Digestive system in arachnids. External structure of arachnids External digestion in spiders

The cross-spider can be found in the forest, park, on the window frames of village houses and cottages. Most of the time, the spider sits in the center of its trapping web of sticky thread - cobwebs.

The body of the spider consists of two sections: a small elongated cephalothorax and a larger spherical abdomen. The abdomen is separated from the cephalothorax by a narrow constriction. Four pairs of walking legs are located on the sides of the cephalothorax. The body is covered with a light, strong and rather elastic chitinous cover.

The spider periodically molts, shedding its chitinous cover. During this time it grows. At the front end of the cephalothorax there are four pairs of eyes, and below a pair of hook-shaped hard jaws - chelicerae. With them, the spider grabs its prey.

There is a canal inside the chelicerae. Through the channel, the poison from the poisonous glands located at their base enters the body of the victim. Next to the chelicerae are short, covered with sensitive hairs, the organs of touch - the leg tentacles.

At the lower end of the abdomen there are three pairs of arachnoid warts that produce cobwebs - these are modified abdominal legs.

The liquid released from the spider webs instantly hardens in the air and turns into a strong cobweb thread. Different parts of spider warts secrete different types of webs. Spider threads vary in thickness, strength, stickiness. The spider uses various types of webs to build a trapping web: at its base, the threads are stronger and not sticky, and the concentric threads are thinner and stickier. The spider uses the web to strengthen the walls of its shelters and to make cocoons for its eggs.

Internal structure

Digestive system

The digestive system of a spider consists of a mouth, pharynx, esophagus, stomach, intestines (anterior, middle and posterior). In the midgut, long blind outgrowths increase its volume and absorption surface.

Undigested residues are brought out through the anus. The spider cannot eat solid food. Having caught prey (any insect), with the help of a web, he kills it with poison and lets digestive juices into his body. Under their influence, the contents of the caught insect liquefies, and the spider sucks it up. Only an empty chitinous shell remains from the victim. This type of digestion is called extraintestinal.

Circulatory system

The spider's circulatory system is not closed. The heart looks like a long tube located on the dorsal side of the abdomen.

Blood vessels branch off from the heart.

In a spider, the body cavity has a mixed nature - in the course of development it arises when the primary and secondary body cavities are connected. Hemolymph circulates in the body.

Respiratory system

The respiratory organs of the spider are the lungs and trachea. Lungs, or lung sacs, are located below, in front of the abdomen. These lungs evolved from the gills of the distant ancestors of aquatic spiders.

The spider-cross has two pairs of non-branching tracheas - long tubes that deliver oxygen to organs and tissues. They are located in the back of the abdomen.

Nervous system

The nervous system of a spider consists of the cephalothoracic ganglion and numerous nerves extending from it.

excretory system

The excretory system is represented by two long tubules - Malpighian vessels. With one end, the Malpighian vessels blindly end in the body of the spider, with the other they open into the posterior intestine. Through the walls of the Malpighian vessels, harmful waste products come out, which are then brought out. Water is absorbed in the intestines. Thus, spiders conserve water, so they can live in dry places.

Reproduction. Development

Fertilization in spiders is internal. The female cross spider is larger than the male. The male carries the spermatozoa into the female genital opening with the help of special outgrowths located on the front legs.

She lays her eggs in a cocoon woven from a thin silky cobweb. The cocoon weaves in various secluded places: under the bark of stumps, under stones. By winter, the female cross spider dies, and the eggs hibernate in a warm cocoon. In the spring, young spiders come out of them. In autumn, they release cobwebs, and on them, like on parachutes, they are carried by the wind over long distances - spiders are resettled.

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 well understood even by specialists. Many arachnologists, myself included, have studied various fields of entomology. Typically, courses in arthropod physiology center around insects. The most significant difference in the respiratory system of spiders and insects is that their blood or hemolymph plays no role in the respiration of insects, while in spiders it is a direct participant in the process.

Insect breath

The exchange of oxygen and carbon dioxide in insects is perfected largely due to the complex system of air tubes that make up the trachea and smaller tracheoles. Air tubes permeate the entire body in close contact with the internal tissues of the insect. For gas exchange between tissues and air tubes of an insect, hemolymph is not needed. This becomes clear in 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 enough for the hemolymph to perform its functions, which are to a greater extent the distribution of nutrients, water and the excretion of waste materials (a kind of equivalent to the kidneys of mammals). The heart starts beating again when the insect stops moving.

