How many legs does a crayfish have and which ones does it use to walk?

Anyone who doesn’t like boiled crayfish simply hasn’t tried them! But even connoisseurs of such a delicacy cannot immediately answer how many pairs of walking legs a crayfish has. After all, the fact is that he does not use all of his limbs specifically for movement.

To understand this issue, you should carefully consider its entire appearance.

Hexapods

Most insects, with all the variety of habits and sizes, have the same characteristics. So, in this case, to the question of how many legs insects have, the correct answer is “Six.” Three pairs of limbs are observed in ants and fleas, mantises and weevils, and in more than a billion species. True, the paws differ in structure, and in connection with this, oddly enough, in purpose. “How is it possible,” you will be surprised, “are the legs really intended not only for moving the body along the surface?” It turns out that this is true. Habitual concepts are undergoing significant changes; you just have to pay attention to the small (in size) inhabitants of the planet. They, as scientists say, mastered the earth long before mammals, have a serious organization that allows them to exist excellently and not pay attention to the “king of nature.”

What are the legs of insects?

The purpose of the limbs determines their name.

to this, when you are asked: “How many legs do insects have?”, feel free to answer with the question: “Which ones?” And they are adjectives, running, digging and others. Usually only one pair of limbs is special. This is due to the lifestyle of a particular creature. For example, the front pair of the praying mantis is grasping. The locust or grasshopper is distinguished from its relatives by a pair of jumping limbs. They are immediately noticeable by their length and thickness. Cockroaches have running legs that are elongated. Digging limbs are observed in mole crickets. They are short and plump, strong. They usually dig with their front paws. Water lovers are the owners of swimming limbs. They are comfortable to row due to the hairs and flattened shins. How many walking legs do insects have in this case? The answer depends on the species. Unspecialized limbs are used for movement. They can be considered walking.

The most important information

In general, even those processes that help him obtain clean water for breathing can be called legs in a crayfish; they are very similar in appearance to the rest of his limbs. But from the name of the order, it is immediately clear that crayfish have 5 pairs of legs, but only in river representatives, not all of them are used exclusively for movement. So how many walking legs does cancer have? In fact, there are only 8, that is, 4 pairs. This is due to the fact that the front claws of the animal have undergone great changes during evolution and are now used only for protection or capturing food, without taking part in movement at all.

How many legs does a crayfish have and which ones does it use for walking on News4Auto.ru.

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Limb structure

Despite the variety of types, all legs are created almost identically. They consist of five departments. The magnifying glass is attached to the chest by a basin. Then comes the vetluga, thigh, and shin. The leg ends with a paw. Such a complex structure ensures the speed and maneuverability of the insect. Any limb ends in a claw. Specialized legs may be underdeveloped - then they lack some elements. Regardless of the degree of development, the number of legs in insects includes all limbs. The structure of the legs is not limited to the described elements. Each of them is divided into subsections and has options. So, for example, the foot can consist of several (up to five) segments. Such difficulties lead to the fact that sometimes only scientists can reliably tell how many legs insects have. Below is an interesting example.

External structure

Precisely due to the fact that the outer shell of the crayfish is a shell, and its legs are divided into segments, the animal is classified as an arthropod. Distinctive features are also the cephalothorax and movable abdomen combined into one whole. The body of the crayfish is hard, so it can grow only for a few hours after molting, until the integument hardens again. That is why in the first years of life the animal has to shed almost every 2 months.

On the head of the crayfish there are compound eyes, antennae and antennules. The latter serve as olfactory receptors and balance organs (after molting, crayfish lose coordination for some time), and the antennae serve as tactile receptors. Interestingly, in times of danger, cancer can hide its protruding eyes in special recesses on its head.

Bee

Everyone knows this hard work. It flies, pollinates flowers, collects honey... How many pairs of legs does an insect have, and are all of its limbs like this? It turns out that the bee has special baskets on its forelimbs into which it places pollen. On the very last segment, the tarsus, there are fibers called brushes. With them the bee collects a valuable product. If you look closely, it turns out that the front pair are almost arms with a very complex structure. But scientists do not recognize this fact. These limbs belong to the legs and are called collective limbs. Let's count the number of walking legs in bee insects. If two legs are devoted to collecting operations, then the insect moves with the rest. This means that she has two pairs of walking legs. This is basically how the calculation is done, but not for everyone.

