The number of antennae in crayfish and their functions. Class Crustaceans (Crustacea). Exercises based on the material covered

Crustaceans are aquatic arthropods that breathe with gills. The body is divided into segments and consists of several sections: the head, thorax and abdomen or the cephalothorax and abdomen. There are two pairs of antennae. The integument of the body contains a special solid substance - chitin, and in some they are also strengthened (impregnated) with calcium carbonate.

About 40 thousand species of crustaceans are known (Fig. 85). Their sizes are varied - from fractions of a millimeter to 80 cm. Crustaceans are widespread in the seas and fresh water bodies; a few, for example, woodlice, palm thief, have switched to a terrestrial lifestyle.

Rice. 85. Various crustaceans: 1 - crab; 2 - hermit crab; 3 - shrimp; 4 - woodlice; 5 - amphipod; 6 - sea duck; 7 - shield

The structural features and vital functions of crustaceans can be considered using the example of crayfish.

Lifestyle and external structure. Crayfish live in various fresh water bodies with clean water: river creeks, lakes, large ponds. During the day, crayfish hide under stones, snags, roots of coastal trees, and in burrows they themselves dug in the soft bottom. In search of food, they leave their shelters mainly at night.

The crayfish is a fairly large representative of arthropods; sometimes specimens over 15 cm in length are found. The color of the crayfish is greenish-black. The entire body is covered with a durable and dense chitinous shell, impregnated with calcium carbonate.

Veils crayfish serve as an exoskeleton. Bundles of striated muscles are attached to it from the inside. The hard shell of the crayfish prevents the animal from growing. Therefore, cancer periodically (2-3 times a year) molts - sheds its old covers and acquires new ones. During molting, until the new shell gets stronger (this takes about a week and a half), the cancer is defenseless and cannot feed. At this time, he hides in shelters. The body of the crayfish consists of two sections - the cephalothorax and abdomen (Fig. 86). At the anterior end of the cephalothorax there is a pair of long and a pair of short antennae - these are the organs of touch and smell. The spherical eyes sit on long stalks. Therefore, cancer can look in different directions at the same time. In case of danger, it hides its eyes in the recesses of its shell.

Rice. 86. External structure of crayfish: 1 - long antennae; 2 - short antennae; 3 - claw; 4 - walking legs; 5 - eye; 6" - cephalothorax; 7 - abdomen; 8 - caudal fin

Cancer's eyes are complex. Each eye consists of many very small eyes directed in different directions - facets (Fig. 87, B). The image of an object in a compound (compound) eye is composed of its individual parts, resembling mosaic pictures.

Rice. 87. Internal structure of crayfish (female): A - general plan of the body structure: 1 - stomach; 2 - liver; 3 - heart; 4 - blood vessels; 5 - ovary; 6 - intestine; B - diagram of the structure of the compound eye

The crayfish has limbs on its cephalothorax. If you turn it over on its back, then at the front end of the body you can find three pairs of jaws: a pair of upper jaws and two pairs of lower jaws. The cancer uses them to tear its prey into small pieces. The jaws are followed by three pairs of short jaws. They serve to bring food to the mouth. Both the mandibles and the maxillomandibles are modified legs. Behind the jaws are five pairs of walking legs. With the help of four pairs of these legs, the crayfish moves along the bottom of reservoirs. And the first pair of walking legs of the crayfish is turned into large claws. With them, the cancer grabs prey and tears off large parts from it. He defends himself with these same claws.

And on the abdomen the crayfish has short limbs (legs), the female has four pairs, the male has five pairs. At the very end of the abdomen there is a flat segment, on the sides of which modified, highly flattened legs are developed. Together they form the caudal fin. By sharply bending its abdomen, the crayfish pushes off the water with its tail fin, like an oar, and in case of danger can quickly swim backwards.

Digestive system(Fig. 87, A) begins with the oral opening. From the mouth, food enters the stomach, which consists of two sections. In the first section there are chitinous formations impregnated with calcium carbonate - millstones, with the help of which food is crushed. Then it ends up in the second section of the stomach, where it is filtered. Large particles of food are retained and returned to the first section, while small particles enter the intestine. The liver ducts empty into the mid-intestine. Digestion of food and absorption of nutrients occurs in the intestines and liver. The digestive system ends with the anus, located on the caudal segment of the abdomen. Crayfish feed on mollusks, insect larvae living in water, decomposing animal corpses, and plants.

Respiratory organs crayfish have gills. They contain blood capillaries and gas exchange occurs. The gills have the appearance of thin feathery outgrowths and are located on the processes of the jaws and walking legs. In the cephalothorax, the gills lie in a special cavity. The movement of water in this cavity is carried out due to very rapid vibrations of special processes of the second pair of jaws.

Circulatory system open

Crustaceans have a mixed body cavity; in the vessels and intercellular cavities of crustaceans (as in other arthropods), it is not blood that circulates, but a colorless or greenish liquid - hemolymph. It performs the same functions as blood and lymph in animals with a closed circulatory system.

The heart is located on the dorsal side of the cephalothorax. Hemolymph flows through the vessels and then enters the cavities located in various organs. Here the hemolymph gives off nutrients and oxygen, and receives waste products and carbon dioxide. Then the hemolymph travels through the vessels to the gills, and from there to the heart.

Excretory system represented by a pair of green glands located in the front of the cephalothorax. They open outward at the base of the long antennae. Through these holes, harmful products that are formed during life are removed.

