And) can reach 20 cm in length. Even larger sizes are some tarantula spiders.

Traditionally, there are two sections in the body of arachnids - asking  (cephalothorax) and opistosome  (abdomen). A millet consists of 6 segments bearing a pair of limbs: chelicera, pedipalps and four pairs of walking legs. Representatives of different orders have different structure, development and function of limbs. In particular, pedipalps can be used as sensitive appendages, serve to capture prey (), act as copulative organs (). In a number of representatives, one of the pairs of walking legs is not used for movement and assumes the functions of the organs of touch. The segments of the millet are tightly connected to each other, in some representatives their back walls (tergites) merge together to form a carapace. In merged tergites of segments, they form three guards: propeltidium, mesopeltidium, and metapeltidium.

An opistosome initially consists of 13 segments, the first seven of which can carry modified limbs: lungs, comb-like organs, spider warts or genital appendages. In many arachnids, the prosom segments merge with each other, up to the loss of external segmentation in most spiders and ticks.

  Integument

Arachnids carry a relatively thin chitinous cuticle, under which there is a hypodermis and a basement membrane. The cuticle protects the body from moisture loss during evaporation, so the arachnids have populated the most arid regions of the globe. Strength in the cuticle is given by proteins encrusting chitin.

  Respiratory system

The respiratory organs are the trachea (y, and some) or the so-called pulmonary bags (y and), sometimes both together (y); the lower arachnid isolated respiratory organs are not present; these organs open outwards on the lower side of the abdomen, less often the cephalothorax, with one or more pairs of respiratory openings (stigma).

Pulmonary bags are more primitive structures. It is believed that they occurred as a result of a modification of the abdominal extremities in the process of developing a land-based lifestyle by the ancestors of the arachnids, while the limb crept into the abdomen. The lung bag in modern arachnids is a recess in the body, its walls form numerous leaf-shaped plates with extensive lacunae filled with hemolymph. Through the thin walls of the plates, gas exchange occurs between the hemolymph and the air entering the lung bag through the openings of the spiracles located on the abdomen. Pulmonary respiration is present in scorpions (four pairs of pulmonary sacs), leg-footed (one or two pairs) and low-organized spiders (one pair).

False scorpions, hayfields, salpugs, and some ticks use the trachea as their respiratory organs, while most spiders (except the most primitive ones) also have lungs (one is preserved - the front pair) and trachea. Tracheas are thin branching (in hayfields) or non-branching (in false scorpions and ticks) tubules. They penetrate the body of the animal inside and open outwards with stigma holes on the first segments of the abdomen (in most forms) or on the I segment of the chest (in the salpuga). Tracheas are better adapted to air gas exchange than lungs.

In some small mites, specialized respiratory organs are absent, in them gas exchange is carried out, as in primitive invertebrates, across the entire surface of the body.

Nervous system and sensory organs

The arachnid nervous system is characterized by a variety of structures. The general plan for its organization corresponds to the abdominal nerve chain, but there are a number of features. There is no deutero-cerebrum in the brain, which is associated with the reduction of acrona appendages - antennules, which are innervated by this part of the brain in crustaceans, millipedes and insects. The anterior and posterior parts of the brain are preserved - protocerebrum (innervates the eyes) and trisocerebrum (innervates chelicera).

The ganglia of the abdominal nerve chain are often concentrated, forming a more or less pronounced ganglion mass. In hayfields and ticks, all the ganglia merge to form a ring around the esophagus, however, scorpions retain a pronounced abdominal chain of ganglia.

Sensory organs arachnids are developed differently. The most important for spiders is touch. Numerous tactile hairs - trichobotria - are scattered in large numbers on the surface of the body, especially on pedipalps and walking legs. Each hair is movably attached to the bottom of a special fossa in the integument and is connected to a group of sensitive cells that are located at its base. The hair perceives the slightest vibrations of the air or the web, sensitively reacting to what is happening, while the spider is able to distinguish the nature of the irritating factor by the intensity of the vibrations.

The organs of chemical sensation are lyre-shaped organs, which are gaps in the integument with a length of 50-160 microns, leading to a recess on the surface of the body where sensitive cells are located. Lyre-shaped organs are scattered throughout the body.

Organs of vision  arachnids are simple eyes, the number of which varies from 2 to 12 in different species. In spiders, they are located on the cephalothorax in the form of two arcs, while in scorpions one pair of eyes is located in front and several more pairs are located on the sides. Despite a significant number of eyes, arachnids have poor eyesight. In the best case, they are able to more or less clearly distinguish objects at a distance of no more than 30 cm, and most species are even smaller (for example, scorpions see only at a distance of a few cm). For some stray species (for example, horse spiders), vision is more important, because with it, the spider looks for prey and distinguishes individuals of the opposite sex.

The characteristic features of the structure of arachnids are due to adaptation to life on land. Their body most often consists of two departments - the cephalothorax and abdomen. Both departments are segmented in some species, and merged in others. The structure and distribution of the limbs is characteristic. The antennae are not developed. The front pair of cephalothorax is located in front of the mouth and is called chelicera. Usually these are powerful hooks that serve to capture and kill the prey. The second pair of limbs is the jaw, or pedipalpa. In some species, they serve as oral limbs, in others they serve as locomotor organs. There are always 4 pairs of walking legs on the chest of the cephalothorax. The abdomen often carries various paired appendages (arachnoid warts, organs of the external genital apparatus, etc.), considered as highly altered limbs. There are no real extremities on the abdomen, they are reduced.

E K O L O G I Y P A U K O O B R A Z N S X Arachnids are the first land animals that mastered land in the Silurian period and switched to air breathing. Lead a day or night lifestyle. They live in forests, meadows, pastures, desert sands. Some weave hunting nets, others attack prey. They feed on insects, but karakurt, scorpions and tarantulas inflict bites on humans, domestic animals (camels, horses), causing painful phenomena, sometimes fatal. Ticks are a particular danger - carriers of diseases from wild animals to humans and domestic animals (tularemia, plague, encephalitis). Scabies mites cause scabies in humans and mammals. For the fight against ticks, there are only chemical agents, biological ones are practically not developed.

