A type of annelids, or kilchaks. The importance of annelids in nature and human life Diversity and importance of annelids message

1. Where do annelids live?

Annelids live in the water column and at the bottom of sea and fresh water bodies, in the soil.

2. What is the reason for the differences in the external structure of annelids belonging to different classes?

The external structure of annelids of different classes differs significantly from each other, which is associated with the characteristics of their habitat and way of life. Thus, polychaete worms are predatory free-living animals of the water column or the bottom of coastal seas and oceans. Their body is divided into sections: the head with sensory organs, the trunk with movable blade-like outgrowths located on the sides with tufts of numerous bristles on them, and the anal lobe. Sense organs (eyes, antennae) allow them to navigate in space and see prey. With the help of blade-shaped outgrowths that perform the function of limbs, they actively swim in the water or move along the bottom in search of prey. They breathe through gills - skin projections on blade-shaped projections. Polychaete worms are dioecious animals, developing with a planktonic larval stage.

The earthworm (a representative of the class Oligochaetes) is an inhabitant of the soil environment. Its uniform, streamlined body is well adapted to movement in the soil. The few short bristles present on each segment are turned back, which prevents the worm's body from moving backward when moving in earthen burrows.

3, 4. What is the role of earthworms in soil formation processes? Who first studied and appreciated the importance of earthworms?

The role of earthworms in soil formation processes is enormous. With their digging activity, they contribute to loosening the soil and the penetration of air and moisture into it, which increases the activity of soil bacteria, and also facilitates the penetration of plant roots into the deep layers of the soil and strengthening it. In addition, earthworms plow the soil, passing it through their intestines and gradually bringing soil from deeper layers to the surface. By dragging vegetation into their burrows, they enrich the soil with organic matter, increasing its fertility. Charles Darwin was the first to reveal the enormous role of earthworms in soil formation processes.

5. What is the role of marine and freshwater annelids in the natural environment?

In seas and fresh water bodies, annelids are excellent food items for fish and other animals. They themselves, in turn, eat organic remains or living prey, thus processing a huge mass of organic matter. Thanks to their feeding activity, they actively participate in the cycle of substances in water bodies.

Subject: Variety of annelids. Classes Polychaetes, Oligochaetes and Leeches.

Educational – get acquainted with the diversity of species and classes of annelids; prove the adaptability of representatives of different classes to the environment; consider the various ecological groups of annelids;

Developmental – continue to develop the skills to substantiate, compare, analyze, and speak publicly.

Educational – fostering positive learning motivation

Lesson type: combined

Lesson type: mixed

Methods : verbal: conversation, explanation

Visual: demonstration of aids

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

During the classes:

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

Frontal survey:

1. What type are animals that have an elongated body divided into similar segments, a circulatory system, an abdominal nerve cord and a peripharyngeal nerve ring?

2. How many types flatworms known by now?

4. The phylum 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 annelids are evolutionarily more advanced animals than flatworms and roundworms. Their body is segmented, there is a skin-muscular sac with internal organs located in it. And it is in annelids that a closed-type circulatory system first appears. Class, how many species of annelids are known today? (9 thousand species).

The type Annelid worms unites several classes, of which three main ones are Polychaetes, Oligochaetes and Leeches.

Comparative characteristics of various classes of annelids.

Working with the textbook text on pages 129-131, tables and figures in the textbook, let's work together to fill out the following table (table header on the board)

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 for creating a creative project. The children are invited to use scrap materials to make one representative from each class and generalize their knowledge about the studied class of annelids.

The class is divided into groups of 4 people.

Distributed to groups (sheet A4 or katron 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 a brief description of annelids:

• there is a secondary body cavity (coelom);
• 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 suprapharyngeal node, connected by jumpers to the ventral nerve cord (usually double);
• excretory organs are located in each ring and are formed from ectoderm, they are equipped with cilia;

Structure

The elongated body of annelids seems to be composed of ring segments, the segments are separated by internal partitions; but they are not completely independent, since along the entire body there is a through intestine with oral and anal openings, an abdominal trunk of the nervous system and trunks of a closed circulatory system. These organ systems, piercing the septa one after another, stretch across the entire body of annelids. Each ring segment has a secondary body cavity (coelom). Most of the segments bear on the outside, on the right and on the left, two bundles of setae - organs of movement or attachment in tubes. In leeches, the bristles are lost for the second time.

Secondary body cavity (coelom)

The secondary body cavity (coelom) 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 ensure the movement of the animal. In addition, the muscles of the intestinal wall, alternately contracting, push food through.

The secondary body cavity performs the following functions:

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

Classification

Annelids are a numerous type of worms that have a more complex body structure compared to flat and protocavitary worms. It is divided into three classes: Polychaetes, Belts (including the subclasses Oligochaetes and Leeches), Mysostomidae.

Origin

According to a comparative study of the structure of worms, annelids evolved from primitive whole worms, similar to flat ciliated 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 other annelids. During the transition to freshwater and terrestrial lifestyles, oligochaete worms separated from them. Leeches evolved from oligochaete worms.

Questions about this material:

Initial level of knowledge:

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

Response plan:

General characteristics of annelids
Body structure of annelids
Reproduction and development of annelids
Classification of annelids, variety of species
Peculiarities of the structure and development of worms of the class Maloschitaceae using the example of an earthworm
Characteristics of the Polyscutaneous 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 creatures crawl along the bottom and burrow into the mud. 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). The body is divided into the head (head lobe), trunk and caudal (anal lobe) sections. 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 also participates 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: circular and longitudinal. The body may have muscular outgrowths - parapodia, which are organs of locomotion, as well as bristles.

Circulatory system first appeared during 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: the dorsal (carries blood from back to front) and the 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” - annular vessels of 7-13 segments of the body.

There is no respiratory system. Annelids are aerobes. Gas exchange occurs across the entire surface of the body. Some polychaetes have developed dermal gills - outgrowths of parapodia.

For the first time in the course of evolution, multicellular organisms appeared 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 formed by the peripharyngeal nerve ring, in which the paired suprapharyngeal (cerebral) ganglion is particularly developed, and by the abdominal nerve chain, consisting of pairwise contiguous abdominal nerve ganglia in each segment. From the “brain” ganglion and the nerve chain, nerves extend to the organs and skin.

Sense organs: eyes - organs of vision, palps, tentacles (antennae) and antennae - organs of touch and chemical sense are located on the head lobe of polychaetes. In oligochaetes, due to their underground lifestyle, the sense organs are poorly developed, but the skin contains light-sensitive cells, organs of touch and balance.

Reproduction and development

They reproduce sexually and asexually - by fragmentation (separation) of the body, thanks to high degree regeneration. Budding also occurs in polychaete worms.
Polychaetes are dioecious, while polychaetes and leeches are hermaphrodites. Fertilization is external; in hermaphrodites, it is cross fertilization, i.e. worms exchange seminal fluid. In freshwater and soil worms, development is direct, i.e. Young individuals 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, Oligochaetes, Leeches.

Oligochaetes mainly live in soil, but there are also freshwater forms. A typical representative living in the soil is the earthworm. It has an elongated, cylindrical body. Small forms are about 0.5 mm, the largest representative reaches almost 3 m (giant earthworm from Australia). Each segment has 8 setae, arranged in four pairs on the lateral sides of the segments. Clinging to uneven soil, the worm moves forward with the help of the muscles of the skin-muscular sac. 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 the muscular pharynx, esophagus, crop and gizzard.

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 themselves to each other with their ventral sides and exchange seminal fluid, which enters the seminal receptacles. After this, the worms disperse. In the anterior third of the body there is a belt that forms a mucous muff in which eggs are laid. As the coupling moves through the segments containing the spermatheca, the eggs are fertilized by sperm belonging to another individual. The muff is shed through the anterior end of the body, becomes compacted and turns into an egg cocoon, where young worms develop. Earthworms are characterized by a high ability to regenerate.

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

The importance of oligochaetes in soil formation. Even Charles Darwin noted their beneficial effect on soil fertility. By dragging the remains of plants into the burrows, they enrich it with humus. By making passages in the soil, they facilitate the penetration of air and water to the roots of plants and loosen the soil.

