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The variety of annelids, the structure of the earthworm, the characteristics of roundworms.

The body of which consists of repeating segments, or rings (hence their name - annelids).

General brief characteristics of annelids:

there is a secondary body cavity (general);
the body is covered on the outside with a cuticle secreted by the ectoderm.
there is a circulatory system;
the nervous system is represented by a paired supraesophageal ganglion connected by jumpers to the abdominal nerve chain (usually double);
the excretory organs are located in each ring and are formed from the ectoderm, they are equipped with cilia;

Structure

The elongated body of annelids is, as it were, assembled from segment rings, the segments are separated by internal partitions; but they are not completely independent, since a through intestine with a mouth and anus, an abdominal trunk of the nervous system and trunks of a closed circulatory system. These organ systems, penetrating the partitions one by one, stretch through the entire body of annelids. Each ring-segment has a secondary body cavity (whole). Most of the segments bear on the outside, on the right and on the left, two tufts of setae - organs of locomotion or fixation in the tubes. In leeches, the bristles are secondarily lost.

Secondary body cavity (general)

The secondary cavity of the body (whole) is of mesodermal origin. It is surrounded by a mesodermal membrane and filled with fluid. The cavity occupies the space between the walls of the body and the intestinal tube. The main part of the mesoderm lining the secondary cavity is the muscles that make up the body wall. They provide the movement of the animal. In addition, the muscles of the intestinal wall, alternately contracting, push food.

The secondary body cavity performs the following functions:

The secondary cavity of the body to one degree or another - feature for all types of multicellular animals following in the evolutionary development, starting with annelids.

Classification

Annelids are a type of worms numerous in species that have a more complex body structure compared to flat and primary cavity worms. It is divided into three classes: Polychaetes, Belts (including subclasses Small-bristle worms and Leeches), Misostomids.

Origin

According to a comparative study of the structure of worms, annelids evolved from primitive whole worms, similar to flatworms. ciliary worms. Important evolutionary acquisitions of annelids are the secondary body cavity (coelom), the circulatory system, and the division of the body into separate rings (segments). Polychaete annelids are the ancestral group for the rest of the annelids. From them, during the transition to a freshwater and terrestrial way of life, oligochaete worms separated. Leeches are descended from low-bristle worms.

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annelids - multicellular, binary-symmetric, three-layered animals that have a secondary body cavity. The kilchak type unites more than 9000 species (in Ukraine - about 450 species). Live in the sea and fresh water ah, as well as in the soil compared with representatives of other types of worms, kilchakiv have a significantly higher level of organization. The progressive features of the organization of annelids are: 1 ) the appearance of a secondary body cavity 2) division of the body into separate segments (metamerism) ; 3 ) appearance of primitive limbs (parapodia in polychaete worms) ; 4 ) appearance of the circulatory and respiratory systems (external gills in polychaete worms) ; 5 ) development of metanephridia.

structural features

Body into kilchak into multicellular, formed by many segments. The repeated repetition of body segments is called metamerism. This principle of body organization arises in the process of evolution in connection with the elongation of the body. Segments - parts of the body that are similar in structure, arranged in series one after the other. The segments outside and inside are the same, therefore, in kilchakiv homonomous metamerism, or segmentation, of the body. Many representatives have bristles on the body segments. The body consists of the head end, trunk and anal lobe. Such a clear division of the body into sections is observed in kilchakiv for the first time.

covers are represented by a well-developed musculocutaneous sac, which includes: dense thin cuticle , hypodermis and two layers of muscles(ring and longitudinal). The skin has many mucous glands.

body cavity secondary (in general) segmented. It differs from the primary cavity in the presence of its own epithelial lining, which, on the one hand, is adjacent to the walls of the sac, and on the other, to the walls of the digestive tube. The leaves of the lining grow together above and below the tube, forming a mesentery, which divides the coelom into right and left parts. Transverse partitions divide the body cavity into chambers, the number of which corresponds to the number of segments. The whole is filled with liquid, which chemical composition very close to sea water. The coelomic fluid is in constant motion and performs a number of important functions: washing the organs of the body, together with the blood supplies them with nutrients and oxygen, helps to remove CO2 and metabolic products, moves biologically active substances and phagocytes, etc.

life features

Support connected with hydroskeleton, functioning thanks to the coelomic fluid.

Motion muscular. In polychaete worms there are muscle growth segments of the body - parapodia, that form the propulsion system. In oligochaetes, in their place are tufts of setae.

Digestion It is provided by a differentiated digestive system, which has three sections: anterior (mouth, pharynx, esophagus with an ax, stomach with muscular walls), middle (middle intestine) and posterior (hind intestine with anus). Each section of the system performs its own specific function. For example, in the wall of the midgut there are cells that secrete digestive enzymes and cells that digest food, so the main function of this section is the digestion and absorption of food.

Transportation of substances in kilchakiv is already being carried out with the participation circulatory system, which appears for the first time. In annelids closed circulatory system a system in which blood moves only through the vessels and does not enter the body cavity. Their circulatory system is formed by the dorsal and abdominal blood vessels, interconnected by annular vessels. Small capillaries depart from these vessels, which, branching out, form a dense network in the skin and internal organs. The movement of blood is due to the pulsation of the annular vessels, they do not have a heart. The blood may be colorless or colored due to the presence of respiratory pigments: chlorocruorin (determines the green color of the blood), hemoglobin and hemoerythrin (cause the red color).