In connection with the terrestrial way of life, arachnids developed respiratory organs. They are represented by either leafy lungs, or trachea, or a combination of lungs and trachea. The lungs in the amount of one or two pairs are located under the ventral covers of the abdomen. Each of them opens outward with a slit-like opening, and inside it is enclosed by plates in which blood circulates. Here it is saturated with oxygen and delivers it to tissues.

Tracheas are a system of branching air tubes. They begin with breathing holes, or spiracles leading to the main tracheal trunks. The latter branch and form increasingly smaller tubes through which air reaches the tissues. Thus, during tracheal breathing, oxygen is delivered to the tissues, bypassing the circulatory system. The circulatory system is better developed in species with pulmonary respiration. The heart is located in the dorsal part of the cephalothorax and is equipped with valves.

The excretory organs in some cases are represented by altered nephridia, opening at the base of the 1-3rd pair of walking legs (coxal glands). They consist of a coelomic sac and a convoluted tubule, sometimes expanding and forming a bladder. Often there is a special type of excretory organs - the so-called malpighian vessels. In arachnids, this is one or more pairs of thin tubes located in the body cavity and opening into the intestine. The excretion products enter the osmotic route and are excreted into the hind gut.

The nervous system, as in all arthropods, consists of the brain (nasopharyngeal ganglion), the periglottal ring and the abdominal nerve chain, the nodes of which often merge with each other. So, for example, in scorpions all the ganglia of the thoracic segments are fused into one large node, followed by a chain of 7 ganglia of the abdomen. In spiders, all the ganglia of the chain are merged into a single node.

The eyes are simple, there are from 2 to 12. Sensitive hairs on the limbs and surface of the body perceive mechanical and tactile irritations. In the small slits of the cuticle are the receptors of the chemical sense.

Most arachnids lead a predatory lifestyle. A number of structural features are associated with this, in particular the presence of poisonous glands (their secret kills prey), extra-intestinal digestion (secrets of special "salivary" glands and liver are introduced into the body of the killed prey, its proteins, which take the form of liquid gruel, quickly break down), powerful muscles pharynx, acting as a pump that draws in semi-liquid food.

The poisonous glands in spiders open on the top of the pointed upper jaws, in scorpions - on the pointed last segment of the abdomen. The spider glands are especially developed in spiders. They are located on the underside of the abdomen in three pairs of spider warts. The spider-web apparatus is especially complicated for spider-crosses (they distinguish six types of spider glands that secrete the thinnest strings of various varieties of spider webs - dry, wet, sticky, etc.). Spiders use the web to make hunting nets, a house, an egg cocoon, etc.

Arachnids are dioecious. Sexual dimorphism is very pronounced. The male is usually much smaller than the female.

Class overview

The class of arachnids includes several orders. The most important of them: scorpions, salpugs, spiders, ticks.

Order Scorpionida (scorpions)

Scorpions are medium-sized animals, usually 5-10 cm, some up to 20 cm. Three parts of the body - the protosome (undivided cephalothorax), the mesosome (wide anteriorly-pointed) and the metasome (narrow tail-shaped posterior-pointed) are well expressed. The cephalothoracic shield is integral, it has a pair of larger median eyes and up to 5 pairs of small lateral eyes. The abdomen adjoins the cephalothorax with a broad base, the pre-genital (7th) segment is atrophied. The anterior abdomen (mesosome) is wider, its segments have isolated tergites and sternites; altered abdominal limbs are presented in a complete set: genital caps on the eighth segment, crest-shaped organs on the ninth, pulmonary sacs on the tenth - thirteenth. The segments of the posterior part (metasomes) are narrow cylindrical, tergite and sternite of each segment are fused into a single sclerite ring; the first segment of the metasome is conical. The metasoma ends with a swollen caudal segment, a poisonous gland is placed in it, the duct of which opens at the end of a curved sharp sting. The body shields and segments of the limbs are formed by a very hard cuticle, often having a ribbed or tuberous sculpture.

In appearance, large pedipalps with claws and a jointed flexible metasome (“tail”) with a poisonous apparatus at the end are most characteristic. Chelicerae are short and end in small claws. On the coxae of the pedipalps and two front pairs of legs there are chewing processes directed to the mouth. Walking legs 4 pairs. Breathing is carried out by leafy lungs.

Scorpions live in countries with a warm or hot climate, and are found in a wide variety of habitats, from moist forests and littoral coasts to barren rocky areas and sandy deserts. Some species are found in the mountains at an altitude of 3-4 thousand meters above sea level.

It is customary to distinguish hygrophilic species of scorpions living in moist places, and xerophilic species found in dry areas. But this division is largely arbitrary, since they are all active at night, and in the daytime they hide in shelters, under stones, under a lagged bark, in burrows of other animals or burrow into the soil, so that in dry areas they find places where the air is sufficiently humid . More distinct differences in relation to temperature. Most species are thermophilic, but some living high in the mountains, as well as at the northern and southern borders of the scorpion distribution area, tolerate cold winters inactive. Some species are found in caves, but they are random aliens here. Scorpions are frequent visitors to a person’s home, but there are no real cohabitants of a person (synanthropes) among them.

Scorpio goes hunting at night and is especially active in hot weather. He walks slowly with a raised tail, pushing forward half-bent pedipalps with open claws. It moves gropingly, the main role in this is played by protruding tactile hairs (trichobotria) of the pedipalp. The scorpion reacts very sensitively to touching a moving object and either grabs it if it is a suitable prey, or retreats in a threatening position: it bends its tail “tail” abruptly and waves it from side to side. The prey is caught by the pedipalp claws and fed to the chelicerae. If it is small, then immediately kneaded by chelicera and the contents are absorbed. If the prey is resisting, the scorpion stings it once or several times, immobilizing and killing it with poison. Scorpions feed on live prey, hunting objects are very diverse: spiders, hayfields, millipedes, various insects and their larvae, there are cases of eating small lizards and even mice. Scorpions can starve for a very long time, they can be stored without food for several months, there have been cases of starvation for up to one and a half years. Most species are likely to live without water all their lives, but some inmates of tropical rainforests drink water. When kept together in small cages, a scorpion often eats a fellow.

