What sense organs does a spider have? Sense organs of arachnids. Classification and phylogeny

106. Look at the drawing. Write the names of the science body parts indicated by numbers.

107. Describe the class of arachnids.
The class of arachnids unites over 36 thousand species of air-breathing arthropods. Arachnids are eight-legged arthropods. The body of an arachnid most often consists of a cephalothorax, bearing limbs, and an abdomen devoid of legs (spiders), or a head with jaws and claws, a cephalothorax and abdomen (ticks). Among arachnids, predators predominate, sucking out the liquid and liquefied contents of their victims (extraintestinal digestion). Ticks have adapted to feed on a variety of animal foods and plant origin. They breathe with the lungs or with the help of tracheas. The organs of excretion are the Malpighian vessels. The sense organs are varied: simple eyes, organs of smell, taste, touch, chemical sense, etc. All arachnids are dioecious. Fertilization is internal, development is direct (except for mites that have a larval stage).

108. Study the table “Class Arachnids. The structure of a spider." Color the spider's internal organ systems with colored pencils and label them. What functions do they perform?

Functions of organ systems:
Circulatory – blood circulation in the body, transport of nutrients.
Respiratory – gas exchange.
Digestive – digestion of food.
Nervous – regulation of life activity.
Sexual – reproduction of one’s own kind.

109. What is a web?
The web is the secretion of the arachnoid glands, which soon after secretion hardens in the form of threads. Chemically it is a protein. The threads are strong, some spiders weave catching nets from them, some use them for egg cocoons.

110. What features of the structure and behavior of the cross spider are associated with a terrestrial lifestyle?
The cross spider leads a terrestrial lifestyle. On the dorsal surface of its abdomen it has a pattern in the form of a cross. The body is covered with a layer of wax, which prevents water evaporation. The cephalothorax is covered with a thick and durable cephalothorax shield, in the front part of which there are eight simple eyes and oral organs, namely: the first pair are jaws, the second pair are legicles, on which there are sensitive hairs that are part of the organs of touch.
Spiders feed on insects and catch prey using webs. The spider bites the prey caught in the net and wraps it in web threads and digests it with the help of digestive enzymes. In spiders, preliminary digestion of food occurs outside the body.
In the front of the abdomen lies a pair of pulmonary sacs. In addition, the spider has two bundles of trachea in its abdomen, opening outward with a common respiratory opening.
Female cross spider larger than the male. In autumn, she lays eggs in a cocoon woven from a thin silky web. She weaves a cocoon in various secluded places - under the bark of stumps, under stones. By winter, the female spider dies, and the eggs overwinter in a warm cocoon. In the spring, young spiders emerge from them and become sexually mature the following year.

The characteristic structural features of arachnids are associated with their adaptability to life on land. Representatives of the class belong to land arthropods with eight pairs of limbs.

Representatives of arachnids have a body consisting of two sections. Moreover, its connection can be represented either by a thin partition or by a tight fastening. Representatives of this class do not have antennae.

The front part of the body contains limbs such as mouth parts and walking legs. Arachnids breathe using the lungs and trachea. simple. Some species are completely absent.

The nervous system is represented by nerve ganglia. The skin is hard, three-layered. There is a brain consisting of a front and a back brain. represented by the heart in the form of a tube and an open circulatory system. Arachnids are dioecious individuals.

Ecology of arachnids

The first insects to adapt to life on land were representatives of arachnids. They can lead both day and night active lifestyles.

Class Overview

Zoological scientists conventionally divide the class of arachnids into several orders. The main ones are scorpions, ticks, salpugs.

Scorpio Squad

Scorpio is an atypical spider, which is why it is separated into a separate order.

Arachnids of the “scorpion” type are small in size, no more than 20 centimeters. Its body consists of three well-defined sections. On the front there are two large eyes and up to five pairs of small lateral ones. The scorpion's body ends with a tail, in which a poisonous gland is located.

The body is covered with a thick and tough covering. A scorpion breathes using its lungs. They chose an area with a warm and hot climate as their habitat. In this case, scorpions are divided into two subspecies: those living in humid areas and those living in dry places. The attitude towards air temperature is also ambiguous: there are subspecies that prefer warm climates and high temperature, but some tolerate the cold well.

Scorpions obtain food in the dark and are more active during the hot season. The scorpion detects its prey by detecting the oscillatory movements of the potential victim.

Reproduction of scorpions

If we talk about which arachnids are viviparous, then it is scorpions for the most part that bear offspring. However, there are also oviparous ones. The growth of embryos located in the female’s body is a rather slow process, and pregnancy can last more than a year.

Babies are born already in a shell, and after birth they immediately attach themselves to the mother’s body using special suction cups. After about 10 days, the brood breaks away from the mother and begins to exist separately. The period of maturation in small individuals lasts about one and a half years.

The scorpion's poisonous tail is the organ of attack and defense. True, the tail does not always save its owner from predators. Some animals know how to avoid blows, and then the predator itself becomes food. But if the scorpion does sting the victim, then many small invertebrates die almost immediately from the sting. Larger animals can survive for a day or two.

