Divisions of the digestive system of arachnids. Type Arthropods. Subtype Helitsera. Class Arachnids. Integuments and cutaneous glands
I) can reach 20 cm in length. Some tarantula spiders have even larger sizes.
Traditionally, two sections are distinguished in the body of arachnids - just(cephalothorax) and opisthosoma(abdomen). Prosoma consists of 6 segments carrying 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 sensitive 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 over the functions of the organs of touch. The segments of the prosoma are tightly connected to each other; in some representatives, their dorsal walls (tergites) merge with each other to form a carapace. In merged tergites of the segments, they form three scutes: propeltidium, mesopeltidium, and metapeltidium.
The opistosoma initially consists of 13 segments, the first seven of which can carry modified limbs: lungs, crest-like organs, arachnoid warts or genital appendages. In many arachnids, the prosoma segments merge with each other, up to the loss of external segmentation in most spiders and ticks.
Veils
Arachnids carry a relatively thin chitinous cuticle, under which is the hypodermis and basement membrane. The cuticle protects the body from moisture loss during evaporation, which is why arachnids have settled in the driest regions of the world. Proteins encrusting chitin give strength to the cuticle.
Respiratory system
The respiratory organs are the trachea (y, and some) or the so-called pulmonary sacs (y and), sometimes both together (y); the lower arachnids do not have separate respiratory organs; these organs open outward on the underside of the abdomen, less often - and the cephalothorax, with one or more pairs of respiratory openings (stigma).
The lung sacs are more primitive structures. It is believed that they occurred as a result of a modification of the abdominal limbs in the process of mastering the terrestrial lifestyle by the ancestors of arachnids, while the limb stuck into the abdomen. The lung sac in modern arachnids is a depression in the body; its walls form numerous leaf-shaped plates with extensive lacunae filled with hemolymph. Through the thin walls of the plates, gas exchange occurs between the hemolymph and the air entering the pulmonary sac through the openings of the spiracles located on the abdomen. Pulmonary respiration is found in scorpions (four pairs of pulmonary sacs), flagellates (one or two pairs), and low-organized spiders (one pair).
In false scorpions, hay makers, salpugs and some ticks, the trachea serve as respiratory organs, and most spiders (except for the most primitive ones) simultaneously have lungs (only one anterior pair is preserved) and trachea. Tracheas are thin branching (in haymaking) or unbranching (in false scorpions and ticks) tubules. They penetrate the inside of the animal's body and open outward with stigma holes on the first segments of the abdomen (in most forms) or on the first segment of the chest (in solpugs). The tracheas are better adapted to air exchange than the lungs.
Some small ticks lack specialized respiratory organs; they exchange gas, like in primitive invertebrates, through the entire surface of the body.
Nervous system and senses
The nervous system of arachnids is characterized by a variety of structures. The general plan of its organization corresponds to the abdominal nerve chain, but there are a number of features. There is no deutocerebrum in the brain, which is associated with a reduction in the appendages of the acron - antennae, which are innervated by this part of the brain in crustaceans, millipedes and insects. The anterior and posterior parts of the brain are preserved - protocerebrum (innervates the eyes) and tritocerebrum (innervates the chelicerae).
The ganglia of the abdominal nerve chain are often concentrated, forming a more or less pronounced ganglion mass. In hay makers and ticks, all ganglia merge, forming a ring around the esophagus, but in scorpions, a pronounced abdominal chain of ganglia remains.
Sense organs in arachnids they are developed in different ways. The most important thing for spiders is the sense of touch. Numerous tactile hairs - trichobothria - are scattered in large numbers over the surface of the body, especially on the pedipalps and walking legs. Each hair is movably attached to the bottom of a special fossa in the integument and is connected to a group of sensitive cells that are located at its base. A hair perceives the slightest vibrations of air or cobwebs, responsive 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 lyre-like organs, which are 50-160 microns long slits in the integument, leading to a depression on the surface of the body where sensitive cells are located. Lyrate organs are scattered throughout the body.
Organs of vision arachnids are simple eyes, the number of which varies from 2 to 12 in different species. In spiders, they are located on the cephalothoracic shield in the form of two arcs, and in scorpions, one pair of eyes is located in the front and several more pairs on the sides. Despite the significant number of eyes, vision in arachnids is weak. At best, they are able to more or less clearly distinguish objects at a distance of no more than 30 cm, and most species even less (for example, scorpions see only at a distance of a few cm). For some stray species (for example, jumping spiders), vision is more important, because with its help the spider looks out for prey and distinguishes between individuals of the opposite sex.
Latin name Arachoidea
General characteristics of arachnids
External structure
As in typical chelicerans, the body of the overwhelming majority of arachnids consists of a fused cephalothorax, bearing six pairs of limbs, and an abdomen. The abdomen, unlike horseshoe crabs, does not bear real limbs. There are only their rudiments or limbs, turned into special organs.
Antennae, or antennae, are absent. The eyes are simple. The first pair of limbs of the cephalothorax is located in front of the mouth. These are short chelicerae, consisting of 2-3 segments, ending in a claw, crochet or stylet. Chelicerae are homologous to the second antennae of crustaceans. Behind the mouth is the second pair of limbs - pedipalps. Their bases have chewing processes, and the rest of the segments can serve as tentacles. Pedipalps can turn into walking legs or into organs of food grabbing - powerful claws (scorpions, false scorpions). All arachnids are characterized by feeding on liquid food, therefore the anterior part of the digestive system is a sucking apparatus.
In connection with the emergence of arachnids on land, some organ systems of the primary-water chelicerans were transformed and new ones arose. Some groups have both old and newly acquired organs at the same time. So, the respiratory organs in arachnids are the lungs, located in pairs on the abdominal segments. Their establishment and development prove that they are modified branchial stalks of aquatic chelicerans. The new respiratory organs of arachnids are trachea - blind invaginations of the outer covers.
The excretory organs are also dual in nature. They are represented by coxal glands of more ancient origin (coelomoducts) and newly arisen malpighian vessels.