Internal organs

So, how many pairs of legs does a crayfish have? The animal has as many as eleven (!) pairs of limbs, all of which are necessary for certain actions. So, the first 3 serve as jaws, another 3 act as jaws, and only the last 5 are necessary for crayfish to move.

It is interesting that the animal’s digestive system has three sections and 2 of them are covered with a chitinous layer, like the shell itself. That is, during molting, the cancer sheds not only the outer shell, but also part of the inner one.

The circulatory system is represented by several large vessels and the heart. The crayfish's breathing is provided by gills located under the cephalothoracic shell on the sides of the body. Clean water is constantly brought to them by the appendages of the second pair of jaws. The nervous system consists of clusters of nerve cells in nodes, from which the endings themselves disperse throughout the body.

Why gears?

While studying the number of legs in insects of different classes, their structure and functions, scientists came across an unexpected fact. Some of them have an interesting mechanism in their structure - a gear. Schematically, it can be represented in the form of two jagged wheels that are interlocked. Through the protrusions they interact and synchronize movement.

what is it? It turns out that this mechanism allows insects to jump at tremendous speed. This miracle lives in America, it is called Jesus. It is not capable of flight, but it makes amazing jumps. Even a speeding car will not be able to overtake it during takeoff. It is interesting that these legs are located not on the sides, but at the bottom of the insect. This makes his life problematic. If you do not push off synchronously, then the jump will not work. The insect simply circles on one leg. Evolution has eliminated this effect with a mechanical device whose purpose is to make the shocks synchronous. The scientists' surprise knew no bounds. This is the first recorded fact of the use of engineering in the structure of living beings.

Many people are confused about the types of invertebrates when answering the question of how many pairs of legs insects have. Spiders and centipedes of all kinds are mistakenly included among them, which is fundamentally incorrect. Later we will say a few words about them, but for now we will turn our attention to representatives of the Insect class.

Cicada

The world of insects also has its own record holders. Thus, the structure of the limbs of the penny cicada allows it to jump to incredible heights, given its small size. If we draw an analogy with a person, we get two hundred and ten meters. It is clear that this insect has a pair of jumping limbs, very strong and fast. They act like a catapult, powerfully sending the body upward. In this case, the acceleration reaches four thousand meters per second. And in order not to slide off the plants on which the insect feeds, its front legs are equipped with sharp spines.

Water bugs

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All aquatic insects are of interest from the point of view of the structure of their limbs. They demonstrate a completely different, but also unique adaptation. Science has asked how they can float on the surface of the water and not drown? It turned out that the water beetle has a kind of oar on its hind legs. Special hairs have grown on them, with which the insect makes rowing movements. This is how it floats on water. Some species are equipped with thickened and widened segments (this is the last section of the leg). Thanks to this structure, they can float perfectly on the water. Although these insects prefer to live in calm waters. It is difficult for them to fight against strong currents. The little creature does not have enough strength for this.

Dragonfly and others

Another amazing representative of the insect world. This flyer uses her limbs in a special way. Her legs are equipped with stiff bristles. When a dragonfly flies, it arranges its limbs in such a way that it forms a kind of net. With this device she gets her food! Small insects, caught in the interweaving of bristles, immediately become prey and are eaten by the dragonfly. The variety of ways and methods of using insect legs is truly enormous. They are not only designed for walking, like mammals. They are used to row, and cut, and grab. Insects also use their legs to clean their antennae. For this purpose, the limbs are equipped with special grooves. But some species of butterflies use their front legs exclusively for rubbing their eyes. These limbs are atrophied and equipped with special hairs.

What about centipedes and spiders?

Contrary to popular belief, and even to the name, the centipede has not forty legs, but only thirty. By the way, they appear in an extremely interesting way in an invertebrate. At the beginning of its existence, it has only eight legs (almost a spider). Then the centipede begins to grow, the body lengthens, and additional limbs gradually grow. It turns out that the question of the number of legs of a centipede is closely related to its life expectancy. And this creature treats its limbs very carelessly. As soon as it senses a threat, for example, a paw is stuck to the web, without thinking twice, they simply get rid of it. We can say that this is a kind of defense mechanism. Very convenient, isn't it? Especially considering that the centipede is capable of regenerating limbs.

Spider... Strange as it may sound, this representative of the animal world is not an insect. It has eight legs, not six, like insects, and the body consists of only two parts (the cephalothorax and the abdomen). In most cases, all spiders are predators, while insects mostly feed on vegetation.