Polychaetes. 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 body and the posterior anal lobe. The head lobe is armed with appendages - tentacles and carries small eyes. The next segment contains a mouth with a pharynx, which can turn outward and often has chitinous jaws. The body segments have two-branched parapodia, armed with setae and often having gill projections.

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

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 unites about 400 species. Leeches have an elongated and dorso-ventrally flattened body. At the anterior end there is one oral sucker and at the rear end there is another sucker. They do not have parapodia or setae; they swim, bending their body in waves, or “walk” along the ground or leaves. The body of leeches is covered with a cuticle. Leeches are hermaphrodites and have direct development. They are used in medicine because... Thanks to their release of the protein hirudin, the development of blood clots that clog blood vessels is prevented.

Origin: Annelids evolved from primitive, flatworm-like, ciliated worms. From polychaetes came oligochaetes, and from them came leeches.

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

Questions for consolidation:

• Why did annelids get their name?
• Why are annelids also called secondary cavities?
• What structural features of annelids indicate their higher organization compared to flat and round worms? What organs and organ systems first appear in annelids?
• What is characteristic of the structure of each body segment?
• 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 guide for applicants to universities. Volume 1. - M.: Novaya Vol-na Publishing House LLC: ONICS Publishing House CJSC, 2000.
3. Kamensky, A. A. Biology. Reference manual / A. A. Kamensky, A. S. Maklakova, N. Yu. Sarycheva // Complete course of preparation for exams, tests, testing. - M.: JSC "ROSMEN-PRESS", 2005. - 399 p.
4. Konstantinov V.M., Babenko V.G., Kuchmenko V.S. Biology: Animals: Textbook for 7th grade students of secondary schools / Ed. V.M.Konstantinova, I.N. Ponoma-roar. – M.: Ventana-Graf, 2001.
5. Konstantinov, V. M. Biology: animals. Textbook for 7th grade 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 7th grade 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, OJSC 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.: Novaya Volna Publishing House LLC, 1998.
11. www.collegemicrob.narod.ru
12. www.deta-elis.prom.ua

1. The diversity of annelids in nature.

Oligochaetes include freshwater tubifex worms that form numerous settlements at the bottom of reservoirs. Some tubifex makers take an active part in the biological treatment of water bodies. Aquatic oligochaetes are the favorite food of many fish.

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

2. Structure and biology of the earthworm.

The earthworm is a typical representative of oligochaete worms that live in the soil. These animals make deep passages, partly pushing the soil apart with muscular movements of the body, and partly swallowing. The burrowing lifestyle was reflected in their external structure. The head section is weakly expressed; there are no tentacles, ocelli or 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 get him out of the hole. There are many glandular cells in the skin of an earthworm. Abundant mucus secretions protect the skin from drying out and 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 lot of earth through the digestive tract. The digestive system is divided into the mouth, pharynx, thin esophagus, crop, muscular stomach, long intestine with a longitudinal groove-shaped invagination. All other organ systems have a structure typical of annelids. Earthworms are hermaphrodites. Cross fertilization. In mature individuals, a glandular belt develops in the anterior third of the body, which, during the maturation of the eggs, secretes thick mucus that forms a muff. By contracting the body, the worm moves it to the anterior end. During movement, eggs and sperm are released into the muff. After the muff slides off the worm's body, 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 increasing soil fertility. By digging a mink, they improve its structure, loosen it, enrich it with organic substances, 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 - the type annelids. To learn a little about them, you need to consider their species components, 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 most numerous groups among animals, which, according to general data, contains about 18 thousand open views. Basically, these animals are presented in the form of non-skeletal vertebrates, which are capable of participating 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 ringlets primarily live? Thus, the area of ​​residence of ringlets is very wide - they include seas and land, as well as fresh water bodies. You can find a lot of annelids that live on the surface of salty seas, as well as oceans. Annelids live everywhere, they can be found at any depth of the World Ocean and can even be found at the bottom of the Mariana Trench. The population density of ocean worms is very high - up to 100,000 ringlets per square meter of bottom surface. Marine species are considered the best food for fish and play one of the main roles in the processes of the sea ecosystem.

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

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

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

What classes of ringworms live on earth?

About 200 years ago, Georges Cuvier did work in the field of animal classification and brought out only 6 rows of its 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.

It is possible to identify a small number of features in annelids, with the help of which they were separated into a whole group. The most important thing is the presence of coelom (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, ringlets have a developed nervous system, which includes the suprapharyngeal nerve ganglion, as well as the ventral nerve cord. The structure of the excretory system in ringlets is metanephridal.

According to experts, annelids were divided into 4 main classes. Main classes of rings:



What does the appearance of an annelid worm look like?

Annelids can be characterized as the most highly organized representatives of the group of worms. Their body lengths range from a few millimeters to 2.5 meters. The body of an individual can be clearly divided into three main parts: head, torso, and anal lobe. The main distinguishing feature of worms is that annelids do not have a clear division into sections, as occurs in higher species of animals.

In the area of ​​the individual's head there are various sensory organs. Most annelids have well-developed vision. Some individuals of 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, but also on the tail, body or tentacles.

Worms have particularly developed taste buds. Worms are able to sense various odors well with the help of developed olfactory cells, as well as ciliary fossae. 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 of fish.

What are the respiratory organs and the hematopoietic system of a creature?



Description of the digestive system and excretory organs of the ringlet

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

The oral cavity, whose second name is the buccal section, can be turned inside out without any problems. Behind this section you can find powerful jaws curved inward. This device is very necessary in order to quickly and deftly capture your prey.

After that comes the mesodeum - the midgut. The anatomy of this section is quite uniform throughout the entire body region. At the same time, the midgut narrows in certain places and expands again; this is where the process of digesting food takes place. The hindgut is quite short and represents the anus.

The excretory system of the worm consists of metanephridia, which are located in pairs in each segment of the ring. They help remove excess waste products from the cavity fluid.

Understanding the sense organs and nervous system of an animal

Each class of annelids has its own gangionary type system. It includes the peripharyngeal nerve ring, which is created by connecting the suprapharyngeal and subpharyngeal ganglia, as well as from pairs of the chain of abdominal ganglia that are present in each segment.

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

Reproduction process in annelids

Experts' description of the annelid worm 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 capable of splitting into several halves, each of which subsequently becomes a full-fledged creature.

With all this, the creature’s tail is considered independent and cannot in any way grow a new head on itself. In some situations, a second head grows independently 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 body area, at which time the posterior ends bud from each segment. During reproduction, additional oral cavities may appear, which over time will become separate, full-fledged individuals.

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

For example, in marine worms, which reproduce only sexually, fertilization is considered external. Individuals of different sexes usually throw their reproductive cells to the surface of the water, where the process of fusion of eggs and sperm occurs. From fertilized eggs, larvae emerge, which are completely different in appearance from adults. Freshwater and terrestrial ringworms do not have a larval stage; they are immediately born with exactly the same structure as that of adult creatures.

Class polychaetes



Curious, sessile worms, serpulids, which live in spiral or twisted tubes of the Izvetian type. Serpulids are accustomed to only sticking out their heads 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 distribution and habitat area of ​​annelids from the class of leeches is very diverse. Leeches can be found in larger numbers 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.

Introduction

More farmers Ancient Egypt They saw earthworms as a guarantee of future harvests. Aristotle called them the intestines of the earth. And this is true: by passing earth and plant debris through their intestines, worms enrich the soil. In the 50s of our century, the question arose about breeding worms specifically as producers of very valuable, environmentally friendly fertilizer. The concept of “Vermiculture” arose - the culture of breeding worms. The red Californian 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 on 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 angles. Another amazing ability is that most worms use their "photon installations" to disorient their 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 tear its body, the tail section of the worm flashes brightly, attracting the attention of the “aggressor”. He grabs the luminous part of the body, and the second (head) disappears in the darkness. Subsequently, the worm's tail grows back. It turns out that annelids, long before lizards, were the inventors of a clever trick with a discarded tail.

The object of study of this course work is a type of annelid. A brief description of this type of worm and the peculiarities of the organization of annelids is given. In the practical part of the work, such classes of this type were considered as the leech class, the polychaete class, the oligochaete class, and the echiurida class. The systems of these worms and their features are described.

