What are the features of annelids? Type annelids

Annelids are the most highly organized worms. They are the most advanced 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.

Features of the organization of the earthworm

Structural featuresand life activity

annelids

Educational tasks:

1. To familiarize students with the organizational features of annelids as the most complexly organized animals compared to flat and round worms.

2. Continue to develop the ability to recognize the animals studied, compare them, and draw conclusions about the more complex organization of annelids compared to flatworms.

3. Reveal the role of soil annelids in nature and for humans, using the example of the earthworm.

Equipment:

Preview:

Biology lesson notes

On the topic : "Structural Featuresand vital activity of annelids"

Spent : teacher of the first qualification category

Skuratov Ilya Vladimirovich

Place of sale: Municipal educational institution secondary school No. 33 of Dzerzhinsky district, Volgograd.

Volgograd, 2013

Structural featuresand life activity

annelids

Educational tasks:

1. To familiarize students with the organizational features of annelids as the most complexly organized animals compared to flat and round worms.

2. Continue to develop the ability to recognize the animals studied, compare them, and draw conclusions about the more complex organization of annelids compared to flatworms.

3. Reveal the role of soil annelids in nature and for humans, using the example of the earthworm.

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 hosts? (No)

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

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

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

While the survey is taking place, a student is called to the board to sketch a diagram: “the development cycle 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, collect task cards.

II Learning new material

Write down the topic of the lesson on the board and in your notebook.

Today in the lesson we will begin to get acquainted with a new type of animal world - 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. Compared to flat 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 associated with? (the body consists of ring segments)

Over the course of 5 lessons, you filled out a comparative table on the main types of worms; it already contains information about the structure of flat and round worms; now you will supplement it with information about annelids. Read the text of the paragraph on pages 128-129 and fill in the table. You need to look for signs of progress in the annelids' structure.

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

All organ systems are studied using educational tables posted at the time of the demonstration.

Basic life forms

What life forms are characteristic of annelids?

Cover and body shape

What are the body coverings of annelids?

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

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

The rain rope has an elongated body, 10-16 cm long. In cross-section, the body is round, but, unlike roundworms, it is divided by annular constrictions into 100-180 segments. On each segment there are small elastic bristles. They are almost invisible, but if we run our fingers from the back end of the worm's body to the front, 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 uneven soil when moving.

During the day, worms stay in the soil, making tunnels in it. If the soil is soft, then the worm drills it with the front end of the body. At the same time, 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 rear part of the body. In dense soil, the worm can eat its way through the soil through its 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, worms stay in the surface layers of the soil, and in winter they dig burrows up to 2 m deep.

If we take a worm in our hands, we will find that its skin is moist and 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 penetrate into the worm’s body.

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

Under the skin there are 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, like 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

Organs of attachment

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 rotting plant debris, which it swallows along with the soil. It can also drag fallen leaves from the surface. Swallowing is done by the muscular pharynx. Then the food enters the crop, stomach and intestines. Undigested remains, along with soil, are expelled through the anus at the rear end of the body.

The appearance of the esophagus, goiter and stomach is associated with 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 organized?

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

Respiratory system

What does the appearance of the respiratory system indicate? How do annelids breathe? What are its functions?

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

Circulatory system

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

The earthworm's circulatory system serves to transport 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 circular vessels. Several thick annular vessels have muscular walls, due to the contraction of which blood moves. From the main vessels, thinner ones depart, branching then into the smallest capillaries. These capillaries receive oxygen from the skin and nutrients from the intestines, and these substances are released from other similar capillaries that branch in the muscles.Which circulatory system is called closed?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 sensory organs

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

What type of nervous system is the annelid worm built on?

What progressive features in the structure of the ringed nervous system can you identify?

The nervous system is represented by the suprapharyngeal ganglion, peripharyngeal nerve ring and ventral nerve trunkwith segmental ganglia. Along the entire body of the worm on the ventral side runs a pairnerve trunks.In each segment they have developed nerve nodes - it turns out nerve chain.In the front part, two large nodes are connected to each other by ring jumpers - aperipharyngeal nerve ring.Nerves extend 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 becomes segmented; this type of nervous system is more progressive than the scalene one in flatworms.

