What features of annelids allowed them. Type annelids. Type Flatworms their characteristics

Annelids are the most highly organized worms. They are the most advanced type of worms. The features that distinguish this type of worm from other types are the presence of cellom and the metamerism of the structure. Based on this, annelids can be called coelomic animals with a high organization.

In addition, annelids play a very important role in the biocenosis. They are ubiquitous. The most diverse are marine forms of rings. An important role is played by annelids living in the earth and decomposing complex organic compounds.

Rings also play an important role not only in the biocenosis of nature, but also for human health. For example, leeches, on which hirudotherapy is based, help to cure patients of rather complex diseases without the use of medicines.

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

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

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

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

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

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

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

When considering the next group, one can also see structural features associated with the lifestyle of worms. And if in the previous case, polychaetes were characterized by a large number of setae for swimming and burrowing into 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, water and single individuals in the sea.

Leeches have the same adaptations for feeding on the blood of various animals: chitinous toothed plates, a large number of glands that secrete mucus, as well as the presence in the body of an enzyme that anesthetizes the bite and liquefies the blood of the victim.
Echiurids are marine burrowing worms. Their body, unlike all other classes of worms, is not segmented and is often equipped with a proboscis.

Features of the organization of the Earthworm

body structure	The body is elongated, round, segmented. The symmetry is bilateral, the ventral, dorsal sides of the body, anterior and posterior ends differ. There is a secondary body cavity lined with epithelium and filled with fluid. Locomotion with the help of the skin-muscular pouch.
Digestive system	Digestive system - oral opening, pharynx, esophagus, goiter, stomach, midgut, hindgut, anus, glands.
Respiratory system. Circulatory system. excretory system	The circulatory system is closed and consists of blood vessels. There are larger vessels - hearts, pushing blood. Blood contains hemoglobin. The cavity fluid provides a connection between the circulatory system and the cells. Breathing with the entire surface of the body. The excretory system contains a pair of nephridia in each segment.
Nervous system, sense organs	Nodal type: paired head ganglion, paired peripharyngeal bands connecting with the abdominal ones. Many annelids have sensory organs: eyes, olfactory pits, organs of touch. In earthworms (due to their underground way of life), the sense organs are represented by tactile and light-sensitive cells throughout the surface of the body.
reproduction	Dioecious or secondary hermaphrodites. Fertilization is cross, internal (in aquatic forms in water). The development is direct. Some marine annelids have metamorphosis and have floating larvae. Capable of regeneration.



Class Polychaetes, Class Low-bristle, Class Leeches

Question 1. Describe the structural features of annelids.

Characteristic features of the type Annelids:

The body is always segmented (segmentation in the internal structure is the repetition of many internal organs).

They have a secondary body cavity - the whole.

The circulatory system is closed.

The nervous system consists of the peripharyngeal nerve ring and the ventral nerve cord. The supraglottic node is the "brain".

The sense organs are located on the head segments.

Organs promoting locomotion are setae (in oligochaetes, 8 on each segment) and parapodia with tufts of setae (in polychaetes).

Question 2. What are parapodia? What do you think their evolutionary significance is?

Parapodia - lateral outgrowths of the body in polychaete worms, arranged in pairs and serving as organs of movement. Evolutionarily, parapodia are the precursors of limbs.

Question 3. Describe the structure of the circulatory system of annelids.

The circulatory system is closed, consisting of vessels, some of which have contracting walls (“hearts”), which ensures blood circulation. Some groups do not have a circulatory system. The blood of a number of forms contains hemoglobin (a red blood protein containing iron and transporting oxygen from the respiratory system to the tissues).

Question 4. Describe the organs of excretion of rings.

The excretory system is represented by segmentally arranged metanephridia. Their funnel faces the body cavity, and the other end opens outward.

Question 5. How does the earthworm reproduce?

Earthworms are hermaphrodites, but they cross fertilize. The two worms approach each other and exchange spermatozoa, which enter their spermatozoa. Then a mucous muff is formed on the body of each worm. With muscle contractions, the worm moves it to the front end of the body. When the muff passes by the openings of the ovarian ducts and sperm receptacles, eggs and sperm enter it. Then the muff slips off the worm and closes into a cocoon, where small worms develop from the fertilized eggs.