The first parts of the work are given general information about the type of annelids. The practical part of the work contains information about some classes of worms of this type.

1. General characteristics of the type of annelids

Annelids are a large group of animals, including about 12 thousand species that live mainly in the seas, as well as 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 digested without residue. At the same time, they all actively participate in the destruction of organic matter in biocenoses, contributing to the biogenic cycle. Marine forms are especially diverse, which are found at different depths down to the extreme (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 population density: 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/

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

2. There is a skin-muscular sac consisting of skin epithelium, circular 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 body functions are carried out (transport, excretory, sexual, musculoskeletal)./2/

4. The intestine consists of three functionally different sections: the foregut, midgut 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 ringlets have a closed circulatory system. This means that blood flows only through 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 generally open funnels, from which the excretory canals continue into the next segment and open there outwards with paired openings. Metanephridia are not only excretory organs, but also the regulation of water balance in the body. In the metanephridia channels, the excretory products are thickened (ammonia is converted into uric acid), and water is absorbed back into the coelomic fluid. This saves moisture in the body and maintains a certain water-salt regime as a whole. Saving moisture is especially necessary for ground and soil rings. /1/

7. The nervous system consists of paired dorsal ganglia and a ventral nerve cord with metamerically repeating 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 brain structure distinguishes ringworms from roundworms. /1/

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

9. Development often occurs with metamorphosis. A typical larva of sea ringers 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 structure, the appearance of a circulatory system, an excretory system such as metanephridia, a more highly organized nervous system and sensory organs. This is how ringworms differ from lower flat and round worms. /1/

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

The type of annelids is divided into classes:

Class Primary ringlets (Archiannelida),

Class Polychaetes (Polychaeta),

Class Oligochaeta,

Class Leeches (Hirudinea),

Class Echiurida,

Class Sipunculida.

1.1 Characteristics and variety of ringlets

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, in which he united all creatures whose body is divided into segments: insects, crayfish, spiders, woodlice, earthworms and leeches. modern science has more extensive information about leeches and earthworms, and therefore these worms are classified as a special type - ringworms. /1/

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

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

1 Primary rings

2 Polychaetes

3 Oligochaetes

5 Echiurides

6 Sipunculidae

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. These are predominantly free-living forms. The body of the ringlets is divided into three parts: the head, the body, consisting of rings, and the anal lobe. Animals that are lower in their organization do not have such a clear division of the body into sections. /1/

The ringlet's head is equipped with various sensory organs. Many ringlets have well-developed eyes. Some species have particularly acute vision, and their lens is capable of accommodation. True, eyes can be located not only on the head, but also on the tentacles, on the body and on the tail. Ringworms also have developed senses of taste. On the head and tentacles, many of them have special olfactory cells and ciliary fossae, which perceive various odors and the actions of many chemical irritants. The ringed birds have well-developed hearing organs, arranged like locators. Recently, the sea ringed echiruids have discovered hearing organs that are very similar to the lateral line organs of fish. With the help of these organs, the animal subtly distinguishes the slightest rustles and sounds, which are heard much better than in the air. /1/

1.3 Internal structure of rings

Digestive system consists of three sections: foregut, midgut and hindgut. The foregut is highly differentiated into a number of organs: mouth, pharynx, esophagus, crop, stomach. /1/

Circulatory system closed. It consists of large longitudinal vessels - dorsal and abdominal, connected in each segment by annular vessels. The movement of blood is carried out due to the pumping activity of the contractile areas of the spinal cord, and less commonly of the annular vessels. Blood plasma contains respiratory pigments similar to hemoglobin, thanks to which ringworms have populated habitats with very different oxygen content. Many annelids have red blood, like humans. It is colored this way, naturally, due to the presence of iron. But at the same time, iron is part of a completely different pigment, not similar to hemoglobin - hemerythrin. It is capable of capturing 5 times more oxygen than hemoglobin. The choice of pigment is determined by the lifestyle characteristics of such worms. These are bottom-dwelling creatures that spend most of their time in the depth of the soil, where they experience an acute lack of oxygen. /1/

Respiratory system in polychaete worms, the gills are thin-walled, leaf-shaped, feathery or bushy outer outgrowths of part of the dorsal lobes of the parapodium, penetrated by blood vessels. Oligochaete worms breathe over the entire surface of the body. /1/

Excretory organs- metanephridia located in pairs in each segment, removing the final waste products from the cavity fluid. The funnel of metanephridium 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 suprapharyngeal and subpharyngeal 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 ringlets have well-developed sensory 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 rear end of the body, on the sides (including on each segment) and even on the tail. Marine polychaetes not only react sensitively to light, but are also capable of independently emitting it. /2/

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

1.4 Peculiarities of reproduction of annelids

Annelids can reproduce either sexually or asexually. The first is most typical of aquatic species, especially some marine polychaetes. Asexual reproduction comes down to either dividing the body into parts or budding. When dividing, the worm's body splits 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 capable of growing a new head. Sometimes this head grows back long before the worm has split in half. In the middle of the body of such a ringlet, preparing to prolong the race, there is a second head. After some time, the two-headed creature disintegrates to give life to two new worms./24/

The cocoon of the medicinal leech easily feeds its numerous cubs until they have their heads./24/

Fertilization in marine worms that reproduce sexually is external. Females and males release reproductive cells into the water, where sperm merge with eggs. Subsequently, the eggs hatch into larvae - trochophores, which are not similar to adult individuals. Terrestrial and freshwater ringers, including leeches, have direct development, with young individuals copying adults almost exactly. Young leeches develop from cocoons containing eggs./24/

Glow plays an important role in the reproduction of annelids. The glow of the worms is ensured 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 towards the release of light particles - photons - by excited atoms. Luciferin is contained in worms in granules that float in the liquid cellular substance, where they are oxidized. Therefore, it seems as if the body tissues of polychaetes glow./24/

Worms are endowed with a relatively efficient oxidation mechanism, the efficiency of which is from 10 to 20 percent and perhaps even more. This means that marine polychaetes have learned to convert over 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/

Biological significance glow may vary. There are cases when invertebrates use their illumination for the purpose of communicating with relatives, primarily with representatives of the opposite sex. Once a year, many tropical worms leave their bottom shelters and swim to the surface of the ocean to swarm. Here females meet males./24/

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

2. Classification of annelids

In total, the phylum includes 9,000 species of animals, which is 1/4 of the total species diversity of worms (scolecids). Zoological scientists distinguish 4 classes in the phylum of annelids, in addition to leeches: archiannelids, or primary annelids, oligochaetes, polychaetes, and echiurids. Oligochaetes and polychaetes are often also called oligochaete and polychaete worms.

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

During evolutionary development, species of flatworms appeared that increased the length of their body, growing segment by segment. These creatures simply added another muscle ring. But then the changes swept through the entire internal structure of the worms. Their organs also began to grow in parts. As a result, animals appeared with external and internal divisions of the body, in which almost each new segment in general copies the previous one. This repetition of homogeneous body segments is called metamerism in science.

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

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

Typically called polymers chemical substances, related to polyethylene. In biology, the same name is given to organs and structures that are repeated many times in the body. Usually these are the organs of the reproductive system. Pseudometamerism and polymer formations are typical for a number of groups of lower worms: cestodes, turbellarians, nemerteans. In scolecids, body cavities are formed, which is why similar segments arise.

Further division of the animal body turned out to be possible thanks to the complication of the nervous system and, mainly, the appearance of the circulatory system. It became possible to separate the branches of nerves (with the formation of neurosomites) and blood vessels (with the formation of angiosomites).

The third and, perhaps, the most significant 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, the separation of areas of longitudinal and circular muscles occurred with the formation of myosomites, separated by transverse partitions-dissepipements.

The growth of the muscular sac and the segmentation accompanying this phenomenon were a single evolutionary breakthrough of ringworms, which allowed them to occupy the most important ecological niches of the sea, fresh water and soil from those only occupied by worms. The Skolecids have struggled throughout their history for reliable defense and speed. Only the descendants of primitive worms were able to solve this problem, which explains the progress of these groups. Snails have “invented” reliable protection for themselves in the form of shells. The squids created a powerful water-jet “engine” from their muscular sac.