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

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

Among other species, there are worms with well-developed eyes and tactile bristles.

Reproductive system and reproduction.

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

Earthworms are hermaphrodites.

Which worms that you have already studied were also hermaphrodites?

Before laying eggs, two worms come into contact for some time and exchange seminal fluid - sperm: Thus, the sperm of another individual is used to fertilize the eggs. Then they disperse, and mucus is released from the thickening (belt) located on the front of the worm. This mucus contains eggs. Then a lump of mucus with eggs slides off the worm's body and hardens into cocoon. Young worms emerge from the cocoon, i.e. the transformation is complete.

Among annelids there are also heterosexual species.

Meaning in nature and for humans

These worms, making passages in the soil, loosen it and facilitate the penetration into the soil of water and air necessary for the development of plants. The mucus secreted by the worms sticks together the smallest particles of soil, thereby preventing it from being dispersed and washed away. By 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 from 50 to 600 tons of soil annually, 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 beneficial animals.

Annelids are part of food chains, being an important link in them.

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

III Consolidation

To summarize the lesson, let's discuss how progress in the structure of annelids is expressed in comparison with flat roundworms?

A frontal survey is carried out to identify the features of the progress of annelids in comparison with flat and round worms.

Thus, annelids exhibit progressive organizational features: the presence of a coelom, a metameric 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 annelids differ from lower ones - flat and round worms.

V Homework

3 students prepare reports:

1. Class Polychaetes

2.Class Oligochaetes

3. Leech class

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

What do all types of worms have in common?

All worms are small organisms with an elongated body shape. Their body consists of several layers that form a skin-muscle 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 food chains, that is, they serve as food for other organisms. Earthworms loosen the soil and enrich it with minerals, promoting the decomposition of organic residues. Annelids, which live in the aquatic environment, are the orderlies of reservoirs.

Questions

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

Annelids are capable of inhabiting various habitats because they have developed systems of internal organs, developed sensory organs, and a hydrostatic skeleton. The segmented structure of the body makes it possible to regenerate.

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

When unfavorable conditions occur, some annelids enter a period of diapause. They crawl into the depths, 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 classify polychaetes, oligochaetes and leeches as one phylum?

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

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

The massive emergence of earthworms to the surface after rain is due to the fact that all underground passages are filled with water. In such conditions, the worms have no way to breathe.

5. Why can we judge the degree of pollution by the number of oligochaetes in a reservoir?

Oligochaetes are unpretentious to the purity of water and the lack of oxygen, so they can live in polluted waters, but leeches do not.

6. Which oligochaetes improve the structure of the soil, the permeability of air and moisture into it and purify water from harmful impurities?

Earthworms improve soil structure. Aquatic annelids clean water bodies of organic pollutants. 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 existing patterns. To select specific places, the doctor collects the information he needs about the disease, the activity of the pathological process, and the patient’s state of health. The duration of blood sucking varies in time and can reach 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. Leeches are not used for a second time; they are destroyed by placing them in chloramine. The therapeutic effect is achieved thanks to:

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

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

Thanks to the body's response to a leech bite.

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

According to the classification, annelids belong to the group of invertebrate animals, the type of protostomes, which have a secondary body cavity (coelom).

The type of annelids (or annelids) includes 5 classes: belt worms (leeches), polychaetes (earthworm), polychaetes (nereid, sandworm) worms, mysostomids, dinophylids. This type includes about 18 thousand species of worms. Free-living ringworms are distributed throughout our planet; they live in freshwater and saltwater bodies of water and soil.

This group includes characteristic representatives of ringworms - oligochaete worms and leeches. Aeration and loosening of 1 sq.m of soil is carried out on average from 50 to 500 rings. Marine forms of annelids are distinguished by their diversity, which are found at different depths and throughout the World Ocean. They play an important role in the food chains of marine ecosystems.

Annelids have been known since the Middle Cambrian period.

