Shell crustaceans belong to the lower crustaceans and make up the order of ostracods (Ostracoda). The body of crustaceans is divided into cephalothorax and abdomen. Widespread are also copepods (Copepoda) - cyclops and diaptomus, which belong to the subclass Maxillopod (Maxillopoda). Daphnia, or water fleas, belong to lower crustaceans, namely to branched crustaceans (suborder Cladocera in the order of leaf-legged - Phyllopoda).

Water donkey (Asellus aquaticus L.) is a representative of the class of crustaceans, belongs to the order of isopods (Isopoda), to the family of donkeys (Asellidae). Donkeys stay at the bottom of reservoirs, where they crawl between the dead parts of plants and, together with them, are carried out with a net. In these bags, clearly visible to the naked eye, the eggs develop and juveniles are formed in the form of fully formed crustaceans, generally similar to adults.

The number of eggs in one female is very different - from a few dozen to a hundred or more. A young donkey reaches maturity within two months on average. Of these, the first two pairs are called rowing tendrils, or antennae, and serve for movement. Like aquatic fleas, there is a well-developed eye on the head, which shines through a thin shell valve.

On the left - swimming of a shellfish. The arrows show the convergence and separation of the antennas. When crawling on the substrate, it plays the role of a pair of legs equipped with claws, and the second pair of antennae is also used. Some species have completely lost the ability to swim and are exclusively bottom dwellers. Ostracods feed on small organisms found in the silt, and very willingly eat the corpses of small animals.

Like water fleas, barnacles are able to reproduce parthenogenetically for some time, and such reproduction alternates with sexual reproduction. Their larvae have the same ability. The body of the water flea (in most species) is enclosed in a transparent bivalve chitinous shell, both halves of which are fastened on the dorsal side and half-opened on the ventral side.

Branched rowing antennae, or antennae, depart from the head; hence the name "branched". They should be caught with a net made of fine mesh fabric. At the same time, it is recommended to drive the net through clean water, without touching the bottom and not picking up a net of aquatic plants in the bag. In our country, this form is found in many lakes of the northern and central strip of Russia. The movements of water fleas can be observed even with the naked eye. The result is a series of successive jumps, which, indeed, I have: some resemblance to the movement of a flea (hence the name "water flea").

Cyclops (Cyclops coronatus). The abdomen carries six pairs of swimming legs and ends with two processes - a fork. In females, paired egg sacs can often be seen on the sides of the body. Copepods are found in a wide variety of water bodies, where they sometimes develop in large numbers, especially in spring and autumn. The most primitive crustaceans belong to the branchiopoda subclass.

lower crustaceans

Daphnia, inhabitants of the water column, are often called water fleas, probably because of their small size and hopping mode of movement. The legs of Daphnia are leaf-shaped, small, they do not take any part in the movement, but they regularly serve for nutrition and respiration. An even smaller owner of a brownish spherical shell - spherical chydorus (Chydorus sphaericus) - can be found both in the water column and among coastal thickets.

Their body consists of a head, segmented chest and abdomen. The main organ of movement is powerful antennae and pectoral legs bearing swimming bristles. The legs work synchronously, like oars. Hence the common name of crustaceans - "copepods". Diaptomuses, like Daphnia, are quite peaceful animals. The elongated body of the crustacean is translucent and colorless, they need to be invisible to predators. Among them there are large forms. More than 40 thousand species of crustaceans are known.

The cephalothorax consists of segments of the head and chest, merging into a common, usually undivided body section. The abdomen is often dissected. The first 2 pairs are represented by jointed antennae; these are the so-called antennules and antennae. Crustaceans are characterized by a two-branched structure of the limbs. In connection with evolution in the aquatic environment, crustaceans developed organs of water respiration - gills. They often represent outgrowths on the limbs.

Significance of crustaceans

Crustaceans, with rare exceptions, have separate sexes. A nauplius larva emerges from the egg with a non-segmented body, 3 pairs of limbs and one unpaired eye. Lower crayfish live both in fresh waters and in the seas. They are important in the biosphere, being an essential part of the diet of many fish and cetaceans.

