Common features of crustaceans. The structure of crayfish: external and internal. Unusual types of crayfish
crustaceans - primary water animals, therefore, as respiratory organs, they have special outgrowths of the limbs - gills. Representatives of this class differ from all other arthropods by the presence on the head two pairs of antennae. The limbs of crustaceans often retain a primitive two-branched type of structure.
Crayfish. Let us consider the main morphophysiological features of this class using the example of a well-known representative - crayfish.
External structure and lifestyle. Crayfish lives in fresh waters: rivers, streams, lakes. The presence of crayfish in a pond indicates the purity of the water. Crayfish lead an active nocturnal lifestyle, and during the day they hide under stones, snags or in minks. Crayfish are omnivorous, they feed on both plants and animals, including their decaying remains. The size of an adult cancer reaches 20 cm or more.
Outside, the cancer is covered with a hard chitinous shell, which serves as a reliable defense against enemies. The dark greenish-brown color of the shell makes the crayfish invisible at the bottom. Like all crustaceans, the body of crayfish consists of the head, thoracic and abdominal sections. However, there are some peculiarities in its structure. The external structure and size of crustaceans can be very diverse. So, in some primitive forms, the segmentation of the departments is almost homonomous, and one part of the body imperceptibly passes into another. In more highly organized species, body parts are clearly differentiated. The head of a crayfish consists of a head lobe (acron), on which the first pair of antennae is located (antennas 1, or antennules, and 4 segments (Fig. 42).
Rice. 42. Limbs of female crayfish: 1 - antennula, 2 - antenna 11, 3 - limbs of the head, 4 - limbs of the chest, 5 - limbs of the abdomen
The limbs of the first segment are the second pair of antennae (antennas), much longer than the antennules. The antennae are mobile, serve for touch and smell. The remaining 3 segments of the head also bear modified 4 limbs: on the second segment - the upper jaws (mandibles), on the third and fourth - two pairs of lower jaws (maxill). The jaws surround the mouth opening and form the oral apparatus that grinds food and feeds it to the mouth.
The chest consists of 8 segments. The first 3 segments are equipped with paired mandibles, involved in grinding, sorting and transferring food particles to the oral apparatus. The next 5 segments are carried in pairs walking legs. Powerful claws on the first pair of walking legs serve to capture food, attack and defend. The cancer uses the remaining walking legs for movement.
The abdomen consists of six movably articulated flattened segments. The first two segments of the male abdomen are provided with sex legs, tube-shaped. With their help, the sperm is transferred to the female genital tract. In females, these legs are rudimentary. On the following segments are small two-branched swimming legs. On the last, sixth segment of the abdomen, the swimming legs are greatly enlarged and, together with a wide anal lobe, form tail fin.
It should be noted that the crayfish head consists of two articulated sections: the protocephalon and the gnathocephalon. The protocephalon is formed by the fusion of the head lobe and the first head segment, while the gnathocephalon is formed by the fusion of the three subsequent head segments that bear the jaws. Moreover, the gnatocephalon fuses with the thoracic region, forming the so-called jaw-thorax (gnathothorax), covered from above and from the sides with a strong solid shell - caropax. Thus, the body of crayfish is divided into the following sections: head - progocephalon (acron and one segment), jaw-thorax - gnathothorax (three head and eight thoracic segments) and abdomen (six segments and anal lobe). Quite often in textbooks they talk about the division of the cancer body into the cephalothorax and abdomen. As you can see, this is not entirely correct, because the cephalic lobe and the first segment of the cephalic region do not fuse with the underlying segments.
In a calm state, the crayfish moves along the bottom on walking legs head first. At the moment of danger, the cancer, having straightened the caudal fin, sharply and often bends the abdomen and swiftly swims backwards in jerks.
COVERS. In primitive crustaceans, the integuments are relatively thin and are formed by cuticle plates that cover the body from all sides. However, in crayfish and other highly organized forms, the outer integument thickens and forms a hard shell. The outer layer of the cuticle is impregnated with salts, which significantly increases the strength of the integument.
The shell reliably protects the body of the animal, but does not allow it to grow. Therefore, the growth and development of crayfish occur during periodic molts. Young crayfish grow rapidly and therefore molt several times a year, adult crayfish molt much less often - once a year. After shedding the old cuticle, the new cuticle remains soft and easily stretchable for a while. At this point, crayfish become vulnerable to enemies and hide in shelters. Then the cuticle hardens, becomes saturated with lime, and the growth of the animal stops until the next molt.
