What are the respiratory organs of arachnids? External structure of arachnids. Sex organs and reproduction

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

Body structure	The body consists of a cephalothorax and abdomen
Coverings of the body	The body is covered with chitinized cuticle
Limbs	On the cephalothorax there are 6 pairs of limbs: 2 pairs of jaws, 4 pairs of walking legs. There are no antennas or aerials
Body cavity	Mixed body cavity in which internal organs are located
Digestive system	Foregut. Pharynx. Midgut. Hindgut. Liver. Spiders have partially external digestion
Respiratory system	Lungs or trachea
Circulatory system	The heart is in the form of a tube with lateral slit-like processes - ostia. The circulatory system is not closed. Hemolymph contains the respiratory pigment hemocyanin
excretorysystem	Malpighian vessels
Nervous system	Consists of the brain - suprapharyngeal node, peripharyngeal ring, ventral nerve cord
Sense organs	Sensitive hairs, which are especially numerous on the pedipalps. The organs of vision are represented by simple eyes from 2 to 12
Reproductive system and development	Arachnids are dioecious. Fertilization is internal. Sexual dimorphism is pronounced

general characteristics

Structure and covers . For arachnids, a characteristic feature is the tendency to merge 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 performs not only digestive functions, secreting digestive enzymes, but also an 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.

Respiratory system of spiders

Robert Gale Breen III

Southwestern College, Carlsbad, New Mexico, USA

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

Insect breathing

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

This is not the case with spiders, although it seems logical that things should happen in a similar way for spiders, at least for those with tracheae.

Respiratory systems of spiders

Spiders have at least five different types of respiratory systems, depending on the taxonomic group and who you talk to:

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

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

3) A pair of book lungs and a pair of tube trachea, such as in weaver spiders, wolves and most species of spiders.

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

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

Blood of Spiders

Oxygen and carbon dioxide are transported through the hemolymph by the respiratory pigment protein hemocyanin. Although hemocyanin has chemical properties similar to vertebrate hemoglobin, unlike the latter, it contains two copper atoms, which gives spiders’ blood a bluish tint. Hemocyanin is not as effective at binding gases as hemoglobin, but spiders are quite capable of it.

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

Spider trachea

Tracheal tubes penetrate the body (or parts of it, depending on the species) and end near the tissues. However, this contact is not close enough for them to supply oxygen and remove carbon dioxide from the body on their own, as happens in insects. Instead, hemocyanin pigments have to pick up oxygen from the ends of the breathing tubes and carry it further, passing carbon dioxide back into the breathing tubes.

Tubular tracheae usually have one (rarely two) opening (called a spiracle or stigma), most of which exit on the underside of the abdomen, next to the spinner appendages.

Book lungs

The pulmonary slits or book lung slits (in some species the pulmonary slits are equipped with various openings that can widen or narrow depending on oxygen needs) are located in front of the lower abdomen. The cavity behind the hole is stretched internally and houses many leaf-like air pockets of a book lung. The book lung is literally stuffed with air pockets covered by an extremely thin cuticle that allows gas exchange by simple diffusion while blood flows through it. Tooth-like formations cover most of the surface of the book lungs on the side of the hemolymph flow to prevent collapse.

Digestive system of arachnids

How do spiders digest food?

» Arthropods » Arachnids » How do spiders digest food?

Spiders kill or paralyze their prey by biting and injecting venom through holes at the ends of their chelicerae. But chelicerae are unable to crush food into small pieces, and spiders have no teeth in their mouths. Therefore, spiders have adapted to feed on liquid food. Having killed prey, the spider first injects its own digestive juices into it. In most animals, food is digested (broken down into simple substances) inside the body - in the stomach and intestines. This type of digestion is called internal digestion. Spiders have external digestion: after some time, the tissues of the victim soften and turn into a nutrient solution, which the spider absorbs, leaving only an empty skin.

Spitting spiders, or hissing spiders (scytodes), catch prey by spraying it with a sticky liquid. Once on the victim, the liquid firmly glues it to the substrate. The “glue” is produced by special glands in the spider’s back and released into the air through the chelicerae. Kills prey with a bite.

Class Arachnida biology

Ability to establish compliance

Establish a correspondence between the characteristics and the classes of animals for which these characteristics are characteristic: for each element of the first column, select the corresponding element from the second column.

Demonstration version Main state exam OGE 2017 – task 2017 – Task No. 25

SIGNS CLASSES

1) insects

2) arachnids

A) Some representatives have a pupal stage in development.