Source: FB.ru

How many legs are there really?

If you take a magnifying glass and look closely, you will notice that the body of any insect, be it a bright grasshopper or a thick-bellied cockroach, consists of three parts. It is in these segments that the paws are located in pairs. Simple calculations will lead to the correct answer - two limbs multiplied by three - a total of six. By the way, the very, very ancient insects (when there was no human being yet) also had legs growing on their abdomen. Scientists discovered this interesting fact when they discovered small processes at the bottom of the body in modern representatives. Therefore, when asked about the number of paws, you can safely say the number - six. But that's not the most interesting thing . There are indeed six legs, but all are different.

ANSWER:

Most insect species are six-legged, that is, have 3 pairs of legs, but there are exceptions, for example, four-legged mites with 2 pairs of legs. How many pairs of insect legs are considered walking? This question cannot be given a definite answer, since the number of walking legs may vary from species to species. For example, the front pair of legs of a bee is used to collect pollen, therefore the remaining 2 pairs of legs are used for walking.

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Insect legs consist of several joints (segments), the movement of which is controlled by a combination of muscles and passive biomechanical non-muscular structures. Some insects also have clawed projections on the last segments of their legs.

The body of all insects has bilateral symmetry, and also consists of 3 main parts: head, thorax and abdomen. Insects begin life as eggs and undergo metamorphosis before becoming adults. Winged insects have either one pair of wings (such as a housefly or mosquito) or two pairs of wings (such as a bee or dragonfly).

Insects have three pairs of legs

And if we don’t talk in pairs, then there are only 6 legs. They can be of different lengths, or they can be the same.

Here, for example, is a grasshopper. Its two pairs of front legs are short, and its back pair is twice as long. There are six legs or paws in total.

And here is a picture showing various insects. As we see, they also have 3 pairs of legs.

the moderator chose this answer as the best

The class of insects is very numerous, but all insects have three pairs of legs , respectively, they have six legs . During the life of insects, their legs adapted in accordance with their lifestyle, so they differ in structure and types, they are: digging, for example in mole crickets, swimming in diving beetles, jumping in locusts.

Typically, insects have six legs (in the imago stage, that is, an adult). But some species of butterflies (this belongs to the genus Vanessa, to which the well-known urticaria and daytime peacock eye belong) have only four legs, since their front pair of legs is underdeveloped.

In different ways...anyone is lucky...we can probably say that all insects have an even number of these same legs - that’s how nature decreed it, although in some we can find three legs, but these are the consequences of birth injuries or life situations

Insects have six legs. Although they are all different, some are beautiful and cute, and some are unpleasant and ugly, they all have 6 legs. Their legs are arranged in pairs, each pair may differ from the other in size and structure.

The legs of insects are located on the thoracic region in pairs. There are three pairs or six of them in total . By the way, all the millipedes and centipedes there are not insects. So the correct answer is number SIX.

Insects have six legs, but spiders and ticks, which have eight legs, are arthropods

Our planet is, in fact, a planet of insects . There are more insects not only in numbers, but even in total weight. Moreover, insects are so different from people and animals that you might think that they are from another planet altogether. This may actually be the case.

But insects are still similar to each other. Insects have six legs arranged in pairs.

The class insects includes all tracheal-breathing arthropods that have 3 pairs of legs. They are divided into primary wingless and winged, and all have 6 legs. Animals whose number of legs does not match the number 6 do not belong to the class insects.

This is the mystery! I'll have to dig deeper into zoology questions - maybe there's a hint there? And the answer lay right on the surface: insects (pleasant to our eyes or, on the contrary, disgusting) have “SIX” legs - now I know about it.

There are about a million species of insects. This includes beetles, butterflies, cockroaches, flies, bees, dragonflies and many other types of insects. By structure, all insects have 3 pairs of legs or 6 legs.

Do you know the answer?

Such different legs

The world around was changing, and insects were reborn. Adapting to new environmental factors , arthropods, one might say, modified themselves and reshaped their own lifestyle. Therefore, everyone’s limbs are different - it all depends on the place and living conditions. Typically, arthropods have two pairs of legs - normal, and one - special, necessary for survival. So, what types of paws are there:

• Walking beetles are strong, not capable of developing high speed, and are necessary for leisurely movement (leaf beetle).
• Runners are simple in structure, long and light, in order to develop the maximum possible speed when moving (cockroaches, ground beetles).
• Swimming - hind, with small hairs that help to stay on the water and can contribute to shallow diving (smooth bug, water strider).
• Digging - the first pair, powerful, short, stocky and flattened (dung beetle, mole cricket).
• Collective - posterior pair with long sticky hairs that serve as a basket (bumblebee, bee).
• Grasping - sharp, equipped with spines, strong, used to hold prey (mantis).
• Suction - a rear pair with a slight expansion at the end, necessary to hold the female during mating (swimmer).
• Jumping - high, strong, necessary to make a push (grasshopper).

