The Latin name for arachnids comes from the Greek ἀράχνη "spider" (there is also a myth about Arachne, which 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 Gipepe, or the daughter of Idmon and Gipepe, or a resident of Babylon.

Proud of her skill, Arachne declared that she had surpassed Athena herself in weaving, who was considered the patroness of this craft. When Arachne decided to challenge the goddess to a contest, 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 wove 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 indignant at the freethinking of the plot (there was disrespect for the gods in her images) and destroyed the creation of Arachne. Athena tore the fabric and hit Arachne in the forehead with a shuttle made of Kitor beech. The unfortunate Arachne could not bear the shame; she twisted the rope, made a noose and hanged herself. Athena freed Arachne from the loop and told her:

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

The structure of arachnids

(or cheliceral)

Nervous system: subpharyngeal ganglion + brain + nerves.

sense organs- 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 about a spider is eyes.

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

reproductive system:

1) spiders have separate sexes; 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 chelicerae.

The nervous system of any living organism receives information about the environment through the senses. The arachnid class is no exception. In this article, we will talk in more detail about all the sense organs in arachnids, their meaning and location.

Sense organs of arachnids

Touch plays the most important role. In spiders, this organ is represented in the form of hairs (trichobothria), which are located throughout the body. Most of them are on pedipalps and walking legs. The structure of each hair is presented as follows:

• mobile hair attached to the bottom of the fossa on the integument of the body;
• in the fossa there is a group of sensitive cells with which the hair is connected.

Rice. 1. Organs of touch

Each oscillation of trichobothria accurately determines all types of mechanical movement. The organs of touch work so precisely that spiders easily catch the smallest swaying of the web or air, while distinguishing the nature of irritation.

Rice. 2 Spider Hair

The lyre-shaped organs, located on the surface of the whole body, perform the function of chemical sense organs. They are presented in the form of cracks on the body, in the depths of which sensitive cells are located. These are the so-called organs of smell. Taste-sensing cells are found on walking legs, leg tentacles, and the lateral part of the pharynx. However, these animals distinguish smells only at a close distance.

Organs of vision of arachnids

Compared to crustaceans, arachnids have a simple structure of the organs of vision. They are located in front of the cephalothorax and can be represented by three, four, less often one pair of eyes. The organs of vision of arachnids in each order and species are presented in their own way. So, for example, in scorpions, the median eyes are larger, and 2-5 pairs of smaller eyes are located on the sides. Spiders have four pairs of eyes arranged in two arcs. At the same time, the middle eyes of the anterior arch are larger than all the other eyes.

Fig.3. Eye location

Arachnids do not see very well. For example, scorpions of their own kind are distinguished only at a distance of 2-3 cm, and some types of spiders - at a distance of 20-30 cm.

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For some species of arachnids, vision plays a very important role. For example, jumping spiders with blurred eyes cease to distinguish between females and perform a dance characteristic of the mating season.

What have we learned?

Arachnids, like all animals, have sensory organs. The most important role for their life is played by touch. The eyes have a simple structure, despite their number, arachnids see poorly.

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distinguish at least 12 detachments, the most important of which are the detachments of Spiders, Scorpions, False Scorpions, Solpugs, Haymakers, Ticks.

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

cross spiders these are ordinary representatives of the class Arachnida. cross spiders this 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 everywhere in the European part of Russia, in the Urals, in Western Siberia.

Cross spiders are predators that feed only on living insects. The spider-cross catches its prey with the help of a very complex, vertically located wheel-shaped trapping net(hence the name of the family - Orb-weaving spiders) . The spinning apparatus of spiders, which ensures the manufacture of such a complex structure, consists of external formations - arachnoid warts- and from the internal organs - spider glands. A drop of sticky liquid is released from the spider warts, which, when the spider moves, is drawn into the thinnest thread. These threads quickly thicken in the air, turning into a strong gossamer thread. The web is made up mainly of protein. fibroin. In terms of chemical composition, the web of spiders is close to the silk of silkworm caterpillars, but is more durable and elastic. The tensile load for the web is 40-261 kg per 1 sq mm of the thread section, and for silk it is only 33-43 kg per sq mm of the thread section.

