Class Arachnida - Arachnida Cross spider. Respiratory and excretory systems of arachnids How do arachnids breathe

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 consist in the distribution of 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, as, for example, 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 in individual species), like in a small family Caponiidae.

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

Blood of Spiders

Oxygen and carbon dioxide are transported through the hemolymph by the respiratory pigment protein hemocyanin. Although hemocyanin 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, complex system The arteries passing to the legs and head region can be considered a predominantly closed system (according to Felix, 1996).

Spider trachea

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

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

Book lungs

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

Digestive system of arachnids

How do spiders digest food?

» Arthropods » Arachnids » How do spiders digest food?

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

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

Class Arachnida biology

Ability to establish compliance

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

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

SIGNS CLASSES

1) insects

2) arachnids

A) Some representatives have a pupal stage in development.

B) The vast majority of representatives are predators.

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

D) Animals are able to absorb only liquid food.

D) Animals have four pairs of walking legs.

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

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

Solution:

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

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

Answer: 121221

Respiratory, digestive, excretory system of spiders

Respiratory system

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

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

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

There has been much controversy regarding the presence or absence of respiratory movements in tarantulas. Do they have active breathing with inhalation and exhalation, like we do? Proponents of this point of view point to the seemingly existing respiratory movements and muscles closely associated with the lungs. Their opponents argue that tarantulas do not make breathing movements when observed. For some reason, it so happened that the results of experiments conducted in this direction were contradictory or ambiguous. However, 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. Smaller particles, about a micron in size (0.001mm), are filtered out using the palatal plate, a special device in the pharynx. By comparison, most mammalian cells and most bacteria are larger than one micron. Spiders and most other arachnids do not like solid food.

While eating, tarantulas regurgitate digestive juices while chewing their prey. The resulting slurry 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 digestive system are:
1. rostrum instead of labrum;
2. sucking stomach instead of pumping stomach;
3. proximal midgut instead of true stomach;
4. gastric cecum instead of gastric diverticulum;
5. medial midgut instead of intestine;
6. cloacal chamber or cloaca instead of stercoral pouch and, finally,
7. The hindgut is the short section of the digestive tract between the stercoral pouch and the anus.

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

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

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

Recently, Butt and Taylor (1991) determined that the coxal glands have a function. They appear to secrete to the mouth saline solution, leaking 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 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 residue of food for the most part consists of inedible parts of the victim's body (i.e. the exoskeleton), which the spider is not able 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 by simply allowing them to dissolve in surrounding water. They usually have plenty of water and little energy is spent on excretion.

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

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

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

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

And finally, 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 in highest degree effective.

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 do they do?

Reproductive system

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

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

In the male, the paired testes are spirally twisted tubes that open into a common duct. The duct, in turn, opens into the 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 not only performs digestive functions, secreting digestive enzymes, but also 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 show 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"

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

a brief description of

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

general characteristics

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Arachnoids, or arachnids, are among the most ancient living creatures on Earth. Character traits the structures of arachnids are determined by their existence on land and their predatory lifestyle.

External structure

The external structure of arachnids is different. In spiders, the body is divided into sections:

elongated cephalothorax;
wide belly.

Between the two parts of the body there is a narrow constriction. The cephalothorax is equipped with organs of vision and digestion. Spiders have several simple eyes (from 2 to 12), providing all-round vision.

Hard, curved jaws grow on the sides of the mouth - chelicerae . With them the predator grabs its prey. Chelicerae are equipped with ducts containing poison, which is injected into the body at the time of the bite. The first pair of limbs serves for defense during an attack.

The oral apparatus of arachnids is supplemented by a second pair - claws . The spider uses them to hold the victim while eating. They also serve as sense organs. The oral tentacles are covered with many hairs. The hairs sensitively pick up the slightest vibrations of the surface and air, helping the spider navigate in space and sense the approach of other creatures.

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The question: how many antennae does a spider have is not difficult to answer. Arachnids do not have antennae.

There are 4 pairs of limbs on the sides of the cephalothorax. The comb-shaped claws on the hind legs are used for weaving webs.

It is visually easy to see what kind of cover spiders have on their bodies. They are protected by a durable chitinous shell. During the growth process, it periodically changes during molting.

Rice. 1 Spider - cross

Internal structure

The structural peculiarity of arachnids is noticeable in the organization of the body cavity. It is a connection between the primary and secondary cavities. The body is filled with hemolymph. The heart is located in the dorsal part of the abdomen and looks like a long tube. Blood vessels branch off from it. Circulatory system is not closed.

Spiders' blood is colorless.

Respiratory system presented:

trachea ;
lung sacs .

Breathing is adapted to life on land. Spiders breathe using tracheas, which resemble two long tubes with numerous holes. Through them, oxygen flows to the internal organs.

Digestive system comprises:

mouth ;
throats ;
stomach ;
foregut, midgut and hindgut ;
cloaca .

Excretory system arachnids in an unusual way. The excretory organs are two Malpighian vessels. These are tubes with one end extending into the internal cavity of the body and the other into the intestines. Waste substances penetrate through the walls of blood vessels. The end products are excreted, and the liquid remains inside the body. In this way, spiders retain moisture and can for a long time live in arid conditions.

Let's study which nervous system in arachnids. It is called nodular because the main center forms 5 pairs of nerve ganglia. A nerve chain runs along the abdomen.