Insect legs are the most important, vital tool. With the help of their paws, they scrupulously clean their antenna horns, wipe their eyes (as butterflies do), protect themselves from enemies and attack unexpectedly. Now it’s worth looking at a few examples - what kind of legs there are, and how representatives of the arthropod class use them. Scroll below.

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How many legs does a cockroach have?

We all know what a cockroach looks like and, probably, almost everyone has encountered one.
The dark brown insect often hides in corners and dusty places, so making out the number of legs is not an easy task. However, there is an answer. The cockroach, like all insects, has three pairs of legs. During molting, a cockroach can lose one of its precious limbs, but this happens quite rarely, and after a certain period of time the leg grows back. Also, the cockroach (male) has wings on its back, but the insect never uses them. This can be considered a useless gift from ancient ancestors. The legs of a cockroach are walking (we have already described what this means above), and each pair of limbs has its own special name:

1. Prothoracic - the shortest pair, necessary for rapid braking during rapid movement.
2. Medium thoracic - a pair that can turn forward and backward, acting as accelerators and decelerators when moving.
3. Metathoracic - a pair that coordinates movement.

Also, the legs of a cockroach have sharp claws that allow it to crawl along walls, ceilings, cabinet doors, etc. For a cockroach, its limbs are even more important than its own head (without which, by the way, the insect can live for a month). In addition to movement, paws help wash, clean, jump and gain speed.

How many legs does a bee have?

The bee has 3 pairs of legs, but it also has powerful wings that can easily carry a hardworking worker in space. However, the bee does not have the simplest legs . The front pair belongs to the collecting limbs, which means that there are special baskets and brushes that collect pollen and prevent it from being lost forever. The bee, as if with its hands, collects the precious product and flies away into the hive. The remaining legs (that is, two pairs) of the bee are ordinary - walking.

What kind of legs does a dragonfly have?

The dragonfly, which everyone often hears rather than sees (after all, the insect flies so quickly and noisily that it can be difficult to notice), also has unusual legs. It would seem that strong, elongated wings, which provide the dragonfly with excellent speed, are all that the charming representative of the fauna needs. However, the legs of the insect are not simple - on the front pair of limbs there are peculiar coarse bristles. When flying, the dragonfly places its legs so deftly that the bristles form a trap net for sweet prey.

Tiny insects, caught in such a trap (a mesh of bristles), instantly become dinner for the dragonfly.

What's with the spiders?

Many people believe that spiders are insects. It crawls around harmlessly and doesn't bother anyone. What's the catch? The fact is that the spider belongs to the arachnid family; it is this fact that determines the presence of not six, but eight legs. And the body of this representative consists of only two parts (and not three, like in insects). Also, all spiders are predators that feed on other insects, luring them into cleverly woven webs. Arthropods, for the most part, are harmless herbivores.
From all of the above, it follows that considering a spider to be an insect is a gross mistake, and should not be made. Insects live everywhere and are close neighbors to humans. Most arthropods live on the ground, but there are also those that huddle in burrows, fruits and pools. Often we, succumbing to pictures in children's books, incorrectly imagine the structure of insects. Therefore, it is important to know what types of paws there are, and why they are still needed in such quantities. You can find out the conjugation of the verbs exception by following the link.

Leg structure

The limbs of insects consist of small segments - that is why these representatives of the animal world are called arthropods. It always seems to everyone that the legs of insects are just some kind of ridiculous sticks covered with hairs.

This is interesting: the structure and functions of cell organelles.

In fact, the complex structure of the foot can be reduced to several elements:

• The coxa is the first and main part of the limb. The shape depends on the type of insect (on how the arthropod moves)
• The trochanter is the connecting part between the elements.
• The thigh is the longest part.
• Knee – connects the thigh to the lower leg.
• Lower leg – slightly longer than the thigh, together they organize and regulate movement (speed, turns, etc.)
• The foot is small, with pointed claws.

