him at all. When the cold weather arrives, earthworm goes deep into the soil.
Earthworm nutrition
The worm's diet is quite typical. Ingesting large quantities of soil along with food. Withered and slightly rotten leaves and mushrooms are suitable for them to eat. But it should not have an unpleasant odor, otherwise the worm will not eat it.
It turns out that earthworms even build entire storage rooms for themselves and store food there for winter. They eat it only in case of critical need. For example, in winter time, when the ground is completely frozen, and there can be no talk of any ground food.
Having sucked in the food along with a lump of earth, through the pharynx, with muscular movements, now expanding his body, now narrowing it, he pushes it to the back of the esophagus into the goiter. Afterwards, it penetrates the stomach. From the stomach it is sent to be poisoned in the intestines, thanks to enzymes, and comes out as useful biomass.
Making moves, and at the same time having a snack, rain to the worm need to crawl out periodically to the surface to throw off the earth. At the same time, he adheres to the hole with his tail edge, as if holding on to it.
And after that, there are always earthen slides. The soil processed by the worm turns out sticky. Then it dries and becomes small balls, about the size of a match head.
These balls are saturated with vitamins, enzymes, and organic substances, which, as a result, kill all bacteria in the soil and prevent rotting, which is very important for plant roots. And they also act on the composition of the earth as an antiseptic, disinfecting it.
Reproduction and lifespan
Earthworms can be heterosexual or hermaphrodite. All earthworms have thickenings on the front third of their body. They contain the ovary and testis. Hermaphrodites release seed into each other. Already ripe testicles, up to ten pieces, are inseminated. And they crawl away in different directions.
When a female individual is ready to reproduce, she approaches her partner and copulates. Something like a cocoon is formed on it, consisting of several dozen thickened segments.
It is divided by a kind of belt. This cocoon receives all the nutrients necessary for the brood. After fertilization, the worm takes off this burden; it simply slides off the animal.
The edges of the cocoon are quickly pulled together on both sides so that the future offspring do not dry out before they are born. Then, over the course of four weeks, small worms mature and hatch.
Once born, they scatter in all directions. And from the first days of their lives they begin active work to process the land. And already at three months of age, grown-up children reach the size of adults.
Another fact about earthworms is the ability to regenerate. If someone or something splits it into two halves. Over time, each half will become a full-fledged individual. This is one of the methods of reproduction, but no longer sexually.
The role of the earthworm very important in agriculture. Firstly, they saturate the soil with oxygen, which is so necessary for everything growing on it. With their moves, they help the roots to fully develop.
Moisture is distributed evenly, and the soil is well ventilated and loosened. Thanks to the constant movement of the earth, with the help of worms, stones are removed from it.
Also, with their recycled adhesive residues, they glue the soil together, preventing it from eroding. Well, and of course they fertilize the soil when leaves and insect larvae are drawn into it. It all rots and serves as excellent, natural biological additives.
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Variety of worms
The phylum Worms includes groups of multicellular animals that have an elongated body and no skeleton. Habitats are usually moist soil, sea and fresh water bodies. They can vary in size from those that can only be detected with a microscope, to large forms several meters long. According to the shape of the body, they are divided into: Flatworms, Roundworms and Ringworms. All types have three body layers. The germ layers - ectoderm, endoderm and mesoderm give rise to the development of all their tissues and organs.
The most striking and famous representatives of flatworms: planaria, liver fluke, pork and bovine tapeworms, echinococcus, schistosome, etc. Well-known annelids include the earthworm, oligochaete worms, leeches and mysostomids. Round protostomes are represented by the well-known roundworms, pinworms, guinea worms, trichinella, etc.
Despite the diversity existing species worms, their types, structural features, methods of reproduction, nutrition, habitats, etc., there are a considerable number of similarities characteristic of all of them. For example, the respiration of flatworms, divided into aerobic and anaerobic, depending on the habitat, is also characteristic of the other two types.