Antennules uniramous, antennae and peduncles of thoracic segments biramous. The antennules reach especially great lengths; they are longer than the body. Scattering them widely, the diaptomuses soar in the water, the thoracic limbs cause spasmodic movements of the crustaceans. The mouth limbs are in constant oscillatory motion and adjust particles suspended in water to the mouth opening. The color of the Cyclopes depends on the type and color of the food they eat (gray, green, yellow, red, brown).

Crustaceans (Ass. F. D. MORDUKHAI-BOLTOVSKOY)

Lower crustaceans (Entomostraca)

The lower crustaceans have an inconsistent number of body segments, usually an indistinctly delimited abdomen that never bears limbs. In fresh and generally inland water bodies of the Rostov region. lower crustaceans are represented by four orders: branchiopods (Branchiopoda), cladocera (Cladocera), copepods (Copepoda) and shellfish (Ostracoda). These are in most cases small, sometimes microscopic animals that live exclusively in water.

1. Branchiopods (Branchiopoda)- these are relatively large crustaceans with a clearly dissected body with a large number of leaf-shaped, equipped with gill appendages, swimming legs (from 10 to 40). They inhabit very shallow temporary reservoirs and puddles, which usually dry up in summer. In the reservoirs of the floodplain Don, formed during the spring flood, you can often find the most interesting representative of these crustaceans - shield - Lepidurus apus. This is an extremely peculiar type of animal up to 4-5 cm, covered on the dorsal side with a greenish armor covering the entire body, with the exception of the posterior abdomen, equipped with two long tail filaments (Fig. 1). Along with Lepidurus, Rpus, very close to it, is found, differing from the first in the absence of a plate between the tail filaments.

Most of the reservoirs in which these crayfish live completely dry up by the middle of summer. However, shields reappear in them next spring, as they lay the so-called "resting" or "winter" eggs, not only equipped with a dense shell that allows them to endure drying and freezing of the reservoir without harm, but even, apparently, needing complete drying. for further development.

In the same temporary reservoirs, there are also other representatives of the described detachment, devoid of armor - gills. Gill legs have an elongated body with a thin tail (abdomen) and 10-20 pairs of long legs bearing gills; the head is separated from the body and equipped with stalked eyes and large curved antennae ("antennas"). Branchinella spinosa was found among the branchiopods in the reservoirs of the Don floodplain. In the salt lakes of the Many-chey basin, another branchiopod, artemia (flrtemia salina v. principalis, Fig. 2), is common. Artemia is a well-known inhabitant of salt water bodies, remarkable in that it cannot exist in fresh water bodies, and in salt water it feels great even at such a concentration of salts at which all other animals die. In this case, Artemia can develop in large quantities. In some saline reservoirs of the Manych Valley, the entire mass of water, devoid of any animals, is filled with floating remains of the leaf-shaped legs of Artemia.

In addition to the scutes and branchiopods, among the branchiopods there is also a group of forms equipped with a bivalve shell, similar to mollusk shells, but usually very thin and transparent. In floodplain lakes and swampy reservoirs one can often find these small (rarely more than 1a/a cm) crustaceans that swim quickly with the help of numerous (10-30 pairs) legs.

In the Rostov region species of Leptestheria, Caenestheria, and Cyzicus were found from this group.

2. Branched mustache, or Cladocera- the overwhelming majority are very small animals with an almost unsegmented body with a small number of swimming legs (no more than 6). The body is dressed in a transparent, thin shell and in front bears a pair of branched antennae - antennas that serve for movement, which occurs abruptly. The head is usually equipped with one large eye, often of a rather complex structure. Cladocera inhabit absolutely all fresh water bodies and are one of the most common groups of crustaceans. The extremely wide distribution of Cladocera is due to a large extent to the presence of "winter" or "resting" eggs, which, due to their negligible size, can be carried over long distances by wind along with dust. Reproduction of Cladocera occurs several, and sometimes many times during the year, and it is remarkable that it can go on for a long time without the participation of males (parthenogenetically), but only ordinary "summer" eggs are formed; with the deterioration of the conditions of existence, males appear, fertilizing females, which then lay "winter" eggs.