Digestive system. The digestive system begins with a mouth opening covered with outgrowths of the cuticle - the upper and lower lip. The anterior intestine includes a short esophagus and stomach (Fig. 43). The stomach of cancer consists of two sections: chewing And filtering (nuloric). The inner walls of the chewing section bear powerful chitinous plates, with the help of which the food is finely ground. There are also white rounded calcareous thickenings - millstones. They accumulate calcium carbonate, which is necessary for cancer to impregnate the cuticle after molting. In the filtering part of the stomach, thin outgrowths of the cuticle form a sieve through which only highly crushed food is filtered. From the stomach, food is sent to the short midgut. In most crustaceans, the midgut has lateral glandular outgrowths, not quite correctly called liver. In crayfish, the liver is formed by two independent lobes (right and left), the ducts of which flow into the middle intestine. The liver produces digestive enzymes that enter the chewing stomach. It also undergoes abdominal and intracellular digestion and absorption of nutrients from the midgut.
Rice. 43. The internal structure of crayfish (female):
1 - antennas II, 2 - antennas 1 (antennales), 3 - eye, 4 - stomach, 5 - digestive gland, 6 - arteries, 7 - ovary, 8 - heart, 9 - abdominal nerve chain, 10 - hindgut, 11 - gills
Since the liver of crustaceans combines the functions of the liver and pancreas, zoologists prefer to call this organ simply the digestive gland. Since the liver partly performs the functions of the midgut, in the class of crustaceans there is an inverse relationship between the development of the midgut and the liver. For example, daphnia have a small liver and a long midgut, and in crayfish, the midgut is a short tube, the length of which is 10 times less than the hindgut.
Undigested food remains enter the long rectum, which passes through the abdomen and opens with an opening in the anal lobe.
The foregut and hindgut, which are of ectodermal origin, are lined with a cuticle that exfoliates during molting and emerges in the form of tubules. Therefore, during molting, crayfish do not feed.
Breath. The crayfish breathes with gills (see Fig. 43). They are located under the carapace in the gill chambers and are reliably protected from damage. Fresh water constantly enters the chambers due to the flow of water created by the extremities. The gills are delicate, numerous filiform outgrowths of the limbs of the chest, covered with a thin cuticle, into which the body cavity enters. Through the thin covers of the gills, gas exchange occurs. The hemolymph, passing through the gill filaments, is saturated with oxygen and releases carbon dioxide.
Many small crustaceans, which have a thin cuticle, are devoid of gills and breathe through the entire surface of the body. Land crustaceans have special respiratory organs. So, woodlice on the abdominal legs have deep branching protrusions of the integuments, resembling tracheas, in which gas exchange occurs.
Circulatory system. Circulatory system open. The heart of cancer is located on the dorsal side of the chest and is a pulsating pentagonal muscle pouch with three pairs of holes (ostium)(see fig. 43). With the contraction of the heart, the hemolymph is pushed into the branching arteries and spreads throughout the body. From the blood vessels, it pours into the body cavity, washes the internal organs, gradually gives off oxygen and goes to the gills. After saturation with oxygen in the gills, the hemolymph enters the pericardium and from it - through the ostia into the heart.
excretory system. Excretory organs of crayfish - green glands, so named for their color. They are located in front of the jawbone. Inner part the gland, which looks like a small sac, is a remnant of the coelom and opens into the body cavity. It is followed by a thin convoluted tubule, consisting of several departments, the last of which expands into bladder. A short canal departs from the bladder, which opens outwards with an excretory opening at the base of the second pair of antennae.
Nervous system. The nervous system of cancer consists of a well-developed brain connected by a peripharyngeal nerve ring to the ventral nerve cord (see Fig. 43). From the brain, nerves run to the eyes and sensory antennae. From the peripharyngeal ring - to the oral apparatus, and from the nodes of the abdominal nerve chain to the rest of the limbs and internal organs of the body.
sense organs. The sense organs are well developed. On the head antennae are the organs of touch and chemical sense. At the base of the first pair of antennae are the organs of balance - statocysts.