B) The vast majority of representatives are predators.

C) The body of animals consists of a head, chest and abdomen.

D) Animals are able to absorb only liquid food.

D) Animals have four pairs of walking legs.

E) Simple and compound eyes can be located on the head.

Write down the selected numbers in the table under the corresponding letters.

Solution:

Signs of Pa-u-to-be-different: the majority of pre-sta-vi-te-leys are predators; the body consists of a head and abdomen; capable of eating only liquid food; have four pairs of walking legs; 8 simple eyes.

Signs of certain people: there is a stage of ku-kol-ki (some of their representatives have a body), a body with -it from the head, chest and abdomen, different types of mouth ap-pa-ra-tov; have three pairs of walking legs; simple and complex eyes can be located on the head.

Answer: 121221


Respiratory, digestive, excretory system of spiders

Respiratory system

It seems that after all that has been said, it will not surprise you that spiders also breathe differently.

Spiders in general can breathe through tracheas, book lungs, or both. The trachea is a system of thin tubes through which air reaches even remote parts of the spider’s body. They are of little interest to us, since tarantulas and their closest relatives do not have tracheas.

But tarantulas have book lungs. There are 4 of them, and they resemble pockets on the underside of the opisthosoma, similar to the back pockets on jeans. The narrow openings are called pulmonary slits (also spiracles, stomata, stigmas). If you turn the tarantula over, at least two of them (the rear pair) are visible. In well-fed individuals, the front pair is hidden by the basal segments of the last pair of legs. The lungs are clearly visible as white spots on the inside of the shed exuvium of the opisthosoma. Inside the lungs there are leaf-shaped folds of a thin membrane - lamellae ( lamellae, units lamella, also called leaves or pages), which resemble the pages of a half-open book, hence the name. Hemolymph circulates inside these folds, exchanging carbon dioxide for air oxygen, which separates the leaves from each other. The lamellas do not stick to each other thanks to the many small spacers and posts. It is believed that book lungs are the result of the development of apodemes.

There has been much controversy regarding the presence or absence of respiratory movements in tarantulas. Do they have active breathing with inhalation and exhalation, like we do? Proponents of this point of view point to the seemingly existing respiratory movements and muscles closely associated with the lungs. Their opponents argue that tarantulas do not make breathing movements when observed. For some reason, it so happened that the results of experiments conducted in this direction were contradictory or ambiguous. However, recently a series of experiments have been conducted and reported (Paul et al. 1987), the results of which may put the debate to rest once and for all. It has been shown that there are small fluctuations in the walls of the lungs, corresponding to the heartbeat and fluctuations in hemolymph pressure.

But the additional volume of air attracted due to these movements is so small that it does not play a significant role in gas exchange. Thus, the tarantula does not know such a thing as inhalation and exhalation, relying entirely on diffusion.

Now that this mystery has been solved, we can breathe a deep sigh of relief, although this is not given to tarantulas.

Digestive system

Spiders don't have jaws. Instead, there are strong, strong chelicerae and fangs on them, and also hard basal segments of the pedipalps with spines and serrations. The mouth is located between the coxae of the pedipalps, directly above a small plate called the labium ( labium) or lower lip. The labium is a small outgrowth of the sternum (sternum). Above the mouth, between the bases of the chelicerae there is another small plate, the labrum ( labrum) or upper lip. However, do not be misled: neither in mobility nor in function do these organs resemble human lips. It was simply more convenient for arachnologists of the past to give familiar names than to come up with something new, even more suitable.

Starting with the mouth, the narrow tube of the pharynx extends inward and upward, not very far. As soon as it reaches the anterior inferior surface of the brain, it bends sharply horizontally and pierces it. (Remember the hole that looks like the hole in a donut?) The horizontal section of the tube is called the esophagus.

The esophagus flows into a hollow muscular organ - the dispenser stomach. The latter, with its elongated posterior end, is connected to the real stomach, which lies between it and the brain. From the real stomach to the bases of the legs extend finger-like projections - gastric (gastric) diverticula ( diverticula, units diverticulum).

The true stomach opens into a relatively straight-lying intestine, which enters the opisthosoma through a stalk.