Cladocera are one of the main constituents of the plankton of fresh water bodies, and also inhabit the coastal zone and thickets in large numbers. They are an important, and sometimes the main object of food for various commercial and non-commercial "plank-eating" fish (herring, sprat, bleak, etc.) and juveniles of most fish that feed on benthic fauna in their adult state. When dried, Cladocera is an all-purpose food for aquarium fish. This food is called daphnia, although in reality daphnia is only one of the very numerous forms of Cladocera.

In the reservoirs of the Rostov region. Cladocera are as rich and diverse as in all water bodies of temperate and southern latitudes (at least 40 species of them were found in the Don basin). Of the planktonic forms often found in the Don River, the aforementioned daphnia (Daphnia longispina) can be mentioned. This is a transparent crustacean 1-2 long mm, whose shell is equipped with a long needle, and the head bears a pointed helmet (Fig. 3). Even more common than daphnia are its close relatives, Moina and Diaphanosoma, which are distinguished by the absence of a helmet and needle. Bosmina (Bosmina longiros tris), very small (no more than 1/2 mm) a rounded crustacean with a long beak, and Chydorus sphaericus, also completely round, but without a beak. In the thickets of the coastal strip and near the bottom, there are many other, related to the latter, cladocerans from the Chydoridae family.

In the salty reservoirs of the Manychs, the majority of Cladocera, generally adapted to fresh water, cannot exist. Only Moina and Diaphanosoma, the most resistant to salinity, remain, but they multiply in large numbers.

Among Cladocera, the Leptodora kindtii, which lives in the plankton of the Don and in general in large reservoirs, stands out. It is relatively very large - about 1 cm- a crustacean, the elongated body of which is almost free from the shell (covering only the "brood pouch" with eggs) (Fig. 4). Leptodora, unlike most other Cladocera, leads a predatory lifestyle and is distinguished by extraordinary transparency. In a living form, it is almost impossible to distinguish it in water, and only when it is killed with formalin or alcohol, it turns white and becomes clearly visible.

Free-living copepods (Euco-pepoda) have a clearly dissected body, subdivided into a wide cephalothorax, equipped with 4 pairs of biramous swimming legs and a narrow abdomen, ending in a biramous fork with bristles ("furka"). The cephalothorax bears in front one small eye and a pair of very long antennae used for swimming.

Like Cladocera, all copepods are very small, often semi-microscopic forms, extremely widespread in all kinds of water bodies. They also form resting eggs and are part of the plankton, representing an important food item for fish fry and adult planktivorous fish.

The way of life of copepods is similar to the way of life of cladocerans; it should, however, be noted that, in contrast to Cladocera, which breed only after the water has completely warmed up and quickly disappears with cooling, copepods are much more resistant to low temperatures and appear in masses even in very early spring, and many live throughout the winter, under the ice.

The most common representatives of copepods are cyclops belonging to the genus Cyclops (currently this genus is divided into several others). Cyclopes have an oval cephalothorax, an elongated abdomen with long caudal setae, and comparatively short swimming antennae. Females carry eggs in two egg sacs on the sides of the abdomen (Fig. 5). Cyclops - small crustaceans (no more than 2-3 mm in length), found in all water bodies, with the exception of heavily polluted ones, and usually leading a planktonic lifestyle. Among the numerous species of this genus (at least 20 species of Cyclops are known for the Rostov Region), Cyclops strenuus, C. vernalis, and C. oithonoides are more common in the plankton of the Don.

Along with cyclops, especially in shallow spring reservoirs, representatives of the genus Diaptomus (Diaptomus) are often found, differing in somewhat large sizes (up to 5 mm), longer antennae and a cephalothorax and short abdomen. Many of them are red or blue in color. D. salinus and D. (Paradiaptomus) asiatlcus are of interest among the numerous (about 15) species of Diaptomus (in Rostov oblast), which develop in mass quantities in the saline reservoirs of the Manychi. Other copepods (Heterocope, Calanipeda, Eurytemora) are also found in the plankton of the Don.

In the coastal zone and at the bottom of reservoirs live copepods belonging to the Harpacticidae group. These are extremely small crustaceans with a long body and poorly developed swimming antennae, running along the bottom and, due to their scarcity and small size, usually elude observation.

