In the world of fauna is the earthworm. He can rightfully be called an earthen worker, since it is thanks to him that the soil on which we walk is fully saturated with oxygen and other minerals. Passing various plots of land up and down, this worm makes them loose, which allows after that to plant cultivated plants there, as well as to engage in gardening.
General characteristics of the species
The earthworm belongs to the kingdom of Animals, to the sub-kingdom of the Multicellular. Its type is characterized as Ringed, and its class is Small-bristled. The organization of annelids is very high in comparison with other types. They have a secondary body cavity that has its own digestive, circulatory and nervous systems. They are separated by a dense layer of mesoderm cells, which serve as a kind of airbags for the animal. Also, thanks to them, each individual segment of the worm's body can autonomously exist and progress in development. The habitats of these terrestrial orderlies are moist soil, salt or fresh waters.
External structure of the earthworm
The body of the worm is round. 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 body of the worm has a slight thickening, in which the so-called genitals are concentrated. Local cells are activated during the breeding season and perform the function of laying eggs. The lateral outer parts of the body of the worm are equipped with short bristles, completely invisible to the human eye. They allow the animal to move in space and sort through the ground. It is also worth noting that the belly of the earthworm is always painted in a lighter tone than its back, which has a maroon, almost brown color.
What is he like from the inside
The structure of the earthworm is distinguished 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 that contain iron. This layer is followed by muscles, which are divided into two categories: annular 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 muscle group, as a result of which its body sometimes stretches, sometimes becomes shorter. This allows him to break through new tunnels and fully loosen the ground.
Digestive system
The structure of the 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, the products are cleaned of acids produced by putrefaction products. The food then passes through the goiter and into the stomach, which contains many small muscles. Here, the products are literally ground and then enter the intestines. The worm has one midgut, which passes into the posterior foramen. In its cavity, all nutrients from food are absorbed into the walls, after which the waste leaves the body through the anus. It is important to know that earthworm excrement is saturated with potassium, phosphorus and nitrogen. They perfectly nourish the earth and saturate it with minerals.
Circulatory system
The circulatory system possessed by the earthworm can be divided into three segments: the abdominal vessel, the dorsal vessel, and the annular vessel, which unites the two previous ones. The blood flow in the body is closed, or annular. The annular vessel, which has the shape of a spiral, unites two arteries vital for the worm in each segment. Capillaries also branch off 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 distilled from the abdominal artery to the dorsal 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 nervous system
The respiration process in an earthworm is through the skin. Every cell on 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 water bodies 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 analogs, smaller in size, are in each of them. Therefore, each segment of the worm's body can exist autonomously.
Reproduction
Immediately, we 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 of the body, and during the mating period (and they have it cross) 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 the embryo will feed on. As a result of these processes, a mucous sleeve is formed in which the embryos develop. Then they leave it with the rear end first and crawl into the ground to continue their race.
And the cylindrical shape provides an optimal ratio of volume and surface area involved in oxygen production. Considering that they 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 species of insects, rain-dissolved hemoglobin, which is carried through the body through the contraction of large vessels during the movement of the worm. This circulates oxygen throughout the body, helping to maintain diffusion. Large vessels are one vein and one artery; this is how many vessels the worm has (except for the capillaries located under the cuticle).
As such, the skin, like mammals, the earthworm, in principle, does not have, there is a very thin cover - the cuticle. Such skin is moistened with epithelial secretions, and due to its minimal thickness allows the worm to breathe. However, such skin is not protected from drying out, because the worms must live in a kind of humid environment in order to protect the skin from drying out. Oxygen is preliminarily dissolved in water, which covers the body of the worm, and only then is absorbed into the blood through the capillaries. If the skin of the worm dries up, it cannot receive oxygen from the environment and dies.
Since the rainwater practically does not come to the surface, such a respiratory 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 particles of the earth to supply them with the worm. During the rain, worms crawl out of the ground to the surface, this is due to the fact that water sticks together the particles of the earth, and there is no air between them. To get the oxygen they need, the worms must rise to the surface.
To test the breathing of an earthworm, you can conduct a simple experiment: earth is poured into the jar, several are placed on top. After a short time, the worms will bury themselves in the ground, but if you pour water on the ground, they will rise to the surface. Similarly, all annelids - with the help of the skin, the entire surface of the body.
The earthworm is a representative of the annelid type. Its long, elongated case consists of separate segments - rings, separated by ring constrictions, which explains the name of the species. Thanks to this structure, it can move freely both in dense soil and on the soil surface.
Instructions
The body of the earthworm is elongated in length by 10-16 cm. It is rounded in cross-section, but longitudinally divided by annular constrictions into 100-180 segments. On them are elastic bristles, with which the worm clings to the unevenness of the soil during movement.