Breath already carried out with the participation respiratory system, which appears for the first time. its appearance is associated with an intensive metabolism in comparison with the previous groups of invertebrates. In some marine kilchaks, organs of water respiration arise - gills, which are thin-walled formations with an extensive network of vessels, which are located on the Parapodia, head and tail. But in most kilchaks, gas exchange is carried out through the covers.

Selection takes place with excretory system formed by special bodies - metanephridia. These organs begin in the body cavity as a funnel, from which a canal extends, opening outward in another segment. Each segment contains a pair of such excretory organs.

Regulation processes carried out by the nervous nodal system of the chain type. CNS formed supraesophageal and subpharyngeal nerve ganglions, supraglottic bridges and abdominal nerve cord. The PNS is represented by nerve branches.

Irritability provide well developed organs feelings. In the integument, cells that distinguish between tastes and smells are sensitive, the organs of touch are the antennae, bristles, the existing organs of vision, and sometimes the organs of balance.

reproduction mainly sexual with the participation of the reproductive system. Polychaete worms are dioecious, while oligochaetes and leeches are hermaphrodites. Fertilization can be both external and internal. In aquatic annelids, asexual reproduction is also found, in which their body can break up into several unequal parts (disordered division) or into separate segments (multiple fragmentation).

Development in oligochaetes and leeches - straight. In polychaetes - indirect, in which a larva is formed trochophores. She swims in the water for some time, then settles to the bottom and turns into an adult organism.

Regeneration well developed in oligochaetes and polychaetes, while this ability is lost in leeches.

Variety of annelids

The type is divided into several classes, including Polychaetes, Low-bristle, Leeches.

polychaete worms, or polychaetes - a class of annelids that have parapodia with numerous setae on each segment of the body. About 5300 species belong to this class, which live mainly in the seas, and only a few representatives have adapted to life in fresh water bodies or wet places on land. They lead a bottom lifestyle (benthic animals), some are free-swimming, there are also sessile forms, they secrete protective tubes around themselves. Mostly predators, but among them there are many herbivorous and omnivorous forms. Among the polychaetes, there are also Commensal species that live inside sponges, in the shells of hermit crabs, or on starfish. The body of polychaete worms consists of a head section, a segmented trunk, and an anal lobe. On the head there are eyes, organs of touch - tentacles, organs of smell - sniffing pits, in some - organs of balance (statocysts). On the trunk segments there are paired lateral outgrowths with bristles - parapodia - primitive limbs with which the worms swim, crawl or burrow into the ground. Bristles mainly have cutaneous respiration, but some species have gills. Most polychaete worms are dioecious animals. The eggs are fertilized in water. The development is indirect, in which free-living trochophore larvae emerge from the eggs, driven by cilia. The best-known members of the class are sandstone, nereid, and palolo.

Sea Sandworm (Arenico / o marina) - marine polychaete worm living in the Black Sea and can reach 30 cm in length. He spends his whole life in a deep burrow of sand. It feeds on small algae, animals and various inanimate lobules, capturing them along with the sand. It is the main food for commercial fish.

Nereis (Nereis virens) , or Nereid,- polychaete worm living in the Sea of Azov. Refers to benthos - crawls along the bottom of the sea using event parameters. It is the main food for commercial fish. Acclimatized in the Caspian Sea, intensively multiplied there and became an important integral part in the diet of sturgeons.

Palolo (Eunice viridis) - marine polychaete worm living in coral reefs tropical islands Pacific Ocean. The color of the body is palolo greenish, the size is up to 1 m. Twice a year, in a certain phase of the moon, sexually mature individuals appear in large numbers on the surface of the water for reproduction.

Small-bristle worms, or oligochaetes- a group of annelids, which have a few bristles on each segment of the body. This class includes more than 5000 species, which are mainly inhabitants of fresh water and soil, much less common in salt water. Most oligochaetes range in size from 0.5 mm to 40 cm, and some species of tropical earthworms reach 3 m. The features of the external structure of oligochaete worms are body segmentation (from 5-6 to 600 rings), the absence of parapodia (in their place there are bundles of a few setae), the presence of a glandular belt in the anterior part of the body in sexually mature individuals, etc. The most famous representatives oligochaetes are earthworms and tubulars.

common earthworm (Lumbricus terrestris) - a species of low-bristle worms that has adapted to life in the soil. These worms belong to the family of true earthworms, which includes about 300 species. Body sizes range from 2 to 50 cm. In the south of Ukraine, worms reach large sizes. Movement in the soil is facilitated by an elongated, segmented, pointed body at both ends. They move by alternately contracting and relaxing the annular and longitudinal muscles of the skin-muscle sac. The bristles directed backwards (8 on each segment) make it possible to cling to the slightest unevenness of the soil. The mucus secreted by the skin glands reduces the friction of the body of the worm, prevents it from drying out, promotes respiration, has

The internal structure of the earthworm: A - cuticle; B - hypodermis; B - circular muscles; G - longitudinal muscles; D - musculocutaneous sac; E - lining the epithelium; There is a ventral nerve chain; G - abdominal blood vessel; WITH - bristles; AND - methonephridia; AND - intestinal wall; TO - generally; L - dorsal blood vessel

antibiotic properties. Earthworms feed on dead plant residues contained in the soil. In the soil, earthworms dig deep passages up to 2 m from the surface of the earth. In warm and humid weather, they crawl out of their burrows at night, looking for damp fallen leaves, half-rotted blades of grass, and drag all this into the burrows. So, earthworms are typical saprophages. They also swallow soil, which can be seen in their intestines. Worms throw the processed soil to the surface in the form of characteristic heaps, the appearance of which in the spring indicates the beginning of the activity of the worms. It is estimated that each worm passes through its intestines such an amount of earth per day, equal to the mass of its body. More than 50 species of earthworms are known in Ukraine, some of them are listed in the Red Book of Ukraine (for example, Eizenia Gordeeva).

