Type Arthropods. Class Crustaceans

General characteristic of the type of Arthropods

Among all groups of invertebrate animals, the type of arthropods is distinguished by the greatest variety of adaptations to the most diverse conditions of existence, an amazing richness of forms and a huge number of species.

General Characteristics of Crustaceans

The body of crustaceans is in length from 0.5 mm to 80 cm. It is covered with chitinous shell and consists of the head, chest and abdomen. On the head there are two pairs of tactile appendages (antennas and antennals) and three pairs of jaws. Chest and abdomen segmented. The number of legs in different groups of crustaceans may vary.

Digestive system   crustaceans includes chewing stomach, intestines and "liver". Respiratory organs - the gills located on the limbs or on the sides of the body, and in some land forms - pseudo-trachea. The organs of excretion are whole-products (ducts connecting the whole with the external environment). Sense organs - statocysts and antennae.

Most cancers are split; barnacles, leading a sedentary lifestyle, are hermaphrodites. Fertilization is external (males attach spermatophores near the genital openings of females). As a rule, these animals develop with several metamorphoses; their larva is called nauplius.

Crustaceans originated either from extinct or directly from annelids. In the fossil state, they are known from the Cambrian. There are about 30,000 species of modern crustaceans, grouped into 5 subclasses (according to other studies - classes): remipedias, cephalocarids, branchic toes, maxillopods (shellfish, usonogie and copepods, tantulokarida, gilliferous) and higher cancers.

Crustaceans, or crayfish, have evolved from trilobites-like arthropods, which have shifted to faster movement at the bottom of water bodies and in the water column. In connection with a more active lifestyle, the organization of crustaceans became much more complicated compared to their ancestors. This is a large and diverse class, whose representatives live in marine, fresh and brackish waters. Only a few crustaceans live on land, but only in humid places.
External structure. The structure of crayfish (see fig. 75, 80) is very diverse. The division of the body into sections in different groups is not similar. Often the head and thoracic regions merge together, forming the cephalothorax, with which the segmented abdomen joins. The size of the body varies widely: a variety of forms - microscopic organisms that live mainly in the water column; bottom forms often reach large sizes. The cuticle of crustaceans, as in all aquatic arthropods, consists of two main layers: the inner — endocuticle, and the outer — exocuticle (Fig. 78). The latter is saturated with tannins and therefore very durable. During molting, the endocuticle dissolves and is absorbed by the hypodermis, and the exocuticle is insoluble and completely discarded. Large crayfish are covered with strong shells. Small forms can also have armor-plated formations, but for the most part the chitinous cuticle covering them is thin. In one order of lower crayfish (shell crustaceans) the body is enclosed in a bicuspid calcareous shell. All crustaceans have two pairs of antennae, or antennas (Fig. 73, 80), whose structure and functions in different groups of the class are not similar (see further).

Nervous system.   In a number of lower forms, the central part of this system consists of a relatively simple brain and abdominal strands, forming a ladder, not a chain (see Fig. 72); in the remaining crustaceans, the brain becomes more complex ( varying degrees   in different groups), the abdominal strands form a chain, the nodes of which, as the concentration of the body increases, can join up to the merging of all the nodes into one (see Fig. 72). The behavior of the highest representatives of the class, which are, as a rule, active predators, reaching a very large size, is very complicated and is ensured by progressive changes throughout the nervous system. The organs of touch in the form of sensitive bristles are scattered throughout the body, but especially there are a lot of them on the antennae. Organs that perceive chemical irritations are rather well developed; in large crayfish, they focus mainly on the antennas of the first pair. Equilibrium organs (statocyst) are distributed mainly in higher cancers and are located in the first segment of the first pair of antennae (Fig. 79).

Eyes can be simple and complex. Complex, or faceted, eyes (Fig. 79) consist of a large number of individual eyes, or ommatidia. Each ommatidia consists of a cornea (the transparent part of the chitinous cuticle), a crystal cone — an elongated transparent body adjoined with nerve, or retinal, cells that emit light-sensitive rods (rhabdoms) at their inner edges. Ommatidia are separated from each other by pigment cells. The rays falling on the ommatidia slantwise are absorbed by the pigment cells, which isolate ommatidia from each other, and do not reach the nerve cells. The latter perceive only those rays that fall perpendicular to the surface of ommatidia. Thus, each ommatidium perceives only a part of the object, yet ommatidia is the whole object. The image of an object in a complex eye is made up of separate parts of it and resembles mosaic pictures (or mosaics) made up of multi-colored stones or plates. Therefore, this vision is called mosaic. Many large crayfish have complex eyes on special stalks.

Propulsion system.   The movement of crayfish is accomplished with the help of various limbs — antennas or legs in plankton, usually small forms (Fig. 80), special walking legs in benthic, usually large forms (see Fig. 73). In addition, the latter can swim, due to the strong bending of the abdomen under the chest. In crayfish, in contrast to terrestrial arthropods, two-legged limbs are widely distributed, which, together with the bristles, have a wide surface and are convenient for use as oars. In large crayfish, for example, in the river, the branches of the back pair of legs turned into two wide plates (see Fig. 73), which, together with the last, very wide abdominal segment, help well when digging water in the abdomen.
Circulatory system.   The heart, like all arthropods, located on the dorsal side, is found in most crustaceans (see Fig. 75, 80, A). The shape of the heart is different: from a long tube to a compact bag. In a number of small forms, the heart is absent and the movement of blood is caused in them by movements of the intestines, as well as movements of the whole body. The development of a network of blood vessels mainly depends on the size of the body: in large crayfish, it can be developed quite well, in small ones it can be completely reduced.

Respiratory system. The organs of respiration in the majority of crustaceans are the gills, which are appendages of the legs that have a different shape: in small crayfish they are rounded leaves (Fig. 80, A), in large crayfish (such as in crayfish) they are finely dissected (see Fig. 75), due to which their surface increases. The change of water near the gills occurs due to the movement of the legs on which they are located, as well as due to the movement of certain limbs that do not have gills. Quite a significant number of small species of gills do not have and the absorption of oxygen occurs through the surface of the body, mainly in its thinner places.
Excretory system.   The excretory system is represented mainly by a pair, rarely more, metanephridium. The decrease in the number of these organs compared to the ringed worms, in which they are numerous, is mainly due to the fact that the crustaceans have a solid body cavity, which is not divided by partitions, like ring-necks, and it is enough for them to have a small number of excretory organs, on a number of departments (Fig. 81). In higher crayfish, metanefridia reach an especially great complexity, they are large (about 1 cm and more) and open at the base of the antennas of the second pair and therefore are called antennal. For the remaining cancers, metanefridia are simpler, they are smaller (see Fig. 80, A) and open at the base of the second pair lower jaws, or maxillus, why got the name maxillary.
Digestive system.   The digestive system is very diverse. Small crustaceans (see Fig. 80) living in the water column receive food (organic pieces, bacteria, algae, microscopic animals) as a result of vigorous work in some antennae, in others in mouth extremities, in the third - thoracic legs creating continuous flow of water. In daphnia crustaceans, the rear pectoral legs strike 200-300 times per minute and ensure the ingestion of food in the mouth. Large crayfish (see fig. 73) seize prey with their feet armed with claws.
Crustaceans, like all arthropods, have limbs that surround the mouth and perform a number of functions. Among the mouth limbs of a river and other crayfish, for example, are (see fig. 73) well-developed mandibles, or upper jaws, with a segmented palpus and lamella, the inner edge of which is jagged and serves for chafing food, and two pairs of lower jaws, which also serve for the mechanical processing of food. In addition, three pairs of legs, already located on the chest, help to hold food and pass it to the mouth. In the anterior part of the digestive apparatus in many species a large chewing stomach develops (see Fig. 75), the walls of which are thickened due to the cuticular formations and are used for the mechanical processing of food. Food digestion occurs in the midgut, into which the ducts of the digestive gland, called the liver, flow. In fact, this gland performs the functions of the pancreas and hepatic glands of vertebrate animals, as it secretes juice, which facilitates the digestion of all the basic organic compounds - proteins, carbohydrates and fats: the liver of vertebrates plays a large role mainly in the digestion of fats. Therefore, the digestive gland of crayfish is more correct to call pancreatic-hepatic. In small crustaceans, these glands are moderately developed, in the form of hepatic processes (see Fig. 80, A, 10), in large crayfish it is a large organ consisting of several lobes (see Fig. 75).
Reproduction.   Reproduction sex. Most species are dioecious. Males, as a rule, are very different from females in body size, limb structure, etc. Parthenogenesis is widespread in some groups of lower cancers. In coniferous crustaceans, which include many species (for example, various daphnias) that serve as food for fish, most females in the warm season are found only to lay unfertilized eggs, from which new crustaceans rapidly develop. Males usually appear before the onset of the cold season or other adverse conditions. Females fertilized by males lay eggs surrounded by strong, thick shells, which develop only in the next year. Many crayfish bear eggs on the abdomen or in a special brood chamber (see fig. 80, A).
Development.   Development with transformation or direct. In the lower crustaceans, developing with transformation, larvae, called nauplius (fig. 82). These larvae have three pairs of legs and one eye. In higher crayfish that live in the sea, the larvae, called zoea, mostly come from eggs (Fig. 82). Zoe have more limbs than nauplii, and two compound eyes; they are studded with thorns, which increase their surface and facilitate evaporation in water. There are other types of larvae that are intermediate between nauplius and the zoe or between the zoe and the adult form. Many lower freshwater crustaceans and crayfish have a direct development.
Crayfish growth is always associated with molting; for example, crayfish molts 10 times during the first year of its life and therefore grows rapidly (from 0.9 to 4.5 cm), it molts 5 times during the second year, only twice during the third year, and then females molt once a year, and males - 2 times. After 5 years, they barely grow; live 15 - 20 years.
Origin.   Crustaceans originated, as noted above, from arthropods close to trilobites. In connection with adapting to a more active and complex way of life, their body’s differentiation into sections intensified, many segments merged, that is, the body’s concentration increased; complicated nervous system; the structure of the limbs (generally the same for trilobites), in connection with the performance of various functions, has become diverse; increased intensity of the work of other organ systems.