To weave its trapping web, the Spider-cross first stretches especially strong threads in several places convenient for this, 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. Further from the middle of this thread, as from the center, the spider conducts radial threads in all directions, like the spokes of a wheel. This is the basis of the entire web. Then the spider starts spinning 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 refuge. In this case, he stretches a strong signal a thread.

When a fly or other insect enters the net, the spider, feeling the signal thread trembling, rushes out of its ambush. By thrusting the claws of the chelicera with poison into the victim, the spider kills the victim and secretes digestive juices into her body. After that, he entangles a fly or other insect with a web and leaves it for a while.

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

Making a trapping net is a series of interconnected unconscious actions. The ability to do so is instinctive and inherited. This is easy to verify by following the behavior of 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 trapping net, other types 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 trapping nets. The trapping web of spiders is a kind of adaptation outside the body.

I must say that not all types of spiders weave trapping nets. Some actively search for and catch prey, others lie in wait for it from an ambush. But all spiders have the ability to secrete webs, and all spiders are made from webs. egg cocoon and spermatic nets.

External structure. The body of the Spider-cross 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.

First pair of limbs chelicerae, which surround the mouth and serve to capture and puncture prey. Chelicerae consist of two segments, the final segment has the form of curved claws. At the base of the chelicerae are poison glands, whose ducts open at the tips of the claws. With chelicerae, spiders pierce the covers of victims and inject poison into the wound. Spider venom has a nerve-paralytic effect. In some species, for example, Karakurt, near the so-called tropical black widow, the poison is 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 pedipalps is to feel and hold prey. In sexually mature males, the pedipalp is formed on the terminal segment copulatory apparatus, which the male fills with sperm before mating. During copulation, the male, using the copulatory apparatus, injects sperm into the female's seminal receptacle. The structure of the copulatory apparatus is species-specific (that is, each species has a different structure).

All arachnids have 4 pairs walking legs. The walking leg consists of seven segments: coxa, swivel, hips, cups, shins, pretarsus and paws armed with claws.

Arachnids have no antennae. On the front of the cephalothorax, the Cross-Spider has two rows of eight simple eyes. Other types of eyes may have three pairs, and even one pair.

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

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

Body covers. The body is covered with chitinous cuticle. The cuticle protects the body from external influences. The most superficial layer is called epicuticle and it is formed by fat-like substances, therefore the covers of spiders are not permeable to either water or gases. This allowed the spiders to colonize the most arid regions 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. shed the cuticle.

musculature arachnids consists of striated fibers that form powerful muscle bundles, i.e. the musculature is represented by separate bundles, and not by a bag like in worms.

body cavity. The body cavity of Arachnids is mixed - mixocoel.

Digestive system typical, consists of front, middle and rear intestines. The foregut is represented 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 the absorption of food gruel. Ducts open into the foregut salivary glands, the secret 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 body of the victim and the food is digested outside the intestines, turning into a semi-liquid slurry, which is absorbed by the spider. In the stomach, and then in the middle intestine, food is absorbed. The midgut has long blind lateral protrusions, which increase the area of ​​absorption and serve as a place for temporary storage of food mass. This is where the ducts open. liver. It secretes digestive enzymes and also ensures the absorption of nutrients. Intracellular digestion takes place in the liver cells. At the border of the middle and posterior sections, the excretory organs flow into the intestine - malpighian vessels. The hindgut ends anal hole located at the posterior end of the abdomen above the arachnoid warts.

Respiratory system. Some arachnids have respiratory organs pulmonary bags, other's tracheal system, the third - both those and others at the same time. Some small arachnids, including some mites, have no respiratory organs; breathing is carried out through thin covers. The lung 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 plunged into the body and formed cavities with lung leaflets. The tracheal system arose independently and later than the lung sacs, as organs more adapted to air breathing. The tracheae are deep protrusions 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.

circulatory system open, comprises hearts, located on the dorsal side of the abdomen, and several large blood vessels extending from it vessels. The heart has 3 pairs of ostia (holes). From the anterior end of the heart anterior aorta disintegrating into arteries. Terminal branches of arteries pour out hemolymph(this is the name of the blood in all arthropods) into the system cavities located between the internal organs. Hemolymph washes all internal organs, delivering nutrients and oxygen to them. Further, the hemolymph washes the lung sacs - gas exchange occurs, and from there it enters 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, therefore they say that arthropods have a mixed body cavity - mixocell.

excretory system in arachnids 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 provide absorption of metabolic products from the body cavity. In addition to Malpighian vessels, some arachnids also have coxal glands- paired saccular formations lying in the cephalothorax. Convoluted canals depart 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 spider-cross has both coxal glands and malpighian vessels.

