The respiratory organs of Arachnida are diverse. In some, these are pulmonary sacs, in others - trachea, in others - both at the same time. Only the lung sacs are found in scorpions, flagellates, and primitive spiders. In scorpions on the abdominal surface of the 3rd - 6th segments of the anterior abdomen there are 4 pairs of narrow slits - spiracles, which lead to the pulmonary sacs (Fig. 389). Numerous leaf-like folds, parallel to each other, protrude into the cavity of the sac, between which narrow slit-like spaces remain, air penetrates into the latter through the respiratory slit, and hemolymph circulates in the pulmonary leaflets. In flagellates and lower spiders, there are only two pairs of pulmonary sacs. In most other arachnids (solpugs, hay makers, false scorpions, some of the ticks), the respiratory organs are represented by tracheas (Fig. 399, Fig. 400). On the 1st - 2nd segments of the abdomen (in solpugs on the 1st segment of the chest) there are paired respiratory holes, or stigmas. A bundle of long, thin, blindly closed air tubes of ectodermal origin (formed as deep invaginations of the outer epithelium) depart from each stigma into the body. In false scorpions and ticks, these tubes, or trachea, are simple and do not branch; in haymakers, they form side branches.

Finally, in the order of spiders, both types of respiratory organs are found together. The lower spiders have only lungs; among 2 pairs, they are located on the underside of the abdomen. The rest of the spiders retain only one anterior pair of lungs, and behind the latter there is a pair of tracheal bundles (Fig. 400), opening outward with two stigmas. Finally, one family of spiders (Caponiidae) has no lungs at all, and the only respiratory organs are 2 pairs of tracheas (Fig. 400).

The lungs and trachea of ​​arachnids arose independently of each other. The lung sacs are undoubtedly more ancient organs. It is believed that the development of the lungs in the process of evolution was associated with a modification of the abdominal gill limbs, which were possessed by the aquatic ancestors of arachnids and which were similar to the gill-bearing abdominal legs of horseshoe crabs. Each such limb stuck inside the body. This formed a cavity for the pulmonary leaflets (Fig. 401). The lateral edges of the leg have grown to the body almost along the entire length, except for the area where the respiratory gap is preserved.

The abdominal wall of the pulmonary sac corresponds, therefore, to the former limb itself, the anterior section of this wall to the base of the leg, and the pulmonary leaflets originated from the gill plates located on the back of the abdominal legs of the ancestors. This interpretation is supported by the development of the pulmonary sacs. The first folded rudiments of the pulmonary plates appear on the posterior wall of the corresponding rudimentary legs before the limb deepens and turns into the lower wall of the lung. Tracheas arose independently of them and later as organs more adapted to air breathing. In some small arachnids, including some of the ticks, the respiratory organs are absent, and breathing takes place through thin integuments.

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

E K O L O G I Z P A U K O O B R A Z N Y X Arachnids are the first terrestrial animals that mastered the land in the Silurian period and switched to air breathing. They lead a daytime or nocturnal lifestyle. They live in forests, meadows, pastures, desert sands. Some weave trapping nets, others attack prey. They feed on insects, but karakurt, scorpions and tarantulas inflict bites on humans, pets (camels, horses), causing painful phenomena, sometimes fatal. Ticks are especially dangerous - they transmit diseases from wild animals to humans and domestic animals (tularemia, plague, encephalitis). Scabies mites cause scabies in humans and mammals. To combat ticks, there are only chemical agents, while biological ones are practically not developed.

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

Tracheas are a system of branching air tubes. They begin with the airways, or spiracles, leading to the main tracheal trunks. The latter branch out and form ever 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 modified 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 to form the bladder. More 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 products of excretion enter them by the osmotic route and are excreted into the hind gut.

The nervous system, like all arthropods, consists of the brain (supraopharyngeal ganglion), the periopharyngeal ring and the abdominal nerve cord, 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 fused into a single node.