A significant role in the plankton of most water bodies is played by peculiar copepod larvae - nauplii. These are very microscopic animals with three pairs of legs and one red eye, often, especially in spring, inhabiting water in countless quantities. All copepods in their development go through this larval stage, which after a few weeks, through a series of successive molts, turns into an adult form.

Very close to the copepods (but now they stand out in a special order of branchiura - Branchiura) are also "fish or carp lice" (flrgulus). These are small (no more than 1/2 cm) crustaceans with a flat body, two compound eyes and two suckers with which they are attached to the skin of fish. They suck blood from fish, but often separate from their prey and swim freely in the water for some time. One of the species of this genus, Argulus foliaceus, is often found in the Don.

4. Shellfish (Ostracoda). Shellfish are small crustaceans that live in oval bivalve shells. The presence of a shell brings them closer, but they differ from the latter only in smaller sizes (usually no more than 5-7 mm) and an undivided body with only three pairs of legs that serve not for swimming, but for running (Fig. 7). In addition, their lime-impregnated shell is usually very durable and fossilized, making Ostracoda important in paleontology.

Most shellfish live among thickets and at the bottom of various water bodies. Although they do not have special "winter" eggs, their eggs, and often adult crustaceans themselves, are also able to tolerate drying and freezing without harm.

In freshwater bodies, they usually do not breed in mass quantities and can easily go unnoticed by the untrained eye.

In the Rostov region shell crustaceans are almost not studied. Only a few widespread species that inhabit small floodplain lakes and puddles can be noted: Candona, one of the largest forms with a white shell; Cyclocypris, smaller, rounded; Limnicythere - with an elongated shell, equipped with several large swellings.

blue cuban crayfish

Crustaceans live in aquatic or humid environments and are close relatives of insects, spiders, and other arthropods (type Arthropoda). The peculiarity of their evolutionary series is to reduce the number of metameric (identical) segments through their merging with each other and the formation of more complex body fragments. According to this feature and other characteristics, two groups are distinguished: lower and higher crustaceans. So, let's get to know these animals closer.

Lower and higher crustaceans: characteristic differences

The lower crustaceans differ in small, up to microscopic sizes. In addition, they do not have abdominal limbs, but only chest ones. Unlike primitive forms, higher crustaceans are characterized by a constant (6 pieces) number of identical body segments. For simply arranged crustaceans, the number of such formations ranges from 10 to 46. Moreover, their limbs, as a rule, are biramous. While, in some highly developed animals, this feature disappears. So, in crayfish, the thoracic limbs have one branch.

cherry shrimp

Shrimp Lysmata amboinensis and giant moray

The lower crustaceans are characterized by a softer chitinous cover. Some of them (daphnia, in particular) have transparent shells through which the internal structure is visible. The respiratory system in higher crustaceans is represented by gills. More primitive forms breathe the entire surface of their body, while the bloodstream in some may be completely lost. The nervous system of highly developed species with a variety of behavioral reactions has a complicated structure.

Daphnia (lat. Daphnia) - a genus of planktonic crustaceans

These animals are characterized by well-developed external formations that perform the function of balance (statocysts); bristles covering the entire body, increasing sensitivity; organs that capture the chemical components of the environment. Some lower crustaceans do not have a peripharyngeal ring, their brain is more primitive, while in more developed organisms ganglia merge, their structure becomes more complex.

Lobster, he is a lobster (lat. Nephropidae)

Diversity of biological forms of lower and higher crustaceans

Shrimp "Red Crystal"

Higher species of crustaceans, in particular crayfish, crab, lobster, spiny lobster, and shrimp, play a special commercial role for humans. A useful product consisting of planktonic crustaceans Bentheuphausia amblyops, is krill meat. Has the same lifestyle Macrohectopus branickii living in Lake Baikal. Land woodlice living in moist soil are also highly developed representatives.

Cambarellus patzcuarensis is an endemic type of crayfish

Amphipod Parvexa, an endemic crustacean that lives in about. Baikal

Cancer - mantis (lat. Odontodactylus scyllarus), also known as shrimp - mantis

And in more detail with the various species belonging to this class, with lower and higher crustaceans, you will be introduced to the new articles of the online magazine "Underwater World and All Its Secrets":

Crustaceans are ancient aquatic animals with a complex dissection of the body covered with a chitinous shell, with the exception of woodlice living on land. They have up to 19 pairs of jointed legs that perform various functions: capturing and grinding food, locomotion, protection, mating, and bearing juveniles. These animals feed on worms, mollusks, lower crustaceans, fish, plants, and crayfish also eat dead prey - the corpses of fish, frogs and other animals, acting as orderlies of reservoirs, especially since they prefer very clean fresh water.