Crustaceans are ancient aquatic animals that have a complex dismemberment of the body covered with chitinous shell, with the exception of woodlice living on the ground. They have up to 19 pairs of jointed legs that perform various functions: capturing and grinding food, moving, protecting, mating, carrying juveniles. These animals feed on worms, mollusks, lower crustaceans, fish, plants, and crayfish eat dead prey - the corpses of fish, frogs and other animals, performing the role of sanitation ponds, especially since they prefer very clean fresh water.

Lower crustaceans - daphnids and cyclops, representatives of zooplankton - serve as food for fish, their fry, toothless whales. Many crustaceans (crabs, shrimps, lobsters, lobsters) are commercial or specially bred animals.

Two species of crustaceans are included in the Red Book of the USSR.

general characteristics

From a medical point of view, some species of planktonic crustaceans are of interest as intermediate hosts of helminths (cyclops and diaptomus).

Until recently, the Class Crustaceans were divided into two subclasses - lower and higher cancers. In the subclass of lower crayfish, leaf-legged, maxillofeed and shell crayfish were combined. It is now recognized that such an association is impossible, since these crayfish groups are different in their origin.

In this section, the Crustaceans will be considered according to the old classification.

The body of the crustaceans is divided into the head and abdomen. The head of the chest consists of segments of the head and chest, merging into a common, usually undifferentiated part of the body. Abdomen more often dissected.

All crustaceans have 5 pairs of limbs of the head. The first 2 pairs are articulate antennae; This so-called antennula and antenna. They carry the organs of touch, smell and balance. The next 3 pairs, the mouthparts, are used to trap and chop food. These include a pair of upper jaws, or mandibles, and 2 pairs of lower jaws - maxilla. Each breast segment carries a pair of legs. These include the maxillary jaws involved in food retention and locomotor limbs (walking legs). The abdomen of higher crayfish also carries limbs - swimming legs. The lower ones do not have them.

For crustaceans, the two-legged limb structure is characteristic. They distinguish the base, the outer (dorsal) and the inner (ventral) branches. Such a structure of the extremities and the presence of gill outgrowths on them confirms the origin of crustaceans from polychaematous annelids with two-branched parapodia.

In connection with the evolution in the aquatic environment of the crustaceans, the organs of water respiration, the gills, developed. They often represent growths on the limbs. Oxygen is delivered by blood from the gill to the tissues. Lower crayfish have colorless blood called hemolymph. Higher cancers have real blood containing oxygen-binding pigments. The blood pigment of the crayfish river - hemocyanin - contains copper atoms and gives the blood a blue color.

The organs of excretion are one or two pairs of modified metanephridium. The first pair is located in the anterior part of the cephalothorax; its duct opens at the base of the antennas (antennal glands). The duct of the second pair opens at the base of the maxillae (maxillary glands).

Crustaceans, with rare exceptions, are dioecious. Develop usually with metamorphosis. From the egg comes the nauplius larva with a non-segmented body, 3 pairs of limbs and one unpaired eye.

• Subclass Entomostraca (lower crayfish).

  Lower crayfish live in freshwater as well as in the seas. They are important in the biosphere, being an essential part of the diet of many fish and cetaceans. Most important are copepods (Copepoda), which serve as intermediate hosts for human helminths (diphyllobothriids and rishta). They are found everywhere in ponds, lakes and other stagnant bodies of water, inhabiting the water column.

general characteristics

The body of the crustacean is dissected into segments. A complex head carries one eye, two pairs of antennas, an oral apparatus plus a pair of legs-jaws. One pair of antennas is much longer than the other. This pair of antennas is highly developed, their main function is movement. Also, they often serve to hold the female as a mate during mating. Chest of 5 segments, chest legs with swimming bristles. Abdomen of 4 segments, at the end - the fork. At the base of the abdomen are females with 1 or 2 egg sacs, in which eggs develop. From the eggs come the nauplii larvae. The nauplios that were hatched out by their appearance are completely different from adult crustaceans. Development is accompanied by metamorphosis. Copepods feed on organic remains, the smallest aquatic organisms: algae, infusoria, etc .. They live in water bodies all year round.

The most common genus is diaptomus (Diaptomus)

Diaptomuses inhabit the open part of water bodies. The size of the crustacean is up to 5 mm. The body is covered with a rather hard shell due to which it is reluctantly eaten by fish. Color depends on the nutrient base of the reservoir. Diaptomuses have 11 pairs of limbs. Antenna antenowules, antennas and legs of the thoracic segments are two-legged. Particularly large lengths reach the antennula; they are longer than the body. Scattering them widely, diptomuses hover in the water, the pectoral limbs cause abrupt movements of the crustaceans. Oral limbs are in constant oscillatory motion and adjust the particles suspended in water to the oral opening. In diptomuses, both sexes take part in breeding. The females of diaptomus, unlike the females of the Cyclops, have only one egg bag.

Species of the genus Cyclops

inhabit mostly coastal zones of water bodies. Their antennas are shorter than those of diptomuses, and participate along with the chest legs in the movement of jumps. The color of the cyclops depends on the type and color of the food they eat (gray, green, yellow, red, brown). Their size reaches 1-5.5 mm. Both sexes take part in breeding. The female bears fertilized eggs in egg sacs (they are two in Cyclops) attached at the base of the abdomen.

In their biochemical composition, copepods are in the top ten high-protein feeds. In aquarism, Cyclops is most often used for feeding grown juvenile and small-sized fish species.

Daphnia, or water fleas

move abruptly. Daphnia body, 1-2 mm long, is enclosed in a bivalve transparent chitinous shell. Head extended to beak-like outgrowth directed to abdominal side. On the head there is one complex facet eye and in front of it is a simple peephole. The first pair of antennae is small, rod-shaped. Antennae of the second pair are strongly developed, two-branched (with their help daphnia swims). On the thoracic region there are five pairs of leafy legs, on which there are numerous feathery setae. Together, they form a filtration apparatus that serves to filter out small organic residues from the water, single-celled algae and bacteria that feed daphnids. At the base of the thoracic legs there are gill lobes, in which gas exchange takes place. On the dorsal side of the body is the barrel-shaped heart. There are no blood vessels. A slightly curved tubular intestine with food, heart, and a brood chamber, in which daphnia larvae develop, are clearly visible through the transparent shell.

• Subclass of Malacostraca (higher crayfish). The structure is much more complicated than that of lower crayfish. Along with small plankton forms there are relatively large species.

  Higher crayfish - the inhabitants of marine and freshwater. On land, only woodlice and some crayfish live in this class (palm cancer). Some species of higher crayfish serve as an object of fishing. In the seas of the Far East, a giant Pacific crab is harvested, whose walking legs are used as food. In Western Europe, lobster and lobster are harvested. In addition, crayfish have sanitary value, since free of water from the corpses of animals. Freshwater crayfish and crabs in the East are intermediate hosts for the pulmonary flukes.