It is believed that they descended from lower flatworms, since certain features of their structure indicate the similarity of these groups of animals. Polychaete worms are distinguished as the main class of the annelid type. Later in the course of evolution, in connection with the transition to a terrestrial and freshwater lifestyle, oligochaetes evolved from them, which gave rise to leeches.

All annelids have a characteristic structure.

Main characteristic: their bilaterally symmetrical body can be divided into a head lobe, a segmented body and a posterior (anal) lobe. The number of body segments can range from tens to several hundred. Dimensions vary from 0.25 mm to 5 m. At the head end of the rings there are sensory organs: eyes, olfactory cells and ciliary fossae, which react to the action of various chemical stimuli and perceive odors, as well as hearing organs, which have a structure similar to locators.

Sensory organs can also be located on the tentacles. The body of annelids is divided into segments in the form of rings. Each segment, in a certain sense, represents an independent part of the whole organism, since the coelom (secondary body cavity) is divided by partitions into segments in accordance with the outer rings.

Therefore, this type is given the name “ringed worms.” The significance of this division of the body is enormous. When damaged, the worm loses the contents of several segments, the rest remain intact, and the animal quickly regenerates.

Metamerism (segmentation) of internal organs, and, accordingly, organ systems of annelids is due to the segmentation of their bodies. The internal environment of the annular organism is coelomic fluid, which fills the coelom in the skin-muscular sac, consisting of the cuticle, skin epithelium and two groups of muscles - circular and longitudinal. In the body cavity, the biochemical constancy of the internal environment is maintained, and the transport, sexual, excretory, and musculoskeletal functions of the body can be realized.

More ancient polychaete worms have parapodia (paired primitive limbs with bristles) on each body segment. Some types of worms move by contracting muscles, while others use parapodia.

The oral opening is located on the ventral side of the first segment. Digestive system of annelids end-to-end

The intestine is divided into the foregut, midgut and hindgut. The circulatory system of annelids is closed, consisting of two main vessels - dorsal and abdominal, which are connected to each other by ring vessels like arteries and veins. The blood of this type of worm can be different colors among different species: red, green or clear. This depends on the chemical structure of the respiratory pigment in the blood. The respiration process is carried out over the entire surface of the worm's body, but some types of worms already have gills.

The excretory system is represented by paired protonephridia, metanephridia or myxonephridia (prototypes of the kidneys), present in each segment. The nervous system of annelids includes a large nerve ganglion (the prototype of the brain) and a ventral nerve cord of smaller ganglia in each segment. Most annelids are dioecious, but some have secondarily developed hermaphroditism (as in the earthworm and leech).

Fertilization occurs inside the body or in the external environment.

The importance of annelids is very great. It is worth noting their important role in food chains in their natural habitat. On the farm, people began to use marine species of ringed fish as a food source for growing valuable commercial fish species, for example sturgeon.

The earthworm has long been used as fishing bait and as bird food. The benefits of earthworms are enormous, as they aerate and loosen the soil, which increases crop yields. In medicine, leeches are widely used for hypertension and increased blood clotting, as they secrete a special substance (hirudin) that has the property of reducing blood clotting and dilating blood vessels.

Related articles:

Worms
2. Flatworms
3. Roundworms
4. Oligochaetes

Structural features of annelids

Annelids are the most highly organized worms. They are the most advanced 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.

Features of the organization of the earthworm

Question 1. What features of ringed worms allowed them to populate most of the planet?

Annelids have acquired a number of features in structure and physiology that allowed them to survive in a variety of environmental conditions.

Firstly, annelids developed specialized organs of locomotion, which gave them relative independence from the physical properties of their habitat.

These are parapodia in polychaetes, which ensure movement in the water column and along the bottom, and bristles in oligochaetes, which help with movement in the soil.

Secondly, in annelids, the nervous system and sensory organs have achieved significant development. Which allows you to increase the activity of your lifestyle.

Thirdly, annelids have mechanisms that make it possible to tolerate unfavorable environmental conditions.

For example, soil species of oligochaetes are characterized by diapause (see answer to the question

2), and some types of leeches are capable of falling into suspended animation (see answer to question 2).