The balance organs of the crayfish are located at the base of the antennules and are open saccular protrusions of the integument that communicate with environment. The bottom of the statocysts is lined with a thin cuticle with sensitive hairs. The grains of sand that enter the statocyst through its outer opening act as statoliths. When the position of the cancer body in space changes, the statoliths irritate the hairs, and the corresponding nerve impulses enter the brain. During molting, the cuticular lining of the statocyst is also shed, so during this period the crayfish loses coordination of movements.
Complex faceted the eyes consist of numerous simple eyes, each of which functions individually and perceives the image of only part of the surrounding space. As a result, the overall visual perception is made up of individual fragments. This vision is called mosaic. The eyes of cancer are mobile, they sit on special outgrowths - eye stalks.
Reproduction and development. Crayfish are dioecious, with pronounced sexual dimorphism. In females, unlike males, the abdomen is wider than the thoracic segments. The first pair of abdominal limbs of the male is turned into a copulatory organ; in females, the legs are rudimentary. In the jaw of the chest are unpaired sex glands with paired genital ducts, opening genital openings at the bases of the third (in females) and fifth (in males) pairs of thoracic walking legs. In late autumn or winter, mating occurs, during which the males, using the first pair of abdominal legs, glue packets of sperm near the genital openings of the females. After that, the females lay eggs, which are glued to the abdominal legs. In this case, the abdomen is pressed against the cephalothorax, forming a brood chamber. Inside the chamber, fertilization and development of eggs takes place. In the spring, small racata hatch from the eggs, which remain on the mother's abdomen for some time. Then the rachata leave the female and move on to an independent life.
In crustaceans, the shape and size of male gametes are very diverse. In many species, the gametes are very large and completely immobile. For example, some small shell crustaceans, whose length is less than 1 mm, have the longest sperm cells among all animals - they are an order of magnitude longer than the crustacean itself and reach 6 mm! Recall that male gametes that do not have organelles of movement are called spermatozoa. It is the same in botany: mobile gametes of spore plants are called spermatozoa, and immobile gametes seed plants- sperm.
Rice. 44. Commercial crustaceans: A- king crab; B- lobster; IN- spiny lobster
The value and diversity of crustaceans. Crustaceans are found in almost all water bodies. Their numbers and biomass are very high, so crustaceans play an important role in aquatic ecosystems.
The plankton of fresh and marine water bodies is inhabited by many small crustaceans that feed on unicellular algae. In turn, they serve as food for larger animals - from fish fry to whales. Thus, small crustaceans (cladocerans and copepods, shrimps, etc.) are an important link in the food chain of any aquatic community.
Among the crustaceans there are many valuable commercial objects that people eat: shrimps, lobsters, lobsters, Kamchatka and other crabs (Fig. 44). The fishery of crustaceans is widely developed and reaches 700 thousand tons per year in the world. Freshwater crayfish are not only caught in nature, but also successfully bred on specially created farms. Small crustaceans (eg daphnia) are grown in fish hatcheries as food for fish.
Crayfish lives in various fresh water bodies with clean water: river backwaters, lakes, large ponds. During the day, crayfish hide under stones, snags, roots of coastal trees, in minks dug by themselves in the soft bottom. In search of food, they leave their shelters mainly at night. It feeds mainly on plant foods, as well as dead and living animals.
External structure
Crayfish has a greenish-brown color. The body is made up of different segments. Together they form three distinct body parts: head, thorax and abdomen. In this case, only segments of the abdomen remain movably articulated. The first two sections are fused into a single cephalothorax. The division of the body into sections arose in connection with the division of the functions of the limbs. The movement of the limbs is provided by powerful striated muscles. Muscle fibers of the same type are found in vertebrates. The cephalothorax is covered on top with a solid strong chitinous shield, which carries a sharp spike in front, on its sides in recesses on movable stalks there are eyes, a pair of short and a pair of long thin antennae.
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 biramous jointed legs; the sixth pair of limbs - wide, lamellar, are part of the caudal fin (they, together with the caudal lobe, play an important role when swimming backwards).
Internal structure
Digestive system
The 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 there are 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 ground food passes. Large food particles are retained and returned to the first section, while small ones enter the intestine.
Under the action of secreted enzymes, food is digested and absorbed through the walls of the middle intestine and gland (it is called the liver, but its secret breaks down not only fats, but also proteins and carbohydrates). Undigested residues enter the hindgut and are excreted through the anus on the caudal lobe.