Annelids acquired dense integuments, cut into lobules - segments corresponding to internal metamerism. Segmentation allowed these invertebrates to freely bend their bodies to move in waves, while developing significant 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 ancient rings, but our body does not consist of segments. Their number in vertebrates sharply decreased, which is why so-called somites were formed instead of somites. departments.

2.1 Class polychaetes ( Polychaeta )

The class of polychaetes differs from other ringlets by a well-separated head section 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 body 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 body segments. The mouth is located ventrally on the perestomium. Many polychaetes have eyes and sensory appendages on their heads. Thus, in a Nereid, on the prostomium of the head there are two pairs of ocelli, tentacles - tentacles and two-segmented palps, on the perestomium there is a mouth below, and on the sides there are several pairs of antennae. The body segments have paired lateral projections 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 parapodium there is a dorsal barbel on the dorsal side, and a ventral barbel on the ventral side. These are the sensory organs of polychaetes. Often the dorsal barbel in some species is transformed into feathery gills. Parapodia are armed with tufts of bristles consisting of an organic substance close to chitin. Among the setae there are several large setae-acicules, to which muscles are attached from the inside that move the parapodia and tuft of setae. The limbs of polychaetes make synchronous movements like oars. In some species leading a burrowing or attached lifestyle, parapodia are reduced.

Skin-muscle bag . The body of polychaetes is covered with a single-layer dermal epithelium, which secretes a thin cuticle onto the surface. In some species, certain parts of the body may have ciliated epithelium (a longitudinal ventral stripe or ciliated bands around the segments). Glandular epithelial cells in sessile polychaetes can secrete a protective horny tube, often impregnated with lime.

Under the skin lies circular and longitudinal muscles. The longitudinal muscles form four longitudinal ribbons: two on the dorsal side of the body and two on the abdominal side. There may be more longitudinal strips. On the sides there are bundles of fan-shaped muscles that move the blades of the parapodia. The structure of the skin-muscle sac varies greatly depending on lifestyle. The inhabitants of the ground surface have the most complex structure of the skin-muscle sac, close to that described above. This group of worms crawls along the surface of the substrate using serpentine body bending and parapodia movements. The inhabitants of calcareous or chitinous tubes 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 retreat into the depths of the tube, which allows them to escape from attacks by predators, mainly fish. In pelagic polychaetes, the muscles are poorly developed, since they are passively transported by ocean currents.

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

The whole performs several functions: musculoskeletal, transport, excretory, sexual and homeostatic. Cavity fluid maintains body turgor. When the circular muscles contract, 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 method of movement, in which the cavity fluid, when muscles contract under pressure, is driven to the front end of the body, providing energetic forward movement. Overall, nutrients are transported from the intestines and dissimilation products from various organs and tissues. The organs for excreting metanephridia by funnels open as a whole and ensure the removal of metabolic products and excess water. In the whole, there are mechanisms to maintain the constancy of the biochemical composition of the fluid and water balance. In this favorable environment, not within the walls of the coelomic sacs, gonads are formed, germ cells mature, and in some species even juveniles develop. Derivatives of the coelom - coelomoducts - serve to remove sexual 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 the oral opening located on the peristomium on the ventral side. The oral cavity passes into the muscular pharynx, which serves to capture food objects. In many species of polychaetes, the pharynx can turn outward, like the finger of a glove. In predators, the pharynx consists of several layers of circular and longitudinal muscles, is armed with strong chitinous jaws and rows of small chitinous plates or spines that can firmly hold, wound and crush captured prey. In herbivorous and detritivorous forms, as well as in sestivorous polychaetes, the pharynx is soft, mobile, adapted for swallowing liquid food. Following the pharynx is the esophagus, into which the ducts of the salivary glands open, also of ectodermal origin. Some species have a small stomach.

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

The hind intestine is of ectodermal origin and can perform the function of regulating water balance in the body, since there water is partially absorbed back into the coelom cavity. Fecal matter forms in the hindgut. The anal opening usually opens on the dorsal side of the anal blade.

Respiratory system. Polychaetes mainly have cutaneous respiration. But a number of species have dorsal cutaneous gills formed from parapodial antennae or head appendages. 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 ventral trunks, connected by annular vessels, as well as peripheral vessels. Blood movement is carried out as follows. Through the dorsal, largest and most 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 in the posterior part of the body, vice versa. Arteries extend from the annular vessels to parapodia, gills and other organs, where a capillary network is formed, from which blood collects into venous vessels that flow into the abdominal bloodstream. In polychaetes, the blood is often red due to the presence of the respiratory pigment hemoglobin dissolved in the blood. Longitudinal vessels are suspended on the mesentery (mesentery), annular vessels pass inside the dissepiments. Some primitive polychaetes (Phyllodoce) lack a 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 phylum annelids. Each segment contains a pair of metanephridia. Each metanephridia consists of a funnel, lined inside with cilia and open as a whole. The movement of the cilia drives solid and liquid metabolic products into the nephridium. A canal extends from the funnel of the nephridium, which penetrates the septum between the segments and in another segment opens outwards with an excretory opening. In the convoluted channels, ammonia is converted into high-molecular compounds, and water is absorbed as a whole. U different types Polychaetes' excretory organs can be of different origins. 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. In some representatives, complex organs are formed - nephromyxia - the result of the fusion of protonephridia or metanephridia with the genital funnels - coelomoducts of mesodermal origin. An additional function can be performed by chloragogenic cells of the coelomic epithelium. These are peculiar storage buds in which grains of excreta are deposited: guanine, uric acid salts. Subsequently, chloragogenic cells die and are removed from the coelom through nephridia, and new ones are formed to replace them.

Nervous system. The paired suprapharyngeal ganglia form the brain, in which three divisions are distinguished: proto-, meso- and deutocerebrum. The brain innervates the sense organs on the head. Periopharyngeal nerve cords extend from the brain - connectives to the abdominal nerve cord, which consists of paired ganglia, repeating in segments. Each segment has one pair of ganglia. The 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 the paired ganglia merge, a nerve chain is formed. In some species, the nervous system becomes more complex due to the fusion of ganglia from several segments.

Sense organs most developed in motile 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 polychaetes living in tubes have numerous eyes on the feathery gills of the head. In addition, they have developed organs of smell and touch in the form of special sensory cells located on the appendages of the head and parapodia. Some species have balance organs - statocysts.

Reproductive system. Most polychaete worms are dioecious. Their gonads develop in all segments of the body or only in some of them. The gonads are of mesodermal origin and form on the wall of the coelom. The germ cells from the gonads enter the whole, where their final maturation occurs. Some polychaetes do not have reproductive ducts and the germ cells enter the water through breaks in the body wall, where fertilization occurs. In this case, the parent generation dies. A number of species have genital funnels with short canals - coelomoducts (of mesodermal origin), through which the reproductive products are excreted out into the water. In some cases, germ cells are removed from the coelom through nephromyxia, which simultaneously perform the function of the reproductive and excretory ducts.

Reproduction Polychaetes can be sexual or asexual. In some cases, alternation of these two types of reproduction (metagenesis) is observed. Asexual reproduction usually occurs by transverse division of the worm's body into parts (strobilation) or budding. This combing is accompanied by the regeneration of missing body parts. Sexual reproduction is often associated with the phenomenon of epitoky. Epitoky is a sharp morphophysiological restructuring of the worm's body with a change in body shape during the maturation of reproductive products: segments become wide, brightly colored, with swimming parapodia. In worms that develop without epitocy, males and females do not change their shape and reproduce in benthic conditions. Species with epitocy may have several variants life cycle. One of them is observed in Nereids, the other in Palolos. Thus, in Nereisvirens, males and females become epitocous and float to the surface of the sea to reproduce, 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 atokny individual, and the posterior end of the body is transformed into an epitokny tail part filled with sexual products. The back parts of the worms break off and float to the surface of the ocean. Here the reproductive products are released into the water and fertilization occurs. Epitocene individuals of the entire population emerge to reproduce simultaneously, 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 massive appearance of breeding polychaetes in the surface layers of water is usually associated with the phases of the Moon. Thus, 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 periods of reproduction of palolos, and fishermen en masse catch palolos stuffed with “caviar” and use them for food. At the same time, fish, seagulls, and sea ducks feast on worms.