This is not the case with spiders, although it seems logical that spiders should proceed in this way, at least for those with tracheae.

Respiratory systems of spiders

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

1) The only pair of book lungs, like the 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 tubular tracheae, as, for example, in weaver spiders, wolves, and most species of spiders.

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

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

Spider blood

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

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

Spider trachea

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

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

book lungs

The lung slits or book lung slits (in some species, the lung slits have various openings that can widen or narrow depending on oxygen demand) are located in front of the lower abdomen. The cavity behind the opening is stretched internally and accommodates many leaf-like air pockets of the book lung. The book lung is literally crammed with air pockets lined with an extremely thin cuticle that allows gas exchange through 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 them and injecting venom through holes at the ends of their chelicerae. But chelicerae are unable to grind food into small pieces, and spiders have no teeth in their mouths. Therefore, spiders have adapted to eat liquid food. After killing the 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 digestion is called internal. Spiders have external digestion: after a while, the tissues of the victim soften and turn into a nutrient solution that the spider absorbs, leaving only an empty skin.

spitter spiders, or hissing spiders (scytodes), catch prey by spraying it with a sticky liquid. Once on the victim, the liquid tightly sticks it to the substrate. The "glue" is produced by special glands in the back of the spider and is released into the air through the chelicerae. Kills prey with a bite.

Class Arachnids biology

Ability to match

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

Demonstration version of the Main state exam of the OGE 2017 - task 2017 - Task No. 25

FEATURES CLASSES

1) insects

2) arachnids

A) Some representatives in development have a pupal stage.

B) The vast majority of representatives are predators.

C) The body of an animal consists of a head, thorax and abdomen.

D) Animals can only eat liquid food.

D) Animals have four pairs of walking legs.

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

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

Decision:

Signs of Pa-at-about-different: pain-shin-stvo before-hundred-vi-te-lei - predator-no-ki; the body consists of the head-lo-chest and abdomen; able to consume only liquid food; have four pairs of walking legs; 8 simple eyes.

Signs on-se-ko-myh: there is a stage of ku-kol-ki (for some-one before-hundred-vi-te-lei), the body is co-hundred -it from the head, chest and abdomen, different types of mouths; have three pairs of walking legs; on the head, simple and complex eyes can diverge.

Answer: 121221

Respiratory, digestive, excretory system of spiders

Respiratory system

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

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

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. Narrow openings are called pulmonary slits (also spiracles, stomata, stigmas). If you turn the tarantula over, then at least two of them (the rear pair) are visible. In well-fed individuals, the anterior 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 discarded opisthosoma exuvia. Inside the lungs are leaf-like folds of a thin membrane - lamellae ( lamellae, units lamella, also called leaflets or pages), which resemble the pages of a half-open book, hence the name. The hemolymph circulates within these folds, exchanging carbon dioxide for atmospheric oxygen, which separates the sheets from each other. The lamellas do not stick together with each other due to the many small spacers and racks. Book lungs are thought to be the result of the development of apodemes.

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

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

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

Digestive system

Spiders have no jaws. Instead, there are strong, strong chelicerae and fangs on them, and also rigid basal segments of 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 mobility nor function, these organs do not 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 at the mouth, a narrow pharyngeal tube extends inward and upward, not very far. As soon as it reaches the anterior lower surface of the brain, it sharply bends horizontally and pierces it. (Remember the donut hole?) The horizontal section of the tube is called the esophagus.

The esophagus empties into a hollow muscular organ - the discharge stomach. The latter, with its elongated posterior end, connects to the real stomach, which lies between it and the brain. Finger-like protrusions extend from the real stomach to the bases of the legs - gastric (gastric) diverticula ( diverticula, units diverticulum).

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

Digestive and circulatory systems of arachnids

There, a bundle of filamentous organs, the Malpighian vessels, is connected to it. They perform the functions of the kidneys. Shortly before the gut opens into the anus, it forms a large protrusion, a blindly closed pouch called the stercoral pouch ( stercoral pocket). The anal opening is located directly above the arachnoid appendages. Tarantulas rely on the chelicerae, fangs, and coxae of the pedipalps for the difficult task of chewing their 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 out by numerous hairs on the bases of the chelicerae and coxae of the pedipalps. Smaller particles, about a micron (0.001 mm) in size, are filtered out using the palatal plate, a special device in the throat. 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 simultaneously chewing their prey. The resulting slurry is diluted with the secretions of the coxal glands. As a result, partially digested liquid food is drawn into the mouth, then through the palatal plate into the pharynx and into the esophagus with the help of an injection stomach; in many ways it is similar to how we draw water through a straw, using the muscles of the cheeks and throat.