Ordinary tube (Tubifex tubifex) - freshwater red thin worm 2-5 cm in size. It lives in silty soils of fresh, very polluted water bodies with insufficient oxygen. The front end of the worm is immersed in silt, and the back end extends outward and continuously wriggles - these movements provide an influx of fresh water necessary for breathing. They can withstand significant pollution of water bodies by various substances (petroleum products, pesticides, etc.). In the skin of the back of the body, there are especially many blood capillaries. A tube is formed around this part of the body, consisting of silt particles glued together by the mucus of the worm. Swallows sand with silt and absorbs the nutrients that it contains. It is used as food for aquarium fish, is the basis of nutrition for freshwater animals, in particular fish.

medical leech (Hirudo medicinalis) has a segmented body 8-12 cm long. On the dark dorsal side of the body there is a characteristic pattern of three pairs of rusty-red or red-yellow longitudinal stripes. Lives in small stagnant reservoirs with a muddy bottom, overgrown with vegetation. It feeds on the blood of amphibians and mammals. The posterior sucker is used for attachment, while the anterior, which has jaws and teeth, is fed. In the oral cavity, located at the bottom of the anterior sucker, there are three jaws. They cut through the skin of the animal in which the leech has stuck. In the morning, saliva containing hirudin is secreted. Hirudin- a substance that is produced salivary glands leeches to prevent blood clotting. Blood treated with leech saliva can be stored for a long time in large pockets of its intestines - thanks to this, the animal can starve for a long time (from several months to a year). Medical leech is a hermaphrodite, which is characterized by direct development. She lays her eggs in clusters near water (but not in water), in dark, damp places. Used in medicine for diseases of the circulatory system, gangrene and organ transplantation.

Annelids are bilaterally symmetrical segmented animals.

Systematics. The type includes 5 classes, of which the most famous classes are Polychaeta (Polychaeta) - 13000 species, Olygochaeta - 3500 species and Leeches (Hirudinea) - about 400 species.

Body shape and size. The body of the rings is overwhelmingly worm-shaped, round or oval in cross section. The trunk has a pronounced both external and internal segmentation. In this case one speaks of true metamerism. At the same time, metamerism extends to internal structure worms. In leeches, external segmentation does not correspond to internal segmentation.

The sizes of annelids range from a few millimeters to 2 m (terrestrial forms) and even up to 3 m ( sea views).

External structure body. In polychaetes, the head section is well expressed, bearing organs for various purposes: tentacles, eyes, palps. In some species, the palps grow into a complex hunting apparatus. The last segment bears one or several pairs of sensory antennae. Each body segment on the sides bears parapodia - complex outgrowths of the body. The main function of these outgrowths is the movement of the worm. Each parapodia consists of two lobes, inside which are numerous setae. Of these, several are larger, they are called atsikuly. A pair of sensitive antennae are attached to the blades. The parapodia often includes the gill apparatus. Parapodia have a rather diverse structure.

In oligochaete worms, the head section is weakly expressed, lateral outgrowths (parapodia) are absent. Only relatively few setae are present. On the body, a “belt” is clearly visible, consisting of thickened segments.

Leeches have powerful suckers at the anterior and posterior ends of the body. Few species have gill outgrowths on the sides.

Skin-muscle bag. Outside, the body of annelids is covered with a thin cuticle, under which lie the cells of the skin epithelium. The skin of worms is rich in glandular cells. The secret of these cells is protective value. In a number of species, skin secretions are used to build peculiar houses. The bristles of the worms are derivatives of the epithelium. Under the skin lies a layer of circular muscles, which allows the animal to change the transverse size of the body. Below are the longitudinal muscles that serve to change the length of the body. In leeches, between the layers of the annular and longitudinal muscles, there is a layer of diagonal muscles. Rings have special muscles that set in motion parapodia, palps, suckers, etc.

body cavity. The space between the body wall and internal organs in annulus it represents the whole - the secondary cavity of the body. It differs from the primary one by the presence of its own epithelial walls, which are called the coelomic epithelium (the whole body). The coelothelium covers the longitudinal muscles of the body wall, intestines, muscle cords and other internal organs. On the walls of the intestine, the whole body is transformed into chloragogenic cells that perform an excretory function. At the same time, the coelomic sac of each body segment is isolated from the neighboring ones by partitions - dessepiments. Inside the coelomic sac is filled with a liquid containing various cellular elements. As a whole, it performs various functions - supporting, trophic, excretory, protective and others. In leeches, the whole has undergone a strong reduction and the space between the body wall and the internal organs is filled with a special tissue - mesenchyme, in which the whole is preserved only in the form of narrow channels.

The midgut is shaped like a simple tube that can become more complex. So, in leeches and some polychaetes, the intestine has lateral outgrowths. The oligochaetes have a longitudinal fold on the dorsal side of the intestine, which protrudes deeply into the intestinal cavity - typhlosol. These devices significantly increase the inner surface of the midgut, which allows the most complete absorption of digested substances. The midgut is endodermic in origin. In small-bristle worms, on the border of the anterior and middle intestines, there is an extension - the stomach. It can be either ectodermal or endodermal.

The hindgut, which is a derivative of the ectoderm, is usually short and opens with an anus.