Digestive and circulatory systems of arachnids

There a bundle of thread-like organs, the Malpighian vessels, connects with it. They perform the functions of the kidneys. Shortly before the intestine opens into the anus, it forms a large protrusion, a blindly enclosed sac called the stercoral pouch ( stercoral pocket). The anus is located directly above the arachnoid appendages. Tarantulas rely on chelicerae, fangs, and pedipalp coxae for the difficult task of chewing prey. Unlike them, other spiders pierce the integument of the victim and suck out the juices through a small hole.

Despite their large size, tarantulas consume only liquid food. Solid particles are filtered by numerous hairs on the bases of the chelicerae and coxae of the pedipalps. Smaller particles, about a micron in size (0.001mm), are filtered out using the palatal plate, a special device in the pharynx. By comparison, most mammalian cells and most bacteria are larger than one micron. Spiders and most other arachnids do not like solid food.

While eating, tarantulas regurgitate digestive juices while chewing their prey. The resulting pulp is diluted with secretions of the coxal glands. As a result, partially digested liquid food is drawn into the mouth, then through the palatine plate into the pharynx and into the esophagus with the help of a pumping stomach; much like how we draw water through a straw, using the muscles in our cheeks and throat.

The pumping stomach is driven by powerful muscles, most of which are attached to the endosternite and carapace. Through it, fluid from the esophagus flows back and down into the real stomach for further digestion and partial absorption. These processes are finally completed in the intestine. In its posterior part, waste products coming from the Malpighian vessels are added to what remains. All this accumulates in the stercoral pocket for some time. Periodically, excrement is expelled through the anus. The Malpighian vessels are another example of parallel evolution. In spiders they do not develop from the same embryonic structures as in insects. They were named after insects because they look almost the same, are located in almost the same place, and perform almost the same function. In short, these organs are analogous (similar but of different origins) rather than homologous (have the same origin and function).

Alternative names for parts of the digestive system are:
1. rostrum instead of labrum;
2. sucking stomach instead of pumping stomach;
3. proximal midgut instead of true stomach;
4. gastric cecum instead of gastric diverticulum;
5. medial midgut instead of intestine;
6. cloacal chamber or cloaca instead of stercoral pouch and, finally,
7. The hindgut is the short section of the digestive tract between the stercoral pouch and the anus.

Duplication of nomenclature occurs as a result of attempts to “fit” spiders to the standards taken from widely different groups of arthropods, instead of developing a new one that best suits them.

Another aspect of spider digestion should also be discussed, namely the coxal glands. They belong to both the digestive and excretory systems, so we talk about them at the intersection of these two topics.

Most arthropods possess coxal glands, which are direct homologs of more primitive excretory organs, nephridia, found in less advanced invertebrates. Tarantulas have them too. There are two pairs of them, and they are located on the back-facing side of the basal segments (coxae) of the 1st and 3rd pairs of legs, where the name of these organs comes from. For many years, arachnologists suffered, trying to guess why they were needed. Many were inclined to think that the coxal glands do not perform any function, being rudiments of more primitive nephridia that are no longer needed. The others weren't so sure. (Nephridia will be mentioned again on page 46.)

Recently, Butt and Taylor (1991) determined that the coxal glands have a function. They appear to secrete a saline solution into the mouth, which leaks through the folds of the pleural membranes between the coxae and the sternum. This serves two purposes. Firstly, this ensures the liquid state of the food gruel that the tarantula drinks; this function is similar to that of our saliva. Secondly, this must be how the salt balance of the tarantula is maintained, since some of the salts are deposited in the dry residue of the food. So, paradoxically, spiders salivate in their armpits!

The final well-chewed dry food residue mostly consists of inedible parts of the victim's body (i.e., the exoskeleton), which the spider is unable to digest, as well as excess salts. Amateurs sometimes call this remnant a pellet; professional arachnologists use the term food bolus.
In a large collection of tarantulas collected by the authors over many years (almost a thousand individuals at the moment), feeding is accompanied by a characteristic heavy, sweetish odor. It is not clear whether this odor is caused by digestive juices or overcooked food.

Excretory system

One of the main problems of all animals is the timely removal of metabolic products before their concentration reaches dangerous levels. The digestible substances consist mainly of carbon, hydrogen, oxygen and nitrogen with traces of other elements. Metabolism converts carbon into carbon dioxide and excretes it through the lungs or gills. Hydrogen becomes water, which is no different from water that enters the body with food or drink. Oxygen can be incorporated into various organic compounds or removed as carbon dioxide.

The most difficult thing is with nitrogen.