During the day, worms are in the soil and make passages in it. They easily drill the soft one with the front end of the body: at first, it becomes thin, and the worm pushes it forward between the lumps of earth, then, thickening, the front end pushes the soil, and the worm pulls up the back of the body. In dense soil, worms can eat their own passages, passing it through the digestive tract. At night, they come to the surface of the soil and leave behind characteristic earthen piles.
The skin of the earthworm is moist to the touch as it is covered, making it easier for the worm to move through the soil. The oxygen needed for breathing can also only penetrate through wet skin. Under it is the musculocutaneous sac - circular (transverse) muscles fused with the skin, under which lies a layer of longitudinal muscles. The former make the body of the animal long and thin, the latter thicken or shortened. The coordinated alternating work of these muscles ensures the movement of the worm.
A fluid-filled body cavity can be seen under the skin-muscle sac. The internal organs of the animal are located in it. In contrast to roundworms, in rainworms, the body cavity is not continuous, but segmented, divided by transverse walls.
And the suborder of earthworms (Haplotaxida). Its body consists of ring-shaped segments, the number of which can be up to 320! These animals are widespread in all corners of our planet. They are not only in Antarctica. Very often children are interested in how earthworms move. In our article, we will analyze this issue in detail, and at the same time we will learn about their appearance, lifestyle and method of reproduction.
Earthworm lifestyle
If in the morning or after the rain you walk through the garden, then, as a rule, you can see on the ground small heaps of soil thrown out by worms, and in the puddles you can see them. Due to the fact that these individuals creep out to the surface of the earth after rain, such a name stuck to them. (the photo above shows this invertebrate) also crawls to the earth's surface at night. As a rule, it prefers humus-rich soil, so it is rarely found in sandstones. Dislikes earthworm and marshy soils. These features are explained by the physiological characteristics of the Lumbricidae. The fact is that worms breathe with the entire surface of their body, covered with a mucous epidermis. Too little air is dissolved in the soil saturated with moisture. As a result, the earthworm suffocates there. By the way, this also explains his behavior during the rain. Dry soil is also detrimental to representatives of Haplotaxida: their skin dries up and breathing stops. In humid and warm weather, earthworms (the photo below shows the Lumbricidae in all its "glory") keep closer to the surface of the earth. With a decrease in temperature, as well as with the onset of a dry period, they crawl into the deep layers of the soil.
earthworms
Adults reach 30 centimeters in length, although there are individual specimens of larger sizes. The body of the earthworm is slippery, smooth, has a cylindrical shape, consists of segments - piece rings. This constitution is explained by the way of life of the Lumbricidae: such a structure facilitates the process of movement in the soil. The number of piecework rings reaches two hundred. The surface of the body, which could be conventionally called the back, is convex, the abdominal surface is flat and lighter. On the body of the earthworm, where its front part ends, there is a thickening, which is called a girdle. It contains special glands that secrete a sticky liquid. During reproduction, an egg cocoon is formed from the girdle, eggs develop in it.
How do earthworms move?
Representatives of Haplotaxida are crawling. First, they stretch the front end of their body and cling to the irregularities of the earth's surface with special bristles, which are located on the ventral side of the rings. After this, muscle contraction occurs, and the back is pulled forward. The movement of a worm in the ground is characterized by the fact that it makes holes in the soil. At the same time, with the pointed end of the body, it pushes the earth apart, and then squeezes between its particles. It is also interesting how earthworms move in denser layers. In the process of movement, they swallow the earth and pass it through the intestines. The worms, as a rule, swallow the soil at a considerable depth, and throw it out through the anus already at the top, near their own burrow. It can often be observed in the summer on the surface of the earth in the form of lumps and elongated "laces".
Earthworm and its biology
Worms have well-developed muscles, thanks to which this method of movement became possible. Their muscles are located under the epidermis, in fact, they, together with the skin, form a kind of musculocutaneous sac. The musculature is arranged in two layers. Directly under the epidermis are the annular muscles, and under them is the second, thicker longitudinal layer (consists of long contractile fibers). When the longitudinal muscles are compressed, the body of the earthworm becomes thicker and shorter. With the contraction of the annular muscles, on the contrary, it is long and thin. The alternate contraction of both layers of muscles, carried out under the influence of the nervous system branching in the muscle tissue, determines the movement of the Lumbricidae.
The movement of worms is greatly facilitated by the presence of small bristles on the lower part of the body. They can be felt if you run a wet finger along the belly of the worm from the back to the front end. Thanks to these bristles, earthworms not only move in the soil, but also "grab" the ground when trying to pull them out. They also help to climb and descend along the already done earthen passages. At this point, we will finish dealing with the question of how earthworms move, and move on to no less interesting facts about the life of the Lumbricidae.