The biology of scorpion breeding is peculiar. Mating is preceded by a "mating walk". The male and female interlock with claws and, lifting their tails vertically, walk together for hours and even days. Usually, the male, backing off, entails a more passive female. Then there is a copulation. At the same time, the individuals hide in some kind of shelter, which the male, without releasing the female, quickly clears it with the help of legs and the “tail”. Fertilization is spermatophore. The specimens touch the ventral sides of the anterior abdomen, and the male introduces sperm packets into the female genital tract, and then secrets a special secret that seals the female’s genital opening. It is believed that when mating scallops play a role - modified limbs of the ninth segment. They are equipped with numerous senses. At rest, the scallops are pressed to the abdomen; when mating, they protrude and oscillate. But they protrude when moving the scorpion, and they are also credited with the role of the balance organs and some other functions.

Scorpions are mostly viviparous, some species lay eggs in which the embryos are already developed, so that young hatch soon. This phenomenon is called egg production. The development of embryos in the mother’s body is long; from several months to a year or more. In some species, the eggs are rich in yolk and the embryos develop in the egg membranes, in others there is almost no yolk and the embryos soon enter the lumen of the ovary. As they grow, numerous swelling of the ovary is formed, in which the embryos are placed. They feed on secretions of special glandular appendages of the ovary. Embryos are from 5-6 to several tens, less often about a hundred. Small scorpions are born wrapped in an embryonic shell, which is soon discarded. They climb onto the mother’s body and usually stay on it for 7-10 days. Scorpions of the first age do not eat actively, they are whitish, with a smooth cover and sparse hairs, the legs are devoid of claws and have suckers at the end. Remaining on the female’s body, they molt, and after a while they leave their mother and begin to search for food on their own. After molting, the integument hardens and stains, claws appear on the paws. Scorpio becomes an adult in a year and a half, after birth, doing 7 links during this time. Life expectancy is not exactly established, but it is usually not less than a few years. There are interesting cases of anomalies arising in the embryonic development of scorpions, for example, doubling of the “tail”, and individuals are viable and grow into an adult state (the “two-tailed scorpion” is mentioned by the famous Roman scientist Pliny the Elder in his “Natural History”, I c. .e.).

Hard integuments and a poisonous apparatus do not always save scorpions from enemies. Large predatory millipedes, saltpugs, some spiders, praying mantises, lizards, birds cope with them. There are species of monkeys that feast on scorpions by carefully removing the tail. But the worst enemy of scorpions is a man. Since ancient times, the scorpion has been the subject of disgust and mystical horror, and, perhaps, there is no other arthropod that would give rise to so many tales and legends. Scorpio appears in the ancient myths of the Egyptians and Greeks, and in the prescriptions of medieval alchemists as a magical attribute of “conversion” - lead into gold, and in astrology, since the name of the scorpion is one of the zodiac constellations, and among Christians as a typical component of the “fauna” of the underworld. Curious assurances that scorpions can end their lives by "suicide": if you surround the scorpion with burning coals, then he, in order to avoid a painful death, as if he is killing himself with a sting. This opinion is untrue, but has a well-founded basis. The fact is that a scorpion, like some other arthropods, under the influence of strong stimuli can fall into a stationary state - the phenomenon of imaginary death (catalepsy, or thanatosis). Being surrounded by burning coals, the scorpion, of course, rushes about in search of a way out, assumes a threatening pose, waves its “tail”, and then suddenly becomes motionless. This picture is taken for "suicide." But after a while such a scorpion "comes to life", if only it has not been baked from the heat.

Equally unreasonably fairly common belief is that a scorpion at night specifically searches for a sleeping person to sting him. Where there are a lot of scorpions, on hot nights, making their hunting walks, they often visit homes and can climb to bed. If a sleeping person presses a scorpion or touches it, then the scorpion can hit with a “tail”, but of course there are no special searches for a person here.

Scorpion injection is a means of attack and defense. On small invertebrates, usually serving as food for a scorpion, the poison acts almost instantly: the animal immediately stops moving. But larger millipedes and insects do not die immediately, and after an injection they live a day or two; there are also insects that are apparently generally insensitive to scorpion venom. For small mammals, scorpion venom is mostly fatal. The toxicity of different types of scorpions is very different. For a person, a scorpion injection is usually not fatal, but a number of cases with very serious consequences are known. With an injection, pain appears with subsequent swelling of the stung site. In severe poisoning, the tumor can take on a phlegmonous character. After the injection, general symptoms appear: weakness, drowsiness, cramps, accelerated shallow breathing, pulse up to 140 per minute, chills, sometimes a temperature reaction. Usually in a day or two these phenomena disappear, but they can also be delayed. Children are more prone to scorpion venom. Some cases of death are described.

With scorpion injections, urgent measures must be taken. E.N. Pavlovsky recommends immediate removal of the poison by exhaustion and cauterization. The patient should be urgently taken to hospital. The poison is destroyed by injecting a solution of potassium permanganate (1: 1000) or bleach (1:60).

Most cases of stinging with scorpions are observed in Central Asia and the Caucasus, where scorpions are common and numerous. About 700 species of scorpions are known, belonging to approximately 70 genera and 6 families.

Order Solpugida (salpugi, or phalanx)

Their body is dissected more than scorpions: not only the abdomen, but also the cephalothorax is partially segmented. Chelicera are adapted to seize and kill prey. The pedipalps look like walking legs, as a result of which the salpugs give the impression of decapod animals. Breathing trachea.

Distributed in warm countries. Within our country are found in the Crimea, the Caucasus, Kazakhstan and Central Asia. Predators When attacking a person, a salpuga bites through his skin and mechanically infects the wound with contaminated chelicera. With a bite, acute pain is felt, the bitten place becomes inflamed and swollen. However, attempts to find poisonous glands ended in failure. The consequences of a bite are caused by infection.

Squad Araneida (spiders)

The body consists of an undivided cephalothorax and an undivided abdomen. The cephalothorax is separated from the abdomen by a deep constriction. Claw-shaped chelicerae; a duct of the poisonous gland opens in them. Pedipalps act as oral limbs. Spiders breathe lightly, and some species breathe lightly and trachea.