The differences between representatives of the orders of arachnids are in the degree of segmentation of the body, primarily the abdomen, and in the specialization of the cephalothoracic limbs, adapted to perform various functions. The body is most strongly segmented in scorpions. It consists of a small fused cephalothorax and abdomen, represented by 12 segments, of which 6 wider are the anterior abdomen, or mesosome, and the remaining 6 narrower are the posterior abdomen, or metasome. Attention should be paid to the similarity in the dismemberment of the body in scorpions and in the extinct gigantic crustaceans. In both, the metasome is represented by six segments. In other groups of arachnids, the posterior part of the abdomen, the metasome, contracts, and the abdomen is shortened. In terms of the degree of dissection of the abdomen, scorpions are close to flagellates and false scorpions, in which, however, the abdomen does not outwardly divide into anterior and posterior belly. Salpugs are, in some respects, even more dismembered animals than scorpions. In addition to the segmented abdomen, which has 10 segments, two thoracic segments are free in solpugs, which are not part of the fused head. The jointed abdomen of the haymakers also consists of 10 segments, which are not separated by a deep constriction from the cephalothorax, like in real spiders. In articular spiders (four-lung), the abdomen consists of 11 segments, and in higher spiders - of 6, while the abdominal segments are completely merged. In ticks, the number of abdominal segments is reduced to 7, and in some - to 4-2. At the same time, in most ticks, not only all segments of the abdomen have merged, but it is also impossible to distinguish the main sections - the cephalothorax and abdomen, which form one whole in them. Thus, it is obvious that the evolution of various orders of arachnids was in the direction of a decrease in the number of abdominal segments and their fusion, a decrease in the degree of general dismemberment of the body.
In representatives of various orders, the chelicerae and pedipalps underwent the greatest changes, and the least changed are four pairs of walking legs, which turned into a jointed leg ending in a paw with claws.
In scorpions, false scorpions and haymakers, chelicerae end in small claws. They play the role of upper jaws, and, in addition, animals hold prey with them. In salpugs, chelicerae have turned into powerful pincers, adapted to seize and kill prey. In real spiders, chelicerae are claw-shaped and consist of two segments. The main segment is very swollen, and the second has a claw-like shape. Near its pointed end, the duct of the poisonous gland opens, which is located at the base of the chelicera. In a calm state, this segment is attached to the main segment and partially enters into a special groove. With two chelicerae, spiders seize and kill prey, letting in the secret of the poisonous gland into the wound. Finally, in ticks, chelicerae and pedipalps form a prickly (dog tick, etc.) or gnawing (itch mite, barn tick, etc.) mouth apparatus.
The second pair of limbs - pedipalps - in solpugs differ little from walking legs, and in scorpions and false scorpions they have turned into organs of grasping - claws. In female spiders, pedipalps play the role of jaws, since they have a chewing plate at the base, at the same time they are mouth tentacles. In male spiders, there is a swelling on the last segment of the pedipalp, which is a device for fertilizing females. During the breeding season, a special pear-shaped appendage with an elongated end develops on this segment, on which there is an opening leading to a narrow canal, ending inside this organ with an expanded ampulla. With the help of this device, male spiders collect sperm inside the ampoule and, when mating, inject it into the genital opening of the female.
The abdominal limbs, as such, are absent in all arachnids. However, some of them have survived in a highly modified form. Rudiments of the abdominal limbs are located only on the mesosome (anterior six segments). The most complete set of them is preserved in scorpions. They have small genital caps on the first segment of the abdomen, on which all arachnids have a genital opening, and on the second segment, special crest-like appendages of unknown purpose. On the next four segments, there are a pair of pulmonary sacs. The four-lung spiders and the flagellates have two pairs of lungs each on the first two segments of the abdomen; in bipulmonary spiders - one pair of lungs (on the first segment), and on the second, instead of the lungs, tracheas develop (they are not connected with the limbs). All spiders on the third and fourth segments develop arachnoid warts - the transformed abdominal limbs of these segments. In some groups of small arachnids (part of the mites), rudiments of the abdominal limbs on the first three segments, the so-called coxal organs, are preserved.
Integuments and cutaneous glands
The body of arachnids is covered with a chitinous cuticle, which is secreted by a layer of flat cells of the hypodermis. In most forms, chitin is poorly developed and the integument is so thin that it shrinks when it dries. Only in some arachnids (scorpions) the chitinous cover is denser, since it contains calcium carbonate.
Various glands belong to skin (hypodermal) formations: poisonous, arachnoid, odor glands of hay makers, frontal and anal glands of flagellates, etc. Not all arachnids are poisonous. Poisonous glands are found only in scorpions, spiders, parts of false scorpions and in some ticks. In scorpions, the posterior belly ends in a curved tail needle. At the base of this needle is a pair of saccular glands that secrete a poisonous secret. At the very end of the needle, the holes of the ducts of these glands are placed. Scorpios use such a device in a peculiar way. Grabbing prey with pedipalp claws, the scorpion bends the posterior belly onto its back and strikes the victim with a needle, from which it releases poison into the wound. In spiders, poisonous glands are located at the base of the cholitzer, and their ducts open on the chelicera claw.
Spider glands are found mainly in representatives of the order of spiders. So, in a female cross-spider (Araneus diadematus), up to 1000 spider glands of various structures are placed in the abdomen. Their ducts open with the smallest holes at the ends of special chitinous cones, which are located on arachnoid warts and partly on the abdomen near them. Most spiders have 3 pairs of spider web warts, but only two of them are formed from the abdominal legs. In some tropical spiders, they are multi-segmented.
Spider glands are also found in false scorpions and spider mites, but they are located in the chelicerae in the former and in the pedipalps in the latter.
Digestive system
The digestive system consists of three main sections - the anterior, middle, and hindgut.
The anterior gut, with its glands, is an organ adapted to liquefy and absorb food. In spiders, the mouth leads to the pharynx, followed by a thin esophagus that flows into the sucking stomach, which is activated by muscles that extend from it to the dorsal integument of the cephalothorax. These three sections (pharynx, esophagus, sucking stomach) are parts of the anterior ectodermal intestine and are lined with chitin from the inside. The ducts of the salivary glands open into the pharynx, secreting a secret that dissolves proteins. By piercing the integuments of prey, the spider lets saliva into the wound, which dissolves the tissues of the victim, and then sucks out the semi-liquid food. The endodermic midgut begins from the sucking stomach, in which food is digested and absorbed.
The midgut, located in the cephalothorax, forms five pairs of blind glandular outgrowths going forward to the cephalic end and bases of the walking legs. Blind outgrowths of the midgut are very characteristic of many arachnids: ticks, hay makers, etc. They increase the intestinal capacity and its absorption capacity. In the abdomen, into the middle intestine, the ducts of the highly developed paired liver flow. The liver is a derivative of the midgut. It consists of many thin tubes, not only secreting digestive enzymes, but also capable of digesting and absorbing nutrients. Intracellular digestion can take place in liver cells. Further, the middle intestine forms an expanded section, the so-called rectal sac or cloaca, into which the excretory organs - the Malpighian vessels - open. From the rectal sac there is an ectodermic posterior (rectum) intestine, ending in the anus.
The digestive system of other arachnids varies in detail, but is generally similar in structure.