For humans, scorpion aggression does not end in death, but modern medicine has recorded cases with very serious consequences. A swelling appears at the site of the lesion, which can be quite painful, and the person himself becomes more lethargic and may experience attacks of tachycardia. After a couple of days, everything goes away, but in some cases the symptoms persist for a longer period.

Children are more sensitive to the effects of scorpion venom. Cases have also been recorded among children fatal outcome. In any case, you should immediately seek qualified help from

Solpuga squad

Recall that we are considering the Arachnida class. Representatives of this order are widespread in countries with warm climate. For example, very often they can be found in the Crimea.

They differ from scorpions in their large body dismemberment. At the same time, the hard jaws of the salpug perform the function of catching and killing the victim.

Salpugs do not have poisonous glands. When attacking a person, salpugs damage the skin with their sharp jaws. Quite often, at the same time as the bite, the wound becomes infected. The consequences are: inflammation of the skin at the site of injury, accompanied by pain.

This was a characteristic of arachnids, the salpuga order, and now let’s look at the next order.

Spiders

This is the most numerous order, numbering more than 20 thousand species.

Representatives differ different types from each other solely in the form of a web. Common house spiders, which can be found in almost any home, weave webs shaped like a funnel. Poisonous representatives of the class create a web in the form of a rare hut.

Some spiders do not weave webs at all, but lie in wait for their prey, sitting on flowers. In this case, the colors of the insects are adapted to the shade of the plant.

There are also spiders in nature that hunt for prey by simply jumping on it. There is another, special category of spiders. They never stay in one place, but constantly move in search of prey. They are called wolf spiders. But there are also hunters who attack from ambush, in particular, the tarantula.

Spider structure

The body consists of two sections connected by a septum. In the front part of the body there are eyes, under them there are hard jaws, inside of which there is a special channel. It is through this that the poison from the glands enters the body of the caught insect.

The sensory organs are the tentacles. The body of the spider is covered with a light but durable cover, which, as it grows, is shed by the spider, to be later replaced by another.

On the abdomen there are small growths-glands that produce cobwebs. Initially, the threads are liquid, but quickly become solid.

The spider's digestive system is quite unusual. Having caught the victim, he injects poison into it, with which he first kills. Then gastric juice enters the victim’s body, completely dissolving the insides of the captured insect. Later, the spider simply sucks out the resulting liquid, leaving only the shell.

Breathing is carried out using the lungs and trachea, located in the front and back of the abdomen.

Circulatory system, like all representatives of arachnids, consists of a heart tube and open circulation. The spider's nervous system is represented by nerve ganglia.

Spiders reproduce by internal fertilization. Females lay eggs. Subsequently, small spiders appear from them.

Squad Ticks

The order Mites includes small and microscopic arachnids with an undivided body. All ticks have twelve limbs. These representatives of arachnids feed on both solid and liquid food. It all depends on the species.

The digestive system of ticks is branched. There are also organs excretory system. The nervous system is represented by the nerve chain and the brain.

The oral apparatus, like all representatives of the class, is located in front of the body and is represented by a proboscis and strong sharp teeth. With their help, the tick is held on the victim's body until it is completely saturated.

It was brief description some representatives of the class Arachnids.

We hope you find the information useful.

, pedipalps and four pairs of walking legs. Representatives of different orders have different structures, development and functions of the limbs of the prosoma. In particular, pedipalps can be used as sensory appendages, serve to capture prey (scorpions), and act as copulatory organs (spiders). In a number of representatives, one of the pairs of walking legs is not used for movement and takes on the functions of the organs of touch. The prosoma segments are tightly connected to each other; in some representatives, their dorsal walls (tergites) merge with each other to form a carapace. In salpugs, the fused tergites of the segments form three shields: propeltidium, mesopeltidium and metapeltidium.

Veils

In arachnids, they bear a relatively thin chitinous cuticle, underneath which lies the hypodermis and basement membrane. The cuticle protects the body from loss of moisture through evaporation, which is why arachnids inhabited the driest areas of the globe. The strength of the cuticle is given by proteins encrusting chitin.

Respiratory organs

Genitals

All arachnids are dioecious and in most cases exhibit pronounced sexual dimorphism. The genital openings are located on the second abdominal segment (VIII body segment). Most lay eggs, but some orders are viviparous (scorpions, bichorchis, flagipes).

Special bodies

Some units have special bodies.

• venom-carrying apparatus - scorpions and spiders
• spinning apparatus - spiders and false scorpions.

Habitat

Spider from the genus Dolomedes

Nutrition

Arachnids are almost exclusively carnivores, with only a few mites and jumping spiders feeding on plant matter. All spiders are predators. They feed mainly on insects and other small arthropods. The spider grabs the caught prey with its tentacles, bites it with its hook-shaped jaws, and injects poison and digestive juice into the wound. After about an hour, the spider uses a sucking stomach to suck out the entire contents of the prey, of which only the chitinous shell remains. This type of digestion is called extraintestinal.

Spreading

Arachnids are ubiquitous.

Representatives of this class are among the oldest land animals, known since the Silurian period.