Question 6. What classes are united by the type of annelids?

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

Question 7. Why are some annelids called polychaetes, while others are called low-bristle? How are oligochaetes different from polychaetes?

Small-bristle worms are one of the subclasses of annelids. The brightest and most familiar representative of the taxon is the most trivial Earthworm.

Polychaete worms are one of the subclasses of annelids. The most famous representatives of the taxon are sandworm and nereid. Sometimes animals are called polychaetes, which in Greek means "a lot of hair."

The difference between low-bristle worms and polychaetes

There are fewer species of oligochaetes than polychaetes. The first are only 3 thousand species, the second - about 10 thousand.

The maximum size of polychaetes exceeds the maximum size of oligochaetes, reaching 3 meters.

Animals have different habitats. Small bristle worms live mainly in the ground, most polychaete worms prefer warm and salty water bodies.

Oligochaetes perceive oxygen with the entire surface of the skin, polychaetes breathe with the help of pseudo-gills-setae.

Small-bristle - hermaphrodites, polychaetes - dioecious animals.

The oligochaetes that emerge from the egg are similar to their parents. Polychaetes go through the larval stage.

Olympians devour dead leaves and corpses, most polychaetes are active predators.

Question 8. When and from whom did the first annelids originate? What major changes accompanied the appearance of the type? Discuss with the class what the meaning of these transformations is. Record the results of the discussion in your notebook.

Annelids are descended from free-living flatworms. From the common ancestors of worms, under the influence of evolutionary factors, annelids also originated. An important point in their evolution is the division of the body into segments (rings). In connection with the active movement of annelids, a circulatory system appeared, supplying the body with nutrients and oxygen. Ancient annelids had a more complex structure compared to other worms.

Question 9. Make a table "Comparative characteristics of the structure of organs and systems in flat, round and annelids" (work in small groups).

Comparative characteristics of the structure of organs and systems in flat, round and annelids

What do worms of all types have in common?

All worms are small organisms with an elongated body shape. Their body consists of several layers that form a skin-muscular sac. They are characterized by a worm-like movement.

What is the significance of annelids in nature and human life?

Annelids are an important link in the food chain, that is, they serve as food for other organisms. Earthworms loosen the soil and enrich it with minerals, contribute to the decomposition of organic residues. Annelids that live in the aquatic environment are orderlies of reservoirs.

Questions

1. What features of annelids allowed them to populate most of the planet?

Annelids are able to inhabit various habitats, since they have developed systems of internal organs, developed sensory organs, and a hydrostatic skeleton. The segmented structure of the body makes it possible for regeneration.

2. What adaptations do annelids have to endure adverse conditions? How does this happen?

When adverse conditions occur, some annelids enter a period of diapause. They crawl to the depth, curl up into a ball, secrete a lot of mucus and form a capsule. Ringworms living in cold climates fall into suspended animation.

3. What allows scientists to attribute polychaetes, oligochaetes and leeches to the same type?

Polychaetes, oligochaetes and leeches belong to the same type, since they have a segmented body structure.

4. After rain, you can observe a massive exit of earthworms to the surface of the earth. What is the reason for this phenomenon?

The mass exit of earthworms to the surface after rain is due to the fact that all underground passages are filled with water. Under such conditions, the worms are unable to breathe.

5. Why is it possible to judge the degree of its pollution by the number of oligochaetes in a reservoir?

Oligochetes are unpretentious to the purity of water and the absence of oxygen, therefore they can live in polluted water bodies, but there are no leeches.

6. What oligochaetes improve soil structure, air and moisture permeability and purify water from harmful impurities?

Earthworms improve soil structure. Aquatic annelids purify water bodies from organic pollution. They feed on silt and various organic suspensions in the water.

7. Why have doctors used leeches since ancient times for hypertension and the threat of hemorrhage?

Leeches are used to treat various diseases. They are attached to the human body according to the available schemes. To select specific places, the doctor collects the information he needs about the disease, about the activity of the pathological process, about the patient's state of health. The duration of blood sucking varies in time and can be up to an hour. The minimum exposure time is 10 minutes. After the procedure, the leeches are removed either by a doctor or fall off on their own. Secondarily, leeches are not used, they are destroyed by placing them in chloramine. The therapeutic effect is achieved through:

Dosed bloodletting. One animal can suck up to 15 ml of blood.