IN sexual reproduction males and females participate. Females are larger in size and often eat their partner. After fertilization, the female lays eggs and weaves a cocoon around them.

Rice. 2 Cocoon

The maximum number of eggs is 20 thousand pieces.

After the offspring appear, the mother looks after it for some time. The development of the young depends on the variety.

Web

Creation

Spiders have their own hunting accessory - a hunting net, in the form of a web. On the abdomen there are arachnoid warts equipped with special glands. They produce a thin but extremely strong thread. The glands of arachnids produce a special substance that quickly hardens in air. Spider thread has different characteristics and purposes:

not adhesive, but durable for the network frame;
sticky and thin for network cells;
soft for the cocoon with eggs and the walls of the hole.

Rice. 3 Web

Meaning

Spiders set their traps among the thickets and hide in a secluded place. When an insect gets into the net, vibrations of the threads inform the hunter about the prey. It tightly wraps the victim with a sticky substance and then injects a poisonous secretion into it. This liquid acts like digestive juice. It softens the prey. After which the predator sucks up the resulting mush. This method of nutrition is called extraintestinal.

The thread helps the spider move in space. With her help, he descends from the heights and finds the way to his refuge.

A giant spider's web was discovered in Madagascar. It was woven by Darwin's spider. The diameter of the miracle net is 25 meters.

Spider thread resembles silk in its appearance and properties. Residents of tropical islands make small fishing nets from it. In the old days, spider webs were applied to wounds instead of dressing material.

What have we learned?

The body of arachnids consists of several connected parts. Distinctive features structures: oral limbs with poisonous ducts, extraintestinal digestion, the presence of arachnoid glands.

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About 25 thousand species of arachnids are known. These arthropods are adapted to living on land. They are characterized by air breathing organs. As typical representative of the Arachnida class, consider the cross spider.

External structure and nutrition of arachnids

In spiders, the body segments merge to form the cephalothorax and abdomen, separated by an interception.

The arachnid's body is covered chitinized cuticle and the underlying tissue (hypodermis), which has a cellular structure. Its derivatives are arachnoid and poisonous glands. The venom glands of the cross spider are located at the base of the upper jaws.

A distinctive feature of arachnids is the presence six pairs of limbs. Of these, the first two pairs - the upper jaws and the claws - are adapted for capturing and grinding food. The remaining four pairs perform the functions of movement - these are walking legs.

During embryonic development, a large number of limbs are formed on the abdomen, but later they are transformed into spider warts, opening by the ducts of the arachnoid glands. Hardening in air, the secretions of these glands turn into spider threads, from which the spider builds a trapping network.

After the insect has fallen into the net, the spider envelops it in a web, plunges the claws of its upper jaws into it and injects poison. Then he leaves his prey and hides in cover. The secretion of the poisonous glands not only kills insects, but acts as digestive juice. After about an hour, the spider returns to its prey and sucks out the semi-liquid, partially digested food. From a killed insect, only one chitinous cover remains.

Respiratory system in the cross spider it is represented by pulmonary sacs and trachea. Lung sacs and the trachea of arachnids open outward with special openings on the lateral parts of the segments. The pulmonary sacs contain numerous leaf-shaped folds in which blood capillaries pass.

Trachea They are a system of branched tubes that connect directly to all organs where tissue gas exchange occurs.

Circulatory system arachnids consists of a heart located on the dorsal side of the abdomen and a vessel through which blood moves from the heart to the front of the body. Because circulatory system unclosed, then blood returns to the heart from the mixed body cavity (mixocoel), where it washes the pulmonary sacs and trachea and is enriched with oxygen.

Excretory system The cross spider consists of several pairs of tubes (Malpighian vessels) located in the body cavity. Of these, waste products enter the posterior intestine.

Nervous system Arachnids are characterized by the fusion of nerve ganglia with each other. In spiders, the entire nerve chain merges into one cephalothoracic ganglion. The organ of touch is the hairs covering the limbs. The organ of vision is 4 pairs of simple eyes.

Reproduction of arachnids

All arachnids are dioecious. The female cross spider lays eggs in the fall in a cocoon woven from a silky web, which she places in secluded places (under stones, stumps, etc.). By winter, the female dies, and spiders emerge from eggs overwintered in a warm cocoon in the spring.

Other spiders also take care of their offspring. For example, a female tarantula carries her young on her back. Some spiders, having laid eggs in a web cocoon, often carry it with them.

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

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

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

Veils

Arachnids have a relatively thin chitinous cuticle, under which lies the hypodermis and basement membrane. The cuticle protects the body from loss of moisture through evaporation, which is why arachnids inhabited the driest areas globe. The strength of the cuticle is given by proteins encrusting chitin.

Respiratory system

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

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

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

Some small ticks specialized bodies There is no breathing; gas exchange occurs in them, as in primitive invertebrates, through the entire surface of the body.

Nervous system and sensory organs

The nervous system of arachnids is characterized by a variety of structures. The general plan of its organization corresponds to the ventral nerve chain, but there are a number of features. There is no deuterocerebrum in the brain, which is associated with the reduction of acron appendages - antennules, which are innervated by this part of the brain in crustaceans, millipedes and insects. The anterior and posterior parts of the brain are preserved - the protocerebrum (innervates the eyes) and the tritocerebrum (innervates the chelicerae).

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

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

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

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