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

Of all the sense organs, the most important for spiders is touch. Numerous tactile hairs - trichobothria- scattered in large numbers 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 hole in the integument and is connected to a group of sensitive cells located at its base. The hair perceives the slightest vibrations of the air or the web, sensitively reacting to what is happening, while the spider is able to distinguish the nature of the irritating factor by the intensity of the vibrations. Tactile hairs are specialized: some register chemical stimuli, others - mechanical, others - air pressure, fourth - perceive sound signals.

The organs of vision are represented simple eyes found in most arachnids. Spiders usually 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 separate sexes. Fertilization internal. Most arachnids lay eggs, but live births have been observed in some arachnids. Development without metamorphosis.

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

Cross-spiders mate in late summer. Sexually mature males of trapping nets do not weave. They wander in search of the webs of females. Having found the trapping net of a sexually mature female, the male somewhere aside on the ground, or on some twig, or on a leaf weaves a small spermatic reticulum in the form of a hammock. On this mesh, the male from his genital opening, which is located on the ventral side of the abdomen closer to the junction of the abdomen with the cephalothorax, squeezes out a drop sperm. Then he sucks this drop into the pedipalps (like a syringe) and proceeds to seduce the female. The spider's eyesight is weak, 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 kind of gift to the female. Hiding behind this gift as a shield, the male very slowly and very 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, puts his pedipalps with sperm on the female's genital opening and

• Class Arachnids Cross-spider

  performs copulation. The female at this moment is good-natured and relaxed. But, immediately after mating, the male must hastily 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 still die. From an evolutionary point of view, the male is no longer needed: he has fulfilled his biological function.) This happens in almost all species of spiders. Therefore, in studies, females are most often found, while males are rare.

  After copulation, the female continues to feed actively. In autumn, a female from a special web makes 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. Cross-spider eggs overwinter. In the spring, young spiders emerge from the eggs, which begin an independent life. Shedding several times, the spiders grow and reach sexual maturity by the end of summer and start breeding.

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

Questions for self-control

Name the classification of the phylum Arthropoda.

What is the systematic position of the Spider-cross?

Where do cross spiders live?

What body shape do cross spiders have?

What is the body of a spider covered with?

What body cavity is characteristic of a spider?

What is the structure of the digestive system of a spider?

What are the digestive characteristics of spiders?

What is the structure of the circulatory system of a spider?

How does a spider breathe?

What is the structure of the excretory system of a spider?

What is the structure of the nervous system of a spider?

What is the structure of the reproductive system of a spider?

How does the cross-spider reproduce?

What is the importance of spiders?

Class Arachnids Cross-spider

Rice. Spider-cross: 1 - female, 2 - male and wheel-shaped trapping net.

Rice. Spider-cross weaves a trapping web

Class Arachnids Cross-spider

Rice. The internal structure of the Spider-cross.

1 - poisonous glands; 2 - throat; 3 - blind outgrowths of the intestine; 4 - malpighian vessels; 5 - heart; 6 - lung sac; 7 - ovary; 8 - oviduct; 9 - spider glands; 10 - pericardium; 11 - ostia in the heart.

And) can reach 20 cm in length. Some tarantulas are even larger.

Traditionally, two sections are distinguished in the body of arachnids - so(cephalothorax) and opisthosoma(abdomen). The prosoma consists of 6 segments each bearing a pair of limbs: chelicerae, pedipalps, and four pairs of walking legs. In representatives of different orders, the structure, development and functions of the limbs of the prosoma differ. In particular, pedipalps can be used as sensitive appendages, serve to capture prey (), act as copulatory organs (). In a number of representatives, one of the pairs of walking legs is not used for movement and takes on the functions of the tactile organs. The segments of the prosoma are tightly connected to each other; in some representatives, their dorsal walls (tergites) merge with each other to form a carapace. The merged tergites of the segments form three scutes: propeltidia, mesopeltidia, and metapeltidia.