Lower crustaceans - daphnia 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.

2 types 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 Crustacea was divided into two subclasses - lower and higher crayfish. In the subclass of lower crayfish, phyllopods, maxillopods and shell crayfish were combined. It is now recognized that such a union is impossible, since these groups of cancers are different in their origin.

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

The body of crustaceans is divided into cephalothorax and abdomen. The cephalothorax consists of segments of the head and chest, merging into a common, usually undivided body section. The abdomen is often dissected.

All crustaceans have 5 pairs of head limbs. The first 2 pairs are represented by jointed antennae; these are the so-called antennules and antennae. They carry the organs of touch, smell and balance. The next 3 pairs - oral limbs - serve to capture and grind food. These include a pair of upper jaws, or mandibles, and 2 pairs of lower jaws - maxilla. Each thoracic segment bears a pair of legs. These include: the jaws involved in holding food, and locomotor limbs (walking legs). The abdomen of higher crayfish also bears limbs - swimming legs. The lower ones don't.

Crustaceans are characterized by a two-branched structure of the limbs. They distinguish between the base, external (dorsal) and internal (ventral) branches. Such a structure of the limbs and the presence of gill outgrowths on them confirms the origin of crustaceans from polychaete annelids with two-branched parapodia.

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

The excretory organs are one or two pairs of modified metanephridia. The first pair is localized in the anterior part of the cephalothorax; its duct opens at the base of the antennae (antennary glands). The duct of the second pair opens at the base of the maxillae (maxillary glands).

Crustaceans, with rare exceptions, have separate sexes. They usually develop with metamorphosis. A nauplius larva emerges from the egg with a non-segmented body, 3 pairs of limbs and one unpaired eye.

• Subclass Entomostraca (lower crayfish).

  Lower crayfish live both in fresh waters and in the seas. They are important in the biosphere, being an essential part of the diet of many fish and cetaceans. The copepods (Copepoda), which serve as intermediate hosts of human helminths (diphyllobotriids and guinea worm), are of the greatest importance. 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 divided into segments. The complex head bears one eye, two pairs of antennae, a mouthpart, and a pair of legs-jaws. One pair of antennas is much longer than the other. This pair of antennae is highly developed, their main function being movement. They also often serve to hold the female by the male during mating. Thorax with 5 segments, pectoral legs with swimming bristles. Abdomen of 4 segments, at the end - a fork. At the base of the abdomen of the female there are 1 or 2 egg sacs in which the eggs develop. Nauplii larvae emerge from the eggs. Hatched nauplii are completely different from adult crustaceans. Development is accompanied by metamorphosis. Copepods feed on organic remains, the smallest aquatic organisms: algae, ciliates, etc. They live in water bodies all year round.

The most common genus is Diaptomus.

Diaptomuses live in 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 in connection with which it is reluctantly eaten by fish. The color depends on the nutrient base of the reservoir. Diaptomuses have 11 pairs of limbs. Antennules uniramous, antennae and peduncles of thoracic segments biramous. The antennules reach especially great lengths; they are longer than the body. Scattering them widely, the diaptomuses soar in the water, the thoracic limbs cause spasmodic movements of the crustaceans. The mouth limbs are in constant oscillatory motion and adjust particles suspended in water to the mouth opening. In diaptomus, both sexes take part in reproduction. Female diaptomus, unlike female cyclops, has only one egg sac.

Species of the genus Cyclops (Cyclops)

predominantly inhabit coastal zones of water bodies. Their antennae are shorter than those of the diaptomus, and along with the thoracic legs, they participate in jerky movement. The color of the Cyclopes 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 reproduction. The female carries fertilized eggs in egg sacs (cyclops have two) attached at the base of the abdomen.