Nervous system. Cancer has a central nervous system - the peripharyngeal nerve ring and ventral nerve cord and a peripheral nervous system - nerves extending from the central nervous system.

Sense organs. In addition to the organs of touch, smell and vision, crayfish also have organs of balance. They are a depression in the main segment of the short antennae, where a grain of sand is placed. The grain of sand presses on the thin sensitive hairs surrounding it, which helps the cancer assess the position of its body in space.

Reproduction. Crayfish are characterized by sexual reproduction. Fertilization is internal. Fertilized eggs laid by the female (from 60 to 200 pieces) are attached to her abdominal legs. Eggs are laid in winter, and young crustaceans appear in spring. Having hatched from the eggs, they continue to hold on to the mother’s abdominal legs (Fig. 88), and then leave her and begin an independent life. Young crustaceans feed only on plant foods.

Rice. 88. Young crustaceans on the abdominal legs of the female

Decapods include crayfish, large sea crayfish - lobsters (up to 60 cm long and weighing up to 15 kg) and lobsters (they lack claws), small crustaceans - shrimp. Some of them move along the bottom, others actively swim in the water column using their abdominal legs. Hermit crabs belong to the same group. They have a soft, unsegmented abdomen. Hermit crabs hide from enemies in the empty shells of sea snails, carrying the shell with them all the time, and in case of danger, completely hiding in it, covering the entrance with a highly developed claw. Decapods include crabs. They have a wide but short cephalothorax carapace, very short antennae, and a short abdomen tucked under the cephalothorax. Crabs most often move sideways.

Listopods include small crustaceans well known to aquarists - daphnia 3-5 mm long (Fig. 89, 1). They live in small fresh water bodies. The entire body (except for the head) of daphnia is enclosed in a transparent chitinous shell-shell. Through the chitinous covers one can see a large complex eye and constantly working chest legs, which ensure the flow of water under the shell. Daphnia has large branched antennae. By flapping them, she jumps in the water, which is why daphnia is sometimes called “water fleas.” Daphnia feed on protozoa, bacteria, and single-celled algae found in the water column.

Rice. 89. Crustaceans: 1 - daphnia: 2 - cyclops

Freshwater bodies of water are inhabited by a small crustacean that vaguely resembles a wood lice - the water donkey. Multipeds are small (up to several centimeters) crustaceans that swim on their sides, for which they are called amphipods. Using different legs, crustaceans can swim, walk along the bottom of reservoirs, along the wet soil of the banks, and also jump. Barnacles are small crustaceans that lead an attached lifestyle as adults, for example sea acorns. They live in the sea. Their entire body is covered with a calcareous shell-house. Most often, the shell is attached to stones, crab shells, the bottoms of ships, and the skin of whales. Barnacles catch their prey (planktonic organisms) using long, movable chest legs.

Crustaceans are primary aquatic arthropods with a hard and durable chitinous shell, impregnated with calcium carbonate, and articulated limbs located on the thoracic and abdominal regions. Crustaceans breathe using gills.

Exercises based on the material covered

1. Find out, using Figure 86, what features arthropods have in their external structure. Name their similarities with annelids.
2. What is the difference between the internal structure of crustaceans and representatives of other classes of arthropods? Explain using the example of crayfish.
3. What are the structural features of the sensory organs of crayfish?
4. Use a few examples and pictures to show the diversity of the class. Describe the habitats of crustaceans.
5. What is the role of crustaceans in nature?

Crustaceans are ancient aquatic animals with a complex body structure covered with a chitinous shell, with the exception of woodlice that live on land. They have up to 19 pairs of jointed legs that perform various functions: capturing and grinding food, movement, protection, mating, and bearing young. 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, and toothless whales. Many crustaceans (crabs, shrimp, lobsters, lobsters) are commercial or specially bred animals.

2 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 Crustacean class was divided into two subclasses - lower and higher crustaceans. The subclass of lower crayfish included phyllopods, jawed crayfish and shell crayfish. It is now recognized that such a unification is impossible, since these groups of crayfish are different in origin.

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

The body of crustaceans is divided into the 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 segmented antennae; These are the so-called antennules and antennae. They carry the organs of touch, smell and balance. The next 3 pairs - oral limbs - are used to capture and grind food. These include a pair of upper jaws, or mandibles, and 2 pairs of lower jaws - maxilla. Each chest segment carries a pair of legs. These include: jaws, which are involved in holding food, and locomotor limbs (walking legs). The abdomen of higher crayfish also bears limbs - swimming legs. The lower ones don't have them.

Crustaceans are characterized by a bibranched limb structure. They distinguish between the base, external (dorsal) and internal (ventral) branches. This structure of the limbs and the presence of gill projections on them confirms the origin of crustaceans from polychaete annelids with bibranched parapodia.

In connection with the evolution in the aquatic environment, crustaceans have developed organs of aquatic respiration - gills. They often appear as outgrowths on the limbs. Oxygen is delivered by blood from the gills to the tissues. Lower crayfish have colorless blood called hemolymph. Higher crayfish 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, are dioecious. They usually develop through metamorphosis. A nauplius larva emerges from the egg with an unsegmented body, 3 pairs of limbs and one unpaired eye.

• Subclass Entomostraca (lower crayfish).