Development. The fertilized egg undergoes uneven, spiral crushing. This means that as a result of fragmentation, quartets of large and small blastomeres are formed: micromeres and macromeres. In this case, the axes of the cell cleavage spindles are arranged in a spiral. The inclination of the spindles changes to the opposite with each division. Thanks to this, the crushing figure has a strictly symmetrical shape. Egg crushing in polychaetes is determinate. Already at the stage of four blastomeres, determination is expressed. Quartets of micromeres give derivatives of ectoderm, and quartets of macromeres give derivatives of endoderm and mesoderm. The first mobile stage is the blastula - a single-layer larva with cilia. The blastula macromeres at the vegetative pole plunge into the embryo and the gastrula is formed. At the vegetative pole, the primary mouth of the animal is formed - the blastopore, and at the animal pole a cluster of nerve cells and a ciliary crest - the parietal sultan of cilia - is formed. Next, the 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 of the trochophore shifts from the vegetative pole closer to the animal along the ventral side, which leads to the formation of bilateral symmetry. The anal opening breaks through later at the vegetative pole, and the intestines become through.

2.2 Class oligochaetes

Oligochaete worms are inhabitants of fresh waters and soil, found occasionally in the seas. More than 5,000 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 girdle in the anterior third of the body in mature individuals. Their head section is not expressed. The head lobe is usually devoid of eyes and appendages. There are also no appendages on the anal lobe (pygidium). On the sides of the body there are setae, usually four pairs of tufts on each segment. These are the rudiments of parapodia. This simplification of the external structure is associated with adaptations to the burrowing lifestyle. Oligochaete worms show convergent similarities with burrowing polychaetes. This confirms the reason for their morphoecological similarity in connection with the development of a similar burrowing lifestyle. The most familiar oligochaetes to us are soil-dwelling earthworms. Their body reaches several centimeters, the largest among them are up to 3 m (in Australia). Small whitish annelids – enchytraeids (5 – 10 mm) are also common in the soil. Earthworms and enchytraeids feed on plant debris in the soil and play an important role in soil formation. In fresh water bodies you can often see oligochaetes with long bristles or living in vertical tubes and forming dense settlements on the bottom. They feed on suspended organic residues and are useful filter feeders that play a significant role in water purification.

General morphophysiological characteristics . Body length varies from a few millimeters to 3 m. The body is long, worm-shaped, segmented. The number of segments ranges 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 blade. Oligochaetes move by contracting the muscles of the body. When digging, the worm uses the front end of its body to push the soil apart, supported by numerous bristles. The bristles rest against the walls of the dug passage, so it is difficult to pull the earthworm out of the hole.

Skin-muscle bag. The body is covered with a layer of skin epithelium, often with a large number of glandular cells. The skin produces a thin cuticle. The abundant secretion of mucus protects the skin of earthworms from mechanical damage and drying out. Under the skin, like polychaetes, they have circular and longitudinal muscles, lined with coelomic epithelium on the inside.

Digestive system. The intestines run the entire length of the body. In the anterior intestine of an earthworm, the oral cavity, muscular pharynx, relatively narrow esophagus, crop and stomach are separated. In the walls of the esophagus there are three pairs of calcareous glands, the secretions of which neutralize humic acids in the food of earthworms. From the stomach, food enters the midgut, where nutrients are absorbed. Undigested food debris and mineral soil particles enter the short hindgut and are removed through the anus to the outside. In the midgut, there is an internal longitudinal fold located dorsally - the typhlosol, which hangs into the intestinal lumen and increases the absorptive 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 oligochaete worms the ring vessels in the esophagus pulsate and are called “ring hearts”. The blood contains a respiratory pigment - hemoglobin, which is dissolved in the blood plasma, unlike vertebrates, in which hemoglobin is found in red blood cells. In oligochaetes, the circulatory system performs the transport function of transporting nutrients, oxygen and metabolic products.

Excretory system represented by metanephridia. The ability of metanephridia to save moisture in the body by reabsorbing water ensures the adaptability of oligochaetes to life on land. Solid excreta accumulates in the chloragogenic cells of the coelomic epithelium. Partially these cells, filled with excreta, are removed through the funnels of the nephridia or through special pores in the body wall.

Nervous system represented, as in all ringlets, by a pair of suprapharyngeal ganglia (brain) and a ventral nerve cord.

Sense organs in polychaete worms they are less developed than in most polychaetes, due to their burrowing lifestyle. Eyes are usually absent. The skin of oligochaetes contains numerous sensory cells: photosensitive, tactile, etc. earthworms are sensitive to factors of light, humidity and temperature. This explains their vertical migrations in the soil during the day and over the seasons.

Reproductive system Oligochaete hermaphroditic. Hermaphrodite individuals of oligochaetes are of the same type, in contrast to sexually mature individuals of polychaetes with sexual dimorphism. Hermaphroditism in the animal world is an adaptation to increase fertility, since all 100% of individuals in a population can lay eggs. Let's look at the structure of the reproductive system using the example of an earthworm. The gonads of oligochaetes are concentrated in the anterior segments of the body. The testes (two pairs) are located in the 10th and 11th body segments and are covered by three pairs of seminal sacs. The sperm sacs accumulate in the sperm that flows from the testes. This is where sperm maturation occurs. Sperm enters 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 body segment. The female reproductive system is represented by a pair of ovaries located on the 13th segment, a pair of oviducts with funnels that open with genital openings on the 14th segment. In the 13th segment, dissipations form egg sacs covering the ovaries and oviduct funnels. The female reproductive system also includes special skin invaginations on the 9th and 10th segments - two pairs of spermatic receptacles with openings on the ventral side of the body.

Reproduction and development. In sexually mature earthworms, a glandular girdle develops on segments 32–37. During the breeding season, at first all individuals become males, as it were, since only their testes are developed. The worms are connected with their head ends facing each other, with the girdle of each worm located at the level of the spermatheca of the other worm. The girdle secretes a mucous “coupler” that connects the two worms. Thus, mating worms are united by two bands of mucous couplings in the area of ​​their girdles. Sperm is released from the male openings of both worms, which enters the spermatheca of the other individual through special grooves on the ventral side of the body. After exchanging male reproductive products, the worms disperse. After some time, the worms’ ovaries mature and all individuals become, as it were, females. The “muff” 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 coupling, and at the level of the 9th – 10th segments, “foreign” seminal fluid is sprayed out. This is how cross-fertilization occurs. Then the muff slides off the head end of the body and closes. An egg cocoon with developing eggs is formed. 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 similar to 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. Embryonic development The embryo of the oligochaete proceeds, as in most polychaetes, according to the spiral type of cleavage and with the teloblastic anlage of the mesoderm.

Asexual reproduction is known in some families of freshwater oligochaetes. In this case, the worm is divided transversely into several fragments, from which whole individuals then develop, or by differentiating the worm into a chain of short daughter individuals. Subsequently, this chain breaks up. In earthworms, asexual reproduction is extremely rarely observed, but the ability to regenerate is well expressed. A 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, 3–5 in number, correspond to one body segment; there are 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 behind the other.

Poroshitsa on the dorsal side above the posterior sucker.

Nervous system consists of a two-lobed suprapharyngeal ganglion or brain, connected to it by short commissures under the pharyngeal node (derived from several fused 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 sensory organs and pharynx, and from each node of the abdominal chain there are 2 pairs of nerves that innervate the corresponding body segments; 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 either with three chitinous serrated plates (jaw leeches - Gnathobdellidae), which serves to cut through the skin when sucking blood in animals, or with a proboscis capable of protruding (in proboscis leeches - Rhynchobdellidae); Numerous salivary glands open into the oral cavity, sometimes secreting a poisonous secretion; 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 consists partly of real, pulsating vessels, partly of cavities - sinuses, representing the remainder of the cavity (secondary) of the body and interconnected by ring canals; The blood of proboscis leeches is colorless, while that of jawed leeches is red, due to hemoglobin dissolved in the lymph.