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

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

Poisonous glands in spiders open at the apex of the pointed upper jaws, in scorpions - on the pointed last segment of the abdomen. Spider glands are especially developed in spiders. They are located on the underside of the abdomen in three pairs of arachnoid warts. The cobweb apparatus is especially complex in spider-spiders (they have six types of spider glands that secrete the finest threads of various types of cobwebs - dry, wet, sticky, etc.). Spiders use cobwebs to make trapping nets, a dwelling house, an egg cocoon, etc.

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

Class overview

Several orders belong to the class of arachnids. The most important of them: scorpions, solpugs, spiders, ticks.

Squad Scorpionida (scorpions)

Scorpions are medium-sized animals, usually 5-10 cm, some up to 20 cm. Three body parts - the protosome (undivided cephalothorax), the mesosome (wide anterior belly) and the metasoma (narrow tail-like posterior belly) - are well expressed. The cephalothoracic shield is whole, with a pair of larger median eyes and up to 5 pairs of small lateral eyes. The abdomen adjoins the cephalothorax with a wide base, the pregenital (7th) segment is atrophied. The anterior part of the abdomen (mesosome) is wider, its segments have separate tergites and sternites; the modified abdominal limbs are represented by a complete set: genital operculums on the eighth segment, crest-like organs on the ninth, pulmonary sacs on the tenth - thirteenth. The segments of the posterior part (metasoma) are narrow, cylindrical; the tergite and sternite of each segment are fused into an integral scleritic ring; the first segment of the metasoma 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 scutes of the trunk and segments of the limbs are formed by a very hard cuticle, often with a ribbed or tuberous sculpture.

In external appearance, the most characteristic are large pedipalps with claws and an articulated flexible metasoma ("tail") with a venomous apparatus at the end. Chelicerae are short and end with small pincers. 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 warm or hot climates, and they are found in a wide variety of habitats, from humid forests and littoral of sea 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 between hygrophilic scorpion species living in humid places and xerophilic ones found in dry areas. But this division is largely arbitrary, since they are all active at night, and during the day they hide in shelters, under stones, under peeling bark, in the holes of other animals, or burrow into the soil, so that in dry areas they find places where the air is sufficiently humid ... The differences are more pronounced in relation to temperature. Most species are thermophilic, but some that live high in the mountains, as well as at the northern and southern borders of the scorpion distribution area, tolerate cold winters well when inactive. Some species are found in caves, but they are occasional aliens here. Scorpios are frequent visitors to human dwellings, but there are no real human cohabitants (synanthropes) among them.

The scorpion goes hunting at night and is especially active in hot weather. He walks slowly with a raised "tail", putting forward half-bent pedipalps with slightly open pincers. It moves by groping, the protruding tactile hairs (trichobothria) of the pedipalps play the main role. Scorpio reacts very sensitively to touching a moving object and either grabs it, if it is a suitable prey, or retreats, assuming a threatening pose: it sharply bends its "tail" over the cephalothorax and swings it from side to side. The prey is seized by the pedipalp claws and brought to the chelicerae. If it is small, then it is immediately kneaded with chelicera and the contents are absorbed. If the prey resists, the scorpion stings it one or more times, immobilizing and killing it with poison. Scorpions feed on live prey, hunting objects are very diverse: spiders, haymakers, millipedes, various insects and their larvae, there are cases of eating small lizards and even mice. Scorpios can starve for a very long time, they can be kept without food for several months, cases of starvation are known for up to one and a half years. Most species probably go their entire lives without water, but some rainforest dwellers drink water. When kept together in small cages, the scorpion often eats a fellow.