Nowadays, some orders are distributed exclusively in tropical and subtropical zones, such as flagipes. Scorpions and bihorchids also live in the temperate zone; spiders, harvestmen and ticks are also found in significant numbers in polar countries.

Classification and phylogeny

Origin

Currently, the relationship between arachnids and horseshoe crabs has been confirmed by morphological and molecular biological data. The similarity with insects in the structure of the organs of excretion (Malpighian vessels) and respiration (trachea) is recognized as convergent.

Modern groups

One of the extinct groups of arachnids is Anthracomarti, whose representatives, like harvestmen, had a dissected 4-9-segmented abdomen and a well-separated cephalothorax, reminiscent of phrynes, but differed from them in pedipalps, devoid of claws; their remains were found only in coal deposits.

Notes

See also

Literature

• Animal life. Encyclopedia in six volumes. Volume 3. (volume dedicated to land arthropods). General edition by Corresponding Member of the USSR Academy of Sciences, Professor L. A. Zenkevich. - Moscow: Education, 1969. - 576 p.

Links

• // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional ones). - St. Petersburg. , 1890-1907.
• Arachnology site, links to other 2500 sites related to spiders and arachnids. Archived from the original on November 28, 2012.

Modern Arthropods, subphyla, superclasses and classes
Cheliceraceae ( Chelicerata)
Centipedes ( Myriapoda)
Hexapods ( Hexapoda)
Crustaceans ( Crustacea)

Wikimedia Foundation. 2010.

There are at least 12 orders, the most important of which are the orders Spiders, Scorpions, False Scorpions, Salpugs, Haymakers, Ticks.

Arachnids are distinguished by the fact that they lack antennae (antennales), and their mouth is surrounded by two pairs of peculiar limbs - chelicerae And maxillary, which in Arachnids are called pedipalps. The body is divided into a cephalothorax and abdomen, but in ticks all sections are fused. walking legs four pairs.

Cross spiders These are ordinary representatives of the Arachnida class. Cross spiders is the collective name of several biological species of the genus Araneus of the family Orb-weaving spiders of the order Spiders. Cross spiders 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 using a very complex, vertically positioned wheel-shaped fishing net(hence the name of the family - Orb-weaving spiders) . The spinning apparatus of spiders, which ensures the production of such a complex structure, consists of external formations - spider warts– and from internal organs – arachnoid glands. From the spider's warts a drop of sticky liquid is released, which, when the spider moves, is pulled out into the thinnest thread. These threads quickly thicken in air, turning into strong spider thread. The web consists mainly of protein fibroin. In terms of its chemical composition, the web of spiders is close to the silk of silkworm caterpillars, but is stronger and more elastic. The breaking load for spider web is 40-261 kg per 1 sq mm of thread cross-section, and for silk it is only 33-43 kg per sq mm of thread cross-section.

To weave its hunting net, the Cross Spider first stretches especially strong threads in several convenient places, forming a supporting frame for 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, draws a strong vertical thread. Then from the middle of this thread, as if from the center, the spider draws radial threads in all directions, like the spokes of a wheel. This is the basis of the entire web. Then the spider begins to weave from the center spiral threads, attaching them to each radial thread with a drop of adhesive. In the middle of the web, where the spider itself then sits, the spiral threads are dry. Other spiral threads are sticky. Insects that fly onto the net stick to them with their wings and paws. The spider itself either hangs head down in the center of the web, or hides in

Class Arachnids Cross spider

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

When a fly or other insect gets into the net, the spider, sensing the trembling of the signal thread, rushes out of its ambush. By inserting chelicerae containing poison into the victim with its claws, the spider kills the victim and secretes digestive juices into its body. After this, he entangles the fly or other insect with a web and leaves it for a while.

Under the influence of secreted digestive juices internal organs victims are quickly digested. After some time, the spider returns to the victim and sucks out all the nutrients from it. All that remains of the insect in the web is an empty chitinous cover.

Making a fishing net is a series of interconnected unconscious actions. The ability to perform such actions is instinctive and is inherited. It is easy to verify this by observing the behavior of young spiders: when they emerge from the eggs, no one teaches them how to weave a trapping net, the spiders immediately weave their web very skillfully.

In addition to the wheel-shaped catching net, other species of spiders have nets in the form of a random interweaving of threads, nets in the form of a hammock or canopy, funnel-shaped nets and other types of catching nets. The trapping web of spiders is a kind of adaptation outside the body.

It must be said that not all types of spiders weave trapping webs. Some actively search for and catch prey, others lie in wait for it in ambush. But all spiders have the ability to secrete webs, and all spiders make webs egg cocoon And spermatic mesh.

External structure. The body of the Cross Spider is divided into cephalothorax And abdomen, which connects to the cephalothorax with a thin movable stalk. There are 6 pairs of limbs on the cephalothorax.

The first pair of limbs - chelicerae, which surround the mouth and serve to capture and pierce prey. Chelicerae consist of two segments, the final segment has the appearance of curved claws At the base of the chelicerae are poison glands, the ducts of which open at the tips of the claws. Spiders use chelicerae to pierce the integument of their victims and inject poison into the wound. Spider venom has a nerve-paralytic effect. In some species, for example, Karakurt, in the so-called tropical black widow, a poison so strong that it can kill

Class Arachnids Cross spider

even a large mammal (instantly!).

