Ringed type. annelids

Annelides- bilaterally symmetrical three-layer animals with a secondary cavity. They live in marine and fresh water bodies, in soil, leaf litter.

In the body of annelids, a head lobe, a segmented body and an anal lobe are distinguished. Metamerism (repeatability) of internal organs is associated with external segmentation. Segments of some annelids (polychaetes) bear paired primary limbs - parapodia.

Annelids have a skin-muscular sac, which includes a cuticle, a single-layer epithelium and two layers of muscles (annular, longitudinal under them). The longitudinal muscles are internally lined with coelomic epithelium.

The secondary body cavity (coelom) is filled with coelomic fluid, which plays the role of the internal environment of the body. In most species, the coelom is metameric, with partitions.

The circulatory system is a closed type.

The digestive system is subdivided into three functionally distinct sections: ectodermal anterior, endodermal middle, and ectodermal posterior. In the anterior and middle sections of the intestine there are differentiated areas (goiter, stomach).

Gas exchange is carried out either through the integument of the body (polychaete worms and leeches), or in the gills (polychaete worms).

The excretory organs of most species are metanephridia, located in pairs in each segment, in some species - protonephridia.

The nervous system includes paired supraglottic, subpharyngeal ganglia and a double abdominal nerve chain extending from the latter. The supraoesophageal and suboesophageal ganglia are "linked" by commissures into the peripharyngeal ring. The ventral nerve cord consists of metamerically repeated ganglia in each segment.

Annelids can be either dioecious or bisexual. The development of many species proceeds with metamorphosis. The larva of marine annelids is called a trochophore. Some species can reproduce asexually.

Type Annelids are divided into classes: Polychaeta (Polychaeta), Oligochaeta, Leeches (Hirudinea), Echiurida (Echiurida).

The section Bilaterally symmetrical (Bilateria) subkingdoms Multicellular also includes.

The circulatory system of annelids

Annelids (Annelida) are the type of the most highly organized worms that have a coelom.

Vessels circulatory system carry red blood. The spinal vessel has the ability to pulsate, i.e., contractile movements of the walls and usually drives blood from back to front.

Ringed worm. Photo: daz smith

Special vessels covering the intestinal tube and located metamerically in each segment (rings of the body) transfer blood to the abdominal vessel, which is not capable of independent pulsation. Blood moves in it from front to back. In addition to these directions of blood currents, the vessels that carry blood from the spinal vessel to the parapodia are important. These are parapodial vessels. In the parapodia, the blood vessels acquire the character of capillaries, where the oxidation of blood occurs, which is in close contact with the oxygen of the external environment.

The dorsal vessel reaches the prostomium, the abdominal vessel ends at the level of the pharynx, i.e., it is somewhat shorter. The skin is also intensively supplied with capillary blood vessels. At the same time, the intestinal tube and all internal organs, as well as dissipations, are also abundantly irrigated with blood.

Nervous system of annelids

The nervous system is much better developed than in the previously considered types of worms: its ganglia are larger, the trunks are thicker and contain a larger number of nerve cells. Its fine structure, as has been clarified by modern electron microscopic studies, is complex. It should be especially noted that the central nervous system in lower worms is still closely connected with the epidermis, while in annulus it has completely separated from the outer integument and is isolated from the tissues surrounding it by well-developed outer shells, which greatly improves its work.

The central section of a typical annular nervous system consists of a head ganglion (brain) lying on the dorsal side of the anterior end of the body above the pharynx, two near-pharyngeal trunks (connectives) extending from the brain, which pass to the ventral side, where they join and form the subpharyngeal ganglion. The abdominal chain departs from the latter, forming in each segment (more often in its middle part) a ganglion, which explains the name given to it.

In lower species, there are two head ganglia, from each of which a thin trunk extends along the ventral side to the posterior end of the body with small ganglia in each segment. Both trunks are connected by transverse bridges. This system is called the ladder nervous system. The latter is less centralized, simpler in fine structure, and somewhat similar to the nervous systems of the lower worms. The foregoing allows us to conclude that the typical central nervous system of the annulus developed in the process of evolution from the ladder system.

Each ganglion of the abdominal chain innervates the organs of the segment in which it is located and coordinates their work. The head ganglion, near-pharyngeal connectives, and sub-pharyngeal ganglion innervate the sense organs, parts of the digestive and other systems located in the anterior part of the body. It should be especially noted that the head ganglion coordinates the work of all parts of the body of worms through the remaining parts of the central nervous system (near-pharyngeal connectives, sub-pharyngeal ganglion and ventral chain), and this function of the brain is much more pronounced in annuli than in lower worms. However, due to the relative independence of the metameric ganglia, the body parts of the annulus, separated from the prostomium, retain motor and other functions for quite a long time.

Ringed worms. Photo: Jacob Levine

Many rings in the abdominal chain have long thick fibers formed by the process of one nerve cell or processes of several nerve cells. Such fibers, often called giant fibers, contribute to the rapid conduction of nerve stimuli.

In the central nervous system of the considered worms there are neurosecretory cells that secrete hormones that affect various life processes (reproduction, development, etc.) of the annulus. Similar cells have also been found in lower standing animals, but in the latter they are scattered diffusely along the central nervous system, while in higher worms they form clusters.

The sense organs are diverse, most of them are concentrated in the skin of the anterior part of the body. Tactile sensations are perceived by the endings of nerve cells with fine hairs. Organs that respond to various chemical stimuli are usually located in special pits in the prostomium, the most sensitive of which are located near the mouth and play an important role in obtaining food. Light-sensitive cells are scattered throughout the skin. At the sea. polychaete rings and most leeches have eyes of varying complexity. Some polychaete worms there are organs of balance, similar in structure to the corresponding organs of jellyfish and other lower animals. Some species have organs associated with the ventral chain and performing the same functions as the organs of the lateral line of fish.

In the supraesophageal ganglion, it is planned, but not yet permanent, to be divided into sections, each of which is associated with certain sensory organs (eyes, chemical receptors, etc.).

The complication of the development of the nervous system of the annulus in comparison with the same systems of the previously considered types of multicellular animals (starting with the coelenterates - approx. biofile.ru) ensures a more active and coordinated work of all systems and organs, more complex behavior, the successful development of new habitats.