  Lower crayfish live in both fresh waters and seas. They are important in the biosphere, being an essential part of the diet of many fish and cetaceans. The most important are copepods (Copepoda), which serve as intermediate hosts of human helminths (diphyllobothriids and guinea worms). They are found everywhere in ponds, lakes and other standing 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, mouthparts, 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. They also often serve to hold the female by the male during mating. Thorax of 5 segments, pectoral legs with swimming setae. Abdomen of 4 segments, at the end - a fork. At the base of the female's abdomen there are 1 or 2 egg sacs in which eggs develop. Nauplii larvae emerge from the eggs. The hatched nauplii look completely different from adult crustaceans. Development is accompanied by metamorphosis. Copepods feed on organic debris, tiny aquatic organisms: algae, ciliates, etc. They live in reservoirs all year round.

The most common genus is Diaptomus.

Diaptomus 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, which makes it reluctant to be eaten by fish. The color depends on the nutrient base of the reservoir. Diaptomuses have 11 pairs of limbs. The antennules are single-branched, the antennae and legs of the thoracic segments are biramous. The antennules reach especially great lengths; they are longer than the body. Scattering them widely, diaptomuses float in the water, the thoracic limbs cause the jerky movements of the crustaceans. The oral limbs are in constant oscillatory motion and drive particles suspended in water towards the mouth opening. In Diaptomus, both sexes take part in reproduction. Diaptomus females, unlike Cyclops females, have only one egg sac.

Species of the genus Cyclops (cyclops)

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

In terms of their biochemical composition, copepods are in the top ten high-protein foods. In aquarium farming, “Cyclops” is most often used to feed grown juveniles and small-sized fish species.

Daphnia, or water fleas

move spasmodically. 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 towards the ventral side. On the head there is one complex compound eye and in front of it a simple ocellus. The first pair of antennae is small and rod-shaped. The antennae of the second pair are highly developed, bibranched (with their help, daphnia swims). On the thoracic region there are five pairs of leaf-shaped legs, on which there are numerous feathery bristles. Together they form a filtration apparatus that serves to filter small organic residues, unicellular algae and bacteria from the water that daphnia feed on. At the base of the thoracic legs there are gill lobes in which gas exchange occurs. On the dorsal side of the body there is a barrel-shaped heart. There are no blood vessels. Through the transparent shell, the slightly curved tube-shaped intestine with food, the heart, and below it the brood chamber in which daphnia larvae develop are clearly visible.

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

  Higher crayfish are inhabitants of marine and fresh water bodies. Only woodlice and some crayfish (palm crayfish) live on land from this class. Some species of higher crayfish serve as commercial fisheries. In the seas of the Far East, a gigantic Pacific crab is caught, whose walking legs are used for food. In Western Europe, lobster and lobster are caught. In addition, crayfish have sanitary significance, because... clear water bodies of animal corpses. Freshwater crayfish and crabs in Eastern countries are intermediate hosts for the pulmonary fluke.

  A typical representative of higher crayfish is the river crayfish.

Crayfish live in flowing fresh water bodies (rivers, streams), feed 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 burrows that it digs with its claws in steep banks. Only when night falls does he come out to look for food. For the winter, crayfish hide in their burrows.

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 the crayfish from damage and serves as an exoskeleton. At a young age, during the growth period, crayfish change their shell. This process is called molting. Over time, when the crayfish reaches a large size, it grows slowly and sheds rarely.

The color of the shell of a living 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 coloring is protective and allows the cancer to become invisible. When caught crayfish are boiled, some of the chemical substances 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 crayfish's body is divided into three sections: head, chest and abdomen. On the dorsal side, the head and thoracic sections are covered with a single cephalothoracic solid, strong chitinous shield, which bears a sharp spike in front; on its sides, in recesses on movable stalks, 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 mouth opening of the crayfish there are six pairs of limbs: the upper jaws, two pairs of lower jaws and three pairs of maxillae. There are also five pairs of walking legs on the cephalothorax, and the three front pairs have claws. The first pair of walking legs is the largest, with the most well-developed claws, which are organs of defense and attack. The oral limbs, together with the claws, hold food, crush it and direct it into the mouth. The upper jaw is thick, jagged, and powerful muscles are attached to it from the inside.

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

Movement of crayfish. Crayfish can crawl and swim forward and backward. It crawls along the bottom of the reservoir with the help of its pectoral walking legs. The crayfish swims forward slowly, moving its abdominal legs. To move backwards, it uses the caudal fin. By straightening it and tucking 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 filtration. On the dorsal and lateral walls of the chewing section, the cuticle forms three powerful chitinous chewing plates impregnated with lime with serrated free edges. In the filtering section, two plates with hairs act like a filter through which only highly crushed food passes. Next, the food enters the midgut, where the ducts of the large digestive gland open. Under the influence 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 secretion breaks down not only fats, but also proteins and carbohydrates, i.e. functionally corresponds to the liver and pancreas of vertebrates). Undigested remains enter the hindgut and are excreted through the anus on the tail blade.

Respiratory system. Crayfish breathe using gills. Gills are feathery outgrowths of the thoracic limbs and lateral walls of the body. They are located on the sides of the cephalothorax shield inside a special gill cavity. The cephalothorax 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 extend from the heart and open into the body cavity, where the blood gives oxygen to tissues and organs. The blood then flows into the gills. The circulation of water 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 per minute). Gas exchange occurs through the thin cuticle of the gills. Oxygen-enriched blood is directed through the gill-cardiac canals into the pericardial sac, from where it enters the heart cavity through special openings. Cancer blood is colorless.