The pumping stomach is driven by powerful muscles, most of which are attached to the endosternitis and carapace. Through it, fluid from the esophagus flows back and down into the real stomach for further digestion and partial absorption. Finally, these processes are completed in the intestine. In the back of it, to what is left, waste products coming from the Malpighian vessels are added. All this accumulates in the stercoral pocket for some time. Periodically, excrement is excreted through the anus. 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 origin), not homologous (same origin and function).

Alternative names for parts of the digestive system are:
1. rostrum (rostrum) instead of labrum;
2. sucking stomach instead of delivery stomach;
3. proximal midgut instead of true stomach;
4. gastral cecum instead of gastral diverticulum;
5. medial midgut instead of gut;
6. cloacal chamber or cloaca instead of stercoral pocket and finally
7. The posterior intestine is the short segment of the digestive tract between the sterocoral pocket and the anus.

Duplication of nomenclature occurs as a result of attempts to "fit" spiders to a measure taken from very 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 the digestive and excretory systems at the same time, so we talk about them at the intersection of these two topics.

Most arthropods possess coxal glands, which are direct homologs of the more primitive excretory organs, the nephridia, found in less advanced invertebrates. The tarantulas have them too. There are two pairs of them, and they are located on the backward side of the basal segments (coxae) of the 1st and 3rd pairs of legs, from which the name of these organs comes. For many years, arachnologists have struggled to figure out why they are needed. Many have been inclined to think that the coxal glands do not perform any function, being vestiges of more primitive nephridia that are no longer needed. The others weren't so sure. (Nefridii will be mentioned again on p. 46.)

Recently, Butt and Taylor (1991) determined that the coxal glands have a function. It seems that they secrete a saline solution to the mouth, seeping through the bends of the pleural membranes between the coxae and the sternum. This serves two purposes. Firstly, this ensures the liquid state of the food slurry 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 part of the salts is deposited in the dry residue of food. So, paradoxically, spiders salivate under the armpits!

The final well-chewed dry food residue mostly consists of inedible parts of the victim's body (i.e. exoskeleton), which the spider is not able to digest, as well as excess salts. Amateurs sometimes refer to this remnant as a riddle; 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 sweet smell. It is not clear what causes this smell, 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 a dangerous level. Digestible substances consist mainly of carbon, hydrogen, oxygen and nitrogen with traces of other elements. During metabolism, carbon is converted to carbon dioxide and excreted through the lungs or gills. Hydrogen becomes water, which is no different from the water that enters the body with food or drink. Oxygen can be incorporated into various organic compounds or removed as part of carbon dioxide.

The hardest part is nitrogen.

Together with hydrogen, it gives 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. Several methods have been devised to avoid poisoning. The first is to convert nitrogen into a less toxic form than ammonia. If this product is less soluble, then even more of it can be accumulated if concentrated. And if there is still an opportunity to isolate the concentrate from the internal environment of the body, then it becomes much safer. Finally, the ideal end 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 of these approaches. And they did it again in their own way.

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 excreted 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, because it is insoluble, it can deposit 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 frequently. Then, since it is a solid, you can store it in safe places. Some intestinal cells (so-called guanocytes) are able to accumulate quite large amounts of guanine. Although they do not remove guanine from the body, they effectively neutralize it, allowing the body to function 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 about Most of the guanine secreted by the Malpighian vessels accumulates in the stercoral pocket and is ejected from there along with the remnants of undigested food. Thus, arachnids (and spiders among them) use all 4 approaches to avoid nitrogen poisoning, and they do it extremely effectively.

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

reproductive system

The sexual life of tarantulas is truly stunning, but it will be discussed a little later. Here, we restrict ourselves to a simple description of the mechanism.