Circulatory system
In cancer, the body cavity is mixed; it is not blood that circulates in the vessels and intercellular cavities, but a colorless or greenish liquid - hemolymph. It performs the same functions as blood in animals with a closed circulatory system.
On the dorsal side of the cephalothorax under the shield is a pentagonal heart, from which blood vessels. Vessels open into the body cavity, the blood gives oxygen there and nutrients tissues and organs, but takes away waste products and carbon dioxide. Then the hemolymph enters the gills through the vessels, and from there to the heart.
Respiratory system
The respiratory organs of cancer are the gills. They contain blood capillaries and gas exchange takes place. The gills look like thin feathery outgrowths and are located on the processes of the mandibles 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 the rapid vibrations of special processes of the second pair of lower jaws), and up to 200 waving movements are performed in 1 minute.) Gas exchange occurs through a thin membrane of the gills. Oxygen-enriched blood is sent through the gill-heart valves to the pericardial sac, from there it enters the heart cavity through special openings.
Nervous system
The nervous system consists of a paired supraoesophageal ganglion (brain), suboesophageal ganglion, ventral nerve cord, and nerves extending from the central nervous system.
From the brain, nerves go to the antennae and eyes. From the first node of the abdominal nerve chain (subpharyngeal node) - to the oral organs, from the following thoracic and abdominal nodes of the chain - respectively to the thoracic and abdominal limbs and internal organs.
sense organs
On both pairs of antennae there are receptors: tactile, chemical sense, balance. Each eye contains more than 3,000 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 organs of balance are a depression in the main segment of the short antennae, where a grain of sand is placed. A grain of sand presses on the thin, sensitive hairs surrounding it, which helps the cancer to assess the position of its body in space.
excretory system
The excretory organs are represented by a pair of green glands located in the anterior part of the cephalothorax (at the base of the long antennae and open outwards). Each gland consists of two sections - the gland itself and the bladder.
In the bladder, harmful waste products formed during the metabolic process accumulate and are excreted through the excretory canal through the excretory pore. The excretory gland in its origin is nothing but a modified metanephridium. It begins with a small coelomic sac (in general, harmful metabolic products come from all organs of the body), from which a tortuous tube extends - the glandular canal.
Reproduction. Development
Crayfish have developed sexual dimorphism. Fertilization is internal. In the male, the first and second pair of abdominal legs are modified into a copulatory organ. In the female, the first pair of ventral legs is rudimentary; on the remaining four pairs of ventral legs, she bears eggs and young crustaceans.
Fertilized eggs laid by the female (60-200 pieces) are attached to her ventral legs. Egg laying occurs in winter, and young crustaceans (similar to adults) appear in spring. Having hatched from eggs, they continue to hold on to the mother's abdominal legs, and then leave her and begin an independent life. Young crustaceans eat only plant foods.
Moult
Adult crayfish molt once a year. Having thrown off the old cover, they do not leave shelters for 8-12 days and wait until the new one hardens. During this period, the body of the animal increases rapidly.
The crustacean class is mainly aquatic animals that inhabit the seas and fresh water bodies. Their body is divided into cephalothorax and abdomen. They have two pairs of antennae, compound or compound eyes. They breathe with gills. The total number of known species is 20,000.
Typical representative - crayfish. Lives in fresh running waters. During the day it hides under rocks or in burrows dug on the bottom, or under tree roots.
At night, they crawl out of their hiding places in search of food. River crayfish are omnivores. The cephalothorax of 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 spike. At its base are two compound eyes located on stalks, so that the cancer can turn them in different directions. Compound eyes consist of many small eyes - up to 3,000 and are called faceted. The cephalothorax 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 mouth organs, which are modified limbs. The first pair forms the upper, and the second and third - the lower jaws, the remaining three pairs - mandibles. There are five pairs of jointed walking legs on the cephalothorax. Of these, the front pair of limbs has the strongest organ of attack and defense - claw. The claw also performs the role of capturing food. The jointed abdomen bears abdominal legs on which the females hatch eggs.
Cancers are omnivores. Food crushed by the mouth organs through the pharynx and esophagus enters the stomach, which consists of two sections - chewing And filtering. Chitinous teeth are located on the inner walls of the chewing section, with the help of which food is ground. In the filter section, it is filtered and enters the intestine, and then into the digestive gland, where it is digested and absorbed nutrients.