  A typical representative of higher cancers is crayfish.

Crayfish live in flowing fresh water (rivers, streams), feeds mainly on plant food, as well as dead and living animals. During the day, crayfish hide in safe places: under stones, between the roots of coastal plants, or in burrows, which they dig up with claws in steep banks. Only at nightfall does he go out to look for his food. For the winter, crayfish hide in their burrows.

Structure and reproduction of crayfish

External structure. The body of a crayfish outside is covered with a cuticle impregnated with calcium carbonate, which gives it strength, so the cuticle is called a shell. The shell protects the crayfish body from damage and acts as an external skeleton. At a young age, during the period of growth, river crayfish change the shell. This process is called molting. Over time, when crayfish reaches a large size, it grows slowly and rarely sheds.

The color of the shell of live crayfish depends on the color of the muddy bottom on which it lives. It can be greenish-brown, light green, dark green and even almost black. This color has a protective character and allows the cancer to become invisible. When the caught crayfish are boiled, part of the chemicals that cause the shell color are destroyed, but one of them, red astaksantin, does not disintegrate at 100 ° C, which determines the red color of boiled cancer.

The body of crayfish is divided into three sections: the head, chest and abdomen. On the dorsal side of the head and thoracic parts, they are covered with a single cephalothoracic continuous strong chitinous shield, which has a sharp spike on the front, with complex eyes, a pair of short and a pair of long, thin antennae in the recesses on the moving stalks. The latter are a modified first pair of limbs.

On the sides and below of the oral opening of the cancer are six pairs of limbs: the upper jaws, two pairs of lower jaws and three pairs of maxillary jaws. Five pairs of walking legs are also placed on the cephalothorax, with three claws on the three front pairs. The first pair of walking legs is the largest, with the most well developed claws, which are the defense and attack organs. Oral limbs with claws hold food, crush it and send it to the mouth. The upper jaw is thick, serrated, powerful muscles are attached to it from the inside.

The abdomen consists of six segments. The extremities of the first and second segments in the male are modified (they participate in copulation), the females are reduced. On the four segments are two-segmented jointed toe; The sixth pair of limbs - wide, lamellar, are part of the caudal fin (it, along with the caudal blade, plays an important role when swimming backwards).

Crayfish movement. Crawfish can crawl and swim back and forth. He crawls along the bottom of the reservoir with the help of walking legs. Forward crayfish swims slowly, turning over the abdominal legs. He uses the tail fin to move backwards. Straightening it and bending the abdomen, crayfish makes a strong push and quickly swims back.

Digestive system   begins with the mouth opening, then food enters the pharynx, short esophagus and stomach. The stomach is divided into two sections - chewing and filtering. On the dorsal and lateral walls of the chewing section, the cuticle forms three powerful lime-infused chitinous chewing plates with jagged free edges. In the filtering department, two plates with hairs act like a filter through which only heavily shredded food passes. Then the food enters the midgut, where the ducts of the large digestive gland open. Under the action of digestive enzymes secreted by the gland, food is digested and absorbed through the walls of the midgut and gland (it is also called the liver, but its secret breaks down not only fats, but also proteins and carbohydrates, that is, functionally corresponds to the liver and pancreas of vertebrate animals). Undigested remnants enter the posterior intestine and are brought out through the anus on the caudal blade.

Respiratory system. Crayfish breathe through the gills. The gills are feathery outgrowths of the thoracic limbs and the side walls of the body. They are located on the sides of the cephalothoracic shield inside a special gill cavity. The cephalic shield protects the gills from damage and rapid drying, so the cancer can live outside the water for some time. But as soon as the gills dry out a little, the cancer dies.

Circulatory organs. The circulatory system of crayfish is open. Blood circulation occurs due to the work of the heart. The heart is pentagonal in shape, located on the dorsal side of the cephalothorax beneath the shield. Away from the heart blood vesselsopening into the body cavity where blood gives oxygen to tissues and organs. Then the blood flows into the gills. Water circulation in the gill cavity is ensured by the movement of a special process of the second pair of lower jaws (it produces up to 200 flapping movements in 1 minute). Gas exchange occurs through the thin cuticle of the gills. The blood enriched with oxygen through the gill-cardiac canals is sent to the pericardial bag, from there through special openings it enters the heart cavity. Blood cancer is colorless.

Discharge organs paired, have the form of round green glands, which are located at the base of the head and open outward with a hole at the base of the second pair of antennae.

Nervous system   consists of a paired supraaryngeal node (brain), peripharyngeal connections and the ventral nerve cord. From the brain, nerves go to the antennae and eyes, from the first node of the abdominal nervous chain, or the subpharyngeal ganglion, to the mouth organs, from the following chest and abdominal nodes of the chain, respectively to the chest and abdominal extremities and internal organs.

Sense organs. The complex, or facet eyes of the crayfish are located in the front part of the head on mobile stalks. Each eye contains more than 3 thousand eyes, or facets, separated from each other by thin layers of pigment. The light-sensitive part of each facet perceives only a narrow beam of rays perpendicular to its surface. The whole image is made up of many small partial images (like a mosaic image in art, so they say that arthropods have mosaic vision).

The antennae of the cancer serve as organs of touch and smell. At the base of the short whiskers there is an organ of equilibrium (statocysts, located in the main segment of the short antennae).

Reproduction and development. In crayfish developed sexual dimorphism. In males, the first and second pairs of abdominal legs are modified into a copulatory organ. In the female, the first pair of abdominal legs is rudimentary; on the other four pairs of abdominal legs, she bears eggs (fertilized eggs) and young crustaceans, which for some time remain protected by the mother, clinging to their abdominal claws with their claws. So the female takes care of her offspring. Young crayfish grow rapidly and molt several times a year. Development in crayfish direct. Crayfish breed rather quickly, despite the fact that they have relatively few eggs: the female lays from 60 to 150-200, rarely up to 300 eggs.

Crustacean meaning

Daphnids, Cyclops, and other small crustaceans consume large amounts of organic residues from dead small animals, bacteria, and algae, thereby purifying the water. In turn, they represent an important food source for larger invertebrates and juvenile fish, as well as for some valuable plankton-eating fish (for example, whitefish). In pond fish farms and fish factories, crustaceans are specially bred in large pools, where they create favorable conditions for their continuous reproduction. Daphnia and other crustaceans feed juvenile sturgeon, sturgeon sturgeon and other fish.

Many crustaceans have commercial value. About 70% of the global crustacean industry is shrimp, and they are also bred in ponds created in the coastal lowlands and connected to the sea by a canal. Shrimps in the ponds are fed rice bran. There is fishing for krill - plankton sea crustaceans, forming large aggregations and serving whales, pinnipeds and fish. From krill get food pasta, fat, feed flour. Less important is fishing for lobsters and crabs. In our country, Kamchatka crab is harvested in the waters of the Bering, Okhotsk and Japanese seas. Commercial fishing of crayfish is carried out in freshwater bodies, mainly in Ukraine.

• Crustacea class (crustaceans)

Theme: Type Arthropods

crustacean class

Purpose:to study the organization of Crustaceans on the example of River Crayfish.

Tasks:

To study the classification of the type Arthropods. Learn arthropod type aromorphosis. Everything should be written in a notebook.

To study the organization of Crustacean class Arthropods on the example of river crayfish. Perform a summary in a notebook.

To consider wet preparations different types    crustaceans - Crab, Shrimp, Mokritsy, Shchitnya, River crayfish, Bokoplav, Daphnia. Under the microscope to examine the appearance of the Cyclops.

Examine the external and internal structure   Crayfish (autopsy cancer). Especially pay attention to the variety of extremities - they have 19 pairs in Crayfish.

In the album, make 2 drawings, marked V (red tick) in the printed manual. In the electronic manual, the necessary pictures are presented at the end of the file.

Know the answers to test questions    Topics:

General characteristic of the type Arthropods. Classification of the type Arthropods. Aromorphosis type Arthropods.

Features of the organization of arthropod class Crustaceans.

Systematic position, lifestyle, body structure, reproduction, meaning in nature and for man River crayfish.

Type Arthropods- Arthropoda

Arthropods are a type of invertebrate. By the number of species, they occupy the first place on Earth - there are more than 1.5 million of them. This is more than in all other types of animals combined. The habitats of arthropods are diverse: soil, fresh and sea ​​water, air, the surface of the earth, plant and animal organisms, including the human body. There are arthropods around the globe, but they are especially diverse in a hot tropical region. Arthropods are two-sidedly symmetric segmented animals with articulate limbs. Articular legs are the brightest and most important feature of the type.