Circulatory system annelids is closed, that is, the blood moves everywhere through the vessels. The main vessels - longitudinal - dorsal and abdominal, connected by annular. The spinal vessel has the ability to pulsate and performs the function of the heart. In oligochaetes, this function is also performed by the annular vessels of the anterior part of the body. Blood moves from back to front along the dorsal vessel. Through the annular vessels located in each segment, the blood passes into the abdominal vessel and moves in it from front to back. Smaller vessels depart from the main vessels, and they, in turn, branch into the smallest capillaries that carry blood to all the tissues of the worms. In leeches, the system of blood vessels is significantly reduced. Blood moves through the system of sinuses - the remnants of the coelom.

The blood of most annelids contains hemoglobin. This allows them to exist in conditions with a low oxygen content.

Special respiratory organs usually not, so gas exchange occurs through the skin by diffusion. Polychaete worms and some leeches have well-developed gills.

excretory system most often represented by metanephridia, which are located metamerically, that is, in pairs in each segment. A typical metanephridium is represented by a long coiled tube. This tube begins with a funnel that opens as a whole (secondary body cavity) of the segment, then it penetrates the septum between the segments (dissepiment) and enters the glandular metanephridial body located in the next segment. In this gland, the tube winds strongly and then opens with an excretory pore on the lateral surface of the body. The funnel and tube are covered with cilia, with the help of which the cavity fluid is forced into the metanephridium. When moving through the tube through the gland, water and various salts are absorbed from the liquid, and only products to be removed from the body (urine) remain in the tube cavity. These products are excreted through the excretory pore. In many species, there is an extension in the posterior part of the metanephridial tube - the bladder, in which urine temporarily accumulates.

In primitive annelids, the excretory organs, like flatworms, are arranged according to the type of protonephridia.

Nervous system consists of the peripharyngeal ring and the ventral nerve cord. Above the pharynx lies a powerfully developed paired complex of ganglia, representing a kind of brain. A pair of ganglia also lie under the pharynx. The brain is connected to the subpharyngeal ganglia by nerve cords covering the pharynx from the sides. All this formation is called the peripharyngeal ring. Further, in each segment under the intestine there is a pair of nerve ganglia, which are connected both to each other and to the ganglia of neighboring segments. This system is called the ventral nerve cord. From all ganglia, nerves depart to various organs.

Sense organs. The head section of polychaete worms has well-developed sense organs: antennae and palps (organs of touch), eyes (sometimes quite complex), and olfactory pits. Some forms have developed organs of balance - statocysts. On the lateral outgrowths of the body (parapodia) there are antennae that perform a tactile function.

In oligochaete worms, the sense organs are much less developed than in polychaete worms. There are organs of chemical sense, sometimes - tentacles, statocysts, poorly developed eyes. A large number of light-sensitive and tactile cells are scattered in the skin. Some tactile cells have a pin.

In leeches, many sensitive cells are scattered in the skin, there are always eyes and chemical sense organs (taste buds).

reproductive system. Among annelids, there are both hermaphroditic and dioecious forms.

Polychaete worms are mostly dioecious. Sometimes there is sexual dimorphism. Sex glands (gonads) are formed in the coelomic epithelium. This process usually occurs in the posterior segments of the worm.

In small-bristle worms, hermaphroditism is more common. The sex glands are usually located in certain segments of the anterior part of the worm. Relatively small male gonads (testes) have excretory ducts, which are either modified metanephridia or canals isolated from them. Larger female sex glands (ovaries) have ducts, which are altered metanephridia. For example, when the ovary is located in the 13th segment, the female genital openings open on the 14th. There are also seminal receptacles, which are filled during mating with the spermatozoa of another worm. Leeches are mostly hermaphrodites. The testes are located metamerically, the ovaries are one pair. Fertilization in leeches occurs by the exchange of spermatophores between partners.

reproduction. Ringed worms are characterized by a wide variety of forms of reproduction.

Asexual reproduction is characteristic of some polychaete and oligochaete worms. In this case, either strobilation or lateral budding occurs. This is a rare example of asexual reproduction among highly organized animals in general.

During sexual reproduction, polychaete individuals containing mature gonads (epitocal) move from a crawling or sedentary lifestyle to a swimming one. And in some species, the sexual segments during the maturation of gametes can even break away from the body of the worm and lead an independent floating lifestyle. Gametes enter the water through breaks in the body wall. Fertilization takes place either in water or in the epitonic segments of the female.

Reproduction of oligochaetes begins with cross-fertilization. At this time, two partners are applied to each other by the abdominal sides and exchange sperm, which enters the seminiferous receptacles. After that, the partners disperse.

Subsequently, abundant mucus is secreted on the girdle, forming a sleeve around the girdle. The worm lays its eggs in this clutch. When the clutch is moved forward, it passes by the holes of the seed receptacles; at this point, fertilization of the eggs occurs. When the clutch with fertilized eggs slides off the head end of the worm, its edges close, and a cocoon is obtained in which further development takes place. The cocoon of earthworms usually contains 1-3 eggs.

In leeches, reproduction occurs in much the same way as in oligochaete worms. Leech cocoons are large, reaching 2 cm in length in some species. Located in a cocoon different types from 1 to 200 eggs.

Development. The zygote of annelids undergoes complete, usually uneven fragmentation. Gastrulation occurs by invagination or epiboly.

In polychaete worms, a larva called a trochophore is subsequently formed from the embryo. She has eyelashes and is quite mobile. It is from this larvae that the adult worm subsequently develops. Thus, in most polychaete worms, development proceeds with metamorphosis. Species with direct development are also known.

Small-bristle worms have direct development without a larval phase. Fully formed young worms emerge from the eggs.