The work of substances with biological activity. They enter the body from the saliva of a leech. The main therapeutic effect is hirudin. This anticoagulant helps to reduce blood clotting.

Due to the body's responses that occur to the bite of a leech.

The depth of the bite of the skin does not exceed 2 mm, after which the leech injects its saliva into the wound. When the required exposure time expires, the leech is removed, but the bite site continues to bleed. It may take up to 16 hours for the bleeding to stop completely.

Consider a number of animals that biology studies - the type of annelids. We learn about their species, lifestyle and habitat, internal and external structure.

general characteristics

Annelids (also called simply annelids, or annelids) are one of the largest, which includes, according to various sources, about 18 thousand species. They are non-skeletal vertebrates that not only participate in the destruction of organic matter, but are also an important component of the nutrition of other animals.

Where can you find these animals? The habitat of annelids is very extensive - these are seas, and land, and fresh water. The annelids living in the salty waters of the ocean are very diverse. Kolchetsov can be found in all latitudes and depths of the World Ocean, even at the bottom of the Mariana Trench. Their density is high - up to 100,000 specimens per square meter of bottom surface. Marine annelids are a favorite food for fish and play an important role in the marine ecosystem.

Aquatic species not only crawl along the bottom or burrow into the silt, some of them can build a protective tube and live without leaving it.

The best known are the annelids that live in the soil, they are called earthworms. The density of these animals in meadow and forest soils can reach up to 600 specimens per square meter. These worms are actively involved in soil formation.

Classes of annelids

Respiratory organs and circulatory system of annelids

Small-bristle worms breathe through the entire surface of their body. But polychaetes have respiratory organs - gills. They are bushy, leaf-like or pinnate outgrowths of the parapodia, penetrated by a large number of blood vessels.

The circulatory system of the annelids is closed. It consists of two large vessels - abdominal and dorsal, which are connected by annular vessels in each segment. The movement of blood is carried out due to contractions of certain sections of the spinal or annular vessels.

The circulatory system of the annelids is filled with the same red blood as in humans. This means that it contains iron. However, the element is not part of hemoglobin, but of another pigment - hemerythrin, which captures 5 times more oxygen. This feature allows worms to live in conditions of oxygen deficiency.

Digestive and excretory systems

The digestive system of annelids can be divided into three sections. The anterior intestine (stomodeum) includes the oral opening and oral cavity, sharp jaws, pharynx, salivary glands, and narrow esophagus.

The oral cavity, which is also called the buccal region, is able to turn inside out. Behind this section are the jaws, which are bent inward. This apparatus is used to capture prey.

Then comes the mesodeum, the midgut. The structure of this department is uniform along the entire length of the body. The middle intestine narrows and expands, it is in it that food is digested. The hindgut is short, ending with an anus.

The excretory system is represented by metanephridia located in pairs in each segment. They remove waste products from the abdominal fluid.

Nervous system and sense organs

All classes of annelids have a ganglionic nervous system. It consists of a parapharyngeal nerve ring, which is formed by the connected supraesophageal and subpharyngeal ganglia, and of pairs of a chain of abdominal ganglia located in each segment.

The sense organs of the rings are well developed. Worms have sharp eyesight, hearing, smell, touch. Some annelids not only capture light, but can also emit it themselves.

reproduction

The characteristic of the annelids suggests that representatives of this type of animal can reproduce both sexually and can be produced by dividing the body into parts. The worm breaks into halves, each of them becomes a full-fledged individual.

At the same time, the tail of the animal is an independent unit and can grow a new head for itself. In some cases, a second head begins to form in the center of the worm's body before separation.

Budding is less common. Of particular interest are species in which the budding process can cover the entire body, when the posterior ends bud off from each segment. In the process of reproduction, additional mouth openings may also form, which will later separate into independent individuals.

Worms can be dioecious, but some species (mainly leeches and earthworms) have developed hermaphroditism, when both individuals simultaneously perform the role of both female and male. Fertilization can occur both in the body and in the external environment.