Second pair of cephalothoracic limbs - pedipalps have the appearance of jointed limbs (they look like short legs sticking forward). The function of the pedipalps is to palpate and hold prey. In sexually mature males, the terminal segment of the pedipalp is formed copulative apparatus, which the male fills with sperm before mating. During copulation, the male, using the copulatory apparatus, injects sperm into the spermatheca of the female. The structure of the copulatory 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, calyxes, shins, pretarsus And paws, armed with claws.

Arachnids have no antennae. On the front part of the cephalothorax of the Cross Spider there are two rows of eight simple eyes. Other types of eyes may have three pairs, or even one pair.

Abdomen in spiders it is not segmented and does not have true limbs. On the abdomen there is pair of lung sacs, two beams trachea and three couples arachnoid warts. The web warts of the Cross Spider consist of a huge number (about 1000) arachnoid glands, which produce various types of web - dry, wet, sticky (at least seven varieties for various purposes). Different types webs perform various functions: one is for catching prey, the other is for building a home, the third is used in making a cocoon. Young spiders also settle on webs of a special property.

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

Covers of the body. The body is covered with chitinized cuticle. The cuticle protects the body from external influences. The most superficial layer is called epicuticle and it is formed by fat-like substances, so the covers of spiders are not permeable to either water or gases. This allowed spiders to populate the driest areas of the globe. The cuticle simultaneously performs the function

Class Arachnids Cross spider

outdoor skeleton: Serves as a site for muscle attachment. Spiders molt periodically, i.e. they shed the cuticle.

Musculature arachnids consists of striated fibers that form powerful muscle bundles, i.e. the muscles are presented in separate bundles, and not in a bag like in worms.

Body cavity. The body cavity of Arachnids is mixed - myxocoel.

Digestive system typical, consists of front, average And rear intestines. The foregut is presented mouth, throat, short esophagus And stomach. The mouth is surrounded by chelicerae and pedipalps, with which spiders grab and hold prey. The pharynx is equipped with strong muscles for absorbing food gruel. Ducts open into the foregut salivary glands, the secretion of which 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 pulp, which is absorbed by the spider. In the stomach, and then in the midgut, food is absorbed. The midgut has long caecum lateral protrusions, increasing the suction area and serving as a place for temporary storage of food mass. Channels open here liver. It secretes digestive enzymes and also ensures the absorption of nutrients. Intracellular digestion occurs in liver cells. At the border of the middle and posterior sections, the excretory organs flow into the intestine - Malpighians vessels. The hindgut ends anal hole, located at the posterior end of the abdomen above the arachnoid warts.

Respiratory system. Some arachnid organs breathing represented pulmonary bags, others tracheal system, still others have both at the same time. Some small arachnids, including some ticks, do not have respiratory organs; breathing occurs through thin integuments. The 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 arachnids sank inside the body and formed cavities with pulmonary leaves. The tracheal system arose independently and later than the pulmonary sacs, as organs more adapted to air breathing. Tracheas are deep invaginations of the cuticle into the body. The tracheal system is perfectly developed in Insects.

Class Arachnids Cross spider

In the Cross Spider, the respiratory organs are represented by a pair lung sacs, forming leaf-like folds on the ventral side of the abdomen, and two bundles trachea that open spiracles also on the underside of the abdomen.

Blood system open, consists of hearts, located on the dorsal side of the abdomen, and several large blood vessels extending from it vessels. The heart has 3 pairs of ostia (holes). Departs from the anterior end of the heart front aorta, disintegrating into arteries. The terminal branches of the arteries pour out hemolymph(this is the name of blood in all arthropods) into the system cavities located between the internal organs. Hemolymph washes all internal organs, delivering nutrients and oxygen to them. Next, the hemolymph washes the lung sacs - gas exchange occurs, and from there it enters the pericardium, and then through ostia- in the heart. The hemolymph of arachnids contains a blue respiratory pigment - hemocyanin, containing copper. Pouring into the secondary body cavity, the hemolymph mixes with the secondary cavity fluid, which is why they say that arthropods have a mixed body cavity - mixocoel.

excretory system in arachnids it is represented Malpighian vessels, which open into the intestine between the midgut and hindgut. Malpighian vessels, or tubules, are blind protrusions of the intestine that ensure the absorption of metabolic products from the body cavity. In addition to the Malpighian vessels, some arachnids also have coxal glands- paired sac-like formations lying in the cephalothorax. Convoluted canals extend from the coxal glands, ending urinary bubbles And output ducts, which open at the base of the walking limbs (the first segment of the walking legs is called coxa, hence the name coxal glands). The Cross Spider has both coxal glands and Malpighian vessels.

