There are three main types of worms: Flatworms, Roundworms and Annelids. Each of them is divided into classes into which the types of worms are combined according to the similarity of certain signs. 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, characteristics, role in nature.
Type Flatworms
Its representatives live in marine and fresh water bodies, in tropical forests (their wet litter). These are different types of parasitic worms. They differ in body shape. A flat, leaf-shaped, bilaterally symmetrical or ribbon-shaped body has a flatworm. Species belonging to this type have muscular, integumentary, excretory, digestive, reproductive, 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, Planarians, Tapeworms.
Planaria class
Black, brown and white planarians live in silted places of ponds, lakes andstreams. At the front end of the body, they have 2 eyes, with which they distinguish darkness from light. The pharynx is located on the ventral side. Planarians are predators. They prey on small aquatic animals that are torn apart or swallowed whole. They move thanks to the work of cilia. From 1 to 3 cm is the body length of freshwater planarians.
Their body is covered with elongated cells with special cilia (which is why they are also called ciliary worms). Deeper are 3 layers of muscle fibers - diagonal, annular and longitudinal. The worm (species related to planarians), due to their relaxation and contraction, shortens or lengthens, 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. A mouth with a muscular pharynx, as well as a three-branched intestine, make up the digestive system. The walls of the intestine are formed by a layer of flask-shaped cells. They capture food particles and then digest them. Digestive enzymes secrete glandular cells in the intestinal wall into the intestinal cavity. The nutrients formed as a result of the breakdown of food penetrate immediately into the tissues of the body. Undigested residues are removed through the mouth.
Ciliary 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 - head pair nodes, nerve trunks extending from them, as well as nerve branches. Most planarians have eyes (from 1 to several dozensteam). They have tactile cells in their skin, and some representatives of this class have small paired tentacles at the front end of the body.
Class Flukes
It includes species of parasitic worms that have a leaf-shaped body without cilia. The best known member of this class is the liver fluke. About 3 cm is the length of his body. This worm settles in the liver ducts of sheep, cows and goats, holding in place with the help of perioral and ventral suckers. It feeds on blood as well as the destructible cells of its host's organ. The liver fluke has a pharynx, mouth, biramous intestine, and other organ systems. Of these, the nervous and muscular are not as developed as in free-living flatworms.
Class Tapeworms
It includes parasitic worms with a ribbon-like body, which consists of an undivided short neck, a small head and many segments. The most famous types of tapeworms are pork and bovine tapeworms, echinococcus, and a wide tapeworm. Where do these organisms live? Bovine and pork tapeworms live in the human intestines, echinococcus in wolves and dogs, and a wide tapeworm parasitizes in the body of predatory mammals and humans. Chains can reach a length of ten meters or even more (for example, bovine). These types of tapeworms have hooks and suckers on the head (echinococcus, tapeworm), or only suckers (like a bovine tapeworm), or 2 deep suction grooves (for example, a wide tapeworm).
The nervous and muscular systems of this class are poorly developed. Skin cells represent their sense organs. Their digestive system has disappeared: tapeworms absorb 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 peculiarity is that the segments do not separate from its body, unlike tapeworms and tapeworms. The main hosts of this worm are the wolf, dog, cat, fox; intermediate - a cow, a sheep, a pig, a deer, a goat (may also be a person). Large blisters develop in the lungs, liver, bones, and muscles of the latter. In each of them, grandchildren and subsidiaries are formed. Inside them are the heads of parasites. Primary hosts can become infected by eating meat with these blisters, while intermediate hosts can become infected by eating food that is contaminated with the faeces of sick wolves, dogs, and other primary hosts of this worm.
Type Roundworms (or Primocavitary)
They have a non-segmented body, usually long, rounded 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 a cavity in the body, which exists due to the destruction of the cells that make up the main tissue, between the internal organs and the body wall. Their muscles are represented by a layer of longitudinal fibers. That is why roundworms can only bend. Their intestines are tube-like. It begins with the oral opening and ends with the anus (anal). Representatives of this type live in the seas, soil, fresh water. The difference between roundworms of different species lies in the fact that some of them are plant pests, while others parasitize humans and animals. More than 400 thousand species are in this type. The largest class is the Nematode class.