Excretory organs paired, they look like 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 suprapharyngeal node (brain), peripharyngeal connectives and a ventral nerve cord. From the brain, nerves go to the antennae and eyes, from the first node of the abdominal nerve chain, or subpharyngeal ganglion, to the oral organs, from the next thoracic and abdominal nodes of the chain, respectively, to the thoracic and abdominal limbs and internal organs.

Sense organs. The compound or compound eyes of crayfish are located in the 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 photosensitive 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, which is why arthropods are said to have mosaic vision).

The crayfish's antennae serve as organs of touch and smell. At the base of the short antennae there is an organ of equilibrium (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. This is how the female takes care of her offspring. Young crayfish grow rapidly and molt several times a year. Development in crayfish is direct. Crayfish reproduce quite quickly, despite the fact that they have relatively few eggs: the female lays from 60 to 150-200, rarely up to 300 eggs.

The meaning of crustaceans

Daphnia, cyclops and other small crustaceans consume large amounts of organic remains of dead small animals, bacteria and algae, thereby purifying the water. In turn, they represent an important source of food for larger invertebrate animals and juvenile fish, as well as for some valuable planktivorous fish (for example, 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 juvenile sturgeon, stellate sturgeon and other fish.

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

• Class Crustacea (crustaceans)

Topic: type Arthropods

class Crustaceans

Target: study the organization of Crustaceans using the example of Crayfish.

Tasks:

Study the classification of the phylum Arthropods. Learn aromorphoses of the Arthropod type. Everything should be written down in a notebook.

Study the organization of Arthropods of the class Crustaceans using the example of Crayfish. Complete the notes in your notebook.

Consider wet preparations of different types of crustaceans - Crab, Shrimp, Woodlice, Shield, Crayfish, Amphipod, Daphnia. Under a microscope, examine the appearance of the Cyclops.

Study the external and internal structure of the Crayfish (autopsy of a crayfish). Pay special attention to the variety of limbs - the Crayfish has 19 pairs of them.

In the album, complete 2 drawings, indicated by V (red tick) in the printed manual. In the electronic manual, the necessary drawings are presented at the end of the file.

Know the answers to Control questions Topics:

General characteristics of the phylum Arthropods. Classification of the phylum Arthropods. Aromorphoses of the Arthropoda type.

Features of the organization of arthropods of the class Crustaceans.

Systematic position, lifestyle, body structure, reproduction, significance in nature and for humans of River Cancer.

Phylum Arthropod- Arthropoda

Arthropods are a type of invertebrate animal. In terms of the number of species, they occupy first place on Earth - there are more than 1.5 million of them. This is more than 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. Arthropods are found throughout the globe, but they are especially diverse in the hot tropical region. Arthropods are bilaterally symmetrical, segmented animals with jointed limbs. Jointed legs are the most striking and important sign of the type.

The type is divided into 4 subtypes:

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

Subtype 2. Gill-breathing(Branchiata). There is one in subtype Class Crustaceans(30 – 35 thousand centuries). They are aquatic arthropods that breathe through gills.

Subtype 3. Cheliceraceae(Chelicerata). In subtype 2 classes: Class Merostomaceae(the so-called crustacean scorpions - now extinct aquatic chelicerates) and Class Arachnids(about 60 thousand centuries).

Subtype 4. Tracheal(Tracheata). Two classes: Class Centipedes(over 53 thousand centuries) and Class Insects(more than 1 million century)

Animals type Arthropods have the following aromorphoses: 1. dense water- and air-tight covers. 2. Jointed limbs of different purposes and different structures. During evolution, the articulated limb of the Arthropod descended from the parapodia of Polychaete annelids. 3. Heteronomous segmentation. 4. Division of the body into sections: head + chest + abdomen, or cephalothorax + abdomen.

Class Crustaceans– Crustacea

Crayfish

Crustaceans there are 30 - 35 thousand species of gill-breathing arthropods leading an aquatic lifestyle. Only some species, e.g. Woodlice and land crabs have adapted to live on land, but they also stick to moist habitats, as they breathe with gills. The body sizes of crustaceans range from fractions of a millimeter to 3 m. This is the most ancient group among living arthropods.

So, the distinctive features of the class are breathing using gills. Small crustaceans do not have gills; gas exchange occurs through the surface of the body. The second distinctive feature is the presence on the head section two pairs of antennae performing tactile and olfactory functions. The third feature of crustaceans is biramous limbs.

More detailed structural features of animals of the class Crustaceans should be considered using an example Crayfish - Astacus astacus(type Arthropods, subtype Gill-breathing, class Crustaceans, subclass Higher crayfish, order Decapod crayfish).

Class Crustaceans Crayfish

Lifestyle. Crayfish are common representatives of our freshwater fauna. Crayfish are medium-sized crayfish: their body length can reach 15-20 cm. Crayfish are found in rivers and lakes with a muddy bottom and steep banks. Crayfish cannot tolerate any kind of water pollution; they live only in clean water. During the day, crayfish hide in burrows they dug in the banks underwater (the burrows are deep, up to 35 cm long). With the onset of darkness, crayfish come out to get their food. Crayfish are polyphagous, i.e. They feed on a wide variety of food: bottom sediments, algae, carrion, thereby being orderlies of reservoirs. In winter, they do not change their place of residence, but simply descend much deeper, to where the water does not freeze. From late autumn to early spring, crayfish lead an inactive lifestyle, staying in shelters for 20 hours a day. The life of females during this period is more eventful than that of males. Indeed, two weeks after mating, which occurs in October, the female lays about 100 eggs on her abdominal legs and bears them for a long 8 months, that is, until the beginning of summer, when young crustaceans hatch from them. For the eggs to fully develop, caring females have to leave the hole from time to time to walk the eggs and clean them. Crayfish become active in the spring, when the water warms up enough. (So ​​there is no mystery at all regarding the place where crayfish spend the winter.)

