The meaning of the rings. Meaning of annelids Type annelids meaning in nature

Introduction

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

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

When a predator attacks a polychaete and begins to tear and tear its body, the tail section of the worm flashes brightly, attracting the attention of the “aggressor”. He grabs the luminous part of the body, and the second (head) disappears in the darkness. Subsequently, the worm's tail grows back. It turns out that annelids, long before lizards, were the inventors of a clever trick with a discarded tail.

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

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

1. General characteristics of the type of annelids

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

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

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

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

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

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

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

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

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

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

There are three main types of worms: Flatworms, Roundworms and Annelids. Each of them is divided into classes into which types of worms are grouped based on the similarity of certain characteristics. In this article we will describe types and classes. We will also touch on their individual types. You will learn basic information about worms: their structure, characteristic features, role in nature.

Type Flatworms

Black, brown and live in silty areas of ponds, lakes and streams. At the front end of the body they have 2 ocelli, with the help of which they distinguish darkness from light. The pharynx is located on the ventral side. Planarians are predators. They hunt small aquatic animals, which they tear into pieces or swallow whole. They move thanks to the work of cilia. The body length of freshwater planarians ranges from 1 to 3 cm.

Their body is covered with elongated cells with special cilia (therefore they are also called ciliated worms). Deeper are 3 layers of muscle fibers - diagonal, circular and longitudinal. The worm (species related to planarians), due to their relaxation and contraction, shortens or lengthens, and can lift parts of the body. A mass of small cells is located under the muscles. This is the main tissue in which the internal organs are located. The mouth with a muscular pharynx, as well as the three-branched intestine, make up the digestive system. The intestinal walls are formed by a layer of flask-shaped cells. They capture food particles and then digest them. Digestive enzymes release glandular cells of the intestinal wall into the intestinal cavity. Nutrients resulting from the breakdown of food penetrate directly into the body tissues. Undigested residues are removed through the mouth.

Ciliated worms breathe oxygen dissolved in water. This process is carried out over the entire surface of the body. they consist of clusters of cells - paired head nodes, nerve trunks extending from them, as well as nerve branches. Planarians mostly have eyes (from 1 to several dozen pairs). They have tactile cells in their skin, and some representatives of this class have small paired tentacles at the anterior end of the body.

Class Flukes

Class Tapeworms

The nervous and muscular systems of this class are poorly developed. Skin cells represent their sensory organs. Their digestive system has disappeared: tapeworms absorb nutrients from the host’s intestines with the entire surface of their body.

Echinococcus

Class Nematodes

Nematodes are herbivorous worms that live on the roots of beans, garlic, onions and other garden plants, in underground shoots of potatoes (species Stem potato nematode), in the organs of strawberries (Strawberry nematode). The length of their almost transparent body is about 1.5 mm. With their piercing-type mouthparts, nematodes pierce plant tissue, after which they inject substances that dissolve the contents and walls of the cells. They then absorb the resulting substances using the expanded part of the esophagus. Its muscular walls act like a pump. Food is digested in the intestines. Many nematodes live in the ground and use plant debris as food. They play an important role in soil formation.

Roundworms

Its representatives live in fresh water bodies, seas, and soil. Their body is long, divided into ring-shaped segments (segments) by transverse constrictions. We are all familiar with the appearance of earthworms. Their length ranges from 2 to 30 cm. The body is divided into segments, which can be from 80 to 300.

Internal segmentation corresponds to external dissection. The body cavity of representatives of this type is lined with a layer of integumentary cells. A delimited portion of this cavity is located in each segment. Annelids have a circulatory system, and many of them also have a respiratory system. Their digestive, muscular, nervous, excretory systems, as well as sensory organs, are more advanced than those of round and flatworms. Their “skin” consists of a layer of integumentary cells. Beneath it are the longitudinal and circular muscles. In annelids, the digestive system is divided into the pharynx, oral cavity, esophagus, stomach (in certain groups), and intestines. Undigested food remains are removed through the anus.

Circulatory system of annelids

All types of annelids have a circulatory system formed by abdominal and dorsal blood vessels, which are connected to each other by ring vessels. Small vessels depart from the latter, which branch and form a network of capillaries in the internal organs and skin. Blood moves mainly due to the relaxation and contraction of the walls of the annular vessels covering the esophagus. It carries oxygen and nutrients supplied to it to all organs, and also relieves the body of metabolic products. Species of annelids are characterized by a closed circulatory system (this biological fluid is located within the vessels and does not flow into the body cavity). Breathing occurs through the skin. Some species have gills.

annelids

The nervous system of representatives of this type consists of paired subpharyngeal and suprapharyngeal nerve nodes, which are connected in a ring by nerve cords, as well as nodes of the chain (abdominal). A paired node is found in each segment of annelids. Nerves extend to all organs. Various stimuli (for example, light) affect sensitive cells. The excitation that arises in them is transmitted to the nearest nerve node along the nerve fibers, and then to the muscles (via other fibers) and causes their contraction. This is how reflexes are carried out. Most representatives of this type do not have sense organs.