This is interesting: human influence on nature, details of the negative impact.

Types of Insect Limbs

The most ancient are the running and walking legs of insects. The remaining types of limbs appeared in the process of long-term development, and, as a rule, are associated with various adaptations to environmental conditions.

• Running limbs

The running legs have an elongated shape. They are slender, and the tarsus, lower leg, thigh and coxa are narrow or wide. This type of limbs is present in cockroaches and ground beetles.

• walking legs

Walking legs are designed for slow movement. These are the legs of beetles - longhorned beetles, leaf beetles, crawling from leaf to leaf, leisurely gnawing leaves.

Insects need limbs to move around.

• Swimming limbs

The hind legs of insects usually become swimming, and less often the middle legs. They are covered with long hairs that form a wide rowing surface - a kind of oar. Basically, representatives with such limbs live in bodies of water and swim and dive excellently. These are swimming beetles, smooth bugs, and water lovers.

• Jumping legs

Representatives of the order Orthoptera have jumping legs. These include locusts, grasshoppers, and crickets. Their last pair of legs is very long and powerful. Many representatives of Orthoptera jump in heights of up to eighty centimeters, and if they spread their wings at the same time, the distance covered in one jump reaches about ten meters.

• Digging legs

Digging legs are characteristic of the mole cricket, dung beetle, and May beetle. Usually the first pair of legs become digging legs. The limbs of this type are powerful, flat and short.

The legs of grasshoppers give them the ability to move tens of meters in a matter of seconds.

• Collective limbs

The limbs of bees and bumblebees are called collective or basket limbs. On the hind legs of these insects there are special areas surrounded by long chitinous hairs; these are baskets. Bees move from flower to flower and get dirty in the pollen that sticks to the hairs of their bodies. With special brushes located on the legs, the bee collects flower pollen into baskets.

the adhesive dust particles form a lump called “polnoka”. The bee carries pollen into the hive and deposits it in the honeycomb. Bee bread soaked in nectar is formed; it serves as a reserve protein food for the entire bee family.

Thanks to the collecting type of legs, the bee can “save” pollen.

• Grasping legs

Grasping legs of a praying mantis. They are armed with sharp spines, which the predator uses to hold its prey.

• Suction limbs

The legs of males of some species of insects - swimming beetles and ground beetles - have expanded segments at the ends of the legs. During the breeding season, males use these devices to grasp females during mating.

Grasping legs help not only to hold prey, but also to the female during mating.

The manta ray is the only animal with three pairs of limbs

The giant sea devil, or manta ray, is the largest ray in the world's oceans. On average, the length of these stingrays is about three meters, the span of their fins is about four meters, and these giants weigh tons. The manta ray is also the only representative of vertebrate animals with three pairs of limbs.

The limbs of manta rays are represented by fins: head, pectoral and caudal. With the help of straightened head fins, whose length is twice as wide as their width, stingrays direct plankton into their mouth and suck it up. When moving, the head fins curl into spirals similar to horns. Moving their pectoral fins like a bird's wings, manta rays move through the water. The caudal fins practically do not take part in movement.

Surprisingly, these huge stingrays can jump, and how. Before the jump, the manta accelerates and jumps out of the water to a height of one and a half meters, falling back with a deafening noise. At the same time, the stingray flaps its pectoral fins. However, it is not known exactly why giant sea devils jump out of the water. Jumping does not help them in any way in obtaining food and is not related to mating games during the mating period. Perhaps in this way they are trying to throw off sea parasites, or they are drowning small fish in order to swallow them later.

Source

How else do insects use their limbs?

On the front legs of many insects, especially representatives of the order Hymenoptera and butterflies, there is an apparatus for cleaning antennae, spiracles and other parts of the body. It is a notch at the end of the tibia, equipped with a comb of hard bristles and spines on the first segment of the tarsus. With this device, insects tidy up their appearance.

Source: bioros.net

Crayfish. Crayfish organ system

Decapods are the most highly organized crustaceans. They live in marine and fresh water bodies; a small number of species have adapted to life on land.

The body consists of a protocephalon, gnathothorax (jaw thorax) and abdomen. The protocephalon and gnathothorax together form the cephalothorax. The protocephalon is formed by the fusion of the acron and the first cephalic segment. It contains antennae, antennules and a pair of stalked compound eyes. Gnathothorax is formed by the complete fusion of three segments of the head and eight segments of the chest. Gnathothorax bears three pairs of jaws, three pairs of maxillaries and five pairs of walking legs. The squad got its name from the number of walking legs. The abdomen consists of separate segments, and in many species it is reduced to one degree or another. There is a carapace that curves along the sides of the body, forming gill covers.