External building. The body of Crustaceans is segmented, and the body segments are not identical in shape and function - this is the so-called heteronomous segmentation. The body consists of two sections: cephalothorax And abdomen. The head part of the cephalothorax bears five steam limbs. On its head blade there are short antennae - antennules(olfactory organs). The first segment has long antennae - antennas(organs of touch). On the other three - pair upper jaws And two couples mandibles. The upper jaws of crayfish are called mandibles, and a pair of lower jaws – maxillae. The jaws surround the mouth. With its jaws, the cancer tears its prey into small pieces and pushes them into the mouth.

At the anterior end of the cephalothorax in cancer there are spherical eyes, which sit on long stems. Therefore, cancer can look in different directions at the same time.

The thoracic part of the cephalothorax includes eight segments: the first three carry maxillary, taking part in maintaining and crushing food. The legjaws are followed five pairs of running gear or, in other words, walking legs (limbs). The first three pairs of walking limbs end claws, which serve for protection and for capturing prey. Of these limbs with claws, the first pair bears especially powerful and large claws. With its claws, the crayfish grabs and holds prey and defends itself during an attack. The two-branched jaws and walking legs consist of a lower branch in the form of an ordinary jointed leg and an upper branch in the form of a delicate leaf or threads. The upper branch of the two-branched limb performs the function of gills.

The segmented, movable abdomen consists of six segments, each of which contains a pair of limbs. In males, the first and second pair of abdominal limbs are modified into copulative organ involved in the mating process. In the female, the first pair of limbs is greatly shortened, the rest

Class Crustaceans Crayfish

Eggs and young are attached to four pairs. The abdomen ends tail fin, formed by the sixth pair of wide two-branched lamellar limbs and an anal flattened lobe - telson. By sharply bending its abdomen, the crayfish pushes off against the water with its tail fin, like an oar, and in case of danger can quickly swim backwards.

Thus, the body of a crayfish begins with the head lobe, followed by 18 segments, and ends with the anal lobe. Four cephalic and eight trunk segments are fused to form the cephalothorax, followed by six abdominal segments. Thus, the crayfish 19 pairs of limbs different structures and purposes.

Covers of the body. The body of Crustaceans is covered with chitinized cuticle The cuticle protects the body from external influences. Lime is deposited in the peripheral layers of the cuticle, as a result of which the skin of the cancer becomes hard and durable, which is why the cuticle is also called shell. The inner layer consists of soft and elastic chitin.

In living crayfish, the shell has a rather variable color - from light green to almost black. This coloring has a protective nature: as a rule, it matches the color of the muddy bottom on which the crayfish lives. The color of the Crayfish depends on several coloring substances contained in the integument - pigments: red, blue, green, brown, etc. If you throw the crayfish into boiling water, all pigments except red are destroyed by boiling. That's why boiled crayfish is always red.

The cuticle simultaneously performs the function outdoor skeleton: Serves as a site for muscle attachment. But such a strong external skeleton prevents the growth of the animal and therefore periodically all Crustaceans (and other arthropods) have to molt. Shedding This is the periodic removal of the old cuticle and replacing it with a new one. After molting, the cuticle remains soft for some time, at which point Crayfish grow intensively. While the new cuticle has not yet formed (and for Crayfish this process takes about a week and a half), Cancer is very vulnerable, so during the molting period Crayfish hide, do not hunt or eat. Before molting, a pair of so-called lentil-shaped “millstones” of calcium carbonate appears in the crayfish’s stomach; this reserve allows the crayfish’s integument to harden faster; the “millstones” disappear after molting.

Sometimes molting is very difficult for cancer: it, not being able to free its claw or walking leg from the old cuticle, breaks it off. But the injured limb is capable of regeneration, that’s why you come across crayfish with one claw smaller than the other. Sometimes a cancer, when it is in danger, with the help of its muscular effort specially breaks off its claw: it sacrifices a limb to save the whole body.

Musculature crustaceans consists of striated fibers that form powerful muscle bundles, i.e. In crustaceans (and in all arthropods), the muscles are represented by separate bundles, and not in a bag like in worms.

Body cavity. Crustaceans, like all arthropods, are secondary cavity(coelomic) animals.

Class Crustaceans Crayfish

Digestive system consists of three departments: front, average And rear intestines. The foregut begins oral hole and has a chitinous lining. Short esophagus flows into stomach, divided into two parts: chewing And filter. IN chewing department mechanical grinding of food occurs with the help of three large thickenings of the cuticle - “teeth”, and in filtering the food gruel is filtered, compacted and then enters the midgut. A duct opens into the midgut digestive glands, which performs the functions of both the liver and pancreas. Here, in the midgut, liquid food gruel is digested. Long back intestine ends anal hole on the anal blade.

Respiratory system Crayfish are represented by gills- branched thin-walled outgrowths of the thoracic limbs, jaws and walking legs. The gills are the upper branch of two-branched limbs. The gills are delicate and look like branched bushes. The gills are located on the sides of the chest in gills cavities covered by a cephalothoracic carapace. Small crustaceans do not have gills and respiration occurs over the entire surface of the body.

