What sense organs are developed in arachnids? The structure and nervous system of arachnids

This class includes arthropods adapted to living on land, breathing through the lungs and trachea. The class unites orders of spiders, ticks, scorpions, and haymakers.

a brief description of

general characteristics

Structure and covers . For arachnids characteristic feature is a tendency towards the fusion of body segments forming cephalothorax And abdomen. Scorpions have a fused cephalothorax and a segmented abdomen. In spiders, both the cephalothorax and abdomen are solid, undivided sections of the body, between which there is a short stalk connecting these two sections. The maximum degree of fusion of body segments is observed in mites, which have even lost the division of the body into the cephalothorax and abdomen. The mite's body becomes solid without boundaries between segments and without constrictions.

The integument of arachnids consists of cuticles, hypodermis And basement membrane. The outer layer of the cuticle is lipoprotein layer. This layer is very protects well from moisture loss upon evaporation. In this regard, arachnids were able to become a true terrestrial group and settle in the driest areas of the earth. The cuticle also contains proteins, tanned phenols And encrusting chitin, what gives the cuticle strength. Derivatives of the hypodermis are arachnoid And poisonous glands.

Limbs. Head limbs, except two pairs of jaws, in arachnids are missing. Jaws as a rule, belong to the limbs of the cephalothorax. The cephalothorax of arachnids bears 6 pairs of limbs, What is a distinctive feature of this class. Two front pairs are adapted

to capture and crush food - chelicerae And pedipalps(Fig. 1). Chelicerae, which look like short claws, are located in front of the mouth. In spiders, chelicerae end in a claw, near the top of which there is a hole poisonous gland. Second pair - pedipalps, on the main segment they have chewing outgrowth, with the help of which food is crushed and kneaded. In some species, the pedipalps turn into powerful claws(for example, in Scorpios) or look like walking legs and in some forms of spiders there may be a pedipalp at the end copulatory organ. The remaining 4 pairs of limbs of the cephalothorax perform the function of movement - these are walking legs. A large number of limbs are formed on the abdomen during embryonic development, but in adult chelicerates the abdomen is devoid of typical limbs. If the abdominal limbs are retained into adulthood, they are usually modified in the genital operculum, tactile appendages (scorpions), lung sacs or spider warts.

Rice. 1. Mouthparts of the cross spider: 1 - terminal claw-shaped segment of the chelicera; 2 - main segment of the helicera; 3 - pedipalp; 4 - chewing outgrowth of the main segment of the pedi-palp; 5 - main segment of walking leg

Digestive system(Fig. 2) has features associated with the peculiar way of feeding arachnids - extraintestinal, or external, digestion. Arachnids cannot eat solid food in pieces. Digestive enzymes are introduced into the victim's body and turn its contents into a liquid pulp that is absorbed. Due to this the pharynx has strong muscles And serves as a kind of pump, sucking in semi-liquid food. Midgut most arachnids have lateral blind-locked protrusions to increase the suction surface. Ducts open into the intestine in the abdomen paired liver. The liver not only performs digestive functions, secreting digestive enzymes, but also absorption function. Intracellular digestion occurs in liver cells. Hindgut ends anus.

Respiratory system arachnids presented lung sacs And trachea. Moreover, some species have lung sacs only(scorpions, primitive spiders). Others have respiratory organs only tracheas

Rice. 2.Spider organization diagram: 1 - eyes; 2 - poisonous gland; 3 - chelicerae; 4 - brain; 5 - mouth; 6 - subpharyngeal nerve node; 7 - glandular outgrowth of the intestine; 8 - bases of walking legs; 9 - lung; 10 - pulmonary opening - spiracle; 11 - oviduct; 12 - ovary; 13 - arachnoid glands; 14 - spider warts; 15 - anus; 16 - Malpighian vessels; 17 - islands; 18 - liver ducts; 19 - heart; 20 - pharynx, connected to the body wall by muscles

(salpugs, harvestmen, some ticks). In spiders, two types of respiratory organs occur simultaneously. Eat four-legged spiders, which have 2 pairs of pulmonary sacs and no trachea; two-legged spiders- one pair of pulmonary sacs and a pair of tracheal bundles and lungless spiders- trachea only. Some small spiders and some ticks do not have respiratory organs and breathe through the thin integument of the body.

Circulatory system , like all arthropods, open. Hemolymph contains respiratory enzyme hemocyanin.

Rice. 3.The structure of the heart in arachnids. A - Scorpio; B - spider; B - tick; G - harvester: 1 - aorta (arrows indicate ostia)

The structure of the heart depends on the degree of segmentation - the more segments, the more spines (Fig. 3). In ticks that lack segmentation, the heart may completely disappear.

Excretory system in adult arachnids it is represented pair of branching Malpighian vessels, opening at the border of the middle and hind intestines into the digestive system.