In leeches, peculiar larvae form from eggs in a cocoon, which swim in the cocoon fluid with the help of a ciliary apparatus. Thus, an adult leech is formed by metamorphosis.

Regeneration. Many annelids are characterized by a developed ability to regenerate lost body parts. In some species, an entire organism can regenerate from just a few segments. However, in leeches, regeneration is very weak.

Nutrition. Among the polychaete worms, there are both predators and herbivorous species. There are also known cases of cannibalism. Some species feed on organic remains (detritivores). Small-bristle worms are mainly detritivores, but there are also predators.

Small-bristle worms are mostly soil inhabitants. In humus-rich soils, the number of, for example, enchitreid worms reaches 100-200 thousand per square meter. They also live in fresh, brackish and salty water bodies. Aquatic inhabitants inhabit mainly the surface layers of the soil and vegetation. Some of the species are cosmopolitan, and some are endemic.

Leeches inhabit fresh water bodies. Few species live in the seas. Some have switched to a terrestrial way of life. These worms either lead an ambush lifestyle or actively seek out their hosts. A single bloodsucking provides leeches with food for many months. There are no cosmopolitans among leeches; they are confined to certain geographic areas.

paleontological finds annelid worms are very few. Polychaetes are more diverse in this respect. Not only prints have been preserved from them, but also in many cases the remains of pipes. On this basis, it is assumed that all the main groups of this class were represented already in the Paleozoic. Reliable remains of oligochaete worms and leeches have not been found to date.

Origin. Currently, the most plausible hypothesis is the origin of annelids from parenchymal ancestors (ciliary worms). The most primitive group is considered to be polychaetes. It is from this group that the oligochaetes most likely originate, and from the latter a group of leeches emerged.

Meaning. In nature, annelids are of great importance. Inhabiting various biotopes, these worms are included in numerous food chains, serving as food for a huge number of animals. Terrestrial worms play a leading role in soil formation. By processing plant residues, they enrich the soil with minerals and organic matter. Their moves contribute to the improvement of soil gas exchange and its drainage.

In practical terms, a number of earthworm species are used as vermicompost producers. The worm - enchitreus is used as food for aquarium fish. Enchitreev breed in huge quantities. For the same purpose, the tubifex worm is mined in nature. medical leeches currently used for the treatment of certain diseases. In some tropical countries are used in food palolo- genital (epitocal) segments of worms that have separated from the front of the animals and floated to the surface of the water.
General characteristics of the type Arthropods.

Arthropods are bilaterally symmetrical segmented animals with metamerically arranged jointed limbs. This is the most species-rich and diverse group of animals.

Systematics. The type of arthropods is divided into several subtypes.

Subtype Gill-breathers (class Crustaceans)

Subphylum Trilobites (extinct group)

Subtype Cheliceraceae (class Merostomaceae, class Arachnids)

Subtype Primary tracheal

Subtype Tracheal breathing (class Millipedes, class Insects).

The Merostomaceae class includes modern horseshoe crabs and extinct shell scorpions. To subtype Primary tracheal small (up to 8 cm) tropical animals are included, which in structure occupy an intermediate position between annelids and arthropods. These groups of animals will not be considered here.

Body dimensions. The body length of arthropods ranges from 0.1 mm (some mites) to 90 cm (horsicle crabs). Terrestrial arthropods reach 15-30 cm. The wingspan of some butterflies exceeds 25 cm. Extinct crustaceans reached 1.5 m in length, and the wingspan of fossil dragonflies reached 90 cm.

External structure. The body of most arthropods consists of a head, thorax, and abdomen. The above departments include different number segments.

Head, the segments of which are fixedly connected, bears the oral organs and sensory organs. The head is movably or immovably connected to the next section - the chest.

Thoracic bears walking limbs. Depending on the number of thoracic limb segments, there may be a different number. In insects, wings are also attached to the chest. The segments of the chest are connected to each other movably or motionless.

Abdomen contains most of the internal organs and most often consists of several segments, movably connected to each other. Limbs and other appendages can be located on the abdomen.

The oral apparatus of arthropods is very complex. Depending on the method of nutrition, it can have a very diverse structure. The parts of the mouth apparatus are for the most part highly modified limbs, adapted to eat almost any food. The apparatus may include 3-6 pairs of limbs.

Covers. The cuticle, consisting of chitin, is a derivative of the submerged epithelium - the hypodermis. Chitin performs the support and protective function. The cuticle can become impregnated with calcium carbonate, becoming very strong shell as it does, for example, in crustaceans. Thus, in arthropods, the integuments of the body represent the external skeleton. The mobile connection of the hard sections of the cuticle is provided by the presence of membranous sections. The cuticle of arthropods is not elastic and cannot be stretched during the growth of animals, so they periodically shed the old cuticle (molt) and, until the new cuticle has hardened, increase in size.

body cavity. In the process of embryonic development in arthropods, coelomic sacs are laid, but later they are torn and their cavity merges with the primary body cavity. Thus, a mixed body cavity is formed - a mixocoel.

musculature represented by separate muscle bundles that do not form a continuous muscle sac. Muscles are attached both directly to the inner wall of the body segments and to their inner processes that make up the internal skeleton. Musculature in arthropods striated.