Flatworms
The organ system of flatworms is represented by a number of main structural components, united by common functional characteristics and type of structure. The main systems include: respiratory, reproductive, excretory, muscular, nervous and integumentary.
Previously, a number of other taxonomic elements characterized by worm-like forms, lack of body cavities, and considered invertebrates were assigned to the class of ciliated protostomes.
The body shape of any type has a bilaterally symmetrical shape, in which the head and caudal ends are pronounced, both ends are slightly flattened, but in large species, flattening is very pronounced. The organ system of flatworms for respiration and blood circulation is absent. A body cavity does not develop, but this is true for all representatives except tapeworms and flukes in certain life cycles.
The structure of the body
Getting to know the muscles
The muscle tissue of flatworms is represented by a muscular sac, which lies under the epithelium. It consists of a number of layers of muscle-type cells that are not divided into muscles. However, some differentiation is observed in the areas of the pharynx and reproductive system. External part of cells muscle layers are oriented transversely, and the internal ones are oriented along the posterior-anterior axis of the body. The outer muscles are called the annular layer, and the inner ones are called the longitudinal muscles layer.
Breathing methods
All groups of flatworms are characterized by the presence of a pharynx, which leads to the intestine. The exceptions are cestodes and tapeworms. This intestine opens into the parenchyma intended for digestion, closes blindly and is connected with the outside world only by the mouth opening. Some large turbellarians have anal pores, however, this is an exception only for some subjects of the species. Small forms are characterized by a straight intestine, while large ones (planaria, fluke) may have a branched one. The pharynx is located on the surface of the abdomen and can often be found in the middle or closer to the back of the body. In some groups of worms the pharynx moves forward.
Features of the nervous system and sensory organs
Characterizing the nervous system of flat protostomes, it is worth noting that they are characterized by the presence of nerve ganglia located in front of the body, and also have ganglia of the brain and nerve columns branching off from them, which are connected by jumpers. Sensitive organs include individual skin cilia, which are processes of nerve-type cells. There are free-living species that have special, light-sensitive eyes of a pigmented nature. Such organs serve as a primitive adaptation to the sense of balance and allow vision, albeit primitively.
Extraction system
Flatworms have an excretory system that takes the form of protonephridia. With their help, the process of osmoregulation and metabolism occurs. The selection system takes the form of channels that branch and combine into 1-2 channels. Initially, these are stellate-type cells, which, branching into tubules, open a lumen for the passage of a bundle of flagella. Merging, the tubules form a larger structure and are brought out in the form of excretory pores to the surface of the body. Such excretory systems are called protonephridial. Metabolic products that are dangerous to the life of the worm are excreted along with fluids through the above-mentioned protonephridia, as well as with the help of special parenchyma cells - atrocytes, which play the role of “storage buds”.
Reproduction
- Germarium is the ovary itself. Produces eggs that are poor in yolk but capable of development.
- Vitellaria - sometimes called vitellaria, it produces abortive type eggs, they are rich in yolk.
These composite reproductive systems form complex, or exolecithal, eggs. The common membrane may contain one egg or a number of yolk spherules secreted by accessory glands.
Conclusion
Summarizing the above text, we can make several conclusions, among which the most significant are: the respiration of flatworms is carried out on the surface of the entire body, predominantly flatworms are predators, there is a muscular sac, the body cover is represented by a tegument, the majority are hermaphrodites and only a few of them are dioecious.
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Annelids have the following aromorphoses: 1. The body was divided into segments (metameres) with repeating sets internal organs. 2. A secondary cavity has appeared - the coelom, which has its own mesodermal lining. 3. There was a further complication of the nervous system: the concentration of nerve cells on the abdominal side in each segment (the abdominal nerve chain was formed), a significant increase in the cerebral ganglia (nodes) (supraglottic, subpharyngeal nerve ganglia, peripharyngeal ring). 4. A closed circulatory system emerged, which ensured rapid transport of substances throughout the body. 5. Respiratory organs appeared, increasing the respiratory surface and the intensity of gas exchange. 6. The digestive system has become more complex: the midgut has differentiated into sections, which has led to a step-by-step process of digestion. 7. Parapodia were formed - limbs for movement. 8. Further complication of the excretory organs occurred: a metanephridial multicellular excretory system was formed.