For example, in sexually reproducing, fertilization is external. Animals of different sexes throw their germ cells into the water, where eggs and sperm merge. From fertilized eggs, larvae appear that do not look like adults. Freshwater and terrestrial annelids do not have a larval stage, they are born immediately similar in structure to adults.

Class Polychaete

Marine annelids belonging to this class are quite diverse in form and behavior. Polychaetes are distinguished by a well-defined head region and the presence of parapodia, peculiar limbs. They are predominantly heterosexual, the development of the worm occurs with metamorphosis.

Nereids actively swim, can burrow into the silt. They have a serpentine body and many parapodia; animals make passages with the help of a retractable pharynx. Sandworms look like earthworms and burrow deep into the sand. An interesting characteristic of the annelids is that it moves in the sand in a hydraulic way, pushing the cavity fluid from one segment to another.

Curious and sedentary worms, serpulids, which live in spiral or twisted calcareous tubes. Serpulids protrude from their dwelling only their heads with large fan-shaped gills.

Class Low-bristle

Small-bristle worms mainly live in the soil and fresh waters; they are found singly in the seas. The structure of annelids of this class is distinguished by the absence of parapodia, homonomous segmentation of the body, and the presence of a glandular girdle in mature individuals.

The head section is not pronounced, it may be devoid of eyes and appendages. On the body are setae, rudiments of parapodia. This body structure is due to the fact that the animal leads a burrowing lifestyle.

Very common and familiar to all low-bristle are earthworms that live in the soil. The body of the worm can be from a few centimeters to three meters (such giants live in Australia). Also in the soil are often found small, about a centimeter in size, whitish enchytreid worms.

In fresh water, you can find worms living in entire colonies of vertical tubes. They are filter feeders feeding on suspended organic residues.

Leech class

All leeches are predators, mostly feeding on the blood of warm-blooded animals, worms, molluscs, and fish. The habitat of annelids of the class of leeches is very diverse. Most often, leeches are found in fresh water, wet grass. But there are also marine forms, and even terrestrial leeches live in Ceylon.

Of interest are the digestive organs of leeches. Their mouth is equipped with three chitinous plates that cut through the skin, or proboscis. The oral cavity contains numerous salivary glands that can secrete a poisonous secret, and the pharynx acts as a sucking pump.

Class Echiuridae

One of the rare species of animals that biology studies is the annelids Echiurids. The Echiurid class is small, it has only about 150 species. These are soft, sausage-like marine worms with a proboscis. The mouth is located at the base of a non-retractable proboscis, which the animal can discard and grow back.

The habitat of annelids of the Echiurid class is the great depths of the sea, sandy burrows or rock crevices, empty shells and other shelters. Worms are filter feeders.

Structural featuresand life

annelids

Educational tasks:

1. To acquaint students with the features of the organization of annelids as the most complex animals in comparison with flat and roundworms.

2. To continue the formation of the ability to recognize the studied animals, compare them, draw conclusions about the more complex organization of annelids compared to flatworms.

3. To reveal the role of soil annelids in nature and for humans, using the earthworm as an example.

Equipment:

Preview:

Biology lesson summary

On the topic : "Features of the structureand life activity of annelids"

Spent : teacher of the first qualification category

Skuratov Ilya Vladimirovich

Place of implementation: MOU secondary school No. 33 of the Dzerzhinsky district, Volgograd.

Volgograd, 2013

Structural featuresand life

annelids

Educational tasks:

1. To acquaint students with the features of the organization of annelids as the most complex animals in comparison with flat and roundworms.

2. To continue the formation of the ability to recognize the studied animals, compare them, draw conclusions about the more complex organization of annelids compared to flatworms.

3. To reveal the role of soil annelids in nature and for humans, using the earthworm as an example.

Equipment :

During the classes

I Checking homework

7 students receive cards with tasks that they complete while a frontal oral survey is being conducted on the following questions:

*Does roundworm change owners? (No)

* What is sexual dimorphism? (differences between male and female)

* List signs of progress in roundworms compared to flatworms? (sexual dimorphism, development of the digestive, nervous and reproductive systems, escape from the cycle with a change of hosts ...)

For a survey, educational tables are posted on the board, according to which students show the named features.