The gonads of spiders - the ovaries in females and the testes in males - are located inside the opisthosome. Single genital opening (gonopore, gonopore) is located on the ventral surface of the opisthosome 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 epiginal plate. In early literature, the epigastric sulcus is sometimes referred to as the generative fold. In the female, two ovaries are connected to a single oviduct, which opens with a gonopore. Directly inside the gonopore are two "pockets", which are called spermatheca or spermatheca ( spermathecae, units spermatheca). During copulation (mating), the male deposits the sperm into the spermatheca, where the spermatozoa remain alive until they need to fertilize the eggs, weeks or months later.

In the male, the paired testicles 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; it is believed that they either contribute to the formation of seminal fluid, or develop a special thread for weaving the sperm web (Melchers 1964).

The male spider does not have a penis or any homologous organ. Its copulatory appendages are the secondary sex organs at the ends of the pedipalps. In adult males, the terminal segment of the pedipalp (pretarsus and claw) transforms from a simple construct seen in immature males to 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 the bulb ( bulb) or a reservoir, and the neck is an embolus ( embolus, pl. emboli). The foot, meanwhile, shortens and thickens. The embolus and bulb are attached to it with a flexible articulation that allows them to move freely in different planes. The modified foot is often called a cymbium ( cymbium, pl. cymbia). The cymbium is connected to the tibia by another elastic joint.

Berce 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 tuck them into this groove when they are not needed. But when the embolus and bulb are filled with sperm and ready to be injected into the female genital tract, they are completely open and turned at the right angle with respect to the pedipalp.

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

a brief description of

body structure	Body consists of cephalothorax and abdomen
body integuments	Body covered with chitinous cuticle
limbs	On the cephalothorax - 6 pairs of limbs: 2 pairs of jaws, 4 pairs of walking legs. No antennas or antennules
body cavity	Mixed cavity of the body, in which the internal organs are located
Digestive system	Anterior gut. Pharynx. Midgut. Hind gut. 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 - supraglottic node, peripharyngeal ring, abdominal nerve chain
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 have separate sexes. Fertilization is internal. Pronounced sexual dimorphism

general characteristics

Structure and integument. For arachnids, a characteristic feature is the tendency to merge the segments of the body that form the cephalothorax and abdomen. Scorpions have a fused cephalothorax and a segmented abdomen. In spiders, both the cephalothorax and the abdomen are continuous 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 ticks, which have lost even the division of the body into the cephalothorax and abdomen. The body of ticks becomes whole without borders between segments and without constrictions.

The integuments of arachnids consist of the cuticle, hypodermis, and basement membrane. The outer layer of the cuticle is a lipoprotein layer. This layer protects very well from loss of moisture during evaporation. In this regard, arachnids were able to become a real terrestrial group and settle in the most arid regions of the earth. The composition of the cuticle also includes proteins, tanned with phenols and encrusting chitin, which gives the cuticle strength. Derivatives of the hypodermis are spider and poisonous glands.

Limbs. Head limbs, except for two pairs of jaws, are absent in arachnids. The jaws, as a rule, are attributed to the limbs of the cephalothorax. The cephalothorax of arachnids bears 6 pairs of limbs, which is a distinctive feature of this class. The two front pairs are fitted

to capture and grind 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 is the opening of the poisonous gland. The second pair is pedipalps, on the main segment they have a chewing outgrowth, with the help of which food is crushed and kneaded. In some species, pedipalps turn into powerful claws (for example, in scorpions) or look like walking legs, and in some forms of spiders, a copulatory organ may be located at the end of the pedipalps. The remaining 4 pairs of limbs of the cephalothorax perform the function of movement - these are walking legs. During embryonic development, a large number of limbs are laid on the abdomen, but in adult chelicerates, the abdomen is devoid of typical limbs. If the abdominal limbs persist into adulthood, they are usually modified into genital opercula, tactile appendages (scorpions), lung sacs, or arachnoid warts.

Rice. one. The mouth organs of the cross spider: 1 - the terminal claw-like segment of the chelicera; 2 - basal segment of helicerae; 3 - pedipalp; 4 - chewing outgrowth of the main segment of the pedi-palp; 5 - main segment of the walking leg

The digestive system (Fig. 2) has features associated with a peculiar way of eating arachnids - extraintestinal, or external, digestion. Arachnids cannot take solid food in chunks. Digestive enzymes are injected into the victim's body and turn its contents into a liquid slurry 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 of most arachnids has lateral blind protrusions to increase the absorptive surface. In the abdomen, the ducts of the paired liver open into the intestine. The liver performs not only digestive functions, releasing digestive enzymes, but also an absorption function. Intracellular digestion takes place in the liver cells. The hindgut ends at the anus.