Subdivided type into 4 subtypes:

Subtype 1. Trilobites   (Trilobitamorhpa). Represented by one by class Trilobites. It is about 10 thousand in. now extinct marine arthropods varied in the Cambrian and Paleozoic Ordovician.

Subtype 2. Toad   (Branchiata). In subtype one the class Crustaceans   (30 - 35 thousand in.). These are aquatic arthropods breathing through the gills.

Subtype 3. Helicer   (Chelicerata). In subtype 2 classes: the class Merostomovye   (the so-called rakoskorpiony - now extinct water helicopter) and the class Arachnids   (about 60 thousand in.).

Subtype 4. Tracheic   (Tracheata). Two classes: the class Centipedes   (over 53 thousand in.) and the class Insects   (more than 1 million in.)

Animal type Arthropods   have the following aromorphosis: 1. dense air- and airtight covers. 2. Articulate limbs for different purposes and different structures. During the evolution, the articulate limb of the Arthropod was descended from the parapodia of the Polychaete Nose worms. 3. Heteronic segmentation. 4. The division of the body into sections: head + chest + abdomen, or cephalothorax + abdomen.

Class Crustaceans   - Crustacea

Crayfish

Crustaceans, there are 30 - 35 thousand species of branch-like arthropods that lead to aquatic life. Only some species, for example, Mokritsy   and land crabs have adapted to live on land, but they also adhere to wetted habitats, as they breathe through the gills. The body sizes of crustaceans range from fractions of a millimeter to 3 m. This is the oldest group among the living arthropods.

Thus, the distinguishing features of the class is breathing with gill. In small crustacean gills are absent, gas exchange occurs through the surface of the body. The second distinguishing feature is the presence on the head section. two pairs of antennaeperforming a tactile and olfactory function. The third feature of crustaceans - two-legged limbs.

More details of the structure of the animal class Crustaceans should be considered on the example River crayfish - Astacus astacus(type Arthropods, subtype of Gillifers, Class Crustaceans, a subclass of Higher Crayfish, detachment Decapods Crayfish).

Class Crustaceans River Cancer

Lifestyle.Crayfish are common representatives of our freshwater fauna. River crayfish are medium-sized crayfish: their body length can reach 15–20 cm. River crayfish are found in rivers, lakes with a silt bottom and steep banks. Cancers do not tolerate any water pollution, they live only in clean water. During the day, crayfish hide in burrows dug by them in the banks under water (burrows deep up to 35 cm long). With the onset of darkness crayfish go out to get their own food. Crayfish are polyphages, i.e. feed on the most varied food: bottom sediments, algae, carrion, being, by that, sanitary workers of reservoirs. In winter, they do not change their place of residence, but simply go down much deeper, to where the water does not freeze. From late autumn to early spring, crayfish lead an inactive lifestyle, sitting in shelters for 20 hours a day. The life of females during this period is richer than that of males. Indeed, two weeks after mating, which occurs in October, the female lays about 100 eggs on her abdominal legs and harvests them for a long 8 months, that is, until the beginning of summer, when young crustaceans hatch from them. For the full development of eggs, caring females have to leave the hole from time to time in order to walk their eggs and clean them. Crayfish become active in the spring when the water is warm enough. (So ​​no mystery concerning the place where the crayfish hibernate does not exist at all.)

External structure.The body of the Crustacean is segmented, and the segments of the body are not identical in shape and function - this is the so-called heteronomic segmentation. The body consists of two sections: cephalic   and abdomen. The head of the cephalic chest carries five steam extremities. On the head of his blade are short antennae - antennulae   (olfactory organs). On the first segment there are long antennae - antennas   (organs of touch). On the other three - couple upper jaws   and two couples lower jaws. The upper jaws of the crayfish are called mandiblesand a pair of lower jaws - maxilla. Jaws surround mouth. Jaws cancer breaks prey into small pieces and pushes them into his mouth.

Even at the front end of the cephalothorax, the cancer has spherical eyesthat sit on long stalks. Therefore, cancer can simultaneously look in different directions.

The thoracic part of the cephalothorax consists of eight segments: the first three bear mandiblesinvolved in maintaining and grinding food. Behind the jaws follow five pairs of travel   or, in other words, walking legs (limbs). The first three pairs of walking limbs end clawsthat serve to protect and capture prey. Of these limbs with claws, the first pair bears claws especially powerful and large. With claws, the cancer seizes and holds the prey, defends itself during the attack. Two-legged jaws and walking legs consist of a lower branch in the form of a usual articulate stem and an upper branch, having the form of a tender leaflet or threads. The upper branch of the limb performs the function of the gills.

The articular mobile belly consists of six segments, each of which contains a pair of limbs. In males, the first and second pair of abdominal limbs are modified to copulative organinvolved in the mating process. The female has the first pair of limbs greatly shortened, to the rest.

Class Crustaceans River Cancer

four pairs of eggs are attached and young. Ends abdomen caudal finformed by the sixth pair of wide two-legged lamellar limbs and anal flattened lobe - telson.   Sharply bending the abdomen, the crayfish pushes off the water with a tail fin, like a paddle, and can quickly swim backwards in case of danger.

Thus, the crayfish body begins with the head lobe, followed by 18 segments, and ends with the anal lobe. Four head and eight trunk segments fused and formed the cephalothorax, followed by six abdominal segments. Thus, in crayfish 19 pairs of limbs   different structure and purpose.

The covers of the body.   Crustacean body covered in chitinized cuticleThe cuticle protects the body from external influences. In the peripheral layers of the cuticle, lime is deposited, as a result of which the lining of the cancer becomes rigid and durable, therefore the cuticle is also called shell. The inner layer consists of soft and elastic chitin.

In living River crayfish, the shell has a rather changeable color - from light green to almost black. This color has a protective character: as a rule, it fits to the color of the oozy bottom on which the cancer lives. The color of the crayfish depends on the several dyes contained in the integuments: pigments: red, blue, green, brown, etc. If you throw the cancer into boiling water, all pigments, except red, are destroyed by boiling. That is why boiled cancer is always red.

The cuticle simultaneously performs the function outdoor skeleton: serves as a place to attach muscles. But such a strong outer skeleton prevents the growth of the animal and therefore, periodically, all Crustaceans (and other arthropods) have to shed. Moult   This is a periodic reset of the old cuticle and its replacement with a new one. After molting, the cuticle remains soft for some time, at this moment the Cancer is growing rapidly. While the new cuticle has not yet formed (and it takes a week and a half for this River Cancer) Cancer is very vulnerable, therefore for the period of molting, the Cancers hide, do not hunt and do not eat. Before molting in the stomach of cancer, a pair of so-called lenticular "carbonate millstones" of calcium carbonate appears, this stock allows for faster hardening of the cancer lining, the "millstones" disappear after molting.

Sometimes shedding is very difficult for cancer: it is not being able to release its claw or walking leg from the old cuticle, it cuts it off. But a damaged limb is capable of regenerationThis is why some crayfish come across in which one claw is smaller than the other. Sometimes cancer, when he is in danger, with the help of his muscular effort specifically breaks down his claw: sacrifices a limb for the sake of the whole body.

Musculaturecrustacean consists of cross-striped fibers forming powerful muscle bundlesi.e. in crustaceans (and in all arthropods), the musculature is represented by individual bundles, and not by a sack as in worms.

Body cavityCrustaceans, like all arthropods, are secondary cavitary   (coelomic) animals.

Class Crustaceans River Cancer

Digestive systemconsists of three departments: front, average   and the back   guts. Anterior gut begins oral hole   and has a chitinous lining. Short esophagus   flows into stomachdivided into two parts: chewing   and filter. AT chewing department   mechanical grinding of food takes place with the help of three large thickenings of the cuticle, the “teeth”, and in filtering The food gruel is filtered, compacted and fed further into the midgut. The duct opens into the midgut. digestive glands, which performs the functions of the liver and pancreas. Here in the midgut, liquid food gruel is digested. Long the back intestine   is ending anal hole   on the anal lobe.

Respiratory system   at River Cancer are represented gills   - branching thin-walled outgrowths of the thoracic limbs of the maxilla and walking legs. The gills are the upper limb of the limbs. Gills tender, have the form of branched bushes. The gills are located on the sides of the chest in gill cavitiescovered by the cephalic chest armor. In small crustacean gills are absent and breathing is carried out the entire surface of the body ..