The reproduction biology of scorpions is peculiar. Mating is preceded by a "mating walk". Male and female mate with claws and, raising their "tails" vertically, walk together for many hours and even days. Usually, the male, backing away, entails a more passive female. Then copulation takes place. In this case, the individuals hide in some kind of shelter, which the male, not letting go of the female, quickly clears with the help of his legs and "tail". Fertilization is spermatophore. Individuals touch the ventral sides of the anterior abdomen, and the male inserts bags with spermatozoa into the female genital tract, and then secretes a special secret that seals the female genital opening. It is believed that during mating, the scallops, the modified limbs of the ninth segment, play some role. They are equipped with numerous senses. At rest, the scallops are pressed against the abdomen; during mating, they bulge and sway. But they also bulge out during the movement of the scorpion, and they are also credited with the role of the organs of balance and some other functions.

Scorpions are mostly viviparous, some species lay eggs in which the embryos are already developed, so that juveniles soon hatch. 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 emerge into the lumen of the ovary. As they grow, numerous ovarian swellings are formed, in which the embryos are placed. They feed on secretions of special glandular ovarian appendages. There are from 5-6 to several dozen embryos, less often about a hundred. Small scorpions are born wrapped in an embryonic shell, which is soon shed. They climb onto the mother's body and usually stay on her for 7-10 days. Scorpions of the first age do not feed 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 the 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, making 7 molts during this time. Life expectancy has not been precisely established, but it is usually at least several years. There are interesting cases of anomalies arising in the embryonic development of scorpions, for example, a doubling of the "tail", and individuals: viable and grow to an adult state ("two-tailed scorpion" is mentioned by the famous Roman scientist Pliny the Elder in his "Natural History", 1st century AD . NS.).

Hard covers and a poisonous apparatus do not always save scorpions from enemies. Large predatory centipedes, solpugs, some spiders, praying mantises, lizards, and birds cope with them. There are species of monkeys that feast on scorpions, carefully removing the "tail". But the worst enemy of scorpions is 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 writings of medieval alchemists as a magical attribute of "transformation" - lead into gold, and in astrology, since the name of the scorpion is one of the zodiacal constellations, and among Christians as a typical component of the "fauna" of the underworld. There are curious assurances that scorpions can end their lives "suicide": if you surround a scorpion with burning coals, then, in order to avoid painful death, as if killing himself with a sting. This opinion does not correspond to reality, but it has a certain basis. The fact is that a scorpion, like some other arthropods, under the influence of strong stimuli can fall into a motionless state - the phenomenon of imaginary death (catalepsy, or thanatosis). Surrounded by burning coals, the scorpion, of course, rushes about in search of a way out, takes a threatening pose, wags its "tail", and then suddenly becomes motionless. This picture is mistaken for "suicide". But after a while, such a scorpion "comes to life", unless it is baked from the heat.

Equally unfounded is the rather widespread opinion that a scorpion at night specifically looks for a sleeping person in order to sting him. Where there are many scorpions, on hot nights, making their hunting walks, they often visit dwellings and can climb onto the bed. If a sleeping person crushes a scorpion or touches it, then the scorpion can strike with its "tail", but of course there is no special search for a person here.

A scorpion thrust is a means of attack and defense. On small invertebrates, which usually serve as food for a scorpion, the poison acts almost instantly: the animal immediately stops moving. But larger centipedes and insects do not die immediately and after the injection they live for a day or two; there are also insects which, apparently, are generally insensitive to the poison of scorpions. For small mammals, scorpion venom is mostly fatal. The poisonousness of different types of scorpions is very different. For humans, a scorpion injection is usually not fatal, but a number of cases with very serious consequences are known. With the injection, pain appears, followed by swelling of the stung site. In severe poisoning, the tumor can take on a phlegmonous character. After the injection, general symptoms appear: weakness, drowsiness, convulsions, rapid shallow breathing, pulse up to 140 per minute, chills, and sometimes a temperature reaction. Usually in a day or two, these phenomena disappear, but they can be delayed. Children are more susceptible to the effects of scorpion venom. Selected fatalities have been reported.