Digestive system in arthropods in general case consists of an anterior, middle and posterior intestine. The anterior and posterior sections are lined from the inside with a thin chitinous cuticle. Depending on the type of nutrition, the structure of the intestine is extremely diverse. Open into the oral cavity salivary glands, which very often produce a number of enzymes, including digestive ones. The anal opening usually opens at the posterior end of the body.

excretory system in primary aquatic arthropods (crustaceans) it is represented by special glands located in the head of the body. The ducts of these glands open at the base of the antennae (antennae). In terrestrial arthropods, the excretory system is represented by the so-called malpighian vessels- tubes that are blindly closed at one end, and open at the other end into the intestine at the border of the middle and posterior sections. These tubules are located in the body cavity, and, being washed by hemolymph, they suck up decay products from it and bring them into the intestine.

Respiratory system arranged quite differently. Crustaceans have true gills. They are branched outgrowths on the limbs, covered with a thin chitinous cuticle, through which gas exchange occurs. Some crustaceans have adapted to live on land (for example, wood lice).

Spiders and scorpions have respiratory organs leaf-shaped lungs, which open outwards with holes (stigmas). Inside the lung sac has numerous folds. In addition to the lung sac, some spiders have a system of tracheal tubes that practically do not branch.

Ticks, centipedes, and insects have a respiratory system tracheae, which open outwards with holes (spiracles, stigmas). The tracheae branch strongly and penetrate into all organs and tissues. The trachea has a thin chitinous lining and is reinforced from the inside with a chitinous spiral, which does not allow the tube to fall off. In addition, flying insects have extensions - air sacs that fill with air and reduce the specific gravity of the animal. Ventilation in the tracheal system is both passive (diffusion) and active (change in the volume of the abdomen).

Some insect larvae have special respiratory organs - tracheal gills. Gas exchange in such arthropods proceeds by diffusion.

Some ticks do not have a respiratory system, and gas exchange occurs through the entire surface of the body.

Circulatory system in all arthropods open I, that is, not everywhere the blood flows through the vessels. Under the chitinous cover of the back there is a heart from which blood vessels depart. However, at some distance from the heart, the walls of the vessels disappear, and the blood makes its further path through the cracks between the internal organs. It then enters the heart through openings called ostia. Crustaceans and mites have a sac-like heart, while scorpions, spiders, and insects have a multi-chambered heart. Some ticks may not have a circulatory system.

The blood of the vast majority of arthropods is colorless and is commonly referred to as hemolymph. This is a rather complex fluid: it consists of both the blood itself and the cavity fluid. Due to the absence of special pigments, hemolymph practically cannot actively participate in the process of gas exchange. Hemolymph of some insects (leaf beetles, ladybugs) contains quite toxic substances, and may play a protective role.

Fat body. Terrestrial arthropods have a storage organ - a fatty body located between the viscera. The fat body takes part in the regulation of water metabolism.

Nervous system. In general, in arthropods, the nervous system is built according to the type of annelids. It consists of a paired supraesophageal ganglion, peripharyngeal nerve ring and ventral nerve cord. Peripheral nerves depart from the ganglia of the chain. The supraesophageal ganglion in insects, in which the presence of a brain is usually said, reaches a special development. Often there is a concentration of ganglia of the abdominal nerve chain and the formation of large ganglions due to their fusion. Such a concentration is often associated with a decrease in the number of segments (merging them together). For example, in ticks that have lost segmentation, the abdominal chain turns into a common nerve mass. And in centipedes, whose body consists of many identical segments, the nerve chain is very typical.

sense organs most arthropods reach a high development.

organs of vision are located on the head and are often represented by complex (compound eyes), which occupy most of the surface of the head in some insects. Many crustaceans have compound eyes that sit on stalks. In addition, insects and arachnids have simple eyes. An unpaired frontal ocellus is characteristic of some crustaceans.

sense organs represented by various bristles and hairs located on the body and limbs.

Organs of smell and taste. Most of the olfactory endings are located on the antennae and jaw palps of insects, as well as on the antennulls of crustaceans. The sense of smell in insects is very well developed: 100 pheromone molecules per 1 cm 2 of air released by the female silkworm are enough for the male to start looking for a partner. The organs of taste in insects are located both on the mouth limbs and on the end segments of the legs.

Organs of balance. In crustaceans, in the main segment of the antennules, there is a statocyst - an invagination of the cuticle, seated from the inside with sensitive hairs. This cavity usually contains small grains of sand, which play the role of statoliths.

Hearing organs. Some insects have well-developed so-called tympanal organs that perceive sounds. For example, in grasshoppers, they are located on the bases of the shins of the front legs. As a rule, those insects that are able to perceive sounds are also able to make them. These include many orthoptera, some beetles, butterflies, etc. For this, insects have special adaptations located on the body, wings and limbs.

Spinning glands. Some arthropods are characterized by the presence of spinning glands. In spiders, they are located in the abdomen and open with arachnoid warts at the tip of the abdomen. Spiders use their webs most often for hunting and building shelters. This thread is one of the strongest in nature.

In the larvae of a number of insects, the spinning glands are located in the anterior part of the body and open near the mouth opening. Their cobweb goes mostly to build a shelter or cocoon.

Sexual system. Arthropods are dioecious animals that often have sexual dimorphism. Males differ from females in brighter coloration and often smaller size. In male insects, the antennae are much more developed.

reproductive system females consists of glands - ovaries, oviducts and vagina. This also includes accessory glands and seminal receptacles. Of the external organs, an ovipositor of various structures may be present.

At males reproductive organs are represented by testes, efferent ducts and accessory glands. A number of forms have differently arranged copulatory organs.