Circulatory system open, comprises hearts, located on the dorsal side of the cephalothorax, and several large blood vessels extending from it vessels- anterior and posterior aortas. The heart has the shape of a pentagonal sac. From vessels hemolymph(this is the fluid that fills the circulatory system) pours into the body cavity, seeps between the organs and reaches the gills. Gas exchange occurs in the gills. Oxidized hemolymph enters pericardial bag and through special holes (there are three pairs of them) it returns to the heart again. The hemolymph of crustaceans can be colorless, reddish from the hemoglobin pigment it contains, and bluish from the hemocyanin pigment.

Excretory system represented by a couple green glands(kind of buds). Each green gland consists of three parts: terminal pouch(section of the coelom) extending from it crimped channel with glandular walls and urinary bubble. In the terminal sac, active absorption of metabolic products from the hemolymph occurs. Metabolic products enter the bladder through the convoluted tubule. The bladders open outward at the base of the antennae excretory at times(i.e. they open somewhere between the eyes!).

Nervous system. Nervous system in Crustaceans staircase type(like annelids). The nervous system consists of couples supraglottic nervous nodes, which is often called the "brain", peripharyngeal nervous rings And couples abdominal nervous trunks with ganglia (nodes) in each segment.

The sense organs are well developed. Short antennules specialize in sense of smell, and long antennas- on touch. In general, all the antennae and all the limbs are covered tactile hairs. Most decapods have balance organs at the base of the antennules. statocysts. Statocysts are depressions at the base of short antennae where ordinary grains of sand are placed. In normal body position, these grains of sand press on the lower sensitive hairs underneath; if the body of a floating crayfish turns upside down, the grains of sand move and press on

Class Crustaceans Crayfish

other sensitive hairs and then the cancer feels that its body has left its normal position and turns over. When a crayfish molts, grains of sand are also shed. Then the cancer itself specially uses its claws to insert new grains of sand into its organ of balance.

River Cancer's eyes are complex, faceted. Each eye consists of many small ocelli; the crayfish has more than three thousand of them. Each eye perceives only part of an object, and their sum makes up the overall picture. This is the so called mosaic vision.

Reproduction and development. Cancers in general dioecious. The crayfish has a pronounced sexual dimorphism- the male’s abdomen is narrower, and the female’s is wider. In the male, the first pair of abdominal limbs has transformed into copulative organs. In crayfish, the gonads are not paired and are located in the cephalothorax. A pair of oviducts depart from the ovary, which open with genital openings at the base of the third pair of walking legs (i.e., on the cephalothorax). In males, a pair of long convoluted vas deferens emerges from the testis, which open into the genital openings at the base of the fifth pair of walking legs. Before mating, the male collects sperm into his copulatory organs, and then these copulatory organs, which look like hollow tubes, are inserted into the female's genital opening. Fertilization in Crustaceans internal. 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 (there are not many eggs: 60 - 150, rarely up to 300). And only at the beginning of summer do the crustaceans emerge from the eggs, which remain under the protection of the female for a long time, hiding on her abdomen on the underside. Young crayfish grow rapidly and molt several times a year, while adults molt only once a year. River crayfish live for 25 years.

Meaning. Crustaceans are of great importance in nature and human economic activity. Countless microscopic crustaceans that inhabit 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, Diaptomus, Amphipods- excellent food for freshwater fish and their larvae.

Many small crustaceans feed by filtration, i.e. detritus suspended in water is filtered. Thanks to their nutritional activity, natural water is clarified and its quality is improved. Many crustaceans are large commercial species (which is why they suffered greatly), for example: Lobsters, Crabs, Lobsters, Shrimps, Cancers river. Medium-sized marine crustaceans are used by humans to prepare nutritious protein paste.

Class Crustaceans Crayfish

Rice. External structure of Crayfish (female).

Questions for self-control

Name the classification of the phylum Arthropods.

What is the systematic position of Crayfish?

Where do crayfish live?

What body shape do crayfish have?

What is the body of the Crayfish covered with?

What body cavity is typical for Crayfish?

What is the structure of the digestive crayfish?

What is the structure of the circulatory system of Crayfish?

How does crayfish breathe?

What is the structure of the excretory system of Crayfish?

What structure does the nervous system of Crayfish have?

What is the structure of the reproductive system of Crayfish?

How does crayfish reproduce?

What is the significance of crayfish?

What is the importance of crustaceans in general?

Class Crustaceans Crayfish

Rice. Opened crayfish (female).

1 - eye; 2 - stomach; 3 - liver; 4 - superior abdominal artery; 5 - heart; 6 - anterior arteries; 7 - gills; 8 - ovary; 9 - abdominal nerve cord; 10 - abdominal muscles; 11 - antennas; 12 - antennas; 13 - hindgut; 14 - mandible muscles.

Class Crustaceans Crayfish

Rice. Internal structure of Crayfish. Digestive, nervous and reproductive systems (male).

Rice. Internal structure of Crayfish. Circulatory, respiratory and excretory systems.

Class Crustaceans Crayfish

Rice. Male reproductive system of Crayfish: 1 - paired part of the testis, 2 - unpaired part of the testis, 3 - vas deferens, 4 - vas deferens, 5 - genital opening, 6 - base of the fifth pair of walking legs.

Rice. Antennal gland (green gland) of Crayfish (expanded).

