• Moscow State University of Technology and Management named after K
• Moscow State University of Technology and Management named after K
• How to write a practice report?
• Interesting facts about the first satellite
• What is included in DNA. The code of life. What is DNA and how does it affect human life. Deoxyribonucleic acid. General information
• Midbrain Neurons in the substantia nigra of the midbrain produce
• Dependence of Norway on Denmark and Sweden in the XIV-XIX centuries State structure of Norway
• Why people go with the flow and do not want to change their lives
• mechanical movement. Trajectory. Path and movement. Addition of speeds. Uneven movement. Instantaneous speed Uneven motion physics
• 2 ways to separate a heterogeneous mixture

Introduction

Even the farmers of ancient Egypt saw earthworms as a guarantee of future crops. Aristotle called them the intestines of the earth. And this is true: by passing earth and plant residues through their intestines, worms enrich the soil. In the 50s of our century, the question arose of breeding worms on purpose, as producers of a very valuable, environmentally friendly fertilizer. The concept of "Vermiculture" arose - the culture of breeding worms. A red California worm was bred, which is used to create vermiculture. Biohumus can be grown both on an industrial scale and in an apartment, on a balcony and in a summer cottage. The Californian is a wonderful "pet". It can be placed at home in a box made of wood or plywood, even in a cardboard box, but lined with polyethylene from the inside, in an old glass aquarium, in a plastic box.

Now the topic of annelids is of particular interest, thanks to the latest research by scientists who are revealing more and more amazing abilities of these animals. For example, it has recently become known that annelids are able to distinguish sharp corners. Another amazing ability is that most worms use their "photonic setups" to disorientate opponents. Worms in the food pyramid of the ocean occupy one of the lower steps, serving as food for a wide variety of organisms - cephalopods, crayfish, crabs, fish, and even aggressive relatives of polychaetes.

When a predator attacks a polychaete and begins to tear and torment its body, the tail section of the worm flares up brightly, attracting the attention of the “aggressor”. He grabs the luminous part of the body, and the second (head) hides in the dark. Subsequently, the tail of the worm grows again. It turns out that annelid worms, long before lizards, were the inventors of a clever trick with a discarded tail.

The object of study of this course work is the type of annelids. A brief description of this type of worms and features of the organization of annelids is given. In the practical part of the work, such classes of this type as the class of leeches, the class of polychaetes, the class of oligochaetes, and the class of echiurids were considered. The systems of these worms and their features are described.

The first part of the work gives general information about the type of annelids. In the practical part of the work, information about some classes of worms of this type.

1. General characteristics of the type of annelids

Annelids are an extensive group of animals, including about 12 thousand species, that live mainly in the seas, but also in fresh waters and on land. This is a group of non-skeletal invertebrates, which for this reason are of particular importance in the nutrition of other animals, as they are assimilated without residue. At the same time, all of them are actively involved in the destruction of organic matter in biocenoses, contributing to the biogenic cycle. Particularly diverse are marine forms that are found at different depths up to the limit (up to 10 - 11 kilometers) and in all latitudes of the World Ocean. They play a significant role in marine biocenoses and have a high density of settlements: up to 100 thousand specimens per 1 square meter of the bottom surface. Sea rings are a favorite food of fish and occupy an important position in the trophic chains of marine ecosystems. / 10 /

In the soil, the most numerous are earthworms, or, as we call them, earthworms. Their density in forest and meadow soils can reach 600 specimens per 1 square meter. Earthworms are involved in the process of soil formation and contribute to an increase in crop yields and the productivity of natural biocenoses. Blood-sucking rings - leeches live mainly in fresh waters, and in tropical areas they are found in the soil and on trees. They are used in medicine for the treatment of hypertension. / 25 /

Let us consider the main features of the organization of the type of annelids as the first coelomic animals. / 1 ​​/

1. Metamerism of the external and internal structure. Metamerism is the repetition of identical parts or rings along the main axis of the body (from the Latin words meta - repetition, mera - part). The body is worm-shaped, divided into segments, or segments. Many organ systems are repeated in each segment. The body of annelids consists of a head lobe, a segmented body and an anal lobe.

2. There is a skin-muscular sac, consisting of skin epithelium, annular and longitudinal muscles, which are lined from the inside by coelomic epithelium. / 2 /

3. The secondary body cavity (coelom) is filled with coelomic fluid, which acts as the internal environment of the body. In general, a relatively constant biochemical regime is maintained and many functions of the body are carried out (transport, excretory, sexual, musculoskeletal). / 2 /

4. The intestine consists of three functionally different sections: the anterior, middle and hindgut. Some species have salivary glands. The anterior and posterior sections are ectodermal, and the middle section of the digestive system is of endodermal origin. / 1 ​​/

5. Most rings have a closed circulatory system. This means that blood flows only through the vessels and has a network of capillaries between arteries and veins. / 1 ​​/

6. The main excretory organs are metanephridia of ectodermal origin. Each pair of metanephridia begins in one segment with funnels, open as a whole, from which the excretory canals continue in the next segment and open there outwards with paired holes. metanephridia are not only organs of excretion, but also the regulation of water balance in the body. In the channels of the metanephridia, the excretion products thicken (ammonia is converted into uric acid), and water is absorbed back into the coelomic fluid. Thus, moisture is saved in the body and a certain water-salt regime is maintained in the whole. Saving moisture is especially necessary for ground and soil rings. / 1 ​​/

7. The nervous system consists of paired dorsal cerebral ganglia and the ventral nerve chain with metamerically repeated paired ganglia in each segment. The appearance of the brain, located dorsally above the pharynx, significantly distinguishes annelids from flatworms. The paired dorsal lobes of the annular brain are divided into anterior, middle, and posterior ganglia. This feature of the structure of the brain distinguishes ringworms from roundworms. / 1 ​​/

8. Annelids are usually dioecious, but often there is a simultaneous development of male and female gonads (hermaphroditism). / 1 ​​/

9. Development often proceeds with metamorphosis. A typical larva in sea rings is a trochophore. / 2 /

Thus, in the organization of annelids, progressive features of the organization of coelomic animals can be traced: the presence of a coelom, metamerism of the structure, the appearance of a circulatory system, an excretory system like metanephridia, a more highly organized nervous system and sensory organs. This ring differs from the lower worms flat and round. / 1 ​​/

However, a number of features in the organization of the rings testify to their relationship with the lower worms. Thus, the larvae of annuli - trochophores - have a primary body cavity, protonephridia, an orthogonal nervous system, and, in the early stages, a caecum. These features are sometimes found in adult rings from primitive groups./1/

The type of annelids is divided into classes:

Class Primary rings (Archiannelida),

Class Polychaeta (Polychaeta),

Class Small-bristle (Oligochaeta),

Leech class (Hirudinea),

Class Echiurida (Echiurida),

Class Sipunculida (Sipunculida).

1.1 Signs and variety of rings

About 200 years ago, the great French naturalist J. Cuvier, working on the creation of a system of the animal world, identified six types of animals, including the articulated type, into which he combined all creatures whose body is divided into segments: insects, crayfish, spiders, wood lice, earthworms and leeches. modern science has more extensive information about leeches and earthworms, and therefore these worms are distinguished into a special type - ringlets. / 1 ​​/

Annelids are characterized by the appearance of the following organizational features: the presence of a secondary body cavity or cellom, the circulatory system, the presence of metamerism - body segmentation / 1 /

In addition to the above features that play an important role in the evolution of animals, annelids are also characterized by the presence of special organs of movement - parapodia, a significant development of the central nervous system, consisting of the supraesophageal ganglion and the abdominal nerve chain with nerve nodes; the presence of a closed circulatory system, the metanephridial structure of the excretory system. / 1 ​​/

1 Primary rings

2 Polychaetes

3 Low-bristle

5 Echiurids

6 Sipunculids

1.2 External structure of annelids

Annelids are the most highly organized representatives of the group of worms. The sizes of the rings range from fractions of a millimeter to two and a half meters. Mostly these are free-living forms. The body of the annulus is subdivided into three parts: the head, the trunk, consisting of rings, and the anal lobe. Such a clear division of the body into sections is not found in animals that are lower in their organization. / 1 ​​/

The head of the rings is equipped with various sense organs. Many ringlets have well developed eyes. Some species have particularly sharp eyesight, and their lens is capable of accommodation. True, the eyes can be located not only on the head, but also on the tentacles, on the body and on the tail. The rings also have developed taste sensations. On the head and tentacles, many of them have special olfactory cells and ciliary pits that perceive various smells and the actions of many chemical stimuli. The organs of hearing, arranged according to the type of locators, are well developed in the rings. Recently, auditory organs have been opened in Echiruid marine rings, very similar to the organs of the lateral line in fish. With the help of these organs, the animal subtly distinguishes the slightest rustles and sounds that are heard much better than in the air. / 1 ​​/

1.3 The internal structure of the rings

Digestive system consists of three sections: anterior, middle and hindgut. The foregut is strongly differentiated into a number of organs: mouth, pharynx, esophagus, goiter, stomach.

Circulatory system closed. It consists of large longitudinal vessels - dorsal and abdominal, connected in each of the segments by annular vessels. The movement of blood is carried out due to the pumping activity of the contractile sections of the spinal, less often annular vessels. The blood plasma contains respiratory pigments close to hemoglobin, thanks to which the ringlets inhabited habitats with a wide variety of oxygen content. Many annelids have red blood, like humans. It is so colored, of course, due to the presence of iron. But at the same time, iron is part of a completely different pigment, not like hemoglobin, hemerythrin. It is able to capture oxygen 5 times more than hemoglobin. The choice of pigment is due to the peculiarities of the lifestyle of such worms. These are bottom creatures, spending most of their time in the thickness of the soil, where they experience an acute oxygen deficiency. / 1 ​​/

Respiratory system in polychaete worms, gills are thin-walled, leaf-like, pinnate or bushy external outgrowths of a part of the dorsal lobes of the parapodia, pierced by blood vessels. Small-bristle worms breathe the entire surface of the body. / 1 ​​/

excretory organs- metanephridia located in pairs in each segment, removing the end products of vital activity from the cavity fluid. The metanephridial funnel is located in the coelom of one segment, and the short tubule extending from it opens outward in the next segment. / 1 ​​/

Nervous system ganglion type. It consists of paired supraoesophageal and suboesophageal ganglia, connected by nerve trunks into the peripharyngeal nerve ring, and many pairs of ganglia of the ventral nerve cord, one pair in each segment. /1/

sense organs. A number of rings have well-developed sense organs, primarily the eyes. Unlike humans and other warm-blooded animals, worms sometimes have a significant number of eyes, which can be located on the head, at the posterior end of the body, on the sides (including on each segment), and even on the tail. Marine polychaetes are not only sensitive to light, but are also able to independently emit it. / 2 /

Reproduction of rings. The vast majority of ringlets are dioecious animals, less often hermaphrodites. The gonads develop either under the coelomic epithelium in all trunk segments (in polychaete worms) or only in some (in oligochaete worms). In polychaete worms, germ cells through ruptures in the coelomic epithelium enter the coelom fluid, from where they are excreted into the water by special sex funnels or metanephridia. In most water rings, fertilization is external, in soil forms it is internal. Development with metamorphosis (in polychaete worms) or direct (in oligochaete worms, leeches). Some types of rings, in addition to sexual reproduction, also reproduce asexually (by fragmentation of the body, followed by regeneration of the missing parts). Type Annelids are divided into three classes - Polychaetes, Low-bristle and Leeches.