Question 2. What adaptations do annelids have to endure unfavorable conditions?

How does this happen?

In soil species, in the event of unfavorable conditions, worms crawl to depths, curl up into a ball and, secreting mucus, form a protective capsule; they enter diapause - a condition in which the processes of metabolism, growth and development slow down.

Leeches living in cold waters can fall into suspended animation in winter - a state of the body in which life processes are so slow that all visible manifestations of life are absent.

Question 3.

What allows scientists to classify polychaetes, oligochaetes and leeches as one phylum?

All named animals have a number of characteristics that characterize their belonging to one type - annelids. All of them are multicellular animals with an elongated worm-like body, which has bilateral symmetry and consists of individual rings (segmental structure).

The internal cavity of these worms is divided by partitions into separate segments, inside of which there is liquid.

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• what features of annelids allowed them to colonize large

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Encyclopedia "Animal Life" (1970)

To the beginning of the encyclopedia

By first letter
BINANDTONABOUTPRWITHTFSCH

TYPE RINGED WORMS (ANNELIDES)

TO ringworms belong primary ringlets, polychaete and oligochaete worms, leeches and echiurids.

In the phylum of annelids there are about 8 thousand species. These are the most highly organized representatives of the group of worms. The sizes of the rings range from fractions of a millimeter to 2.5 m. 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.

The ringlet's head is equipped with various sensory organs.

Many ringlets have well-developed eyes. Some 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 effects of many chemical irritants.

The ringed birds have well-developed hearing organs, arranged like locators. Recently, hearing organs have been discovered in sea ringed echiurids, 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 in water than in air.

The body of the ringlets consists of rings, or segments. The number of rings can reach several hundred. Other ringlets consist of only a few segments. Each segment to some extent represents an independent unit of the whole organism.

Each segment includes parts of vital organ systems.

Special organs of movement are very characteristic of ringlets. They are located on the sides of each segment and are called parapodia. The word "parapodia" means "foot-like". Parapodia are lobe-shaped outgrowths of the body from which tufts of bristles protrude outward. In some pelagic polychaetes, the length of the parapodia is equal to the diameter of the body. Parapodia are not developed in all ringlets. They are found in primary ringworms and polychaete worms.

In oligochaetes only the setae remain. Primitive leech acanthobdella has bristles. Other leeches move without parapodia and setae. U ehiurid there is no parapodia, and setae are present only at the posterior end of the body.

Parapodia, nodes of the nervous system, excretory organs, gonads and, in some polychaetes, paired intestinal pouches are systematically repeated in each segment. This internal segmentation coincides with the external annulation. The repeated repetition of body segments is called the Greek word “metamerism”.

Metamerism arose in the process of evolution in connection with the elongation of the body of the ancestors of ringlets. Lengthening the body necessitated repeated repetition, first of the organs of movement with their muscles and nervous system, and then of the internal organs.

Extremely characteristic of ringlets is the segmented secondary body cavity, or coelom. This cavity is located between the intestines and the body wall. The body cavity is lined with a continuous layer of epithelial cells, or coelothelium.

These cells form a layer covering the intestines, muscles and all other internal organs. The body cavity is divided into segments by transverse partitions - dissepiments. A longitudinal septum, the mesenterium, runs along the midline of the body, dividing each compartment of the cavity into right and left parts.

The body cavity is filled with liquid, which in its chemical composition is very close to sea water. The fluid filling the body cavity is in continuous motion. The body cavity and abdominal fluid perform important functions. Cavity fluid (like any fluid in general) does not compress and therefore serves as a good “hydraulic skeleton”.

The movement of the cavity fluid can transport various nutritional products, secretions of the endocrine glands, as well as oxygen and carbon dioxide involved in the respiration process inside the body of the ringlets.

Internal partitions protect the body in case of severe injuries and ruptures of the body wall.

For example, an earthworm cut in half does not die. The septa prevent cavity fluid from flowing out of the body. The internal partitions of the rings thus protect them from death. Sea ships and submarines also have internal hermetic partitions. If the side is broken, then the water pouring into the hole fills only one damaged compartment. The remaining compartments, not flooded with water, maintain the buoyancy of the damaged ship.