According to their biochemical composition, copepods are in the top ten high-protein foods. In the aquarium trade, "cyclops" is most often used for feeding grown-up juveniles and small-sized fish species.

Daphnia, or water fleas

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

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

  Higher crayfish are inhabitants of marine and fresh water bodies. Only wood lice and some crayfish (palm crayfish) live on land from this class. Some species of higher crayfish serve as an object of fishing. In the seas of the Far East, the gigantic Pacific crab is harvested, the walking legs of which are used for food. In Western Europe, lobster and lobster are mined. In addition, crayfish are of sanitary importance, because. free water bodies from the corpses of animals. Freshwater crayfish and crabs in the countries of the East are intermediate hosts for the lung fluke.

  A typical representative of higher crayfish is crayfish.

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

The structure and reproduction of crayfish

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

The color of the shell of a 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 coloration is protective and allows the cancer to become invisible. When caught crayfish are boiled, some of the chemicals that give color to the shell are destroyed, but one of them, the red pigment astaxanthin, does not decompose at 100 ° C, which determines the red color of the boiled crayfish.

The body of crayfish is divided into three sections: the head, chest and abdomen. On the dorsal side, the head and thoracic sections are covered with a single cephalothoracic solid solid chitinous shield, which carries a sharp spike in front, on its sides in recesses on movable stems there are compound eyes, a pair of short and a pair of long thin antennae. The latter are a modified first pair of limbs.

On the sides and below the oral opening of the crayfish are six pairs of limbs: upper jaws, two pairs of lower jaws and three pairs of mandibles. There are also five pairs of walking legs on the cephalothorax, and claws on the three front pairs. The first pair of walking legs is the largest, with the most well-developed claws, which are the organs of defense and attack. The mouth limbs, together with the claws, hold food, crush it and direct it into 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), in the female they are reduced. On four segments there are two-branched jointed zeros; the sixth pair of limbs - wide, lamellar, are part of the caudal fin (it, together with the caudal lobe, plays an important role when swimming backwards).

Movement of crayfish. The crayfish can crawl and swim back and forth. He crawls along the bottom of the reservoir with the help of chest walking legs. Forward crayfish swims slowly, sorting through the abdominal legs. It uses its tail fin to move backwards. Straightening it and bending its abdomen, the 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-impregnated chitinous chewing plates with serrated free edges. In the sieve section, two plates with hairs act like a filter through which only highly crushed food passes. Further, 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 middle intestine and gland (it is also called the liver, but its secret breaks down not only fats, but also proteins and carbohydrates, i.e. functionally corresponds to the liver and pancreas of vertebrates). Undigested residues enter the hindgut and are excreted through the anus on the caudal lobe.

Respiratory system. Crayfish breathe with gills. 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 cephalothoracic shield protects the gills from damage and rapid drying, so the crayfish can live out of 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 not closed. Blood circulation occurs due to the work of the heart. The heart is pentagonal in shape, located on the dorsal side of the cephalothorax under the shield. Blood vessels depart from the heart, opening into the body cavity, where blood gives oxygen to tissues and organs. The blood then flows to the gills. The circulation of water in the gill cavity is provided by the movement of a special process of the second pair of lower jaws (it produces up to 200 waving movements in 1 minute). Gas exchange occurs through the thin cuticle of the gills. Oxygen-enriched blood is sent through the gill-cardiac canals to the pericardial sac, from there it enters the heart cavity through special openings. Cancer blood is colorless.

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

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

sense organs. Compound, or compound eyes in crayfish are located in front of the head on movable stalks. Each eye contains more than 3 thousand ocelli, 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 cancer serve as organs of touch and smell. At the base of the short antennae is the organ of balance (statocyst, located in the main segment of the short antennae).

Reproduction and development. Crayfish have developed sexual dimorphism. In the male, 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 remaining four pairs of abdominal legs, she bears eggs (fertilized eggs) and young crustaceans, which remain under the protection of the mother for some time, clinging to her abdominal limbs with their claws. So the female takes care of her offspring. Young crayfish grow intensively and molt several times a year. The development of crayfish is direct. Crayfish breed quite quickly, despite the fact that they have relatively few eggs: the female lays from 60 to 150-200, rarely up to 300 eggs.

