Among arachnids, development with metamorphosis. Class arachnids or arachnids (arachnida)

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Arachnids, or arachnids (Agacchnida) 1, are the collection of all terrestrial chelicerans.

The Latin name of the class, in this transcription is now more accepted, was formerly written Arachnoidea.

Arachne is Greek for "spider". In ancient Greek myths, this is the name of a girl who, according to legend, achieved such a high weaving art that she challenged the goddess Athena herself. Arachne weaved cloth no worse than Athena, but she, as punishment for her audacity to compete with the gods, did not recognize her merits. In desperation, Arachne wanted to hang herself, then Athena turned her into a spider, forever weaving its web.

There are about 35,000 species of them, and they are very different in appearance. Distinguish from 9 to 13 orders of modern arachnids and several fossils. Among them, seven detachments are generally accepted: scorpions(Scorpiones), kenya(Palpigradi), solpugi(Solifugae), false scorpions(Pseudoscorpiones), haymakers(Opiliones), ricinules(Ricinulei) and spiders(Aranei). But there are contradictions in the understanding of several groups. This telephones(Uropygi), phryne(Atblypygi) and tartarids(Tartarides) grouped harp legs(Pedipalpi), and pincers(Acarina), on the classification of which we will dwell on.

With a large variety of arachnids, the main features of the chelicerae are characteristic of all of them. The body consists of a cephalothoraxis and an abdomen - an opisthosoma, connected in the area of ​​the seventh, presexual, segment. There are no antennae, the eyes are simple. The limbs of the cephalothorax - chelicera, pedipalps and 4 pairs of legs - serve to capture food and move; the limbs of the abdomen are modified, perform respiratory and other special functions, and in large part atrophy. The differences between arachnids and primary-water chelicerans are due to adaptations to life on land. The main ones are: the transformation of the gill legs into lungs and then replacing them with breathing tubes - trachea; further concentration of body parts; the adaptation of the legs for movement on land, and the perioral limbs for feeding on semi-liquid food - the contents of the victim, previously dissolved by the digestive juices; a number of changes life cycle and an overall reduction in size.

The structure of the cephalothorax (prosoma) is generally of the same type. Usually, all 6 segments of the prosoma are fused and covered with a solid cephalothorax. But in solpugs, kenenii, and parts of ticks, only four anterior segments are fused, corresponding to the segments of the head of trilobites. They are covered with a head shield (propeltidium), and the segments of the third and fourth pairs of legs are dissected and have their own tergites, a condition more primitive than even in Merostomaceae. The structure and functions of the perioral limbs are related to the way of feeding. The vast majority of arachnids are carnivores that feed on live prey, mainly insects. In this case, the integuments of the victim are torn and digestive juices are introduced inside, which have a proteolytic effect (the ability to dissolve proteins). The liquefied contents of the victim are then absorbed. Eating semi-liquid food led to the fact that in arachnids the perioral limbs did not acquire the character of jaws in the form that in insects. Chelicerae serve for seizing and tearing prey. They are usually short, pincer-shaped; sometimes the terminal segment of the chelicera has the form of a claw, at the end of which the duct of the poisonous gland opens (for example, in spiders), or stitching chelicerae, acicular (in many ticks). The coxae of the pedipalps have processes - endites, but they usually do not serve for chewing food, but limit the pre-oral cavity, at the bottom of which the oral opening is located.

The upper wall of this cavity is formed by the epistome with the upper lip. From the inside, on the endites of the pedipalps and in the pharynx, there are hairs through which semi-liquid food is filtered. After feeding, hard particles are peeled off the hairs and discarded. The tentacles of the pedipalps serve as organs of touch, but sometimes they are involved in movement (solpugi, kenenii), or they are prehensile, with claws (scorpions, false scorpions) or claw-like outgrowths (flagellates). The structure of the legs is characterized by the formation of a jointed paws with claws - an adaptation to walking on land. The chewing function of the legs is lost in arachnids, but coxendites are partially preserved in primitive forms. The legs, especially the front ones, are richly equipped with tactile hairs and, along with the tentacles of the pedipalps, imitate the disappeared antennae.