Circulatory system
Consists of two longitudinal vessels - the abdominal and dorsal, as well as the branches connecting them. Due to the muscle contraction of the walls, blood flows throughout the body. The blood of earthworms is scarlet. With its help, a connection is established between the internal organs, and metabolism is also carried out. Circulating, the blood carries nutrients from the digestive organs, as well as oxygen from the skin. At the same time, carbon dioxide is removed from the tissues. In addition, the blood removes unnecessary and harmful compounds into the excretory organs.
Eating earthworms
The diet of the representatives of Haplotaxida is based on semi-decayed plant remains. As a rule, at night, earthworms drag leaves, stems, etc. into their holes. They can also pump humus-rich soil through their intestines.
Irritation of earthworms
There are no special earthworms. They perceive external stimuli thanks to the nervous system. The sense of touch is highly developed in worms. The nerve cells responsible for this are located over the entire surface of the skin. The sensitivity of earthworms is so great that the lightest vibrations of the soil make them hide as fast as possible in burrows or in deeper layers of the earth. However, the significance of sensitive nerve endings is not limited to the function of touch. Scientists have found that with the help of these cells, earthworms are able to sense rays of light. So, if a flashlight beam is directed at a worm at night, it will hide at a high speed in a safe place.
The response of animals to any stimulus carried out by the nervous system is called a reflex. It is customary to distinguish between different kinds of reflexes. So, the contraction of the body of an earthworm from touching it, as well as its movement under sudden illumination, is a protective function. This is a defense reflex. Scientists have shown that earthworms can smell. Through their sense of smell, they find food.
Reproduction
Earthworms reproduce sexually, although in general Protostomes are hermaphrodites. Each Haplotaxida has male organs called testes (sperm develop in them) and female organs called ovaries (eggs are produced in them). The earthworm lays its eggs in a slimy cocoon. It is formed from a substance that is released through the belt. Further, the cocoon in the form of a sleeve slides off the body and contracts at the ends. It remains in the ground until the young worms come out of it. The cocoon serves to protect eggs from dampness and other adverse effects.
What are worms for?
This section will be useful for those who think that earthworms are needed only for fishing. Of course, a fisherman has nothing to do without them on the river without them, but this is not all the benefit of the representatives of the Lumbricidae. The role of the earthworm in nature is so great that it is impossible to overestimate it. They promote the decomposition of organic matter in the soil. In addition, earthworms enrich the land with the most valuable fertilizer - humus. They are also a kind of indicator: if the soil contains a lot of worms, then it is fertile.
A complete understanding of the role of Haplotaxida came to humanity relatively recently. However, even now, many farmers prefer to use chemical fertilizers, despite the fact that they kill all living things. Today they found an alternative to chemicals - vermicompost and vermicompost. In fact, this is a magic wand for the earth, because they contain a large amount of phosphorus, potassium, nitrogen, that is, exactly those substances that are vital for plants for their full growth.
Conclusion
Earthworms are the most important link in soil formation. Let's take a look at the process. In autumn, foliage falls from the trees and covers the entire surface of the earth. Immediately after that, they get down to business and decompose the leaves to the compost stage. And then the worms pick up the baton, which process the foliage to the vermicompost stage. Thus, the most valuable fertilizers get into the soil.
Type Ringworms
General characteristics of the type of annelids (rings)
General characteristics of the type
Ringworms (annelids) are a large type (about 9 thousand species) of higher free-living marine, freshwater and soil animals, which have a more complex organization than flat and round worms. These primarily include To marine polychaete worms, which are the nodal group in the evolution of higher invertebrates: mollusks and arthropods originated from their ancient ancestors.
The main progressive features of the structure of rings are as follows:
1. The body consists of numerous (5-800) segments(rings). Segmentation is expressed not only in the external, but also in the internal organization, in the repetition of many internal organs, which increases the survival rate of the animal with partial damage to the body.
2. Groups of segments similar in structure and function in polychaete worms are combined into parts of the body- head, trunk and anal lobe. The head section was formed by the fusion of several anterior segments. In small-bristle worms, body segmentation homogeneous.
3. Body cavity secondary, or overall, lined with coelomic epithelium. In each segment, the whole is represented by two isolated sacs filled with coelomic fluid.
Figure 11.7. The head end of the Nereid: I1-eyes; 2 - tentacles; 3 -antennae; 4 - parapodia with tufts of bristles.
4. The musculocutaneous sac consists of a thin elastic cuticles, located under it monolayer epithelium and two muscle layers: outer - annular, and internal - highly developed longitudinal.