Circulatory system unlocked, consists of hearts,   located on the dorsal side of the cephalothorax, and several large blood vessels departing from it. vessels   - front and rear aorta. The heart has the shape of a pentagonal pouch. From vessels hemolymph   (this is the fluid that fills the circulatory system) is poured into the body cavity, it leaks between the organs and goes to the gills. Gas exchange occurs in the gills. The oxidized hemolymph enters pericardial bag   and through special openings (three pairs), it returns to the heart. The crustacean hemolymph may be colorless, reddish from the hemoglobin pigment contained in it and bluish from the hemocyanin pigment.

Excretory system   represented by a pair green glands   (original kidney). Each green gland consists of three parts: terminal pouch   (site coelom), departing from it twisted channel   with iron walls and urinary bubble. In the terminal sac the active absorption of metabolic products from the hemolymph occurs. Metabolism through the convoluted tubule enters the bladder. Bladders open out at the base of the antennas secretory pores   (ie, open somewhere between the eyes!).

Nervous system.   Crustacean nervous system staircase like   (as in Ringworms). The nervous system consists of couples epiglottic nervous knotswhich are often called the “brain” pharyngeal nervous rings   and couples abdominal nervous trunks   with ganglia (nodes) in each segment.

The sense organs are well developed. Short antennulae   specialize in smellingrather long antennas   - on touch. In general, all antennae and all limbs are dotted tactile hairs. Most decapods have antennas at the base of antennas. statocyst. Statocysts are depressions in the base of the short antennae, where ordinary grains of sand are placed. In the normal position of the body, these grains of sand press on the lower sensitive hairs under them; if the floating cancer body turns upside down, the grains of sand move and press already

Class Crustaceans River Cancer

other sensitive hairs and then the cancer feels that his body is out of its normal position and turns over. When molting cancer, the grains of sand are discarded. Then the cancer itself specifically pushes new grains of sand into its equilibrium organ.

The eyes of River Cancer are complex, faceted. Each eye consists of many small ocelli, in Crayfish there are more than three thousand. Each peephole perceives only a part of the object, and from their sum the overall picture is formed. This is the so-called mosaic vision.

Reproduction and development.   Crayfish in general delimiters. Crayfish is pronounced sexual dimorphism   - the male's abdomen is narrower, and the female - wider. In the male, the first pair of abdominal limbs transformed into copulative organs. In River cancer, the sex glands are not paired, are located in the cephalothorax. A pair of oviducts leaves the ovary, which open with sexual openings at the base of the third pair of walking legs (ie, on the cephalothorax). In males, a pair of long, convoluted seed tubes leaves the testicle, which are opened by the genital openings at the base of the fifth pair of walking legs. Before mating, the male collects sperm in their copulatory organs, and then these copulatory organs, which have the appearance of hollow tubes, are inserted into the female's genital opening. Fertilization in Crustaceans inner. Males reach sexual maturity by three years, and females by four. Mating occurs in the fall. Somewhere in late autumn, females lay fertilized eggs on the abdominal limbs (not a lot of eggs: 60 - 150, rarely up to 300). And only at the beginning of summer, racats emerge from the eggs, which for a long time are under the protection of the female, hiding on its abdomen from the underside. Young crayfish grow intensively and molt several times a year, adults molt only once a year. River crabs live 25 years.

Value.Crustaceans are of great importance in nature and human activities. Countless microscopic crustaceans that inhabit the marine and fresh waters and are the main part of zooplankton serve as food for many species of fish, cetaceans and other animals. Daphnia, Cyclops, Diaptomuses, Bokoplavy   - Great food for freshwater fish and their larvae.

Many small crustaceans feed on the filtration method, i.e. filter suspended in water detritus. Thanks to their food activity, natural water is clarified and its quality is improved. Many crustaceans are large commercial species (which have been severely affected), for example: Lobsters, Crabs, Lobster, Shrimp, Crayfish river. Medium-sized marine crustaceans are used by humans for the preparation of nutritious protein paste.

Class Crustaceans River Cancer

Fig. External structure of River Cancer (female).

Questions for self-control

Name the classification of the type Arthropods.

What is the systematic position of river crayfish?

Where do river crayfish live?

What form of body do River Crayfish have?

What is covered by the body of river crayfish?

What body cavity is characteristic of River Cancer?

What is the structure of the digestive River Cancer?

What is the structure of the circulatory system of river cancer?

How does the crayfish breathe?

What is the structure of the excretory system of river crayfish?

What is the structure of the nervous system of river cancer?

What is the structure of the reproductive system of River Cancer?

How to reproduce river cancer?

What is the significance of river cancer?

What is the value of crustaceans in general?

Class Crustaceans River Cancer

Fig. Opened River Cancer (female).

1 - an eye; 2 - the stomach; 3 - the liver; 4 - abdominal upper artery; 5 - heart; 6 - anterior arteries; 7 - gills; 8 - ovary; 9 - abdominal nerve chain; 10 - abdominal muscles; 11 - antennas; 12 - antennas; 13 - posterior intestine; 14 - muscles of the mandibles.

Class Crustaceans River Cancer

Fig. The internal structure of river cancer. The digestive, nervous and reproductive systems (male).

Fig. The internal structure of river cancer. Circulatory, respiratory and excretory systems.

Class Crustaceans River Cancer

Fig. Male reproductive system of River Cancer: 1 - the paired part of the testes, 2 - the unpaired part of the testes, 3 - the seed tube, 4 - the spermatic cord, 5 - the sex hole, 6 - the base of the fifth pair of walking legs.

Fig. Antenna gland (green gland) River crayfish (in expanded form).

1 - coelomic pouch; 2 - “green channel”; 3 - intermediate channel; 4 - “white channel”; 5 - bladder; 6 - excretory duct; 7 - external opening of the gland.

DRAWINGS TO BE PERFORMED IN THE ALBUM

(Total 2 pictures)

Subject matter:

Type Arthropods -Arthropoda.

Subtype Gillbird -Branchiata. Class Crustaceans -Crustacea.

Type: Arthropods

Subtype: Toad

Class: Crustaceans

Subclass: Supreme Crayfish

Order: Decapods

Species: Crayfish Broad - Astacus astacus

Fig. 1. Crayfish.

Internal structure (female from the dorsal side).

1-stomach 10-bunched striated

2-midgut muscles

3-posterior gut 11-cephalothorax

4-liver 12-belly

5-gills 13-head shield (carapax)

6-heart 14-headed spike (rostrum)

7-antenna glands 15-eyes

(green glands) 16-cut mandible muscle

8-floor gland 17-telson

9-nerve chain of 18-uropodia

Subject matter:

Type Arthropods -Arthropoda.

Subtype Gillbird -Branchiata. Class Crustaceans -Crustacea.

Signatures to Fig. 2. A variety of limbs of River Cancer.

1- short antenna (antenna) - the olfactory organ;

2- long antenna (antenna) - organ of touch;

3, 4, 5 - jaws: 3 - upper jaw (mandible), 4, 5 - two pairs of lower jaws (two pairs of maxilla) - jaws are used for grinding food;

6, 7, 8 - the legs of the jaw - are involved in the retention and grinding of food pieces;

9, 10, 11, 12, 13 - five pairs of walking legs, the first pair of walking legs (No. 9) is transformed into claws for seizing prey and for defense;

14, 15, 16, 17, 18, 19 - abdominal limbs, with the first pair (No. 14) and sometimes the second (No. 15) abdominal limbs in males transformed into copulatory organs, the last pair of abdominal legs (No. 19) together with the last segment of the body is part of the caudal fin.

Fig. 2. A variety of limbs of River Cancer.

Structure and covers.The segmented crustacean body is covered with a chitinous cuticle, which consists of several layers. Lime is deposited in the outer layers, so the integuments become hard and durable. The inner layer consists of soft and elastic chitin. The cuticle performs the function of the external skeleton (exoskeleton), protects the crustaceans from external influences and provides support for the attachment of muscle bundles formed by striated muscle tissue.

In comparison with other arthropods, the body of crustaceans is most segmented. In the head section there are five segments: the first ( acron) and the next ( antennal) the segments are carried by a pair of antennae - long antennae and short antennas. The remaining three segments of the head section are equipped with limbs to trap and grind food (mandibles and maxilla). The posterior segment of the head of the higher crustaceans forms the head shield, or carapaxwhich grows together with the segments of the breast and forms the cephalothorax. The number of segments in the chest and abdomen varies from one form to another. A constant number of segments is observed only in higher crayfish, which have 8 segments in the chest, and 6 segments in the abdomen. The abdomen ends with an anal lobe, or telson.