Main classes of annelids

Ringed fish can be either hermaphrodite or dioecious. How many worms (species) does this type include? Today there are about 9 thousand of them, among which the main classes stand out: Polychaetes and Oligochaetes. The former live mainly in the soil (for example, such a type of earthworms as burrows), as well as in fresh water bodies (in particular, tubifex worms). Polychaete worms are a class that includes sandworms, nereids and serpules. Sandworms live in burrows they dig, Nereids live mainly in muddy soil, in coastal parts of the seas, Serpuls live in “houses” that they build from various materials.

Nereids

Nereids are the species of worms that are most diverse in the seas. Their color is green or reddish. The head is formed by the anterior segments of the body. She has palps, a mouth, tentacles (tactile organs), as well as 2 pairs of eyes and 2 pits located behind them (these are olfactory organs). On the segments on the sides of the body there are paired muscular short lobe-shaped projections with tufts of bristles. These are limbs. In addition, Nereids develop gills - special skin outgrowths. Often these are dioecious animals. Fertilization of eggs occurs in water, from which free-swimming larvae with a belt of cilia emerge. They eventually develop into adult worms.

The meaning of annelids

They are food for many types of crabs and fish (nereids and other sea worms). Earthworms are the main food of hedgehogs, moles, starlings, toads and other animals. Ringed fish, feeding on silt and various suspensions, rid the water of excess organic matter. In addition, earthworms and some other soil worms eat plant debris and also pass soil through their intestines. By doing this they contribute to the formation of humus.

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

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

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

The biological and practical significance of polychaete worms in the ocean is very great. The biological significance of polychaetes lies in the fact that they represent an important link in trophic chains, and are also important as organisms that take part in the purification of sea water and the processing of organic matter.

CLASS POLYCHETATE WORMS

Habitats, structure and lifestyle.

Oligochaete worms live mainly in the soil (earthworms) and in fresh water bodies (tubifex). Earthworms (about 1,500 species) have a long body consisting of 80 or more rings. On the sides of each ring, except for the oral one, there are setae (usually two tufts). There are no sensory organs (there are olfactory, tactile, gustatory, and light-sensitive cells). Earthworms feed mainly on rotting organic matter and the bacteria they contain. Food is captured with the mouth located on the first segment of the body. Earthworms come to the soil surface at dusk and at night. They move by alternately contracting and relaxing the circular and longitudinal muscles. The bristles have a supporting role in moving and making passages in the soil. Moving in loose soil, the worm pushes its particles apart, and in dense soil passes them through the intestines. With the onset of drought or cold weather, earthworms go deep into the soil. Tubifex live at the bottom of reservoirs, forming dense settlements. The front part of their filamentous body (2/3) is usually located in a tube of mucus and soil particles, the back part is free and makes “breathing” movements. Tubifex worms feed on organic soil debris. Reproduction. Earthworms are hermaphrodites. Before laying eggs, two worms approach each other with their anterior ends of the body and exchange seminal fluid containing sperm, which enters their seminal receptacles. Then, when the eggs mature, a cocoon begins to form on the girdle of each worm (this is a glandular thickening of the skin of several specific segments): the girdle secretes mucus, which forms a muff. Contractions of the worm's body move the muff towards the anterior end of the body. It contains eggs and fluid with sperm. The muff turns into a cocoon, where fertilization of the eggs occurs. The developed worms break the cocoon and emerge from it.

CLASS POLYCHETATE WORMS

Polychaete worms include various types of nereids, sandworms, and serpules. Nereids live mainly in coastal parts of the seas, in muddy soil; Sandworms - in the minks they dug; serpuls sit in "houses" built from various materials. At their front end there is a plume of tentacles, with which they filter water.

Nereids are most diverse in the seas. They have a reddish or green color, cast in all the colors of the rainbow. The anterior segments of the body form a head with a mouth, palps and tentacles (tactile organs), two pairs of ocelli and two pits behind them (olfactory organs). On the sides of the body of Nereids, on the segments there are short, muscular paired lobe-like projections - parapodia with tufts of bristles. These are the limbs of Nereids. Nereids develop special skin outgrowths - gills.

Nereids are dioecious animals. Fertilization of eggs occurs in water. The eggs hatch into free-swimming larvae with a belt of cilia. Over time, the larvae take on the appearance of adult worms.

ORIGIN AND IMPORTANCE OF ANNELED WORMS

Origin. Scientists believe that ancient annelids evolved from ancient free-living flatworms. Proof of this is, for example, the presence of cilia in the larvae of marine annelids, excretory organs beginning with stellate cells with a ciliated flame, and the similarity of the nervous system with the nervous system of planarians. Polychaete worms are older than oligochaete worms, although they have the most complex structure. The simplification of the structure of oligochaete worms occurred mainly in connection with the transition to life in the soil.