The limbs of the abdomen in arachnids are transformed into lungs and other special formations. They are present only on mesosomal segments. The most complete set of modified abdominal limbs is preserved in scorpions: the genital operculum on the eighth segment, crest-like organs on the ninth, four pairs of lungs on the tenth - thirteenth segments. Telephones, phrens and four-lung spiders have a pair of lungs on the eighth and ninth segments, in tartarids and bipulmonary spiders - a pair of lungs on the eighth segment, and in the latter, tracheas are formed in place of the lungs on the ninth segment. In all spiders, the limbs of the tenth and eleventh segments are turned into arachnoid warts. In other arachnids, the lungs disappear. Sometimes trachea (solpugi, haymakers) open in their place, in other cases the trachea have nothing to do with the lungs. The rudiments of the limbs of the abdomen are also the so-called coxal organs, which are present on the eighth to tenth segments in the kenenii and part of the ticks, which have no respiratory organs on the abdomen. They have the appearance of small protruding sacs filled with hemolymph, and, apparently, serve as the sense organs that determine humidity (hproreceptors). They are confined to the basins of the legs and, if the latter are lost, they remain in their place. In kenenii, they are located openly on the abdomen, and in some of the ticks they are part of the complex external reproductive apparatus, indicating the participation in its formation of three pairs of modified limbs of the eighth to tenth segments. Note that the system of such coxal organs is most fully developed in some millipedes and lower insects. The presence of coxal organs on the abdomen of the kenenii and lower mites indicates that these small forms of lungs never had.

As predators, arachnids are forced to cope with sometimes strong prey. The musculature is well developed, especially the muscles of the cephalothorax, which set the limbs in motion.

The glands of the integumentary (hypodermal) origin are diverse: the glands of the pre-oral cavity of spiders, the frontal and anal glands of the flagellates, the scent glands of the haymakers, etc. Poisonous and spider glands belong to the same category. The first are found in scorpions in the terminal segment of the abdomen, in spiders, in which chelicerae open on hooks, in false scorpions, and some ticks. The poisonous apparatus of scorpions and spiders is very effective remedy attack and defense. Spider glands are found in false scorpions, some ticks and spiders. In the latter, they are especially developed and open with numerous openings on the abdominal arachnoid warts.

The sense organs are formed by differentiation of the cells of the integumentary epithelium. Eyes are present on the prosom in different numbers: up to 5 pairs in scorpions, usually 4 pairs in spiders and gut-footed spiders, 2-1 pairs in most others; Keneny. many ticks, ricinules are blind. The eyes are built like simple ocelli. In the eye there is a diopter apparatus - a lens formed by a transparent thickening of the cuticle, and a vitreous body, and under it a layer of sensitive cells (retina) connected by fibers of the optic nerve to the brain. The pair of median (main) eyes and the lateral ones differ in the details of the structure. The visual capabilities of most arachnids are limited, they perceive variations in illumination and movement. Salpugi and wandering spiders see better than others. Among the latter, jumping spiders have object vision, but distinguish shape at a relatively close distance.

Poor vision is compensated by the sense of touch, which plays a primary role in the behavior of arachnids. On the body and limbs there are numerous tactile hairs, to the bases of which the nerve endings of sensitive cells fit. In size and shape, these hairs are extremely diverse in arachnids. In addition, there are special hairs that perceive vibrations - trichobothria.

These peculiar organs are usually present in a certain amount on the pedipalps and legs, sometimes on the trunk (in some of the ticks). A long protruding hair, sometimes thickened at the end, is attached by a thin membrane at the bottom of the funnel-shaped depression. The slightest shock or breath of air causes it to vibrate, which are perceived by a group of sensitive cells. Arachnids also have chemical sense organs, olfactory and gustatory. The first are the so-called lyre-like organs, numerous on the trunk and limbs. These are microscopic slits in the cuticle, covered with a thin membrane, to which the end of the sensitive cell fits. However, other functions are attributed to the lyre-like organs, in particular, mechanoreceptors, which perceive the degree of cuticle tension. The olfactory tarsal organs on the tarsi of the forelegs are more complex. Sensitive taste cells are found in the lining of the pharynx in spiders.

The nervous system is concentrated. The absence of a separate head, antennae, and compound eyes led to the fact that the epopharyngeal ganglion (brain), which innervates these organs in arthropods, is to some extent combined with the cephalothoracic nerve mass. Scorpions have a paired supraopharyngeal ganglion, connected by cords with a subopharyngeal ganglion accumulation, and 7 ganglia of the abdominal nerve chain. In solpugs, in addition to the general nervous mass, one abdominal node remains; in most arachnids, the entire nerve chain merges into the cephalothoracic mass.