The respiratory system of arachnids is represented by lung sacs and tracheae. At the same time, some species have only lung sacs (scorpions, primitive spiders). In others, the respiratory organs are represented only by tracheae.

2. Spider organization scheme: 1 - eyes; 2 - poisonous gland; 3 - chelicera; 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 - spider glands; 14 - arachnoid warts; 15 - anus; 16 - Malpighian vessels; 17 - os-ti; 18 - ducts of the liver; 19 - heart; 20 - pharynx connected with the body wall by muscles

(salpugs, haymakers, some ticks). In spiders, two types of respiratory organs occur simultaneously. There are four-lung spiders that have 2 pairs of lung sacs and no tracheae; bipulmonary spiders - one pair of lung sacs and a pair of tracheal bundles and lungless spiders - only tracheas. Some small spiders and some mites have no respiratory organs and respiration is carried out through the thin integuments of the body.

Circulatory system, as in all arthropods, open. Hemolymph contains the respiratory enzyme hemocyanin.

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

The structure of the heart depends on the degree of segmentation - the more segments, the more ostia (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 circulatory, depends on the segmentation of the body. The least concentrated nerve chain in scorpions. 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 ganglionic mass in the cephalothorax and ganglia of the abdominal chain. With a decrease in segmentation, the ventral chain disappears. So, in spiders, the entire abdominal chain merges into the cephalothoracic ganglion. And in harvestmen and ticks, the brain and cephalothoracic ganglion form a continuous ganglionic ring around the esophagus.

sense organs mainly represented by special hairs that are located on the pedipalps, legs and body surface and respond to air vibrations. On the pedipalps there are also 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, rarely 2.

Development. Most arachnids lay eggs, but live births have also been observed. Development is direct, but ticks have metamorphosis.

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

Respiratory system of spiders

Robert Gale Breen III

Southwestern College, Carlsbad, New Mexico, USA

Insect breath

This is not the case with spiders, although it seems logical that spiders should do things this way, at least for those with tracheae.

Respiratory systems of spiders

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

1) The only pair of book lungs, like the 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 tubular tracheae, as, for example, in weaver spiders, wolves, and most species of spiders.

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

Spider blood

Oxygen and carbon dioxide are carried along the hemolymph by the respiratory pigment protein, hemocyanin. Although hemocyanin is similar in chemical properties to vertebrate hemoglobin, unlike the latter, it contains two copper atoms, which gives the blood of spiders a bluish tint. Hemocyanin is not as effective at binding gases as hemoglobin, but its capabilities are quite enough for spiders.

Spider trachea

book lungs

The lung slits or book lung slits (in some species, the lung slits have various openings that can widen or narrow depending on oxygen demand) are located in front of the lower abdomen. The book lung is literally crammed with air pockets lined with an extremely thin cuticle that allows gas exchange through 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.

Breath of tarantulas

Since tarantulas are large and easier to study, many physiologists focus on them when considering the mechanism of respiration of spiders. The geographical habitat of the studied species is rarely specified, it can be assumed that most of them come from the United States. Almost universally, the taxonomy of tarantulas is not taken into account. Only rarely do physiologists engage a competent spider taxonomist. More often, they believe anyone who says they can identify test species. This disregard for systematics is evident even among the most famous physiologists, including R.F. Felix, author of the only widely circulated, but, alas, not the most accurate book on spider biology.

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

A few popular scientific names, both comical and sad for those who have any idea of taxonomy, are most often found in articles of this kind. The first name is Dugesiella, most commonly referred to as Dugesiella hentzi. The genus Dugesiella disappeared from the Aphonopelma family a long time ago, and even if it was once assigned to Aphonopelma hentzi (Girard), this cannot be accepted as a credible identification. If a physiologist refers to D. hentzi or A. hentzi, it only means that someone was researching a species of Aphonopelma that someone else thought was a species from Texas.

It's sad, but the name is still walking among physiologists Eurypelmacalifornicum. Genus Eurypelmawas dissolved in another genus some time ago, and the speciesAphonopelmacalifornicumwas declared invalid. These spiders, perhaps, should be attributed toAphonopelmaeutylenum. When you hear these names, it only means that someone thinks that these species are native to California.