5. The specialized organs of movement that appeared for the first time - parapodia - represent lateral bilobate outgrowths of the body walls of the trunk segments, into which the whole enters. Both lobes (dorsal and ventral) have more or fewer setae (Fig. 11.7). In small-bristled worms, parapodia are absent, there are only bundles with a few bristles.
6. In the digestive system, which has three sections, the anterior gut is strongly differentiated into a number of organs (mouth, pharynx, esophagus, goiter, stomach).
7. Newly developed circulatory system closed. It consists of large longitudinal dorsal and abdominal vessels, connected in each segment ring vessels(fig.11.8). The movement of blood is carried out due to the pumping activity of the contractile sections of the dorsal, less often annular vessels. The blood plasma contains respiratory pigments close to hemoglobin, thanks to which the ringlets have populated habitats with a wide variety of oxygen content.
8. Respiratory organs in polychaete worms -gills; these are thin-walled leaf-shaped, feathery or bushy outer outgrowths of the part of the dorsal lobes of the parapodia, penetrated by blood vessels. Small-bristled worms breathe over the entire surface of the body.
9. Excretory organs - located in pairs in each segment metanephridia, removing the end products of vital activity from the cavity fluid. The metanephridium funnel is located in the coelom of one segment, and the short tubule extending from it opens outward in the subsequent segment (see fig. 11.8.6).
10. Nervous system ganglionic type. It consists of paired supraopharyngeal and subopharyngeal ganglia, connected nerve trunks into the periopharyngeal nerve ring, and many pairs of ganglia abdominal nerve chain, one pair in each segment (Figure 11.8, a). The sense organs are diverse: sight (in polychaete worms), touch, chemical sense, balance.
11. Overwhelming majority ringlets dioecious animals, less often hermaphrodites. The sex glands develop either under the coelomic epithelium in all trunk segments (in polysetal worms), or only in some (in small-bristle worms). In polychaete worms, the germ cells through the ruptures of the coelomic epithelium enter the coelomic fluid, from where they are excreted into the water by special funnels or metanephridia. In most aquatic rings, fertilization is external, in soil forms - internal. Development with metamorphosis(in polychaete worms) or direct (in small bristle worms, leeches). Some types of ringlets, in addition to sexual, reproduce asexually (fragmentation of the body with subsequent regeneration of the missing parts). The type of annelids is subdivided into three classes - Polychaetae, Malobeta and Leech.
Type Ringed worms. general characteristics
The main characteristic features of annelids are:
-secondary, or coelomic, cavity body;
Emergence circulatory and respiratory systems;
The excretory system in the form metanephridium.
a brief description of
|
Habitat |
Marine and freshwater, terrestrial and underground animals |
|
|
Body structure |
The body is elongated, worm-shaped, metameric structure. Bilateral symmetry. Three-layer. Polychaetes have parapodia |
|
|
Body covers |
Cuticle. Each segment has 8 or more setae for movement. There are many glands in the skin. In the musculocutaneous sac, the longitudinal and transverse muscles | |
|
Body cavity |
Secondary body cavity - whole, filled with fluid that acts as a hydroskeleton | |
|
Digestive system |
Mouth, pharynx, esophagus, goiter, stomach, intestines, anus | |
|
Respiratory system |
Breathing over the entire surface of the body. Polychaetes have external gills. | |
|
Circulatory system |
Closed. One circle of blood circulation. There is no heart. Blood red | |
|
Excretory system |
A pair of tubules in each metamere - metanephridia | |
|
Nervous system |
Periopharyngeal nerve ring, abdominal ladder chain | |
|
Sense organs |
Tactile and light-sensitive cells, polychaetes have eyes | |
|
Reproductive system and development |
Hermaphrodites. Fertilization is cross. Development without metamorphosis. Fertilization is internal. Polychaete dioecious, external fertilization, development with metamorphosis | |
Small bristle class
Class Small bristle worms unites 4-5 thousand species. Their body length ranges from 0.5 mm to 3 m.
Audio fragment "Class Small-bristle worms"(00:54)
The internal structure of the earthworm
The integuments of the body and muscles. The skin of the worm consists of one layer of integumentary cells. Among them are cells that produce mucus. The annular and longitudinal muscles are located under the skin. With the contraction of the annular muscles, the body of the earthworm lengthens, becomes thinner and moves forward. With the contraction of the longitudinal muscles, the back is pulled up to the front. The movement takes place in waves.
Virtual lab
Body cavity. As we already know, the earthworm belongs to three-layer animals. Its body consists essentially of two tubes nested one inside the other. The outer tube is the body wall and the inner tube is the wall of the digestive tract. Body cavity, lined from the inside with a layer of cells located between them. In the cavity fluid (it gives the body elasticity) are the internal organs.