Nervous system. Like all Arthropods, Arachnids nervous system - ladder type. But in Arachnids there was a further concentration of the nervous system. A pair of suprapharyngeal nerve ganglia is called the “brain” in Arachnids. It innervates (controls) the eyes, chelicerae and pedipalps. All the cephalothoracic nerve ganglia of the nerve chain merged into one large nerve ganglion located under the esophagus. All the abdominal nerve ganglia of the nerve chain also merged into one large abdominal nerve ganglion.

Of all the sense organs, the most important for spiders is touch. Numerous tactile hairs - trichobothria- scattered in large quantities over the surface of the body, especially on the pedipalps and walking legs.

Class Arachnids Cross spider

Each hair is movably attached to the bottom of a special pit in the integument and connected to a group of sensitive cells that are located at its base. The hair perceives the slightest vibrations in the air or 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, and others - perceive sound signals.

The organs of vision are presented with simple eyes, found in most arachnids. Spiders most often have 8 eyes. Spiders are myopic, their eyes perceive only light and shadow, the outlines of objects, but details and color are not available to them. There are organs of balance - statocysts.

Reproduction And development. Arachnids dioecious. Fertilization internal. Most arachnids lay eggs, but some arachnids exhibit viviparity. Development without metamorphosis.

The Cross Spider has a well-defined sexual dimorphism: the female has a large abdomen, and in mature males they develop on the pedipalps copulative organs. In each species of spider, the male's copulatory organs fit the female's epigyne like a key to a lock, and the structure of the male's copulatory organs and the female's epigyne is species-specific.

Mating in Cross Spiders occurs at the end of summer. Sexually mature males do not weave trapping nets. They wander in search of females' networks. Having discovered the fishing net of a sexually mature female, the male somewhere to the side on the ground, or on some branch, or on a leaf, weaves a small sperm mesh in the form of a hammock. The male squeezes a drop onto this mesh 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 droplet into the pedipalps (like a syringe) and begins to seduce the female. The spider's eyesight is poor, so the male needs to be very careful so that the female does not mistake him for prey. To do this, the male, having caught some insect, wraps it in a web and presents this unique 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 is looking at the presented gift, the male quickly climbs onto the female, applies his pedipalps with sperm to the female’s genital opening and

• Class Arachnids Cross spider

  carries out copulation. The female at this moment is good-natured and relaxed. But, immediately after mating, the male must quickly leave, since the behavior of the spider after copulation changes dramatically: it becomes aggressive and very active. Therefore, slow 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 has completed his biological function.) This happens in almost all types of spiders. Therefore, in studies, females are most often found, while males are rare.

  After copulation, the female continues to actively feed. In autumn, the female makes from a special web cocoon, in which it 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. The eggs of Cross Spiders overwinter. In the spring, young spiders emerge from the eggs and begin an independent life. Molting several times, the spiders grow and by the end of summer they reach sexual maturity and begin to reproduce.

Meaning. The role of spiders in nature is great. They act as second-order consumers in the ecosystem structure (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

Name the classification of the phylum Arthropods.

What is the systematic position of the Cross Spider?

Where do Cross Spiders live?

What body shape do Cross Spiders have?

What is a spider's body covered with?

What body cavity is characteristic of a spider?

What is the structure of the spider's digestive system?

What are the features of digestion in spiders?

What is the structure of the spider's circulatory system?

How does a spider breathe?

What is the structure of the spider's excretory system?

What is the structure of the spider's nervous system?

What structure does it have? reproductive system spider?

How does the Cross Spider reproduce?

What is the significance of spiders?

Class Arachnids Cross spider

Rice. Cross spider: 1 - female, 2 - male and a wheel-shaped trapping net.

Rice. A cross spider weaves a trapping web

Class Arachnids Cross spider

Rice. Internal structure of the Cross Spider.

1 - poisonous glands; 2 - pharynx; 3 - blind outgrowths of the intestine; 4 - Malpighian vessels; 5 - heart; 6 - pulmonary sac; 7 - ovary; 8 - oviduct; 9 - arachnoid glands; 10 - pericardium; 11 - ostia in the heart.

The characteristic structural features 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, fused in others. The structure and distribution of the limbs are characteristic. The antennae are not developed. The anterior pair of limbs of the cephalothorax are located in front of the mouth and are called chelicerae. These are usually powerful hooks used to capture and kill prey. The second pair of limbs are the jaws, or pedipalps. 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 thoracic part of the cephalothorax. The abdomen often bears various paired appendages (arachnoid warts, organs of the external genitalia, etc.), considered as highly modified limbs. There are no real limbs on the abdomen; they are reduced.

E C O L O G Y A P A U C O O O R S Arachnids are the first terrestrial animals to master land in the Silurian period and switch to air breathing. Lead daytime or night look life. They live in forests, meadows, pastures, and desert sands. Some weave trapping nets, others attack prey. They feed on insects, but karakurts, scorpions and tarantulas bite humans and domestic animals (camels, horses), causing painful effects, sometimes fatal. Of particular danger are ticks - carriers of 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 chemicals, biological ones have practically not been developed.

Due to their terrestrial lifestyle, arachnids have developed atmospheric respiration organs. 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 to the outside with a slit-like hole, and inside is blocked by plates in which blood circulates. Here it is saturated with oxygen and delivers it to the tissues.