The chest limbs are very diverse and perform. various functions. Most often they serve as organs of movement — swimming or moving on a solid substrate. Abdominal limbs are present only in higher cancers and perform the respiratory function or organs of copulation. The last pair of abdominal limbs can turn into plate-shaped swimming legs.

Digestive systems.The digestive organs of crustaceans are difficult to differentiate. The anterior section includes the esophagus, chewing and pyloric regions of the stomach. The walls of the anterior intestine are lined with cuticle, which can form thickening in the esophagus to rub food. .

The midgut forms outgrowths called hepatic appendages that can secrete digestive enzymes. The back intestine has the form of a straight tube.

Respiratory system.Crustaceans have specialized respiratory organs - gills , which are thin skin processes on the pectoral limbs . Sometimes the gills are located on the ventral extremities. Breath of lower crustaceans is carried out across the entire surface of the body.

Circulatory system open type . Hemolymph partially moves through the vessels, partly in the body cavity. Venous blood approaches the gills, where it is oxidized and returned to the pericardial sinus. The heart has a metameric structure. . It is a tube that stretches along the body along the dorsal side and in each segment is equipped with a pair of ostes.

The circulatory system depends on the respiratory system: if the gills are located on the thoracic limbs, the heart is located in the chest, and if the gills on the abdominal limbs - the heart in the abdomen. In lower crustaceans, in which breathing is carried out through the entire surface of the body, the circulatory system disappears or only the heart remains.

The hemolymph may be colorless or red-colored with hemoglobin dissolved in plasma. Some crabs have a bluish hemolymph due to the presence of copper-containing hemocyanin-containing respiratory pigment.

Excretory system represented by two pairs of glandular organs. The organs of excretion are one or two pairs of modified metanefridia. One pair opens at the base of the antenna - the antennal glands. Another pair opens at the base of the second maxillus - maxillary glands. In the adult state, only one pair of glands is present, although both pairs develop in the larval stage.

Nervous systemcrustaceans consists of the paired brain, peri-pharyngeal connections and a pair of abdominal nerve trunks with ganglia in each segment. In crustaceans, the concentration of the nervous chain is noted and the number of ganglia decreases. For example, crabs have only two nerve masses - the brain and the pectoral, formed as a result of the fusion of all the nerve ganglia of the ventral chain.

Sense organs.The organs of touch are represented by hairs and bristles on the surface of antennas, antennas, and other limbs. Equilibrium organs are located in antennas and are represented by statocyst. The organs of vision in crustaceans are represented by a pair of complex faceted eyes. Faceted eyes consist of many small eyes - ommatidia   and often sit on mobile processes of the head - stalks.

The reproductive system.Most crustaceans are antiseptic. Sexual dimorphism is usually observed. The sex glands are unpaired, but the genital ducts are paired. The gonads are located in the chest region. Genital openings are located on the 6th thoracic segment in females and on the 8th thoracic segment in males. Limbs near the sex openings in males can turn into copulatory organs.

Direct development   or with metamorphosis. Growth occurs through molting, so it is called stepped. The molting process is controlled by the hormonal system. Most crayfish show progeny care. Females of decapod crayfish attach eggs to the abdominal legs and carry them until the larvae appear. For freshwater crayfish, direct development is characteristic when a small crustacean emerges from the egg.

Medical value of higher crustaceans.Crustaceans support the circulation of pathogens of opisthorchiasis, clonorchosis, paraganimosis in natural foci. Freshwater Crayfish ( r. Camboroides) and crabs ( r. Potamon, p. Eriocher) - the second intermediate owners of the pulmonary fluke ( Paragonimus westermani). Crayfish r. Caridinaserve as second intermediate hosts for the Chinese flukes ( Clonorchis sinensis). A person becomes infected with these helminths by eating the thermally unprocessed meat of crayfish and crabs that contain the metacercaria of these trematodes.

Subclass of Maxillopods ( Maxillopoda)

Crustacean squad(Copepoda) refer to the subclass of jawbones ( Maxillopoda). The number of types of copepods is from 10 to 20 thousand. Copepods live in freshwater as well as in the seas, making up an essential part of plankton.

The body of copepods consists of a complex head, which includes the anterior thoracic segment (sometimes referred to as the cephalothorax), the chest, consisting of five segments, and the abdomen of four segments. On the complex head there is a mouth, a nauplial eye, all head appendages and a pair of maxillary jaws. Single-branch antennulae are very long, they are actively involved in swimming. Two-sided antennas. The pectoral legs retain a primitive double-stranded form and carry swimming bristles. The abdomen has no legs and ends with an anal lobe with a fork (furca). The crustaceans are well developed muscles, which is represented by bundles of muscles. They are clearly visible through the thin chitinous cover of the crustacean.

central nervous systemit consists of the brain and the okolo-pharyngeal nerve ring of the ventral nerve cord, which is located in the cephalothorax, which does not enter the abdomen.

Circulatory system and respiratory systemare missing. Breathing is carried out all over the body.

Excretory system.At the larval stages, the organs of excretion are paired antennal glands, and adult stage   - maxillary glands. They consist of a closed sac (remnant of a coelomic cavity) and a convoluted exit channel.

The reproductive system.Most species of copepods are split animals. The female lays eggs, which are glued together in two egg sacs attached near the base of the abdomen. A larva leaves the egg nauplius (ortonauplius), which repeatedly sheds and turns into an adult form.

Medical value.Cyclops (eng. water flea) support the circulation of diphyllobotriosis and dracunculiasis in natural foci. They serve as intermediate hosts for the development of tape ( Diphyllobothriun latum) and round ( Dracunculus medinensis) worms. In the body cavity of the cyclope, coracidia of a wide tapeworm turns into the next larval stage, the procercoid. When the infected cyclops is eaten by fish in its muscles, the next larva, the plerocercoid, develops from the procercoid, which is an invasive stage for the main hosts, human and fish-eating animals.

Rishta larvae ( Dracunculus medinensis) swallow cyclops kind Cyclopsor Eucyclops(intermediate hosts), in which they molt and become invasive in 4–14 days. A person becomes infected with dracunculiasis by drinking raw water that contains infected cyclops.

Helicer Subtypes ( CHELICERATA)

Helicer include about 40,000 species. The body of the helix consists of a cephalothorax and abdomen. The cephalothorax results from the union of 7 segments (head and chest), often the seventh segment is reduced by the majority of helium representatives. The abdomen in some forms is subdivided into the anterior and the posterior-abdominal. A characteristic feature of the Helicere - the lack of antennae. On the cephalothorax there are 6 pairs of single-limbed limbs, the abdominal legs are missing or modified. The first pair of cephalothoracic limbs is turned into chelicerathat serve to grind food. The second pair of limbs - pedipalps   - It has a sensitive and pretentious function. They are followed by four pairs of walking legs.

Heliceric bisexuals. Most representatives of arachnids lay eggs. However, many scorpions, false corpions and some ticks livebreed. Eggs are mostly large, rich in yolk.

Three classes belong to the subtypical species. Representatives of the arachnid class have medical significance ( Arachnida).

Arachnid class ( Arachnida)

The class of arachnids has about 36,000 mostly terrestrial species.

Troops:   scorpions, spiders, ticks.

Spider-like animals have six pairs of limbs, the first two pairs of which are turned into chelicera and pedipalps, exciting and grinding food. The remaining four pairs are walking legs. On the abdomen of arachnids there are homologues of the limbs: spider warts, pulmonary sacks, trachea.

The integuments are formed by a solid, three-layer chitinous cuticle, under which, like in crustaceans, there is a layer of hypodermal epithelium. The cuticle protects the animal from draining. The characteristics of the cuticle ensured the distribution of arachnids in the most arid regions.

Digestive systemcharacterized by the presence of muscular sucking throat and salivary glands, the secrets of which break down proteins. Most arachnids are predators. Spiders catch prey in a fishing net - a web, formed by the sticky secret of the spider glands and woven with the legs of a spider. Spiders eat liquid food. They have extraintestinal digestion: the prey is killed first, diluted with the secret of the salivary glands, and then sucked in by the pharynx.

Excretory systemrepresented by malpighian vessels.

Circulatory systemnot closed.

Respiratory systemrepresented by pulmonary bags or trachea, or both. Gas exchange occurs in the folds of the lung sacs, which are washed by the hemolymph. Trachea begin with holes - spiracles, which are located on the lateral surfaces of the abdominal segments (one pair on each segment).

Nervous systemconsists of a brain and an abdominal nervous chain; the senses are simple eyes and organs of touch located on the dorsal side of the chest.