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

DRAWINGS THAT NEED TO BE COMPLETED IN THE ALBUM

(2 pictures in total)

Lesson topic:

Phylum Arthropods -Arthropoda.

Subtype Gill-breathing -Branchiata. Class Crustaceans -Crustacea.

Type: Arthropod

Subtype: Gill-breathing

Class: Crustaceans

Subclass: Higher crayfish

Order: Decapods

Species: Broad-clawed crayfish - Astacus astacus

Rice. 1. Crayfish.

Internal structure (female from the dorsal side).

1-stomach 10-tufts of striated

2-midgut muscles

3-hindgut 11-cephalothorax

4-liver 12-abdomen

5-gills 13-cephalothoracic shield (carapace)

6-heart 14-cephalothoracic spine (rostrum)

7-antennary glands 15-eyes

(green glands) 16-cut mandible muscle

8-gonad 17-telson

9-nerve chain 18-uropodia

Lesson topic:

Phylum Arthropods -Arthropoda.

Subtype Gill-breathing -Branchiata. Class Crustaceans -Crustacea.

Captions for Fig. 2. Diversity of crayfish limbs.

1- short antennae (antennae) – olfactory organ;

2- long antennae (antennae) – organ of touch;

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

6, 7, 8 – jaws – are involved in holding and crushing pieces of food;

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

14, 15, 16, 17, 18, 19 – abdominal limbs, while the first pair (No. 14) and sometimes the second (No. 15) of the abdominal limbs in males are 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.

Rice. 2. Diversity of crayfish limbs.

The class Crustaceans are mainly aquatic animals that inhabit seas and fresh water bodies. Their body is divided into the cephalothorax and abdomen. They have two pairs of antennae and compound or compound eyes. They breathe with gills. The total number of known species is 20,000.

A typical representative is crayfish. Lives in fresh running waters. During the day it hides under stones or in holes dug at the bottom, or under the roots of trees.

At night they crawl out of their hiding places in search of food. Crayfish are omnivores. The cephalothorax of the cancer is formed from fused segments of the head and chest: The anterior part of the cephalothorax is elongated, pointed and ends with a sharp spine. At its base there are two compound eyes located on stalks, thanks to which the cancer can turn them in different directions. Compound eyes consist of many small ocelli - up to 3,000 and are called faceted. The cephalothorax of the crayfish bears two pairs of antennae. The long ones serve as organs of touch, and the short ones serve as organs of smell. Below the antennae are the mouthparts, which are modified limbs. The first pair forms the upper, and the second and third - the lower jaws, the remaining three pairs - maxillary. On the cephalothorax there are five pairs of jointed walking legs. Of these, the front pair of limbs has the most powerful organ of attack and defense - claw. The claw also serves as a food grabber. The segmented abdomen bears abdominal legs on which females carry eggs.

Crayfish are omnivores. Food crushed by the oral organs enters the stomach, which consists of two sections, through the pharynx and esophagus. chewable And filter. On the inner walls of the chewing section there are chitinous denticles, with the help of which food is ground. In the filtering section, it is filtered and enters the intestine, and then into the digestive gland, where it is digested and absorbed nutrients.

Respiratory organs cancer - gills located on the sides of the cephalothorax. Oxygen penetrates into the blood flowing through the gill vessels, and carbon dioxide is released from the blood. The circulatory system of cancer is open and consists of saccular heart, lying on the dorsal side of the body, and the vessels extending from it.

The nervous system of cancer consists of large suprapharyngeal and subpharyngeal nerve nodes, forming a peripharyngeal ring, and the abdominal nerve cord.

Cancer excreting organs - pair of green glands located in the head of the body. Their excretory channels open outward at the base of the antennae. Through green glands, harmful metabolic products dissolved in the blood are removed from the cancer body.

Crayfish are dioecious. In winter, the female lays eggs, gluing each one to her abdominal legs. At the beginning of summer, young crustaceans emerge from the eggs (eggs), which the female carries on her legs for a long time.

The class Crustaceans belongs to several orders. Among them: decapod crustaceans, isopods, Cladocera, copepods, carp eaters.

Order Decapods. This includes the one described above crayfish, and planktonic shrimp species, large-sized sea crayfish - lobster, lobsters, various crabs. All of them are valuable food items and are used as food for preparing all kinds of delicious dishes. This group includes Cancer hermit leading a unique lifestyle. Young crustaceans find gastropods with shells of appropriate sizes, kill and eat them, and hide their abdomen in the shell. After each molt, the size of the crayfish increases and they have to look for a new mollusk with a larger shell, and everything repeats all over again.

Order Isopods. This includes both aquatic and terrestrial crustaceans, the abdominal and thoracic limbs of which differ little, as, for example, in woodlice. These are small (up to 10-15 mm) gray or whitish animals that live in damp places, in leaf litter, some are even found in deserts.

Order Cladocera, whose representative is daphnia. Because of its way of moving by jumping, it is popularly called the “water flea.”

Order copepods, which refers to Cyclops. These are planktonic crustaceans that feed on many species of marine and freshwater commercial fish, and even such large animals as the baleen whale.

In total, there are about 50,000 species of crustaceans.

Crayfish - the same age as dinosaurs. Few people know that it dates back to ancient times. These crustaceans appeared and formed during the Jurassic period as a separate species, approximately 130 million years ago. The appearance of the crayfish remained virtually unchanged during this period. Its population is actively growing, spreading throughout all water bodies of Europe.

general characteristics

Crayfish live in fresh, clean waters:

• in lakes;
• in river backwaters;
• in large ponds.