Digestive system. The digestive tract begins with the mouth, followed by the pharynx, esophagus, goiter, stomach, intestines and anus. 
Circulatory system. The circulatory system is designed to move oxygen, carbon dioxide, nutrients and other substances inside the body. In an earthworm, blood does not flow freely into the body cavity, but moves only inside the vessels. This circulatory system is called closed ... The circulatory system consists of two main vessels : dorsal and abdominal. The blood flows along the spinal cord forward, along the abdominal - backward. In the area of the esophagus, these vessels are connected by annular vessels called "hearts". They have muscle walls, with the help of which they pump blood into the abdominal vessel. Small blood vessels extend to all organs and to the walls of the body.
Respiratory system.
Respiratory system. Respiratory organs of the earthworm are absent. Breathing is carried out through moist skin laced with blood vessels.
Excretory system. The excretory system is represented by paired organs (excretory tubes) located in each segment of the body. With the help of the excretory system, the body removes excess water and other substances.
Nervous system. The nervous system consists of the periopharyngeal nerve ring and the abdominal nerve cord, with thickenings in each segment from which nerves extend. The periopharyngeal ring consists of the supraopharyngeal and suboesophageal nerve nodes, connected by an annular bridge. There are no special senses, but the sensitive cells in the skin allow the earthworm to sense touch and distinguish light from darkness. The excitement arising in these cells is transmitted along nerve fibers to the nearest nerve node, and from there along other nerve fibers to the muscles, which causes their contraction. Thus, the nervous system carries out the body's response to irritation (reflex).
2. Reproduction and development
The earthworm is capable of reproducing both asexually and sexually. During asexual reproduction, the body of the earthworm splits into two parts, and then, by regeneration, each of them "completes" the missing parts of the body.
3. The meaning of earthworms
Ringed worms serve as important links in the food chains of natural biogeocenoses. Earthworms, for example, feed on moles, hedgehogs, frogs, toads, birds. Other worms (for example, pipe worker) - fish (carp, crucian carp).
Earthworms are of great benefit to humans by loosening the soil. They make it more porous, more accessible for the penetration of air and water, which facilitates plant growth and increases crop yields. Digging in the ground, the worms swallow pieces of soil, grind them and throw them away with organic matter.
Charles Darwin became interested in earthworms at a young age. In 1837, he made a report at the Geological Society of London on the topic: "On the formation of the soil layer", in which he outlined the theory according to which earth particles are constantly carried by earthworms from the depths to the surface, due to which objects lying on the ground turn out to after a few years at a depth of 6–10 cm under the sod. Thus, the entire soil layer is passed through the stomach of the earthworms.
Charles Darwin was struck by the following observations: worms pull leaves into the burrow by grabbing them by the top (not by the petiole), so the leaf has the least resistance when being pulled into the burrow (after all, the top of the leaf is narrower than its base). But worms always pull pine needles by the petiole, that is, the base common to twin needles. And in this case, the object offers the least resistance. Darwin in his experiments put triangles cut out of paper into worms, and they pulled them in the most expedient way: for one of the sharp corners. Further research showed that reflexes play a leading role in this process. 
Earthworms are capable of learning. They were placed in a T-shaped labyrinth: in the longest corridor that forms the base of the letter T. When the worms crawled to its end, they were given the choice to turn right or left. On the right they were waiting for blackout and food, on the left - a blow with a weak discharge of electric current. After a series of such "lessons", the worms developed a reflex to unmistakably head in the right direction, to food.
Type Ringed worms. Class Small-bristled
GENERAL CHARACTERISTICS
Structure and integuments . Body of small-bristled worms (oligochaete) strongly elongated, cylindrical, composed of one behind the other rings, or segments... All segments have a similar structure, i.e. the organization of oligochaetes (and all annelids) is characterized by repeatability of structure, or metamerism... Each segment, except the very first one, is equipped with small bristles, usually arranged in four beams - a pair of side and a pair of abdominal... The anterior segment is head lobe - prostomium devoid of eyes and antennas. He carries mouth opening... The last segment is anal lobe, or pygidium, - carries powder.
The covers of oligochaetes are presented epithelium forming on the surface a thin elastic cuticle (fig. 1). The epithelium is rich glandular cells.
Musculocutaneous sac . Under the epithelium are well-developed muscle layers. Outer layer presented circular muscle fibers... Due to the contraction of this layer, the body of the worm becomes thinner and stretched. The inner layer, more powerful, is presented longitudinal muscle fibers, due to the contraction of which the body of the worm thickens and shortens.