1.4 Features of reproduction of annelids

Annelids can reproduce both sexually and asexually. The first is most typical of aquatic species, especially some marine polychaetes. Asexual reproduction is reduced either to the division of the body into parts, or to budding. When dividing, the body of the worm breaks into halves, each of which subsequently restores the missing end.

It is curious that the tail end, after separation, is an independent creature and is able to grow a new head for itself. Sometimes this head grows back long before the worm has split in half. In the middle of the body of such a ring, which is preparing to prolong the genus, there is a second head. After some time, the two-headed creature disintegrates to give life to two new worms./24/

The cocoon of a medical leech easily feeds its numerous cubs until they have heads. / 24 /

Fertilization in sexually reproducing marine worms is external. Females and males throw germ cells into the water, where the spermatozoa merge with the eggs. In the future, larvae hatch from the eggs - trochophores, which do not look like adults. Terrestrial and freshwater ringworms, including leeches, have direct development, with juveniles replicating adults almost exactly. Young leeches develop from cocoons containing eggs./24/

An important role in the reproduction of annelids is played by luminescence. The glow of worms is provided by the presence in the body of a special substance called luciferin. Under the action of a special enzyme luciferase, luciferin is oxidized by oxygen to form carbon dioxide. In this case, the released chemical energy goes to the release of excited atoms of light particles - photons. Luciferin is contained in worms in granules that float in the liquid cellular substance, where they are oxidized. Therefore, it seems that the tissues of the body are luminous in polychaetes. / 24 /

Worms are endowed with a relatively efficient oxidation mechanism, with a return of 10 to 20 percent and possibly even more. This means that marine polychaetes have learned to convert more than 10 percent of the chemical energy of luciferin into light, and the rest is useless losses. Compared to incandescent lamps, polychaete cells are extremely economical and compact biological devices. Thus, for every 3 molecules of luciferin, there are 3 oxygen molecules, and as a result of the reaction, 3 molecules of carbon dioxide and 2 photons are released. / 24 /

The biological significance of the glow can be different. There are cases when invertebrates use their illumination in order to communicate with relatives, primarily with representatives of the opposite sex. Once a year, many tropical worms leave their benthic shelters and swim up to the surface of the ocean to swarm. Here females meet males./24/

Polychaetes of the Bermuda Triangle use flashlights just during swarming. Females attract males with an intense glow, causing them to dance, during which gentlemen must encourage their ladies to release sexual products into the water. If the female does not glow, then she has already performed her “dance of love”. She is not interested in males. Probably, the "moving candles" that X. Columbus observed in the waters of the Caribbean Sea were such swarming worms. / 24 /

2. Classification of annelids

In total, the type includes 9000 species of animals, which is 1/4 of the total species diversity of worms (scolecid). Zoologists distinguish 4 classes in the type of annelids, in addition to leeches: archiannelids, or primary rings, oligochaetes, polychaetes, echiurids. Oligochaetes and polychaetes are often also called oligochaetes and polychaetes.

Rings are the most highly organized of all other scolecids, they represent the pinnacle of the evolution of this vast group of living beings. At the same time, annelids are considered the ancestors of many different organisms, among which arthropods, represented by insects, spiders, crayfish, crabs, etc., are of paramount importance in nature. The annelids themselves originated from flatworms.

In the course of evolutionary development, species of flatworms appeared that increased the length of their body, growing segment by segment. These creatures simply added another muscular ring. But then the changes covered the entire internal structure of the worms. Their organs also began to grow in parts. As a result, animals appeared with external and internal division of the body, in which almost each new segment copies the previous one in general terms. Such a repetition of homogeneous segments of the body has received the name of metamerism in science.

In reality, of course, the development of the metameric structure of the body proceeded much longer and more complicated. Even in primitive microscopic rhizopods of foraminifera, the division of shells into similar segments is observed. Thus, the segmentation of the body underlay the evolution of the organic world. It was a consequence of the adaptation of living beings to the environment and the evolution of body symmetry types, which increases the adaptive capabilities of species. Metamerism itself is considered by scientists as a special type of symmetry.

Jellyfish and their coelenterate relatives, as well as lower worms, lack true metameres (somites). However, many of them are characterized by either polymeric organs or pseudometamerism, i.e. the presence of false segments. Such coelenterates as hydrozoans, scyphozoans, anthozoans, and ctenophores have polymeric organs.

Chemicals related to polyethylene are commonly referred to as polymers. In biology, the same name was given to organs and structures that are repeatedly repeated in the body. Usually these are the organs of the reproductive system. Pseudometamery and polymer formations are typical for a number of groups of lower worms: cestodes, turbellarians, nemertines. In scolecids, body cavities are laid, which is why there are similarities of segments.

Further division of the body of animals was possible due to the complication of the nervous system and, mainly, the appearance of the circulatory system. It became possible to isolate the branches of nerves (with the formation of neurosomites) and blood vessels (with the formation of angiosomites).

The third and, perhaps, the most essential condition for the progress of metamerism was the growth of muscles. Ringworms have the most developed muscle sac among worms, the volume of which reaches 60–70 percent of the total body volume. Due to the intensive development of muscles, there was a separation of sections of the longitudinal and annular muscles with the formation of myosomites, separated by transverse partitions-dissepiments.

The growth of the muscular sac and the segmentation that accompanies this phenomenon were a single evolutionary breakthrough of the annulus, which allowed them to occupy the most important ecological niches of the sea, fresh water and soil from those that are only occupied by worms. The scolecides have fought for reliable protection and speed throughout their history. Only the descendants of primitive worms were able to solve this problem, which explains the progress of these groups. Snails "invented" for themselves reliable protection in the form of shells. Squids have created a powerful jet "engine" from their muscle bag.

Annelids acquired dense integuments, cut into lobules - segments corresponding to internal metamerism. Segmentation allowed these invertebrates to freely bend their body to move in waves, while developing considerable speed. Subsequently, insects, crayfish and other arthropods were covered with a dense segmented shell. Man in his organization bears the imprint of the metamerism of the ancient rings, but our body does not consist of segments. Their number in vertebrates has sharply decreased, which is why instead of somites, the so-called somites were formed. departments.

2.1 Polychaete class ( Polychaeta )

The class of polychaetes differs from other annulus in a well-separated head region with sensory appendages and the presence of limbs - parapodia with numerous setae. Mostly dioecious. development with metamorphosis.

General morphofunctional characteristics. The body of polychaete worms consists of a head section, a segmented trunk, and an anal lobe. The head is formed by the head lobe (prostomium) and the oral segment (perestomium), which is often complex as a result of fusion with 2–3 trunk segments. The mouth is located ventrally on the perestomium. Many polychaetes have ocelli and sensory appendages on their heads. So, in a Nereid, on the prostomium of the head there are two pairs of eyes, tentacles - tentacules and two-segmented palps, on the bottom of the perestomium there is a mouth, and on the sides there are several pairs of antennae. On the trunk segments there are paired lateral outgrowths with setae - parapodia. these are primitive limbs with which polychaetes swim, crawl or burrow into the ground. Each parapodia consists of a basal part and two lobes - dorsal (notopodium) and ventral (neuropodium). At the base of the parapodia, on the dorsal side, there is a dorsal antennae, and on the ventral side, there is a ventral antennae. These are the sensory organs of polychaetes. Often, the dorsal barbel in some species is turned into feathery gills. Parapodia are armed with tufts of setae, consisting of organic matter close to chitin. Among the setae there are several large aciculous setae, to which muscles are attached from the inside, setting the parapodia and the tuft of setae in motion. The limbs of polychaetes make synchronous movements like oars. In some species leading a burrowing or attached lifestyle, the parapodia are reduced.

Skin-muscular sac . The body of polychaetes is covered with a single layer of skin epithelium, which exposes a thin cuticle to the surface. In some species, some parts of the body may have ciliated epithelium (longitudinal abdominal band or ciliary bands around segments). Glandular epithelial cells in sessile polychaetes can secrete a protective horny tube, often impregnated with lime.

Under the skin lies the annular and longitudinal muscles. The longitudinal muscles form four longitudinal bands: two on the dorsal side of the body and two on the ventral side. Longitudinal tapes may be more. On the sides there are bundles of fan-shaped muscles that set in motion the blades of the parapodia. The structure of the skin-muscular sac varies greatly depending on the lifestyle. The inhabitants of the ground surface have the most complex structure of the skin-muscular sac, close to that described above. This group of worms crawls along the surface of the substrate with the help of a serpentine bending of the body and movements of the parapodia. The inhabitants of calcareous or chitinous pipes have limited mobility, as they never leave their shelters. In these polychaetes, strong longitudinal muscle bands provide a sharp lightning-fast contraction of the body and withdrawal into the depth of the tube, which allows them to escape from the attack of predators, mainly fish. In pelagic polychaetes, the muscles are poorly developed, as they are passively carried by ocean currents.

Secondary body cavity- in general - polychaetes have a very diverse structure. In the most primitive case, separate groups of mesenchymal cells cover the inside of the muscle bands and the outer surface of the intestine. Some of these cells are capable of contraction, while others are able to turn into germ cells that mature in a cavity, only conditionally called secondary. In a more complex coelomic epithelium may completely cover the intestines and muscles. The coelom is fully represented in case of development of paired metameric coelomic sacs. When paired coelomic sacs close in each segment above and below the intestine, the dorsal and abdominal mesentery, or mesentery, are formed. Between the coelomic sacs of two adjacent segments, transverse partitions are formed - dissipations. The wall of the coelomic sac lining the inside of the muscles of the body wall is called the parietal mesoderm, and the coelomic epithelium covering the intestines and forming the mesenterium is called the visceral mesoderm. The coelomic septa contain blood vessels.

In general, it performs several functions: musculoskeletal, transport, excretory, sexual and homeostatic. The cavity fluid supports the turgor of the body. With the contraction of the ring muscles, the pressure of the cavity fluid increases, which provides the elasticity of the worm's body, which is necessary when making passages in the ground. Some worms are characterized by a hydraulic mode of movement, in which the abdominal fluid, when the muscles contract under pressure, is distilled to the anterior end of the body, providing vigorous forward movement. In general, there is a transport of nutrients from the intestines and dissimilation products from various organs and tissues. The excretory organs of metanephridia open as a whole with funnels and ensure the removal of metabolic products, excess water. In general, there are mechanisms to maintain the constancy of the biochemical composition of the liquid and water balance. In this favorable environment, gonads are formed on the walls of coelomic sacs, germ cells mature, and in some species, juveniles even develop. Derivatives of the coelom - coelomoducts serve to remove the reproductive products from the body cavity.