Respiratory system
Due to the terrestrial lifestyle, the arachnids breathe atmospheric air. The respiratory organs in arachnids can be the lungs and trachea. At the same time, it is curious that some arachnids (scorpions, flagellates and four-legged spiders) have only lungs, others (false scorpions, solpugs, haymakers, partly ticks) have only trachea, and finally, still others (most spiders) have lungs and trachea.
Four pairs of lungs in scorpions are placed on the 3-6th segments of the anterior abdomen. From the ventral side, 4 pairs of slit-like holes are clearly visible - stigmas leading to the lungs. The arachnid lung is a saccular organ that lies on the underside of the abdominal segments. The stigma leads to the lung cavity, which in the front of the pulmonary sac is blocked by the plates lying one above the other, which are the outgrowths of the lung wall. Narrow cavities remain between them, into which air enters. Blood circulates inside the pulmonary plates, and thus there is an exchange of gases between the blood and the air that fills the lungs. Most spiders have one pair of lungs (two-lung spiders), some have two pairs (four-lung spiders).
Comparison of the structure of the lung with the structure of the abdominal limbs and gills of horseshoe crabs indicates their great similarity. The position of the lungs on the underside of the abdomen, where the abdominal limbs should have been, increases this similarity. The data of comparative anatomy and embryology fully confirm the assumption that the lungs of arachnids were formed from the gill legs of fossil Merostomidae. The transformation of an abdominal limb with gills into a lung can be imagined as follows. In the abdominal wall of the body, to which the gills adjoined, a depression formed, and the lamellar limb adhered to the integument from the sides. The cavity formed in this way communicated with the external environment in the rear part by a narrow, slit-like opening. From the branchial lobes, attached only by a wide base to the limb, pulmonary plates with their rather complex structure were formed.
In most arachnids, the trachea serve as respiratory organs (solpugs, haymakers, etc.), and in bipulmonary spiders, tracheas exist along with the lungs. Tracheas begin with spiracles (stigmata), usually on the underside of the abdomen. Respirator can be from one unpaired (in some spiders) to three pairs (in solpugs). The spider's spider is located on the abdomen just in front of the spider's warts. It leads into two pairs of tracheal tubes, lined from the inside with a thin layer of chitin, which in some arachnids (solpugs, haymakers, and some spiders) forms spiral filamentous thickenings that prevent the tubes from collapsing.
In solpugs, haymakers and other arachnids, in which the trachea are the only respiratory organs, they form a very complex system of branching tubes that penetrate into all parts of the body and into the limbs. Some small arachnids are deprived of special respiratory organs, they breathe with the entire surface of the body (a number of species of ticks, etc.).
Circulatory system
The circulatory system of arachnids exhibits a metameric structure. In scorpions and most flagellates, the heart is long, tubular, bearing seven pairs of spines. In spiders, the number of pairs of awns is reduced to five or even two. In other arachnids, the heart is more shortened, and in ticks it is a small vesicle.
Arterial vessels move forward, backward and sideways from the heart, and the degree of development and branching of arterial vessels is very different and is directly dependent on the structure of the respiratory system. Scorpions, which have lungs localized in a certain place, and spiders, whose tracheas are not very branched, have the most highly developed system of arterial vessels. In solpugs, haymakers and other forms breathing tracheas, the system of blood vessels is poorly developed, and sometimes even absent. This is explained by the fact that with a sufficiently strong branching of the trachea, the exchange of gases occurs directly between the trachea and tissues of the animal and the blood hardly takes part in the transport of gases. This is a very interesting example of the correlation in the development of various organ systems, even more pronounced in insects.
The degree of development of the circulatory system also depends on the size of the animal. In ticks, it is the least developed: some ticks have only a bubble-shaped heart, while others do not.
Excretory system
The main excretory organs in arachnids are completely new organs associated with the intestines - the Malpighian vessels. They represent one or two pairs of thin tubes, more or less branched and located on the abdomen. These tubules are the protrusion of the midgut, that is, they are of endodermal origin. Malpighian vessels, blindly closed at the free end, open into the rectal bladder, or cloaca, the last section of the midgut. Guanine accumulates in their lumens - the main product of the secretion of arachnids.
Along with malpighian vessels, arachnids have other excretory organs - coxal glands. There can be one or two pairs. They open outward most often at the base of the first and third pairs of walking legs. Typically, the coxal glands consist of a coelomic sac, a nephridial canal, sometimes expanding to form the bladder, and an excretory orifice. These organs, apparently, are homologous to the coelomoducts of annelids and correspond to the coxal glands of horseshoe crabs. In adult arachnids, the coxal glands are usually reduced and do not function; they are replaced by malpighian vessels.
Nervous system and senses
The nervous system of arachnids is represented by the abdominal nerve chain typical of all arthropods. Arachnids are characterized by a significant concentration and fusion of groups of nerve ganglia. The least degree of convergence and fusion of ganglia is observed in scorpions. They have a paired supraopharyngeal ganglion (brain) connected by connectives to the cephalothoracic ganglion mass that innervates the limbs (2-6 pairs). This is followed by the seven ganglia of the abdominal nerve chain. In solpugs, flagellates and false scorpions, only one of the abdominal ganglia remains free, and the rest join the total ganglion mass. In spiders, all the ganglia of the abdominal nerve chain form a single subopharyngeal ganglion. In ticks, the fusion of the subpharyngeal node is also observed with the brain.
From the sense organs there are the organs of touch and sight. The organs of touch are the hairs covering the limbs, especially the pedipalps. The eyes of arachnids are simple (not faceted), usually several pairs. Spiders have 8 eyes, located on the head in two rows.
Genitals and reproduction
Arachnids dioecious, and sexual dimorphism is quite pronounced (in spiders and ticks). In spiders, males are often much smaller than females, and their pedipalps are turned into a copulatory apparatus.
The genitals of all arachnids consist of paired glands or of unpaired, but bearing traces of the fusion of paired glands. Females have an unpaired gland in the form of a “frame with crossbars” and paired oviducts. Males have paired testes with characteristic crossbeams and copulatory apparatus.
Female spiders have paired seminal receptacles that open with independent openings in front of the unpaired genital opening on the first abdominal segment. In addition, each of them communicates through a special channel with the uterus, formed by the fusion of the terminal sections of the oviducts.
With the help of the appendix of the copulatory apparatus of the pedipalp, spiders inject sperm into the seminal receptacles of females through their external openings. From there, the sperm enters the uterus, where fertilization takes place.
With the help of ticks, partnerogenesis is characteristic. Some species of scorpions are viviparous, and the development of fertilized eggs takes place in the ovaries. Newborn scorpions do not leave the mother, and she carries them for some time on her back.
Development
The development of fertilized eggs in most arachnids is direct. Only in ticks, due to the small size of the eggs, development proceeds with metamorphosis. Eggs in most cases are rich in yolk, and crushing is either superficial (spiders, hay makers, solpugs, ticks), or discoidal (oviparous scorniopes).