Respiratory organs of cancer - gills located on the sides of the cephalothorax. Oxygen enters 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 supraglottic and subpharyngeal ganglions, forming a peripharyngeal ring, and an abdominal nerve chain.
cancer excretory organs pair of green glands located in the head of the body. Their excretory canals open outward at the base of the antennae. Through the green glands, harmful metabolic products dissolved in the blood are removed from the cancer body.
Cancers are dioecious. In winter, the female lays eggs, gluing each 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.
Several orders belong to the class of crustaceans. Among them: decapods, isopods, cladocerans, copepods, karpoedy.
Order of decapods. This includes the above crayfish, and planktonic shrimp species, sea crayfish large sizes - lobster, lobsters, various crabs. All of them are valuable food objects and are used as food for preparing all kinds of gourmet dishes. This group includes Cancer hermit leading a peculiar way of life. Young crustaceans find gastropods with shells of the appropriate size, 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 size, and everything repeats from the beginning.
Detachment isopods. This includes both aquatic and terrestrial crustaceans, the abdominal and thoracic limbs of which are not much different, such as, for example, in woodlice. This small size(up to 10-15 mm) gray or whitish animals that live in wet places, in leaf litter, some are found even in deserts.
Order cladocerans, whose representative is daphnia. For the way it moves by jumping, it is popularly called the "water flea".
Detachment copepods to which it refers 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 general, about 50,000 species belong to crustaceans.
To study the classification of the type Arthropods. Learn aromorphoses of the type Arthropods. Everything should be written down in a notebook.
To study the organization of Arthropods of the Crustacea class using the example of River Crayfish. Complete the outline in your notebook.
Consider wet preparations different types crustaceans - Crab, Shrimp, Woodlice, Shchitnya, Crayfish, Amphipod, Daphnia. Under a microscope, consider the appearance of the Cyclops.
To study the external and internal structure of River Cancer (opening of cancer). Especially pay attention to the variety of limbs - they have 19 pairs of crayfish.
In the album, complete 2 drawings marked 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 Arthropoda. Type classification Arthropods. Aromorphoses of the Arthropod type.
Features of the organization of arthropods of the class Crustaceans.
Systematic position, lifestyle, body structure, reproduction, significance in nature and for humans Cancer river.
Type Arthropods- Arthropoda
Arthropods are a type of invertebrate animal. In terms of the number of species, they rank first on Earth - there are more than 1.5 million of them. This is more than in all other types of animals combined. The habitats of arthropods are diverse: soil, fresh and sea water, air, earth's surface, plant and animal organisms, including the human body. Arthropods are found all over 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 feature of the type.
The type is divided into 4 subtypes:
Subtype 1. trilobites(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(Branciata). In subtype one Class Crustaceans(30 - 35 thousand century). They are aquatic arthropods that breathe with gills.
Subtype 3. Cheliceric(Chelicerata). In subtype 2 class: Class merostomy(the so-called crustacean scorpions - now extinct aquatic chelicerae) and Class arachnids(about 60 thousand century).
Subtype 4. Tracheal(Traceata). Two classes: Class Centipedes(over 53 thousand w.) and Class Insects(more than 1 million in.)
Type Animals arthropods have the following aromorphoses: 1. dense waterproof and airtight covers. 2. Jointed limbs for different purposes and different structures. In the course of evolution, the jointed limb of the Arthropoda originated from the parapodia of the Polychaete Annelids. 3. Heteronomic segmentation. 4. Subdivision of the body into sections: head + chest + abdomen, or cephalothorax + abdomen.
Class Crustacea - Crustacea Crayfish
Crustaceans, there are 30 - 35 thousand species of gill-breathing arthropods that lead an aquatic lifestyle. Only some species, for example, Woodlice and land crabs have adapted to live on land, but they also adhere 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 oldest group among living arthropods.
So, the distinguishing features of the class is breathing with the help of gill. Small crustaceans have no 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 characteristic of crustaceans is biramous limbs.
More structural features of animals of the class Crustaceans should be considered on the example Cancer river - Astacus astacus(type Arthropods, subtype Gillbreathers, class Crustacea, 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. River crayfish are found in rivers, lakes with a muddy bottom and steep banks. Cancers cannot stand any water pollution, they live only in clean water. During the day, crayfish hide in holes dug by them in the banks under water (burrows are deep up to 35 cm long). At nightfall, the crayfish come out to get their own food. Crayfish are polyphages, i.e. they feed on a wide variety of food: bottom sediments, algae, carrion, thus being the orderlies of reservoirs. In winter, they do not change their place of residence, but simply sink much deeper, to where the water does not freeze. From late autumn to early spring, crayfish lead an inactive lifestyle, sitting in shelters for 20 hours a day. The life of females during this period is 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 full development of eggs, 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 the crayfish hibernate.)