In the phylogenetic series of annelids there are groups with well-developed sense organs (polychaete worms). In these animals, three sections are separated in the supraesophageal ganglion. The anterior section innervates the tentacles, the middle part innervates the eyes and antennae. And finally, the back part develops in connection with the improvement of the chemical senses.

A developed nervous system and musculature allow the ringlets to lead a varied life and use different types of plant and animal food. They are characterized by all types of reflexes, they are capable of conditioned reflex learning and have associative memory, which allows them to exhibit relatively complex behavior.

The circulatory system of annelids is closed.

It is quite simple and resembles the circulatory system of other primitive animals such as the lancelet.

The type of breathing of different types of annelids differs, which is why some have red blood, others have green, and others have colorless.

The structure of the circulatory system

The basis of the circulatory system of worms is:

abdominal vessel;
dorsal vessel;
Ring vessels.

Ring vessels encircle each segment and resemble veins and arteries. However, in general, the vessels of worms are not such, since “venous” and “arterial” blood almost do not differ from each other in composition.

Blood movement

Annelids don't have a heart at all. It is replaced by large 5 annular vessels (heart), the walls of which are able to contract. They drive blood from the back of the body to the front.

From there, the blood passes into the abdominal vessel, where it moves in the opposite direction - from front to back; the walls of the abdominal vessel cannot contract.

structure of the circulatory system of annelids photo

The ventral vessel is somewhat longer than the dorsal. In addition, individual vessels carry blood to the parapodia (organs of movement) and the skin, where they are crushed and become like capillaries. Here the blood is saturated with oxygen; this is how the breathing of the annelids takes place, carried out by this surface of the body.

Marine species have gills on the parapodia, with which the worms breathe. In other species, the gills are located on the palps - organs in the head of the body. A network of vessels also covers the intestinal tube - the most main body ringed worm.

Meaning

Annelids are the most highly organized of the most primitive animals. This group of organisms is the first to have a circulatory system, as well as others. important systems- respiratory organs, the secondary cavity of the body (as a whole) and even some kind of brain. The body of annelids is characterized by repeatability.

Thanks to this, the parts of the worm separated from each other continue to live, because blood from the dorsal vessel still flows into the abdominal through the annular vessels. At the same time, in a separate group of annelids - leeches - the circulatory system is reduced. There are no vessels, their function is performed by voids in the parenchyma - tubules, which are the remains of the coelom.

The ability of worms to breathe through the entire surface of the body makes them sensitive to moisture. environment. Ringed worms live either in water or in soil - in those places where it is quite humid. After rain, the worms crawl to the surface to "breathe freely."

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In most species, the circulatory system is closed, it is based on the dorsal and abdominal vessels, connected by annular vessels that resemble arteries and veins. Depending on the type of respiratory pigments, some annelids have red blood, while others have colorless or green blood. The blood vessels of the circulatory system carry red blood. The dorsal vessel has the ability to pulsate, i.e., contractile movements of the walls and usually drives blood from back to front. Special vessels covering the intestinal tube and located metamerically in each segment (rings of the body) transfer blood to the abdominal vessel, which is not capable of independent pulsation .

Blood moves in it from front to back.

In addition to these directions of blood currents, the vessels that carry blood from the spinal vessel to the parapodia are important. These are parapodial vessels. In the parapodia, the blood vessels acquire the character of capillaries, where the oxidation of blood occurs, which is in close contact with the oxygen of the external environment. The dorsal vessel reaches the prostomium, the abdominal vessel ends at the level of the pharynx, i.e., it is somewhat shorter. The skin is also intensively supplied with capillary blood vessels. At the same time, the intestinal tube and all internal organs, as well as dissipations, are also abundantly irrigated with blood.

Task 1. Fill in the gaps in the text "A group of cells similar to ______, performing a function in the body ______, is called ______."

Task 2. Fill in the table "The structure and functions of the organ systems of polychaete annelids."

Task 3. Look at the picture and make inscriptions

Task 4. For the first time in the evolution of the animal world, the circulatory system appeared in annelids. Schematically draw the structure and describe the functions of the circulatory system of annelids.
The circulatory system of annelids is closed, consists of two main vessels - dorsal and abdominal, which are interconnected by annular vessels like arteries and veins.
The main function of the circulatory system is transport and distribution.

annelids- bilaterally symmetrical segmented animals.

Systematics. The type includes 5 classes, of which the most well-known classes are Polychaeta (Polychaeta) - 13000 species, Olygochaeta - 3500 species and Leeches (Hirudinea) - about 400 species.

Body shape and size. The body of the rings is overwhelmingly worm-shaped, round or oval in cross section. The trunk has a pronounced both external and internal segmentation. In this case one speaks of true metamerism. At the same time, metamerism extends to the internal structure of worms. In leeches, external segmentation does not correspond to internal segmentation.

The sizes of annelids range from a few millimeters to 2 m (terrestrial forms) and even up to 3 m ( sea views).

The external structure of the body. In polychaetes, the head section is well expressed, bearing organs for various purposes: tentacles, eyes, palps. In some species, the palps grow into a complex hunting apparatus. The last segment bears one or several pairs of sensory antennae. Each body segment on the sides bears parapodia - complex outgrowths of the body. The main function of these outgrowths is the movement of the worm. Each parapodia consists of two lobes, inside which are numerous setae. Of these, several are larger, they are called atsikuly. A pair of sensitive antennae is attached to the blades. The parapodia often includes the gill apparatus. Parapodia have a rather diverse structure.

In oligochaete worms, the head section is weakly expressed, lateral outgrowths (parapodia) are absent. Only relatively few setae are present. On the body, a “belt” is clearly visible, consisting of thickened segments.

Leeches have powerful suckers at the anterior and posterior ends of the body. Few species have gill outgrowths on the sides.