The opisthosoma initially consists of 13 segments, the first seven of which may bear modified limbs: lungs, ridge-like organs, arachnoid warts, or genital appendages. In many arachnids, the segments of the prosoma fuse with each other, to the point of losing the outer segmentation in most spiders and mites..

covers

Arachnids have a relatively thin chitinous cuticle, under which lies the hypodermis and basement membrane. The cuticle protects the body from loss of moisture during evaporation, so arachnids inhabited the most arid regions of the globe. The strength of the cuticle is given by proteins that encrust chitin.

Respiratory system

The respiratory organs are the trachea (y, and some) or the so-called lung sacs (y and), sometimes both together (y); the lower arachnids do not have separate respiratory organs; these organs open outward on the underside of the abdomen, less often on the cephalothorax, with one or more pairs of respiratory openings (stigma).

The lung sacs are more primitive structures. It is believed that they occurred as a result of a modification of the abdominal limbs in the process of mastering the terrestrial way of life by the ancestors of arachnids, while the limb was pushed into the abdomen. The lung sac in modern arachnids is a depression in the body, its walls form numerous leaf-shaped plates with extensive gaps filled with hemolymph. Through the thin walls of the plates, gas exchange occurs between the hemolymph and the air entering the lung sac through the openings of the spiracles located on the abdomen. Pulmonary respiration is available in scorpions (four pairs of lung sacs), flagellates (one or two pairs) and low-organized spiders (one pair).

Pseudo-scorpions, haymakers, salpugs, and some ticks have tracheae as respiratory organs, and most spiders (except the most primitive ones) have lungs at the same time (there is only one - the front pair) and trachea. The trachea are thin branching (for harvesters) or non-branching (for pseudoscorpions and ticks) tubules. They penetrate the inside of the body of the animal and open outwards with holes in the stigmas on the first segments of the abdomen (in most forms) or on the first segment of the chest (in the salpugs). The tracheae are better adapted to air gas exchange than the lungs.

Some small mites have no specialized respiratory organs; in them, gas exchange is carried out, like in primitive invertebrates, through the entire surface of the body.

Nervous system and sense organs

The nervous system of arachnids is distinguished by a variety of structures. The general plan of its organization corresponds to the ventral nerve chain, but there are a number of features. The deutocerebrum is absent in the brain, which is associated with the reduction of the appendages of the acron - antennules, which are innervated by this part of the brain in crustaceans, centipedes and insects. The anterior and posterior sections of the brain are preserved - the protocerebrum (innervates the eyes) and the tritocerebrum (innervates the chelicerae).

The ganglia of the ventral nerve cord are often concentrated, forming a more or less pronounced ganglionic mass. In harvestmen and ticks, all ganglia merge, forming a ring around the esophagus, but in scorpions, a pronounced ventral chain of ganglia is retained.

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

The organs of chemical sense are lyre-shaped organs, which are slits in the covers 50-160 microns long, leading to a depression on the surface of the body where sensitive cells are located. The lyre-shaped organs are scattered throughout the body.

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

class arachnids, unlike crustaceans, live mainly on land, breathe with the help of trachea and lungs. The class includes three orders, on the representatives of which one can trace the process of fusion of body parts. So, in a detachment of spiders, the body is divided into a cephalothorax and abdomen, in scorpions it consists of a cephalothorax, anterior abdomen and posterior abdomen, in ticks all sections are merged into one shield.

Common signs of arachnids: lack of antennae, four pairs of walking legs, tracheal or pulmonary respiration, permanent perioral appendages - upper tentacles and leg tentacles. On the cephalothorax are four pairs of simple eyes, mouth organs and limbs (walking legs). The most common are spiders and mites.

Spider Squad

A typical representative of the order of spiders is cross spider. It can be found in forests, parks, on estates, in houses where they weave large trapping nets from cobwebs. In a spider, the first pair of oral organs are the upper jaws, equipped with sharp, downward-curved claws.