External building. The body of crustaceans is segmented, and the segments of the body are not the same in shape and function - this is the so-called heteronomous segmentation. The body is made up of two sections: cephalothorax And abdomen. The head of the cephalothorax bears five steam limbs. On its head blade there are short antennae - antennules(organs of smell). The first segment has long antennae - antennas(organs of touch). For the other three - pair top jaws And two couples lower jaws. The upper jaws of crayfish are called mandibles, and a pair of lower jaws - maxilli. The jaws surround the mouth. With its jaws, the crayfish tears its prey into small pieces and pushes them into its mouth.
Even at the anterior end of the cephalothorax in cancer are spherical eyes that sit on long stalks. Therefore, cancer can simultaneously look in different directions.
The composition of the thoracic part of the cephalothorax includes eight segments: the first three carry mandibles involved in maintaining and grinding food. The jaws are followed five pairs of walking 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 clawed limbs, the first pair bears especially powerful and large claws. With claws, the crayfish grabs and holds prey, defends itself when attacked. Biramous mandibles 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 biramous limb performs the function of gills.
The segmented mobile 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 in copulative organ involved in the mating process. In the female, the first pair of limbs is greatly shortened, to the rest
Class Crustaceans Crayfish
eggs and juveniles are attached to four pairs. The abdomen ends tail fin, formed by the sixth pair of wide biramous lamellar limbs and an anal flattened lobe - telson. Sharply bending the abdomen, the Crayfish pushes against the water with its caudal fin, like an oar, and in case of danger it can quickly swim backwards.
Thus, the crayfish body begins with a cephalic lobe followed by 18 segments and ends with an anal lobe. Four head and eight trunk segments have fused to form a cephalothorax, followed by six abdominal segments. Thus in the crayfish 19 pairs of limbs different structures and purposes.
Body covers. The body of crustaceans is covered with chitinous 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 integuments of the cancer become hard and strong, which is why the cuticle is also called shell. The inner layer consists of soft and elastic chitin.
In live crayfish, the shell has a rather variable color - from light green to almost black. This coloration has a protective character: as a rule, it matches the color of the muddy bottom on which the crayfish lives. The color of crayfish depends on several coloring substances contained in the integument - pigments: red, blue, green, brown, etc. If you throw 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 hinders the growth of the animal, and therefore periodically all Crustaceans (and other arthropods) have to molt. Moult this is a periodic reset 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 this process takes a week and a half for river Cancer), Cancer is very vulnerable, therefore, during the molting period, Cancers hide, do not hunt and do not eat. Before molting, a pair of so-called lenticular "millstones" of calcium carbonate appears in the stomach of the crayfish, this reserve allows the crayfish integument to harden faster, the "millstones" disappear after molting.
Sometimes molting is very difficult for cancer: he, not being able to free his claw or walking leg from the old cuticle, cuts it off. But the injured limb is capable of regeneration, that's why crayfish come across, in which one claw is smaller than the other. Sometimes cancer, when it is in danger, with the help of its muscular effort, specially breaks off its claw: it sacrifices a limb in order 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 by 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, middle 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 food slurry is filtered, compacted and enters further into the middle intestine. A duct opens into the midgut digestive glands, which performs the functions of both the liver and pancreas. Here, in the midgut, the liquid food slurry is digested. Long rear intestine ends anal hole on the anal lobe.
Respiratory system Cancer River presents gills- branched thin-walled outgrowths of the thoracic limbs of the mandibles and walking legs. The gills are the upper branch of the biramous limbs. The gills are tender, look like branched bushes. The gills are located on the sides of the chest in gill cavities covered by the cephalothorax. Small crustaceans have no gills and respiration is carried out by 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 looks like a pentagonal bag. From vessels hemolymph(this is the fluid that fills the circulatory system) pours into the body cavity, seeps between the organs and enters the gills. Gas exchange takes place in the gills. Oxidized hemolymph enters pericardial bag and through special holes (there are three pairs of them) returns to the heart again. Crustacean hemolymph may be colorless, reddish from the hemoglobin pigment it contains, and bluish from the hemocyanin pigment.
excretory system represented by a couple green glands(peculiar kidneys). Each green gland has three parts: terminal bag(section of the coelom) extending from it tortuous channel with iron walls urinary bubble. In the terminal sac, there is an active absorption of metabolic products from the hemolymph. Metabolic products through the convoluted tubule enter the bladder. The bladders open outwards at the base of the antennae. excretory pores(i.e. open somewhere between the eyes!).