Skin-muscle bag. Outside, the body of annelids is covered with a thin cuticle, under which lie the cells of the skin epithelium. The skin of worms is rich in glandular cells. The secret of these cells has a protective value. In a number of species, skin secretions are used to build peculiar houses. The bristles of the worms are derivatives of the epithelium. Under the skin lies a layer of circular muscles, which allows the animal to change the transverse size of the body. Below are the longitudinal muscles that serve to change the length of the body. In leeches, between the layers of the annular and longitudinal muscles, there is a layer of diagonal muscles. Rings have special muscles that set in motion parapodia, palps, suckers, etc.

body cavity. The space between the body wall and internal organs in annulus it represents the whole - the secondary cavity of the body. It differs from the primary one by the presence of its own epithelial walls, which are called the coelomic epithelium (the whole body). The coelothelium covers the longitudinal muscles of the body wall, intestines, muscle cords and other internal organs. On the walls of the intestine, the whole body is transformed into chloragogenic cells that perform an excretory function. At the same time, the coelomic sac of each body segment is isolated from the neighboring ones by partitions - dessepiments. Inside the coelomic sac is filled with a liquid containing various cellular elements. As a whole, it performs various functions - supporting, trophic, excretory, protective and others. In leeches, the whole has undergone a strong reduction and the space between the body wall and the internal organs is filled with a special tissue - mesenchyme, in which the whole is preserved only in the form of narrow channels.

The midgut is shaped like a simple tube that can become more complex. So, in leeches and some polychaetes, the intestine has lateral outgrowths. The oligochaetes have a longitudinal fold on the dorsal side of the intestine, which protrudes deeply into the intestinal cavity - typhlosol. These devices greatly increase inner surface the middle intestine, which allows the most complete absorption of digested substances. The midgut is endodermic in origin. In small-bristle worms, on the border of the anterior and middle intestines, there is an extension - the stomach. It can be either ectodermal or endodermal.

The hindgut, which is a derivative of the ectoderm, is usually short and opens with an anus.

The circulatory system of annelids is closed, that is, blood moves everywhere through the vessels. The main vessels - longitudinal - dorsal and abdominal, connected by annular. The spinal vessel has the ability to pulsate and performs the function of the heart. In oligochaetes, this function is also performed by the annular vessels of the anterior part of the body. Blood moves from back to front along the dorsal vessel. Through the annular vessels located in each segment, the blood passes into the abdominal vessel and moves in it from front to back. Smaller vessels depart from the main vessels, and they, in turn, branch into the smallest capillaries that carry blood to all the tissues of the worms. In leeches, the system of blood vessels is significantly reduced. Blood moves through the system of sinuses - the remnants of the coelom.

The blood of most annelids contains hemoglobin. This allows them to exist in conditions with a low oxygen content.

There are usually no special respiratory organs, so gas exchange occurs through the skin by diffusion. Polychaete worms and some leeches have well-developed gills.

The excretory system is most often represented by metanephridia, which are located metamerically, that is, in pairs in each segment. A typical metanephridium is represented by a long coiled tube. This tube begins with a funnel that opens as a whole (secondary body cavity) of the segment, then it penetrates the septum between the segments (dissepiment) and enters the glandular metanephridial body located in the next segment. In this gland, the tube winds strongly and then opens with an excretory pore on the lateral surface of the body. The funnel and tube are covered with cilia, with the help of which the cavity fluid is forced into the metanephridium. When moving through the tube through the gland, water and various salts are absorbed from the liquid, and only products to be removed from the body (urine) remain in the tube cavity. These products are excreted through the excretory pore. Many species have an extension in the posterior part of the metanephridial tube - bladder in which urine temporarily accumulates.

In primitive annelids, the excretory organs, like flatworms, are arranged according to the type of protonephridia.

The nervous system consists of the peripharyngeal ring and the ventral nerve cord. Above the pharynx lies a powerfully developed paired complex of ganglia, representing a kind of brain. A pair of ganglia also lie under the pharynx. The brain is connected to the subpharyngeal ganglia by nerve cords covering the pharynx from the sides. All this formation is called the peripharyngeal ring. Further, in each segment under the intestine there is a pair of nerve ganglia, which are connected both to each other and to the ganglia of neighboring segments. This system is called the ventral nerve cord. From all ganglia, nerves depart to various organs.

Sense organs. On the head section of polychaete worms there are well-developed sense organs: antennae and palps (organs of touch), eyes (sometimes quite complex), olfactory pits. Some forms have developed organs of balance - statocysts. On the lateral outgrowths of the body (parapodia) there are antennae that perform a tactile function.

In oligochaete worms, the sense organs are much less developed than in polychaete worms. There are organs of chemical sense, sometimes - tentacles, statocysts, poorly developed eyes. A large number of light-sensitive and tactile cells are scattered in the skin. Some tactile cells have a pin.

In leeches, many sensitive cells are scattered in the skin, there are always eyes and chemical sense organs (taste buds).

Sexual system. Among annelids, there are both hermaphroditic and dioecious forms.

Polychaete worms are mostly dioecious. Sometimes there is sexual dimorphism. Sex glands (gonads) are formed in the coelomic epithelium. This process usually occurs in the posterior segments of the worm.

In small-bristle worms, hermaphroditism is more common. The sex glands are usually located in certain segments of the anterior part of the worm. Relatively small male gonads (testes) have excretory ducts, which are either modified metanephridia or canals isolated from them. Larger female sex glands (ovaries) have ducts, which are altered metanephridia. For example, when the ovary is located in the 13th segment, the female genital openings open on the 14th. There are also seminal receptacles, which are filled during mating with the spermatozoa of another worm. Leeches are mostly hermaphrodites. The testes are located metamerically, the ovaries are one pair. Fertilization in leeches occurs by the exchange of spermatophores between partners.

Reproduction. Ringed worms are characterized by a wide variety of forms of reproduction.

Asexual reproduction is characteristic of some polychaete and oligochaete worms. In this case, either strobilation or lateral budding occurs. This is a rare example asexual reproduction among highly organized animals in general.

During sexual reproduction, polychaete individuals containing mature gonads (epitocal) move from a crawling or sedentary lifestyle to a swimming one. And in some species, the sexual segments during the maturation of gametes can even break away from the body of the worm and lead an independent floating lifestyle. Gametes enter the water through breaks in the body wall. Fertilization takes place either in water or in the epitonic segments of the female.

Reproduction of oligochaetes begins with cross-fertilization. At this time, two partners are applied to each other by the abdominal sides and exchange sperm, which enters the seminiferous receptacles. After that, the partners disperse.