The spider squad includes more than 15,000 species. Distributed almost universally. Spiders are predators. They feed on insects that are caught in their snares. A large tropical spider - a tarantula - attacks birds. Most species are beneficial because they exterminate insects. There are spiders whose bite is dangerous to humans.

Karakurt (Lathrodectus tredecimguttatus)  - a small spider. The size of the female is 10-12 mm, the male is 3-4 mm. It has a velvety black body, decorated with reddish spots. It lives in the south of the Asian and European parts of the USSR in clay-solonetz and clay-sand steppes, as well as in wastelands, virgin lands and in arable fields. The female builds a tenet on the ground among the stones. It feeds on insects, spiders, scorpions, etc. The poison of karakurt is highly toxic. Horses, cows and camels often die from his bites. Sheep and pigs are immune to the poison of karakurt.

In humans, the bite of this spider causes severe intoxication. The bitten person feels a burning pain that spreads from the injection site and after an hour covers the whole body. There is no tumor at the site of the bite. The patient is anxious, feels a sense of fear, dizziness, headache. Cold sweat appears on his face. The skin is cold, bluish in color. Later, vomiting, trembling, bone pain appears. The patient rushes about in bed, sometimes falls into a state of stupor. Recovery occurs slowly, after 2-3 weeks. Weakness remains 1-2 months. In severe poisoning, death occurs in 1-2 days.

Squad Acarina (ticks)

It includes small, sometimes even microscopic (from 0.1 to 10 mm) arachnids, usually with an undivided and not segmented body; the cephalothorax is merged with the abdomen; less often, the abdomen is dissected. Chitin is leathery, easily extensible, but some parts of it are densified (shields). The shape and location of the guards is important for taxonomy.

All ticks have six pairs of limbs. Two pairs (chelicerae and pedipalps) are transformed into a piercing-sucking or gnawing-sucking mouth apparatus, designed to pierce the host's skin and nourish it with blood. The remaining four pairs (walking legs) consist of several segments (6-7), the first of which (main, basin or coke) is fused to the body.

The digestive system of blood-sucking forms is highly branched, especially in females. The digestive canal is characterized by the presence of blind outgrowths; they serve as a reservoir for food intake. The excretory organs are malpighian vessels. Respiratory organs - trachea. There is one pair of stigmas located either at the base of the chelicera, or at the base of the legs. Stigmas are on a small shield (peritrem).

The nervous system is characterized by the fusion of all the ganglia of the nervous chain and brain into a common mass. The sensory organs are represented mainly by the organs of touch and smell. Eyes may be missing.

Mites are dioecious. The genital opening is located between the bases of a pair of legs. Females are larger than males. A six-legged larva emerges from the fertilized eggs laid by the female. She molts and turns into an octopus nymph. Unlike an adult tick, the nymph has an underdeveloped reproductive apparatus; there is usually no external genital opening. There may be several nymphal stages. At the last molt, the nymph turns into a mature form - an imago.

Life cycle. Unlike other arachnids, development occurs with metamorphosis, including an egg, a larva, a nymph, and an adult (mature form). The larva has three pairs of legs and breathes through the surface of the body. After molting, she turns into a nymph. The nymph has four pairs of legs, breathes with the help of the trachea (stigma appears), but does not have a genital opening. There may be several nymphal stages. After molting, the nymph turns into an adult. Most medical mites are blood-sucking. Mammals, birds and reptiles are the animals that feed ticks.

There are single, double and triple-mite ticks. With the same owners, all stages of development take place on the same owner. In the case of a dual-type development, the larva and nymph feed on one host, and the imaginal form on another. In three-mite ticks (taiga tick), each stage is looking for a new owner. In the latter case, development can stretch for a long period, for example, in a taiga tick up to 5 years.

Along with the host blood, pathogens of various diseases penetrate into the flare organism, which, when transferred to another host, can be transmitted to it, which contributes to the circulation of pathogens. The life of ticks is quite long - from 6 months to 20-25 years.

The most important from the point of view of medicine are ticks of the ixodid and argaz family, as well as scabies mite of the acariform family.

Ixodidae ticks (Ixodidae)

Of interest are both a natural reservoir and carriers of a number of serious diseases: tick-borne encephalitis, tick-borne typhus, tyularemia, hemorrhagic fevers, etc.

They have large sizes of 4-5 mm. Female blood sucked reaches 10 mm or more. The male has a shield on its back, covering the entire dorsal surface. In females, nymphs and larvae, the shield occupies only the front of the body; on the rest of the surface, chitin is thin, easily extensible. This is important, since the female absorbs a large amount of blood, which is 200-400 times its mass in a hungry state, when feeding. The oral apparatus is located terminally on the front end of the body. It consists of a massive pedipalp base, on which four-membered palps are located on the sides and in the middle of the proboscis. Its lower part is hypostome - an outgrowth of the base. The back side of the hypostome is equipped with sharp teeth directed back. On top of the hypostome are the cases in which the two-membered chelicera lie. The terminal segment of the chelicera has large, sharp teeth and is movably connected to the previous one. When a tick pierces the skin of the victim and spreads the movable segments of the chelicera to the sides, it is impossible to remove its oral apparatus from the skin. After saturation, the tick reduces the chelicera and releases the oral apparatus.

Eggs are laid in the soil. In the process of development, a larva, one generation of nymphs and an imaginal form are formed. The change of stages occurs only after bloodsucking. Among the ixodidae there are one-, two- and three-household ticks. Larval stages usually feed on small vertebrates (rodents, insectivores), adult forms - large animals (cattle, deer) and humans. After drinking the blood, the females lay their eggs, and then die.

The main direction of prevention is protection from bites (special clothing, repellents).

Argasidae ticks (Argasidae)

  carriers of pathogens of some vector-borne diseases of humans and animals. The species of the genus Ornithodorus are of the greatest importance.

The ornithodorus tick (Ornithodorus papillipes) is a settlement tick - a blood-sucking tick, a vector of tick-borne typhoid (tick-borne recurrence) pathogens. The body is dark gray, up to 8.5 mm long. Unlike ixodic ones, they do not have shields. The lateral edges in the middle part of the body are almost parallel to each other, the presence of an edge welt is characteristic. The chitinous cover of hungry ticks lays in folds. The set of oral organs and adjacent integument forms the so-called "head". It is relatively small, located in the front of the body on the ventral side and is not visible from the dorsal side. There are no eyes. On the midline of the body, behind the first pair of legs, is the genital opening, and a little behind the middle of the body is the anal opening.