Nervous system. Nervous system in crustaceans staircase type(as in annelids). The nervous system is made up of couples supraesophageal nervous nodes often referred to as 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 smell, and long antennas- on touch. In general, all antennae and all limbs are dotted 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 the normal position of the body, these grains of sand press on the lower sensitive hairs below them; if in a floating crayfish the body turns upside down, the grains of sand move and press already on
Class Crustaceans Crayfish
other sensitive hairs and then the cancer feels that its body has left its normal position and is turning over. When the cancer molts, grains of sand are also shed. Then the cancer itself deliberately thrusts new grains of sand into its organ of balance with its claws.
The eyes of River Cancer are complex, faceted. Each eye consists of many small eyes, the Crayfish has more than three thousand of them. Each eye perceives only a part of the object, and the total picture is formed from their sum. This so-called mosaic vision.
Reproduction and development. Cancers in general separate sexes. Crayfish has a pronounced sexual dimorphism- the male has a narrower abdomen, while the female has a wider one. In the male, the first pair of abdominal limbs has been transformed into copulative bodies. In Crayfish, the sex glands are not paired, 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 departs from the testis, which open with 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 takes place in autumn. Somewhere at the end of autumn, females lay fertilized eggs on their abdominal limbs (there are not many eggs: 60 - 150, rarely up to 300). And only at the beginning of summer, rachata emerge from the eggs, which for a long time are under the protection of the female, hiding on her abdomen from the underside. Young crayfish grow intensively and molt several times a year, adults molt only once a year. Crayfish live for 25 years.
Meaning. Crustaceans are of great importance in nature and human activities. 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, Diaptomuses, amphipods- excellent food for freshwater fish and their larvae.
Many small crustaceans feed by filtration, i.e. filter detritus suspended in water. Thanks to their food 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, crayfish river. Medium-sized marine crustaceans are used by humans to make a nutritious protein paste.
Class Crustaceans Crayfish
Rice. The external structure of River Cancer (female).
Questions for self-control
Name the classification of the phylum Arthropoda.
What is the systematic position of Cancer river?
Where do crayfish live?
What body shape do crayfish have?
What is the body of River Cancer covered with?
What body cavity is typical for River Cancer?
What is the structure of the digestive cancer of the river?
What is the structure of the circulatory system of Cancer river?
How does crayfish breathe?
What is the structure of the excretory system of River Cancer?
What structure does nervous system River cancer?
What is the structure of the reproductive system of River Cancer?
How does river cancer reproduce?
What is the significance of River Cancer?
What is the significance of crustaceans in general?
Class Crustaceans Crayfish
Rice. Opened Cancer river (female).
1 - eye; 2 - stomach; 3 - liver; 4 - upper artery of the abdomen; 5 - heart; 6 - anterior arteries; 7 - gills; 8 - ovary; 9 - abdominal nerve chain; 10 - abdominal muscles; 11 - antennas; 12 - antennas; 13 - hindgut; 14 - muscles of the mandibles.
Class Crustaceans Crayfish
Rice. The internal structure of Cancer river. Digestive, nervous and reproductive systems (male).
Rice. The internal structure of Cancer river. Circulatory, respiratory and excretory systems.
Class Crustaceans Crayfish
Rice. The male reproductive system of River Cancer: 1 - the paired part of the testis, 2 - the unpaired part of the testis, 3 - the vas deferens, 4 - the vas deferens, 5 - the genital opening, 6 - the base of the fifth pair of walking legs.
Rice. Antennal gland (green gland) River cancer (in a straightened form).
1 - coelomic pouch; 2 - "green channel"; 3 - intermediate channel; 4 - "white channel"; 5 - bladder; 6 - excretory duct; 7 - external opening of the gland.
PICTURES TO BE COMPLETED IN THE ALBUM