Class Nematodes
Nematodes are herbivorous worms that live on the roots of beans, garlic, onions and other garden plants, in underground potato shoots (species Stem potato nematode), in the organs of strawberries (Strawberry nematode). About 1.5 mm is the length of their almost transparent body. The nematodes pierce the tissues of plants with the mouth apparatus of the stabbing type, after which they introduce substances that dissolve the contents and walls of the cells. Then they absorb the resulting substances, using the expanded part of the esophagus for this. As a pump, its muscular walls act. 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.
Some representatives of this class are parasites. They live in the host organism (human and animals). These are, for example, roundworms (pork, horse, human, etc.), trichinella, pinworms, whipworms, guinea worms.
Ascarids
Ascarids live in the small intestine of the host. Up to 40 cm is the length of the body of the female (males are somewhat smaller). They eat semi-digested food. The females lay eggs(about 200 pieces per day), which are brought out with human feces. In them, mobile larvae develop in the external environment. When eating poorly washed vegetables, as well as food chosen by flies, a person becomes infected with roundworms. The larvae in the intestines of the host emerge from the eggs. After that, they are introduced into the blood vessels and migrate through them to the lungs, heart and liver. The grown larvae enter the mouth, and then into the intestines, in which they become adults. They feed on the food of the host, whose body is poisoned by their secretions. As a result of their activity, ulcers form on the intestinal walls, and with a large number of parasites, its obstruction and rupture of the walls may occur.
Type Annelids
Its representatives live in fresh water, seas, soil. Their body is long, divided into annular segments (segments) by transverse constrictions. We are all well aware of 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 segmentation. The body cavity of representatives of this type is lined with a layer of integumentary cells. A delimited area 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 the sense organs, are more perfect than those of round and flatworms. Their "skin" consists of a layer of integumentary cells. Under herare longitudinal and circular muscles. In annelids, the digestive system is divided into the pharynx, oral cavity, esophagus, stomach (in some groups), and intestines. Undigested food residues are removed through the anus.
Circulatory system of annelids
All types of annelids have a circulatory system formed by the abdominal and dorsal blood vessels, which are interconnected by annular. 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 that enter it to all organs, and also frees 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). Breathing takes place through the skin. Some types of worms (marine) have gills.
Nervous system of annelids
The nervous system in representatives of this type consists of paired subpharyngeal and suprapharyngeal nerve nodes, which are connected into a ring by nerve cords, as well as nodes of the chain (abdominal). A paired node is located in each segment of annelids. Nerves go to all organs. Various stimuli (for example, light) affect sensitive cells. The excitation that has arisen in them is transmitted to the nearest nerve node along the nerve fibers, and then to the muscles (via other fibers) andcauses them to shrink. In this way, reflexes are carried out. Most representatives of this type have no sense organs.
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 stand out: Polychaete and Low-bristle. The former live mainly in the soil (for example, such a type of earthworm as burrow), as well as in fresh water (in particular, tubifex). Polychaete worms - a class that includes sandworms, nereids and sickles. Sandworms live in the burrows dug by them, Nereids live mainly in silty soil, in the coastal parts of the seas, sickles live in "houses" that they build from various materials.
Nereids
Nereids are the most diverse worm species 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 (organs of touch), as well as 2 pairs of eyes and 2 pits behind them (these are the organs of smell). On the segments on the sides of the body there are paired muscular short lobe-like outgrowths with tufts of setae. These are limbs. In addition, nereids develop gills - special outgrowths of the skin. Often they are dioecious animals. In water, eggs are fertilized, from which free-swimming larvae appear, having a belt of cilia. They develop into adult worms over time.
Meaning of annelids
They are the food of manyspecies of crabs, fish (nereids and other marine worms). Earthworms are the main food of hedgehogs, moles, starlings, toads and other animals. Ringed, feeding on silt, as well as various suspensions, free water from 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.
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 peculiar living organisms. Some of them are parasites, while others are of great benefit to our planet.