The ornithodorus tick is distributed in the south of Kazakhstan, in Central Asia, Iran and India. It lives in natural (caves) or artificial (dwellings) shelters, and each species is associated with a shelter of a certain type (a rodent hole, a cave with bats, porcupines, etc.). It is found in the dwelling of a person, in stables, pigsties and other outbuildings. It hides like bugs in cracks and cracks of adobe walls. It feeds on blood, attacking humans or animals. Blood sucking lasts 30-40 minutes, after which the tick returns to the wall cracks.

In the process of development, males go through the larval stage and 3 nymphal stages, in female nymphal stages 4 or 5. Life expectancy is extremely long - 20-25 years. In the absence of hosts, the tick is able to live without food for 10-11 years. When smearing the cracks with clay, the immured tick remains alive for more than a year.

The body is wide-oval, dimensions 0.3-0.4 x 0.2-0.3 mm. A notch runs across the oval body, delimiting the cephalothorax from the abdomen. On the surface of the body there are many short spines and long bristles. The legs are very shortened, which is associated with the intradermal lifestyle. Two pairs of legs are located on the sides of the oral apparatus, two are assigned to the posterior end of the body. There are no eyes. Breathing occurs through the surface of the body.

The entire period of development from egg laying to a mature form lasts 9-12 days. An adult tick lives approximately 1.5 months.

Ticks can affect any part of the skin, but are most often found on the back of the hands, in the interdigital spaces, axillary hollows, and perineum. The strokes are visible on the skin in the form of straight or winding lines of a whitish-dirty color.

Prevention. Isolation and treatment of people with scabies; disinsection of clothes and items that they used; fight against scabies of farm animals, maintaining a clean body and home.

• Arachnoidea class (arachnids)

allocate at least 12 units, the most important of which are Spiders, Scorpions, False Scorpions, Solpugs, Hayfields, Mites.

Arachnids are distinguished by the fact that they do not have antennae (antennae), and two pairs of peculiar limbs surround the mouth - chelicera  and jawwhich are called arachnids pedipalps. The body is divided into the cephalothorax and abdomen, but in ticks all sections are merged. Walking legs four pairs.

Cross spiders   these are ordinary representatives of the class Arachnids. Cross spidersthis is the collective name of several biological species of the Araneus genus of the Spider-family Orbiting Spiders family. Spider-crosses are found in the warm season throughout the European part of Russia, the Urals, and Western Siberia.

Cross spiders are predators that feed only on live insects. The cross-spider catches its prey with the help of a very complex, vertically arranged wheeled nets(hence the name of the family - Orbiting Spiders) .   Spider spinning apparatus, which provides the manufacture of such a complex structure, consists of external formations - spider warts- and from internal organs - spider glands.  A drop of sticky liquid is released from the spider warts, which, when the spider moves, stretches into the thinnest thread. These strings quickly thicken in the air, turning into a strong spider web. The web consists mainly of protein fibroin. In terms of chemical composition, the web of spiders is close to silk of silkworm caterpillars, but more durable and elastic. The breaking load for the web is 40-261 kg per 1 sq mm of the cross-section of the thread, and for silk only 33-43 kg per sq mm of the cross-section of the thread.

To weave its hunting net, the Spider-Spider first stretches especially strong threads in several places convenient for this, forming a support framefor the future network in the form of an irregular polygon. Then he moves along the upper horizontal thread to its middle and, going down from there, holds a strong vertical thread. Further from the middle of this thread, as from the center, the spider spends radial threads  in all directions, like wheel spokes. This is the basis of the entire web network. Then the spider begins to weave from the center spiral threadsby attaching them to each radial thread with a drop of sticky substance. In the middle of the web, where the spider itself then sits, the spiral threads are dry. Other spiral threads are sticky. To them, wings and paws stick to them, flying on the net. The spider itself either hangs head down in the center of the web, or hides in

Class Arachnids Spider-Cross

side under the leaf - there he shelter. In this case, he extends a strong signal a thread.

When a fly or other insect enters the network, the spider, sensing the trembling of the signal thread, rushes out of its ambush. Plunging a chelicera with poison into the claws of a victim, the spider kills the victim and releases digestive juices into its body. After that, he entangles a fly or other insect with a web and leaves it for a while.

Under the influence of the isolated digestive juices, the victim’s internal organs are quickly digested. After some time, the spider returns to the victim and sucks all the nutrients out of it. From the insect in the web remains only an empty chitinous cover.

Making a hunting net is a series of interconnected unconscious actions. The ability to do so is instinctive and inherited. This is easy to verify by following the behavior of the young spiders: when they exit the eggs, no one teaches them how to weave a hunting net, the spiders immediately very skillfully weave their webs.

In addition to the wheeled hunting net, other types of spiders also have networks in the form of random weaving of threads, networks in the form of a hammock or canopy, funnel-shaped networks and other types of hunting networks. The hunting net of spiders is a kind of adaptation outside the body.

I must say that far from all types of spiders weave hunting nets. Some actively seek out and catch prey, while others lurk it in an ambush. But all spiders have the ability to secrete the web, and all spiders make from the web egg cocoon  and spermatic nets.

External structure. The body of the spider-cross is divided into cephalothorax  and abdomenwhich connects to the cephalothorax thin movable the stalk. There are 6 pairs of limbs on the cephalothorax.

The first pair of limbs is chelicerathat surround the mouth and serve to capture and puncture the prey. Chelicerae consist of two segments, the final segment is curved claws.  At the base of the chelicera are poisonous glandswhose ducts open on the tips of the claws. Chelicerae spiders pierce the integument of the victims and inject poison into the wound. Spider venom has a nerve agent effect. In some species, for example, in Karakurtat the so-called tropical Black widow, the poison is so strong that it can kill

Class Arachnids Spider-Cross

even a large mammal (instantly!).