The intestine is subdivided into the anterior, middle, and hindgut. The mouth opening leads to the expansion - the pharynx equipped with muscles, which serves to suck in semi-liquid food. The pharynx passes into a thin esophagus, which in some forms, for example, spiders, has another extension - the sucking stomach. The midgut usually forms several pairs of blind outgrowths that increase its capacity and suction surface. In the abdomen, the blind outgrowths of the intestine are well developed and form a large glandular organ-liver. Liver cells secrete digestive enzymes, and intracellular digestion of food takes place in them. The posterior part of the midgut forms a cloaca, in which excrement and excretion of the excretory malpighian tubes accumulate. Waste is excreted through the short hind gut and anus. In most cases, only liquid food enters the intestines of arachnids, all large particles are retained by the filters of the pre-oral cavity and pharynx. Being voracious predators, arachnids are able to take large amounts of food and then starve for a long time. The latter is possible due to the accumulation of nutrients in the storage tissue, similar to the fatty body of insects.

The excretory organs are coxal glands and Malpighian vessels. The first, as mentioned, represent the remains of coelomoducts - segmented excretory organs of the ancestors of arthropods - annelids.

They consist of an excretory sac, a convoluted duct (labyrinth) and an excretory canal and usually persist only in 1-2 pairs, opening at the bases of the legs. Malpighian vessels of arachnids - neoplasm. These are 1-2 pairs of blindly closed, sometimes branching tubules that open into the intestine near the cloaca. Excretions accumulate in the cells of their walls, which are then excreted into the cloaca. In addition, the excretory function is performed by the intestines, liver, cloaca and special cells - nephrocytes, which are present in the cavities between the organs. The main product of the isolation of arachnids is guanine. This substance in the body is in a certain biochemical relationship with the black pigment melanin, together with it, determining the color of the integument.

The structure of the respiratory and circulatory systems is closely related. The respiratory organs of arachnids are dual in nature. These are the organs of localized respiration - the lungs, formed from the abdominal gill legs of aquatic forms, and the organs of diffuse respiration - the trachea, which arise again as a more perfect device for breathing atmospheric air. Each pulmonary sac protrudes inward from a slit stigma. Numerous leaf-shaped pockets, folded like the pages of a book, extend from its inner wall. Blood circulates in the pockets, and air enters between them. Tracheas are tubes, unbranched or branched, that deliver air directly to organs and tissues. Their walls are formed by a continuation of the outer cover and are lined with a cuticle, which usually has supporting thickenings: the trachea is easily bent, and their walls do not collapse. The number of pairs of lungs, as said, is different, and in some cases they are absent, being replaced by tracheas, and in some small forms there are neither lungs nor tracheas, and skin respiration (Keneny, part of ticks). The number of tracheal trunks is also different, and they can open with stigmas in different places: on the segments of the abdomen, on the sides of the cephalothorax, at the bases of the chelicerae, which indicates their independent origin in different arachnids. In some cases, the trachea take the place of the lungs (in solpugs, bipulmonary spiders) and, apparently, arose from them, although as organs they are not homologous to the lungs. In general, in arachnids, the tracheal system is much less developed than in insects; usually, respiratory contractions of the abdomen, which are so characteristic of many insects, are not usually observed in them.

The circulatory system is well developed in large forms that breathe with the lungs. There is a pulsating dorsal vessel - a heart with several pairs of lateral openings - ostia, equipped with valves. The anterior and posterior aortas and several segmental pairs of arteries branch off from the heart. Blood (hemolymph) from the heart through the arteries is poured into the system of lacunae - the spaces between the organs, is collected in the pulmonary sinuses, is enriched with oxygen in the pulmonary pockets, through the pulmonary veins it returns to the pericardial space and through the ostia - to the heart. As the transition from pulmonary respiration to tracheal respiration, the circulatory system becomes less developed, the number of arteries and the spine of the heart decreases. So. scorpions and most flagellates have 7 pairs of spines, 6 in solpugs, from 5 to 2 in spiders, 2 pairs in haymakers, in ticks the heart is in the form of a small sac with a pair of spines or it is absent. Blood is usually colorless and contains several types of blood cells.

Arachnids are dioecious. The sex glands - the ovaries and testes - are located in the abdomen and in the initial state are paired. In some cases, there is a union of the right and left gonads. So, in male scorpions, the testes are paired, each consisting of two tubes connected by jumpers; in females, the ovary is one and consists of three tubes, of which the middle one is the result of the longitudinal fusion of two tubes. In many arachnids, paired gonads grow together at the ends into a ring. Paired oviducts and seminal ducts open with an unpaired genital opening on the eighth segment. The device of the excretory part of the reproductive system and copulatory devices are diverse. Females usually have an enlargement of the oviducts - the uterus and seminal receptacles, in which sperm are stored.