Digestive system consists of three departments. The entire anterior section consists of derivatives of the ectoderm. The anterior section begins with a mouth opening located on the peristomium from the ventral side. The oral cavity passes into a muscular pharynx, which serves to capture food objects. In many species of polychaetes, the pharynx can turn outward, like a finger of a glove. In predators, the pharynx consists of several layers of annular and longitudinal muscles, armed with strong chitinous jaws and rows of small chitinous plates or spikes that can firmly hold, injure and crush captured prey. In herbivorous and detritivorous forms, as well as in seston-eating polychaetes, the pharynx is soft, mobile, adapted to swallowing liquid food. The pharynx is followed by the esophagus, into which the ducts of the salivary glands, also of ectodermal origin, open. Some species have a small stomach.

The middle section of the intestine is a derivative of the endoderm and serves for the final digestion and absorption of nutrients. In predators, the middle section of the intestine is relatively shorter, sometimes equipped with paired blind side pockets, while in herbivores, the middle section of the intestine is long, tortuous, and usually filled with undigested food debris.

The posterior intestine is of ectodermal origin and can perform the function of regulating the water balance in the body, since there water is partially absorbed back into the coelom cavity. Fecal masses are formed in the hindgut. The anal opening usually opens on the dorsal side of the anal lobe.

Respiratory system. Polychaetes mainly have cutaneous respiration. But a number of species have dorsal skin gills, which are formed from the parapodial antennae or appendages of the head. They breathe oxygen dissolved in water. Gas exchange occurs in a dense network of capillaries in the skin or gill appendages.

Circulatory system closed and consists of the dorsal and abdominal trunks connected by annular vessels, as well as peripheral vessels. The movement of blood is carried out as follows. Through the dorsal, the largest and pulsating vessel, blood flows to the head end of the body, and through the abdominal - in the opposite direction. Through the annular vessels in the anterior part of the body, blood is distilled from the dorsal vessel to the abdominal one, and vice versa in the posterior part of the body. Arteries depart from the annular vessels to parapodia, gills and other organs, where a capillary network is formed, from which blood is collected into venous vessels that flow into the abdominal bloodstream. In polychaetes, the blood is often red in color due to the presence of the respiratory pigment hemoglobin dissolved in the blood. Longitudinal vessels are suspended on the mesentery (mesenterium), annular vessels pass inside the dissipations. Some primitive polychaetes (Phyllodoce) have no circulatory system, and hemoglobin is dissolved in nerve cells.

excretory system polychaetes are most often represented by metanephridia. This type of nephridia appears for the first time in the type of annelids. Each segment contains a pair of metanephridia. Each metanephridium consists of a funnel lined with cilia and open as a whole. The movement of cilia into the nephridium drives solid and liquid metabolic products. A channel departs from the funnel of nephridium, which penetrates the septum between the segments and in another segment opens outwards with an excretory opening. In convoluted channels, ammonia is converted into macromolecular compounds, and water is absorbed as a whole. In different types of polychaetes, the excretory organs can be of different origin. Thus, some polychaetes have protonephridia of ectodermal origin, similar in structure to those of flatworms and roundworms. Most species are characterized by metanephridia of ectodermal origin. Individual representatives form complex organs - nephromixia - the result of the fusion of protonephridia or metanephridia with genital funnels - coelomoducts of mesodermal origin. An additional function can be performed by chloragogenic cells of the coelomic epithelium. These are peculiar accumulation kidneys in which excreta grains are deposited: guanine, salts of uric acid. Subsequently, chloragogenic cells die and are removed from the coelom through nephridia, and new ones are formed to replace them.

Nervous system. Paired supraesophageal ganglia form the brain, in which three sections are distinguished: proto-, meso- and deutocerebrum. The brain innervates the sense organs on the head. Near-pharyngeal nerve cords depart from the brain - connectives to the ventral nerve chain, which consists of paired ganglia, repeating segment by segment. Each segment has one pair of ganglia. Longitudinal nerve cords connecting the paired ganglia of two adjacent segments are called connectives. The transverse cords connecting the ganglia of one segment are called commissures. When paired ganglia merge, a neural chain is formed. In some species, the nervous system is complicated by the fusion of the ganglia of several segments.

sense organs most developed in mobile polychaetes. On the head they have eyes (2-4) of a non-inverted type, goblet-shaped or in the form of a complex eye bubble with a lens. Many sessile tube-dwelling polychaetes have numerous eyes on the feathery gills of the head region. In addition, they have developed organs of smell, touch in the form of special sensory cells located on the appendages of the head and parapodia. Some species have organs of balance - statocysts.

reproductive system. Most polychaete worms have separate sexes. Their gonads develop in all segments of the body or only in some of them. Sex glands of mesodermal origin and are formed on the wall of the coelom. Sex cells from the gonads fall into the whole, where their final maturation takes place. Some polychaetes do not have reproductive ducts, and the germ cells enter the water through ruptures in the body wall, where fertilization occurs. In this case, the parental generation dies. A number of species have genital funnels with short channels - coelomoducts (of mesodermal origin), through which the reproductive products are brought out into the water. In some cases, germ cells are removed from the coelom through nephromixia, which simultaneously perform the function of the reproductive and excretory ducts.

reproduction polychaetes can be sexual and asexual. In some cases, there is an alternation of these two types of reproduction (metagenesis). Asexual reproduction usually occurs by transverse division of the body of the worm into parts (strobilation) or by budding. This combing is accompanied by the regeneration of the missing parts of the body. Sexual reproduction is often associated with the phenomenon of epitokia. Epitokia is a sharp morphophysiological restructuring of the worm's body with a change in the shape of the body during the maturation of reproductive products: the segments become wide, brightly colored, with swimming parapodia. In worms that develop without epitokia, males and females do not change their shape and reproduce in bottom conditions. Species with epitokia may have several life cycle variants. One of them is observed in Nereids, the other in Palolo. Thus, in Nereisvirens, males and females become epitonic and float to the surface of the sea for reproduction, after which they die or become prey to birds and fish. From eggs fertilized in water, larvae develop, settling to the bottom, from which adults are formed. In the second case, as in the palolo worm (Euniceviridis) from the Pacific Ocean, sexual reproduction is preceded by asexual reproduction, in which the anterior end of the body remains at the bottom, forming an atonic individual, and the posterior end of the body is transformed into an epitonic tail filled with reproductive products. The backs of the worms break off and float to the surface of the ocean. Here the reproductive products are released into the water and fertilization takes place. Epitoke individuals of the entire population emerge for reproduction at the same time, as if on a signal. This is the result of the synchronous biorhythm of puberty and biochemical communication of sexually mature individuals of the population. The mass appearance of breeding polychaetes in the surface layers of water is usually associated with the phases of the moon. So, the Pacific palolo rises to the surface in October or November on the day of the new moon. The local population of the Pacific Islands knows these palolo breeding dates, and fishermen en masse catch palolo stuffed with "caviar" and use them for food. At the same time, fish, gulls, sea ducks feast on worms.

Development. The fertilized egg undergoes uneven, spiral crushing. This means that as a result of crushing, quartets of large and small blastomeres are formed: micromeres and macromeres. In this case, the axes of the spindles of cell fragmentation are arranged in a spiral. The inclination of the spindles is reversed with each division. Due to this, the crushing figure has a strictly symmetrical shape. Cleavage of the egg in polychaetes is deterministic. Already at the stage of four blastomeres, determination is expressed. Quartets of micromeres give derivatives of the ectoderm, and quartets of macromeres give derivatives of the endoderm and mesoderm. The first mobile stage is the blastula, a single-layered larva with cilia. The macromeres of the blastula at the vegetative pole sink into the embryo and a gastrula is formed. At the vegetative pole, the primary mouth of the animal, the blastopore, is formed, and at the animal pole, an accumulation of nerve cells and a ciliary tuft, the parietal sultan of cilia, are formed. Then a larva develops - a trochophore with an equatorial ciliary belt - a troch. The trochophore has a spherical shape, a radially symmetrical nervous system, protonephridia, and a primary body cavity. The blastopore at the trochophore is displaced from the vegetative pole closer to the animal along the ventral side, which leads to the formation of bilateral symmetry. The anus erupts later at the vegetative pole, and the intestine becomes through.

2.2 Class low-bristle

Small-bristle worms are inhabitants of fresh waters and soil, which are sporadically found in the seas. More than 5000 species are known. Distinctive features of the external structure of oligochaete worms are homonomous segmentation of the body, the absence of parapodia, and the presence of a glandular belt in the anterior third of the body in sexually mature individuals. Their head section is not expressed. The head lobe, as a rule, is devoid of eyes and appendages. There are also no appendages on the anal lobe (pygidium). Setae are located on the sides of the body, usually four pairs of tufts per segment. These are the rudiments of parapodia. Such a simplification of the external structure is associated with adaptations to a burrowing lifestyle. in oligochaetes, there is a convergent resemblance to burrowing polychaetes. This confirms the reason for their morphoecological similarity in connection with the development of a similar, burrowing lifestyle. The oligochaetes most familiar to us are earthworms living in the soil. Their body reaches several centimeters, the largest among them - up to 3 m (in Australia). In the soil, small whitish annelids are also common - enchytreids (5 - 10 mm). Earthworms and enchytreids feed on plant residues in the soil and play an important role in soil formation. In freshwater bodies one can often see oligochaetes with long bristles or living in vertical tubes and forming dense settlements at the bottom. They feed on suspended organic residues and are useful filter feeders that play an essential role in water purification.

General morphophysiological characteristics . The body length varies from a few millimeters to 3 m. The body is long, worm-shaped, and segmented. The number of segments varies from 5 - 6 to 600. The mouth is located on the first segment of the body after the head lobe. The anal opening is located on the anal lobe. Oligochaetes move by contracting the muscles of the body. When digging, the worm spreads the soil with the front end of the body, relying on numerous bristles. The bristles rest against the walls of the dug passage, so it is difficult to pull the earthworm out of the mink.

Skin-muscular sac. The body is covered with a layer of skin epithelium, often with a large number of glandular cells. The skin exudes a thin cuticle. Abundant secretion of mucus protects the skin of earthworms from mechanical damage and drying. Under the skin, like in polychaetes, they have circular and longitudinal muscles, lined from the inside with coelomic epithelium.

Digestive system. The intestine runs along the entire length of the body. In the anterior intestine of the earthworm, the oral cavity, muscular pharynx, relatively narrow esophagus, goiter and stomach are separated. In the walls of the esophagus there are three pairs of calcareous glands, the secrets of which neutralize humic acids in the food of earthworms. From the stomach, food enters the midgut, where nutrients are absorbed. Undigested food residues and mineral soil particles enter the short hindgut and are removed through the anus to the outside. In the midgut, an internal longitudinal fold is located dorsally - tiflozol, hanging into the intestinal lumen and increasing the absorption surface of the intestine.