Polymorphism. In the colonies of social insects there are individuals that differ from each other in structure, physiology and behavior. In the nests of bees, ants and termites, there is usually only one female capable of laying eggs (womb or queen). Males in the colony are either constantly present, or appear as the sperm reserve in the uterus from the previous mating is depleted. All other individuals are called workers, which are females with depressed sexual function. In termites and ants, workers are divided into castes, each of which performs a specific function (gathering food, protecting the nest, etc.). The appearance of males and full-fledged females in the nest occurs only at a certain time.
Biology of reproduction. As already mentioned, arthropods are dioecious animals. However, among them, cases of parthenogenesis (aphids, daphnia) are not uncommon. Sometimes mating is preceded by a courtship ritual, and even fights between males for a female (in stag beetles). After mating, the female sometimes eats the male (mantises, some spiders).

Most often, eggs are laid in groups or one at a time. In some arthropods, the development of eggs and larvae occurs in the body of the female. In these cases, there is a live birth (scorpions, some flies). In the life of many species of arthropods, care for offspring takes place.

Fertility arthropod varies over a very wide range and depends very often on environmental conditions. In some aphids, for example, females lay only one overwintering egg. Uterus honey bee able to lay up to 3,000 eggs per day, and termite queens up to 30,000 per day. These insects lay millions of eggs during their lifetime. On average, fertility is several tens or hundreds of eggs.

Development. In most arthropods, development occurs with metamorphosis, that is, with transformation. A larva emerges from the egg, which, after several molts, the larva turns into an adult animal (imago). Often the larva is very different from the adult both in structure and in lifestyle.

In the development cycle of a number of insects, there is pupal phase(butterflies, beetles, flies). In this case, one speaks of complete metamorphosis. Others (aphids, dragonflies, bugs) do not have such a phase, and the metamorphosis of these insects is called incomplete.

Some arthropods (spiders, scorpions) have direct development. In this case, fully formed young animals emerge from the eggs.

Lifespan arthropods is usually calculated in several weeks or months. In some cases, development is delayed for years. For example, the larvae of May beetles develop for about 3 years, deer beetles - up to 6 years. In cicadas, the larvae live in the soil for up to 16 years, and only after that they turn into adult cicadas. Mayfly larvae live in water bodies for 1-3 years, and an adult insect lives only a few hours, during which it manages to mate and lay eggs.

Distribution and ecology. Representatives of the arthropod type are found in almost any biotope. They are found on land, in fresh and salt water, and in the air. Among arthropods, there are both widespread and endemic species. The first one is the butterfly. cabbage white, crustaceans - daphnia, soil mites. Endemic species include, for example, large and very beautiful butterfly brameya, which is found only in the Colchis lowland.

The distribution of individual species is limited by various environmental factors.

From abiotic factors the most important are temperature and humidity. The temperature limits of the active existence of arthropods lie in the range from 6 to 42°C. With a decrease or increase in temperature, animals fall into a state of stupor. Different phases of development of arthropods tolerate temperature fluctuations in different ways.

The humidity of the environment also largely determines the possibility of the existence of arthropods. Excessively low humidity of the environment, as well as high, can lead to death. For aquatic arthropods, the presence of liquid moisture is a necessary condition for active existence.
On the distribution of arthropods big influence provides human activity anthropogenic influence ). Changing environmental conditions lead to a change species composition. As a result of human industrial and agricultural activities, some species disappear, while other species multiply extremely rapidly, becoming pests.

Origin. Most researchers agree that arthropods descended from ancestors close to annelids. Crustaceans, chelicerae, and extinct trilobites are thought to have evolved from annuli by one common root, and centipedes and insects by another.

Paleontological material on arthropods is very extensive. Thanks to the chitinous cuticle, their remains are quite well preserved in a petrified form. Terrestrial arthropods are exceptionally well preserved in amber as well. However, despite this, it is difficult to accurately trace the evolution of arthropods: the distant ancestors of arthropods in the geological layers have not been preserved. Therefore, the main methods of studying this issue are comparative anatomical and comparative embryological.
In practical human activity, it is customary to distinguish between beneficial and harmful species.

Let's take a closer look at a number of animals that biology studies very carefully - a type of annelids. To learn a little about them, you need to consider their species components, a special way of life, habitat, as well as the external and internal structure of their body.

General signs and features of the type annelids

Ringed worms or otherwise rings, annelids - this is one of the largest groups among animals, which, according to general data, carries about 18 thousand open species. Basically, these animals are presented as non-skeletal vertebrates that are able to participate in the destruction of organic substances, and are also considered the basis of nutrition for other species of the animal world.
In what environment do ringworms mainly live? So, the area of residence of the Rings is very wide - they include seas and land, as well as freshwater reservoirs. You can find a lot of annelids that live on the surface salty seas as well as the oceans. Ringed worms live everywhere, they can be found at any depth of the oceans and even found at the bottom Mariana Trench. The density of the population of ocean worms is very high - up to 100,000 units of rings per square meter of the bottom surface. Marines are considered best food for fish and play one of the main roles in the processes of the ecosystem of the seas.

In fresh water areas you can find predominantly blood-sucking individuals, for example, leeches, which are very often used in the medical field. On the territory of tropical latitudes, leeches can live both in the soil and on trees.

aquatic individuals not only crawl along the bottom or burrow into the surface, but can also create a protective tube on their own and live there for a long time until someone disturbs the animal.

The most popular are the rings that live in the surface of the soil, their name is earthworms. The density of these individuals in meadow and forest soils can reach 600 units per square meter. Also, these worms are involved in the formation of soil and soil.

What classes of rings live on earth?

About 200 years ago, Georges Cuvier did work in the field of animal classification and brought out only 6 rows of his representatives. This number also included arthropods - creatures whose bodies were previously divided by nature into segments. This group includes: woodlice, earthworms, leeches, insects, spiders, and crayfish.