During the daytime, the crayfish hides under snags, stones, roots of coastal trees, and in burrows that it digs in the soft bottom. At night he leaves his shelter in search of food. It feeds mainly on plant foods, live and dead animals.

External structure

The color of crayfish is greenish-brown. Its body consists of segments that together form three body sections:

• breast;
• head;
• abdomen.

In this case, only the abdominal segments remain movably articulated. The chest and head are fused into a single whole. The movement of the limbs is ensured by powerful striated muscles. The top of the cephalothorax is covered with a continuous chitinous shield, in front of which there is a sharp spike. On the sides of the shield there are eyes, a pair of long antennae and a pair of short ones on movable stalks.

Below the mouth opening on the sides there are 6 pairs of limbs:

• upper jaws;
• mandibles - 3 pairs;
• lower jaws - 2 pairs.

There are five pairs of legs on the cephalothorax. The three front pairs have claws. The largest pair of walking paws is the first. The claws on it are the most developed. They are simultaneously organs of attack and defense. The claws and mouthparts hold what the crayfish eats, crush it and put it in the mouth. The thick upper jaw of the crayfish is jagged. Strong muscles are attached to it from the inside.

The abdomen of a crayfish consists of 6 segments. Four segments have two-branched segmented legs. The limbs of the first and second segments in the female are reduced, in the male they are modified (participate in copulation). The sixth pair is wide and lamellar, part of the caudal fin and plays an important role in moving backwards.

The internal structure of crayfish consists of:

Digestive system

The digestive system begins with the mouth. Food enters the pharynx, then into the short esophagus and into the stomach, which has two sections: filtering and chewing.

The dorsal and lateral walls of the chewing region have three lime-impregnated, powerful chitinous chewing plates with loose, jagged edges. The straining section is equipped with two plates with hairs. Only crushed food passes through it, like through a filter.

Small food particles enter the intestines, and large ones return back to the intestines.

Food is digested and absorbed through the glands and walls of the midgut. Undigested residues exit through the anus located on the tail blade.

Circulatory system

The crayfish's body cavity is mixed; a greenish or colorless liquid circulates in the intercellular cavities and vessels - hemolymph, which performs functions identical to those of blood in animals that have a closed circulatory system.

Under the shield on the dorsal side of the chest there is a pentagonal heart. Blood vessels depart from it, which open into the body cavity. The blood gives oxygen and nutrients to organs and tissues and takes away carbon dioxide and waste products.

Then the hemolymph flows through the vessels into the gills, and then into the heart.

Respiratory system

Crayfish breathes with the help of gills, in which gas exchange takes place and blood capillaries are located. The gills are thin feathery projections located on walking legs and on the processes of the maxillaries. The gills lie in a special cavity in the cephalothorax.

In this cavity, due to rapid vibrations of the processes of the second pair of lower limbs, water moves and gas exchange occurs through the gill shell. Oxygen-enriched blood flows through the gill-heart valves into the pericardial sac. Then it enters the oral cavity through a special opening.

The nervous system of crayfish consists of the subpharyngeal node, the paired suprapharyngeal node, the central nervous system and the ventral nerve cord.

Nerves from the brain go to the eyes and antennae, from the first node of the abdominal nerve chain to the oral organs. From the following abdominal and thoracic nodes, the chains go, respectively, to the internal organs, thoracic and abdominal limbs.

Sense organs

On both pairs of crayfish antennae there are receptors: chemical sense, balance and touch. Each eye has more than 3,000 ocelli, or facets. They are separated from each other by thin layers of pigment. The photosensitive parts of the facets perceive only a narrow beam of rays perpendicular to its surface. The complete picture consists of numerous partial small images.

The balance organs are represented by depressions in short antennae in the main segment, where a grain of sand is placed. It presses on the thin, sensitive hairs surrounding it. This helps Cancer evaluate the position of his body in space.

The excretory organs of cancer are a pair of green glands that are located in the front of the cephalothorax. Each gland consists of two sections: the bladder and the gland itself.

Harmful waste products formed during the metabolic process accumulate in the bladder. They are expelled through the excretory pore along the excretory canal.

By its origin, the excretory gland is a modified metanephridium, which begins as a small coelomic sac. A glandular canal extends from it - a winding tube.

Features of the habitat and behavior of cancer

Crayfish live only in reservoirs with fresh water at a depth of at least three meters. It is desirable to have depressions up to 5-6 meters. The water temperature is pleasant for crayfish from 16 to 22 degrees. They are nocturnal, preferring to sleep during the day, huddled in snags, in depressions at the bottom of a reservoir, or simply in bottom debris.

Crayfish move in an unusual way - moving backwards. However, in case of danger, they can swim quite quickly, which is facilitated by the caudal fin.

Fertilization in crayfish is internal. It has developed sexual dimorphism. The first two pairs of abdominal legs of the male are modified into a copulatory organ. The first feather of the abdominal legs of the female is rudimentary. The remaining four pairs of abdominal legs bear eggs and young crustaceans.

The fertilized eggs laid by the female are attached to her abdominal legs. Crayfish lay eggs in winter. In the spring, young crustaceans hatch from the eggs. They hold on to their mother's abdominal legs. Young animals feed only on plant foods.

Once a year, adult crayfish molt. They shed the old cover and stay in the shelter for 8-12 days, without leaving it until the new one hardens. The body of the animal, at the same time, quickly increases.