Subsequently, abundant mucus is secreted on the girdle, forming a sleeve around the girdle. The worm lays its eggs in this clutch. When the clutch is moved forward, it passes by the holes of the seed receptacles; at this point, fertilization of the eggs occurs. When the clutch with fertilized eggs slides off the head end of the worm, its edges close, and a cocoon is obtained in which further development takes place. The cocoon of earthworms usually contains 1-3 eggs.

In leeches, reproduction occurs in much the same way as in oligochaete worms. Leech cocoons are large, reaching 2 cm in length in some species. Located in a cocoon different types from 1 to 200 eggs.

Development. The zygote of annelids undergoes complete, usually uneven fragmentation. Gastrulation occurs by invagination or epiboly.

In polychaete worms, a larva called a trochophore is subsequently formed from the embryo. She has eyelashes and is quite mobile. It is from this larvae that the adult worm subsequently develops. Thus, in most polychaete worms, development proceeds with metamorphosis. Species with direct development are also known.

Small-bristle worms have direct development without a larval phase. Fully formed young worms emerge from the eggs.

In leeches, peculiar larvae form from eggs in a cocoon, which swim in the cocoon fluid with the help of a ciliary apparatus. Thus, an adult leech is formed by metamorphosis.

Regeneration. Many annelids are characterized by a developed ability to regenerate lost body parts. In some species, an entire organism can regenerate from just a few segments. However, in leeches, regeneration is very weak.

Nutrition. Among the polychaete worms, there are both predators and herbivorous species. There are also known cases of cannibalism. Some species feed on organic remains (detritivores). Small-bristle worms are mainly detritivores, but there are also predators.

Small-bristle worms for the most part are soil dwellers. In humus-rich soils, the number of, for example, enchitreid worms reaches 100-200 thousand per square meter. They also live in fresh, brackish and salty water bodies. Aquatic inhabitants inhabit mainly the surface layers of the soil and vegetation. Some of the species are cosmopolitan, and some are endemic.

Leeches inhabit fresh water bodies. Few species live in the seas. Some have switched to a terrestrial way of life. These worms either lead an ambush lifestyle or actively seek out their hosts. A single bloodsucking provides leeches with food for many months. There are no cosmopolitans among leeches; they are confined to certain geographic areas.

Paleontological finds of annelids are very few. Polychaetes are more diverse in this respect. Not only prints have been preserved from them, but also in many cases the remains of pipes. On this basis, it is assumed that all the main groups of this class were represented already in the Paleozoic. Reliable remains of oligochaete worms and leeches have not been found to date.

Origin. Currently, the most plausible hypothesis is the origin of annelids from parenchymal ancestors ( ciliary worms). The most primitive group is considered to be polychaetes. It is from this group that the oligochaetes most likely originate, and from the latter a group of leeches emerged.

Significance. In nature, annelids are of great importance. Inhabiting various biotopes, these worms are included in numerous food chains, serving as food for a huge number of animals. Terrestrial worms play a leading role in soil formation. By processing plant residues, they enrich the soil with mineral and organic substances. Their moves contribute to the improvement of soil gas exchange and its drainage.

In practical terms, a number of earthworm species are used as vermicompost producers. The worm - enchitreus is used as food for aquarium fish. Enchitreans breed in huge quantities. For the same purpose, the tubifex worm is mined in nature. Medicinal leeches are currently used to treat certain diseases. In some tropical countries, they eat palolo - sexual (epitocal) segments of worms that have separated from the front of the animals and floated to the surface of the water.

Annelids are bilaterally symmetrical segmented animals.

Systematics. The type includes 5 classes, of which the most well-known classes are Polychaeta (Polychaeta) - 13000 species, Olygochaeta - 3500 species and Leeches (Hirudinea) - about 400 species.

Body shape and size. The body of the rings is overwhelmingly worm-shaped, round or oval in cross section. The trunk has a pronounced both external and internal segmentation. In this case one speaks of true metamerism. At the same time, metamerism extends to the internal structure of worms. In leeches, external segmentation does not correspond to internal segmentation.

The sizes of annelids range from a few millimeters to 2 m (terrestrial forms) and even up to 3 m (marine species).

The external structure of the body. In polychaetes, the head section is well expressed, bearing organs for various purposes: tentacles, eyes, palps. In some species, the palps grow into a complex hunting apparatus. The last segment bears one or several pairs of sensory antennae. Each body segment on the sides bears parapodia - complex outgrowths of the body. The main function of these outgrowths is the movement of the worm. Each parapodia consists of two lobes, inside which are numerous setae. Of these, several are larger, they are called atsikuly. A pair of sensitive antennae is attached to the blades. The parapodia often includes the gill apparatus. Parapodia have a rather diverse structure.

Leeches have powerful suckers at the anterior and posterior ends of the body. Few species have gill outgrowths on the sides.

Skin-muscle bag. Outside, the body of annelids is covered with a thin cuticle, under which lie the cells of the skin epithelium. The skin of worms is rich in glandular cells. The secret of these cells has a protective value. In a number of species, skin secretions are used to build peculiar houses. The bristles of the worms are derivatives of the epithelium. Under the skin lies a layer of circular muscles, which allows the animal to change the transverse size of the body. Below are the longitudinal muscles that serve to change the length of the body. In leeches, between the layers of the annular and longitudinal muscles, there is a layer of diagonal muscles. Rings have special muscles that set in motion parapodia, palps, suckers, etc.

body cavity. The space between the wall of the body and the internal organs of the annulus represents the whole - the secondary cavity of the body. It differs from the primary one by the presence of its own epithelial walls, which are called the coelomic epithelium (the whole body). The coelothelium covers the longitudinal muscles of the body wall, intestines, muscle cords and other internal organs. On the walls of the intestine, the whole body is transformed into chloragogenic cells that perform an excretory function. At the same time, the coelomic sac of each body segment is isolated from the neighboring ones by partitions - dessepiments. Inside the coelomic sac is filled with a liquid containing various cellular elements. As a whole, it performs various functions - supporting, trophic, excretory, protective and others. In leeches, the whole has undergone a strong reduction and the space between the body wall and the internal organs is filled with a special tissue - mesenchyme, in which the whole is preserved only in the form of narrow channels.

The midgut is shaped like a simple tube that can become more complex. So, in leeches and some polychaetes, the intestine has lateral outgrowths. The oligochaetes have a longitudinal fold on the dorsal side of the intestine, which protrudes deeply into the intestinal cavity - typhlosol. These devices significantly increase the inner surface of the midgut, which allows the most complete assimilation of digested substances. The midgut is endodermic in origin. In small-bristle worms, on the border of the anterior and middle intestines, there is an extension - the stomach. It can be either ectodermal or endodermal.