Together with hydrogen it produces ammonia, a very toxic compound. Aquatic animals can get rid of nitrogen in the form of ammonia or other soluble substances by simply allowing them to dissolve in the surrounding water. They usually have plenty of water and little energy is spent on excretion.

Land animals are not so lucky. If nothing is done, the concentration of nitrogen compounds quickly increases to lethal levels. Several ways have been invented to avoid poisoning. The first is to convert nitrogen into a form that is less toxic than ammonia. If this product is less soluble, then even more can be accumulated if concentrated. And if it is still possible to isolate the concentrate from the internal environment of the body, then it becomes significantly safer. Finally, the ideal final product should be easy to hatch, with a minimum of water, salt and energy consumption.

Arachnids in general and spiders in particular have developed a technology that combines all these approaches. And they did it their way again.

First, it is necessary to develop a relatively safe substance. The main excreted product in spiders is guanine; other nitrogen-containing wastes (adenine, hypoxanthine, uric acid) are released in small quantities. In this, arachnids stand in stark contrast to the rest of the animal kingdom, which never excrete guanine as waste (Anderson 1966; Rao and Gopalakrishnareddy 1962). Although they also produce it, rest assured. In cats and deer, for example, guanine is the main substance that provides the reflective properties of the retina. But, unlike spiders, cats and deer do not excrete it as waste. Since guanine is insoluble, it is completely harmless to the spider.

Again, since it is insoluble, it can be deposited as a solid and accumulate more efficiently. Compared to urea, for example, it takes up much less space and needs to be disposed of less often. Then, since it is a solid, it can be stored in safe places. Some intestinal cells (called guanocytes) are capable of accumulating quite large amounts of guanine. Although they do not remove guanine from the body, they effectively neutralize it, allowing the body to function peacefully without worrying about the energy and material costs of excretion.

And finally, by concentrating waste products to a solid state, the spider can get rid of them with little loss of water, salts and energy. B O The majority of the guanine secreted by the Malpighian vessels accumulates in the stercoral pouch and is released from there along with the remains of undigested food. Thus, arachnids (and spiders among them) use all 4 approaches to avoid nitrogen poisoning, and they do so extremely effectively.

An interesting consequence of all of the above is that spiders do not have kidneys, they do not produce urine, and therefore are not familiar with the concept urinate, at least in the sense in which we usually use it. In that case, what are they doing?

Reproductive system

The sex life of tarantulas is truly stunning, but we will talk about it a little later. Here we will limit ourselves to a simple description of the mechanism.

Spider gonads: ovaries in females and testes in males, are located inside the opisthosoma. The only genital opening (gonoporus, gonopore) is located on the ventral surface of the opisthosoma and is located along a groove called epigastric groove, which runs in the transverse direction, connecting the upper lungs. This is the posterior edge of the epigynal plate. In early literature, the epigastric groove is sometimes called the generative fold. In the female, two ovaries are connected to a single oviduct, which opens with a gonopore. Directly inside the gonopore there are two “pockets” called seminal receptacles or spermathecae ( spermathecae, units spermatheca). During copulation (mating), the male deposits sperm into the spermatheca, where the sperm remain alive until the eggs need to be fertilized, weeks or months later.

In the male, the paired testes are spirally twisted tubes that open into a common duct. The duct, in turn, opens into the outside world, again by the gonopore. Next to the gonopore are the epiandral glands; they are thought to either contribute to the formation of seminal fluid or to produce a special thread for weaving sperm webs (Melchers 1964).

The male spider does not have a penis or any homologous organ. Its copulatory appendages are secondary reproductive organs at the ends of the pedipalps. In adult males, the terminal segment of the pedipalp (pretarsus and claw) is transformed from the simple structure seen in immature males into a complex, highly specialized organ for introducing sperm into the female genital tract. This segment resembles an exotic bottle, bulbous, with an elaborately curved and twisted neck. The body of the bottle is called bulba ( bulb) or reservoir, and the neck is an embolus ( embolus, plural emboli). Meanwhile, the foot shortens and thickens. The embolus and bulb are attached to it using a flexible joint that allows them to move freely in different planes. The modified tarsus is often called a cymbium ( cymbium, plural cymbia). The cymbium is connected to the shank by another elastic joint.