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

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

Reproductive system and reproduction Leeches are hermaphrodites: Most male genital organs consist of vesicles (testes), a pair in 6 to 12 middle segments of the body, connected on each side of the body by a common excretory duct; these ducts open outward 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 sac-like ovaries. Two individuals copulate, each simultaneously playing the role of a female and a male. During the laying of eggs, leeches secrete, through the glands located in the genital area, thick mucus that surrounds the middle part of the leech's body in the form of a sheath; eggs are laid in this sheath, after which the leech crawls out of it, and the edges of its holes come together, stick together and form like a capsule with eggs inside, usually attached to the lower surface of a seaweed sheet; The embryos, leaving the egg shell, sometimes (Clepsine) remain for some time on the underside of the mother’s body.

Variety of leeches. All leeches are predators, feeding on the blood of most warm-blooded animals, or mollusks, worms and the like; they live mainly in fresh waters or in wet grass; but there are also marine forms (Pontobdella), just as there are terrestrial forms (in Ceylon). Hirudo medicinalis - a medical leech up to 10 cm in length and 2 cm in width, black-brown, black-green, with a longitudinal patterned reddish pattern on the back; the belly is light gray, with 5 pairs of eyes on the 3rd, 5th and 8th rings and strong jaws; distributed in the swamps of the south. Europe, southern Russia and the Caucasus. In Mexico, Haementaria officinalis is used medicinally; another species, leech mexicana, is poisonous; In tropical Asia, Hirudo ceylonica and other related species living in humid forests and grass are common, causing painful, bleeding bites to humans and animals. Aulostomum gulo - horse leech, black-green in color, with a lighter underside, has weaker mouth armament and is 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 it is the original Archaeobdella Esmonti, pink in color, without a posterior sucker; lives on the silt bottom in the Caspian and Azov seas. Clepsiue tesselata - Tatar leech, with a broad oval body, greenish-brown 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; Acanthobdella peledina, found in Onezhskomozero, occupies a transitional place to the order of chaetopoda Oligochaeta worms.

2.4 Class Echiurida

External structure of echiurids. Marine, bottom, worm-like animals burrowing in the ground with an unsegmented body, an unsegmented coelom, possessing, like annelids, a typical larva - a trochophore. The absence of metamerism represents the primary feature of the echiurid organization. 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 there is a mouth, and at the rear end of the body there is powder.

The proboscis is sometimes forked 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 corollas of small setae, reminiscent of the setae of Polychaeta.

The body is covered with a single-layer epithelium, secreting a cuticle from its surface. Under the cuticle there is a skin-muscular sac. The peritoneal epithelium limits a large continuous body cavity (coelom).

Digestive system of echiurids forms a long convoluted canal consisting of the foregut, midgut and hindgut, opening at the posterior end with the anus. Thanks to its tortuous course, the length of the intestine is sometimes 10 times the length of the body. A pair of protrusions flow into the hindgut: the 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 are used for breathing and excretion.

Circulatory system of echiurides consists of a dorsal longitudinal vessel passing over the anterior part of the intestine, which continues into the proboscis. This vessel bifurcates in front and gives rise to two lateral proboscis vessels. The latter, upon exiting 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 through two transverse vessels covering the intestine. Blood is colorless and contains colorless white blood cells.

Nervous system of echiurids rather poorly developed. The central nervous system consists of an abdominal trunk, which bifurcates at the anterior end of the body, goes around the intestine and forms a peripharyngeal nerve ring. So, the general plan of the structure of the nervous system is reminiscent of Polychaeta, but the nervous trunk of Echiurida is strewn with nerve cells throughout its entire length, and even the peripharyngeal ring is devoid of ganglion thickenings.

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

Excretory system. Nephridia echiurids are represented by three types of organs. At the trochophore larvae stage, zhiurids possess a pair of protonephridia, which are reduced during metamorphosis (as in the class Polychaeta). In adult animals, primarily the anal sacs with their funnels, considered by some zoologists as metanephridia, are used for secretion. In addition to the sacs, adult echiurids have more or less typical nephromyxia, generally open with ciliated funnels. However, their main purpose is the removal of reproductive products. Nephromyxia lie in the anterior part of the body and open outward on the ventral side. Their number varies from 1 to 4 pairs, but in some forms there are significantly more of them. For example, in the large Ikeda tenioides there are from 100 to 200 nephridia on each side of the abdominal 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 lifestyle of males is original. First they crawl along the surface of the female's proboscis; later they penetrate into the foregut, then into the nephridia of the female and live there for a long time, waiting for the ripe eggs to pass through the nephridia, which are fertilized, releasing the viper.

Echiurid development At first it resembles that of a polychaete. Spiral and determinative cleavage 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 greatly and merging together, form a common whole. The body of the larva behind the prototroch grows uniformly in length. The larva swims freely in plankton and only after metamorphosis settles to the bottom.

2.5 Practical significance of all annelids in nature and in human life

Freshwater oligochaetes play a significant role in fish nutrition. For example, tubifex worms, which often form dense settlements at the bottom of reservoirs, are a favorite food for many fish. They are used to feed aquarium fish. Tubifex worms are ground eaters that play a significant role in the biological purification of water bodies. They are red in color because their blood contains hemoglobin. The presence of hemoglobin ensures their normal breathing even in polluted water bodies with a low oxygen content in the water. By ingesting soil, they digest organic matter and promote their mineralization.

Small whitish annelids of the enchytraeid family, less than 10 mm long, can live in fresh water bodies, but are more often found in soil. Soil enchytraeids include about 400 species. Their density in the soil can reach 150–200 thousand per 1 square meter. They were easily learned to be bred in boxes with soil and used as food for aquarium fish, as well as for commercial species in fish hatcheries. Enchytraeids feed on organic debris and participate in soil formation along with earthworms.

The earthworm family (Lumbricidae) includes about 200 species, most of which live in the soil. Arboreal and semi-aquatic inhabitants are less common. The most common species is Lumbricusterrestris, 20–30 centimeters long and up to 1 centimeter thick. Large tropical earthworms (up to 1 - 3 meters long) local population South America, Africa, Southeast Asia are used as food boiled or fried. 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. Their role in soil was first noticed by Charles Darwin. Later, their significance in the biological cycle was studied experimentally. Earthworms ingest soil, fallen leaves, and plant remains and help accelerate the formation of humus and mineralization of the soil. In addition, earthworms loosen the soil, mix it, dragging organic residues into the deep layers of the soil and bringing soil depleted in organic matter from the deep layers to the surface. The soil passed through the intestines of worms has better structure. Improving soil fertility is facilitated by the removal of manure and peat to the fields, which are important not only as fertilizer, but also as food for worms. Soil enriched with organic matter helps to increase the number of earthworms, which accelerate the soil-forming process. Experiments were conducted on the acclimatization of earthworms in the regions of Kazakhstan and Central Asia to improve soil fertility in irrigation areas.

Biological and practical significance Polychaete worms are very numerous in the ocean. The biological significance of polychaetes lies in the fact that they represent an important link in trophic chains, and are also important as organisms that take part in the purification of sea water and the processing of organic matter. Polychaetes have food value. To strengthen the food supply of fish in our country, for the first time in the world, Nereids (Nereis diversicolor) were acclimatized in the Caspian Sea, which were brought from the Azov Sea. This successful experiment was carried out under the leadership 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. Features that distinguish this type of worm from other types are the presence of cellome and 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 widespread everywhere. The most diverse are the marine forms of ringlets. An important role is played by annelids that live in the ground and decompose complex organic compounds. Also, ringlets 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 cure patients from quite complex diseases without the use of medications.

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

If we consider the internal structure, we can also note many features indicating 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, like annelids, also has a special structure, because blood is pumped through blood 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 the brain, located dorsally above the pharynx.

Of particular interest is the reproduction of annelids and methods of attracting individuals of the opposite sex. One of these methods 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 unimportant for the worm, which it can easily restore without damage to the body.

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

Polychaete worms are the most diverse in shape and color, most of which live in the seas. Most of them lead a burrowing lifestyle, burrowing into the substrate or attaching to it. Sessile polychaetes and crawling polychaetes are also known. They carry out movement due to bristles, which often have bright colors of all colors of the rainbow.