The second pair of cephalothoracic limbs - pedipalps  have the appearance of jointed limbs (they look like short legs sticking forward). The function of the pedipalpus is to feel and hold the prey. In mature males, a pedipalp is formed on the final segment copulative apparatus, which the male fills with sperm before mating. When copulating, the male, using the copulative apparatus, introduces sperm into the female sperm. The structure of the copulative apparatus is species-specific (i.e., each species has a different structure).

All arachnids have 4 pairs walking legs. The walking leg consists of seven segments: basin, trochanter, hips, cups, lower legs, pre-flaps  and pawsarmed with claws.

The antennae of the Arachnids are absent. On the front of the cephalothorax in the spider-cross in two rows are eight simple eyes. Other types of eyes can have three pairs, and even one pair.

Abdomen  in spiders it is not segmented and does not have true limbs. On the abdomen there a pair of lung bagstwo beams trachea  and three pairs spider web warts. The spider web warts of the spider-cross consist of a huge amount (about 1000) spider web glandsthat produce various types of cobwebs - dry, wet, sticky (at least seven varieties of very different purposes). Different types of webs perform different functions: one for catching prey, the other for building a dwelling, the third is used in the manufacture of cocoons. Young spiders also settle on cobwebs of a special property.

On the ventral side of the abdomen, closer to the junction of the abdomen with the cephalothorax sexual hole. In females, it is surrounded and partially covered by a chitinized plate. epigina. The structure of epigines is species-specific.

The integument of the body.  The body is covered in chitinous cuticle.The cuticle protects the body from external influences. The surface layer is called epicuticle  and it is formed by fat-like substances, therefore, the covers of spiders are not permeable to either water or gases. This allowed the spiders to populate the driest areas of the globe. The cuticle simultaneously performs the function

Class Arachnids Spider-Cross

outdoor skeleton: serves as a place for muscle attachment. Periodically, spiders molt, i.e. dropping the cuticle.

Musculaturearachnids consists of striated fibers forming powerful muscle bundles, i.e. the muscles are represented by separate bundles, and not by a bag like in worms.

Body cavity.  The body cavity of the Arachnids is mixed - a mixocell.

Digestive system   typical consists of front, middle   and back   guts. The foregut is represented by mouth, throatshort esophagus   and the stomach. The mouth is surrounded by chelicerae and pedipalps, with which spiders grab and hold prey. The pharynx is equipped with strong muscles for absorption of food gruel. Ducts open in the anterior intestine salivary glandswhose secretion effectively breaks down proteins. All spiders have the so-called extraintestinal digestion. This means that after killing the prey, digestive juices are introduced into the victim’s body and the food is digested outside the intestine, turning into a semi-liquid gruel, which is absorbed by the spider. In the stomach, and then in the middle intestine, food is absorbed. The middle intestine has long blind side bulging, increasing the area of \u200b\u200babsorption and serving as a temporary storage of food mass. The ducts open here liver. It secretes digestive enzymes and also provides nutrient absorption. Intracellular digestion occurs in liver cells. At the border of the middle and posterior sections, the organs of excretion flow into the intestine - malpighiev vessels. The hind gut ends anal holelocated at the posterior end of the abdomen above the arachnoid warts.

Breathing system. Some arachnids have respiratory organs pulmonary bags, other's tracheal the system, for the third, both of them at the same time. In some small arachnids, including some ticks, the respiratory organs are absent, breathing is carried out through thin integuments. Pulmonary sacs are more ancient (from an evolutionary point of view) formations than the tracheal system. It is believed that the gill limbs of the aquatic ancestors of the arachnids plunged into the body and cavities with pulmonary leaves formed. The tracheal system arose independently and later than the pulmonary sacs, as organs more adapted to air breathing. Trachea is a deep protrusion of a cuticle into the body. The tracheal system is perfectly developed among Insects.

Class Arachnids Spider-Cross

In the Spider-Cross, the respiratory organs are represented by a pair lung bagsforming foliate folds on the ventral side of the abdomen, and two bundles tracheathat open spiracles   also on the underside of the abdomen.

Circulatory system open, comprises hearts   located on the dorsal side of the abdomen, and several large blood vessels extending from it vessels.   The heart has 3 pairs of spikes (holes). Departs from the front end of the heart front aortadisintegrating into arteries. End branches of arteries pour out hemolymph   (the so-called blood of all arthropods) to the system cavitieslocated between the internal organs. Hemolymph washes all internal organs, delivering nutrients and oxygen to them. Then hemolymph washes lung bags - gas exchange occurs, and from there it enters pericardium,   and then through ostia   - in the heart. The arachnoid hemolymph contains a blue respiratory pigment - hemocyanin   containing copper. Being poured into the secondary body cavity, the hemolymph mixes with the secondary cavity liquid, therefore it is said that arthropods have a mixed body cavity - mixocell.

Excretory system   in arachnids represented malpigian vesselsthat open into the intestine between the middle and hind gut. Malpighian vessels, or tubules, are blind protrusions of the intestine that ensure the absorption of metabolic products from the body cavity. In addition to malpigium vessels, some arachnids also have coxal glands   - paired sack-shaped formations lying in the cephalothorax. From the coxal glands, convoluted canals, ending in urinary blistering   and lead ductsthat open at the base of the walking limbs (the first segment of the walking legs is called coke, hence the name - coxal glands). The spider-cross has both coxal glands and malpighian vessels.

Nervous system. Like all arthropods, the arachnids have a nervous system - stair type. But the Arachnids experienced a further concentration of the nervous system. A pair of nasopharyngeal nerve ganglia are called in the Arachnids “brain”. It innervates (controls) the eyes, chelicera and pedipalps. All the cephalothoracic nerve ganglia of the neural chain merged into one large nerve node located under the esophagus. All the abdominal nerve ganglia of the neural chain also merged into one large abdominal nerve node.

Of all the senses, the most important thing for spiders is touch.  Numerous tactile hairs - trichobotria - in large quantities scattered over the surface of the body, especially a lot of them on pedipalps and walking legs.

Class Arachnids Spider-Cross

Each hair is movably attached to the bottom of a special fossa in the integument and is connected to a group of sensitive cells that are located at its base. The hair perceives the slightest vibrations of the air or the web, sensitively reacting to what is happening, while the spider is able to distinguish the nature of the irritating factor by the intensity of the vibrations. Tactile hairs are specialized: some register chemical stimuli, others - mechanical, others - air pressure, fourth - perceive sound signals.

