Habitat of annelids. Features of annelids

Consider a number of animals that are studied by biology - the type of Ringworm. We learn about their types, lifestyle and habitat, internal and external structure.

general characteristics

Ringworms (also called simply rings, or annelids) - this is one of their vast groups of animals, which includes, according to various sources, about 18 thousand species. They are non-skeletal vertebrates, which not only participate in the destruction of organic substances, but also are an important component of the nutrition of other animals.

The body of annelids is divided by internal partitions into segments, which correspond to outer rings. It is this feature that gave the name to the type. Among the annelids, they can be found only on soil reprocessing, but also mutualists (worms living in symbiosis with another organism), ectoparasites (living on the surface of the body), blood-sucking parasites, predators, scavengers, filterers.

Habitat of annelids

Where can you find these animals? The habitat of annelids is very extensive - it is the sea, and the land, and fresh water. The annelids inhabiting the salt waters of the ocean are very diverse. Kolchetsov can be found in all latitudes and depths of the World Ocean, even at the bottom of the Mariana Trench. Their density is high - up to 100 000 copies per square meter of the bottom surface. Marine annelids are a favorite fish food and play an important role in the marine ecosystem.

In fresh water bodies there are mainly blood-sucking parasites - leeches, which, in particular, are used in medicine. In tropical countries, leeches can live on trees and in the soil.

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 common annelids that inhabit the soil 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

About 200 years ago, Georges Cuvier worked on the classification of the animal world and identified 6 types of its representatives. These included arthropods - creatures, whose bodies are divided into segments: crayfish, spiders, insects, lice, earthworms and leeches.

It is possible to name some features of annelids, due to which they were isolated in a separate type. This is the presence of celloma (secondary body cavity), metamerism (segmentation) of the body and the circulatory system. In addition, annelids are characterized by the presence of specific organs of motion - parapodia. The nerves have a nervous system, which consists of the supra-pharyngeal nerve node and the abdominal neural chain. The structure of the excretory system is metanephridial.

The type of annelid worms is divided into 4 classes. Classes of Ringworms:

1. Polychaete annelids (they are also called polychaetes). In this class, three subclasses can be distinguished: free-mobile, sit-attached and misostomies.
2. Pancake annelids (oligochaetes).
3. Leeches. In this class there are 4 orders: pharyngeal, maxillary, proboscis and setiform leeches.
4. Ehiurids.

External structure of annelid worm

Kolchetsov can be called the most highly organized representatives of a group of worms. Dimensions of their body vary from several fractions of a millimeter to two and a half meters! The body of the worm can be conditionally divided into three parts: the head, trunk and anal lobe. The features of ringworms are that there is no definite division into divisions, as in higher animals, in annelids.

On the head of the worm are various sensory organs. Many annelids have well developed eyesight. Some types of annunciators can boast a particularly sharp eye and a complex eye structure. However, the organs of vision can be located not only on the head, but also on the tail, body or tentacles.

Worms and taste sensations are also developed. Worms smell through the presence of olfactory cells and ciliated pits. Hearing organs are arranged in the form of locators. Some echiruids are able to distinguish very quiet sounds thanks to the organs of hearing, similar in structure to the lateral line in fish.

Respiratory organs and circulatory system of the annelid worm

Pupil worms breathe the entire surface of their body. But in polychaetes there are respiratory organs - gills. They are bushy, leaf-shaped or feathery parapodia, permeated with a large number of blood vessels.

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

The circulatory system of the annelid worm is filled with the same type as in humans, with red blood. This means that there is iron in it. However, the element is not part of hemoglobin, but of another pigment - hemaritrine, which captures 5 times more oxygen. This feature allows worms to live in conditions of oxygen deficiency.

Digestive and excretory systems

The digestive system annelid can be divided into three departments. The anterior colon (stomodeum) includes the oral opening and oral cavity, acute jaws, pharynx, salivary glands and narrow esophagus.

The oral cavity, which is also called the buccal department, is capable of turning inside out. Behind this department are jaws that are bent inside. This unit is used to capture prey.