When considering the next group, you 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 setae for swimming and burrowing in silt, then the oligochaetes are characterized by a non-separated head section, a streamlined body, a small number of setae, all this is associated with a burrowing lifestyle, because many oligochaetes live in the ground and water and isolated individuals in the sea.

Leeches have adaptations for feeding on the blood of various animals: chitinous serrated 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. Zoology of Invertebrates. M. Higher school.

3 Beklemishev K.V. 1966. Ecology and biogeography of the pelagic zone. – M. Science. 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 USSR Academy of Sciences.

12 Ivanov A.V. 1968. The 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. Course of comparative embryology of invertebrate animals. – L. Publishing house Leningrad State University 1988.

15. Comparative embryology of invertebrate animals: Protozoa and multicellular organisms. – Novosibirsk.

16 Trochophores, tentacles, setaceous jaws, pogonophores. – M. 1977

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

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

20 Malakhov V.V. Mysterious groups of marine invertebrates. Trichoplax, orthonectids, dicyemids, sponges. – M. Moscow State University Publishing House. 1990.

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

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

23 Hausman K. 1988. Protozoology (translated from German). – M. Mir.

24 L.A. Zenkevich Life of Animals. Invertebrates. T. 1 – M: Education, 1968

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

Annelids - multicellular, binometric, three-layered animals that have a secondary body cavity. The kilchakiv type unites more than 9,000 species (in Ukraine - about 450 species). They live in sea and fresh waters, as well as in soil, compared to representatives of other types of worms, kilchakids have a significantly higher level of organization. The progressive features of the organization of annelids are: 1 ) appearance of a secondary body cavity 2) division of the body into separate segments (metamerism) ; 3 ) appearance of primitive limbs (parapodia in polychaete worms) ; 4 ) appearance of the circulatory and respiratory systems (external gills in polychaete worms) ; 5 ) development of metanephridia.

structural features

Body in kilchak multicellular, formed by many segments. Repeated repetition of body segments is called metamerism. This principle of body organization arises in the process of evolution in connection with the elongation of the body. Segments - parts of the body that are similar in structure, located sequentially one after another. The segments outside and inside are the same, so in kilchakiv Metamerism, or segmentation, of the body is homonomic. Many representatives have setae on the body segments. The body consists of the head end, the trunk and the anal lobe. Such a clear division of the body into sections is observed for the first time in Kilchakiv.

Veils are represented by a well-developed skin-muscular sac, which includes: dense, thin cuticle , hypodermis And two layers of muscles(circular and longitudinal). There are many mucous glands in the skin.

Body cavity secondary (in general) segmented. It differs from the primary cavity by the presence of its own epithelial lining, which is adjacent to the walls of the sac on one side and to the walls of the digestive tube on the other. The lining leaves grow together above and below the tube, forming a mesentery, which divides the whole into right and left parts. Transverse partitions divide the body cavity into chambers, the number of which corresponds to the number of segments. The whole is filled with liquid, which in chemical composition is very close to sea water. Coelomic fluid is in constant motion and performs a number of important functions: washing the organs of the body, supplying them with nutrients and oxygen together with blood, promoting the removal of CO2 and metabolic products, moving biologically active substances and phagocytes, etc.

features of life

Support associated with hydroskeleton, functioning thanks to coelomic fluid.

Movement muscular. In polychaete worms there are muscular growing segments of the body - parapodia, which form the motor apparatus. In oligochaetes there are tufts of bristles in their place.

Digestion is provided by a differentiated digestive system, which has three sections: anterior (mouth, pharynx, esophagus with an ax, stomach with muscular walls), middle (midgut) and posterior (hindgut with anus). Each department of the system performs its own special function. For example, in the wall of the midgut there are cells that secrete digestive enzymes and cells that digest food, so the main function of this section is the digestion and absorption of food.

Transportation of substances in Kilchakiv is already being carried out with the participation circulatory system, which appears for the first time. In annelids closed circulatory system - a system in which blood moves only through vessels and does not enter the body cavity. Their circulatory system is formed by dorsal and abdominal blood vessels connected to each other by ring vessels. Small capillaries depart from these vessels, which, branching, form a dense network in the skin and internal organs. The movement of blood is due to the pulsation of annular vessels; they do not have a heart. Blood may be colorless or colored due to the presence of respiratory pigments: chlorocruorin (determines the green color of blood), hemoglobin and hemoerythrin (determine the red color).

Breath is already carried out with the participation respiratory system, which appears for the first time. its appearance is associated with intensive metabolism compared to previous groups of invertebrates. In some sea shells, aquatic respiration organs arise - gills, constituting thin-walled formations with an extensive network of vessels, which are located on the Parapodia, head and tail. But in most kilchaks, gas exchange occurs through the integument.

Selection occurs with the participation of the excretory system formed by special organs - metanephridia. These organs begin in the body cavity as a funnel, from which a canal extends, opening outward in another segment. Each segment contains a pair of such excretory organs.

Regulation processes carried out by a chain-type nervous nodal system. The central nervous system is formed suprapharyngeal and subpharyngeal nerve ganglia, navcolognotcal jumpers and ventral nerve cord. The PNS is represented by nerve branches.

Irritability provide well-developed sense organs. In the integument there are sensitive cells that distinguish tastes and smells; the organs of touch are antennae, bristles, the existing organs of vision, and sometimes the organs of balance.

Reproduction mainly sexual with the participation of the reproductive system. Polychaete worms are dioecious, while oligochaetes and leeches are hermaphrodites. Fertilization can be either external or internal. Asexual reproduction is also found in aquatic annelids, in which their body can break up into several unequal parts (disordered division) or into separate segments (multiple fragmentation).

Development in oligochaetes and leeches - straight. In polychaetes - indirect, in which a larva is formed trochophores. It floats in the water for some time, then settles to the bottom and turns into an adult organism.

Regeneration well developed in oligochaetes and polychaetes, but in leeches this ability is lost.

Variety of annelids

The phylum is divided into several classes, including Polychaetes, Oligochaetes, and Leeches.

Polychaete worms, or polychaetes - a class of annelids that have parapodia with numerous setae on each body segment. This class includes about 5,300 species that live mainly in the seas, and only a few representatives have adapted to life in fresh water bodies or wet land areas. They lead a bottom-dwelling lifestyle (benthic animals), some are free-swimming, there are also sessile forms, and they secrete protective tubes around themselves. Mostly predators, but among them there are many herbivorous and omnivorous forms. Among the polychaetes there are also commensal species that live inside sponges, in the shells of hermit crabs or on starfish. The body of polychaete worms consists of a head section, a segmented body and an anal lobe. On the head there are eyes, organs of touch - tentacles, organs of smell - smelling pits, and in some - organs of balance (statocysts). On the body segments there are paired lateral outgrowths with bristles - parapodia - primitive limbs with the help of which worms swim, crawl or burrow into the ground. Rich-chaetes mainly have cutaneous respiration, but some species have gills. Most polychaete worms are dioecious animals. Fertilization of eggs occurs in water. Development is indirect, in which free-living trochophore larvae emerge from the eggs, driven by the movement of cilia. The most famous representatives of the class are sand vein, nereid and palolo.

Marine sandstone (Arenico/o marina) - a marine polychaete worm that lives in the Black Sea and can reach 30 cm in length. He spends his entire life in a deep hole made of sand. It feeds on small algae, animals and various inanimate pieces, capturing them along with sand. It is the main food for commercial fish.

Nereis (Nereis virens) , or Nereid,- polychaete worm living in the Sea of ​​Azov. Refers to benthos - crawls along the seabed using event parameters. It is the main food for commercial fish. Acclimatized in the Caspian Sea, multiplied intensively there and became important integral part in the nutrition of sturgeon fish.

Palolo (Eunice viridis) - a marine polychaete worm that lives in the coral reefs of the tropical islands of the Pacific Ocean. The body color is palolo greenish, the size is up to 1 m. Twice a year, at a certain phase of the Moon, sexually mature individuals appear in large numbers on the surface of the water to reproduce.