Rice. 1.Cross section of the middle part of the body of the earthworm: 1 - cuticle; 2 - epidermis; 3 - a layer of annular muscles; 4 - a layer of longitudinal muscles; 5 - coelomic epithelium; 6 - metanephridium; 7 - bristle; 8 - mesentery; 9 - abdominal vessel; 10 - subneural vessel; 11 - abdominal nerve chain; 12 - chloragogenic cells; 13 - intestinal cavity; 14 - vascular plexus; 15 - typhlozol; 16 - typhlozol vessel; 17 - dorsal vessel
Between the intestines and the musculocutaneous sac is secondary body cavity , or the whole -space bounded by its own epithelial walls of mesodermal origin and containing coelomic fluid (fig. 2). In structure, the whole differs from the primary body cavity by the presence coelomic lining - own wall. The lining is formed two sheets... One is adjacent to the body wall, the other to the intestinal wall. Above and below the intestine, both sheets grow together, forming mesentery(mesentery), which divides the whole to the left and right side... In addition, there are transverse partitions that divide the body cavity into cameras, corresponding to the boundaries of the rings... The whole is filled with liquid in which phagocytes, eggs, sperm float. The coelomic fluid, washing the internal organs, supplies them with oxygen and nutrients, and also promotes the removal of metabolic products and the movement of phagocytes. Just like the fluid that fills the primary body cavity in roundworms, the coelomic fluid can play a role hydroskeleton.
Digestive system oligochaete well differentiated (fig. 3). It starts mouth opening... The intestines are from three departments - front, middle and rear... The most differentiated is the anterior part of the intestine, consisting of the pharynx, esophagus and gizzard. Sometimes there is a goiter in front of the stomach. In the midgut, in order to increase the absorption surface, an invagination into the intestinal lumen - typhlozol is formed.
Rice. 2.Development of the coelom in annelids. А-В - cross sections of three consecutive stages of segment development: 1 - intestine; 2 - primary body cavity; 3 - whole; 4 - the outer wall of the coelomic sac; 5 - dorsal mesentery; 6 - the inner wall of the coelomic sac; 7 - abdominal mesentery; 8 - abdominal nerve trunks
Circulatory system closed and consists of two main longitudinal vessels - dorsal and abdominal. The dorsal vessel runs along the entire body above the intestine, the abdominal vessel - below it. The blood vessel cavity is the remnants of the primary body cavity. Both vessels are connected by annular vessels located metamerically. The movement of blood through the vessels is provided by the pulsation of the dorsal vessel and some of the annular vessels of the anterior part of the body, which are therefore called lateral, or annular, hearts. In the dorsal vessel, blood flows forward, in the abdominal - back. Through the annular vessels, blood moves from the dorsal vessel to the abdominal vessel in the front of the body and in the opposite direction - in the posterior segments. The blood can be red from iron-containing close to vertebrate hemoglobin, dissolved in the blood fluid.
Rice. 3.The structure of the earthworm (opened worm): 1 - pharynx; 2 - esophagus; 3 - calcareous glands; 4 - goiter; 5 - stomach; 6 - midgut; 7 - dorsal fold of the intestine (in section); 8 - supraopharyngeal ganglion; 9 - node of the abdominal nerve chain; 10 - dorsal blood vessel; 11 - annular vessels covering the pharynx; 12 - abdominal nerve chain; 13 - metanephridia; 14 - testes; 15 - vas deferens; 16 - seed bags; 17 - ovaries; 18 - oviducts; 19 - seminal receptacles; 20 - septa of the body cavity
Excretory system presented metanephridia. Metanephridium begins in the body cavity with a funnel - nephrostomy. From the funnel there is a duct that passes through the septum, enters the adjacent segment and opens outward excretory occasion in the side wall of the body. Each segment contains a pair of metanephridia - right and left. The funnel and duct are provided with cilia, which cause the movement of the secreted fluid.
Nervous system. central part the nervous system consists of paired cerebral ganglia - supraopharyngeal and subpharyngeal, connected by two periopharyngeal connectives (nerve trunks connecting the opposite ganglia). Thus is formed periopharyngeal ring. The central part of the nervous system includes and paired abdominal nerve trunk. In each segment, the trunks have thickenings - ganglia, which are connected by jumpers - commissars (transverse nerve trunks connecting the ganglia of one segment). Formed abdominal nerve cord, like a ladder. Each ganglion innervates all organs of the segment in which it is located.
Sense organs Oligochaetes have very poorly developed due to the burrowing way of life. Eyes almost always absent. However, there are light-sensitive cells, in large numbers scattered in the skin, which allows oligochaetes to have sensitivity to light.
The reproductive system. Oligochaetes - hermaphrodites, but fertilization they have - cross internal. The genital gonads are localized in the genital segments. Male gonads - testes - lie in seed capsules, which are in the seed sacs. Female reproductive system presented a pair of ovaries, a pair of oviducts and egg sacs.