Circulatory system oligochaetes are similar in structure to the circulatory system of polychaetes. There are dorsal and abdominal pulsating vessels, which are connected by annular vessels. Unlike polychaetes, in oligochaetes, the annular vessels in the esophagus pulsate and are called "ring hearts". The blood contains a respiratory pigment - hemoglobin, which is dissolved in the blood plasma, in contrast to vertebrates, in which hemoglobin is located in red blood cells. The circulatory system performs a transport function in oligochaetes for the transfer of nutrients, oxygen and metabolic products.

excretory system represented by metanephridia. The ability of metanephridia to conserve moisture in the body by reabsorbing water ensures that oligochaetes are adapted to life on land. Solid excretions accumulate in the chloragogenic cells of the coelomic epithelium. Partially these cells filled with excreta are removed through funnels of nephridia or through special pores in the body wall.

Nervous system it is represented, as in all rings, by a pair of supraesophageal ganglia (brain) and an abdominal nerve cord.

sense organs in oligochaetes, they are less developed than in most polychaetes, due to a burrowing lifestyle. The eyes are usually absent. In the skin of oligochaetes there are numerous sensory cells: light-sensitive, tactile, and other earthworms sensitively react to factors of light, humidity, and temperature. This explains their vertical migrations in the soil during the day and in seasons.

reproductive system oligochaete hermaphroditic. Hermaphroditic individuals of oligochaetes are of the same type, in contrast to sexually mature individuals of polychaetes with sexual dimorphism. Hermaphroditism in the animal kingdom is an adaptation to increase fertility, since all 100% of the individuals in the population can lay eggs. Consider the structure of the reproductive system using the example of an earthworm. The gonads in oligochaetes are concentrated in the anterior segments of the body. The testicles (two pairs) are located in the 10th and 11th segments of the body and are covered by three pairs of seed sacs. In the seminal sacs accumulates sperm flowing from the testicles. This is where spermatozoa mature. Sperm enter the ciliated funnels of the vas deferens. The vas deferens merge in pairs on the left and right sides of the body, and two longitudinal canals are formed, opening with paired male genital openings on the 15th segment of the body. The female reproductive system is represented by a pair of ovaries located on the 13th segment, a pair of oviducts with funnels opening with genital openings on the 14th segment. In the 13th segment, dissipiments form egg sacs that cover the ovaries and funnels of the oviducts. The female reproductive system also includes special skin protrusions on the 9th and 10th segments - two pairs of seed receptacles with holes on the ventral side of the body.

Reproduction and development. In sexually mature earthworms, a glandular belt develops on the 32nd - 37th segments. During the breeding season, at first all individuals become, as it were, males, since only the testes are developed in them. The worms are connected by their head ends towards each other, while the girdle of each worm is located at the level of the seminal receptacles of the other worm. The girdle secretes a mucous "clutch" that connects the two worms. Thus, mating worms are united by two bands of mucous muffs in the region of their girdle. From the male openings of both worms, sperm is released, which, through special grooves on the ventral side of the body, enters the seminal receptacles of another individual. After exchanging male reproductive products, the worms disperse. After some time, the ovaries mature in the worms and all individuals become, as it were, females. The "clutch" from the girdle area slides to the anterior end of the body due to the peristaltic movements of the worm's body. At the level of the 14th segment, eggs from the female genital openings enter the clutch, and at the level of the 9th - 10th segments, "foreign" seminal fluid is injected. This is how cross fertilization occurs. Then the muff slips from the head end of the body and closes. An egg cocoon is formed with developing eggs. The cocoon of earthworms is shaped like a yellow-brown lemon; its dimensions are 4 - 5 mm in diameter.

Development in oligochaetes proceeds without metamorphosis, i.e. without larval stages. Small worms that look like adults hatch from the egg cocoon. Such direct development without metamorphosis arose in oligochaetes in connection with the transition to life on land or to living in fresh water bodies, which often dry up. The embryonic development of the oligochaete embryo proceeds, as in most polychaetes, according to the spiral type of crushing and with the teloblastic anlage of the mesoderm.

Asexual reproduction is known in some families of freshwater oligochaetes. In this case, a transverse division of the worm into several fragments occurs, from which whole individuals then develop, or by differentiation of the worm into a chain of short daughter individuals. Later, this chain breaks down. In earthworms, asexual reproduction is extremely rare, but the ability to regenerate is well expressed. The cut worm, as a rule, does not die, and each part of it restores the missing ends. The worm most easily restores the posterior end of the body. The head end of the body is restored rarely and with difficulty.

2.3 Leech class

Leeches (Hirudinei) are a detachment of the class of annelids.

Body elongated or oval, more or less flattened in the dorsal-abdominal direction, clearly divided into small rings, which in number 3-5 correspond to one segment of the body; numerous glands in the skin that secrete mucus; at the posterior end of the body there is usually a large sucker, often at the anterior end there is a well-developed sucker, in the center of which the mouth is placed; more often, the mouth is used for suction. At the anterior end of the body there are 1–5 pairs of eyes arranged in an arc or in pairs one after the other.

powder on the dorsal side above the posterior sucker.

Nervous system consists of a two-lobed supraoesophageal ganglion or brain, connected to it by short commissures under the pharyngeal node (derived from several merged nodes of the abdominal chain) and the abdominal chain itself, located in the abdominal blood sinus and having about 20 nodes. The head node innervates the sense organs and the pharynx, and 2 pairs of nerves depart from each node of the abdominal chain, innervating the body segments corresponding to them; the lower wall of the intestine is equipped with a special longitudinal nerve that gives branches to the blind sacs of the intestine.

Digestive organs they begin with a mouth armed with either three chitinous toothed plates (jaw leeches - Gnathobdellidae), which serves to cut through the skin when sucking blood in animals, or a proboscis capable of protruding (in proboscis leeches - Rhynchobdellidae); numerous salivary glands open into the oral cavity, sometimes secreting a poisonous secret; the pharynx, which plays the role of a pump during sucking, is followed by an extensive, highly extensible stomach, equipped with lateral sacs (up to 11 pairs), of which the posterior ones are the longest; the hindgut is thin and short.

Circulatory system partly consists of real, pulsating, vessels, partly from cavities - sinuses, representing the remainder of the cavity (secondary) of the body and interconnected by annular channels; blood in proboscis leeches is colorless, in jaw leeches it is red, due to hemoglobin dissolved in the lymph.

Special respiratory organs are available only at the river. Branchellion, in the form of leaf-like appendages on the sides of the body.

excretory organs arranged according to the type of metanephridia or segmental organs of annelids, and most leeches have a pair in each of the middle segments of the body.

Reproductive system and reproduction Leeches are hermaphrodites: Most of the male genital organs consist of vesicles (testes), in pairs in 6-12 middle segments of the body, connected on each side of the body by a common excretory duct; these ducts open outwards with one opening lying on the ventral side of one of the anterior rings of the body; the female genital opening lies one segment behind the male and leads into two separate oviducts with saccular ovaries. Two individuals copulate, each simultaneously playing the role of a female and a male. During the laying of eggs, leeches secrete thick mucus, which surrounds the middle part of the body of the leech in the form of a cover, into this cover, after which the leech crawls out of it, and the edges of its holes come together, stick together and form such in the form of a capsule with eggs inside, usually attached to the lower surface of the algae leaf; the embryos, leaving the egg shell, sometimes (Clepsine) keep for some time on the underside of the mother's body.

Variety of leeches. All leeches are predators, feeding on the blood of mostly warm-blooded animals, or mollusks, worms, and the like; they live mainly in fresh waters or in wet grass; but there are marine forms (Pontobdella) as well as terrestrial forms (in Ceylon). Hirudo medicinalis - medicinal leech up to 10 cm long and 2 cm wide, black-brown, black-green, with a longitudinal patterned reddish pattern on the back; the belly is light grey, with 5 pairs of eyes on the 3rd, 5th and 8th rings and strong jaws; distributed in the marshes of the south. Europe, southern Russia and the Caucasus. In Mexico, Haementaria officinalis is used in medicine; another species, the mexicana leech, is poisonous; in tropical Asia, Hirudo ceylonica and other related species living in humid forests and in the grass are common, causing painful bleeding bites to humans and animals. Aulostomum gulo - horse leech, black-green in color, with a lighter bottom, has a weaker mouth armament and therefore unsuitable for therapeutic purposes; the most common species in the north. and central Russia. Nephelis vulgaris is a small leech with a thin narrow body, gray in color, sometimes with a brown pattern on the back; equipped with 8 eyes located in an arc at the head end of the body; related to her original Archaeobdella Esmonti, pink, without posterior sucker; lives on the silt bottom in the Caspian and Azov seas. Clepsiue tesselata - Tatar leech, with a wide oval body, greenish brown in color, with several rows of warts on the back and 6 pairs of triangular eyes located one after the other; lives in the Caucasus and Crimea, where it is used by the Tatars for medicinal purposes; the transitional place to the order of bristle-footed worms (Chaetopoda Oligochaeta) is occupied by Acanthobdella peledina, found in Onega Lake.

2.4 Echiuridae class

The external structure of Echiuridae. Marine, benthic, worm-like animals burrowing in the ground with a non-segmented body, an unsegmented whole, possessing, like annelids, a typical larva - a trochophore. The absence of metamerism represents a primary feature of the organization of the echuririds. This is a small group of about 150 species.

The sizes of echiurids vary from 3 to 185 cm (with an elongated proboscis).

The sausage-shaped, non-segmented body is equipped with a long non-retractable proboscis. At its base is a mouth, and at the rear end of the body is a powder.

The proboscis is sometimes bifurcated at the end. The ventral side of the proboscis is somewhat concave and covered with cilia, which drive water with small food particles to the mouth. Behind the mouth on the ventral side there are 2 large setae; in addition, the posterior end of the body is sometimes surrounded by 1–2 rims of small setae resembling those of Polychaeta.

The body is covered with a single-layered epithelium, which secretes a cuticle from its surface. Under the cuticle is a skin-muscular sac. The peritoneal epithelium limits the extensive continuous body cavity (coelom).

Digestive system of Echiuride forms a long convoluted canal, consisting of the anterior, middle and posterior intestine, opening at the posterior end with the anus. Due to the tortuous course, the length of the intestine is sometimes 10 times the length of the body. A pair of its protrusions flows into the hindgut: anal sacs. They are seated with 12-300 small ciliated funnels, which open as a whole, and the other end into the cavity of the anal sac.

The bags serve for breathing and for excretion.

The circulatory system of Echiurid consists of a dorsal longitudinal vessel passing over the anterior part of the intestine, continuing into the proboscis. This vessel bifurcates in front and gives rise to two lateral proboscis vessels. The latter, when leaving the proboscis, merge into a common longitudinal abdominal vessel, stretching under the intestine to the posterior end of the body. The posterior end of the dorsal vessel communicates with the abdominal one with the help of two transverse vessels covering the intestines. The blood is colorless and contains colorless leukocytes.