The hindgut, which is a derivative of the ectoderm, is usually short and opens with an anus.

Circulatory system annelids is closed, that is, the blood moves everywhere through the vessels. The main vessels - longitudinal - dorsal and abdominal, connected by annular. The spinal vessel has the ability to pulsate and performs the function of the heart. In oligochaetes, this function is also performed by the annular vessels of the anterior part of the body. Blood moves from back to front along the dorsal vessel. Through the annular vessels located in each segment, the blood passes into the abdominal vessel and moves in it from front to back. Smaller vessels depart from the main vessels, and they, in turn, branch into the smallest capillaries that carry blood to all the tissues of the worms. In leeches, the system of blood vessels is significantly reduced. Blood moves through the system of sinuses - the remnants of the coelom.

The blood of most annelids contains hemoglobin. This allows them to exist in conditions with a low oxygen content.

Special respiratory system usually not, so gas exchange occurs through the skin by diffusion. Polychaete worms and some leeches have well-developed gills.

excretory system most often represented by metanephridia, which are located metamerically, that is, in pairs in each segment. A typical metanephridium is represented by a long coiled tube. This tube begins with a funnel that opens as a whole (secondary body cavity) of the segment, then it penetrates the septum between the segments (dissepiment) and enters the glandular metanephridial body located in the next segment. In this gland, the tube winds strongly and then opens with an excretory pore on the lateral surface of the body. The funnel and tube are covered with cilia, with the help of which the cavity fluid is forced into the metanephridium. When moving through the tube through the gland, water and various salts are absorbed from the liquid, and only products to be removed from the body (urine) remain in the tube cavity. These products are excreted through the excretory pore. In many species, there is an extension in the posterior part of the metanephridial tube - the bladder, in which urine temporarily accumulates.

In primitive annelids, the excretory organs, like flatworms, are arranged according to the type of protonephridia.

Nervous system consists of the peripharyngeal ring and the ventral nerve cord. Above the pharynx lies a powerfully developed paired complex of ganglia, representing a kind of brain. A pair of ganglia also lie under the pharynx. The brain is connected to the subpharyngeal ganglia by nerve cords covering the pharynx from the sides. All this formation is called the peripharyngeal ring. Further, in each segment under the intestine there is a pair of nerve ganglia, which are connected both to each other and to the ganglia of neighboring segments. This system is called the ventral nerve cord. From all ganglia, nerves depart to various organs.

Sense organs. The head section of polychaete worms has well-developed sense organs: antennae and palps (organs of touch), eyes (sometimes quite complex), and olfactory pits. Some forms have developed organs of balance - statocysts. On the lateral outgrowths of the body (parapodia) there are antennae that perform a tactile function.

In leeches, many sensitive cells are scattered in the skin, there are always eyes and chemical sense organs (taste buds).

reproductive system. Among annelids, there are both hermaphroditic and dioecious forms.

reproduction. Ringed worms are characterized by a wide variety of forms of reproduction.

Asexual reproduction is characteristic of some polychaete and oligochaete worms. In this case, either strobilation or lateral budding occurs. This is a rare example of asexual reproduction among highly organized animals in general.

Subsequently, abundant mucus is secreted on the girdle, forming a sleeve around the girdle. The worm lays its eggs in this clutch. When the clutch is moved forward, it passes by the holes of the seed receptacles; at this point, fertilization of the eggs occurs. When the clutch with fertilized eggs slides off the head end of the worm, its edges close, and a cocoon is obtained, in which further development. The cocoon of earthworms usually contains 1-3 eggs.

In leeches, reproduction occurs in much the same way as in oligochaete worms. Leech cocoons are large, reaching 2 cm in length in some species. In a cocoon, there are from 1 to 200 eggs in different species.

Development. The zygote of annelids undergoes complete, usually uneven fragmentation. Gastrulation occurs by invagination or epiboly.

Small-bristle worms have direct development without a larval phase. Fully formed young worms emerge from the eggs.

In leeches, peculiar larvae form from eggs in a cocoon, which swim in the cocoon fluid with the help of a ciliary apparatus. Thus, an adult leech is formed by metamorphosis.

Regeneration. Many annelids are characterized by a developed ability to regenerate lost body parts. In some species, an entire organism can regenerate from just a few segments. However, in leeches, regeneration is very weak.

Food. Among the polychaete worms, there are both predators and herbivorous species. There are also known cases of cannibalism. Some species feed on organic remains (detritivores). Small-bristle worms are mainly detritivores, but there are also predators.

Small-bristle worms are mostly soil inhabitants. In humus-rich soils, the number of, for example, enchitreid worms reaches 100-200 thousand per square meter. They also live in fresh, brackish and salty water bodies. Aquatic inhabitants inhabit mainly the surface layers of the soil and vegetation. Some of the species are cosmopolitan, and some are endemic.

paleontological finds annelid worms are very few. Polychaetes are more diverse in this respect. Not only prints have been preserved from them, but also in many cases the remains of pipes. On this basis, it is assumed that all the main groups of this class were represented already in the Paleozoic. Reliable remains of oligochaete worms and leeches have not been found to date.

Origin. Currently, the most plausible hypothesis is the origin of annelids from parenchymal ancestors (ciliary worms). The most primitive group is considered to be polychaetes. It is from this group that the oligochaetes most likely originate, and from the latter a group of leeches emerged.

Meaning. In nature, annelids are of great importance. Inhabiting various biotopes, these worms are included in numerous food chains, serving as food for a huge number of animals. Terrestrial worms play a leading role in soil formation. By processing plant residues, they enrich the soil with minerals and organic matter. Their moves contribute to the improvement of soil gas exchange and its drainage.

In practical terms, a number of earthworm species are used as vermicompost producers. The worm - enchitreus is used as food for aquarium fish. Enchitreev breed in huge quantities. For the same purpose, the tubifex worm is mined in nature. Medicinal leeches are currently used to treat certain diseases. In some tropical countries they eat palolo- genital (epitocal) segments of worms that have separated from the front of the animals and floated to the surface of the water.