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

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

Detachment Solpugida (solpugi, or phalanx)

Their body is more dissected than that of scorpions: not only the abdomen, but also the cephalothorax is partially segmented. Chelicerae are adapted for seizing and killing prey. Pedipalps look like walking legs, as a result of which solpugs give the impression of decapods. Breathe with trachea.

Distributed in warm countries. Within our country, they are found in the Crimea, the Caucasus, Kazakhstan and Central Asia. Predators. When attacking a person, the salpuga bites through his skin and mechanically infects the wound with contaminated chelicera. When bitten, there is a sharp pain, the bitten area becomes inflamed and swollen. However, attempts to find the poisonous glands ended in failure. The consequences of a bite are caused by the introduction of an 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-like chelicerae; the duct of the poisonous gland opens in them. The pedipalps act as mouth limbs. Spiders breathe with the lungs, and some species breathe with the lungs and trachea.

The order of spiders includes more than 15,000 species. Distributed almost everywhere. Spiders are predators. They feed on insects, which they catch in their snares. Large tropical spider - tarantula - attacks birds. Most species are useful as 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 inhabits the south of the Asian and European parts of the USSR in clay-solonetz and clay-sandy steppes, as well as on wastelands, virgin lands and arable fields. The female builds snares 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 its bites. Sheep and pigs are immune to karakurt poison.

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 entire body. There is no tumor at the site of the bite. The patient is restless, experiences a feeling of fear, dizziness, headache. Cold sweat appears on the face. The skin is cold, bluish in color. Later, vomiting, trembling, bone pains appear. The patient rushes about in bed, at times falls into a state of numbness. Recovery comes slowly, after 2-3 weeks. Weakness remains for 1-2 months. In case of severe poisoning, death occurs after 1-2 days.

Order Acarina (ticks)

Includes small, sometimes even microscopic (from 0.1 to 10 mm) arachnids, usually with an undivided and non-segmented body; the cephalothorax is fused with the abdomen; less often the abdomen is dissected. Chitin is leathery, easily extensible, but some parts of it are compacted (shields). The shape and nature of the location of the scutes 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 oral apparatus designed to pierce the host's skin and feed 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 with the body.

The digestive system of blood-sucking forms is highly ramified, especially in females. The alimentary canal is characterized by the presence of blind outgrowths; they serve as a reservoir for ingested food. Excretory organs - Malpighian vessels. Respiratory organs - trachea. There is one pair of stigmas located either at the base of the chelicerae or at the base of the legs. The stigmas are found on a small shield (peritreme).

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

Ticks are dioecious. The genital opening is located between the bases of a particular 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 eight-legged nymph. Unlike an adult tick, the nymph has an underdeveloped reproductive apparatus; the external genital opening, as a rule, is not present. There can be several nymphal stages. At the last molt, the nymph turns into a sexually mature form - an imago.

Life cycle... Development, unlike other arachnids, occurs with metamorphosis, including the egg, larva, nymph and imago (sexually 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 trachea (stigmas appear), but does not have a genital opening. There can be several nymphal stages. After molting, the nymph turns into an imago. Most of the ticks that are of medical importance are blood-sucking. Mammals, birds and reptiles serve as hosts for ticks.

Distinguish between one-, two- and three-hosted ticks. In the same owner, all stages of development take place on the same owner. With a two-host type of development, the larva and the nymph feed on one host, and the imaginal form - on the other. In three-host ticks (taiga tick), each stage looks for a new host. In the latter case, development can be extended over a long period, for example, in a taiga tick, up to 5 years.

Together with the host's blood, pathogens of various diseases penetrate into the body of the flare, which, when switching to another host, can be transmitted to it, which contributes to the circulation of pathogens. The life span 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 the itch mite of the acariform family.

Ixodid ticks (Ixodidae)

They are of interest as a natural reservoir and carriers of a number of serious diseases: tick-borne encephalitis, tick-borne typhus, tularemia, hemorrhagic fevers, etc.