Earthworm – Lumbricus terrestris(type Annelids, class Oligochaetes, family Lumbricidae) lives in moist, humus-rich soil. It feeds on organic matter, passing soil and plant debris through its intestines. Even Charles Darwin noted the beneficial effect of earthworms on soil fertility. By dragging the remains of plants into the burrows, they enrich it with humus. By making passages in the soil, they facilitate the penetration of air and water to the roots of plants.
Earthworms are active in the warm season. In winter they hibernate. Freezing kills 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 level and the ground is saturated with rainwater, their mating season begins. They reproduce very quickly, producing about a hundred young worms per year. In summer, worms are not as active. There is very little food - dying plant debris - at this time, and the soil is deprived of moisture, which can cause the death of worms. The autumn period is again characterized by worm activity. At this time, reproduction of offspring begins again, which lasts until the onset of winter.
Earthworms live relatively long. Some manage to live for about ten years if they do not become victims of birds and moles. Another threat to their life is the pesticides that are so widely used in gardening today.
So, the earthworm has an elongated, cylindrical body from 10 to 30 cm long. Dorsal side more rounded, it is darker, the dorsal blood vessel is visible through its skin. Abdominal side somewhat flattened and lighter colored. The anterior end of the body is thicker and darker in color. The body consists of rings - segments. In an adult worm, their number reaches 200. In the area of 32-37 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 segmental (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 uneven soil, the worm moves forward with the help of the muscles of the skin-muscular sac.
Veils. The earthworm's body is covered skin-muscle bag. He is educated cuticle, single layer epithelium and two layers of muscles - external circular and internal longitudinal. The skin epithelium of the worm is rich mucous glands, which produce slime, covering the entire body of the worm and protecting it from drying out. Mucus also makes crawling in burrows easier by reducing friction with the soil.
Movement of an earthworm. When a worm crawls, waves of muscle contractions run through its body, and both the length and thickness of individual parts of its body are constantly changing. The movements produced by each part of the body consist in the fact that its constituent segments either stretch and become thinner, or contract and become thicker. As a result of such alternating stretching and contraction, 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 this, the rear end of the body remains in place, and the head end is pushed even further forward, and thus the further advancement of the worm continues (it is convenient to observe it by letting the worm crawl along paper spread on the table).
Body cavity. Inside the skin-muscle sac of annelids there is secondary cavity body, or in general. This body cavity is not limited by muscles, like in roundworms, but has its own epithelial(coelomic) lining, 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 - dissepiments. The secondary cavity is divided into chambers, each segment containing a pair of coelomic sacs. The coelomic fluid is under pressure and plays a role hydroskeleton, so the worm feels elastic to the touch.
Digestive system comprises front, average And rear guts. Mouth located on the second segment on the ventral side of the body. Anal hole
type Annelids Earthworm
- at the rear end of the body, it looks like a small slit. Due to feeding on rotting plant remains and humus, the digestive system has a number of features. Its anterior section is differentiated into muscular throat, esophagus, goiter and muscular stomach. To increase the absorption surface, a fold has formed on the upper part of the intestine typhlosol(typhlozolis). Please note: differentiated sections of the foregut - pharynx, esophagus, crop, 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 worm’s body covers do not dry out, but excessive moisture (for example, very wet soil after rain) is just as destructive for them.
Circulatory system closed, that is, blood moves through the vessels without spilling into the body cavity. The movement of blood is determined by the pulsation of large vessels, mainly surrounding the esophagus. These are kind of hearts. Blood supplies all organs and tissues with nutrients, transporting them from the intestines, and oxygen entering the skin capillaries from the external environment. By spinal vessel blood moves from the back end of the body to the front, and along abdominal vessel- in the opposite direction. An earthworm's blood is red. An iron-containing protein, similar to vertebrate hemoglobin and transporting oxygen, is found in a dissolved state in the blood plasma, and red blood cells are absent.