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

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

In test tarantulas, it was found that the first (anterior) pair of book lungs controls the flow of blood from the prosoma (cephalothorax), while the second pair of lungs controls blood from the abdomen, before it returns to the heart.

In insects, the heart is predominantly a simple tube that sucks blood from the abdomen, pushes it through the aorta, and ejects it into the head compartment of the insect's body. With spiders, the situation is different. After the blood has passed through the aorta, then through the isthmus between the cephalothorax and abdomen and into the cephalothorax, its flow is divided into what can be defined as a closed system of arteries. It branches and goes to separate parts of the head and legs. Other arteries, called lateral abdominal arteries, originate from the heart on both sides and branch inside the abdomen. From the back of the heart to the arachnoid appendages stretches the so-called. abdominal artery.

When the tarantula's heart contracts (systole), blood is pushed not only forward through the aorta into the cephalothorax, but also from the sides through the lateral arteries and from behind, down through the abdominal artery. Such a system is operable at various levels of blood pressure for the cephalothorax and abdomen. In conditions of increased activity, the blood pressure in the cephalothorax significantly exceeds the blood pressure in the abdomen. In this case, a point is quickly reached when the pressure of the hemolymph in the cephalothorax becomes so great that the blood cannot be pushed from the abdomen into the cephalothorax through the aorta. When this happens, after a certain time, the spider suddenly stops.

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

From a physiological point of view, there are two main reasons why spiders freeze. The muscles so actively involved in the escape attempt are attached to the cephalothorax. This gives reason to many to believe that the muscles simply run out of oxygen, and they stop working. Perhaps it is. And yet: why does this not lead to stammering, twitching, or other manifestations of muscle weakness? However, this is not observed. The main consumer of oxygen in the cephalothorax of tarantulas is the brain. Could it be that the muscles can work a little longer, but the spider's brain takes oxygen a drop earlier? A simple explanation could be that these maniacal escapees are simply passing out.

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

Representatives of arachnids are eight-legged land arthropods, in which the body is divided into two sections - the cephalothorax and abdomen, connected by a thin constriction or fused. Arachnids do not have antennae. Six pairs of limbs are located on the cephalothorax - two front pairs (mouth organs), which serve to capture and grind food, and four pairs of walking legs. There are no legs on the abdomen. Their respiratory organs are lungs and trachea. The eyes of arachnids are simple. Arachnids are dioecious animals. The class Arachnida includes more than 60 thousand species. The body length of various representatives of this class is from 0.1 mm to 17 cm. They are widely distributed around the globe. Most of them are land animals. Among ticks and spiders there are secondary water forms.

The biology of arachnids can be considered using the example of a spider-cross.

External structure and lifestyle. The cross-spider (so named for the cross-shaped pattern on the dorsal side of the body) can be found in the forest, garden, park, on the window frames of village houses and cottages. Most of the time, the spider sits in the center of its trapping web of sticky thread - cobwebs.

The body of the spider consists of two sections: a small elongated cephalothorax and a larger spherical abdomen (Fig. 90). The abdomen is separated from the cephalothorax by a narrow constriction. At the anterior end of the cephalothorax, there are four pairs of eyes above, and below, a pair of hook-shaped hard jaws - a chelicerae. With them, the spider grabs its prey. There is a canal inside the chelicerae. Through the channel, poison from the poisonous glands located at their base enters the body of the victim. Next to the chelicerae are short, covered with sensitive hairs, the organs of touch - the leg tentacles. Four pairs of walking legs are located on the sides of the cephalothorax. The body is covered with a light, strong and rather elastic chitinous cover. Like crayfish, spiders periodically molt, dropping their chitinous cover. At this time they are growing.

Rice. 90. The external structure of the spider: 1 - leg tentacle; 2 - leg; 3 - eye; 4 - cephalothorax; 5 - abdomen

At the lower end of the abdomen there are three pairs of arachnoid warts that produce cobwebs (Fig. 91) - these are modified abdominal legs.

Rice. 91. Trapping nets of various types of spiders (A) and the structure (with magnification) of the spider web (B)

The liquid released from the spider web warts instantly hardens in the air and turns into a strong spider web. Different parts of spider warts secrete different types of webs. Spider threads vary in thickness, strength, stickiness. The spider uses various types of webs to build a trapping web: at its base, the threads are stronger and not sticky, and the concentric threads are thinner and stickier. Spiders use the web to strengthen the walls of their shelters and to make cocoons for their eggs.