In viviparous scorpions, embryos developing in the mother's ovary consume protein substances secreted by the female's organs. Therefore, despite the small supply of yolk in the eggs of viviparous scorpions, they are characterized by complete crushing.
During embryonic development, arachnids develop more segments than adult forms. The rudiments of the abdominal limbs appear on the abdominal segments, which are further reduced or transformed into other organs.
Classification
Phylogeny of arachnids
Above, a number of facts were cited, on the basis of which one can imagine the origin of arachnids and phylogenetic relations between the orders of this class.
Undoubtedly, the kinship of terrestrial cheliceral - arachnids with aquatic chelicerae - crustaceans, and through them with a very ancient and even more primitive group - trilobites. Thus, the evolution of this branch of arthropods proceeded from the most homogeneous in terms of segmentation forms, as evidenced by trilobites, to more and more heteronomous animals.
Of the science-like, the most primitive and ancient group are scorpions, the study of which gives a lot for understanding the evolution of arachnids. Within a class, the evolution of certain groups led to a greater or lesser fusion of abdominal segments, to a greater development of the tracheal system, replacing the more ancient respiratory organs - the lungs, and finally, to the development of special adaptations characteristic of representatives of individual orders.
Among the true spiders, the four-lung spiders are undoubtedly the more primitive group. Two pairs of lungs, the absence of trachea, the presence of two pairs of coxal glands, and in some of them the articulation of the abdomen - all these signs indicate their greater primitiveness in comparison with the group of bipulmonary spiders.
Gallery
Arachnids are known about 25 thousand species. These arthropods are adapted to live on land. They are characterized by organs of air respiration. As a typical representative of the class Arachnids, consider a spider-cross.
External structure and nutrition of arachnids
In spiders, the body segments merge, forming the cephalothorax and abdomen, separated by an interception.
The body of arachnids is covered chitinized cuticle and the underlying tissue (hypodermis), which has a cellular structure. Its derivatives are spider and venom 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 legs - are adapted to capture and grind food. The other four pairs perform the functions of locomotion - these are walking legs.
During embryonic development, a large number of limbs are laid on the abdomen, but later they are transformed into spider warts, opening by the ducts of the spider glands. Solidifying in air, the secretions of these glands turn into spider threads, from which the spider builds a trapping net.
After the insect has fallen into the net, the spider envelops it in cobwebs, plunges the claws of the upper jaws into it and injects poison. Then he leaves his prey and hides for cover. The secret of the poisonous glands not only kills insects, but acts as a digestive juice. After about an hour, the spider returns to its prey and sucks out semi-liquid, partially digested food. From the killed insect, one chitinous cover remains.
Respiratory system in the spider-spider it is represented by pulmonary sacs and trachea. Pulmonary 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 are a system of branched tubes that go directly to all organs, where tissue gas exchange takes place.
Circulatory system arachnids consist of a heart on the dorsal side of the abdomen and a vessel through which blood moves from the heart to the front of the body. Since the circulatory system is not closed, the blood returns to the heart from the mixed cavity of the body (myxocel), where it washes the pulmonary sacs and trachea and is enriched with oxygen.
Excretory system The spider-spider consists of several pairs of tubules (malpighian vessels) located in the body cavity. Of these, waste products enter the posterior part of the intestine.
Nervous system arachnids are characterized by the fusion of nerve nodes with each other. In spiders, the entire nerve chain merges into one cephalothoracic ganglion. The organ of touch is the hairs that cover 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 silky cobwebs, which she attaches in secluded places (under stones, stumps, etc.). By winter, the female dies, and spiders emerge from the eggs that have 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 their eggs in a spider's cocoon, often carry it with them.
The class of arachnids unites over 36,000 species of terrestrial chelicerans, belonging to more than 10 orders.
Arachnida- higher cheliceral arthropods with 6 pairs of cephalothoracic limbs. They breathe through the lungs or trachea and, in addition to the coxal glands, have an excretory apparatus in the form of malpighian vessels lying in the abdomen.
Structure and physiology. External morphology. The body of arachnids most often consists of the cephalothorax and abdomen. Acron and 7 segments participate in the formation of the cephalothorax (the 7th segment is underdeveloped). In solpugs and some other lower forms, only segments of 4 anterior pairs of limbs are soldered together, while the posterior 2 segments of the cephalothorax are free, followed by clearly demarcated segments of the abdomen. Thus, solpugs have: the anterior part of the body, corresponding in segmental composition to the head of trilobites (acron + 4 segments), the so-called propeltidium; two free thoracic segments with legs and a segmented abdomen. Salpugi, therefore, belong to the arachnids with the most richly dissected body.
The next group in terms of dissection is scorpions, in which the cephalothorax is fused, but it is followed by a long 12-segment one, like in Gigantostraca, the abdomen, subdivided into a wider anterior abdomen (of 7 segments) and a narrow posterior abdomen (of 5 segments). The body ends with a telson carrying a twisted poisonous needle. The same is the nature of segmentation (only without the division of the abdomen into two sections) in representatives of the orders of flagellates, false scorpions, hay makers, in some ticks and in primitive arthropod spiders.
The next stage of fusion of the trunk segments is found by most spiders and some ticks. In them, not only the cephalothorax, but also the abdomen are continuous undivided parts of the body, however, the spiders have a short and narrow stalk between them, formed by the 7th segment of the body. The maximum degree of fusion of body segments is observed in a number of representatives of the order of ticks, in which the whole body is whole, without boundaries between segments and without constrictions.
As already mentioned, the cephalothorax carries 6 pairs of limbs. The two front pairs are involved in the capture and crushing of food - these are chelicerae and pedipalps. Chelicerae are located in front of the mouth, most often in arachnids they are in the form of short pincers (solpugi, scorpions, false scorpions, haymakers, some ticks, etc.). They usually consist of three segments, the terminal segment plays the role of a movable claw finger. Less often, chelicerae end with a movable claw-shaped segment or have the form of two-segmented appendages with a pointed and serrated edge, with which ticks pierce the integuments of animals.
The limbs of the second pair, pedipalps, consist of several segments. With the help of the chewing outgrowth on the main segment of the pedipalp, food is crushed and kneaded, while the other segments make up the genus of the tentacle. In representatives of some orders (scorpions, false scorpions), pedipalps are turned into powerful long claws, in others they look like walking legs. The remaining 4 pairs of cephalothoracic limbs consist of 6-7 segments and play the role of walking legs. They end in claws.