Nervous system rather underdeveloped. The central nervous system consists of the ventral trunk, which bifurcates at the anterior end of the body, goes around the intestine and forms the peripharyngeal nerve ring. So, the general plan of the structure of the nervous system resembles Polychaeta, but the nerve trunk of Echiurida is dotted with nerve cells throughout, and even the peripharyngeal ring is devoid of ganglionic thickenings.

sense organs, except for individual sensitive cells and papillae in the skin, are absent.

excretory system. The nephridia of the echiurids are represented by three kinds of organs. At the trochophore larval stage, chiurids have a pair of protonephridia, which are reduced during metamorphosis (as in the class Polychaeta). In adult animals, anal sacs with their funnels, considered by some zoologists as metanephridia, serve primarily for excretion. In addition to sacs, adult Echiurids have more or less typical nephromixia, which are generally open with ciliated funnels. However, their main purpose is the excretion of reproductive products. Nephromyxia lie in front of the body and open outward on the ventral side. Their number varies from 1 to 4 pairs, but in some forms there are much more. So, for example, in large Ikeda tenioides, from 100 to 200 nephridia are located on each side of the ventral nerve trunk. In the vast majority of genera there is a gradual oligomerization of the number of excretory organs from 4 pairs in Thalassema to 1 in the female Bopellia.

The way of life of males is original. First, they crawl along the surface of the female's proboscis; later they penetrate into the anterior intestine, then into the nephridia of the female and live there for a long time in anticipation of the passage of mature eggs through the nephridia, which fertilize, releasing gum.

Echiuride development at first it resembles that of a polychaete. Spiral and determinative fragmentation leads to the formation of a more or less typical trochophore. The growth of the trochophore is accompanied by the formation of two mesodermal stripes. However, the latter are not segmented, but, growing strongly and merging together, form a common whole. The body of the larva behind the prototroch grows evenly in length. The larva swims freely in plankton and only after metamorphosis settles to the bottom.

2.5 The practical significance of all annelids in nature and in human life

Freshwater oligochaetes play an essential role in fish nutrition. For example, tubifex, which often forms dense settlements at the bottom of water bodies, is a favorite food for many fish. They are used to feed aquarium fish. Tubifex - soil beetles that play a significant role in the biological treatment of water bodies. They are red in color because their blood contains hemoglobin. The presence of hemoglobin provides them with normal breathing even in polluted water bodies with a low oxygen content in the water. Swallowing the soil, they digest organic matter and promote their mineralization.

Small whitish annelids less than 10 mm long can live in fresh water, but are more common in the soil. Soil enchytreids include about 400 species. Their density in the soil can reach 150-200 thousand per 1 square meter. They are easily learned to breed in boxes of soil and use as food for aquarium fish, as well as for commercial species in fish hatcheries. Enchytreids feed on organic residues and participate in soil formation along with earthworms.

The family of earthworms (Lumbricidae) includes about 200 species, most of which live in the soil. Arboreal and semi-aquatic inhabitants are less common. The most common type of Lumbricusterrestris is 20 - 30 centimeters long and up to 1 centimeter thick. Large tropical earthworms (up to 1 - 3 meters long) are used by the local population of South America, Africa, Southeast Asia as food in boiled or fried form. Many animals feed on earthworms: moles, shrews, frogs, many birds and some predatory beetles. But the biological significance of earthworms in soil formation is especially great. Ch. Darwin was the first to pay attention to their role in the soil. Later, their significance in the biological cycle was experimentally studied. Earthworms swallow the soil, fallen leaves, plant remains and help to accelerate the humus formation and mineralization of the soil. In addition, earthworms loosen the soil, mix it up, dragging organic residues into the deep layers of the soil and bringing the soil depleted in organic matter from the deep layers to the surface. The soil passed through the intestines of worms has better structure. The improvement of soil fertility is facilitated by the export of manure and peat to the fields, which are important not only as a fertilizer, but also as food for worms. The soil enriched with organic matter contributes to an increase in the number of earthworms, which accelerate the soil-forming process. Experiments were carried out on the acclimatization of earthworms in the regions of Kazakhstan in Central Asia to improve soil fertility in irrigation areas.

The biological and practical importance of polychaete worms in the ocean is very great. The biological significance of polychaetes lies in the fact that they represent an important link in the trophic chains, and are also important as organisms that take part in the purification of sea water and the processing of organic matter. Polychaetes are of food value. To strengthen the food base of fish in our country, for the first time in the world, nereids (Nereisdiversicolor) were acclimatized in the Caspian Sea, which were brought from the Sea of ​​Azov. This successful experiment was carried out under the guidance of Academician L.A. Zenkevich in 1939–1940.

Conclusion

Thus, having studied the characteristics and structural features of the type of annelids, the following features can be determined: annelids are the most progressive type of worms. The features that distinguish this type of worm from other types are the presence of cellom and the metamerism of the structure. Based on this, annelids can be called coelomic animals with a high organization.

In addition, annelids play a very important role in the biocenosis. They are ubiquitous. The most diverse are marine forms of rings. An important role is played by annelids living in the earth and decomposing complex organic compounds. Rings also play an important role not only in the biocenosis of nature, but also for human health. For example, leeches, on which hirudotherapy is based, help to cure patients of rather complex diseases without the use of medicines.

If you dwell in more detail on the structure of annelids, you will find that some annelids have sharpened vision, and their eyes can be located not only on the head, but also on the body, tentacles. Also, this type of worm has developed taste sensations, and, based on the research of biologists, they have the beginnings of logical thinking. This is due to the fact that worms can find sharp corners.

If we consider the internal structure, then we can also note many features that indicate the progressive structure of annelids. An example of this is that most annelids are dioecious, only a small part are hermaphrodites. Development with metamorphosis occurs in polychaete worms and without metamorphosis in oligochaetes and leeches.

The circulatory system of the type of annelids also has a special structure, because blood is pumped through the vessels. In addition, the circulatory system is closed, which also in turn indicates the progressive structural features of annelids.

Also, the most important difference between annelids and all major types of worms is the appearance of a brain located dorsally above the pharynx.

Of particular interest is the reproduction of annelids and ways to attract persons of the opposite sex. One of these ways is glow. Worms use it not only for reproduction, but also for protection. They lure predators to themselves and, with the help of glow, teach them to eat parts of the body that are not important for the worm, which it can easily restore without harming the body.

If we consider the classes of worms, some of which are described in detail in the term paper, we can also highlight certain features of each class.

Polychaete worms are the most diverse in form and color, most of which live in the seas. Most of them lead a burrowing lifestyle, burrowing into the substrate or attaching to it. Sedentary polychaetes and crawling polychaetes are also known. They move through the bristles, which often have a bright color of all colors of the rainbow.

When considering the next group, one can also see structural features associated with the lifestyle of worms. And if in the previous case, polychaetes were characterized by a large number of bristles for swimming and burrowing into silt, then the oligochaetes are characterized by a non-separated head section, a streamlined body, a small number of bristles, all this is associated with a burrowing lifestyle, because many oligochaetes live in the ground, water and single individuals in the sea.

Leeches have the same adaptations for feeding on the blood of various animals: chitinous toothed plates, a large number of glands that secrete mucus, as well as the presence in the body of an enzyme that anesthetizes the bite and liquefies the blood of the victim.

Echiurids are marine burrowing worms. Their body, unlike all other classes of worms, is not segmented and is often equipped with a proboscis.

List of used literature

1 Dogel V.A. 1938. Comparative anatomy of invertebrates. - L. Uchpedgiz. Ch.

2 Dogel V.A. 1981. Invertebrate zoology. M. Higher school.

3 Beklemishev K.V. 1966. Ecology and biogeography of the pelagial. - M. Science. The biological structure of the ocean. 1977. M. Science.

4 Gilyarov M.S. 1970. Patterns of adaptation of arthropods to life on land. - M. Science.

5 Darlington F. 1966. Zoogeography (translated from English). M. Mir.

6 Beklemishev V.N. 1964. Fundamentals of comparative anatomy of invertebrates. – Ed. 3rd. M. Science. T. 1.

7 Dogel V.A. 1940. Comparative anatomy of invertebrates. - L. Uchpedgiz. Ch.

10 Zenkevich L.A. Fauna and biological productivity of the sea. - M. Soviet science. 1947.

11 Zenkevich L.A. 1963. Biology of the seas of the USSR. - M. Publishing House of the Academy of Sciences of the USSR.

12 Ivanov A.V. 1968. Origin of multicellular animals. - L. Science.

13 Ivanov P.P. 1945. Guide to General and Comparative Embryology.

14 HP Ivanova-Kazas O.M., E.B. Krichinskaya. A course in comparative embryology of invertebrates. - L. Publishing house of Leningrad State University 1988.

15. Comparative embryology of invertebrates: Protozoa and multicellular. - Novosibirsk.

16 Trochophores, tentacles, chaetognaths, pogonophores. - M. 1977

17 Konstantinov A.S. 1986. General hydrobiology. - M. Higher school.

18 Livanov N.A. 1945. Ways of evolution of the animal world. - M. Ed. "Soviet Science".

20 Malakhov V.V. Mysterious groups of marine invertebrates. Trichoplax, orthonectids, dicyemides, sponges. - M. Publishing house of Moscow State University. 1990.

21 Malakhov V.V., Adrianov A.V. Cephalorhyncha is a new type of animal kingdom. – M. KMK ScientificPress.

22 Raikov I.B. 1978. The nucleus of protozoa. - L. Science.

23 Houseman K. 1988. Protozoology (translated from German). - M. Mir.

24 L.A. Zenkevich Life of animals. Invertebrates. T. 1 - M: Enlightenment, 1968

25Perel T.S. Distribution and patterns of distribution of earthworms in the fauna of the USSR. - M.: Nauka, 1979

Subject: Variety of annelids. Classes Polychaetes, Few-bristle and Leeches.

educational - get acquainted with the variety of species and classes of annelids; to prove the adaptability to the habitat of representatives of different classes; consider various ecological groups of annelids;

Educational – to continue the formation of skills to substantiate, compare, analyze, speak publicly.

Educational – education of positive motivation for learning

Lesson type: combined

Type of lesson: mixed

Methods : verbal: conversation, explanation

Visual: demonstration of benefits

Equipment: m. Type flatworms, Type annelids, Type roundworms.

During the classes:

1. Org. moment (3 min)
2. Updating knowledge (7-10 min)

Front poll:

1. In what type are animals united with an elongated body divided into similar segments, the circulatory system, the ventral nerve chain and the peripharyngeal nerve ring?

2. How many species of flatworms are known so far?

4. Type Annelids includes classes ...

6. Roundworm eggs enter the human body from ...

7. The intermediate host of liver fluke larvae is ...

1. Learning new material (20-25 min)

In the previous lesson, we found out that annelid worms are more advanced animals in evolutionary terms than flat and round worms. Their body is segmented, there is a skin-muscular sac with internal organs located in it. And it is in annelids that the circulatory system of a closed type first appears. Class, how many species of annelids are known today? (9 thousand species).

Type Annelids combines several classes, of which three are the main ones - polychaete, Small-bristle and Leeches.

Comparative characteristics of various classes of annelids.