The reproductive system.Direct development (with the exception of ticks). Spider-like - dioecious animals with internal fertilization. They lay eggs or viviparous.

Squad of scorpions ( Scorpiones)

Scorpions are common in South and North America, Africa, India, the Middle East, Central Asia, and the southern regions of the CIS.

Morphological features.In scorpions, pedipalps have become claws. They have a long segmented abdomen with a flexible, thin bastard, which ends in a telson. At its top open channels of poisonous glands. Most scorpions are viviparous, and for some time the female carries cubs on itself.

During the day, scorpions hide under roots and in other secluded places, go hunting at night. They feed on terrestrial arthropods and small lizards. Scorpions seize their prey with claws and immobilize it with a poisonous needle at the end of the abdomen.

Medical value.Scorpions sting man only in self-defense. The bites of most scorpions are painful, but not dangerous to humans. Are possible allergic reactions   on scorpion venom. However, among the 1000 species of scorpions, there are about 30 species, the bites of which are deadly. Every year more than 5,000 people die from them in the world.

In the southern regions of the CIS lives 15 species of scorpions, the majority in Central Asia, where there is a motley scorpion - Buthus eupeus(up to 6.5 cm in length). Scorpio Centraroides exilicaudalives in the southwest of the USA and in the north of Mexico. It has a yellow color and reaches a length of 7 cm. The poison of this scorpion contains a neurotoxin, which converts the fast sodium channels to a constantly open state and thus causes a constant impulse in neurons. Bite Centraroides exilicaudacan be fatal.

Other scorpion bites (for example, Leirus quinquestriatus, Androctonus spp., Titus serrulatus), living in the Middle East, North Africa, the Mediterranean, India and Brazil, lead to a massive release of catecholamines. At the same time, cardiac arrhythmia, pulmonary edema, and myocardial damage are observed. In South Africa, scorpion bites Parabuthusand kind Buthotuscause damage to the central nervous system. Dwells in the middle east Hemiscorpius lepturus, whose poison causes tissue necrosis and hemolysis.

Preventive actions.In areas where scorpions are common, before using clothes, shoes, bed linen, towels, they should be shaken and inspected. Removing stones, drifts and garbage from personal plots and picnic sites deprives scorpions of shelter; treating dwellings with insecticides deprives them of food.

Squad spiders ( Aranei)

The squad includes more than 20,000 species of spiders, which are widespread throughout. About 1,500 species of spiders live in the CIS.

Morphological features.Spiders have a solid abdomen, which connects to the cephalothorax by a narrow stalk formed by the seventh segment. Chelicera end claw-shaped segment. Pedipalps of males play the role of aggregate organs. There are one or two pairs of lungs, and most spiders also have two tracheal beams. The extremities of the two segments of the abdomen are turned into spider warts.

Medical value.The poisonous spiders include tarantula widely distributed in Central Asia and the southern and central regions of the European part ( Lycosa singoriensis) and karakurt ( Latrodectus tredecimguttatus). Tarantula Lycosa singoriensislives in deserts, semi-deserts and forest-steppe zone in the south of Russia and the CIS camp. All tarantulas are poisonous to one degree or another. Tarantula bites are painful, but not dangerous for humans. They cause swelling and flushing of the skin.

  Unlike the tarantula, the karakurt bite is very dangerous for humans and domestic animals (camels, horses and others). Poison spiders kind Latrodectuscontains neurotoxin. Only females bite. Karakurt Latrodectus tredecimguttatusdistributed in North Africa, western Asia, in southern Europe. The color of the spider is black, on the abdomen of the male and immature females there are red spots with a white border. Spider bites cause severe pain, cramps, shortness of breath. Especially poisonous females.

Their bites cause gangrenous tissue breakdown, severe poisoning, sometimes fatal.

In Central and North America, the Black Widow Spider Latrodectus mactans. The length of the body is about 1 cm, the spread of the legs is 5 cm. This brilliant black spider with two red hourglass markings on the ventral surface of the abdomen. One hour after being bitten, a neurotoxin called alpha-latrotoxin spreads through the lymphatic system.

The abdominal muscles contract and harden. Possible vomiting, excessive sweating, pain in the joints. The victim is excited, fearful.

In cases of severe damage, loss of consciousness develops. Mortality of outcomes is observed in 5% of cases.

  The poison that spiders use to immobilize and digest prey in humans causes skin necrosis and intoxication.

Poison spiders kind Loxoscelesliving in central America, Africa and the Middle East, causes extensive necrosis of the skin and subcutaneous tissue. The body length of all these spiders is 7–15 mm, the foot span is 2–4 cm. Representatives of the genus Loxosceleshave a brown color with a dark violin pattern on the dorsal surface of the cephalothorax.

Bird Spiders (family Theraphosidae) - long-lived hairy spiders. In the United States, mainly in the southwest, 30 representatives of this family live. Bird-eating spiders, which are increasingly being kept at home, are usually brought from other countries; they have a bright color, and the span of the legs reaches 25 cm. Tarantulas bite only for self-defense. Their bites are not dangerous, but possible strong pain   and swelling at the site of the bite. In addition, in some species of tarantulas, the body is covered with special clipping hairs that, on contact with the skin, cause the formation of itchy papules. The rash lasts for several weeks.

Preventive actionsinclude the destruction of spiders in their habitats and the use of caution in areas of distribution of poisonous spiders. When a bite is necessary to determine the species of the spider. When poisonous spider bites require the introduction of antitoxic serum and specific treatment.

Nodoryad pincers ( Acari)

Morphological features.The body of ticks is usually non-segmented. The mouth apparatus consists of chelicera, pedipalps, and upper lip. The segments of the helicer and the pedipalps are combined into a mobile proboscis. Four pairs of walking legs of ticks consist of six segments: a swivel, a thigh, a knee, a shin, a pre-lap and a foot. Tracheal breathing, in small ticks and larvae skin breathing. Mites are split-off, sexual dimorphism is manifested in smaller sizes of males, in different shapes and sizes of the genital opening in females, in different degrees of chitinization of the body in females and males.

The development of ticks.Most females lay eggs. The development of ticks occurs with metamorphosis: a six-legged larva emerges from the egg, which differs from the imago in the absence of the last pair of legs, stigmas, trachea and genital opening.

After the first molt, the larva turns into a nymph, which already has four pairs of legs and differs from the adult form in its smaller size, the absence of the genital opening and the underdevelopment of the sex glands. After the last molt, the nymph is transformed into an adult - sexually mature form. The number of stages of nymphs ranges from 1 to 6.

Acariform mites(Acariformes) feed on dead or living derivatives of the epidermis of birds, mammals and humans. These include flour mite, barn mite, bed mite.

Pliers granary affect food: grain, flour, cheese, dried fruits. When eating foods infected with these ticks, inflammation can develop in gastrointestinal tract. Ticks are found in urine, feces, gastric and duodenal contents, in saliva and sputum. The waste products, fragments of dead mites and larval skins, falling with dust in airways   and the digestive tract, cause allergic diseases ( bronchial asthma, bronchitis). Therefore, this group is called allergenic mites from residential premises.

Of acariform mites, a scabies mite is of particular medical importance.

Morphological features.The body of the scabies mite is wide, oval, folded, covered with triangular scales. The size of the female is 0.4 mm, the male is 0.3 mm. Mouthparts of claw-like, gnawing type. Legs short, consist of 6 segments. On the front legs are suckers.

The eyes are absent, breathing is carried out all over the body surface.

To penetrate the skin, itchies choose the most delicate areas of the skin (between the fingers, on the abdomen, in the perineum). Ticks feed on the epidermis cells. The length of the stroke that the female punches in a day reaches 2–3 mm (males do not make moves). They live up to 2 months, laying 30-40 eggs during this time. 3-5-day larvae, 0.15 mm in size, emerge from the eggs 3-5 days after laying. After 10–15 days, after passing through a series of developmental stages, they reach puberty and begin to lay eggs. Adult ticks live 40–45 days.

Ways of human infection.A person becomes infected through direct contact with sick people through a handshake, a common bed, clothes, a towel, gloves, toys.

When scabies usually affects the hands, elbows, armpits, as well as the skin of the abdomen, thighs, buttocks. The patient is worried about severe itching and inflammation on the skin. Moves of mange pruritus can be viewed with a magnifying glass. The length of the strokes is 5 mm, dark dots are visible along the course - holes. At the blind end of such a passage, a bubble is sometimes visible, where the tick is located.

Laboratory diagnostics   consists in microscopic examination of scrapings from skin and detection of ticks.