Development is direct or with transformation.

Many decapods are of commercial importance: lobsters, crabs, lobsters, shrimp, crayfish, etc.

Crayfish are a family of decapod crustaceans whose representatives live in fresh water bodies. The most common in the European part of Russia and of greatest commercial importance are two species: the broad-toed crayfish (Astacus astacus) and the narrow-toed crayfish (A. leptodactilus). The species are very similar in appearance and have the same biology. The narrow-clawed crayfish is more prolific and more resilient in relation to the chemical composition of water and its oxygen regime. These species are usually not found together. When narrow-clawed crayfish are artificially introduced into water bodies in which broad-clawed crayfish live, after 10–20 years the broad-clawed crayfish completely disappear.

The body of the crayfish consists of a head lobe (acron), eighteen segments (four cephalic, eight thoracic and six abdominal) and an anal lobe (telson). Like all decapods, crayfish have some segments that merge with each other. Thus, the following sections can be distinguished in the body of crayfish: protocephalon, gnathothorax and abdomen. The protocephalon together with the gnathothorax was previously called the cephalothorax. The protocephalon is formed as a result of the fusion of the acron and the first head segment, bears antennules, antennae and compound eyes. Olfactory receptors are concentrated on the antennules, and tactile receptors are concentrated on the antennae. Single-branched antennules extend from the acron (head lobe), double-branched antennae from the first head segment.

The gnathothorax (maxillary thorax) is formed as a result of the fusion of three head and eight thoracic segments, bears eleven pairs of limbs: three pairs of jaws, three pairs of maxillaries, five pairs of walking legs. Three pairs of jaws arise from the thoracic segments: one pair of upper jaws (mandibles) and two pairs of lower jaws (maxillae). Three pairs of two-branched jaws and five pairs of one-branched walking legs extend from the thoracic segments. The jaws are involved in maintaining and crushing food. Of the five pairs of walking limbs, the first three pairs have claws, the claws of the first pair are very large and serve for protection and for capturing food. The epipodites of all thoracic limbs have turned into skin gills; the thoracic limbs perform, among others, a respiratory function.

The articulated movable abdomen (abdomen) consists of six unfused segments, each of which bears a pair of two-branched limbs. In males, the first and second pairs of abdominal limbs are long, groove-shaped, and represent a copulatory organ. In the female, the first pair of abdominal limbs is greatly shortened; eggs and young are attached to the rest during the breeding season. The abdomen ends with a caudal fin formed by the sixth pair of wide lamellar abdominal limbs and a telson (anal flattened blade).

The integument is represented by a chitinous cuticle and a single-layer hypodermis. Chitin forms complexes with calcium carbonate and pigments. Calcium carbonate gives the shell rigidity and strength. Between the segments, segments of the legs and appendages, the cuticle is soft and elastic, since it is not impregnated with calcium carbonate. The carapace is the exoskeleton and the site of muscle attachment. The covers are periodically shed. Crayfish growth occurs in the first hours after molting before the new integument hardens.

The digestive system is divided into three sections - anterior, middle and posterior. The anterior section begins with the oral opening and has a chitinous lining. The short esophagus flows into the stomach, which is divided into two parts: chewing and filtering. In the chewing section, mechanical grinding of food occurs with the help of three large thickenings of the cuticle “teeth”, and in the filtering section, the food gruel is filtered, compacted and then enters the midgut (middle section). The ducts of the paired liver open into it. The long hindgut (posterior section) ends with the anus on the telson. The hindgut is lined with cuticle. During molting, not only the integument is shed, but also the chitinous lining of the anterior and posterior sections of the intestine.

The circulatory system consists of a heart in the form of a pentagonal sac located on the dorsal side of the maxillary thorax, and several large blood vessels extending from it - the anterior and posterior aorta. From them, hemolymph flows into the body cavity, and then through the venous sinuses enters the gills. The oxidized hemolymph enters the pericardium and through the ostia (three pairs) returns to the heart.

The gills are located on the sides of the chest in the gill cavities, covered by the cephalothorax carapace. The gills are constantly washed with fresh water. Water circulation in the gill cavity is ensured by the operation of “scoops”. “Scoopers” are appendages of the second pair of jaws and make 200 movements per minute.