Reproduction and development. Direct development without larval stage. The eggs develop inside the egg cocoon, which forms in the region of the girdle.
In addition to sexual reproduction, oligochaetes have asexual reproduction, similar to asexual reproduction of ciliary worms. The body of the worm is divided into two halves: in the front, the back part of the body regenerates, in the back - the head part of the body.
Earthworm – Lumbricus terrestris(type Ringworms, class Small-bristle worms, Lumbricida family) lives in moist, humus-rich soil. It feeds on organic matter, passing soil with plant debris through the intestines. Even Ch. Darwin noted the beneficial effect of earthworms on soil fertility. Dragging plant residues into the burrow, they enrich it with humus. Laying 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. Frosts kill worms instantly, so they must burrow deeper into the ground, where low temperatures do not penetrate. In the spring, when the temperature reaches a suitable value and the land is saturated with rainwater, they have a mating season. They multiply very quickly, producing about a hundred young worms a year. In summer, the worms are not so active. There is very little food - dying plant debris - at this time, and the soil is devoid of moisture, which can cause the death of worms. The autumn period is again characterized by the activity of worms. At this time, 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 lives is the pesticides that are so widely used in horticulture today.
So, an earthworm has an elongated, cylindrical body from 10 to 30 cm long. Dorsal side more rounded, it is darker, a dorsal blood vessel is visible through its skin. Abdominal side somewhat flattened and lighter in color. The anterior end of the body is thicker and darker colored. The body is made of rings - segments. In an adult worm, their number reaches 200. In the area of 32-37 body segments there is girdle 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) location of a number of internal organs. Each segment has 8 bristles(they are easy to detect if you slide your finger along the body of the worm in the direction from the back of the body to the front). Setae are arranged in four pairs on the lateral sides of the segments. Clinging to the irregularities of the soil, the worm moves forward with the help of the muscles of the skin-muscular sac.
Veils. The body of the earthworm is covered musculocutaneous sac... He is educated cuticle, single layer epithelium and two layers of muscles - outer circular and internal longitudinal... The skin epithelium of the worm is rich mucous glands that generate slime covering the entire body of the worm and protecting it from drying out. The mucus also makes it easier to crawl in burrows by reducing friction against the soil.
The movement of the earthworm. When the worm crawls, waves of muscle contractions run through its body, and 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 the segments that make it up are stretched and at the same time become thinner, then they contract and become thicker. As a result of such alternating stretching and contractions, the worm gradually moves forward: first, its head end is pulled forward, and then the posterior segments of the body are gradually pulled towards it; after that, the posterior end of the body remains in place, and the head end is pushed even further forward, and thus the further advance of the worm continues (it is convenient to observe it by letting the worm crawl on the paper spread on the table).
Body cavity. Inside the musculocutaneous sac in annelids is located secondary body cavity, or the whole... This body cavity is not limited by muscles, as in roundworms, but has its own epithelial(coelomic) pavement, i.e. the inner side of the longitudinal muscles is lined with epithelium of mesodermal origin, and there is also an epithelial lining on the side of the intestine lying in the body cavity. Due to the coelomic epithelium, internal bilayer transverse septa are formed between the segments - dissentions... The secondary cavity is divided into chambers, each segment contains a pair of coelomic sacs. The coelomic fluid is under pressure and plays a role hydroskeleton, therefore, the worm is elastic to the touch.
Digestive system comprises front, average and hindgut. Mouth located on the second segment on the ventral side of the body. Anal hole
type Ringed worms Earthworm
At the posterior end of the body, it looks like a small slit. Due to feeding on rotting plant residues and humus, the digestive system has a number of features. Its front section is differentiated into muscular throat, esophagus, goiter and muscular stomach... To increase the suction surface, a fold has formed on the upper intestine typhlozol(typhlozolis). Please note: the differentiated areas of the anterior intestine - the pharynx, esophagus, goiter, stomach - were absent in the previous types of worms.
Breath. The earthworm breathes with its entire surface due to the presence of a dense subcutaneous network of capillary blood vessels. Therefore, it is important that the integuments of the worm's body do not dry out, but excessive moisture (for example, very wet soil after rain) is just as destructive for them.
Circulatory system closed, that is, the blood moves through the vessels without pouring out into the body cavity. The movement of blood is caused by the pulsation of large vessels, mainly encircling the esophagus. These are kind of hearts. The blood provides the supply of all organs and tissues with nutrients, transporting them from the intestines, and oxygen entering the capillaries of the skin from the external environment. By dorsal vessel blood moves from the back of the body to the front, and along abdominal vessel- in the opposite direction. The blood of the earthworm is red. An iron-containing protein, close to vertebrate hemoglobin and transporting oxygen, is contained in a dissolved state in the blood plasma, and erythrocytes are absent.
