Kinds of worms: description, structure, their role in nature

There are three main types of worms: Flat, Round and Ring. Each of them is divided into classes into which species of worms are united by the similarity of certain characteristics. In this article, we describe the types and classes. We will also touch upon some of their types. You will learn basic information about worms: their structure, their characteristics, their role in nature.

Type Flatworms

Its representatives live in marine and fresh water bodies, in tropical forests (their wet bedding). These are different types of worms-parasites. They differ in the shape of the body. A flat leaf-like two-sidedly symmetrical or ribbon-like body has a flat worm. Species belonging to this type have a muscular, integumentary, excretory, digestive, genital, nervous systems that develop from 3 germ layers (inner, outer and middle layers of cells). In total, more than 12 thousand of their species are known. Main classes: Flukes, Planariae, Tape worms.

Class of Planaria

Black, brown and white planarians live in silted places of ponds, lakes and streams. At the anterior end of the body they have two eyelets, with which they distinguish darkness from light. The pharynx is on the ventral side. Planaria are predators. They hunt small aquatic animals, which are torn to pieces or swallowed whole. They are moved by the work of cilia. From 1 to 3 cm is the body length of freshwater planaria.

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, annular and longitudinal. The worm (species related to planarians) due to their relaxation and contraction is shortened or lengthened, can lift up parts of the body. The mass of small cells is under the muscles. This is the main tissue in which the internal organs are located. The mouth with a muscular pharynx, and also the three-branch intestine make up the digestive system. The walls of the intestine are formed by a layer of bulbous cells. They grab food particles and then digest them. Digestive enzymes release into the intestinal cavity the glandular cells of its wall. Nutrients, resulting from the splitting of food, penetrate immediately into the tissues of the body. Undigested residues are removed through the mouth.

Ciliated worms breathe oxygen dissolved in water. This process is carried out by the entire surface of the body. Their nervous system consists of clusters of cells - the head paired nodes, the nerve trunks that depart from them, as well as the nerve branches. Planarians mostly have eyes (from 1 to several dozen pairs). In the skin they have tactile cells, and some members of this class have small paired tentacles at the anterior end of the body.

Class Flukes

It includes species of parasitic worms, which have a leaf-shaped body without cilia. The most famous representative of this class is the hepatic trematode. About 3 cm is the length of his body. This worm settles in the ducts of the liver of sheep, cows and goats, being held in place by the perioral and abdominal suckers. It feeds on the blood, as well as the cells of the organ that the host destroys. The hepatic trematode has a pharynx, a mouth, a two-branched intestine, and also other systems of organs. Of these, the nervous and muscular are not as developed as in free-living flatworms.

Class Tape Worms

It includes parasitic worms having a ribbon-like body, which consists of an undivided short neck, a small head and a plurality of segments. The most famous types of tapeworms are pork and bovine chains, echinococcus, broad ribbon. Where do these organisms live? Bovine and pork chain live in the human intestine, echinococcus - in wolves and dogs, and a wide ribbon parasitizes in the body of predatory mammals and humans. Chains can reach a length of ten meters and even more (for example, bullish). These types of tapeworms on the head have hooks and suckers (echinococcus, pork tapeworm), or only suckers (as in bovine tapeworms), or 2 deep suction grooves (for example, in a wide ribbon).

The nervous and muscular systems of this class are poorly developed. Skin cells represent their senses. They disappeared digestive system: tapeworms suck nutrients from the host's intestines with the entire surface of their body.

Echinococcus

Echinococcus is a small worm, the length of which is up to 6 mm. Its feature is that the segments do not separate from its body, unlike the lentils and the chain. The main owners of this worm are a wolf, a dog, a cat, a fox; Intermediate - a cow, a sheep, a pig, a deer, a goat (maybe also a person). Large lungs develop in the lungs, liver, bones, muscles of the latter. In each of them, grandchildren and daughter departments are formed. Inside them there are heads of parasites. The main owners can become infected by eating meat with these blisters, and the intermediate ones after eating food that is contaminated by the excrement of sick wolves, dogs and other major hosts of this worm.

Type Roundworms (or Primary)

They have a non-segmented body, usually long, round in cross section. This is the main similarity of roundworms of different species. On the surface of their skin there is a dense, non-cellular formation called the cuticle. They have in the body a cavity that exists because of the destruction of the cells that make up the main tissue, between the internal organs and the wall of the body. Their musculature is represented by a layer of longitudinal fibers. That's why roundworms can only bend. Their intestines look like a tube. It begins with a mouth opening and ends with anal (anal). Representatives of this type live in the seas, soil, fresh water. The difference between roundworms of different species is that some of them are plant pests, while others are parasites on humans and animals. More than 400 thousand species are found in this type. The largest class is the Nematode class.