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

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

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

Argasidae

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

Ornithodorus tick (Ornithodorus papillipes) is a village tick - a blood-sucking tick, a carrier of pathogens of tick-borne relapsing fever (tick-borne recurrence). The body is dark gray, up to 8.5 mm long. Unlike ixodids, they do not have scutes. The lateral edges in the middle part of the body are almost parallel to each other, the presence of a marginal welt is characteristic. The chitinous cover of hungry ticks lies in folds. The totality of the oral organs and the integuments adjacent to them forms the so-called "head". It is relatively small, located in the anterior part of the body on the ventral side and is not visible from the dorsal side. No eyes. On the midline, the body, behind the first pair of legs, is the genital opening, and slightly behind from the middle of the body is the anus.

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

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

The body is broadly 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 setae. The legs are greatly shortened, which is associated with the intradermal lifestyle. Two pairs of legs are located on the sides of the mouth apparatus, two are assigned to the posterior end of the body. No eyes. Breathing occurs through the surface of the body.

The entire period of development from laying eggs to the sexually mature form lasts 9-12 days. An adult tick lives for about 1.5 months.

Mites can affect any part of the skin, but most often they are found on the dorsum of the hands, in the interdigital spaces, armpits, and perineum. Moves are visible on the skin in the form of straight or sinuous lines of a whitish-dirty color.

Prophylaxis... Isolation and treatment of people with scabies; disinsection of clothing and items that they used; fighting scabies of farm animals, keeping the body and home clean.

• Class Arachnoidea (arachnids)

Respiratory system of spiders

Robert Gale Breen III

Southwestern College, Carlsbad, New Mexico, USA

Breathing, or gas exchange of oxygen and carbon dioxide, in spiders is often not entirely clear even to specialists. Many arachnologists, myself included, have studied various areas of entomology. Typically, courses in arthropod physiology focus on insects. The most significant difference in the respiratory system of spiders and insects is that their blood or hemolymph does not play any role in the respiration of insects, whereas in spiders it is a direct participant in the process.

Breathing insects

The exchange of oxygen and carbon dioxide in insects reaches perfection largely due to the complex system of air tubes that make up the trachea and smaller tracheoles. Air tubes penetrate the entire body in close contact with the inner tissues of the insect. For gas exchange between the tissues and the air tubes of the insect, hemolymph is not needed. This becomes clear by the example of the behavior of certain insects, say, some species of grasshoppers. As the grasshopper moves, blood presumably circulates throughout the body as the heart stops. The blood pressure caused by movement is sufficient for the hemolymph to perform its functions, which are more in the distribution of nutrients, water and the excretion of waste substances (a kind of equivalent to the mammalian kidney). The heart begins to beat again when the insect stops moving.

This is not the case with spiders, although it seems logical that spiders should do this in a similar way, at least for those with trachea.

Respiratory systems of spiders

Spiders have at least five different types of respiratory systems, depending on the taxonometric group and who you are talking with about it:

1) The only pair of book lungs, like haymakers Pholcidae;

2) Two pairs of book lungs - at the suborder Mesothelae and the vast majority of migalomorphic spiders (including tarantulas);

3) A pair of book lungs and a pair of tubular tracheas, such as in weaver spiders, wolves, and most spider species.

4) A pair of tubular tracheas and a pair of sieve tracheas (or two pairs of tubular tracheas, if you are one of those who are sure that the differences between tubular and sieve tracheas are not enough to distinguish them into separate species), as in a small family Caponiidae.

5) A single pair of sieve tracheas (or for some tubular tracheas), as in a small family Symphytognathidae.

Spider blood

Oxygen and carbon dioxide are carried along the hemolymph by the respiratory pigment protein - hemocyanin. Although hemocyanin chemically resembles vertebrate hemoglobin, unlike the latter, it contains two copper atoms, which gives spider blood a bluish tint. Hemocyanin is not as effective at binding gases as hemoglobin, but spiders are quite capable of it.