Digestive system the spider consists of a mouth, pharynx, esophagus, stomach, intestines (Fig. 92). In the midgut, long blind outgrowths increase its volume and absorption surface. Undigested residues are brought out through the anus. The cross spider cannot eat solid food. Having caught prey, such as some kind of insect, with the help of a web, he kills him with poison and lets digestive juices into his body. Under their influence, the contents of the caught insect liquefies, and the spider sucks it out. Only an empty chitinous shell remains from the victim. This type of digestion is called extraintestinal.

Rice. 92. The internal structure of the spider-cross: 1 - poisonous gland; 2 - mouth and esophagus; 3 - stomach; 4 - heart; 5 - lung sac; 6 "- sex gland; 7 - trachea; 8 - spider gland; 9 - intestine; 10 - Malpighian vessels; 11 - outgrowths of the intestine

Respiratory system. The respiratory organs of the spider are the lungs and trachea. Lungs, or lung bags, are located below, in front of the abdomen. These lungs evolved from the gills of distant ancestors of aquatic spiders. The spider-cross has two pairs of non-branching tracheas - long tubes that deliver oxygen to organs and tissues. They are located in the back of the abdomen.

Circulatory system spiders are open. The heart looks like a long tube located on the dorsal side of the abdomen. Blood vessels branch off from the heart.

In a spider, as in crustaceans, the body cavity is of a mixed nature - in the course of development it arises when the primary and secondary cavities of the forehead are connected. Hemolymph circulates in the body.

excretory system It is represented by two long tubes - Malpighian vessels.

With one end, the Malpighian vessels blindly end in the body of the spider, with the other they open into the posterior intestine. Through the walls of the Malpighian vessels, harmful waste products come out, which are then brought out. Water is absorbed in the intestines. In this way, spiders conserve water, so they can live in dry places.

Nervous system The spider consists of the cephalothoracic ganglion and numerous nerves extending from it.

Reproduction. Fertilization in spiders is internal. The male carries the spermatozoa into the female genital opening with the help of special outgrowths located on the front legs. The female, some time after fertilization, lays eggs, braids them with cobwebs and forms a cocoon (Fig. 93).

Rice. 93. Female spider with a cocoon (A) and the resettlement of spiders (B)

The eggs develop into small spiders. In autumn, they release cobwebs, and on them, like on parachutes, they are carried by the wind over long distances - spiders are resettled.

Variety of arachnids. In addition to the cross-spider, about 20 thousand more species belong to the order Spiders (Fig. 94). A significant number of spiders build trapping webs from the web. Y different web spiders differ in shape. So, in a house spider living in a person’s housing, the trapping net resembles a funnel, in a poisonous, deadly for humans karakurt, the trapping net resembles a rare hut. Among spiders there are also those that do not build trapping webs. For example, side-walker spiders sit in ambush on flowers and wait for small insects arriving there. These spiders are usually brightly colored. Jumping spiders are able to jump and thus catch insects.

Rice. 94. Various spiders: 1 - cross-spider; 2 - karakurt; 3 - spider regiment; 4 - crab spider; 5 - tarantula

Wolf spiders roam everywhere looking for prey. And some spiders sit in minks in ambush and attack insects crawling nearby. These include a large spider that lives in southern Russia - a tarantula. The bites of this spider are painful for humans, but not fatal. The Haymakers include very long-legged arachnids (about 3,500 species) (Fig. 95, 2). Their cephalothorax is indistinctly separated from the abdomen, the chelicerae are weak (therefore, haymakers feed on small prey), the eyes are located in the form of a “turret” on top of the cephalothorax. Harvestmen are capable of self-mutilation: when a predator grabs a haymaker by the leg, he discards this limb, and he runs away. Moreover, the severed leg continues to bend and unbend - “mow”.

Scorpions are well represented in the subtropics and deserts by small animals 4-6 cm long (Fig. 95, 3). Large scorpions up to 15 cm long live in the tropics. The body of a scorpion, like that of a spider, consists of a cephalothorax and abdomen. The abdomen has a fixed and wide anterior part and a narrow, long movable posterior part. At the end of the abdomen there is a swelling (the poisonous gland is located there) with a sharp hook. With it, the scorpion kills its prey and defends itself from enemies. For a person, the injection of a large scorpion with a poisonous sting is very painful, and can lead to death. The chelicerae and tentacles of scorpions are claw-shaped. However, chelicerae claws are small, while leg tentacle claws are very large and resemble those of crayfish and crabs. In total, there are about 750 species of scorpions.