In adult arachnids, the abdomen is devoid of typical limbs, although they undoubtedly descended from ancestors with well-developed legs on the anterior abdominal segments. In embryos of many arachnids (scorpions, spiders), the rudiments of legs are laid on the abdomen, which only subsequently undergo regression. However, even in adulthood, the abdominal legs are sometimes preserved, but in a modified form. So, in scorpions on the first segment of the abdomen there is a pair of genital caps, under which the genital opening opens, on the second - a pair of comb organs, which are equipped with numerous nerve endings and play the role of tactile appendages. Both those and others represent modified limbs. The same is the nature of the lung sacs located on the abdominal segments of scorpions, some spiders and false scorpions.
Spider warts of spiders also originate from the limbs. On the lower surface of the abdomen, in front of the powder, they have 2-3 pairs of tubercles, seated with hairs and carrying the tubular ducts of numerous arachnoid glands. The homology of these arachnoid warts to the abdominal limbs is proved not only by their embryonic development, but also by their structure in some tropical spiders, in which the warts are especially strongly developed, consist of several segments and even in appearance resemble legs.
Covers of the chelicera consist of the cuticle and the underlying layers: the hypodermal epithelium (hypodermis) and the basement membrane. The cuticle itself is a complex three-layer formation. Outside, there is a lipoprotein layer that reliably protects the body from moisture loss during evaporation. This allowed the Chelicerovs to become a real land group and populate the driest regions of the world. Proteins hardened with phenols and encrusted with chitin give the cuticle strength.
Derivatives of the skin epithelium are some glandular formations, including poisonous and arachnoid glands. The former are characteristic of spiders, stinging legs and scorpions; the second - to spiders, false scorpions and some ticks.
Digestive system in representatives of different orders, the Cheliceraceae varies greatly. The anterior gut usually forms an extension - a pharynx equipped with strong muscles, which serves as a pump that sucks in semi-liquid food, since arachnids do not take solid food in pieces. A pair of small "salivary glands" open into the anterior gut. In spiders, the secret of these glands and the liver is able to vigorously break down proteins. It is introduced into the body of the killed prey and brings its contents into a state of liquid slurry, which is then absorbed by the spider. Here the so-called extraintestinal digestion takes place.
In most arachnids, the midgut forms long lateral protrusions that increase the capacity and absorption surface of the intestine. So, in spiders, 5 pairs of blind glandular sacs go from the cephalothoracic part of the midgut to the bases of the limbs; similar protrusions are found in ticks, haymakers and other arachnids. In the abdominal part of the midgut, the ducts of the paired digestive gland — the liver — open; it secretes digestive enzymes and serves to absorb nutrients. Intracellular digestion takes place in the liver cells.
Excretory system arachnids in comparison with horseshoe crabs has a completely different character. On the border between the middle and hind gut, a pair of mostly branching Malpighian vessels opens into the alimentary canal. Unlike Tgacheata they are of endodermal origin, that is, they are formed at the expense of the midgut. Both in the cells and in the lumen of the Malpighian vessels there are numerous grains of guanine, the main product of the secretion of arachnids. Guanine, like uric acid excreted by insects, has low solubility and is removed from the body in the form of crystals. At the same time, moisture loss is minimal, which is important for animals that have switched to life on land.
In addition to malpighian vessels, arachnids also have typical coxal glands - paired saccular formations of mesodermal nature, lying in two (less often in one) segments of the cephalothorax. They are well developed in embryos and at a young age, but in adult animals they more or less atrophy. Fully formed coxal glands consist of a terminal epithelial sac, a loop-like convoluted canal and a more direct excretory duct with a bladder and an external opening. The terminal sac corresponds to the ciliary funnel of the coelomoduct, the opening of which is closed by the remainder of the coelomic epithelium. The coxal glands open at the base of the 3rd or 5th pair of limbs.
Nervous systemArachnida varied. Associated in origin with the ventral nerve chain of annelids, in arachnids it exhibits a distinct tendency towards concentration.
The brain has a complex structure. It consists of two sections: the anterior, innervating the eyes, the protocerebrum, and the posterior, the tritocerebrum, which sends the nerves to the first pair of limbs, the chelicera. The intermediate part of the brain, characteristic of other arthropods (crustaceans, insects), is absent in arachnids, the deutocerebrum. This is due to the disappearance in them, like in the rest of the cheliceral, appendages of the acron - antennae, or antennae, which are innervated precisely from the deutocerebrum.
Metamerism of the abdominal nerve chain is most clearly preserved in scorpions. In addition to the brain and periopharyngeal connectives, they have a large ganglionic mass in the cephalothorax on the ventral side, giving nerves to the 2-6 pairs of limbs and 7 ganglia, along the abdominal part of the nerve chain. In solpugs, in addition to the complex cephalothorax ganglion, one more node is preserved on the nerve chain, and in spiders the entire chain has already merged into the cephalothorax ganglion.
Finally, in hay makers and ticks, there is not even a clear distinction between the brain and the cephalothoracic ganglion, so that the nervous system forms a continuous ganglionic ring around the esophagus.
Sense organsArachnida varied. Mechanical, tactile stimuli, which are very important for arachnids, are perceived by variously arranged sensitive hairs, which are especially numerous on pedipalps. Special hairs - trichobothria, located on the pedipalps, legs and surface of the body, register air vibrations. The so-called lyre-like organs, which are small slits in the cuticle, to the membranous bottom of which the sensitive processes of nerve cells fit, are organs of chemical sense and serve for smell. The organs of vision are represented by simple eyes, which are found in most arachnids. They are located on the dorsal surface of the cephalothorax and usually there are several of them: 12, 8, 6, less often 2. Scorpions, for example, have a pair of larger median eyes and 2-5 pairs of lateral ones. Spiders most often have 8 eyes, usually located in two arcs, and the middle eyes of the anterior arch are larger than the rest.
Scorpions recognize their own kind only at a distance of 2-3 cm, and some spiders - for 20-30 cm. Salticidae) vision plays an especially important role: if males cover their eyes with an opaque asphalt varnish, then they cease to distinguish females and produce a "love dance" characteristic of the mating period.
Respiratory system Arachnids are diverse. Some have pulmonary sacs, others have trachea, others have both at the same time.
Only the lung sacs are found in scorpions, flagellates, and primitive spiders. In scorpions, on the abdominal surface of the 3-6th segments of the anterior abdomen, there are 4 pairs of narrow slits - spiracles, which lead to the pulmonary sacs. Numerous leaf-like folds, parallel to each other, protrude into the cavity of the sac, between which narrow slit-like spaces remain, air penetrates into the latter through the respiratory slit, and hemolymph circulates in the pulmonary leaves. In flagellates and lower spiders, there are only two pairs of pulmonary sacs.