General characteristics of the type Arthropods.

Arthropods are bilaterally symmetrical segmented animals with metamerically arranged jointed limbs. It is the richest in species and diverse group animals.

Systematics. The type of arthropods is divided into several subtypes.

Subtype Gill-breathers (class Crustaceans)

Subphylum Trilobites (extinct group)

Subtype Cheliceraceae (class Merostomaceae, class Arachnids)

Subtype Primary tracheal

Subtype Tracheal breathing (class Millipedes, class Insects).

The Merostomaceae class includes modern horseshoe crabs and extinct crustacean scorpions. To subtype Primary tracheal small (up to 8 cm) tropical animals are included, which in structure occupy an intermediate position between annelids and arthropods. These groups of animals will not be considered here.

Body dimensions. The body length of arthropods ranges from 0.1 mm (some mites) to 90 cm (horsicle crabs). Terrestrial arthropods reach 15-30 cm. The wingspan of some butterflies exceeds 25 cm. Extinct crustaceans reached 1.5 m in length, and the wingspan of fossil dragonflies reached 90 cm.

External structure. The body of most arthropods consists of a head, thorax, and abdomen. The listed departments include a different number of segments.

Head, the segments of which are fixedly connected, bears the oral organs and sensory organs. The head is movably or immovably connected to the next section - the chest.

Thoracic bears walking limbs. Depending on the number of thoracic limb segments, there may be a different number. In insects, wings are also attached to the chest. The segments of the chest are connected to each other movably or motionless.

Abdomen contains most of the internal organs and most often consists of several segments, movably connected to each other. Limbs and other appendages can be located on the abdomen.

The oral apparatus of arthropods is very complex. Depending on the method of nutrition, it can have a very diverse structure. The parts of the mouth apparatus are for the most part highly modified limbs, adapted to eat almost any food. The apparatus may include 3-6 pairs of limbs.

Covers. The cuticle, consisting of chitin, is a derivative of the submerged epithelium - the hypodermis. Chitin performs the support and protective function. The cuticle can be impregnated with calcium carbonate, thus becoming a very strong shell, as happens, for example, in crustaceans. Thus, in arthropods, the integuments of the body represent the external skeleton. The mobile connection of the hard sections of the cuticle is provided by the presence of membranous sections. The cuticle of arthropods is not elastic and cannot be stretched during the growth of animals, so they periodically shed the old cuticle (molt) and, until the new cuticle has hardened, increase in size.

body cavity. In the process of embryonic development in arthropods, coelomic sacs are laid, but later they are torn and their cavity merges with the primary body cavity. Thus, a mixed body cavity is formed - a mixocoel.

musculature represented by separate muscle bundles that do not form a continuous muscle sac. Muscles are attached both directly to the inner wall of the body segments and to their inner processes that make up the internal skeleton. Musculature in arthropods striated.

Digestive system in arthropods, it generally consists of the anterior, middle, and posterior intestines. The anterior and posterior sections are lined from the inside with a thin chitinous cuticle. Depending on the type of nutrition, the structure of the intestine is extremely diverse. Salivary glands open into the oral cavity, which very often produce a number of enzymes, including digestive ones. The anal opening usually opens at the posterior end of the body.

excretory system in primary aquatic arthropods (crustaceans) it is represented by special glands located in the head of the body. The ducts of these glands open at the base of the antennae (antennae). In terrestrial arthropods, the excretory system is represented by the so-called malpighian vessels- tubes that are blindly closed at one end, and open at the other end into the intestine at the border of the middle and posterior sections. These tubules are located in the body cavity, and, being washed by hemolymph, they suck up decay products from it and bring them into the intestine.

Respiratory system arranged quite differently. Crustaceans have true gills. They are branched outgrowths on the limbs, covered with a thin chitinous cuticle, through which gas exchange occurs. Some crustaceans have adapted to live on land (for example, wood lice).

Spiders and scorpions have respiratory organs leaf-shaped lungs, which open outwards with holes (stigmas). Inside the lung sac has numerous folds. In addition to the lung sac, some spiders have a system of tracheal tubes that practically do not branch.

Ticks, centipedes, and insects have a respiratory system tracheae, which open outwards with holes (spiracles, stigmas). The tracheae branch strongly and penetrate into all organs and tissues. The trachea has a thin chitinous lining and is reinforced from the inside with a chitinous spiral, which does not allow the tube to fall off. In addition, flying insects have extensions - air sacs that fill with air and reduce specific gravity animal. Ventilation in the tracheal system is both passive (diffusion) and active (change in the volume of the abdomen).

Some insect larvae have special respiratory organs - tracheal gills. Gas exchange in such arthropods proceeds by diffusion.

Some ticks do not have a respiratory system, and gas exchange occurs through the entire surface of the body.

Circulatory system in all arthropods open I, that is, not everywhere the blood flows through the vessels. Under the chitinous cover of the back there is a heart from which blood vessels depart. However, at some distance from the heart, the walls of the vessels disappear, and the blood makes its further path through the cracks between the internal organs. It then enters the heart through openings called ostia. Crustaceans and mites have a sac-like heart, while scorpions, spiders, and insects have a multi-chambered heart. Some ticks may not have a circulatory system.

The blood of the vast majority of arthropods is colorless and is commonly referred to as hemolymph. This is a rather complex fluid: it consists of both the blood itself and the cavity fluid. Due to the absence of special pigments, hemolymph practically cannot actively participate in the process of gas exchange. Hemolymph of some insects (leaf beetles, ladybugs) contains quite toxic substances and may play a protective role.

Fat body. Terrestrial arthropods have a storage organ - a fatty body located between the viscera. The fat body takes part in the regulation of water metabolism.

Nervous system. In general, in arthropods, the nervous system is built according to the type of annelids. It consists of a paired supraesophageal ganglion, peripharyngeal nerve ring and ventral nerve cord. Peripheral nerves depart from the ganglia of the chain. The supraesophageal ganglion in insects, in which the presence of a brain is usually said, reaches a special development. Often there is a concentration of ganglia of the abdominal nerve chain and the formation of large ganglions due to their fusion. Such a concentration is often associated with a decrease in the number of segments (merging them together). For example, in ticks that have lost segmentation, the abdominal chain turns into a common nerve mass. And in centipedes, whose body consists of many identical segments, the nerve chain is very typical.

sense organs most arthropods reach a high development.

organs of vision are located on the head and are often represented by complex (compound eyes), which occupy most of the surface of the head in some insects. Many crustaceans have compound eyes that sit on stalks. In addition, insects and arachnids have simple eyes. An unpaired frontal ocellus is characteristic of some crustaceans.

sense organs represented by various bristles and hairs located on the body and limbs.