Excretory organs – two antennal buds (Fig. 4).

The central nervous system is represented by paired suprapharyngeal ganglia, the peripharyngeal ring, subpharyngeal ganglia and the ventral nerve cord. The nodes and connectives of the abdominal chain are so close together that it does not have a double appearance, but a single one. Nerves extend from the ganglia to the internal organs, limbs, and sensory organs.

The crayfish's visual organs are a pair of compound eyes. The eyes sit on stalks and can turn in different directions. Tactile receptors are located mainly on the antennae, as well as on the surface of the antennules and other limbs. Olfactory receptors are located on the antennules. In addition, at the base of the antennules there are statocysts - organs of balance. The statocyst has the appearance of a deep open invagination of the integument. The inside of this invagination is lined with a thin cuticle with sensory cells. Statoliths are grains of sand that enter the statocyst from the environment through the external opening. During molting, the lining of the statocyst changes; during this period, the crayfish loses coordination of movements.

Crayfish are dioecious animals with pronounced sexual dimorphism: in the male, the first and second pairs of abdominal legs turn into copulatory organs, the abdomen is narrower than in females. Male genital openings are located at the base of the fifth pair of walking legs, female ones - at the base of the third pair of walking legs. At the end of winter, females lay fertilized eggs on their abdominal limbs. At the beginning of summer, young crustaceans emerge from the eggs and remain for a long time under the protection of the female, hiding on her abdomen on the underside. The crustaceans grow intensively, in the first year of life they molt 6 times, in the second year of life - 5 times; in subsequent years of life, females molt only once a year, males - 2 times.

The palm thief (Birgus latro) (Fig. 5) reaches a body length of 32 cm. It lives on the tropical islands of the Indian and western Pacific Oceans. As an adult, it lives on land, but reproduction and larval stages take place in seawater. The gills are reduced, the gill cavities under the carapace turn into a kind of “lungs”, allowing the palm thief to breathe atmospheric air. He owes his name to the ease with which he climbs coconut trees. Despite the strength of his claws, he could never knock down coconuts himself, much less split them. So the stories that the palm thief feeds exclusively on the pulp of coconuts are just a legend. It feeds on the remains of fish and shellfish that it finds on the shore.

Hermit crabs are a family of marine decapods (Paguridae) with an abdomen devoid of hard coverings. In many species of hermit crabs, asymmetry of the claws and abdomen occurs. To protect their soft, asymmetrical abdomen, these crayfish settle in the empty shells of gastropods. Hermit crabs with a symmetrical abdomen use straight shells of spadefoot mollusks for housing. Hermit crabs carry their shells with them and, when in danger, hide entirely in it. They often enter into symbiosis with sea anemones (Fig. 6), some species with sponges.

Source: licey.net

Types of crayfish

Crayfish are fairly common arthropods. They live in fresh water bodies and rivers . There are 4 types of crayfish:

1. Thick-fingered. Considered endangered. The number of individuals is now so small that it is on the verge of extinction. For a long time, thick-clawed crayfish were caught uncontrollably. This is why this species is now endangered. It lives in the Azov, Black and Caspian seas, in slightly salty water. Does not tolerate rapid increases in temperature. The body length is 8-10 cm. It has a brownish-green color. A characteristic feature is that it has a sharp notch located in the stationary part of the claw. It also only eats dismembered prey.
2. Broad-fingered. It lives in most clean and fresh water bodies, where the water warms up above +22 degrees Celsius in the summer months. The body length reaches 20 cm. The color is brown-blue or olive-brown. Moves quite quickly. This animal cannot be found in dirty water. In recent years it has been under protection, as the number of individuals has decreased significantly.
3. Narrow-toed. He likes slightly brackish and fresh water. It lives in certain areas of the Caspian and Black Seas, in places with slow currents. The body length reaches 18 cm. There are individuals measuring 30 cm in size. The carapace is brown. The two-branched limbs and abdominal region are highly elongated. Resistant to water pollution.
4. American signal. This species is distributed throughout Europe. Outwardly similar to a broad-fingered crayfish. A distinctive feature is a green or white spot on the claw joint. The body length is about 8 cm, but some individuals reach a size of 18 cm. The body color is brown. These crayfish tolerate plague well.

“American” was brought in when the population of European river arthropods declined significantly due to the “crayfish plague.” In Russia, it lives in only one region - the Kaliningrad region.