Breeding biology is diverse. External fertilization, characteristic of aquatic chelicerans, is replaced on land by internal, first free spermatophores, and then different ways copulation. In spermatophore fertilization, the sperm are enclosed in a special bag - the spermatophore, secreted by the male and protecting the sperm from drying out. In the most primitive cases, in many ticks living in moist soil, false scorpions, males leave spermatophores on the substrate, and females capture them with their external genitals. In this case, individuals perform characteristic mutual movements - mating dances. In many arachnids, the male in one way or another transfers the spermatophore into the female genital opening, which is often done with the help of chelicera, which have special devices for this. Finally, a number of forms do not have spermatophores, and sperm is injected using special copulatory organs. The latter are formed either as part of the external reproductive apparatus itself, or completely different organs serve for copulation, for example, the terminal segments of the tentacles of the pedipalps in male spiders, the third pair of legs in ricinules. Copulation is accompanied by sometimes very complex behavior of partners and the manifestation of a whole chain of instincts, especially in spiders.

In some mites, parthenogenesis is observed, that is, the development of unfertilized eggs. Sometimes males appear periodically, and the rest of the time development is parthenogenetic. There are also forms in which males are generally unknown.

Due to the large supply of yolk, the crushing of the egg is in most cases superficial: the nuclei, dividing, emerge on the surface of the yolk, where a layer of cells (blastoderm) is formed. The yolk usually does not divide. The embryonic leaves of arachnids were first discovered in scorpions in 1870 by I.I.Mechnikov and later found in other forms. Studying embryonic development allows for a better understanding of the structure of adult forms. For example, in cases where segmentation disappears in adults, it is expressed in the embryo (spiders, etc.). In embryonic development, it is possible to trace how the rudiments of the limbs of the abdomen are transformed into lungs and other organs, etc. Of great interest is the embryonic development of lower ticks, which retained primitive features, which we will dwell on later.

In many arachnids, offspring protection is observed. The female lays eggs in a specially dug hole and remains with them. In spiders, eggs are entwined with a spider cocoon, which the female usually guards in the nest or carries with her. The hatched young individuals usually do not feed actively at first, they are fed by the embryonic yolk that remains in the intestine. During this period, juveniles keep in the nest or on the mother's body (in scorpions, teliphons, a number of stray spiders, etc.) and, only after molting, they move on to independent life.

In terms of the general nature of the life cycle, arachnids are very different. In this respect, two types can be outlined, between which there are transitions. One extreme type is represented by large, durable forms that live for many years and reproduce periodically. These are, for example, some tropical scorpions, flagellates, large bird spiders. Among the latter, some live up to 20 years and do not lose their ability to shed all their lives. In this type of life cycle, individual development is long-term and sexual maturity is achieved after long growth. Individuals usually do not form massive clusters, and in general the number of such forms in nature is relatively small. This long-lived way of life, associated with large size or even gigantism and multiple periodic reproduction, is obviously inherited by arachnids from aquatic chelicerans and is generally not characteristic of terrestrial arthropods. Among aquatic forms, merostomaceous, as well as many large crustaceans, are just such in life type. On land, this type was retained only in some arachnids, living mainly in the humid tropics, where living conditions are, so to speak, hothouse. Among trachea breathing, a well-known analogy is represented by some giant tropical centipedes - kivsaki. Note that among terrestrial animals, vertebrates followed the path of long-lived life with large sizes of individuals, but they had their own special biological prerequisites for this.

Most arachnids are characterized by a different, opposite life type, which in its extreme variants is represented in many ticks. These small arachnids are short-lived, but they develop very quickly, and generations follow each other as long as the conditions are right. As soon as conditions become unfavorable, all active individuals die, but resting eggs or special forms (young or adults) that can carry unfavourable conditions(drying out, low temperature, lack of food, etc.). With the onset of suitable conditions, the dormant forms awaken, active life begins, reproduction, and in a short time the number is restored. This ephemeral type of life, associated with small size, high rate of development and usually with the presence of special surviving stages, is very characteristic of terrestrial arthropods in general, in particular for insects. It is undoubtedly the most important biological adaptation to life on land, where conditions are much more variable than at sea. In addition to all kinds of random changes in the environment, the development of this life type is affected by periodic seasonal phenomena, especially sharp in a temperate climate. Most arachnids, for example spiders, like many insects, are represented by one-season forms, which manage to complete one generation during the summer. Eggs or juveniles usually overwinter, which reproduce the next year. Less often, arachnids have 2-3 generations per year, and only some mites have time to make many generations.