While the survey is being seen, a student is called to the board, sketching a diagram: "the cycle of development of the human roundworm."

The rest of the students should carefully follow the story and show according to the diagram and, if necessary, correct errors in the answer.

At the end of the survey, cards with tasks are collected.

II Learning new material

Write the topic of the lesson on the board and in a notebook.

Today in the lesson we will begin our acquaintance with a new type of animal world - annelids.

Annelids are a vast group of animals, including about 12 thousand species that live mainly in the seas, as well as in fresh waters and on land. Compared to flatworms and roundworms, they are more highly organized.

Read the first paragraph of the paragraph and answer the question: what is the name of the type related to? (the body consists of ring segments)

For 5 lessons, you filled out a comparative table on the main types of worms, it already contains information about the structure of flatworms and roundworms, now you will supplement it with information about annelids. Read the text of the paragraph on pages 128-129 and complete the table. You need to look for signs of progress in the structure of annelids.

Signs of comparison	Type: Flatworms	Type: Roundworms	Type: Annelids
Basic life forms
body integuments
body shape
Attachment organs
Organs of locomotion
Digestive system
excretory system
Respiratory system
Circulatory system
reproductive system

After 10 minutes, the results of filling in the table are discussed.

All organ systems are studied according to educational tables posted at the time of the show.

Basic life forms

What life forms are characteristic of annelids?

Integument and body shape

What are the body coverings of annelids?

The outer epithelium of annelids is covered with a cuticle and bears epidermal chitinous bristles - parapodia, with the exception of leeches.

Did previously studied worms have a cuticle, what is its role?

The rain rope has an elongated body 10-16 cm long. In cross section, the body is rounded, but, unlike roundworms, it is divided into 100-180 segments by annular constrictions. On each segment sit small elastic bristles. They are almost invisible, but if you run your fingers from the back end of the worm's body to the front, then we will immediately feel them.

What do you think is the role of parapodia in the life of annelids?

With these bristles, the worm clings to the unevenness of the soil when moving.

During the day, the worms stay in the soil, making passages in it. If the soil is soft, then the worm bores it with the front end of the body. In doing so, he first compresses the front end of the body, so that it becomes thin, and pushes it forward between the lumps of soil. Then the front end thickens, pushing the soil apart, and the worm pulls up the back of the body. In dense soil, the worm can eat its own way, passing the earth through the intestines. Heaps of earth can be seen on the surface of the soil - they are left here by worms at night. They also come to the surface after heavy rain (hence the name - rain). In summer, the worms stay in the surface layers of the soil, and for the winter they dig minks up to 2 m deep.

If we take the worm in our hands, we will find that its skin is moist, covered with mucus. This mucus facilitates the movement of the worm in the soil. In addition, only through moist skin does the oxygen necessary for breathing enter the body of the worm.

What is the reason for the ability of an earthworm to compress the body, and not just bend it like a roundworm?

Under the skin are located circular muscles fused with it, and under them a layer of longitudinal muscles - a skin-muscular sac is obtained. The circular muscles make the body of the worm thin and long, while the longitudinal muscles shorten and thicken. Thanks to the alternating work of these muscles, the movement of the worm occurs.

body cavity. Under the skin-muscle sac is a fluid-filled body cavity in which the internal organs are located.This body cavity is not continuous, as in roundworms, but is divided by transverse partitions according to the number of segments. It has its own walls and is located under the skin-muscle sac.

Attachment organs

Digestive system

What organs appear in the digestive system of annelids? What is the reason for their appearance?

The mouth is located at the anterior end of the body. The earthworm feeds on decaying plant debris, which it swallows along with the earth. It can also drag fallen leaves from the surface. Swallowing is done with a muscular pharynx. Then the food enters the crop, stomach and intestines. Undigested residues, together with the earth, are ejected through the anus at the posterior end of the body.

The appearance of the esophagus, goiter and stomach is associated with a free life in the soil and the need for thorough digestion of food.

excretory system

What is the excretory system of an earthworm?

The excretory system is represented by metanephridia.

How are metanephridia arranged?

Liquid waste, processed substances enter the body cavity. Each segment contains a pair of tubules. Each tube has a funnel at the inner end, processed unnecessary substances enter it and are removed through the tube through the opposite end to the outside.