Preventive actions

Ways of human infection.Infection occurs through contact with a sick person.

Action on the human body.Cause inflammation of the skin ( acne) as a result of blockage of the sebaceous glands.

Diagnosticsdemodicosis is a microscopic examination of skin scrapings and purulent discharge of acne in order to detect ticks.

Preventive actionsinclude the identification and treatment of sick people, compliance with the rules of personal hygiene, improvement of sanitary conditions, disinfection of clothing and linen in public institutions.

Ticks - carriers of pathogens of vector-borne diseases (detachment Parasitiformes)

Ixodid mites trap prey in nature. They may also starve for a long time, but having stuck to their host, they feed on blood for several days.

They stick unnoticed, releasing anesthetic substances with saliva.

Morphological features.Ixodes ticks are rather large in size and are covered on top by a dense dorsal scute. In males, the shield covers the entire upper surface of the body, and in females, nymphs and larvae, only the front part. The female lays from 2,000 to 17,000 eggs. The larvae have three pairs of legs, breathe all over the body and feed on the blood of small animals.

After 10–30 days, the larva turns into a nymph, which for several days feeds on the blood of animals, molts and turns into an adult tick - imago.

  The whole period of development from an egg to a mature individual in different species of ticks can last from six months to several years. From an epidemiological point of view, ticks of the genera are most significant. Ixodes, Dermacentor, Hyalloma.

Taiga tick(Ixodes persulcatus) - carrier of taiga encephalitis.

It is found in the forests of Siberia and the Far East. The female has an oval body, tapered towards the front end, about 3 mm in size. At the front end of the body there is a long proboscis, the base of which has a rectangular shape. Four-segmented palps are attached to the base of the proboscis, covering the proboscis from above. Palpi - these are the senses used by the tick to select a place for suction. With the help of a proboscis mite is attached to the skin. On the ventral side of the female mite, at the level of the third pair of legs, there is a sexual opening in the form of a transverse slit. The anal opening is located closer to the posterior end of the body. On the lateral surface of the body are the oval respiratory plates surrounding the respiratory openings (stigmas).

Larvae and nymphs feed on small animals and birds. The development of each stage takes about a year. The taiga tick maintains the circulation of the taiga tick-borne encephalitis virus in natural foci. The main reservoir of encephalitis virus is chipmunks, as well as hedgehogs, vole mice and birds.

Dog tick(Ixodes ricinus). Occurs in forest and forest-steppe zones, as well as in mountainous areas. The period of tick development is from 3 to 7 years. Larvae and nymphs with low air temperature (10–15 ° C) can go hungry for up to 2 years. The body of the tick is oval, on the dorsal side is the shield. In males, it covers the entire dorsal side; in females, larvae and nymphs, it covers only

the dorsal side of the dorsal side, on the remaining parts of the body, the integuments are soft, which makes it possible to stretch and increase the volume of the body.

The dog tick maintains in the foci of tularemia among rodents. It transmits the causative agent of tularemia and spring-summer encephalitis to humans and animals.

Pasture mites of the genus(Dermacentor) carry the pathogens of tick-borne typhus, tick-borne encephalitis, tularemia, brucellosis. They differ from other ticks by a shield, which is covered with a white pattern. Along the edges of the anterior third of the shield are flat eyes.

Different kinds   This genus is found in forest zones, steppes and deserts. Especially often they are found in river valleys with shrub vegetation and grazing areas. Species mites have medical significance. D. pictus, D.marginatus, D. nuttalli.

Adult ticks are most active from March to June, feeding on ungulates. Larvae and nymphs feed on small mammals (hares, hedgehogs, mice). Females lay eggs next year.

Family argas mites (Argasidae).

Argasi mites are common in countries with warm and tropical climates. They live in caves, animal burrows, livestock buildings, semi-deserts and deserts, and feed on the blood of vertebrates at all stages of development.

Morphological features.The body of the mites is oblong, soft, has no shields, 2-30 mm in size. The oral apparatus is placed on the ventral side.

Medical value. Pliers kind Ornithodorusof which the most important Ornithodorus papillipes, they spread tick-borne relapsing fever (countries of Central Asia, Middle East, India). Ticks receive causative agents of various diseases (viruses, bacteria, spirochetes, protozoa) by feeding on wild animals, and the possibility of ticks moving from one host to another ensures the circulation of these pathogens in nature. Thus, in nature for a long time there can be a focus of the disease, which is a danger to humans.

SUBTIP TRACH ( TRACHEATA)

The tracheal subtype includes terrestrial arthropods, only few species have adapted for the second time to life in water. They breathe with trachea. Tracheal openings - stigmas - are arranged in pairs on the sides of each body segment. The walls of the trachea have spiral chitin thickenings, so that air flows to all organs of the body.

The torso is divided into the head, chest and abdomen. Most tracheal has a well-separated head, which consists of an acron and four segments. The head carries one pair of antennas (antennae) and three pairs of mouth extremities: one pair of upper jaws (mandibles) and two pairs of lower jaws (maxillae). The number of body segments varies greatly within the group.

Terrestrial tracheal acquired morphophysiological adaptation to existence in conditions of moisture deficiency.

Classification.Tracheal subtype traditionally includes two classes:

Мног class centipedes ( Myriapoda);

♣ class insects ( Insecta).

However, it is now known that centipedes unite into a superclass - Myriapoda, which includes 4 classes: symphiles ( Symphyla), pawropods ( Pauropoda), Kipsyaks, or two-legged ( Diplopoda), and low-legged ( Chilopoda). Traditional combining them into one class Myriapoda(centipedes) is not currently accepted, but is retained in manuals and textbooks.

The centipede of the centipede ( Myriapoda)

Class bogodogie ( Chilopoda)   - Scolopendra ( Scolopendromorpha), includes the largest representatives of this class. These are nocturnal predators hunting large insects and attacking even small vertebrates. The most poisonous scolopendra lives in Jamaica and South America - Scolopendra gigantea. In length, it reaches 26 cm. It attacks lizards, toads, and birds.

The bite of scolopendra causes paralysis and cardiac disturbance in its victim. The chemical nature of the poison of these centipedes is poorly understood. It identifies acetylcholine and biologically active amines - histamine and serotonin. There is an indication of the presence of a number of enzymes, including proteolytic. The bite of scolopendra is lethal for its victims, but does not pose a serious danger to human health.

Insect class ( Insecta)

Insects appeared in the Late Paleozoic, in the Devonian period. Occurred from worm-shaped centipedes.

The body of insects is divided into head, chest and abdomen. The head consists of five fused segments. On the underside of the head is a mouth. On its sides are two complex eyes. Between them there can be simple eyes. On the head there is one pair of antennae, or syazhk, performing the functions of touch and smell. The chest consists of three fused segments, each of which carries one pair of limbs. In total, insects have three pairs of limbs; on the back can be one or two pairs of wings.

By the presence and nature of the wings, insects are divided into winged and wingless. In winged insects, one or two pairs of identical or different wings. In coleoptera or hemiptera, one pair of wings has become rigid elytra. In whitefish insects (lice, fleas), wings are reduced or absent.

The abdomen consists of eight or more segments, which depends on the level of development of the insect: the more primitive it is, the more segments; there are homologues of the limbs: ovipositor, aggregate organ, sting.

Respiratory systeminsects formed trachea, providing gas exchange in the body of the insect. The trachea open outward with spiracles (stigmas), which are located on the lateral surface of the abdomen.

Nervous systemnodal type. The epopharyngeal ganglion forms the brain, consisting of three sections: anterior, middle, and posterior. The development of the nervous system led to the emergence of insects in complex instincts, care for the offspring, separation of functions in social insects.

Digestive systeminsects are represented by a differentiated digestive tract and salivary glands. The anterior intestine is divided into the mouth, pharynx, esophagus, often expanding into goiter and stomach. Insects have no liver. There are salivary glands, midgut glandular cells and rectal glands that provide water absorption. Medium intestine folds. The back gut removes the products of digestion and metabolism.

Mouth apparatus of insects are different in structure and type. Distinguish gnawing (bugs, cockroaches), piercing-sucking (mosquitoes), licking (flies) mouthpieces.

Excretory systemrepresented by malpighian vessels and fat body, in which the products of exchange accumulate.

Circulatory system   open and formed by a tubular heart and one vessel directed to the head (head aorta). From the opening of the aorta hemolymph pours into the body cavity. The hemolymph is yellowish and is not involved in respiration.

Reproductive systemrepresented by paired gonads, sexual dimorphism is pronounced, internal fertilization, development is direct or indirect (with metamorphosis).