Organs of smell and taste. Most of the olfactory endings are located on the antennae and jaw palps of insects, as well as on the antennulls of crustaceans. The sense of smell in insects is very well developed: 100 pheromone molecules per 1 cm 2 of air released by the female silkworm are enough for the male to start looking for a partner. The organs of taste in insects are located both on the mouth limbs and on the end segments of the legs.

Organs of balance. In crustaceans, in the main segment of the antennules, there is a statocyst - an invagination of the cuticle, seated from the inside with sensitive hairs. This cavity usually contains small grains of sand, which play the role of statoliths.

Hearing organs. Some insects have well-developed so-called tympanal organs that perceive sounds. For example, in grasshoppers, they are located on the bases of the shins of the front legs. As a rule, those insects that are able to perceive sounds are also able to make them. These include many orthoptera, some beetles, butterflies, etc. For this, insects have special adaptations located on the body, wings and limbs.

Spinning glands. Some arthropods are characterized by the presence of spinning glands. In spiders, they are located in the abdomen and open with arachnoid warts at the tip of the abdomen. Spiders use their webs most often for hunting and building shelters. This thread is one of the strongest in nature.

In the larvae of a number of insects, the spinning glands are located in the anterior part of the body and open near the mouth opening. Their cobweb goes mostly to build a shelter or cocoon.

Sexual system. Arthropods are dioecious animals that often have sexual dimorphism. Males differ from females in brighter coloration and often smaller size. In male insects, the antennae are much more developed.

reproductive system females consists of glands - ovaries, oviducts and vagina. This also includes accessory glands and seminal receptacles. Of the external organs, an ovipositor of various structures may be present.

At males reproductive organs are represented by testes, efferent ducts and accessory glands. A number of forms have differently arranged copulatory organs.

Polymorphism. In the colonies of social insects there are individuals that differ from each other in structure, physiology and behavior. In the nests of bees, ants and termites, there is usually only one female capable of laying eggs (womb or queen). Males in the colony are either constantly present, or appear as the sperm reserve in the uterus from the previous mating is depleted. All other individuals are called workers, which are females with depressed sexual function. In termites and ants, workers are divided into castes, each of which performs a specific function (gathering food, protecting the nest, etc.). The appearance of males and full-fledged females in the nest occurs only at a certain time.

Biology of reproduction. As already mentioned, arthropods are dioecious animals. However, among them, cases of parthenogenesis (aphids, daphnia) are not uncommon. Sometimes mating is preceded by a courtship ritual, and even fights between males for a female (in stag beetles). After mating, the female sometimes eats the male (mantises, some spiders).

Most often, eggs are laid in groups or one at a time. In some arthropods, the development of eggs and larvae occurs in the body of the female. In these cases, there is a live birth (scorpions, some flies). In the life of many species of arthropods, care for offspring takes place.

Fertility arthropods varies over a very wide range and depends very often on environmental conditions. In some aphids, for example, females lay only one overwintering egg. A honey bee queen can lay up to 3,000 eggs a day, and a termite queen can lay up to 30,000 eggs a day. These insects lay millions of eggs during their lifetime. On average, fertility is several tens or hundreds of eggs.

Development. In most arthropods, development occurs with metamorphosis, that is, with transformation. A larva emerges from the egg, which, after several molts, the larva turns into an adult animal (imago). Often the larva is very different from the adult both in structure and in lifestyle.

In the development cycle of a number of insects, there is pupal phase(butterflies, beetles, flies). In this case, one speaks of complete metamorphosis. Others (aphids, dragonflies, bugs) do not have such a phase, and the metamorphosis of these insects is called incomplete.

Some arthropods (spiders, scorpions) have direct development. In this case, fully formed young animals emerge from the eggs.

Lifespan arthropods is usually calculated in several weeks or months. In some cases, development is delayed for years. For example, the larvae of May beetles develop for about 3 years, deer beetles - up to 6 years. In cicadas, the larvae live in the soil for up to 16 years, and only after that they turn into adult cicadas. Mayfly larvae live in water bodies for 1-3 years, and an adult insect lives only a few hours, during which it manages to mate and lay eggs.

Distribution and ecology. Representatives of the arthropod type are found in almost any biotope. They are found on land, in fresh and salt water, and in the air. Among arthropods, there are both widespread and endemic species. The first include the cabbage white butterfly, crustaceans - daphnia, soil mites. Endemic species include, for example, a large and very beautiful butterfly brameya, which is found only in the Colchis lowland.

Spreading certain types limited by various environmental factors.

From abiotic factors the most important are temperature and humidity. The temperature limits of the active existence of arthropods lie in the range from 6 to 42°C. With a decrease or increase in temperature, animals fall into a state of stupor. Different phases of development of arthropods tolerate temperature fluctuations in different ways.

The humidity of the environment also largely determines the possibility of the existence of arthropods. Excessively low humidity of the environment, as well as high, can lead to death. For aquatic arthropods, the presence of liquid moisture is a necessary condition for active existence.

On the distribution of arthropods big influence provides human activity anthropogenic influence). Changing environmental conditions lead to a change in species composition. As a result of human industrial and agricultural activities, some species disappear, while other species multiply extremely rapidly, becoming pests.

Origin. Most researchers agree that arthropods descended from ancestors close to annelids. Crustaceans, chelicerae, and extinct trilobites are thought to have evolved from annuli by one common root, and centipedes and insects by another.

Paleontological material on arthropods is very extensive. Thanks to the chitinous cuticle, their remains are quite well preserved in a petrified form. Terrestrial arthropods are exceptionally well preserved in amber as well. However, despite this, it is difficult to accurately trace the evolution of arthropods: the distant ancestors of arthropods in the geological layers have not been preserved. Therefore, the main methods of studying this issue are comparative anatomical and comparative embryological.

AT practical activities It is customary for humans to distinguish between beneficial and harmful species.