There is no doubt that all arachnids are descended from aquatic chelicerans. As we have seen, the transition to life on land was accompanied by the development of many adaptations. Gill breathing was replaced by pulmonary breathing, and then it began to be supplemented and replaced by tracheal breathing. The number of body segments was reduced, the abdomen was concentrated as a single section. Further specialization of the limbs of the cephalothorax took place. The legs lost their chewing function, the legs were dismembered, and feet were walking. Extraintestinal liquefaction of food has become widespread, and the perioral limbs have adapted to this peculiar way of feeding. Differentiated a complex system of cutaneous sensory organs, especially tactile Ho Changes also occurred in the internal structure - the concentration of the nervous system, the addition and replacement of the excretory coxal glands with Malpighian vessels, the contraction of the circulatory system in connection with the transition to tracheal and cutaneous respiration, especially in small forms, etc. Breeding biology has changed. The water type of external fertilization was replaced by internal, first free spermatophores, and then by various copulation methods. In a number of cases, viviparity, the protection of offspring, arose. An ephemeral type of life characteristic of terrestrial arthropods has developed: the ability to complete development in a limited time, the fragility and relatively small size of the adult form, the presence of experiencing stages. So the problem of transition to land life was solved.

However, as mentioned above, the ancestors of the arachnids were quite specialized aquatic chelicerans, and when they went on land, new adaptations could develop only on the basis of an already established, very peculiar organization of aquatic forms, which created a number of restrictions. And if you look at the arachnid not from the usual point of view - admiration for the perfection of adaptations to environment, and on the opposite, from the point of view of the limitations and difficulties that were created thanks to the former specialization and which had to be overcome or bypassed, then much in their evolution will become more understandable. Comparison with insects - trachea breathing animals, terrestrial in nature is also very indicative. So, breathing with the help of the lungs formed from the gill legs, in arthropods with their open circulatory system, is a much less perfect way of gas exchange than tracheal breathing. Protection from drying out - the main danger on land - with localized pulmonary breathing is imperfect, and indeed, most arachnids need highly humidified air for breathing. Since the arachnids took the path of pulmonary respiration, the tracheal system did not develop to the proper extent. Despite numerous attempts in this direction, it has not reached such perfection as in insects. Only solpugs and haymakers, in terms of the degree of development of the trachea, somewhat resemble the latter. It is characteristic that small thin-skinned arachnids (many mites, kenenii) living in humid soil air are generally spared from the contradictory nature of the pulmonary-tracheal apparatus and breathe through the integument. Many restrictions on life on land were created due to the absence of a separate movable head with antennae and jaws, and in particular the atrophy of compound eyes. Arachnids were forced to follow the path of improving mainly the sense of touch, imitating antennae with their limbs, and orientation in the outside world "by touch", which, among other inconveniences, limits the hunting efficiency of a wandering predator. Instead of feeding with the help of a set of special mouth limbs - jaws, adapted to receive a variety of food, which is characteristic of insects, arachnids have developed a very uniform way of feeding on the liquefied contents of the prey, that is, almost universal predation. Only part of the ticks managed to get out of this monotony. Direct shortened post-embryonic development associated with an abundance of yolk in the egg and late hatching, with all the advantages, had the same negative side that on its basis complex forms of metamorphosis, which are characteristic of insects, could not arise and opened up to them the broadest possibilities of adaptation to various living conditions. Only ticks, with their peculiar metamorphosis, began to compete with insects in this respect.

In how and to what extent these historically established limitations were overcome or circumvented, the orders of arachnids are different. The evolutionary possibilities of arachnids are clearly revealed when comparing the species diversity and distribution of orders. Of the total number of 35,000 species, the lion's share is accounted for only by spiders (20,000) and ticks (10,000). Of the remaining 5000 species, 2500 are haymen, 1100 are false scorpions, and the rest comprise several hundred or even dozens of species. Such relationships are not accidental. Small-species orders are just arachnids, in the way of life and distribution of which the restrictions that have just been mentioned are clearly manifested. All of them are closely related to the soil and various shelters where the air is humid enough. These are wandering predators, mostly nocturnal, which catch prey "by touch" and hide during the day in cracks in the soil, under stones, in burrows, or permanently live under a canopy of vegetation, in forest floor, wood dust, etc. In their distribution, these groups limited to warm countries, many forms do not go beyond the tropics. Only part of the species of hay makers and false scorpions is found in temperate latitudes.