The trachea is a system of branching air tubes. They begin with respiratory openings, or spiracles, leading into the main tracheal trunks. The latter branch and form smaller and 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 1st-3rd pair of walking legs (coxal glands). They consist of a coelomic sac and a convoluted tubule, sometimes expanding to form the bladder. More common is a special type of excretory organs - the so-called Malpighian vessels. In arachnids, these are one or more pairs of thin tubes located in the body cavity and opening into the intestines. Excretion products enter them osmotically and are excreted into the hindgut.

The nervous system, like that of all arthropods, consists of the brain (suprapharyngeal ganglion), the peripharyngeal ring and the ventral nerve cord, the nodes of which often merge with each other. For example, in scorpions, all the ganglia of the thoracic segments are fused into one large node, followed by a chain of 7 abdominal ganglia. In spiders, all 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 surface of the body perceive mechanical and tactile stimulation. In small crevices of the cuticle there are chemical sense receptors.

Most arachnids lead a predatory lifestyle. A number of features of their structure are associated with this, in particular the presence of poisonous glands (their secretion kills prey), extraintestinal digestion (secrets of special “salivary” glands and liver are introduced into the body of killed prey, quickly break down its proteins, taking on the appearance of liquid gruel), powerful muscles pharynx, which acts as a pump drawing in semi-liquid food.

Venom glands in spiders open at the top of the pointed upper jaws, in scorpions - on the pointed last segment of the abdomen. Arachnoid glands are especially developed in spiders. They are located on the underside of the abdomen in three pairs of arachnoid warts. The arachnoid apparatus of cross spiders is especially complex (they have six types of arachnoid glands that secrete the finest threads of various types of web - dry, wet, sticky, etc.). Spiders use webs to make catching nets, living houses, egg cocoons, 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 sections of the body - protosoma (unsegmented cephalothorax), mesosoma (wide anterior abdomen) and metasoma (narrow tail-shaped posterior abdomen) - are well defined. The cephalothorax is solid, it has a pair of larger median eyes and up to 5 pairs of small lateral eyes. The abdomen is adjacent to the cephalothorax with a wide base, the pregenital (7th) segment is atrophied. The anterior section of the abdomen (mesosoma) is wider, its segments have separate tergites and sternites; modified abdominal limbs are represented by a complete set: genital operculum on the eighth segment, crest-shaped organs on the ninth, pulmonary sacs on the tenth to thirteenth. The segments of the posterior section (metasomes) are narrow cylindrical, the tergite and sternite of each segment are fused into a single sclerite ring; the first segment of the metasoma is conical. The metasoma ends in a swollen tail segment, which contains a poisonous gland, 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 tuberculate sculpture.

In appearance The most characteristic features are large pedipalps with claws and a segmented flexible metasoma (“tail”) with a poisonous apparatus at the end. The 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 towards the mouth. There are 4 pairs of walking legs. Breathing is carried out through leafy lungs.

Scorpios live in countries with warm or hot climates, and are found in the most various places habitat, from rain forests and littoral zones of sea coasts to barren rocky areas and sandy deserts. Some species are found in the mountains at an altitude of 3-4 thousand m above sea level.

It is customary to distinguish between hygrophilic species of scorpions, living in humid places, and xerophilic species, 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 loose bark, in the burrows of other animals, or burrow into the soil, so that even 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 living high in the mountains, as well as at the northern and southern borders of the scorpion distribution area, tolerate cold winters well in an inactive state. Some species are found in caves, but they are random newcomers. Scorpions are frequent visitors to human homes, but there are no real human cohabitants (synanthropes) among them.

Scorpio hunts at night and is especially active in hot weather. He walks slowly with his “tail” raised, his half-bent pedipalps with slightly open claws thrust forward. He moves by touch, main role in this case, protruding tactile hairs (trichobothria) of the pedipalps play. Scorpio reacts very sensitively to touching a moving object and either grabs it if it is suitable prey, or retreats, accepting threatening pose: It bends its tail sharply over its cephalothorax and swings it from side to side. Prey is grasped by the claws of the pedipalps and brought to the chelicerae. If it is small, it is immediately kneaded by the chelicerae and the contents are absorbed. If the prey resists, the scorpion stings it one or more times, immobilizing it and killing it with poison. Scorpions feed on live prey; their hunting objects are very diverse: spiders, harvestmen, millipedes, various insects and their larvae; there are known cases of eating small lizards and even mice. Scorpions can fast for a very long time; they can be kept without food for several months; there are known cases of fasting for up to a year and a half. Most species probably survive their entire lives without water, but some inhabitants of tropical rainforests drink water. When kept together in small cages, the scorpion often eats its fellow.