At the end of the claws, the excretory ducts of the poisonous glands open. The jaws serve the spider for killing prey and for protection. The second pair of mouth organs are the leg tentacles, with which the spider feels and turns the victim while eating.

Four pairs of jointed walking legs are covered with sensitive hairs. The abdomen of arachnids is larger than the cephalothorax. At the posterior end of the abdomen, spiders have arachnoid warts, into which the arachnoid glands open. The substance secreted by the glands hardens in air, forming arachnoid threads. Some glands secrete a strong and non-adhesive cobweb, which goes to form the skeleton of a trapping network. Other glands secrete small sticky threads with which the spider builds a trapping web. Third glands secrete a soft silky web used by the female to weave a cocoon.

The spider that has fallen into the trapping net entangles the victim with a sticky web, sticks the claws of the upper jaws into the prey and injects into it a poisonous liquid that dissolves soft tissues and acts as digestive juice. Leaving the victim wrapped in a web, the spider steps aside, waiting for its contents to be digested. After a while, the spider sucks in partially digested food. So in spiders, partial digestion of food occurs outside the body.

The respiratory organs of the spider are represented by lung sacs that communicate with the environment. In addition to them, the spider has tracheae in its abdomen - two bundles of respiratory tubes that open outwards with a common respiratory opening.

The circulatory system of a spider is basically the same as that of a cancer.

The role of the excretory organs is performed by the Malpighian vessels, the spider has one pair of them, but they branch. The hemolymph (blood mixed with lymph) of the spider washes these vessels and the metabolic products exit through the gaps, then enter the intestines and are then excreted.

The nervous system is formed by the subpharyngeal ganglion, the brain, from which the nerves extend to various organs.

Spiders have numerous and varied sense organs: organs of touch (hairs on the body of the spider and on the tentacles), smell and taste (on the tentacles and walking legs), taste organs are also present on the lateral parts of the pharynx; organs of vision (eight simple eyes). Some spiders are able to distinguish color, especially those. which are looking for prey on the flowers of plants (crab spiders).

Spiders are dioecious animals. Females are larger than males. In autumn, the female spins a cocoon of cobwebs and lays her eggs in it. In it, eggs hibernate, and in spring spiders hatch from them. Most spiders are beneficial: many small mammals, birds, lizards, and some insects feed on them. Among the spiders there are also poisonous ones - tarantula and karakurt. They are very dangerous for humans and pets.

Squad of pincers

In most representatives of the order of ticks, the body does not have a clear division into segments or sections. There are a lot of ticks. Some of them live in the soil, others - in plants, animals and humans.

Unlike spiders, flares have an indirect development. A six-legged larva emerges from the egg, in which, after the first molt, a fourth pair of legs appears. After several molts, the larva turns into an adult.

Red spider mite settles on the leaves of cotton and other valuable plants. It reduces cotton yields and causes plant death.

flour mite settles in onions and grains. Eating the germ of the future plant in the grain, it causes the death of the seeds. It causes food spoilage in warehouses. for example, various cereals, bread products, sunflower seeds. Cleanliness and ventilation of the premises where food is stored is one of the main measures to combat flour mites.

scabies mite (scabies itch) causes diseases such as scabies in humans. Females of this type of mites are introduced into the more delicate areas of human skin and gnaw their moves in it. Here they lay their eggs. Young flares come out of them, again gnawing passages in the skin. Keeping your hands clean prevents this dangerous disease.

Scorpion Squad

Scorpions live in countries with warm and hot climates, and are found in a wide variety of habitats: from humid forests and sea coasts to barren rocky areas and sandy deserts. Often scorpions settle in human dwellings.

Scorpions are mostly viviparous, some species lay eggs in which the embryos are already developed, so that juveniles soon hatch. This phenomenon is called ovoviviparous. A scorpion becomes an adult a year and a half after birth, making 7 molts during this time.

A scorpion sting 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. For small mammals, scorpion venom is mostly fatal. For a person, a scorpion sting is usually not fatal, but a number of cases are known with very serious consequences and even death.