Using the text in the textbook on pages 129-131 and the tables and pictures in the textbook, let's complete the following table together (table heading on the board)

Building features	Class Polychaete	Class Low-bristle	Leech class
1. Habitat	marine and fresh waters	marine and fresh waters
2. Body shape	long cylindrical	long cylindrical	elongated flattened in the dorsal-abdominal direction.
3. Isolation of the head	clearly isolated	clearly isolated	weakly isolated
4. The presence of appendages (parapodia, setae and gills)	numerous	few	missing
5. Gas exchange	through the surface of the parapodia, which have an extensive network of blood vessels		entire body surface by diffusion
6. Reproduction	dioecious, gonads are located throughout the body, fertilization is external	hermaphrodites, gonads are in several segments, copulation and cross fertilization, eggs are laid in a cocoon	hermaphrodites, gonads are in very few segments, copulation and cross fertilization, eggs are laid in a cocoon
8. Representatives	nereid, lepidonotus, palolo, sandworm, spirorbis, serpula	tubifex, earthworm, earthworm	fish leech, false horse leech, horse leech, medicinal leech

Find in the text the answer to the question: What is the medical significance of leeches? (Used in medical practice in the treatment of hypertension and atherosclerosis).

1. Consolidation of knowledge

Group method of creating a creative project. The children are invited to make one representative from each class from improvised materials and summarize their knowledge about the studied class of annelids.

The class is divided into groups of 4 people.

Distributed to groups (sheet A4 or cartridge A4)

1 - colored paper, scissors, glue

2- felt-tip pens, pencils

The body of which consists of repeating segments, or rings (hence their name - annelids).

General brief characteristics of annelids:

• there is a secondary body cavity (general);
• the body is covered on the outside with a cuticle secreted by the ectoderm.
• there is a circulatory system;
• the nervous system is represented by a paired supraesophageal ganglion connected by jumpers to the abdominal nerve chain (usually double);
• the excretory organs are located in each ring and are formed from the ectoderm, they are equipped with cilia;

Structure

The elongated body of annelids is, as it were, assembled from segment rings, the segments are separated by internal partitions; but they are not completely independent, since a through intestine with a mouth and anus, an abdominal trunk of the nervous system and trunks of a closed circulatory system pass along the whole body. These organ systems, penetrating the partitions one after another, stretch through the entire body of annelids. Each ring-segment has a secondary body cavity (whole). Most of the segments bear on the outside, on the right and on the left, two bundles of setae - organs of locomotion or fixation in tubes. In leeches, the bristles are secondarily lost.

Secondary body cavity (general)

The secondary cavity of the body (whole) is of mesodermal origin. It is surrounded by a mesodermal membrane and filled with fluid. The cavity occupies the space between the walls of the body and the intestinal tube. The main part of the mesoderm lining the secondary cavity is the muscles that make up the body wall. They provide the movement of the animal. In addition, the muscles of the intestinal wall, alternately contracting, push food.

The secondary body cavity performs the following functions:

The secondary body cavity, to one degree or another, is a characteristic feature for all types of multicellular animals that follow in the evolutionary development, starting with annelids.

Classification

Annelids are a type of worms numerous in species that have a more complex body structure compared to flat and primary cavity worms. It is divided into three classes: Polychaetes, Belts (including subclasses Small-bristle worms and Leeches), Misostomids.

Origin

According to a comparative study of the structure of worms, annelids evolved from primitive whole worms, similar to flat ciliary worms. Important evolutionary acquisitions of annelids are the secondary body cavity (coelom), the circulatory system, and the division of the body into separate rings (segments). Polychaete annelids are the ancestral group for the rest of the annelids. From them, during the transition to a freshwater and terrestrial way of life, oligochaete worms separated. Leeches are descended from low-bristle worms.

Questions about this item:

Initial level of knowledge:

kingdom, type, cell, tissues, organs, organ systems, heterotroph, predation, saprophyte, detritophage, eukaryotes, aerobes, symmetry, body cavity, larva.

Answer plan:

General characteristics of annelids
Body structure of annelids
Reproduction and development of annelids
Classification of annelids, variety of species
Features of the structure and development of worms of the class Small-shchitinous on the example of an earthworm
Characteristics of the class
Characteristics of the Leech class
Origin of annelids

General characteristics of annelids

Number of species: about 75 thousand.

Habitat: in salt and fresh waters, found in soil. Aquatic crawl along the bottom, burrow into the silt. Some of them lead a sedentary lifestyle - they build a protective tube and never leave it. There are also planktonic species.

Structure: bilaterally symmetrical worms with a secondary body cavity and a body divided into segments (rings). In the body, the head (head lobe), trunk and tail (anal lobe) sections are distinguished. The secondary cavity (coelom), unlike the primary cavity, is lined with its own internal epithelium, which separates the coelomic fluid from the muscles and internal organs. The fluid acts as a hydroskeleton and is also involved in metabolism. Each segment is a compartment containing external outgrowths of the body, two coelomic sacs, nodes of the nervous system, excretory and genital organs. Annelids have a skin-muscular sac, consisting of one layer of skin epithelium and two layers of muscles: annular and longitudinal. On the body there may be muscular outgrowths - parapodia, which are organs of movement, as well as bristles.

Circulatory system first appeared in the course of evolution in annelids. It is of a closed type: blood moves only through the vessels, without entering the body cavity. There are two main vessels: dorsal (carries blood from back to front) and abdominal (carries blood from front to back). In each segment, they are connected by annular vessels. Blood moves due to the pulsation of the spinal vessel or "hearts" - the annular vessels of 7-13 segments of the body.

Respiratory system missing. Annelids are aerobes. Gas exchange occurs across the entire surface of the body. Some polychaetes have developed skin gills - outgrowths of parapodia.

For the first time in the course of evolution, multicellular excretory organs- metanephridia. They consist of a funnel with cilia and an excretory canal located in the next segment. The funnel faces the body cavity, the tubules open on the surface of the body with an excretory pore through which decay products are removed from the body.

Nervous system It is formed by the peripharyngeal nerve ring, in which the paired supraesophageal (cerebral) ganglion is especially developed, and by the ventral nerve cord, consisting of pairwise contiguous abdominal nerve nodes in each segment. From the "brain" ganglion and the nerve chain, nerves depart to the organs and skin.

Sense organs: eyes - organs of vision, palps, tentacles (antennas) and antennae - organs of touch and chemical sense are located on the head lobe of polychaetes. Due to the underground way of life, the sense organs are poorly developed in oligochaetes, but the skin has light-sensitive cells, organs of touch and balance.

Reproduction and development

They reproduce sexually and asexually - by fragmentation (separation) of the body, due to the high degree of regeneration. Budding is also found in polychaete worms.
Polychaetes are dioecious, while oligochaetes and leeches are hermaphrodites. Fertilization is external, in hermaphrodites - cross, i.e. worms exchange seminal fluid. In freshwater and soil worms, development is direct, i.e. juveniles emerge from the eggs. In marine forms, development is indirect: a larva, a trochophore, emerges from the egg.

Representatives

Type Annelids are divided into three classes: Polychaetes, Low-bristle, Leeches.

Small bristle worms (oligochaetes) mainly live in the soil, but there are also freshwater forms. A typical representative that lives in the soil is an earthworm. It has an elongated, cylindrical body. Small forms - about 0.5 mm, the largest representative reaches almost 3 m (a giant earthworm from Australia). Each segment has 8 setae, located in four pairs on the lateral sides of the segments. Clinging to the unevenness of the soil with them, the worm moves forward with the help of the muscles of the skin-muscular sac. As a result of feeding on rotting plant remains and humus, the digestive system has a number of features. Its anterior section is divided into a muscular pharynx, esophagus, goiter and muscular stomach.

An earthworm breathes over the entire surface of its body due to the presence of a dense subcutaneous network of capillary blood vessels.

Earthworms are hermaphrodites. Cross fertilization. The worms attach to each other with their ventral sides and exchange seminal fluid, which enters the seminal receptacles. After that, the worms disperse. In the anterior third of the body there is a belt that forms a mucous sleeve, eggs are laid in it. When the clutch is advanced through the segments containing the seed receptacles, the eggs are fertilized by sperm belonging to another individual. The clutch is dropped through the front end of the body, compacted and turns into an egg cocoon, where young worms develop. Earthworms are characterized by a high ability to regenerate.

Longitudinal section of the body of an earthworm: 1 - mouth; 2 - throat; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - gut; 7 - peripharyngeal ring; 8 - abdominal nerve chain; 9 - "hearts"; 10 - dorsal blood vessel; 11 - abdominal blood vessel.

Importance of oligochaetes in soil formation. Even Ch. Darwin noted their beneficial effect on soil fertility. Dragging the remains of plants into the mink, they enrich it with humus. Laying passages in the soil, they contribute to the penetration of air and water to the roots of plants, loosen the soil.

Polychaete. Representatives of this class are also called polychaetes. They live mainly in the seas. The segmented body of polychaetes consists of three sections: the head lobe, the segmented trunk, and the posterior anal lobe. The head lobe is armed with appendages - tentacles and bears small eyes. On the next segment is a mouth with a pharynx that can turn outward and often has chitinous jaws. The body segments bear biramous parapodia, armed with setae and often with gill outgrowths.

Among them there are active predators that can swim quite quickly, bending their body in waves (nereids), many of them lead a burrowing lifestyle, making long minks (sandworms) in the sand or in the silt.

Fertilization is usually external, the embryo turns into a larva characteristic of polychaetes - a trochophore, which actively swims with the help of cilia.

Class leeches includes about 400 species. In leeches, the body is elongated and flattened in the dorsal-abdominal direction. There is one oral sucker at the anterior end and another sucker at the posterior end. They do not have parapodia and bristles, they swim, bending their bodies in waves, or "walk" on the ground or leaves. The body of leeches is covered with a cuticle. Leeches are hermaphrodites, development is direct. They are used in medicine, because. due to the release of hirudin protein by them, the development of blood clots that clog blood vessels is prevented.

Origin: Annelids evolved from primitive, similar to flat ciliary worms. From the polychaetes, the little bristles originated, and from them - the leeches.

New concepts and terms:, polychaetes, oligochaetes, coelom, segments, parapodia, metanephridia, nephrostome, closed circulatory system, skin gills, trochophore, hirudin.

Questions to reinforce:

• Why did worms get such a name?
• Why are annelids also called secondary worms?
• What structural features of annelids testify to their higher organization compared to flat and round ones? What organs and organ systems first appear in annelids?
• What is characteristic of the structure of each segment of the body?
• What is the significance of annelids in nature and human life?
• What are the structural features of annelids in connection with their lifestyle and habitat?