The biology of scorpion reproduction is peculiar. Mating is preceded by a "mating walk". The male and female cling together with their claws and, raising their “tails” vertically, walk together for many hours and even days. Usually the male, backing away, drags the more passive female with him. Then copulation occurs. In this case, the individuals hide in some kind of shelter, which the male, without letting go of the female, quickly clears with the help of his legs and “tail”. Fertilization is spermatophore. The individuals touch the ventral sides of the anterior sections of the abdomen, and the male introduces packets of sperm into the female’s genital tract, and then secretes a special secretion, which seals the female’s genital opening. It is believed that during mating, scallops - modified limbs of the ninth segment - play some role. They are equipped with numerous sense organs. At rest, the scallops are pressed to the abdomen; during mating, they protrude and oscillate. But they also protrude when the scorpion moves, and they are also credited with the role of balance organs and some other functions.

Scorpions are mostly viviparous; some species lay eggs in which the embryos are already developed, so that the young hatch soon. This phenomenon is called ovoviviparity. The development of embryos in the mother's body is long; from several months to a year or more. In some species, 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 the secretions of special glandular appendages of the ovary. There are from 5-6 to several dozen embryos, less often about a hundred. Small scorpions are born wrapped in an embryonic membrane, which is soon shed. They climb onto the mother's body and usually stay on her for 7-10 days. Scorpions of the first instar do not feed actively; they are whitish, with a smooth coat and sparse hairs; their paws 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 look for food on their own. After molting, the integument hardens and becomes colored, and claws appear on the paws. A Scorpio becomes an adult a year and a half after birth, making 7 molts during this time. Life expectancy is not precisely established, but it is usually at least several years. Meet interesting cases anomalies that arise in the embryonic development of scorpions, for example, doubling of the “tail”, and individuals: are viable and grow to an adult state (“two-tailed scorpion” is mentioned by the already famous Roman scientist Pliny the Elder in his “Natural History”, 1st century AD. ).

Hard coverings and a poisonous apparatus do not always save scorpions from their enemies. Large predatory centipedes, salpugs, some spiders, praying mantises, lizards, and birds cope with them. There are species of monkeys that feast on scorpions by carefully removing the “tail.” But worst enemy Scorpio man. Since ancient times, the scorpion has been an object of disgust and mystical horror, and, perhaps, there is no other arthropod that has given 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 the “transformation” of lead into gold, and in astrology, since the name of Scorpio is one of the zodiac constellations, and among Christians as a typical component of the “fauna” of the underworld. Interesting are the assurances that scorpions can end their lives by “suicide”: if you surround a scorpion with burning coals, then in order to avoid a painful death, it seems to kill itself with a sting. This opinion does not correspond to reality, but has a certain basis. The fact is that the scorpion, like some other arthropods, under the influence of strong stimuli can fall into 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, takes a threatening pose, swings its “tail”, and then suddenly becomes motionless. This picture is taken for “suicide”. But after a while such a scorpion “comes to life”, unless it is baked from the heat.

Equally unfounded is the fairly widespread belief that a scorpion at night specifically looks for a sleeping person in order to sting him. Where there are a lot of scorpions, on hot nights, during their hunting walks, they often visit homes and can climb onto the bed. If a sleeping person crushes a scorpion or touches it, then the scorpion can hit with its “tail”, but, of course, there is no special search for the person here.

The scorpion sting is a means of attack and defense. On small invertebrates, which usually serve as food for the scorpion, the poison acts almost instantly: the animal immediately stops moving. But larger centipedes and insects do not die immediately and live for a day or two after the injection; There are also insects that, apparently, are generally insensitive to the venom of scorpions. For small mammals, scorpion venom is mostly fatal. The toxicity of different types of scorpions varies greatly. For humans, a scorpion sting is usually not fatal, but there are a number of cases with very serious consequences. When an injection occurs, pain occurs, followed by swelling of the stung area. In severe poisoning, the tumor can become phlegmonous. After the injection they appear general symptoms: weakness, drowsiness, convulsions, rapid shallow breathing, pulse up to 140 per minute, chills, sometimes temperature reaction. Usually these phenomena pass in a day or two, but they can drag on. Children are more susceptible to scorpion venom. Isolated cases of death have been described.

When scorpion injections occur, immediate 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 scorpion stings occur 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 (solpugs, or phalanxes)

Their body is more dissected than that of scorpions: not only the abdomen, but also the cephalothorax is partially segmented. Chelicerae are adapted for grasping and killing prey. Pedipalps have the appearance of walking legs, as a result of which salpugs give the impression of decapods. They breathe through tracheas.

Common in warm countries. Within our country they are found in 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 chelicerae. When bitten, acute pain is felt, the bitten area becomes inflamed and swollen. However, attempts to find poisonous glands ended in failure. The consequences of a bite are caused by infection.

Order Araneida (spiders)

The body consists of an unsegmented cephalothorax and an unsegmented abdomen. The cephalothorax is separated from the abdomen by a deep constriction. Chelicerae claw-shaped; the duct of the poisonous gland opens in them. The pedipalps serve as oral limbs. Spiders breathe through lungs, and some species breathe through lungs and trachea.