A small number of features can be distinguished in annelids, with the help of which they were separated into a whole group. The most important thing is that they have a celloma (secondary body cavity), metamerism (segmentation) of the body and a well-developed circulatory system. In addition to all this, annelids have unusual organs of movement - parapodia. Also, the rings have a developed nervous system, which includes the supraesophageal ganglion, as well as the abdominal nerve chain. The structure of the excretory system in the rings is metanephridal.

Annelids, according to experts, were divided into 4 main classes. Basic classes of rings:

What does the appearance of an annelids look like?

Annelids can be characterized as the most highly organized representatives of the group of worms. The length of their body ranges from a few millimeters to 2.5 meters. The body of an individual can be visually divided into three main parts: the head, the trunk, and the anal lobe. Home hallmark worms is that there is no clear division into departments, as occurs in higher varieties of animals, in annelids.

In the area of the head of an individual there are various sensory organs. Most annelids have a well-developed vision. Some annelids can be proud of their special eyes, as well as very clear vision. The organ of vision in these animals can be located not only in the head region, but also on the tail, body or tentacles.

Taste buds are especially developed in worms. Worms are able to sense various odors well with the help of developed olfactory cells, as well as ciliary pits. The auditory part of the rings is created on the principle of locators. It happens that Echiruids are able to hear and recognize even the quietest sound with the help of their hearing organ, which is similar in structure to the lateral line in fish.

What are the respiratory organs, as well as the hematopoietic system in a creature?

Description of the digestive system and excretory organs of the annulus

The digestive system in annelids can be roughly divided into three areas. The anterior intestine (or stomodeum) contains the mouth opening, as well as the oral cavity of the worm, sharp and powerful jaws, pharynx, salivary glands, and a very narrow esophagus.

The oral cavity, the second name of which is the buccal region, can turn inside out without problems. Behind this section, you can find powerful jaws bent inward. This device is very necessary in order to quickly and deftly capture your prey.

Then comes the mesodeum - the middle intestine. The anatomy of this department is quite homogeneous throughout the body area. The middle intestine is certain places narrows and expands again, it is here that the process of digestion of food is carried out. The hindgut is rather short and is an anus.

The excretory system of the worm consists of metanephridia, which are located in pairs in each of the segments of the annulus. They help highlight extra products vital activity from the cavity fluid.

The concept of the sense organs and the nervous system of the animal

Each of the classes of annelids has its own gangion type system. It includes the parapharyngeal nerve ring, which is created by connecting the supraesophageal and subpharyngeal ganglia, as well as from pairs of the chain of abdominal ganglia that are present in each of the segments.

The sense organs of annelids are quite well developed. So, worms have sharp eyesight, good hearing and smell, as well as touch. Some individuals of annelids can not easily capture light, but also emit it on their own.

The process of reproduction in annelids

Description by experts annelids reports that these individuals are able to reproduce both sexually and asexually. Asexual reproduction occurs by dividing the body into several parts. The worm is able to break up into several halves, each of which subsequently becomes a full-fledged creature.

With all this, the creature's tail is considered independent and cannot grow a new head on itself. In some situations, the second head grows on its own in the middle of the worm's body even before the separation process.

Reproduction by budding is quite rare. Particularly interesting are those individuals whose budding can cover the entire area of the body, at which time the posterior ends bud from each segment. During reproduction, additional oral cavities may appear, which over time will become separate full-fledged individuals.

Worms in most cases are dioecious, but some species (leeches and earthworms) have developed hermaphroditism in themselves - a process in which both individuals perform two functions at once, the role of female and male. The process of fertilization can be carried out both in the external environment and in the organism of creatures.

For example, in marine worms that reproduce only sexually, fertilization is considered external. Individuals of different sexes usually throw their germ cells to the surface of the water, where the process of fusion of eggs and spermatozoa takes place. From eggs of the fertilized type, larvae arise, which are quite distinctive in appearance from adults. Freshwater, as well as terrestrial rings, do not have a larval stage, they are immediately born with exactly the same structure as in adult creatures.

Polychaete class

Curious, sessile worms, serpulids, that live in helical or twisted tubes of the Izvet type. Serpulids are accustomed only to protrude their head with large fan-shaped gills from their house.

leeches

All leeches are predators, which for the most part feed only on the blood of warm-blooded creatures, worms, fish and mollusks. The area of distribution and habitat of annelids from the class of leeches is very diverse. V more leeches can be found on fresh water or wet grass. But there are marine species, and in Ceylon you can even find ground view leeches.

In addition to earthworms, many others similar to them live in the soil. Their body segments have several short bristles invisible to the naked eye. These worms, making passages in the soil, loosen it and contribute to the penetration of water and air into the soil, which are necessary for the development of plants. The mucus secreted by the worms sticks together the smallest particles of the soil, thereby preventing its spraying and erosion. Dragging plant residues into the soil, they contribute to their decomposition and the formation of fertile soil. Therefore, earthworms should be protected as useful animals.

Pattern: polychaete worms

Many other annelids, similar to earthworms, live at the bottom of fresh water bodies. Most of them are small, but often found in huge quantities - more than 100,000 per 1 m 2 of the bottom.

Many annelids have numerous long setae. They are collected in bundles and located on special muscular outgrowths on the sides of each segment. Raking these outgrowths, clinging to the bottom, the worm crawls. Thus, these outgrowths represent the rudimentary form of paired limbs. These worms are found in the seas, where many fish feed on them.