Nervous system more complex than that of flatworms and roundworms. It consists of peripharyngeal nerve ring with ganglia and abdominal nervous chains. This is the so-called nervous system ladder type. Suprapharyngeal doubles ganglion performs the functions of the brain and is more developed than subpharyngeal. The nerve chain originates from the subpharyngeal node and consists of segmentally located pairs of ganglia, connected to each other by transverse and longitudinal commissures. Nerves extend from the ganglia to various organs. The earthworm's sense organs are poorly developed: there are no eyes or tentacles, but their skin contains numerous sensory cells and nerve endings.
Excretory organs presented segment by segment (i.e. in each segment) arranged in pairs metanephridia. They look like convoluted tubes and begin in the body cavity as a funnel with cilia. A channel departs from the funnel, which penetrates the transverse septum and passes into the cavity of the next segment. The terminal section of the metanephridium has an extension - uric bubble, which opens outward on the side of the worm’s body (i.e., in each segment there is a pair of very small excretory holes). In addition to metanephridia, the secretion involves chloragogenous cells, covering the surface of the intestine 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 girdle can be examined only during the breeding season - in the spring. To male
type Annelids Earthworm
the reproductive system includes two pairs of testes, located in segments 10 and 11, four vas deferens, which merge in pairs and open outwards doubles male sexual hole, located in the 15th segment. The female reproductive system includes pair ovaries located in segment 13, oviducts, which open outwards in the 14th segment a couple women's sexual holes. There are two pairs in segments 9 and 10 spermatheca, each of which opens outward with an independent hole.
Earthworms reproduce sexually. Cross fertilization, in a cocoon. Two worms meet, tightly wrap their bodies around each other, attach their ventral sides to each other and exchange sperm, which ends up in the spermatic receptacles. After this, the worms disperse. Next, the belt forms a mucous muff, in which eggs are laid. As the coupling moves through the segments containing the spermatheca, the eggs are fertilized by sperm belonging to another individual. The muff is shed through the anterior end of the body, becomes 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 the aromorphoses of the annelid type.
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 worm's circulatory system?
What is the structure of the worm's excretory system?
What is the structure of the worm's nervous system?
What structure does the reproductive system of an earthworm have?
How does an earthworm reproduce?
What is the significance of an earthworm?
type Annelids Earthworm
Rice. Earthworm, its passages in the ground and movement.
Rice. Internal structure of an earthworm.
1, 16 - intestine; 2 - partitions; 3 - epithelial lining of the secondary body cavity; 4 - dorsal (back) blood vessel; 5 - ring blood vessel; 6 - skin-muscle bag; 7 - cuticle; 8 - skin epithelium; 9 - whole; 10 - metanephridium; 11 - eggs; 12 - ring muscles; 13 - longitudinal muscles; 14 - ventral (abdominal) blood vessel; 15 - abdominal nerve cord.
type Annelids Earthworm
Rice. The structure of the anterior end of the earthworm's body.
The prostomium is the protrusion of the upper part of the first segment, covering the mouth. Peristomium is the name of the first segment of the body.
type Annelids Earthworm
Rice. The structure of an 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 - ring blood vessels; 12 - abdominal blood vessel; 13 - metanephridia; 14 - ovaries; 15 - testes; 16 — seed sacs; 17 - seminal receptacles; 18 - peripharyngeal nerve 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 - pharynx; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - intestine; 7 - peripharyngeal ring; 8 - abdominal nerve chain; 9 - “hearts”; 10 - dorsal blood vessel; 11 - abdominal blood vessel.
Rice. Reproduction of the Earthworm.
1 - mucous coupling; 2 - cocoon; 3 - emergence of young worms from the cocoon.
type annelids
Rice. The structure of the Nereid polychaete worm.
type annelids
Rice. Appearance Medical leech.