Literature:

1. Bilich G.L., Kryzhanovsky V.A. Biology. Full course. In 3 volumes - M .: LLC Publishing House "Onyx 21st Century", 2002
2. Biology: A Handbook for Applicants to Universities. Volume 1. - M .: Novaya Vol-na Publishing House LLC: ONIKS Publishing House CJSC, 2000.
3. Kamensky, A. A. Biology. Reference manual / A. A. Kamensky, A. S. Maklakova, N. Yu. Sarycheva // Full course of preparation for exams, tests, tests. - M.: CJSC "ROSMEN-PRESS", 2005. - 399s.
4. Konstantinov V.M., Babenko V.G., Kuchmenko V.S. Biology: Animals: A textbook for students of the 7th grade of a comprehensive school / Ed. V.M. Konstantinova, I.N. Ponoma-roar. – M.: Ventana-Graf, 2001.
5. Konstantinov, V. M. Biology: animals. Proc. for 7 cells. general education schools /V. M. Konstantinov, V. G. Babenko, V. S. Kuchmenko. - M.: Ventana-Graf, 2001. - 304 p.
6. Latyushin, V. V. Biology. Animals: textbook. for 7 cells. general education institutions / V. V. Laktyushin, V. A. Shapkin. - 5th ed., stereotype. - M.: Bustard, 2004. - 304 p.
7. Pimenov A.V., Goncharov O.V. Biology manual for applicants to universities: Electronic textbook. Scientific editor Gorokhovskaya E.A.
8. Pimenov A.V., Pimenova I.N. Zoology of invertebrates. Theory. Tasks. Answers.: Saratov, JSC publishing house "Lyceum", 2005.
9. Taylor D. Biology / D. Taylor, N. Green, W. Stout. - M.: Mir, 2004. - T.1. - 454s.
10. Chebyshev N.V., Kuznetsov S.V., Zaichikova S.G. Biology: a guide for applicants to universities. T.2. - M .: New Wave Publishing LLC, 1998.
11. www.collegemicrob.narod.ru
12. www.deta-elis.prom.ua

1. Variety of annelids in nature.

The oligochaetes include freshwater tube worms that form numerous settlements at the bottom of water bodies. Some pipe makers take an active part in the biological treatment of water bodies. Aquatic oligochaetes are a favorite food for many fish.

Polychaete worms inhabit the seas, living both in shallow water and at considerable depths. Nereids lead a benthic lifestyle, moving along the bottom with the help of parapodia. Some can swim by rising to the surface of the water during the breeding season. Sandworms inhabit sandbars, burrowing deep into the ground, making passages with the help of highly developed body musculature.

2. Structure and biology of the earthworm.

An earthworm is a typical representative of low-bristle worms that live in the soil. These animals lay deep passages, partly pushing the soil apart with muscular movements of the body, partly swallowing. The digging way of life was reflected in their external structure. The head section is weakly expressed; there are no tentacles, ocelli, and parapodia. On numerous segments of the body there are small bristles, with the help of which the worm rests against the walls of the dug passage. Therefore, it is very difficult to pull it out of the mink. There are many glandular cells in the skin of an earthworm. Abundant secretions of mucus protect the skin from drying out, mechanical damage, facilitate movement in the ground and promote breathing. Earthworms breathe through their skin, which contains a dense network of capillaries. They feed on rotting plant debris, passing a mass of earth through the digestive tract. The digestive system is subdivided into the mouth, pharynx, thin esophagus, goiter, muscular stomach, long intestine with a longitudinal groove-like protrusion. All other organ systems have a structure typical of annelids. Earthworms are hermaphrodites. Cross fertilization. In sexually mature individuals, a glandular belt develops in the anterior third of the body, which, during the maturation of the eggs, secretes a thick mucus that forms a muff. With contractions of the body, the worm shifts it to the front end. During movement, eggs and spermatozoa are released into the muff. After the muff slips off the body of the worm, it turns into a cocoon with fertilized eggs. After some time, small worms develop from the eggs. Thus, development is direct, without transformation.

Earthworms play an important role in improving soil fertility. By swarming mink, they improve its structure, loosen it, enrich it with organic matter, promote aeration and moisture penetration, and stimulate nitrification processes.

3. General characteristics of roundworms.material from the site

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, a special way of 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 meet a lot of annelids that live on the surface of salty seas, as well as 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 they 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 is 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. The main distinguishing feature of 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 have a 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 reproduction, additional oral cavities may appear, 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 process of fertilization can be carried out both in the external environment and in the organism of creatures.

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 also marine species, and in Ceylon you can even find a terrestrial species of leeches.

Type annelids, or annelids, covers about 9,000 species of higher worms. This group of animals is of great importance for understanding the phylogenesis of higher invertebrates. Annelids are more organized than flatworms and roundworms. They live in sea and fresh waters, as well as in the soil. The type is divided into several classes. Let's get acquainted with the representative of the class of low-bristle (earthworm).

general characteristics

The body of the rings consists of segments. The segments of the body are outwardly identical. Each segment, except for the anterior one, which bears the oral opening, is provided with small bristles. These are the last remnants of the disappeared parapodia.

In annelids, worms have a well-developed skin-muscular sac, consisting of one layer of epithelium and two layers of muscles: the outer layer of the annular muscles and the inner layer formed by longitudinal muscle fibers.

Between the skin-muscular sac and the intestines is a secondary body cavity, or coelom, which is formed during embryogenesis inside the growing mesodermal sacs.

Morphologically, the secondary cavity differs from the primary cavity in the presence of an epithelial lining adjacent on one side to the body wall, and on the other, to the walls of the digestive tube. The lining sheets grow together above and below the intestines, and the mesentery formed from them is divided as a whole into the right and left sides. Transverse partitions divide the body cavities into chambers corresponding to the boundaries of the outer rings. The whole is filled with liquid.

Organ systems

The appearance of a secondary body cavity provides annelids with a higher level of vital processes than other worms. Coelomic fluid, washing the organs of the body, along with the circulatory system, supplies them with oxygen, and also helps to remove waste products and move phagocytes.

excretory

Each segment of the earthworm has a paired organ of the excretory system, consisting of a funnel and a convoluted tubule. Waste products from the body cavity enter the funnel. From the funnel comes a tubule, which enters the adjacent segment, forms several loops and opens outward with an excretory pore in the side wall of the body. Both the funnel and the tubule are provided with cilia that cause the movement of the secreted fluid. These excretory organs are called metanephridia.

Circulatory and respiratory systems

In most annelids, it is closed, consists of abdominal and dorsal vessels, which pass into each other at the anterior and posterior ends of the body. In each segment, an annular vessel connects the dorsal and abdominal vessels. Blood moves through the vessels due to the rhythmic contractions of the spinal and anterior annular vessels.

In the earthworm, gas exchange occurs through the skin rich in blood vessels, and some sea rings have gills.

digestive

It begins with the oral opening at the anterior end of the body and ends behind the anal. The intestine consists of three sections:

• Anterior (ectodermal);
• average ( endodermal, unlike other departments).
• posterior (ectodermal).

The foregut is often represented by several departments; oral cavity and muscular pharynx. The so-called salivary glands are located in the wall of the pharynx.

Some predatory annelid worms have cuticular "teeth" that serve to grasp prey. A layer of muscles appears in the intestinal wall, which ensures its independent peristalsis. The middle intestine passes into a short hindgut, ending in the anus.

Nervous system

Significantly more complicated than flatworms and roundworms. Around the pharynx there is a near-pharyngeal nerve ring, consisting of supra-esophageal and sub-esophageal nodes connected by bridges.

On the ventral side there are two nerve trunks, which have thickenings in each segment - ganglia, which are connected to each other by jumpers. In many types of rings, the right and left nerve trunks converge, resulting in the formation of the abdominal nerve chain.

Of the sense organs, annelids have antennae, eyes, balance organs, which are more often located on the head lobe.

Regeneration

An earthworm, like hydra and ciliary worms, is capable of regeneration, that is, restoring lost parts of the body. If the earthworm is cut into two parts, then the missing organs will be restored in each of them.

The reproductive system consists of female gonads (ovaries), which are a complex of germ cells surrounded by epithelium, and male gonads (testes), which lie inside the voluminous seminal sacs.

Reproduction of annelids: 1 - copulation, 2 - oviposition, 3 - fertilization of eggs, 4 - cocoon laying

Earthworms are hermaphrodites, but dioecious forms are also found among the rings. On the body of the earthworm there is a girdle that produces mucus, from which a cocoon is formed. Eggs are laid in it and their development takes place there.

Development

In an earthworm, development is direct, but in some rings, a larva develops from a fertilized egg, that is, development occurs with transformation.

Thus, annelids have a number of progressive features, which include the appearance of segmentation, coelom, circulatory and respiratory systems, as well as an increase in the organization of the excretory and nervous systems.

The value of annelids in nature

Many of the polychaete worms serve as the main food of fish, and therefore they are of great importance in the cycle of substances in nature.

For example, one of the species of annelids - nereis, living in the Sea of ​​\u200b\u200bAzov, serves as food for commercial fish. It was acclimatized by Soviet zoologists in the Caspian Sea, where it multiplied intensively and is now an important part of the diet of sturgeon fish. The polychaete worm, called "palolo" by the natives of Polynesia, is eaten by them.

Earthworms feed on plant debris in the soil, which is passed through the intestines, leaving heaps of excrement consisting of earth on the surface. In this way, they contribute to mixing and, consequently, loosening the soil, as well as enriching it with organic substances, improving the water and gas balance of the soil. Even C. Darwin noted the beneficial effect of annelids on soil fertility.

Type annelids. The structure of the earthworm: external structure (view from the ventral side), cross section, circulatory and digestive systems (front end of the worm)

Representatives of the type Annelids (Annelida) are the most highly organized worms. Mostly live freely in the seas, fresh water, soil. About 9 thousand species are known.

The body is elongated, divided into relatively uniform (homonomic) segments (metameres) , separated by internal partitions, has a head, sometimes back, blades. Almost every segment has paired organs (nerve ganglia, excretory organs, etc.). They are round in cross section. The segments have bristles.

The integument is represented by a skin-muscular sac. Covered with a cuticle that is secreted by the epidermis. There are many mucous glands in the skin. Two layers of muscles: the outer layer is circular and the inner one is longitudinal. Most polychaete worms have organs of movement - parapodia . These are mobile muscular outgrowths of the body (primitive limbs), which consist of the dorsal and abdominal branches. They can cling to nearby objects.

They are filled with liquid secondary abdominal cavity (in general) , while in each segment there are a pair of coelomic sacs (except for the head and posterior lobe), which are located between the intestine and the body wall. In general, it differs from the primary cavity in that it is lined with a special epithelium, which, on the one hand, is adjacent to the wall of the body, and on the other, to the walls of the digestive tube and separates the cavity fluid from tissues and organs. The lining sheets grow together above and below the intestine and form the mesentery, which divides the whole into the right and left parts. The fluid is in constant motion, due to which it carries nutrients, oxygen, carbon dioxide, and gland secretions. Forms a hydrostatic skeleton. The secondary cavity develops in the middle of the mesoderm and is lined with epithelium of mesodermal origin.

Appearance (a) and structural diagram (b) of an earthworm

Digestive system of annelids

Digestive system of annelids

The digestive system consists of three sections: anterior (ectodermal), middle (endodermal) and posterior (ectodermal). It is represented by the mouth, pharynx, esophagus (maybe goiter), muscular stomach, intestines, which ends with the anus. Muscle cells appear in the digestive tract. Predators have grasping appendages, sharp spikes or jaws in the throat.

excretory organs of annelids

excretory system of annelids

Excretory organs are represented by excretory tubes (metanephridia) , which begin with a funnel with cilia in the body cavity, continue with ducts and open outwards with an opening in the next segment. Each segment contains a pair of metanephridia.