Spiders and ticks present a different picture. Among the arachnids, in essence, only they were able to completely overcome, or rather, to get around the historical limitations of their class. The few primitive representatives of these groups - the lower burrowing and wandering spiders and primitive ticks - in their ecological appearance still stand on a par with other arachnids, but the further fate of spiders and ticks is completely different.

The cobweb was of decisive importance in the evolution of spiders, which was originally used to build egg cocoons and lining shelters, and then began to be used to build trapping nets. In the life of the highest snake spiders, the cobweb is everything. It is a refuge and a trap. A favorable microclimate is created in the shelter, which is especially important for breathing, here the spider lies in wait for prey, takes refuge from enemies and bad weather. The prey falls into a trapping net, is seized "by touch" with minimal involvement of sight and is killed with the help of chelicera, which inject poison. Mating takes place on the web, an egg cocoon is woven from it, immature juveniles hide in it, young spiders are carried by the wind on the cobwebs, etc. Having provided themselves with everything necessary, the spiders with their cobweb adaptations penetrated into all kinds of habitats, widely populated the land and reached an unprecedented flourishing. With a rather stereotypical general appearance, higher snake spiders are extremely diverse in habitat, shape and color, designs of trapping nets and habits. In terms of the complexity of behavior and the perfection of instincts, spiders resemble insects.

As we said, due to the small size of the eggs, ticks develop with metamorphosis. With adaptation to new conditions, not only the adult form changed, but also the methods of metamorphosis, and this significantly expanded the evolutionary possibilities. In particular, extremely rapidly multiplying forms arose, capable of reaching colossal numbers in the shortest possible time, special surviving and settling stages developed, etc. In terms of diversity and abundance in nature, ticks surpassed spiders, although they are inferior to them in the number of known species.

Thus, most of the detachments of arachnids turned out to be limited in the development of land, and only spiders and ticks went much further and turned from poor settlers into conquerors of land. Spiders and ticks are very widespread, from the tropics to the polar countries and highlands. They can be found where life is scarce and there are almost no insects. In terms of number in nature, they are not inferior to the latter. However, one should not think that the rest, smaller in the number of species, orders are more similar to each other. On the contrary, each of them has its own unique characteristics and its own variants of adaptations, which fully ensure life in its inherent conditions. Only these adaptations are of a more private nature and do not lead to such grandiose evolutionary consequences as in spiders and ticks. Comparing the detachments of arachnids, one can somehow outline the face of each.

So, scorpions are the most ancient arachnids, in essence eurypterids that came out onto land. A minimum of adaptations to land life (pulmonary respiration, foot walking, arachnid type of predation) are combined in them with very peculiar features (a poisonous apparatus at the end of the metasome, the transition to live birth, bearing juveniles on oneself, etc.). In their way of life and primitiveness, teliphones and phryns somewhat resemble scorpions, but these units, very poor in species, are more narrowly confined to humid warm habitats, mainly to tropical forests, and differ in structure (a different number and position of the lungs, the absence of a poisonous apparatus on the metasome and etc.). Phryne, at the same time, have so much in common with spiders that they are considered spiderless relatives of the latter and are called otherwise stinging spiders.

Two orders - solpugs and hay makers - stand out so much in the degree of development of the tracheal system that they can be called tracheal breathing arachnids. The main tracheal trunks open with stigmas on the abdomen where the arachnids have lungs, and it is very likely that the trachea here arose from the lungs, which may be the reason for their powerful development. In other respects, solpugs and haymakers are very different and far from each other. In solpugs, a powerful tracheal system is combined with a primitive organization (completeness of trunk segmentation, dissected prosoma, pedipalps like legs, etc.). Like most arachnids, solpugs are nocturnal predators hiding in shelters during the day. But they are distributed mainly in dry and hot regions, are extremely mobile, and there are even several species running on the sand under the scorching sun in the deserts. All this indicates the perfection of the regulation of respiration and water exchange. However, the tracheal system itself, with other primitive arachnid properties, is apparently insufficient for the transition to more advanced forms of open terrestrial life, and the species diversity of solpugs is small.