The organs of vision are represented simple eyesfound in most arachnids. Spiders often have 8 eyes. Spiders are shortsighted, their eyes perceive only light and shadow, the outlines of objects, but details and color are not accessible to them. There are organs of balance - statocysts.

Breeding and development. Arachnids diclinous. Fertilization internal. Most arachnids lay their eggs, but some arachnids show live births. Development without metamorphosis.

The spider-cross is well expressed sexual dimorphism: the female has a large abdomen, and in mature males on the pedipalps develop copulative bodies. In each species of spiders, the copulative organs of the male approach the female’s epigin as a key to the castle, and the structure of the male’s copulative organs and the female’s epigina are species-specific.

Mating in the Spider-Spiders occurs at the end of summer. Sexually mature males of hunting nets do not weave. They wander in search of networks of females. Having discovered the catching net of a sexually mature female, the male somewhere on the side of the earth, or on some twig, or on a leaf weaves a small spermatic mesh   in the form of a hammock. On this mesh, a male squeezes a drop from his genital opening, which is located on the ventral side of the abdomen closer to the junction of the abdomen with the cephalothorax sperm. Then he sucks this drop into the pedipalps (like a syringe) and sets about seducing the female. The spider’s eyesight is weak, so the male needs to be very careful that the female does not mistake him for prey. For this, the male, having caught some insect, wraps it in a spider web and presents this peculiar gift to the female. Hiding behind this gift as a shield, the male very slowly and extremely carefully approaches his lady. Like all women, the spider is very curious. While she looks at the presented gift, the male quickly climbs onto the female, applies her pedipalps with sperm to the female’s genital opening and

• Class Arachnids Spider-Cross

  carries out copulation. The female at this moment is good-natured and relaxed. But, immediately after mating, the male should hastily retire, since the behavior of the spider changes dramatically after copulation: it becomes aggressive and very active. Therefore, sluggish males are often killed by the female and eaten. (Well, after mating, the male will die anyway. From an evolutionary point of view, the male is no longer needed: he fulfilled his biological function.) This happens in almost all species of spiders. Therefore, in studies, females are most often found, males are rare.

  After copulation, the female continues to eat actively. In the fall, a female from a special web makes cocoonwhich lays several hundred eggs. She hides the cocoon in some secluded place, for example, under the bark of a tree, under a stone, in the cracks of a fence, etc., and the female herself dies. Eggs hibernate at the Spider-Spiders. In the spring, young spiders come out of the eggs, who begin an independent life. Shedding several times, spiders grow and by the end of summer reach puberty and begin to reproduce.

Value.The role of spiders in nature is great. They act in the ecosystem structure as second-class consumers (i.e., consumers of organic matter). They destroy many harmful insects. They are food for insectivorous birds, toads, shrews, and snakes.

Questions for self-control

What is the Arthropod type classification?

What is the systematic position of the Cross Spider?

Where do the spider-crosses live?

What shape do spiders-crosses have?

What is the body of the spider covered with?

What body cavity is typical for a spider?

What structure does the digestive system of a spider have?

What are the digestive features of spiders?

What structure does the spider circulatory system have?

How does a spider breathe?

What structure does the spider excretory system have?

What structure does the spider nervous system have?

What structure does the spider's reproductive system have?

How does a spider-cross breed?

What do spiders matter?

Class Arachnids Spider-Cross

Fig. Cross-spider: 1 - female, 2 - male and wheeled hunting net.

Fig. Cross spider weaves a hunting net

Class Arachnids Spider-Cross

Fig. The internal structure of the Spider-cross.

1 - poisonous glands; 2 - pharynx; 3 - blind outgrowths of the intestine; 4 - malpighian vessels; 5 - heart; 6 - a pulmonary bag; 7 - ovary; 8 - oviduct; 9 - spider glands; 10 - pericardium; 11 - Ostia in the heart.

Chelicerae.

Representatives of this subtype are characterized by the fusion of the cephalic and thoracic segments, resulting in the formation of a single cephalothorax, consisting of seven merged segments. The cephalothorax carries six pairs of limbs, of which the first pair has changed into chelicera,   with which the animal pierces and breaks the prey. Chelicerae are homologous to antennas because they evolved from the first pair of parapodial legs. The second pair of limbs (it is the homologues of the mandibles of the crayfish) mutated into pedipalps,   serving to hold and manipulate food, and also carries sensitive structures. Rest four pairs   limbs are walking legs. The abdominal limbs in them are most often modified into lung and spider warts.

p / type Chelicer

class Arachnids

squad spiders

cross spider

The body of arachnids is divided into cephalothorax  and abdomen.  These departments are connected by a short stalk, which was formed from 7 segments.

Chelicerae consist of two segments. The main large segment is movably connected to the claw-shaped second segment. At the end of the claw, the duct of the nucleus gland located in the cephalothorax opens. With the help of chelicera, spiders kill their prey and also defend themselves.

The second pair of limbs - pedipalps - is much longer than the chelicera and resembles walking ones. In males, they are used in copulation.

Four pairs of walking legs have the same structure, they are formed by 6-7 segments and end with a claw. In spiders, the third pair of legs is shorter than the rest.

On the abdomen there are external openings of the respiratory organs - lung bags and trachea, as well as the anal and genital openings. Spiders have three pairs of arachnoid warts, but only the front and back are individual altered limbs, respectively, of 10 and 11 abdominal segments.

In spiders, five types of glands are distinguished: lobate; pear-shaped; tubular glands are present only in females; the web secreted by them goes to the formation of a cocoon; ampuloid; tree-like. The thick secret secreted by the spider glands quickly hardens in the air and turns into web threads. The thickest and most durable threads of the frame are formed from ampoule glands; pear-shaped glands secrete strong but thinner threads, with which the axial threads of the frame are attached to surrounding objects; a sticky thread located in a spiral form lobate and tree glands;

Cover.

It is represented by a single layer of hypodermis cells secreting chitin. Poisonous and spider glands are derivatives of the skin.

Digestive system.