As shown in the above image of the cephalothorax spider, the complex system of arteries extending to the legs and head region can be considered a predominantly closed system (according to Felix, 1996).

Spider trachea

Tracheal tubes penetrate the body (or parts of it, depending on the species) and end near the tissues. Yet this contact is not close enough for them to supply oxygen and remove carbon dioxide from the body on their own, as it does in insects. Instead, the hemocyanin pigments have to pick up oxygen from the ends of the breathing tubes and carry it on, allowing the carbon dioxide back into the breathing tubes. Tubular trachea usually have one (rarely two) orifices (called spiracles or stigma), most of which extend to the underside of the abdomen, next to the spinning appendages.

Book lungs

The pulmonary slits, or book lungs (in some species, the pulmonary slits have different openings that can widen or narrow depending on oxygen demand) are located in front of the lower abdomen, and the cavity behind the opening is stretched internally to accommodate many leaf-like air pockets of the book lung. The book lung is literally stuffed with air pockets covered with extremely thin cuticles that allow gas exchange by simple diffusion while blood flows through it. Tooth formations cover most of the surface of the book lungs from the side of the hemolymph flow to prevent collapse.

Breath of tarantulas

Since tarantulas are large and easier to study, many physiologists, when considering the mechanism of respiration of spiders, stop at them. The geographic habitat of the studied species is rarely specified; it can be assumed that most of them are from the United States. Almost everywhere the taxonomy of tarantulas is not taken into account. Only rarely do physiologists recruit a competent spider taxonomist. More often than not, they believe anyone who says they can identify test species. Even the most famous physiologists, including R.F. Felix, the author of the only widely published, but alas, not the most accurate book on spider biology.

Book lung, consisting of leaf-like intermittent air pockets with venous hemolymph flowing in one direction between the pockets. The layer of cells that isolate the air pockets from the hemolymph is so thin that it becomes possible to exchange gas through diffusion (according to Felix, 1996).

Several popular scientific names, both comical and sad for those who have at least some idea of ​​taxonomy, are most often found in this kind of articles. The first name is Dugesiella, most often referred to as Dugesiella hentzi. The genus Dugesiella disappeared into the Aphonopelma family a long time ago, and even if it was once classified as Aphonopelma hentzi (Girard), this cannot be taken as a credible identification. If a physiologist refers to D. hentzi or A. hentzi, it only means that someone has researched the Aphonopelma species, about which someone else has assumed that this species is from Texas.

It's sad, but the name still walks among physiologists Eurypelmacalifornicum... Genus Eurypelmawas dissolved in a different kind some time ago, and the viewAphonopelmacalifornicumwas invalidated. These spiders, perhaps, should be attributed toAphonopelmaeutylenum... When you hear these names, it only means that someone thinks that these species are native to California.

Some "scientific" names are really interspersed. In the 1970s, someone did research on a species calledEurypelmahelluo... Apparently, they were mistaken in assigning the species to wolf spiders.Lycosahelluo(now Hognahelluo(Valkenaer)) and changed the name of the genus to make it more similar to the name of the tarantula. God knows who these people investigated.

With varying success, physiologists have studied spiders, sometimes even tarantulas, and they have achieved some noteworthy results.

In the tarantulas tested, the first (front) pair of book lungs were found to control blood flow from the prosoma (cephalothorax), while the second pair of lungs controlled blood from the abdomen before it returned to the heart.

In insects, the heart is predominantly a simple tube that sucks blood from the abdomen, pushes it through the aorta and ejects it in the region of the head compartment of the insect's body. This is not the case with spiders; after blood has passed through the aorta, then through the isthmus between the cephalothorax and the abdomen and into the cephalothorax, its flow is divided into what can be defined as a closed system of arteries. It branches out and travels to specific areas of the head and legs. Other arteries, called the lateral abdominal arteries, originate from the heart on both sides and branch out within the abdomen. From the back of the heart to the arachnoid appendages stretches the so-called. abdominal artery.