Oligochaete worms or oligochaetes- a group of annelids that have a few setae on each segment of the body. This class includes more than 5,000 species, which are mainly inhabitants of fresh water and soil, and are much less common in salt water. Most oligochaetes have sizes from 0.5 mm to 40 cm, and some types of tropical earthworms reach 3 m. Features of the external structure of oligochaetes are body segmentation (from 5-6 to 600 rings), the absence of parapodia (in their place there are tufts of small setae), the presence of a glandular girdle in the anterior part of the body in sexually mature individuals, etc. The most famous representatives of oligochaetes are earthworms and tubule worms.

Common earthworm (Lumbricus terrestris) - a species of oligochaete worms that has adapted to life in the soil. These worms belong to the family of true earthworms, which includes about 300 species. Body sizes range from 2 to 50 cm. In the south of Ukraine, worms reach large sizes. Movement in the soil is facilitated by an elongated, segmented body, pointed at both ends. They move by alternately contracting and relaxing the circular and longitudinal muscles of the musculocutaneous sac. The bristles directed backwards (8 on each segment) make it possible to cling to the slightest unevenness in the soil. The mucus secreted by the skin glands reduces friction of the worm's body, prevents it from drying out, promotes respiration, and has

Internal structure of an earthworm: A - cuticle; B - hypodermis; B - circular muscles; G - longitudinal muscles; D - skin-muscular sac; E - lining epithelium; Yes - ventral nerve chain; F - abdominal blood vessel; WITH - bristles; AND - metonephridia; AND - intestinal wall; TO - generally; L - dorsal blood vessel

antibiotic properties. Earthworms feed on dead plant debris contained in the soil. In the soil, earthworms dig deep tunnels up to 2 m from the surface of the earth. In warm and humid weather, they crawl out of their burrows at night, look for damp fallen leaves, half-rotten blades of grass, and pull all this into their burrows. So, earthworms are typical saprophages. They also swallow soil, which can be seen in their intestines. The worms throw the processed soil to the surface in the form of characteristic heaps, the appearance of which in the spring indicates the beginning of worm activity. It is calculated that in one day each worm passes through its intestines an amount of earth equal to the weight of its body. More than 50 species of earthworms are known in Ukraine, some of them are listed in the Red Book of Ukraine (for example, Eizenia Gordeeva).

Ordinary pipe maker (Tubifex tubifex) - freshwater red thin worm 2-5 cm in size. Lives in muddy soils of fresh, very polluted, oxygen-poor water bodies. The front end of the worm is immersed in silt, and the rear end moves out and continuously wriggles - these movements provide an influx of fresh water necessary for breathing. They can withstand significant pollution of water bodies with various substances (petroleum products, pesticides, etc.). The skin on the back of the body has especially many blood capillaries. A tube is formed around this part of the body, consisting of silt particles glued together with the mucus of the worm. Swallows sand and silt and absorbs the nutrients it contains. It is used as food for aquarium fish and is a nutritional source for freshwater animals, in particular fish.

Medical leech (Hirudo medicinalis) has a segmented body 8-12 cm long. On the dark dorsal side of the body there is a characteristic pattern of three pairs of rusty-red or red-yellow longitudinal stripes. Lives in small standing reservoirs with a muddy bottom, overgrown with vegetation. It feeds on the blood of amphibians and mammals. The rear sucker is used for attachment, while the front sucker, which has jaws and teeth, is used for feeding. In the oral cavity, located at the bottom of the anterior sucker, there is three jaws. They cut through the skin of the animal in which the leech has attached itself. In the morning, saliva containing hirudin is released. Hirudin- a substance that is produced by the salivary glands of the leech to prevent blood clotting. Blood treated with leech saliva can be stored for a long time in reserve in the large pockets of its intestines - thanks to this, the animal can starve for a long time (from several months to a year). The medicinal leech is a hermaphrodite, which is characterized by direct development. She lays her eggs in clusters near the water (but not in the water), in dark, damp places. Used in medicine for diseases of the circulatory system, gangrene and organ transplantation.

Taxonomy. The phylum Annelidae includes the classes: Oligochaetes, Polychaetes and Leeches.

Structure. Bilateral symmetry of the body. Body dimensions range from 0.5 mm to 3 m. The body is divided into a head lobe, a trunk and an anal lobe. Polychaetes have a separate head with eyes, tentacles and antennae. The body is segmented (external and internal segmentation). The body contains from 5 to 800 identical ring-shaped segments. The segments have the same external and internal structure (metamerism) and perform similar functions. The metameric structure of the body determines the high ability to regenerate.

The body wall is formed skin-muscle bag, consisting of a single-layer epithelium covered with a thin cuticle, two layers of smooth muscle: outer circular and internal longitudinal, and single-layer epithelium of the secondary body cavity. When the circular muscles contract, the body of the worm becomes long and thin; when the longitudinal muscles contract, it shortens and thickens.

Organs of movement - parapodia(available in polychaetes). These are outgrowths of a skin-muscular sac on each segment with tufts of bristles. In oligochaetes only tufts of setae are retained.

Body cavity secondary - in general(has an epithelial lining that covers the skin-muscular sac from the inside and the organs of the digestive system from the outside). In most representatives, the body cavity is divided by transverse partitions, corresponding to the body segments. Cavity fluid is a hydroskeleton and internal environment; it is involved in the transport of metabolic products, nutrients and reproductive products.

Digestive system consists of three sections: anterior (mouth, muscular pharynx, esophagus, crop), middle (tubular stomach and midgut) and posterior (hindgut and anus). The glands of the esophagus and midgut secrete enzymes to digest food. Absorption of nutrients occurs in the midgut.

Circulatory system closed. There are two main vessels: dorsal And abdominal, connected in each segment by ring-shaped vessels. Blood moves through the dorsal vessel from the rear end of the body to the front, and through the abdominal vessel - from front to back. The movement of blood is carried out thanks to the rhythmic contractions of the walls of the spinal vessel and the annular vessels (“heart”) in the pharynx area, which have thick muscle walls. Many people have red blood.

Breath. Most annelids have cutaneous respiration. Polychaetes have respiratory organs - feathery or leaf-shaped gills. These are modified dorsal antennae of the parapodia or head lobe.

Excretory system metanephridial type. Metanephridia They look like tubes with funnels. Two in each segment. A funnel surrounded by cilia and convoluted tubules are located in one segment, and a short tubule opening outward with an opening - the excretory pore - is in the adjacent segment.

Nervous system represented by suprapharyngeal and subpharyngeal nodes ( ganglia), peripharyngeal nerve ring (connects the suprapharyngeal and subpharyngeal ganglia) and ventral nerve cord, consisting of paired nerve ganglia in each segment, connected by longitudinal and transverse nerve trunks.

Sense organs. Polychaetes have organs of balance and vision (2 or 4 eyes). But the majority have only separate olfactory, tactile, gustatory and light-sensitive cells.

Reproduction and development. Soil and freshwater forms are mostly hermaphrodites. The gonads develop only in certain segments. Insemination is internal. Type of development - direct. In addition to sexual reproduction, asexual reproduction (budding and fragmentation) is also characteristic. Fragmentation is carried out through regeneration - the restoration of lost tissues and body parts. Marine representatives of the type are dioecious. Their gonads develop in all or in certain segments of the body. Development with metamorphosis, larva - trochophore.

Origin and aromorphoses. The following aromorphoses led to the emergence of the type: locomotor organs, respiratory organs, closed circulatory system, secondary body cavity, body segmentation.

Meaning. Earthworms improve the structure and fertility of the soil. The ocean worm Palolo is eaten by humans. Medical leeches are used for bloodletting.

Class Oligochaetes(Oligochaetes)

Representatives: earthworms, tubifex worms, etc. Most oligochaetes live in soil and fresh water. Detritivores(feed on semi-decomposed remains of plants and animals). There are no parapodia. The setae extend directly from the body wall. The head lobe is poorly expressed. Sense organs are often absent, but there are olfactory, tactile, gustatory, and light-sensitive cells. Hermaphrodites. Insemination is internal, cross. Development is direct, takes place in cocoon, which after fertilization forms on the body of the worm in the form of a belt, and then slides off it.

The role of earthworms in soil formation is enormous. They promote the accumulation of humus and improve the soil structure, thereby increasing soil fertility.

Class Polychaetes(Polychaetes)

Leech class

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