Nervous system more complex than flat and round worms. It consists of nervous periopharyngeal ring with ganglia and abdominal nerve chain... This is the so-called nervous system. ladder type. Supraesophageal paired ganglion performs the functions of the brain and is more developed than subpharyngeal... The neural chain originates from the suboesophageal node and is segmented pairs of nerve nodes, connected to honey by transverse and longitudinal commissars... Nerves extend from the ganglia to various organs. The sense organs are poorly developed in the earthworm: eyes and tentacles are absent, but numerous sensory cells and nerve endings are embedded in their skin.
Excretory organs are represented by segment (i.e. in each segment) located paired metanephridia... They look like convoluted tubules, starting in the body cavity with a funnel with cilia. A channel departs from the funnel, which penetrates the transverse partition, passes into the cavity of the next segment. The end section of metanephridia has an extension - bladder, which opens outward on the lateral side of the body of the worm (i.e., in each segment, a pair of very small excretory holes). In addition to metanephridia, chloragenic cells covering the intestinal surface with a thin brownish-yellow coating. Chloragenous cells accumulate excretion products. Filled with metabolic products, these cells die off, and their contents enter the body cavity, from where they are removed by metanephridia.
Reproduction. Earthworms hermaphrodites... The reproductive organs and the girdle can only be seen during the breeding season - in the spring. To male
type Ringed worms Earthworm
reproductive system include two pairs of testes located in 10 and 11 segments, four vas deferens that merge in pairs and open outward paired male genital opening located in the 15th segment. The female reproductive system includes pair of ovaries located in the 13th segment, oviducts that open outward in segment 14 a pair of female genital holes... There are two pairs in the 9th and 10th segments seminal receptacles, each of which opens outward with an independent hole.
Earthworms reproduce sexually. Fertilization is cross, in a cocoon. Two worms meet, closely wrap their bodies around each other, attach their ventral sides to each other and exchange sperm, which enters the seminal receptacles. After that, the worms disperse. Further, the belt forms a mucous sleeve, eggs are laid in it. As the sleeve moves through the segments containing the seminal receptacles, the eggs are fertilized with sperm belonging to another individual. The sleeve is thrown off through the front end of the body, thickens 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 the earthworm, a whole worm is restored.
Questions for self-control
Name aromorphoses of the Ringworm type.
What is the classification of the type of annelids.
What is the systematic position of the earthworm?
Where do earthworms live?
What body shape do earthworms have?
What is the body of the earthworm covered with?
What body cavity is typical for an earthworm?
What is the structure of the worm's digestive system?
What is the structure of the worm's circulatory system?
How does an earthworm breathe?
What is the structure of the excretory system of the worm?
What is the structure of the worm's nervous system?
What is the structure of the reproductive system of the earthworm?
How does an earthworm reproduce?
What is the significance of an earthworm?
type Ringed worms Earthworm
Rice. Earthworm, its moves in the ground and movement.
Rice. Internal structure of the Earthworm.
1, 16 - intestine; 2 - partitions; 3 - epithelial lining of the secondary body cavity; 4 - dorsal (back) blood vessel; 5 - annular blood vessel; 6 - skin-muscular sac; 7 - cuticle; 8 - cutaneous epithelium; 9 - whole; 10 - metanephridium; 11 - eggs; 12 - ring muscles; 13 - longitudinal muscles; 14 - ventral (abdominal) blood vessel; 15 - abdominal nerve cord.
type Ringed worms Earthworm
Rice. The structure of the anterior end of the body of the Earthworm.
Prostomium is the protrusion of the upper part of the first segment that covers the mouth. Peristomium is the name of the first segment of the body.
type Ringed worms Earthworm
Rice. The structure of the Earthworm.
A - head end; B - internal structure; B - the nervous system.
1 - mouth opening; 2 - male genital opening; 3 - female genital opening; 4 - belt; 5 - pharynx; 6 - esophagus; 7 - goiter; 8 - stomach; 9 - intestines; 10 - dorsal blood vessel; 11 - annular blood vessels; 12 - abdominal blood vessel; 13 - metanephridia; 14 - ovaries; 15 - testes; 16 - seed bags; 17 - seminal receptacles; 18 - periopharyngeal nerve node; 19 - periopharyngeal nerve ring; 20 - abdominal nerve chain; 21 - nerves.
type Ringed worms Earthworm
Rice. Longitudinal section of the body of the Earthworm.
1 - mouth; 2 - pharynx; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - intestine; 7 - periopharyngeal ring; 8 - abdominal nerve chain; 9 - "hearts"; 10 - dorsal blood vessel; 11 - abdominal blood vessel.
Loading...