Bertse bears a special groove (alveolus, alveolus), the shape of which corresponds to the shape of the embolus and bulb. Thanks to the mobility of the cymbium, the spider can put them in this groove when they are not needed. But when the embolus and bulb are filled with sperm and are ready for insertion into the female’s reproductive tract, they are completely open and turned at the desired angle in relation to the pedipalp.

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

Body structure	The body consists of a cephalothorax and abdomen
Coverings of the body	The body is covered with chitinized cuticle
Limbs	On the cephalothorax there are 6 pairs of limbs: 2 pairs of jaws, 4 pairs of walking legs. There are no antennas or aerials
Body cavity	Mixed body cavity in which internal organs are located
Digestive system	Foregut. Pharynx. Midgut. Hindgut. Liver. Spiders have partially external digestion
Respiratory system	Lungs or trachea
Circulatory system	The heart is in the form of a tube with lateral slit-like processes - ostia. The circulatory system is not closed. Hemolymph contains the respiratory pigment hemocyanin
excretorysystem	Malpighian vessels
Nervous system	Consists of the brain - suprapharyngeal node, peripharyngeal ring, ventral nerve cord
Sense organs	Sensitive hairs, which are especially numerous on the pedipalps. The organs of vision are represented by simple eyes from 2 to 12
Reproductive system and development	Arachnids are dioecious. Fertilization is internal. Sexual dimorphism is pronounced

general characteristics

Structure and covers. For arachnids, a characteristic feature is the tendency to merge body segments, forming the 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 a cuticle, hypodermis and basement membrane. The outer layer of the cuticle is a lipoprotein layer. This layer protects very well from moisture loss due to evaporation. In this regard, arachnids were able to become a true terrestrial group and settle in the driest areas of the earth. The composition of the cuticle also includes proteins hardened with phenols and encrusting chitin, which gives the cuticle strength. Derivatives of the hypodermis are arachnoid and poisonous glands.

Limbs. Arachnids lack head limbs, except for two pairs of jaws. The jaws, as a rule, are classified as the limbs of the cephalothorax. The cephalothorax of arachnids bears 6 pairs of limbs, which 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, the chelicerae end in a claw, near the top of which there is an opening for the venom gland. The second pair are pedipalps; on the main segment they have a chewing outgrowth, with the help of which food is crushed and kneaded. In some species, the pedipalps turn into powerful claws (for example, in scorpions) or look like walking legs, and in some forms of spiders there may be a copulatory organ at the end of the pedipalps. 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 persist into adulthood, they are usually modified into genital operculum, tactile appendages (scorpions), pulmonary sacs, or arachnoid 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 pedipalp; 5 - main segment of walking leg

The 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. In this regard, the pharynx has strong muscles and serves as a kind of pump that draws in semi-liquid food. The midgut in most arachnids has lateral blind-closed protrusions to increase the absorption surface. In the abdomen, the ducts of the paired liver open into the intestine. The liver performs not only digestive functions, secreting digestive enzymes, but also an absorption function. Intracellular digestion occurs in liver cells. The hindgut ends at the anus.

The respiratory system of arachnids is represented by pulmonary sacs and trachea. Moreover, some species have only pulmonary sacs (scorpions, primitive spiders). In others, the respiratory organs are represented only by the trachea

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. There are four-legged spiders that have 2 pairs of pulmonary sacs and no trachea; bipulmonary spiders - one pair of pulmonary sacs and a pair of tracheal bundles and lungless spiders - only tracheas. 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, not closed. Hemolymph contains the 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 by a pair of branching Malpighian vessels that open 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. In arachnids, the 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 should control. There is a large ganglion mass in the cephalothorax and the ventral chain ganglion. As segmentation decreases, the ventral chain disappears. Thus, in spiders the entire abdominal chain merges into the cephalothoracic ganglion. And in harvestmen and ticks, the brain and cephalothoracic ganglion form a continuous ganglion ring around the esophagus.

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

Development. Most arachnids lay eggs, but viviparity has also been observed. Development is direct, but mites have metamorphosis.

A.G. Lebedev "Preparing for the biology exam"

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 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 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 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 of webs perform different functions: one is for catching prey, another is for building a home, and the third is used for 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 arachnids have respiratory organs 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- 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 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 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 is the structure of the spider's reproductive system?

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.

Excretory system. The excretory system is represented by Malpighian vessels, which are neoplasms in Arachnoidea, and coxal glands, which correspond to coelomoducts. The Malpighian vessels are a pair of branching tubes, blindly closed at the ends, that open at the border of the middle and hind intestines.

