Respiratory and excretory systems of arachnids. Phylum Arthropod

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 in to a greater extent are to distribute nutrients, water and the release of waste substances (a kind of equivalent to the kidneys of mammals). 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 various types respiratory systems, which depends on the taxometric group and who you talk to about it:

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 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 transported through the hemolymph by the respiratory pigment protein hemocyanin. Although hemocyanin is chemical properties and resembles 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 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 prey 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 anterior pair is hidden by the basal segments last pair 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, in Lately 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. More fine particles, about a micron in size (0.001mm), are filtered using a 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 similar (similar, but of different origins), and not 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 a short segment digestive tract between the stercoral recess 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 for long years(almost a thousand individuals at the moment), feeding is accompanied by a characteristic heavy sweetish smell. 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 built into various organic compounds or released 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, simply allowing them to dissolve into 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 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, 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 (so-called guanocytes) are capable of accumulating quite large quantities 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, concentrating waste products to 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 spermatheca ( 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 world again with gonopor. 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 characteristic feature there is a tendency to merge the body segments that form 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 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. On the abdomen during embryonic development is laid big number limbs, but in adult chelicerates the abdomen lacks 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"

Representatives of arthropods are the class Arachnida. The most famous of them are ticks, scorpions and spiders. In this article you will learn external structure arachnids, get acquainted with the peculiarities of the nervous system and sensory organs of arachnids.

Arachnids are everywhere. There are orders that live in the tropics and subtropics. Scorpions are found in the temperate zone, and some species of ticks and spiders can live in polar conditions.

External structure

The animal's body consists of two sections:

cephalothorax;
abdomen.

There are two pairs of mouthparts on the cephalothorax: the pedicles and the chelicerae. The first pair of limbs are chelicerae; they have claws at the ends. It is on them that there are ducts of poisonous glands, with the help of which the animal defends itself and kills prey.

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The second pair of limbs, covered with bristles, are the tentacles. They are also an organ of smell and touch.

The next 4 pairs are walking legs. They have claws at the ends and are also covered with bristles. As a result, we get 6 pairs of limbs.

The abdomen is covered by a soft membrane. There are no limbs on it, and in some spiders they are modified into arachnoid warts. On top of the warts, ducts of glands open, forming a web. On the abdomen there are exits for the respiratory, digestive and reproductive organs.

Fig.1. External structure

Most arachnids lack muscles in their limbs. They move due to the influence of hemolymph pressure. Some species of scorpions have a muscle that can bend two joints at once.

The body cover is complexly organized and is formed by a single-layer epithelium, which forms a chitinous membrane. To protect against damage and excess water loss, chitin is covered with a wax-like film. Many species have hairs on the surface of the body that perform a protective function and are sensory organs.

Features of the nervous system

The nervous system of arachnids is also diverse in its structure. Externally, it is a solid abdominal chain, but there are a number of features:

The brain lacks the section responsible for the functioning of the antennules in crustaceans and insects;
The anterior and posterior sections regulate the functioning of the eyes of arachnids, as well as the chelicerae;
Ganglia in most cases are concentrated, forming a ganglion mass.

Fig.2. Nervous system (blue)

Sense organs

Spiders have a sense of touch great importance, the presence of hairs on the body confirms this. Each individual hair is attached to the bottom of a special hole, which connects it with sensitive cells.

Sensitive hairs are able to detect the slightest vibrations in the air or web. Depending on the intensity of the vibrations, spiders distinguish the nature of the irritation.

The lyre-shaped organs, located throughout the body, are responsible for chemical senses.

The organs of vision are the eyes, which have a simple structure. Answer the question: “How many eyes do arachnids have?” difficult, since it all depends on the species. In general, their number varies from 2 to 12. Despite the number of pairs of eyes, the vision of this class is weak and they see at a short distance.

Fig.3. Diagram of eye arrangement in different species

What have we learned?

Arachnids by external signs belong to the phylum arthropods. This class has adapted to a terrestrial habitat and is distributed everywhere. The body of the animal consists of two sections, on which there are 6 pairs of limbs. Among the senses, touch plays an important role.

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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 enhanced muscular system, 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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Respiratory system of spiders

Robert Gale Breen III

Southwestern College, Carlsbad, New Mexico, USA

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.