When the tarantula heart contracts (systole), blood is pushed not only forward through the aorta into the cephalothorax, but also laterally through the lateral arteries and posteriorly down through the abdominal artery. A similar system works at different levels of blood pressure for the cephalothorax and abdomen. In conditions of increased activity, the blood pressure in the cephalothorax significantly exceeds the blood pressure in the abdomen. At the same time, the point is quickly reached when the hemolymph pressure in the cephalothorax becomes so great that the blood cannot be pushed from the abdomen into the cephalothorax through the aorta. When this happens, after a certain time, the spider suddenly stops.

Many of us have observed similar behavior in our pets. When the tarantula has an opportunity to escape, some of them immediately fly out of captivity with a bullet. If the tarantula does not reach a place where it feels safe enough quickly, it can run for a while and freeze unexpectedly, allowing the keeper to catch the fugitive. Most likely, it stops as a result of the fact that blood ceases to flow into the cephalothorax.

Physiologically, there are two main reasons for freezing spiders. The muscles that are so actively involved in the escape attempt are attached to the cephalothorax. This gives many reasons to believe that the muscles are simply running out of oxygen, and they stop working. Perhaps it is. And yet: why does this not lead to stuttering, twitching, or other manifestations of muscle weakness? However, this is not observed. The main consumer of oxygen in the cephalothorax of tarantulas is the brain. Maybe the muscles can work a little longer, but the spider's brain takes oxygen a drop earlier? A simple explanation may be that these manic runaways rushing to freedom simply lose consciousness.

The general circulatory system of the spider. When the heart contracts, blood moves not only forward along the aorta and through the pedicela into the cephalothorax, but also laterally through the abdominal arteries downward, and through the posterior artery behind the heart towards the arachnoid appendages (According to Felix, 1996)

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

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

Proud of her skill, Arachne declared that she surpassed Athena herself in weaving, who was considered the patroness of this craft. When Arachne decided to challenge the goddess to a competition, she gave her a chance to change her mind. Under the guise of an old woman, Athena came to the craftswoman and began to dissuade her from a reckless act, but Arachne insisted on her own. The competition took place: Athena weaved on the canvas the scene of her victory over Poseidon. Arachne depicted scenes from the adventures of Zeus. Athena recognized the skill of her rival, but was outraged by the freethinking of the plot (in her images there was disrespect for the gods) and destroyed the creation of Arachne. Athena tore the fabric and hit Arachne in the forehead with a Kitora beech shuttle. Unhappy Arachne could not bear the shame; she twisted a rope, made a noose and hanged herself. Athena freed Arachne from the noose and said to her:

Live, disobedient. But you will forever hang and weave forever, and this punishment will last in your offspring.

The structure of arachnids

(or chelicera)

Nervous system: subopharyngeal ganglion + brain + nerves.

Organs of touch- hairs on the body, on the legs, on almost all the bodies of arachnids, there are organs of smell and taste, but the most interesting thing in 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 short-sighted - they cannot see in the distance, but a large number of eyes provide a 360 ° view.

Reproductive system:

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

2) lay eggs, but there are many viviparous species.

Arachnids also include scorpions and ticks. Ticks are much simpler, they are one of the primitive representatives of the chelicerae.

The scientific name for the Class Arachnids is Arachnoids. It was appropriated in honor of the heroine of the ancient Greek myth, the skillful spinner Arachne. As punishment for her disobedience, the gods turned her into a spider.

Number, detachments

Arachnids are one of the oldest inhabitants of the Earth. According to scientists, they appeared 2-2.5 million years ago in the Carboniferous period of the Paleozoic. Paleozoologists count up to 2 thousand species of fossil arachnids. Over the long history of their existence, they have skillfully adapted to the terrestrial habitat. Representatives of the class are found on all continents (with the exception of Antarctica) and in all natural zones (with the exception of circumpolar ones).