Significance of crustaceans

Daphnia, cyclops and other small crustaceans consume a large amount of organic remains of dead small animals, bacteria and algae, thereby purifying the water. In turn, they are an important food source for larger invertebrates and juvenile fish, as well as for some valuable planktivorous fish (eg whitefish). In pond fish farms and fish hatcheries, crustaceans are specially bred in large pools, where favorable conditions are created for their continuous reproduction. Daphnia and other crustaceans are fed to young sturgeon, stellate sturgeon and other fish.

Many crustaceans are of commercial importance. About 70% of the world's crustacean fishery is shrimp, and they are also bred in ponds created on the coastal lowlands and connected to the sea by a canal. Shrimps in ponds are fed with rice bran. Krill is fished for - planktonic marine crustaceans that form large aggregations and serve as food for whales, pinnipeds and fish. Food pastes, fat, fodder meal are obtained from krill. Of lesser importance is the fishing of lobsters and crabs. In our country, in the waters of the Bering, Okhotsk and Japanese seas, king crab is harvested. Commercial fishing for crayfish is carried out in fresh water, mainly in Ukraine.

• Class Crustacea (crustaceans)

The most primitive crustaceans belong to the subclass Gillnopods(Branchiopoda). Daphnia(Daphnia) are representatives of the Leaf-legged order, the branched mustache suborder. Daphnia, inhabitants of the water column, are often called water fleas, probably because of their small size and hopping mode of movement. Let's put some living D. magna in a glass jar and observe them. The body of the crustaceans is up to 6 mm long, covered with a bivalve shell flattened laterally. A large black spot stands out on a small head - an eye, and in the trunk section a brownish-greenish intestine clogged with food shines through.

Daphnia never rest for a second. The main role in the movement is played by the flapping of long lateral antennae. The legs of Daphnia are leaf-shaped, small, they do not take any part in the movement, but they regularly serve for nutrition and respiration. The legs are constantly working, making up to 500 strokes per minute. So they create a current of water that carries algae, bacteria, yeast and oxygen.

The cladocerans also include such pelagic crustaceans as a small (less than 1 mm in length) bosmina longnosed(Bosmina longirostris). It is easily recognizable by its long, curved nose - the rostrum - with a tuft of bristles in the middle. An even smaller owner of a brownish spherical shell - hydrorus spherical(Chydorus sphaericus) - can be found in the water column and among coastal thickets.

Also widespread copepods(Copepoda) - Cyclops and Diaptomus, which belong to the subclass Maxillopod(Maxillopoda). Their body consists of a head, segmented chest and abdomen. The main organ of movement is powerful antennae and pectoral legs bearing swimming bristles. The legs work synchronously, like oars. Hence the common name of crustaceans - "copepods".

Diaptomuses, like Daphnia, are quite peaceful animals. In a glass vessel, you can easily observe their movement. Diaptomuses(Eudiaptomus graciloides) soar smoothly, balancing with outstretched antennae, the length of which is almost equal to the length of the entire body. Having descended, they make a sharp stroke with their pectoral legs and short abdomen and "jump" up. The current of water carrying food is created by crustaceans with short second antennae, making several hundred beats per minute. The elongated body of the crustacean is translucent and colorless, they need to be invisible to predators. Diaptomus females often carry a small pouch filled with eggs under their belly. Males are easy to distinguish by the right antenna with a knot in the middle and the last pair of legs, complexly arranged, with long hooked outgrowths. These devices are used by the male to hold the female.

More common in fresh waters cyclops, named after the one-eyed hero of ancient Greek myths. There is only one eye on the head of these crustaceans! Cyclops (Cyclops kolensis) have short antennae; adult females carry their eggs in two bags on the sides of the abdomen. Males hold their partners with both anterior loop-shaped antennae. Cyclopes differ in fussy, seemingly erratic movement. They "jump" often and sometimes somersault in the water. The fast and chaotic movement of the Cyclopes is aimed at achieving two main goals: firstly, not to get caught in the mouth of a fish, and secondly, to have time to grab something edible. Cyclopes are by no means vegetarians. If a large algae comes across, they will also eat it, but they still prefer the juveniles of their branched and copepod neighbors and other aquatic trifles, for example, ciliates and rotifers.