With spiders the situation is different, although it seems logical that things should happen in a similar way for spiders, at least for those with tracheas.

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.

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

Book lungs

The pulmonary slits or booklung slits (in some species the pulmonary slits are equipped with various openings that can widen or contract depending on oxygen needs) are located at the front of the lower abdomen. The cavity behind the opening is stretched internally and houses many of the booklung's leaf-like air pockets. 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.

Breathing of tarantulas

Since tarantulas are large in size and easier to study, many physiologists, when considering the mechanism of spider respiration, focus on them. Geographical location The habitat of the studied species is rarely specified; it can be assumed that most of them come from the USA. The taxonomy of tarantulas is almost universally ignored. Only rarely do physiologists engage a competent spider taxonomist. More often than not, they believe anyone who says they can identify the test species. Such disregard for systematics is manifested 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.

A book lung consisting of sheet-like interspersed 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 (after Felix, 1996).

Several popular scientific names, both comical and sad for those who have at least some idea of taxonomy, are most often found in this kind of articles. The first name is Dugesiella, most often referred to as Dugesiella hentzi. The genus Dugesiella disappeared from the family Aphonopelma 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 just means that someone studied a species of Aphonopelma that someone else decided was a Texas native.

It’s sad, but the name is still circulating among physiologists Eurypelmacalifornicum. Genus Eurypelmawas dissolved in another genus some time ago, and the speciesAphonopelmacalifornicumwas declared invalid. These spiders should probably be classified asAphonopelmaeutylenum. When you hear specified names, it just means that someone thinks these species are native to California.

Some “scientific” names really make you blush. In the 1970s, someone conducted research on a species calledEurypelmahelluo. Apparently, they were mistaken in classifying the species as a wolf spider.Lycosahelluo(Now Hognahelluo(Valkenaer)) and changed the genus name to make it more similar to the name of the tarantula. God knows who these people were researching.

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

In tested 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 flow 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 discharges it in the region of 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 area, its flow is divided into what can be defined as a closed system of arteries. It branches and goes to separate areas of the head and legs. Other arteries, called the lateral abdominal arteries, arise 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. A similar system is operational at different blood pressure levels for the cephalothorax and abdomen. Under conditions of increased activity, blood pressure in the cephalothorax significantly exceeds 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 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 this behavior in our pets. When a tarantula has the 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 may run for a while and suddenly freeze, allowing the keeper to catch the fugitive. Most likely, it stops as a result of the blood stopping flowing to the cephalothorax.

From a physiological point of view, there are two main reasons for spiders to freeze. The muscles so actively involved in an escape attempt are attached to the cephalothorax. This gives many people reason to believe that the muscles simply run out of oxygen and they stop working. Perhaps this is true. And yet: why doesn’t this lead to stuttering, 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 little earlier? A simple explanation may be that these maniacally eager fugitives simply lose consciousness.

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

Like any other living beings, spiders are distinguished by various abilities, among which the ability to breathe stands out. Of course, the respiratory system of arachnids is significantly different from the breathing of other mammals, not to mention humans.

Respiratory system of spiders

It is worth noting that the breathing characteristic of spiders is not entirely clear even for specialists, since the process of exchange of oxygen and carbon dioxide in these representatives of arachnids is quite interesting and difficult.

The main difference between the respiratory system of spiders and insects is that the respiration of spiders is directly related to the participation of blood in this process. The respiratory system of any insect is a rather complex system of a complex of tubes that penetrate its body from all sides. In this case, the tubes form the trachea and are in close contact with the tissues.

The respiratory system of arachnids is a complex of five various systems, and their number depends on the taxometric group. Much here, of course, also depends on the type of spider, since large species have the most advanced respiratory system.

Trachea of arachnids

The tracheae of spiders penetrate the body of representatives of the class along the entire perimeter, thus constituting the basis for the breathing of spiders. The tracheal tubes end near the tissues, which ensures their contact with each other. However, this contact is not close enough to supply oxygen to the spiders’ respiratory system and remove carbon dioxide from it, as happens in the body of ordinary insects.

Accordingly, the breathing of spiders using a tubular trachea occurs in a slightly different way. Typically, the tubular trachea has no more than one or less than two openings, and they emerge on the underside of the abdomen next to the appendages.

Thus, breathing occurs, which is characteristic of arachnids.