There are over 112 thousand species of arachnids in the world. Three groups stand out among them:

• pincers (55 thousand species);
• spiders (44 thousand species);
• scorpions (750 species).

Common features

According to the presence of the front grasping jaws - chelicera, the class of Arachnids is also called Chelitsera. Arachnids, the general characteristics of which are presented below, have similar features:

• eight walking legs;
• perioral tentacles;
• tracheal - pulmonary respiration;
• lack of antennae;
• simple eye device.

At the same time, the features of the body structure of representatives of each order are visually noticeable:

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• ticks - a single torso;
• spiders - two parts (cephalothorax and abdomen);
• scorpions - 3 parts (cephalothorax, anterior abdomen, posterior abdomen).

The body length of different types of chelicerae varies from 0.1 mm to 30 cm.

The South American tarantula goliath spider reaches an average diameter of 10 cm, and the maximum diameter is 25-30 cm.

Variety of species

Spiders

Spiders are mainly land dwellers. They are predatory arthropods that hunt insects, beetles, as well as small birds and mammals. Hunting methods are different. A huge tarantula makes an ambush in an earthen hole and attacks oncoming insects. Spiders - side walkers are located in the corolla of flowers and wait for flying midges. House spiders spread their nets to catch flies. Jumping spiders are capable of grabbing prey while jumping.

In fresh waters, there is a silver spider, weaving an underwater house from a cobweb. In karakurt, dangerous with its deadly poison, the web resembles a hut. House arachnoids weave a network in the form of a funnel.

Certain species are capable of producing a poison that is highly toxic. For example, the karakurt living in the Crimea, the Caucasus and Central Asia has a poison 15 times stronger than that of a rattlesnake. An arthropod bite can be fatal if serum is not injected into a person in time.

Fig 1. Spider tarantula

Mites

Dangerous diseases, especially encephalitis, are transmitted through tick bites. Scabies itching gnaw through the subcutaneous passages and cause scabies. To prevent infection, you must follow the rules of hygiene, wash your hands thoroughly, and inspect your clothes and body after walking in the warm season. A tick that has sucked blood grows to the size of a pea. It is carefully removed by rotating movements using tweezers.

If the severed head of the tick remains in the wound, it will quickly fester.

Depending on the type of nutrition, ticks have mouth limbs of different structures:

• gnawing;
• piercing-sucking.

Development with metamorphosis is characteristic of ticks, which distinguishes them from other arachnoids. The insect goes through several stages in succession. First, the female lays eggs. A larva emerges from them, which has 3 pairs of limbs. After the first molt, the individual grows another pair of legs. After passing several molts, the larva transforms into an adult insect.

Fig 2. Appearance of the tick

Scorpions

Scorpions are found in areas with hot climates. They resemble miniature crayfish due to their claw-shaped legs. The size of scorpions is from 1.3 cm to 15 cm. Their bite is dangerous for small animals, and sometimes for humans.

The most poisonous Israeli scorpion lives in the north of Africa.

Fig 3. The appearance of a scorpion

Meaning

Arachnids take their place in the overall ecological system. They are beneficial by destroying many harmful insects (flies, aphids) and, in turn, are food for birds, amphibians, mammals.

You can make a message about the lifestyle of some members of the class in biology lessons. For example, make a short report on the topic: "Encephalitis mite is a carrier of a dangerous disease." The description includes answers to the questions: where do ticks live, how does development and reproduction take place, what harm do they bring?

In the books for grade 1, you can find out what the species are called, how many there are, which animals belong to different groups.

What have we learned?

Arachnids or chelicerae are arthropods of land animals. Plays an important role in the food chain. They differ in a variety of species. Some are dangerous to humans and harm the economy.

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