Then follows the mesodeum, the middle gut. The structure of this department is uniform throughout the entire length of the trunk. The middle gut narrows and expands, it is in it that food digestion takes place. The hindgut is short, ends with the anal opening.

The excretory system is represented by metanephridia, pairwise located in each segment. They excrete the products of vital activity from the cavity fluid.

Nervous system and sense organs

All classes of annelids have a ganglionic-type nervous system. It consists of the oclo-pharyngeal nerve ring, which is formed by the connected super-arterial and sub-pharyngeal ganglia, and from pairs of the abdominal ganglion chain located in each segment.

The sensory organs of the rings are well developed. Worms have sharp eyesight, hearing, smell, touch. Some annelids not only catch light, but they can also radiate it.

Reproduction

The characteristic of the ringed worm suggests that representatives of this type of animal can reproduce both sexually and asexually. Asexual reproduction can be performed by dividing the body into parts. The worm splits into halves, each of which becomes a full-fledged individual.

In this case, the tail of the animal is an independent unit and can grow a new head. In some cases, the second head begins to form in the center of the body of the worm before separation.

Puncture is less common. Of particular interest are species in which the budding process can cover the whole body when the posterior ends bud from each segment. In the process of reproduction, additional oral openings can also be formed, which later will separate into independent individuals.

Worms can be dioecious, but in some species (primarily leeches and earthworms), hermaphroditism developed when both individuals perform both the female and male roles simultaneously. Fertilization can occur both in the body and in the external environment.

For example, in marine worms reproducing sexually, fertilization is external. Heterogeneous animals throw their germ cells into the water, where the fusion of eggs and spermatozoa occurs. From the fertilized eggs appear larvae, not similar to adults. Freshwater and terrestrial annelids do not have a stage of the larva, they are immediately born similar in structure to adults.

Class Polychaete

Polychaete worms have the largest number of species among the rings. The class is mainly represented by free-living marine animals. There are isolated freshwater and parasitic species.

Marine annelids belonging to this class are very diverse in form and behavior. The polychaetes differ in a well-marked head section and the presence of parapodia, peculiar limbs. They are predominantly heterosexual, the development of the worm occurs with metamorphosis.

Nereid swim actively, they can burrow into the mud. They have a serpentine body and a lot of parapodia, the animals lay their way with the help of a retractable pharynx. Peskozhily in appearance resemble earthworms and burrow deep into the sand. An interesting feature of the ringed worm-sandworm is that it moves in the sand hydraulically, pushing the cavity fluid from one segment to the other.

Curious and sedentary worms, serpulids, which live in spiral or twisted lime tubes. Serpulids stick out of their home only a head with large fan-shaped gills.

Class Fewer

Small-wormed worms predominantly inhabit the soil and fresh waters, they are encountered in the seas only once. The structure of the ringworm of this class is distinguished by the absence of parapodia, the homogeneous segmentation of the body, the presence of a glandular girdle in sexually mature individuals.

The head section is not expressed, it can be devoid of eyes and appendages. On the body there are setae, rudiments of parapodia. This structure of the body is due to the fact that the animal leads a burrowing lifestyle.

Very widespread and familiar to all maloshchetinkovymi are earthworms that inhabit the soil. The body of the worm can be from several centimeters to three meters (such giants live in Australia). Also in the soil there are often small, about a centimeter in size, whitish worms of enchytraeids.

In fresh water bodies, you can find vertical pipes of worms living in whole colonies. They are filter feeders fed by suspended organic residues.

Class of Leeches

All leeches are predators, mostly feeding on the blood of warm-blooded animals, worms, mollusks, fish. The habitat of annelid worms of the class of leeches is very diverse. Most often leeches are found in fresh water, wet grass. But there are also marine forms, and even chernozems live on Ceylon.

Interest are the digestive organs of leeches. Their mouth is supplied with three chitinous plates, which cut through the skin, or the proboscis. In the oral cavity there are numerous salivary glands that can secrete a toxic secret, and the pharynx serves as a pump when sucking.

The Ehiurid class

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

The environment of ringworms of the Ehiurid class is the great depths of the sea, sand holes or clefts of rocks, empty shells and other shelters. Worms belong to the filter.