Haymakers in their life appearance are the most, if I may say so, insect-like arachnids. Along with a well-developed tracheal breathing, this order is dominated by that armor-like life form, which is characteristic of some insects that do not fly or have little use of their wings, for example, beetles. The compact body is protected by a leathery or very hard shell. The abdominal segments are closed, and in many forms their tergites grow together with the cephalothorax into a common dorsal shield. At the same time, the body of the haymakers is, as it were, suspended on long legs, which, at a low frequency of movements, provide a high speed of movement: the step of the haymakers is very large. Along with nocturnal predators, there are many species among haymakers that are active during the day, roaming freely in the bright sun, even in dry areas. Not having the advantages that are inherent in species-rich orders, the haymakers nevertheless spread widely and achieved significant diversity (2500 species).

Several orders of small arachnids - kenenii, false scorpions, ricinules - have adapted to hidden life in natural cavities and cracks in the soil, in forest litter, wood debris, etc. In this respect, they resemble ticks. However, all of them are larger and have not crossed that step of grinding, behind which the microscopic life form of ticks with its evolutionary capabilities arose. Keneny and ricinulei are represented by a few rare, mainly tropical species, 1100 species of false scorpions are known and they are more widespread. Keneny are typical inhabitants of soil wells, one of the most primitive arachnids, resembling, on the one hand, a miniature salpug, on the other, some lower mites. False scorpions are also very primitive, but they have some very peculiar features: grasping pedipalps with claws, like scorpions, an extremely peculiar way of viviparity, etc. They live hidden in the forest floor, wood dust, under peeled bark, under stones and can settle by attaching to insects. Apparently, this way of life contributed to the fairly wide distribution of false scorpions, although they clearly predominate in the tropics. Little is known about the way of life of casters. These sluggish forms with a very hard cover are remarkable in that in their development, like ticks, there is a six-legged larva.

The change of habitats in the evolution of arachnids can be illustrated by the diagram. Coming onto land, the arachnids were forced to confine themselves to humid habitats, in which many of them still live. The most important condition for reaching land was terrestrial vegetation. Many found shelter under its canopy, others, especially small ones, settled the decomposition products of plants, organic litter and soil. The arachnids' ability to make dens and burrows for themselves and their offspring, combined with nighttime activity, significantly expanded the possibilities of land development and made it possible to get out of the wet vegetation cover. The close connection of arachnids with soil at this stage of their evolution is in good agreement with the ideas of M.S. ed. of the Academy of Sciences of the USSR, 1949).

To go to more detailed review orders of arachnids, it is necessary to dwell on some issues of classification. As mentioned, the Arachnida class is a collection of chelicerans that have passed over to land life. The orders of arachnids are very different. With a deep commonality of all of them as representatives of the Chelicerata subtype, almost every order is unique in the combination of characters, and not only is it impossible to derive it from any neighboring order, but in some cases it is difficult to say exactly which of the other orders it is closer to. This uniqueness of the detachments is explained, on the one hand, by various options for adapting to land life, which were mentioned above. But on the other hand, the signs of the orders are such that it is impossible to reduce them to these devices alone, they lead somewhere deeper and make one think that arachnids more or less independently descended from various aquatic chelicerans. The immediate ancestors of most orders have not yet been discovered. But in relation to one order, namely the scorpions, they are now known. A number of transitional fossils, independently of other arachnids, associate scorpions with some Silurian eurypterids. In other words, the Arachnida class in its traditional composition must be considered artificial. In this regard, recently, attempts have been made more than once to group the detachments according to their possible origin and divide the arachnids into several classes. But the opinions of zoologists differ, and the work on streamlining the classification cannot be considered complete.

As mentioned, the majority of the arachnid orders are beyond doubt as clear systematic groupings. There are contradictions in relation to flagellates (Pedipalpi) and ticks (Acarina). With the former, the situation is somewhat simpler. Under the flagellates are understood three quite clearly demarcated, albeit close in some respects, groups: Teliphones, Phryns and Tartarids. Most authors quite thoroughly consider the Teliphones and Phryns to be independent units. Tartaride alone is left in the composition of telephones. others, including us, consider it a separate detachment.

The situation with ticks is much more complicated. Ticks represent a huge collection of small arachnids. very different in structure and way of life and in most of them have changed greatly in comparison with others. Until recently, all this diversity was combined into one order Acarina with many suborders and special more fractional subdivisions (cohorts, phalanges, series, etc.), the systematic composition of which is different for different authors. And, perhaps, there is no other such group of arthropods, which, in terms of the confusion and inconsistency of the classification, would be similar to ticks. Ticks were considered as very special arachnids, which degraded and deviated from their original state so much that it is even difficult to compare them with the rest. It was believed, and even now it is written, especially in the textbooks of zoology, that all ticks have three main features that distinguish them from other arachnids. First, the body segments in ticks have merged and the boundaries between them have disappeared, and if there is a division of the body into sections, the latter do not correspond to the body sections of other arachnids. Secondly, ticks have a special mobile anterior section - the head, or gnatosome, which combines the chelicerae and pedipalps. Third, in ticks, a six-legged larva hatches from the egg, which then turns into an eight-legged form.