The spider's anterior intestine is divided into the pharynx, esophagus and sucking stomach. The ducts of the salivary glands open into the throat, their secrets contain potent enzymes. When bitten, these enzymes are introduced into the victim’s body and dissolve its tissue to a semi-liquid state. After waiting a while, the spider sucks in a semi-digested slurry, leaving only an empty shell from the victim. Thus, the digestion of the spider partially occurs outside the body.

The middle intestine is differentiated into the stomach and small intestine. The ducts of the liver open into the small intestine. It plays a major role in the processing and assimilation of food.

Excretory system.

Submitted by malpighian vessels. The highlight product is guanine.

Coxal glands. The gland includes a sac and a convoluted tubule, which opens at the base of the third lil of the fifth pair of walking legs. In adult forms, there are 1-2 pairs of glands.

Special cells nephrocytes.

Circulatory system.

Unclosed. The heart in the form of a tube with ostia is located in the front of the abdomen above the intestine. Hemolymph.

Respiratory system.

It is presented by pulmonary bags and tracheas. The lung bag in modern arachnids is a recess in the body, its walls form numerous leaf-shaped plates with extensive gaps filled with hemolymph. Tracheas open outwards with stigmas on the first segments of the abdomen.

Nervous system.

There is no deutero-cerebrum in the brain. Protocerebrum innervates the eyes, tritotserebrum innervates chelicera. The ganglia of the abdominal nerve chain are often concentrated.

  The sensory organs.

Numerous tactile hairs - trichobotria.   The organs of chemical sensation. The number of simple ocelli varies from 2 to 12. They are arranged in two rows. Statocysts.

Reproductive system.

Dioecious. Sexual dimorphism. Two testes. The vas deferens, open in the seminal sac. Two ovaries. Oviducts open into an unpaired uterus. Mating spiders is often accompanied by ritual behavior. The particular difficulty is that a larger female can easily mistake a young male for her prey. Before mating, male spiders construct a “hammock” and squeeze out sperm into it, then the spider immerses its pedipalps into a drop of sperm and introduces them into the female genital tract. In some species, the male introduces sperm using pedipalps.

In the fall, the female builds a spider web cocoon, where she lays her eggs, and then dies. Development is direct, without a larval stage.

Tarantula.

He catches prey in sheer mines dug by him. Bites are very painful, cause quite severe irritation.

Karakurt spider.

Black color. Toxic.

Silver Spider.

Water spider. He builds a nest from a web in water.

Scorpion squad.

It has a short cephalothorax and a long abdomen of 13 segments. The last segment ends with a spike - a sting with a poisonous gland inside.

Pedipalps grow and become powerful claws.

Four pairs of lung bags.

Viviparous.

Troop Ticks.

All segments are merged into one common whole.

Ixodid ticks .

Argas Mites .

Are carriers of tick-borne relapsing fever.

Gamasid ticks .

Dog tick.

The proboscis is attached to the front of the body, which is chelicera and pedipalps, which have turned into a piercing-sucking mouth apparatus. No eyes.

Between the second legs there is a genital opening. Behind and slightly above the hind legs is a pair of stigma.

To prevent pain during the injection and coagulation of blood in the body of the tick there is a pair of glands that secrete the corresponding anticoagulant secretion and open at the base of the chelicera.

Nervous system.

The nasopharyngeal nodal node and the periopharyngeal ring and the abdominal neural chain. The sensory organs are represented by receptor cells.

Digestive system.

It consists of the anterior and middle intestine ending blindly. The pharynx functions like a pump. They feed not only on the blood and juices of the victim, but also on the tissues. Blood is conserved.

Circulatory system.

Reduced. Its remains are in the form of a dorsal vessel.

Respiratory system.

Excretory system.

Malpighian vessels.

The reproductive system.

Dioecious. Females are larger than males. Development with metamorphosis.

After abundant masonry, which reaches several thousand eggs, the female's body shrinks and she dies. From eggs, larvae develop, characterized by the absence of a posterior pair of legs, stigma, trachea and genital opening. After the first molt, the larva turns into a nymph, the reproductive system is underdeveloped. Only after a few nymphal stages does it turn into imago - sexually mature individual.

The Latin name for arachnids comes from the Greek ἀράχνη "spider" (there is also the myth of Arachne, which the goddess Athena turned into a spider).

Arachne  or Arachnei  (dr. Greek Ἀράχνη "spider") in ancient Greek mythology - the daughter of dyer Idmon from the Lydian city of Kolofon, a skilled weaver. It is called the Meonian from the city of Gipepa, either the daughter of Idmon and Gipepa, or a resident of Babylon.

Proud of her mastery, Arakhna declared that she surpassed Athena itself in weaving, which was considered the patroness of this craft. When Arachne decided to call the goddess to the contest, she gave her a chance to change her mind. Under the guise of an old woman, Athena came to the mistress and began to dissuade her from a reckless act, but Arachne insisted on her. The contest took place: Athena wove on the canvas the scene of her victory over Poseidon. Arachne depicted scenes from the adventures of Zeus. Athena recognized the rival's skill, but was outraged by the freethinking of the plot (in her images there was disrespect for the gods) and destroyed the creation of Arakhna. Athena tore the fabric and struck Arachne in the forehead with a shuttle from a Kitor beech. The unfortunate Arachne did not suffer shame; she twisted a rope, made a loop and hanged herself. Athena freed Arachne from the loop and told her:

Live, rebellious. But you will always hang and weave forever, and this punishment will continue in your offspring.

Arachnid structure

(or cheliceric)

Nervous system:  subpharyngeal nerve node + brain + nerves.

Organs of touch  - the hairs on the body, on the legs, on almost all arachnid bodies, there are organs of smell and taste, but the most interesting thing for a spider is eyes.

The eyes are not faceted, like many, but simple, but there are several of them - from 2 to 12 pieces. At the same time, spiders are shortsighted - they do not see into the distance, but a large number of eyes provide a 360 ° view.

The reproductive system:

1) spiders of dioecious; the female is clearly larger than the male.

2) lay eggs, but many live-bearing species.

Scorpions and ticks also belong to arachnids. Ticks are much simpler arranged, they are one of the primitive representatives of chelicerae.