Meaning. Nereids and other sea worms are the main food of many species of fish, crabs and other sea inhabitants; Many fish and freshwater invertebrates feed on tubifex; earthworms are the main food of moles, hedgehogs, toads, starlings and other land animals. By feeding on silt and various suspensions, annelids rid the water of excess organic matter. Earthworms and some other soil worms, by eating various plant debris and passing soil through their intestines, contribute to the formation of humus. The burrows they make are filled with air necessary for the breathing of plant roots and various soil-forming organisms living in the ground.

The phylum annelids, or ringworms, covers about 9,000 species of higher worms. This group of animals is of great importance for understanding the phylogeny of higher invertebrates. Annelids have a higher organization than flatworms and roundworms. They live in sea and fresh waters, as well as in soil. The type is divided into several classes. Let's get acquainted with a representative of the class of oligochaetes (earthworm).

general characteristics

The body of the ringlets consists of segments. The body segments are externally identical. Each segment, except the anterior one, which bears the oral opening, is equipped with small bristles. These are the last remnants of the disappeared pair of podia.

Annelids have a well-developed skin-muscle sac, consisting of one layer of epithelium and two layers of muscles: an outer layer of circular muscles and an inner layer formed by longitudinal muscle fibers.

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

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

Organ systems

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

excretory

Each segment of the earthworm has a paired organ of the excretory system, consisting of a funnel and a convoluted tubule. Waste products from the body cavity enter the funnel. A canaliculus extends from the funnel, which enters the adjacent segment, forms several loops and opens outwards with an excretory pore in the lateral wall of the body. Both the funnel and the tubule are equipped with cilia, causing the movement of the secreted fluid. Such excretory organs are called metanephridia.

Circulatory and respiratory systems

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

In earthworms, gas exchange occurs through the skin, rich in blood vessels, and some ringworms have gills.

Digestive

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

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

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

Some predatory annelids have cuticular “teeth” that are used to grasp prey. A layer of muscle appears in the intestinal wall, which ensures its independent peristalsis. The midgut passes into a short posterior intestine, ending in the anus.

Nervous system

Significantly more complicated compared to flat and roundworms. Around the pharynx there is a peripharyngeal nerve ring, consisting of the suprapharyngeal and subpharyngeal nodes, connected by jumpers.

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

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

Regeneration

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

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

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

Earthworms are hermaphrodites, but among the ringworms there are also dioecious forms. The earthworm has a girdle on its body that produces mucus from which the cocoon is formed. Eggs are laid in it and their development occurs there.

Development

In earthworms, development is direct, but in some ringworms a larva develops from a fertilized egg, i.e. development occurs with metamorphosis.

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

The importance of annelids in nature

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

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

Earthworms feed on plant debris found in the soil, which is passed through their guts, leaving piles of excrement consisting of soil on the surface. By doing this, they contribute to mixing and, consequently, loosening the soil, as well as enriching it with organic substances, improving the water and gas balance of the soil. Even Charles Darwin noted the beneficial effect of annelids on soil fertility.

The value in medicine of annelids

TO ringworms include the well-known leeches. They are of great importance in medicine. They are used in the treatment of hypertension, decreased blood clotting, and blood resorption. For this purpose, leeches are specially grown and their enzyme hydrurin is extracted, which has medicinal properties.

Biological significance of annelids in the ecosystem

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

Polychaetes used as food for fish.

• Freshwater representatives of oligochaetes They are also fish food and are often used for aquarium fish. Pipe makers from the class of Oligochaetes they function as a filter for reservoirs. They are also called ground eaters. By ingesting soil, they directly digest organic matter, turning them into useful minerals that the soil needs so much.
• Earthworms are also consumers in the ecosystem. Many animals feed on them: moles, shrews, frogs, many birds and some predatory beetles.

Note 1

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

The importance of worms in soil formation

As a result of digging up the earth and making passages, worms increase the porosity of the soil, thus making it looser and increasing in volume up to $30\%$. Loose soil facilitates access to deep layers of soil, water and atmospheric air. This is necessary for plant roots and the activity of beneficial microorganisms that are found in the soil. Constant mixing of the surface layers of the soil by worms saturates it with foliage and other organic residues.

Worms, through their vital activity, change the chemical properties of the soil. So mixed soil with the intestinal mucus of the worm contains more calcium, magnesium, ammonia, nitrates and phosphoric acid. The glands of the esophagus help neutralize harmful soil acids. Worm waste dries out and breaks down into microporous lumps that are not washed away by water.

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

Note 2

Enchytraeids feed on organic debris and participate in soil formation along with earthworms.

Negative meaning of annelids

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

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