The circulatory system of annelids

The circulatory system of annelids

The circulatory system is closed, consists of interconnected abdominal and spinal vessels, which in each segment are connected by annular ones. The blood flow is provided by contractions of the dorsal and several anterior annular vessels. Through the abdominal vessel, blood moves to the back of the body, through the dorsal - to the front. The blood of most annelids is red, sometimes green, depending on the type of respiratory pigments. May be colorless, transparent or blue. In leeches, the circulatory system is reduced. The function of the blood is performed by the coelomic fluid.

Respiration of annelids

Breathing is through the surface of the body. Marine animals have gills (outgrowths of the body wall with blood vessels on the dorsal branch of the parapodia).

Nervous system of annelids

Nervous system of annelids

The nervous system (of the ladder-nodular type) consists of the supraglottic and subpharyngeal nerve nodes, which are connected by the peripharyngeal nerve ring, and the abdominal nerve chain.

Sense organs of annelids

The sense organs are poorly developed. Sensory cells and nerve endings are found in the epidermis. Individual active species have developed eyes, organs of chemical sense (olfactory pits), organs of touch (antennae, bristles, etc.), organs of balance.

Reproductive system of annelids

Sexual, sometimes asexual reproduction (budding, fragmentation). Mostly the genitals are only in certain segments of the body, sometimes in all. The oligochaete worms are hermaphrodites, the polychaetes are predominantly dioecious. Sexual dimorphism is not expressed. Fertilization is both internal and external. In marine forms, indirect metamorphosis is developed (with a larva, incomplete metamorphosis), in freshwater and terrestrial forms, direct metamorphosis.

Some annelids are capable of regeneration.

Variety of annelids

Type annelids: class Polychaetes or Polychaetes, class Oligochetes or Oligochaetes and class Leeches

Class Polychaete worms or Polychaetes (Polychaeta)

Class Polychaete worms or Polychaeta (Polychaeta): Amphitrite, Sea mouse, Green Nereis, Peskozhil and Serpula

Some species have respiratory organs - gills (body outgrowths on parapodia). Others breathe through the entire surface of the body.

The circulatory system is closed. They have organs of vision, a pair of tentacles (organs of touch). Expressed regeneration.

Separate animals. Sexual dimorphism is not expressed. Development in polychaetes is indirect. A larva emerges from an egg (trochophore) covered with cilia. Some species can reproduce asexually.

Representatives: peskozhil, nereis, pacific palolo and etc.

Class Small-bristle worms or Oligochetes (Oligocheta)

Class Small-bristle worms or Oligochetes (Oligocheta): Ripistes, Stilaria, Elosoma and Hetogaster

About 5 thousand species are known. Distributed mainly in fresh water and soil. Sizes vary greatly. Parapodia are absent. The head lobe is weakly expressed. Hermaphrodites. Fertilization is internal. The development is direct. The eggs are laid in a cocoon. Asexual reproduction occurs by fragmentation. Representatives: pipe maker, earthworm and etc.

Earthworm (Lumbricus terrestris)

Earthworm: appearance, internal structure, cross section, worm movement pattern in the soil, reproduction, mating of two individuals, exchange of sexual products. Earthworms in summer and worms wintering in deep burrows

Dimensions reach 15 - 30 cm. Lives in the soil. Forms the soil, increases its fertility. It feeds on the remains of plants. The body is elongated, consists of segments, the number of which is 140 - 180. Near the 31st segment there is a special formation - a girdle. This is an organ that secretes a substance from which a cocoon is built, two individuals stick together during mating. Each segment has four pairs of setae (remnants of parapodia). The skin is covered with mucus secreted by the skin glands. The integuments are represented by a musculoskeletal sac, which consists of four layers: the mucous membrane of the cuticular lining, epithelial cells, the muscle layer, and a thin film. Musculature is represented by two layers of muscle fibers: annular septa. The body cavity is lined with epithelium, divided by partitions. It is filled with a liquid that performs the function of a hydrostatic skeleton.

Digestive system of an earthworm

The mouth opening at the anterior end of the body (cephalic lobe) leads to a thick-walled pharynx, which is located in the first 6 segments. The pharynx passes into a narrow esophagus, into which special limestone glands open, which neutralize humic acids (from the soil). Behind the esophagus is a goiter, which passes into the muscular stomach (the ectodermal section ends). Then the food passes into the middle and hind intestines, which end in the anus - in the posterior segment.

Excretory system of the earthworm

The excretory system is represented by metanephridia. The openings of the metanephridia are on the dorsal side. They open and then close. Not visible to the naked eye.

The circulatory system of the earthworm

The circulatory system is closed, consists of dorsal, abdominal and annular vessels. The six pairs of annular vessels that surround the esophagus and connect the dorsal and abdominal vessels are called hearts. Their walls, like the walls of the spinal vessel, pulsate. The blood is red, has hemoglobin in the plasma. It flows in the dorsal vessel to the head end, in the abdominal - in the opposite direction.

Respiratory system of an earthworm

There is no respiratory system. They breathe the entire surface of the body, so a large number of capillaries branch in it.

The nervous system of the earthworm

The nervous system is represented by the peripharyngeal nerve ring and the ventral nerve cord.

Sense organs of the earthworm

Sense organs: light-sensitive, tactile, chemical sensation cells. Light-sensitive cells are located on the head lobe.

The reproductive system of the earthworm

Reproduction is only sexual. On the ventral side, segment 14 has a pair of small, rounded female genital openings. On the 15th segment - in the form of transverse slits, a pair of male genital openings. Hermaphrodites. Gonads are located at the level of 9-15 segments. Fertilization is predominantly cross. During reproduction, two individuals exchange seminal fluid, which is stored in the seed receptacles. The secretions of the girdle form a kind of mucous sleeve. The worm crawls out of the clutch with its rear end forward. The edges of the muff stick together and form a cocoon. Eggs are laid in a cocoon (the egg and sperm are released from the seed receptacle). The cocoon lies in the ground. Young individuals develop from eggs. Development is direct. Such complex reproduction is due to the habitat, a small opportunity to meet a sexual partner.

Earthworms are capable of regeneration.

Leech class (Hirudinea)

Leech class (Hirudinea): False horse leech and Medicinal leech

Well developed digestive system. In bloodsuckers, the salivary glands produce a substance that prevents blood clotting. (hirudin) . The midgut forms lateral protrusions in which blood is stored. Metanephridia are located only in a few segments.

The function of the blood is performed by the coelomic fluid. The blood is colorless or red (has hemoglobin).

Hermaphrodites. Lose the ability to regenerate. Fertilization is internal. Direct development is typical.

Representatives: medicinal leech, horse leech and etc.

Meaning of annelids

Annelids are an important link in the food chain. Many species make up the food base of fish (for example, nereis). From the Sea of ​​Azov, Nereis was relocated to the Caspian Sea in order to maintain the food base of valuable industrial fish species.

Earthworms are soil formers, improve soil properties, enrich it with oxygen, organic matter, make it loose, facilitate moisture access, and mix soil layers. Through the digestive system, the earthworm passes as much soil as its body weighs (approximately 4 - 5 g). Abroad (in Japan, America, etc.), earthworm cultures are bred to obtain soil, various plants (vegetables, herbs, etc.) are grown on them. The importance of earthworms as soil formers was noted by C. Darwin.

Some species of annelids are eaten by humans (palolo), used as live bait for fishing (sandworms, etc.). The ringed worm is used as food for aquarium fish.

Medical leeches are used for hypertension (high blood pressure), to reduce blood clotting, resorption of blood clots. For this, leeches are caught or specially bred. Get the substance hirudin, which is used in medicine, the perfume industry.

Significance in medicine of annelids

TO annelids include the well-known leeches. They are of great importance in medicine. They are used in the treatment of hypertension, reducing blood clotting, with blood resorption. For this, leeches are specially grown and their enzyme hydrurin is extracted, which has a medicinal property.

The biological significance of annelids in the ecosystem

polychaete worms in the ocean are known for their biological significance. Worms are an important link in the trophic chains of an ecosystem. Also, representatives of polychaete worms take part in the purification of sea water, by processing organic substances in it.

Polychaetes used as food for fish.

• Freshwater representatives of oligochaetes are also fish food, more often used for aquarium fish. Tubifex from the class of oligochaetes act as a filter feeder for water bodies. They are also called ground beetles. Swallowing the soil, they directly digest organic matter, turning them into useful minerals that the soil needs so much.
• earthworms are also consumers in the ecosystem. Many animals feed on them: moles, shrews, frogs, many birds and some predatory beetles.

Remark 1

Some representatives of annelids are eaten by humans. For example, palolo.

The importance of worms in soil formation

As a result of digging the earth and laying passages, the worms increase the soil porosity, thus it becomes looser and increases in volume up to $30\%$. In loose soil, access to the deep layers of soil, water and atmospheric air is facilitated. This is necessary for the roots of plants and the activity of beneficial microorganisms that are in the soil. The constant mixing of the surface layers of the soil by the worms saturates it with foliage and other organic residues.

Worms change the chemical properties of the soil with their vital activity. So mixed soil with intestinal mucus of the worm contains a greater amount of calcium, magnesium, ammonia, nitrates and phosphoric acid. The glands of the esophagus contribute to the neutralization of harmful soil acids. The waste products of the worms dry out and break up into microporous lumps that are not washed away by water.

Thus, earthworms change and improve the composition, structure and fertility of the soil.

Remark 2

Enchytreids feed on organic residues and participate in soil formation along with earthworms.

Negative meaning of annelids

medical leech its medicinal properties can lead to complications. But not the leech itself, but the presence of Aeromonas hydrophila bacteria in its throat. These bacteria cause skeletal muscle necrosis and sepsis. And the enzyme hydrurin itself can cause too much bleeding in the patient.

Leeches in natural conditions can attack animals and humans, thereby causing great harm. After all, for a person who did not suffer from thrombosis, a leech becomes dangerous. So after a bite, the wound bleeds for a long time, and can be infected. Water leeches can penetrate the oral cavity, nose and urinary tract, where they stick to the mucous membrane.

• Synopsis of the lesson of the Russian language according to the federal state educational institution "spelling of the roots -rast-, -ros-"
• adp molecules. The structure of ATP. The value of ATP. Conducting a biological dictation "Organic compounds of living matter"
• Funny tests for girls What are you 15 years old test
• Meged "Your Child's Personality: Diagnosis, Abilities, Relationships"
• OAO RZD aptitude test train compiler
• Analytical reference of the preschool teacher
• Self-education plan for older preschoolers
• Modeling lesson: “Our Cosmodrome” Modeling in the preparatory group on the theme of astronauts
• Pedagogical competition "loyalty to the profession"
• How to write a self-education report: to help young teachers

• Now let's move on to the parts of the face
• Evgeny Tikhonov Words-healers
• 1001 ways to commit suicide
• The role of RNA in the process of realization of hereditary information
• Soviet aces pilots in the Korean War Losses of American aviation in Korea
• What monster killed Theseus. Greek mythology. theseus. Theseus and Pirithous in the Underworld of Hades
• Patterns of variability: modification variability Algorithm for solving problems
• Writing a book: How to regain inspiration and lost interest
• How to explain to a friend that you need free space The game “What relates to nature?
• SamArt chief architect: "We want to prepare the audience for the performance"