In most other arachnids (solpugs, haymakers, false scorpions, part of ticks), the respiratory organs are represented by trachea. On the 1-2nd segments of the abdomen (in solpugs on the 1st segment of the chest) there are paired respiratory openings, or stigmas. A bundle of long, thin, blindly closed air tubes of ectodermal origin (formed as deep invaginations of the outer epithelium) depart from each stigma into the body. In false scorpions and ticks, these tubes, or trachea, are simple and do not branch; in haymakers, they form side branches.
Finally, in the order of spiders, both types of respiratory organs are found together. The lower spiders, as already noted, have only lungs; among 2 pairs, they are located on the underside of the abdomen. In the rest of the spiders, only one anterior pair of lungs is preserved, and behind the latter there is a pair of tracheal bundles that open outward with two stigmas. Finally, in one family of spiders ( Caponiidae) there are no lungs at all, and the only respiratory organs are 2 pairs of trachea.
The lungs and trachea of arachnids arose independently of each other. The lung sacs are undoubtedly more ancient organs. It is believed that the development of the lungs in the process of evolution was associated with a modification of the abdominal gill limbs, which were possessed by the aquatic ancestors of arachnids and which were similar to the gill-bearing abdominal legs of horseshoe crabs. Each such limb stuck inside the body. In this case, a cavity was formed for the pulmonary leaflets. The lateral edges of the leg have grown to the body almost along the entire length, except for the area where the respiratory gap is preserved. The abdominal wall of the pulmonary sac corresponds, therefore, to the former limb itself, the anterior section of this wall to the base of the leg, and the pulmonary leaflets originated from the gill plates located on the back of the abdominal legs of the ancestors. This interpretation is supported by the development of the lung sacs. The first folded rudiments of the pulmonary plates appear on the posterior wall of the corresponding rudimentary legs before the limb deepens and turns into the lower wall of the lung.
Tracheas arose independently of them and later as organs more adapted to air breathing.
In some small arachnids, including some of the ticks, the respiratory organs are absent, and breathing takes place through thin integuments.
Circulatory system. In forms with pronounced metamerism (scorpions), the heart is a long tube lying in the anterior abdomen above the intestine and equipped on the sides with 7 pairs of slit-like awns. In other arachnids, the structure of the heart is more or less simplified: for example, in spiders it is somewhat shortened and carries only 3-4 pairs of awns, while in haymen the number of the latter is reduced to 2-1 pairs. Finally, in ticks, the heart, at best, turns into a short sac with one pair of ostia. In most ticks, due to their small size, the heart completely disappears.
From the anterior and posterior ends of the heart (scorpions) or only from the anterior (spiders), the anterior and posterior aorta departs along the vessel. In addition, in a number of forms, a pair of lateral arteries depart from each chamber of the heart. The terminal branches of the arteries pour out hemolymph into the lacunae system, that is, into the gaps between the internal organs, from where it enters the pericardial section of the body cavity, and then through the ostia into the heart. The hemolymph of arachnids contains a respiratory pigment - hemocyanin.
The reproductive system. Arachnid dioecious. The sex glands lie in the abdomen and, in the most primitive cases, are paired. Very often, however, there is a partial fusion of the right and left gonads. Sometimes in one sex the gonads are still paired, while in the other the fusion has already occurred. So, male scorpions have two testicles (each of two tubes connected by bridges), and females have one whole ovary, consisting of three longitudinal tubes connected by transverse adhesions. In spiders, in some cases, the gonads remain separate in both sexes, in others, in the female, the posterior ends of the ovaries grow together, and a whole gonad is obtained. From the gonads, there are always paired genital ducts, which at the anterior end of the abdomen merge together and open outward with the genital opening, the latter in all arachnids lies on the first segment of the abdomen. Males have various additional glands; females often develop spermatozoa.
Development. Instead of external fertilization, which was characteristic of the distant aquatic ancestors of arachnids, they developed internal fertilization, accompanied in primitive cases by spermatophore insemination or, in more developed forms, by copulation. The spermatophore is a sac secreted by the male, which contains a portion of semen, thus protected from drying out during exposure to air. The male in false scorpions and in many ticks leaves the spermatophore on the soil, and the female captures it with the external genitals. At the same time, both individuals perform a "mating dance" consisting of characteristic postures and movements. The males of many arachnids carry the spermatophore into the female genital opening with the help of chelicerae. Finally, some forms have copulatory organs, but spermatophores are absent. In some cases, parts of the body that are not directly related to the reproductive system are used for copulation, for example, the modified end segments of the pedipalps in male spiders.
Most arachnids lay eggs. However, many scorpions, false scorpions and some ticks have live births. Eggs are mostly large, rich in yolk.
In arachnids, there are various types of crushing, but in most cases, surface crushing takes place. Later, due to the differentiation of the blastoderm, an embryonic stripe is formed. Its surface layer is formed by the ectoderm, the deeper layers represent the mesoderm, and the deepest layer adjacent to the yolk is the endoderm. The rest of the embryo is covered only with ectoderm. The formation of the body of the embryo occurs mainly due to the germinal strip.
In further development, it should be noted that in embryos, segmentation is more pronounced, and the body consists of a larger number of segments than in adult animals. So, in embryos of spiders, the abdomen consists of 12 segments, similar to adult crustaceans and scorpions, with the rudiments of legs on 4-5 front ones. With further development, all abdominal segments merge, forming a whole abdomen. In scorpions, the limbs are laid on 6 segments of the anterior abdomen. The anterior pair of them gives the genital caps, the second - the comb organs, and the development of other pairs is associated with the formation of the lungs. All this indicates that the class Arachnida descended from ancestors with rich segmentation and with limbs developed not only on the cephalothorax, but also on the abdomen (anterior abdomen). Almost all arachnids have direct development, but ticks have metamorphosis.
Literature: A. Dogel. Zoology of invertebrates. Edition 7, revised and expanded. Moscow "Higher School", 1981
there are at least 12 detachments, the most important of which are the Spiders, Scorpions, False Scorpions, Solpugs, Haymakers, Ticks.
Arachnids differ in that they do not have antennae (antennae), and the mouth is surrounded by two pairs of peculiar limbs - chelicerae and jaw, which the Arachnids call pedipalps... The body is divided into the cephalothorax and abdomen, but in ticks all sections are fused. Walking legs four pairs.
Spider spiders these are common members of the Arachnid class. Spider spiders This is the collective name of several biological species of the genus Araneus of the family Orb-weaving spiders of the order Spiders. Cross spiders are found in the warm season throughout the European part of Russia, in the Urals, in Western Siberia.