Nervous system arachnids, like the circulatory system, depend on body segmentation. The nerve chain in scorpions is the least concentrated. Arachnids have a brain, unlike crustaceans and insects, consists of two sections - anterior and posterior, the middle section of the brain is absent, since arachnids do not have head limbs, antennules or antennae, which this section must control. There is a large ganglion mass in the cephalothorax And ventral chain ganglia. As segmentation decreases, the ventral chain disappears. So, in spiders the entire abdominal chain merges into holothoracic ganglion. And in harvestmen and ticks, the brain and cephalothoracic ganglion form a continuous ganglion ring around the esophagus.

Sense organs mainly represented special hairs, which are located on the pedipalps, legs and surface of the body And react to air vibrations. The pedipalps also contain sensory organs that perceive mechanical And tactile stimulation. Organs of vision presented with simple eyes. The number of eyes can be 12, 8, 6, less often 2.

Development . Most arachnids lays eggs, but it is also observed live birth. Development direct, but ticks have metamorphosis.

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

Sense organs of arachnids

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

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

Rice. 1. Organs of touch

Each vibration of the trichobothria accurately identifies all species mechanical movement. The organs of touch work so precisely that spiders easily detect the smallest vibrations of the web or air, while distinguishing the nature of the irritation.

Rice. 2. Hairline spiders

The lyre-shaped organs, located on the surface of the entire 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 olfactory organs. Taste cells are found on walking legs, tentacles, and the side of the pharynx. However, these animals distinguish odors only at close range.

Organs of vision of arachnids

Compared to crustaceans, arachnids have a simple structure of their visual organs. They are located in the front part of the cephalothorax and can be represented by three, four, or less often one pair of eyes. The visual organs of arachnids are presented differently in each order and species. So, for example, scorpions have more middle eyes large size, and on the sides there are 2-5 pairs of smaller eyes. 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 other eyes.

Fig.3. Eye location

Arachnids do not see very well. For example, scorpions can distinguish their own kind 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 important role. For example, jumping spiders with blackened eyes cease to distinguish between females and cease to perform the dance characteristic of the mating season.

What have we learned?

Arachnids, like all animals, have sense 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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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 conduct both day and night active image existence.

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 forage for food in the dark, increased activity differ in 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 in the majority 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. There have also been cases of death among children. 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 climates. 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.

The circulatory system, like that of all arachnids, consists of a heart tube and an 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 a brief description of some representatives of the class Arachnids.

We hope you find the information useful.

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 with the help of a very complex, vertically positioned wheel-shaped catching 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 your catching 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 a 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, the internal organs of the victim are quickly digested. After some time, the spider returns to the victim and sucks everything out of it nutrients. 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 different 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 colonize the driest areas 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, other's 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, 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). 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 pericardium, and then through ostia- in 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 have a 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- V large quantities scattered over the surface of the body, there are especially many of them 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 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 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 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.

And) can reach 20 cm in length. More large sizes Possessed by some tarantula spiders.

Traditionally, the body of arachnids is divided into two sections - simply(cephalothorax) and opisthosoma(abdomen). The prosoma consists of 6 segments 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 sensory appendages, serve to capture prey (), and 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 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. The fused tergites of the segments form three shields: propeltidium, mesopeltidium and metapeltidium.

The opisthosoma initially consists of 13 segments, the first seven of which may bear modified limbs: lungs, comb-like organs, arachnoid warts or genital appendages. In many arachnids, the prosomal segments merge with each other, up to the loss of external segmentation in most spiders and mites.

Veils

Arachnids have a relatively thin chitinous cuticle, under 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 system

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

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

In false scorpions, harvestmen, salpugs and some ticks, tracheas serve as respiratory organs, and in most spiders (except the most primitive) there are both lungs (one is preserved - the anterior pair) and tracheas. Tracheas are thin branching (in harvestmen) or non-branching (in false scorpions and ticks) tubes. They penetrate the inside of the animal’s body and open outward with the openings of the stigmata on the first segments of the abdomen (in most forms) or on the first segment of the chest (in salpugs). The trachea is better adapted to air gas exchange than the lungs.

Some small ticks do not have specialized respiratory organs; in them, gas exchange occurs, like in primitive invertebrates, through the entire surface of the body.

Nervous system and sensory organs

The nervous system of arachnids is characterized by a variety of structures. The general plan of its organization corresponds to the ventral nerve chain, but there are a number of features. There is no deuterocerebrum in the brain, which is associated with the reduction of acron appendages - antennules, which are innervated by this part of the brain in crustaceans, millipedes and insects. The anterior and posterior parts of the brain are preserved - 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 ganglion mass. In harvestmen and ticks, all the ganglia merge to form a ring around the esophagus, but in scorpions a pronounced ventral chain of ganglia is retained.

Sense organs in arachnids they are developed differently. Highest value for spiders has a sense of 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 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.

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

Organs of vision arachnids are simple eyes, the number of which varies from 2 to 12 in different species. In spiders, they are located on the cephalothorax shield in the form of two arcs, and in scorpions, one pair of eyes is located in front and several more pairs on the sides. Despite the 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 several cm). For some vagrant species (for example, jumping spiders), vision is more important, since with its help the spider looks out for prey and distinguishes between individuals of the opposite sex.