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 annelids that you can find that some ringlets have sharpened 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 logical thinking. This is due to the fact that worms can find sharp corners.

If we consider internal structure, then one 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 main 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

Nervous system, sensory organs

Nodal type: paired cephalic ganglion, paired peripharyngeal cords connecting to the abdominal ones. Many annelids have sensory organs: eyes, olfactory pits, and organs of touch. In earthworms (due to their underground lifestyle), the sense organs are represented by tactile and photosensitive cells throughout the surface of the body.

Reproduction Dioecious or secondary hermaphrodites. Fertilization is cross, internal (in aquatic forms in water). Development is direct. Some marine annelids with metamorphosis have a floating larva. Capable of regeneration. Let's consider a number of animals that biology studies - the type Annelids. We will learn about their types, lifestyle and habitat, internal and external structure.

general characteristics Annelids (also called simply ringworms, or annelids) are one of their extensive species, which includes, according to various sources, about 18 thousand species. They are non-skeletal vertebrates that not only participate in the destruction organic matter

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

The most famous are 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 actively participate in soil formation.

Classes of annelids

Respiratory organs and circulatory system of the annelid worm

Oligochaete worms breathe over the entire surface of their body. But polychaetes have respiratory organs - gills. They are bushy, leaf-shaped or feathery outgrowths of parapodia, penetrated by a large number of blood vessels.

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

The circulatory system of the annelid 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 the worms to live in conditions of oxygen deficiency.

Digestive and excretory systems

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

The oral cavity, which is also called the buccal region, is capable of turning inside out. Behind this section are the jaws, which are curved inward. This apparatus is used to capture prey.

Next comes the mesodeum, the midgut. The structure of this section is uniform along the entire length of the body. The midgut contracts and expands, and is where food is digested. The hindgut is short and ends at the anus.

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

Nervous system and sensory organs

All classes of annelids have nervous system ganglion type. It consists of a peripharyngeal nerve ring, which is formed by the united suprapharyngeal and subpharyngeal ganglia, and of pairs of a chain of abdominal ganglia located in each segment.

The sense organs of ringworms are well developed. Worms have acute vision, hearing, smell, and touch. Some annelids not only capture light, but can also emit it themselves.

Breathing through the entire surface of the body.

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

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

Budding is less common. Of particular interest are species in which the budding process can cover the entire body, when the posterior ends bud from each segment. During 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 those who reproduce sexually, fertilization is external. Animals of different sexes release their reproductive cells into the water, where the fusion of eggs and sperm occurs. From fertilized eggs, larvae emerge that are not similar to adults. Freshwater and terrestrial annelids do not have a larval stage; they are immediately born similar in structure to adult individuals.

Class Polychaetes

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

Nereids actively swim and can burrow into mud. They have a serpentine body and many parapodia; the animals make passages using a retractable pharynx. Sand veins by appearance They resemble earthworms and burrow deep into the sand. An interesting characteristic of the annelid sandworm is that it moves in the sand hydraulically, pushing cavity fluid from one segment to another.

Also interesting are sessile worms, serpulids, which live in spiral or twisted calcareous tubes. Serpulids only stick out their heads with large fan-shaped gills from their home.

Class Oligochaetes

Oligochaete worms primarily live in soil and fresh waters, are found sporadically in the seas. The structure of annelids of this class is distinguished by the absence of parapodia, homonomic segmentation of the body, and the presence of a glandular girdle in mature individuals.

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

Very common and familiar to all oligochaetes are earthworms that live in the soil. The body of the worm can be from several centimeters to three meters (such giants live in Australia). Small, about a centimeter in size, whitish enchytraeid worms are also often found in the soil.

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

Leech class

All leeches are predators, mostly feeding on the blood of warm-blooded animals, worms, mollusks, and fish. The habitat of annelids of the leech class is very diverse. Most often, leeches are found in fresh water bodies and 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 a proboscis. In the oral cavity there are numerous salivary glands that can secrete a poisonous secretion, and the pharynx acts as a pump during sucking.

Echiurida class

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

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

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 Annelids: 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.

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 minerals, promote 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 allows for regeneration.

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. Therapeutic effect 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 does it expire required time exposure, the leech is removed, but the bite site continues to bleed. It may take up to 16 hours for the bleeding to stop completely.