They are of endodermal origin, that is, they belong to the midgut. Grains of guanine, the main excretion product of arachnids, accumulate in the epithelium and lumen of the Malpighian vessels. The coxal glands are formed by a sac-like part of mesodermal origin, a convoluted duct (labyrinth), a reservoir and an external excretory duct. They are present in one or two pairs, open at the bases of the legs and rarely function in adult forms.

Reproductive system. Arachnids are dioecious. The gonads are located in the abdomen and are initially paired. In some cases, fusion of the right and left gonads is observed. So, in male scorpions the testes are paired and each consists of two tubes connected by jumpers; in female scorpions the ovary is one and consists of three tubes, of which the middle one is obviously the result of the fusion of two medial tubes, similar to those of the male. In many spiders, harvestmen and ticks, paired gonads are fused at the ends into a ring. Paired oviducts and vas deferens open with an unpaired genital opening always on the second abdominal segment. The structure of the excretory part of the reproductive system and the copulatory adaptations of males are very diverse. Females usually have an extension of the oviducts - the uterus and seminal receptacles. In males, the copulatory organs are either associated with the genital opening orserve as pedipalps (spiders) or chelicerae (some mites). In some cases, fertilization is spermatophoric - with the help of sperm packets.

Development. Most arachnids lay eggs, but there are also viviparous forms (scorpions, some ticks, etc.). Eggs are richyolk, due to which the fragmentation is partial, superficial, all segments of the body and limbs are formed in embryonic development, and a small full-segmented individual similar to an adult hatches from the egg. Post-embryonic development is direct, accompanied mainly by growth. Only in ticks, due to the small size of the eggs, a six-legged larva hatches and metamorphosis takes place. Studying the embryos of primitive arachnids allows us to more fully understand the structure of adults. Thus, in the scorpion embryo, abdominal limbs are formed on all segments of the mesosome, of which the first pair then disappears, the second turns into genital operculum, the third into crest-shaped organs, and the remaining four pairs into lungs.

A feature of the Arachnida class is extraintestinal digestion. In addition, these animals develop excretory organs that allow them to save water. Read more about the work of the digestive and excretory systems of arachnids in this article.

Digestive system

The organs of the digestive system of arachnids include the intestine, which consists of three sections: front, middle and back.

Anterior section presented in the form of a pharynx, which, tapering, passes into the sucking stomach. The inside of the entire intestine is covered with cuticle. The stomach itself is designed so that it is possible to suck out the contents of the victim. At the base of the pharynx, near the mouth opening, there are excretory canals, the so-called salivary glands.

Middle section , located in the cephalothorax, has 5 pairs of glandular blind processes. Their function, like the salivary glands, is to dissolve proteins. The secretion of these glands is injected into the victim, where extraintestinal digestion occurs. The entrails of the prey turn into a liquid paste, which is absorbed through the stomach. In the abdominal region, the midgut is curved in an arc. Here branching glandular appendages or the so-called liver open into it.

The main function of the liver is intracellular digestion and absorption of nutrients. In this place, food is finally digested under the influence of special enzymes.

Posterior presented in the form of a rectum. At the border between the middle and posterior sections, the excretory organs open - the Malpighian vessels. Residues from digestion and secretions from excretory vessels accumulate in the rectal bladder. Next, waste is excreted through the rectum through the anal tubercle.

Fig.1. Digestive system (green)

Excretory system

What the excretory system of arachnids is represented by was said earlier - this is malpighian vessels. They are excretory tubes, with one blind end immersed in the hemolymph and the other open end in the intestine. Thus, metabolic products can be released through the walls of these vessels from the hemolymph and excreted through the intestines.

Fig.2. Malpighian vessels (9)

The excretion product is guanine. It, like uric acid, is slightly soluble, so it is removed in the form of crystals. Moisture loss is insignificant, and this is important for arachnids that have adapted to life on land.

Rice. 3. The structure of arachnids

In addition to the Malpighian vessels, young individuals also have coxal glands - paired sac-like formations. However, in adults they completely or partially atrophy.

What have we learned?

The digestive system is adapted to extraintestinal digestion. To do this, the spider’s body produces special enzymes that are introduced into the victim’s body. The digestive organs themselves are equipped with a reinforced muscular system in order to be able to absorb the dissolved contents of the prey. The excretory organs are the Malpighian vessels, which help save excess moisture, and metabolic products are eliminated through the intestines.

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