The spider order includes more than 15,000 species. Distributed almost everywhere. Spiders are predators. They feed on insects that they catch in their nets. A large tropical spider - a tarantula - attacks birds. Most species are useful because they kill 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 clayey-solonetz and clayey-sandy steppes, as well as in wastelands, virgin lands and arable fields. The female builds a net on the ground among stones. It feeds on insects, spiders, scorpions, etc. Karakurt poison 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, feels fear, dizziness, headache. Cold sweat appears on the face. The skin is cold, bluish in color. Later, vomiting, trembling, and bone pain appear. The patient rushes about in bed and at times falls into a state of stupor. Recovery occurs slowly, after 2-3 weeks. Weakness remains for 1-2 months. In case of severe poisoning, death occurs within 1-2 days.

Order Acarina (mites)

Includes small, sometimes even microscopic (from 0.1 to 10 mm) arachnids, usually with an undifferentiated and non-segmented body; the cephalothorax is fused with the abdomen; less often the abdomen is dismembered. Chitin is leathery, easily extensible, but some parts of it are compacted (scutellum). The shape and nature of the arrangement of the scutes is important for taxonomy.

All ticks have six pairs of limbs. Two pairs (chelicerae and pedipalps) are transformed into piercing-sucking or gnawing-sucking oral apparatus, designed to pierce the host’s skin and feed on its blood. The remaining four pairs (walking legs) consist of several segments (6-7), the first of which (the main one, coxa or coxa) is fused with the body.

The digestive system of blood-sucking forms is highly branched, especially in females. The alimentary canal is characterized by the presence of blind outgrowths; they serve as a reservoir for ingested food. The organs of excretion are the 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. Stigmas are located on a small scutum (peritreme).

The nervous system is characterized by the fusion of all the ganglia of the nerve chain and the brain into total weight. 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 one or another pair of legs. Females are larger than males. From the fertilized eggs laid by the female, a six-legged larva emerges. She molts and turns into an eight-legged nymph. Unlike an adult tick, the nymph has an underdeveloped reproductive apparatus; As a rule, there is no external genital opening. There may be several nymphal stages. During the last molt, the nymph turns into a sexually mature form - an adult.

Life cycle. Development, unlike other arachnids, occurs with metamorphosis, including egg, larva, nymph and adult (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 using tracheas (stigmas appear), but does not have a genital opening. There may be several nymphal stages. The nymph after molting turns into an adult. Most ticks that have medical significance, are blood-sucking. Animals that feed ticks are mammals, birds and reptiles.

There are one-, two- and three-host ticks. In monohost animals, all stages of development take place on the same host. In the two-host type of development, the larva and nymph feed on one host, and the imaginal form feeds on another. In three-host ticks (taiga tick), each stage looks for a new host. In the latter case, development can last for a long time, for example, in the taiga tick up to 5 years.

Pathogens enter the body of the tick along with the host’s blood. various diseases, which, when switching to another host, can be transmitted to him, which contributes to the circulation of pathogens. The lifespan of ticks is quite long - from 6 months to 20-25 years.

Highest value from a medical point of view, they have mites of the ixodid and argasid families, as well as the scabies 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.

Have large sizes 4-5 mm. The blood sucked by females reaches 10 mm or more. The male has a scute 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 and easily extensible. This is important, since the female, when feeding, absorbs large number blood, 200-400 times its mass in a fasted 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-jointed palps are located on the sides and a proboscis in the middle. Its lower part makes up the hypostome - an outgrowth of the base. The back side of the hypostome is equipped with sharp teeth directed backwards. Adjacent to the hypostome are cases containing two-segmented chelicerae. The terminal segment of the chelicerum bears 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 chelicerae apart, it is impossible to remove its mouthparts from the skin. After saturation, the tick contracts the chelicerae and releases the mouthparts.

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

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

Argasid mites (Argasidae)

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

The ornithodorus tick (Ornithodorus papillipes) - the village tick - is a blood-sucking tick, a carrier 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 falls into folds. The combination of the oral organs and the integument adjacent to them forms the so-called “head”. It is relatively small, located in the front part of the body on the ventral side and is not visible from the dorsal side. No eyes. On the midline of the body, behind the first pair of legs, is the genital opening, and somewhat behind the middle of the body is the anal opening.

The ornithodorus mite is widespread in the south of Kazakhstan, Central Asia, Iran and India. Lives in natural (caves) or artificial (dwellings) shelters, and each species is 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 adobe walls. Feeds on blood, attacking humans or animals. Sucking blood lasts 30-40 minutes, after which the tick returns to the cracks of the walls.

During the development process, males go through the larval stage and 3 nymphal stages, while females have 4 or 5 nymphal stages. Life expectancy is exceptionally long - 20-25 years. In the absence of hosts, the tick is capable of living for 10-11 years without food. When the cracks are covered with clay, the walled up tick 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, separating the cephalothorax from the abdomen. There are many short spines and long setae on the surface of the body. The legs are greatly shortened, which is associated with an intracutaneous lifestyle. Two pairs of legs are located on the sides of the mouthparts, 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 egg laying to the sexually mature form lasts 9-12 days. An adult tick lives approximately 1.5 months.

Ticks can infect any area of ​​the skin, but are most often found on the back of the hands, in the spaces between the fingers, armpits, and perineum. The passages 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; disinfestation of clothes and items they used; combating mange in farm animals, keeping the body and home clean.

• Class Arachnoidea (arachnids)