Cross spiders are predators that feed only on living insects. The spider-spider catches its prey with a very complex, vertical wheel-shaped trapping net(hence the name of the family - Orb-web spiders) . The spider spinning apparatus, which ensures the manufacture of such a complex structure, consists of external formations - spider warts- and from internal organs - spider glands. A droplet of sticky liquid is released from the spider warts, which, when the spider moves, is pulled into the finest thread. These threads quickly thicken in the air, turning into a strong cobweb thread... The web is made up mostly of protein. fibroin... In terms of chemical composition, the spider's web is close to the silk of silkworm caterpillars, but more durable and elastic. The breaking load for spider webs is 40-261 kg per 1 sq mm of thread cross section, and for silk it is only 33-43 kg per sq mm of thread cross section.
To weave its trapping net, the Cross Spider first stretches especially strong threads in several convenient places, forming a support frame for the future network in the form of an irregular polygon. Then he moves along the upper horizontal thread to its middle and, going down from there, draws a strong vertical thread. Further, from the middle of this thread, as from the center, the spider conducts radial threads in all directions, like the spokes of a wheel. This is the backbone of the entire web. Then the spider starts to weave from the center spiral threads attaching them to each radial thread with a drop of adhesive. In the middle of the net, where the spider itself then sits, the spiral threads are dry. Other spiral threads are sticky. Insects that fly onto the net stick to them with their wings and paws. The spider itself either hangs head down in the center of the spider web, or hides in
Class Arachnids Cross-spider
to the side under the sheet - there he has asylum... In this case, he stretches towards himself from the center of the web a strong signal a thread.
When a fly or other insect enters the net, the spider, feeling the trembling of the signal thread, rushes out of its ambush. Plunging the claws of a chelicera with poison into the victim, the spider kills the victim and secretes digestive juices into its body. After that, he entangles a fly or other insect with a cobweb and leaves it for a while.
Under the influence of the secreted digestive juices, the internal organs of the victim are quickly digested. After some time, the spider returns to the victim and sucks out all the nutrients from it. From the insect in the web, only an empty chitinous cover remains.
Making a trapping net is a series of interconnected unconscious actions. The ability to do this is instinctive and inherited. It is easy to be convinced of this by following the behavior of young spiders: when they come out of their eggs, no one teaches them how to weave a trapping net, the spiders immediately very skillfully weave their webs.
In addition to the wheel-shaped trapping nets, other types of spiders have nets in the form of a random interweaving of threads, nets in the form of a hammock or canopy, funnel-shaped nets and other types of trapping nets. The spider's web is a kind of adaptation outside the body.
I must say that not all types of spiders weave trapping webs. Some are actively looking for and catching prey, others lie in wait for it from an ambush. But all spiders have the ability to secrete webs, and all spiders are made from webs. egg cocoon and spermatic nets.
External structure... The body of the Cross Spider is subdivided into cephalothorax and abdomen which connects to the cephalothorax with a thin movable stalk... There are 6 pairs of limbs on the cephalothorax.
The first pair of limbs - chelicerae that surround the mouth and serve to capture and puncture prey. Chelicerae consist of two segments, the end segment looks like curved claws. At the base of the chelicera are poison glands, the ducts of which open at the tips of the claws. Spiders with chelicera pierce the integuments of the victims and inject poison into the wound. Spider venom has a nerve effect. In some species, for example, in Karakurt, in the so-called tropical Black widow, the poison is so strong that it can kill
Class Arachnids Cross-spider
even a large mammal (instantly!).
The second pair of cephalothoracic limbs - pedipalps have the appearance of articulated limbs (they look like short legs sticking out forward). The function of the pedipalps is to feel and hold the prey. In sexually mature males, on the terminal segment of the pedipalp, copulatory apparatus, which the male fills with sperm before mating. When copulating, the male uses the copulatory apparatus to inject sperm into the female's sperm. The structure of the copulatory apparatus is species-specific (i.e., each species has a different structure).
All arachnids have 4 pairs walking legs... The walking leg consists of seven segments: basin, swivel, hips, cups, shins, precuts and paws armed with claws.
Arachnids have no antennae. On the front of the cephalothorax, the spider-spider has two rows of eight simple eyes... Other types of eyes may have three pairs, or even one pair.
Abdomen in spiders it is not segmented and has no true limbs. There is a pair of pulmonary sacs, two beams trachea and three pairs cobweb warts... Spider-spider spider warts consist of a huge number (about 1000) cobweb glands that produce various types of cobwebs - dry, wet, sticky (at least seven varieties of very different purposes). Different types of web perform different functions: one is for catching prey, the other is for building a dwelling, the third is used in the manufacture of a cocoon. Young spiders also settle on special webs.
On the abdominal side of the abdomen, closer to the junction of the abdomen with the cephalothorax is located sexual hole... In females, it is surrounded and partially covered by a chitinized plate. epigine... The structure of the epigina is species-specific.
Body covers. The body is covered with chitinized cuticle. The cuticle protects the body from external influences. The most superficial layer is called epicuticle and it is formed by fat-like substances, therefore, the integuments of spiders are impermeable to either water or gases. This allowed spiders to populate the driest regions of the globe. The cuticle simultaneously performs the function
Class Arachnids Cross-spider
outdoor skeleton: serves as a site for muscle attachment. From time to time, spiders shed, i.e. shedding the cuticle.
Musculature arachnids consists of striated fibers that form powerful muscle bundles, i.e. the musculature is represented by separate bundles, and not by a bag like in worms.
Body cavity. The body cavity in Arachnids is mixed - mixocel.
Digestive system typical, consists of front, average and back intestines. The anterior gut is presented mouth, by the throat, short esophagus and stomach... The mouth is surrounded by chelicerae and pedipalps, with which spiders grab and hold prey. The pharynx is equipped with strong muscles for absorbing food gruel. Ducts open into the anterior intestine salivary glands, the secret of which effectively breaks down proteins. All spiders have the so-called extraintestinal digestion... This means that after killing the prey, digestive juices are introduced into the victim's body and the food is digested outside the intestines, turning into a semi-liquid gruel, which is absorbed by the spider. In the stomach, and then in the midgut, food is absorbed. The midgut has long blind lateral protrusions, increasing the area of absorption and serving as a place for temporary storage of food mass. The ducts also open here liver... It secretes digestive enzymes and also ensures the absorption of nutrients. Intracellular digestion takes place in the liver cells. On the border of the middle and rear sections, the excretory organs flow into the intestine - malpighian vessels... The hindgut ends anal hole located at the posterior end of the abdomen above the arachnoid warts.
Respiratory system... In some arachnids, the respiratory organs are represented pulmonary bags, other's tracheal system, for others - both at the same time. In some small arachnids, including some of the ticks, the respiratory organs are absent, breathing is carried out through thin integuments. The lung sacs are more ancient (from an evolutionary point of view) formations than the tracheal system. It is believed that the gill limbs of the aquatic ancestors of arachnids sank into the body and formed cavities with pulmonary leaflets. The tracheal system arose independently and later than the pulmonary sacs, as organs more adapted to air breathing. Tracheas are deep incisions of the cuticle into the body. The tracheal system is perfectly developed in Insects.