Rice. 95. Various representatives of arachnids: 1 - tick; 2 - haymaker; 3 - scorpion; 4 - phalanx

Ticks. There are more than 20 thousand species of ticks. The length of their body usually does not exceed 1 mm, very rarely - up to 5 mm (Fig. 95, 1 and 96).

Unlike other arachnids, ticks do not have a body divided into cephalothorax and abdomen. Ticks that feed on solid food (microscopic fungi, algae, etc.) have gnawing jaws, while those that feed on liquid food form a piercing-sucking proboscis. Ticks live in the soil, among fallen leaves, on plants, in water, and even in human homes. They feed on rotting plant debris, small fungi, algae, invertebrates, suck plant sap; in human living quarters, microscopic mites feed on dry organic residues contained in dust.

Rice. 96. Ixodid tick

The meaning of arachnids. Arachnids play a big role in nature. Known among them are both herbivores and predators that eat other animals. Arachnids, in turn, feed on many animals: predatory insects, birds, animals. Soil mites are involved in soil formation. Some ticks are carriers of serious diseases of animals and humans.

Arachnids are the first terrestrial arthropods that have mastered almost all habitat conditions. Their body consists of the cephalothorax and abdomen. They are well adapted to life in the ground-air environment: they have dense chitinous covers, they have pulmonary and tracheal breathing; save water, play an important role in biocenoses, are important for humans.

Lesson learned exercises

What are the signs of the external structure of arachnids that distinguish them from other representatives of arthropods
Using the example of a spider-cross, tell about the methods of obtaining and digesting food. How are these processes related to the internal organization of the animal?
Give a description of the structure and activity of the main organ systems, confirming the more complex organization of arachnids compared to annelids.
What is the importance of arachnids (spiders, ticks, scorpions) in nature and human life?

Respiratory system. The respiratory organs of the cross are a pair of leaf-folded lungs and tubular tracheae. The lungs are located at the base of the abdomen on the sides of the genital opening, where there are two transverse slits - stigmas of the lungs.

The stigma leads to the lung cavity, on the wall of which there are a number of flat pockets that diverge in a fan-like fashion. The pockets are connected with jumpers and do not fall off, so that air freely penetrates between them. Blood circulates in the cavities of the pockets, the exchange of gases occurs through their thin cuticular walls.

The tracheal system consists of two non-branching tubes, which are directed forward from a common pocket, which opens with an inconspicuous transverse slit in front of the arachnoid warts.

excretory system. There are two types of excretory organs: Malpighian vessels and coxal glands. In addition, the excretory function is performed by special cells (nephrocytes and guanocytes) lying in the body cavity. The Malpighian vessels are represented by four branching tubes blindly closed at the ends, which flow into the rectal bladder along its sides at the border of the middle and posterior intestines. Malpighian vessels are lined with squamous epithelium, in the cells of which grains of guanine, the main excretion product, are formed. The coxal glands, which in arachnids are the remains of the coelomoduct system, are located at the base of the first pair of legs. In an adult spider, they do not function.

poison glands. Poisonous glands are located in the anterior part of the cephalothorax at the base of the chelicerae. This is a pair of rather large cylindrical glands that enter the cavity of the main segments of the chelicerae. The outer lining of the gland is formed by a spirally curled ribbon-like muscle, during the contraction of which the poison is poured out through a thin duct that opens at the end of the claw-like segment of the chelicerae.

Spinning apparatus. The spinning apparatus is represented by three pairs of spider warts and spider glands. At rest, spider warts, together with the anal tubercle, form a common closed group. At the tops of the warts there are numerous arachnoid tubes through which a secret is secreted - a web that hardens when it comes into contact with air. Spider glands fill the lower part of the female's abdominal cavity.

Their structure and size are not the same; distinguish tubular, ampulloidal, dendritic and pear-shaped glands. The latter are especially numerous and connected in bundles according to the number of warts (Plate X). The role of various glands and warts is different, the tubular glands secrete a web for the egg cocoon, the ampullic glands for building a network, the pear-shaped glands for braiding prey; arboreal secrete a sticky secret that covers the network.