Let's take a closer look at a number of animals that biology studies very carefully - a type of annelids. To learn a little about them, you need to consider their species components more, special image life, habitat, as well as the external and internal structure of their body.

General signs and features of the type annelids

Ringed worms or otherwise rings, annelids are one of the largest groups among animals, which, according to general data, contains about 18 thousand open species. Basically, these animals are presented as non-skeletal vertebrates that are able to participate in the destruction of organic substances, and are also considered the basis of nutrition for other species of the animal world.

In what environment do ringworms mainly live? So, the area of residence of the Rings is very wide - they include seas and land, as well as freshwater reservoirs. You can find a lot of annelids that live on the surface salty seas as well as the oceans. Ringed worms live everywhere, they can be found at any depth of the oceans and even found at the bottom of the Mariana Trench. The density of the population of ocean worms is very high - up to 100,000 units of rings per square meter of the bottom surface. Marine specimens are considered the best food for fish and play one of the main roles in the processes of the ecosystem of the seas.

In fresh water areas you can find predominantly blood-sucking individuals, for example, leeches, which are very often used in the medical field. On the territory of tropical latitudes, leeches can live both in the soil and on trees.

aquatic individuals not only crawl along the bottom or burrow into the surface, but can also create a protective tube on their own and live there for a long time until someone disturbs the animal.

The most popular are the rings that live in the surface of the soil, their name earthworms. The density of these individuals in meadow and forest soils can reach 600 units per square meter. Also, these worms are involved in the formation of soil and soil.

What classes of rings live on earth?

About 200 years ago, Georges Cuvier did work in the field of animal classification and brought out only 6 rows of his representatives. This number also included arthropods - creatures whose bodies were previously divided by nature into segments. This group includes: woodlice, earthworms, leeches, insects, spiders, and crayfish.

A small number of features can be distinguished in annelids, with the help of which they were separated into a whole group. The most important thing is that they have a celloma (secondary body cavity), metamerism (segmentation) of the body and a well-developed circulatory system. In addition to all this, annelids have unusual organs of movement - parapodia. Also, the rings have a developed nervous system, which includes the supraesophageal ganglion, as well as the abdominal nerve chain. The structure of the excretory system in the rings is metanephridal.

Annelids, according to experts, were divided into 4 main classes. Basic classes of rings:

What does the appearance of an annelids look like?

Annelids can be characterized as the most highly organized representatives of the group of worms. The length of their body ranges from a few millimeters to 2.5 meters. The body of an individual can be visually divided into three main parts: the head, the trunk, and the anal lobe. Home hallmark worms is that there is no clear division into departments, as occurs in higher varieties of animals, in annelids.

In the area of the head of an individual there are various sensory organs. Most annelids carry well developed vision. Some annelids can be proud of their special eyes, as well as very clear vision. The organ of vision in these animals can be located not only in the head region, but also on the tail, body or tentacles.

Taste buds are especially developed in worms. Worms are able to sense various odors well with the help of developed olfactory cells, as well as ciliary pits. The auditory part of the rings is created on the principle of locators. It happens that Echiruids are able to hear and recognize even the quietest sound with the help of their hearing organ, which is similar in structure to the lateral line in fish.

What are the respiratory organs, as well as the hematopoietic system in a creature?

Description of the digestive system and excretory organs of the annulus

The digestive system in annelids can be roughly divided into three areas. The anterior intestine (or stomodeum) contains the mouth opening, as well as the oral cavity of the worm, sharp and powerful jaws, pharynx, salivary glands, and a very narrow esophagus.

The oral cavity, the second name of which is the buccal region, can turn inside out without problems. Behind this section, you can find powerful jaws bent inward. This device is very necessary in order to quickly and deftly capture your prey.

Then comes the mesodeum - the middle intestine. The anatomy of this department is quite homogeneous throughout the body area. At the same time, the middle intestine narrows in certain places and expands again, it is here that the process of digestion of food is carried out. The hindgut is rather short and is an anus.

The excretory system of the worm consists of metanephridia, which are located in pairs in each of the segments of the annulus. They help to release excess waste products from the abdominal fluid.

The concept of the sense organs and the nervous system of the animal

Each of the classes of annelids has its own gangion type system. It includes the parapharyngeal nerve ring, which is created by connecting the supraesophageal and subpharyngeal ganglia, as well as from pairs of the chain of abdominal ganglia that are present in each of the segments.

The sense organs of annelids are quite well developed. So, worms have sharp eyesight, good hearing and smell, as well as touch. Some individuals of annelids can not easily capture light, but also emit it on their own.

The process of reproduction in annelids

The description of the annelids by specialists indicates that these individuals are capable of reproducing both sexually and asexually. Asexual reproduction occurs by dividing the body into several parts. The worm is able to break up into several halves, each of which subsequently becomes a full-fledged creature.

With all this, the creature's tail is considered independent and cannot grow a new head on itself. In some situations, the second head grows on its own in the middle of the worm's body even before the separation process.

Reproduction by budding is quite rare. Particularly interesting are those individuals whose budding can cover the entire area of the body, at which time the posterior ends bud off from each segment. During breeding, additional oral cavities, which over time will become separate full-fledged individuals.

Worms in most cases are dioecious, but some species (leeches and earthworms) have developed hermaphroditism in themselves - a process in which both individuals perform two functions at once, the role of female and male. The fertilization process can be carried out under conditions external environment, and in the body of beings.

For example, in marine worms that reproduce only sexually, fertilization is considered external. Individuals of different sexes usually throw their germ cells to the surface of the water, where the process of fusion of eggs and spermatozoa takes place. From eggs of the fertilized type, larvae arise, which are quite distinctive in appearance from adults. Freshwater, as well as terrestrial rings, do not have a larval stage, they are immediately born with exactly the same structure as in adult creatures.

Polychaete class

Curious, sessile worms, serpulids, that live in helical or twisted tubes of the Izvet type. Serpulids are accustomed only to protrude their head with large fan-shaped gills from their house.

leeches

All leeches are predators, which for the most part feed only on the blood of warm-blooded creatures, worms, fish and mollusks. The area of distribution and habitat of annelids from the class of leeches is very diverse. In a larger number of leeches can be found in fresh water or in wet grass. But there are marine species, and in Ceylon you can even find ground view leeches.