Likewise, in ringworms, disruption of one segment of their body does not entail the death of the entire animal. But not all annelids have well-developed septa in the body cavity. For example, in echiurids the body cavity does not have partitions. A puncture in the body wall of an echiurid can lead to its death.

In addition to the respiratory and protective role, the secondary cavity acts as a container for reproductive products that mature there before being excreted.

Rings, with few exceptions, have a circulatory system. However, they have no heart. The walls of large vessels themselves contract and push blood through the thinnest capillaries.

In leeches, the functions of the circulatory system and the secondary cavity are so identical that these two systems are combined into a single network of lacunae through which blood flows. In some rings the blood is colorless, in others it is colored green by a pigment called chlorocruorin. Often ringlets have red blood, similar in composition to the blood of vertebrates.

Red blood contains iron, which is part of the hemoglobin pigment. Some ringlets, burrowing into the ground, experience an acute oxygen deficiency.

Therefore, their blood is adapted to bind oxygen especially intensively. For example, the polychaete Magelona papillicornis has a pigment called hemerythrin, which contains five times more iron than hemoglobin.

In ringlets, compared to lower invertebrates, metabolism and respiration are much more intense. Some polychaete ringlets develop special respiratory organs - gills. A network of blood vessels branches out in the gills, and through their wall oxygen penetrates into the blood and is then distributed throughout the body.

Gills can be located on the head, parapodia and tail.

The through intestine of ringlets consists of several sections. Each section of the intestine performs its own special function. The mouth leads into the throat. Some ringlets have strong horny jaws and teeth in their throats, which help them grasp live prey more firmly. In many predatory ringlets, the pharynx serves as a powerful weapon of attack and defense.

The pharynx is followed by the esophagus. This section is often supplied with a muscular wall. Peristaltic movements of the muscles slowly push food into the next sections. In the wall of the esophagus there are glands, the enzyme of which serves for the primary processing of food.

Following the esophagus is the midgut. In some cases, goiter and stomach are developed. The wall of the midgut is formed by epithelium, very rich in glandular cells that produce digestive enzymes. Other cells in the midgut absorb digested food. Some ringlets have a midgut in the form of a straight tube, in others it is curved in loops, and still others have metameric outgrowths on the sides of the intestine.

The hindgut ends at the anus.

Special organs - metanephridia - serve to secrete liquid metabolic products. Often they serve to bring out germ cells - sperm and eggs. Metanephridia begins as a funnel in the body cavity; from the funnel there is a convoluted channel, which opens outward in the next segment.

Each segment contains two metanephridia.

Rings reproduce asexually and sexually. Asexual reproduction is common in aquatic ringworms. At the same time, their long body breaks up into several parts. After some time, each part restores its head and tail.

Sometimes a head with eyes, tentacles and a brain forms in the middle of the worm's body before it splits into parts. In this case, the separated parts already have a head with all the necessary sensory organs. Polychaetes and oligochaetes are relatively good at restoring lost body parts. Leeches and echiurids do not have this ability. These ringlets have lost their segmented body cavity. This is partly why, apparently, they lack the ability to reproduce asexually and restore lost parts.

Fertilization of eggs in ringed fish most often occurs outside the body of the mother's body. In this case, males and females simultaneously release reproductive cells into the water, where fertilization occurs.

In marine polychaetes and echiurids, the crushing of fertilized eggs leads to the development of a larva, which is not at all similar to adult animals and is called a trochophore.

The trochophore lives in the surface layers of water for a short time, and then settles to the bottom and gradually turns into an adult organism.

Freshwater and terrestrial ringworms are most often hermaphrodites and have direct development.

Freshwater and terrestrial ringworms do not have a free larva. This is due to the fact that fresh water has a salt composition of a completely different nature than sea water. Sea water is more favorable for the development of life. Fresh water even contains some toxic compounds (for example, magnesium) and is less suitable for the development of organisms.