Class of Nematode

Nematodes are herbivorous worms that live on the roots of kidney beans, garlic, onions and other garden plants, in potato shoots under the ground (the species Stem cell potato nematode), in strawberry organs (strawberry nematode). About 1.5 mm is the length of their almost transparent body. The rotary apparatus of the piercing type of the nematode pierces the tissues of the plants, and then substances that dissolve the contents and walls of the cells are introduced. Then they suck the formed substances, using for this purpose the expanded part of the esophagus. How the pump operates its muscular walls. In the intestine, food is digested. Many nematodes live in the earth and use plant remains as food. They play an important role in soil formation.

Some members of this class are parasites. They live in the host organism (humans and animals). This, for example, ascarids (pork, horse, human, etc.), trichinella, pinworms, vysokoglavy, rishty.

Ascaris

Ascarids live in the small intestine of the host. Up to 40 cm is the body length of the female (males somewhat smaller). They eat half-digested food. Females lay eggs (about 200 pieces per day), which are discharged outside with human feces. In them, mobile larvae develop in the external environment. When eating poorly washed vegetables, as well as a meal flattered by flies, a person becomes infected with ascarids. Larvae in the intestines of the host come out of the eggs. After that, they enter the blood vessels and through them migrate to the lungs, heart and liver. The grown-up larvae enter the mouth, after which they enter the intestines, in which they become adults. They feed on the food of the host, whose organism is poisoned by its secretions. As a result of their activity ulcers are formed on the walls of the intestine, and with a large number of parasites, its obstruction and rupture of walls may occur.

Type Ringworms

Its representatives live in fresh water bodies, seas, soil. Their body is long, divided into annular segments (segments) by transverse constrictions. We all know the appearance of earthworms. Their length varies from 2 to 30 cm. The body is divided into segments, which can be from 80 to 300.

Internal segmentation corresponds to external dismemberment. The body cavity of representatives of this type lays a layer of integumentary cells. The border of this cavity is located in each segment. Ringworms have a circulatory system, and many of them have a respiratory system. Their digestive, muscular, nervous, excretory systems, as well as sense organs are more perfect than round and flat worms. "Skin" consists of a layer of integument cells. Under it there are longitudinal and ring muscles. In annular worms, the digestive system is divided into the pharynx, the oral cavity, the esophagus, the stomach (in separate groups), and the intestine. Undigested food remains removed through the anus.

The circulatory system of annelids

All types of annelid worms have a circulatory system formed by the ventral and dorsal blood vessels, which are joined together by annular blood vessels. From the latter depart small vessels that branch and form a network of capillaries in internal organs and skin. Blood moves mainly due to relaxation and contraction of the walls surrounding the esophagus of the ring vessels. It transfers oxygen and nutrients that enter it to all organs, and also releases the body from metabolic products. Types of annelids are characterized by a closed circulatory system (this biological fluid is located within the vessels and does not pour into the body cavity). The skin breathes. Some species of worms (marine) have gills.

Nervous system of annelids

The nervous system in representatives of this type consists of paired nasopharyngeal and supra-angular nerve nodes, which are connected to the ring by nerve strings, as well as nodes of the chain (abdominal). The twin node is located in each segment of annelid worms. To all organs nerves leave. Various stimuli (for example, light) affect sensitive cells. Excitation, which has arisen in them, is transmitted to the nearest nerve node along the nerve fibers, and then to the muscles (along other fibers) and causes their contraction. In this way reflexes are carried out. The majority of representatives of this type have no sense organs.

The main classes of annelids

Ringed can be both hermaphrodites and dioecious. How many worms (species) does this type include? Today there are about 9 thousand of them, among which the main classes are distinguished: Polychaete and Feminine. The former live primarily in the soil (for example, a type of earthworm, such as northerners), as well as in fresh water bodies (in particular, tubers). Polychaete worms are a class that includes sand dwellers, Nereids and Serpula. Peskozhily dwell in dug mink, the Nereids - mostly in the muddy ground, in the coastal parts of the seas, the Serpula - in the "houses", which they build from various materials.

Nereids

Nereids are species of worms that are most diverse in the seas. Their color is green or reddish. The anterior segments of the body form the head. She has palps, mouth, tentacles (organs of touch), as well as 2 pairs of eyes and 2 holes behind them (these are the organs of smell). On the segments along the sides of the body are paired muscular short lobate-like outgrowths with tufts of setae. It's a limb. In addition, the Nereids develop gills - special outgrowths of the skin. Often, these are dioecious animals. In the water, fertilization of eggs takes place, from which free-floating larvae with a ciliary band appear. They eventually turn into adult worms.

The Importance of Ringworms

They are the food of many species of crabs, fish (Nereids and other sea worms). Earthworms are the main food of hedgehogs, moles, starlings, toads and other animals. Ringed, feeding on silt, as well as various suspensions, release water from excess organic substances. In addition, rain and some other soil species of worms eat plant remains, and also let soil through their intestines. This they contribute to the formation of humus.

So, you got acquainted with the above classification, learned about what types, classes and types of worms exist. Photos from this article give a visual representation of some of their representatives. Worms are rather original living organisms. Some of them are parasites, while others are of great benefit to our planet.