Respiratory system

What does the appearance of the respiratory system indicate? How is the respiration of annelids carried out? What are its functions?

Breathing in various ways: the entire surface of the body (earthworm) or gills (water).

Circulatory system

What does the appearance of the circulatory system indicate? What is the structure of the circulatory system? What are its functions?

The circulatory system of the earthworm serves to carry oxygen and nutrients primarily to the muscles. An earthworm has two main blood vessels: dorsal, through which blood moves from back to front, and abdominal, through which blood flows from front to back. Both vessels in each segment are connected ring vessels. Several thick annular vessels have muscular walls, due to the contraction of which blood moves. Thinner ones depart from the main vessels, then branching into the smallest capillaries. Oxygen from the skin and nutrients from the intestines enter these capillaries, and these substances are released from other similar capillaries branching in the muscles.What is a closed circulatory system?This is when the blood moves all the time through the vessels and does not mix with the cavity fluid. This circulatory system is called closed

Nervous system and sense organs

What type of nervous system is built in flat and roundworms?

And according to what type is the nervous system of annelids built?

What progressive features in the structure of the nervous system of the rings can you highlight?

The nervous system is represented by the supraesophageal ganglion, peripharyngeal nerve ring and ventral nerve trunk.with segmental ganglia. A pair ofnerve trunks.In each segment they have developed nerve knots - it turns out nerve circuit.In the front part, two large nodes are connected to each other by ring bridges - aperipharyngeal nerve ring.Nerves depart from all nodes to various organs. The appearance of the brain significantly distinguishes annelids from representatives of other types of worms.

Thus, the nervous system acquires segmentation, this type of nervous system is more progressive than the ladder one in flatworms.

There are no special sense organs, but sensitive cells in the skin allow the earthworm to feel touch on its skin and distinguish light from darkness.

The body surface of the earthworm is covered with photoreceptors. Knowing this, you can conduct an interesting experiment: if you cut the worm in half, then its head will move away from the light, and the tail, on the contrary, will turn towards the light.

Other species include worms with well-developed eyes and tactile bristles.

The reproductive system and reproduction.

What features in the structure of the reproductive system of the rings can you highlight?

Earthworms are hermaphrodites.

What worms that you have already studied were also hermaphrodites?

Before laying eggs, two worms touch for a while and exchange seminal fluid - sperm: Thus, the sperm of another individual is used to fertilize the eggs. Then they diverge, and mucus is released from the thickening (girdle) on the front of the worm. Eggs enter this mucus. Then a lump of mucus with eggs slides off the body of the worm and freezes in cocoon. Young worms emerge from the cocoon, i.e. the transformation is complete.

Among annelids, there are also heterosexual species.

Significance in nature and for man

These worms, making passages in the soil, loosen it and contribute to the penetration of water and air into the soil, which are necessary for the development of plants. The mucus secreted by the worms sticks together the smallest particles of the soil, thereby preventing its spraying and erosion. Dragging plant residues into the soil, they contribute to their decomposition and the formation of fertile soil. On one hectare of soil, the biomass of earthworms (Lumbricus) reaches 2-4 tons. These worms process annually from 50 to 600 tons of soil, turning it into small soil aggregates enriched with humus. Earthworms can burrow into the ground to a depth of 8 m

Therefore, earthworms should be protected as useful animals.

Ringed worms are included in food chains, being their important link.

In addition, in a number of Eastern countries, earthworms are used as food by humans as delicacies.

III Consolidation

Summing up the lesson, let's discuss what is the progress in the structure of annelids in comparison with flat roundworms?

A frontal survey is carried out in order to identify the features of the progress of annelids in comparison with flatworms and roundworms.

Thus, in annelids, progressive features of organization are traced: the presence of a coelom, the metamerism of the structure, the appearance of a circulatory system, an excretory system like metanephridia, a more highly organized nervous system and sensory organs. In this, annelids differ from the lower ones - flat and round worms.

V Homework

3 students prepare reports:

1. Class Polybristle

2.Class Low-bristle

3. Leech class

Read the text of the paragraph on pages 128-129, complete the tasks in the workbook.