Class Arachnids Cross-spider
In the Cross Spider, the respiratory organs are represented by a pair pulmonary sacs forming leaf-shaped folds on the ventral side of the abdomen, and two bundles trachea that open spiracles also on the underside of the abdomen.
Circulatory system open, comprises hearts, located on the dorsal side of the abdomen, and several large blood vessels extending from it vessels. The heart has 3 pairs of spines (holes). From the front end of the heart departs front aorta decaying into arteries. The terminal branches of the arteries pour out hemolymph(this is the name of the blood in all arthropods) into the system cavities located between the internal organs. Hemolymph washes all internal organs, delivering nutrients and oxygen to them. Further, the hemolymph washes the pulmonary sacs - gas exchange occurs, and from there it enters pericardium, and then through ostia- in heart. Arachnid hemolymph contains a blue respiratory pigment - hemocyanin, containing copper. Pouring out into the secondary body cavity, the hemolymph mixes with the secondary cavity fluid, therefore it is said that arthropods have a mixed body cavity - mixocel.
Excretory system arachnids have malpighian vessels that open into the intestine between the mid and hind intestines. Malpighian vessels, or tubules, are blind protrusions of the intestine that ensure the absorption of metabolic products from the body cavity. In addition to malpighian vessels, some arachnids also have coxal glands- paired saccular formations lying in the cephalothorax. From the coxal glands, convoluted canals depart, ending in urinary bubbles and output ducts, which open at the base of the walking limbs (the first segment of the walking legs is called coke, hence the name - coxal glands). The spider-spider has both coxal glands and malpighian vessels.
Nervous system... Like all Arthropods, Arachnids have a nervous system - ladder type... But in the Arachnids there was a further concentration of the nervous system. A pair of supraopharyngeal nerve ganglia is called the "brain" of the Arachnids. It innervates (controls) the eyes, chelicerae and pedipalps. All the cephalothoracic ganglia of the nerve chain merged into one large nerve node located under the esophagus. All abdominal nerve ganglia of the nerve chain also fused into one large abdominal nerve node.
Of all the senses, the most important thing for spiders is touch. Numerous tactile hairs - trichobothria- scattered in large numbers over the surface of the body, especially on the pedipalps and walking legs.
Class Arachnids Cross-spider
Each hair is movably attached to the bottom of a special fossa in the integument and is connected to a group of sensitive cells that are located at its base. A hair perceives the slightest vibrations of air or cobwebs, responsive to what is happening, while the spider is able to distinguish the nature of the irritating factor by the intensity of the vibrations. Tactile hairs are specialized: some register chemical stimuli, others - mechanical, others - air pressure, and the fourth - perceive sound signals.
The organs of vision are represented with simple eyes found in most arachnids. Spiders most often have 8 eyes. Spiders are short-sighted, their eyes perceive only light and shadow, the outlines of objects, but details and color are not available to them. There are organs of balance - statocysts.
Class Arachnids Cross-spider
performs copulation. The female at this moment is good-natured and relaxed. But, immediately after mating, the male must hastily leave, since the behavior of the spider after copulation changes dramatically: she becomes aggressive and very active. Therefore, sluggish males are often killed by a female and eaten. (Well, after mating, the male will die anyway. From an evolutionary point of view, the male is no longer needed: he has fulfilled his biological function.) This happens in almost all species of spiders. Therefore, in research, females are most often found, while males are rare.
After copulation, the female continues to actively feed. In the fall, the female from a special web makes cocoon, in which he lays several hundred eggs. She hides the cocoon in some secluded place, for example, under the bark of a tree, under a stone, in the crevices of a fence, etc., and the female herself dies. Eggs overwinter at Cross Spiders. In the spring, young spiders emerge from the eggs, which begin an independent life. Molting several times, the spiders grow and by the end of summer reach sexual maturity and begin to reproduce.
Reproduction and development... Arachnids dioecious... Fertilization internal... Most arachnids lay eggs, but some arachnids have live births. Development without metamorphosis.
The spider-spider has a well-defined sexual dimorphism: the female has a large abdomen, while mature males develop on pedipalps copulative organs... In each spider species, the copulatory organs of the male approach the female's epigyne as a key to the lock, and the structure of the male's copulatory organs and the female's epigyne is species-specific.
Mating in Cross Spiders occurs at the end of summer. Sexually mature males do not weave trapping nets. They wander in search of female nets. Having found a fishing net of a sexually mature female, the male somewhere off to the side on the ground, or on some twig, or on a leaf, weaves a small spermatozoa in the form of a hammock. On this mesh, the male from his genital opening, which is located on the abdominal side of the abdomen closer to the junction of the abdomen with the cephalothorax, squeezes out a drop sperm... Then he sucks this droplet into the pedipalps (like a syringe) and proceeds to seduce the female. The spider's eyesight is weak, so the male needs to be very careful so that the female does not mistake him for prey. For this, the male, having caught some insect, wraps it in a web and presents this peculiar gift to the female. Hiding behind this gift as a shield, the male approaches his lady very slowly and extremely cautiously. Like all women, the spider is very curious. While she is looking at the presented gift, the male quickly climbs onto the female, applies his pedipalps with sperm to the female's genital opening and
Meaning. The role of spiders in nature is great. They act as consumers of the second order in the structure of the ecosystem (i.e., consumers of organic matter). They destroy many harmful insects. They are food for insectivorous birds, toads, shrews, snakes.
Questions for self-control
What is the classification of the type Arthropods?
What is the systematic position of the Cross Spider?
Where do Cross Spiders live?
What is the shape of the body of the Cross Spiders?
What is the spider's body covered with?
What body cavity is typical for a spider?
What is the structure of the spider's digestive system?
What are the features of digestion in spiders?
What is the structure of the spider's circulatory system?
How does a spider breathe?
What is the structure of the spider's excretory system?
What is the structure of the spider's nervous system?
What is the structure of the spider's reproductive system?
How does the Cross Spider reproduce?
What do spiders matter?
Class Arachnids Cross-spider
Rice. Cross spider: 1 - female, 2 - male and wheel-shaped hunting net.
Rice. The cross spider weaves a trapping net
Class Arachnids Cross-spider
Rice. Internal structure of the Cross-Spider.
1 - poisonous glands; 2 - pharynx; 3 - blind outgrowths of the intestine; 4 - Malpighian vessels; 5 - heart; 6 - pulmonary sac; 7 - ovary; 8 - oviduct; 9 - spider glands; 10 - pericardium; 11 - ostia in the heart.