Therefore, the development of freshwater animals almost always occurs under the cover of special low-permeable shells. Even more dense shells - shells - are formed in the eggs of ground rings.

Dense shells here protect the eggs from mechanical damage and from drying out under the scorching rays of the sun.

The practical importance of annelids is increasingly increasing due to the development of the intensity of biological research.

Here in the USSR, for the first time in the history of world science, the acclimatization of some invertebrates was carried out to strengthen the food supply of the sea. For example, the polychaete Nereis, acclimatized in the Caspian Sea, became the most important food item for sturgeon and other fish.

Earthworms not only serve as fishing bait and food for birds.

They bring great benefits to humans by loosening the soil, making it more porous. This facilitates the free penetration of air and water to the roots of plants and increases crop yields.

While burrowing in the ground, worms swallow pieces of soil, crush them and throw them to the surface well mixed with organic matter. The amount of soil brought to the surface by worms is amazingly large. If we were to distribute the soil plowed by earthworms every 10 years over the entire surface of the land, we would get a layer of fertile soil 5 cm thick.

Leeches are used in medical practice for hypertension and the threat of hemorrhage.

They release the substance hirudin into the blood, which prevents blood clotting and promotes the dilation of blood vessels.

Type of rings includes several classes. The most primitive are the marine primary rings - archiannelids.

Polychaetes and echiurids- inhabitants of the sea. Oligochaete ringlets and leeches- mainly inhabitants of fresh water and soil.

To the beginning of the encyclopedia

Annelids are a fairly large group of invertebrate organisms. In addition, they are considered the most organized representatives of worms. They live mainly in fresh and salt water bodies, as well as in soil. Some species of tropical leeches have adapted to a terrestrial way of existence.

Type Annelid worms: general characteristics

The sizes of representatives of this group range from a few millimeters to six meters. A rather characteristic feature of such an organism is the presence of segmentation - their body consists of many rings, which explains the name of the type. External ringing corresponds to internal segmentation. That is why, when the body is wounded or damaged, the annelid loses only a few segments, which are soon regenerated.

From the outside, the body is covered with a cuticle that is not shed. Chitinous bristles grow from it - another characteristic feature of this species. Some representatives may have parapodia on their segments - rather primitive limbs, which in some cases are equipped with sensitive bristles or gills.

Ringed worms: structural features of internal organs

Representatives of this type are characterized by the presence of a secondary body cavity - the coelom. This cavity is filled with a specific liquid, thanks to which normal indicators are maintained.

There is a skin-muscular sac, which consists of epithelial balls, as well as muscles grouped into circular and longitudinal groups.

The digestive system is continuous, beginning with the mouth and ending with the anus. Annelids have three intestinal sections - anterior, middle and posterior. Some species have primitive salivary glands.

The body breathes through the skin. The only exceptions are some marine species of animals that have gills on their parapodia. As for the circulatory system, it is usually closed. It consists of the abdominal and dorsal aorta, which are connected to each other by annular vessels. These organisms do not have a heart - the movement of blood is ensured by contraction of the dorsal aorta. Blood can contain a wide variety of respiratory pigments.

Still quite simple. At the anterior end of the body there is a large nerve ganglion, which performs the functions of the brain. A nerve chain extends from it, which in each segment of the body forms a small ganglion - a collection of neurons. are represented by the eyes, organs of chemical sensitivity, as well as mechanoreceptors, which are distributed throughout the body of the worm.

Ringed worms: features of reproduction and development

Organisms of this group can be either heterosexual or hermaphrodite (they are much less common). For example, it has a hermaphroditic reproductive system, but two individuals are needed for fertilization. It can occur both in the external environment and through the introduction of sperm into the internal canals of the female.

Another interesting fact is that annelids with pronounced segmentation have a tendency to rapid and intense regeneration. Due to this, some species are characterized by direct development of organisms, without metamorphosis.

It is worth noting that the role of annelids is quite significant. For example, the well-known one is responsible for soil aeration. This group also includes leeches, which are often used in modern medicine. Hirudin, produced by the leech, is of particular value, as it thins the blood and is used in the fight against thrombosis and other dangerous diseases.