Despite the factual irrefutability of the independence of tick orders, the new classification causes a different attitude of specialists. Some have a positive attitude towards it, for example, such an outstanding zoologist and comparative anatomist of our time, like V. N. Beklemishev, cites it in his "Foundations of the comparative anatomy of invertebrates" (editions 1962, 1964). Others are vague and some are negative. The reasons for the contradictions are different and, oddly enough, have little to do with facts. It is mainly the strength of tradition that has its effect. Some authors try to find a way out in the fact that, recognizing the three orders of ticks, they combine them all into a special subclass or even a class. This is what, for example, our well-known expert on ticks VB Dubinin does in his essay on the chelicerans, published in the major academic publication "Foundations of Paleontology" (1962). But such an operation does not essentially change the matter: raising the rank does not make the mites unite naturally. On the other hand, a purely formal attitude to this issue prevails, which is due to the very nature of the study of ticks. The fact is that due to the variety of ticks and the complexity of their study, the overwhelming majority of specialists are engaged in separate systematic groups. And for a taxonomist who studies, for example, only scabies or only gall mites, it is not so important whether they belong to the order Acariformes or to the order Acarina. And thinking about ticks as a whole is more familiar. It is also important that, thanks to the medical and economic significance of ticks, a whole independent branch of knowledge arose, the science of ticks - acarology, parallel to the science of insects - entomology, - a branch of knowledge with its own methods, its own range of scientific and practical problems, the most complex terminology, its symposia and congresses, their traditions. But if entomology has an object of a natural group of arthropods - the class of insects, then acarology, with a new approach to ticks, turns out to be the science of just a few heterogeneous orders of small arachnids. Such "abolition" of a single object of a whole branch of knowledge sometimes provokes a purely psychological protest.

The division of ticks into groups appears quite differently, as soon as we turn from private and applied acarology to general acarology, the task of which is to organize all the vast material on ticks, according to their structure, development, lifestyle, distribution, etc., and in ultimately in elucidating the origin and evolution of ticks. Here, the ways and results of the analysis of facts entirely depend on whether we recognize ticks as a single group or three independent orders, no more related to each other than arachnids in general. In the first case, we are forced to study ticks as such, distracting at first from other arachnids, and our main efforts are directed at imagining and, if possible, finding the initial prototypical form for ticks as a whole, to trace how all the diversity arose from this prototype. ticks, and then establish what is the relationship of this prototype with other orders. In the second case, the search for a single prototype of ticks becomes meaningless. We must study the orders of mites separately and in each case find out the initial state, the path of evolution of each order and the place of each in the general evolution of the arachnids. And all the factual material on ticks with complete convincingness shows that there is no single prototype of ticks, so to speak, "ticking" in nature and never has been. The traditional approach to ticks as a group is not good. It is enough to reveal general monographs on ticks, for example, the most famous voluminous summary of the German acarologist G. Fitztum of 1943, as we come across a pile of facts, an endless enumeration of unrelated options for structure, development, lifestyle, etc. Attempts to reduce these data to something then one invariably leads to contradictions, and sometimes to such fantastic hypotheses, which are hardly appropriate to consider here.

Speaking about the convergence of ticks, one should not forget the other side of this phenomenon. So far we have talked about the heterogeneity of ticks as three orders.

But after all, they are all cheliceral and in this sense are deeply related, like other arachnids, so that the phenomena of convergent convergence of orders of mites played out in evolution on a common arachnid basis for all of them, and this is also the reason for the depth of convergence. We have to talk about this also because some scientists, desperate to understand the originality of ticks, generally separate them from arachnids, which is the other extreme in matters of classification and is absolutely unacceptable. Just as it is impossible to combine ticks into one group, so it is impossible and. throw them out of the arachnids. Ticks, or, more precisely, tick-like arachnids, are three independent orders, as unique as spiders, hay makers, solpugs and others, and to the same extent related to the collection of terrestrial chelicerans called arachnids.

In a word, the ticks were a decent riddle, the solution of which only now, after being divided into detachments, was on solid ground. In this respect, ticks are an excellent example of how the classification of organisms is not only a means of identifying them, or, as some people think, a conditional "unfolding" on the shelves, but has a much deeper meaning. Being itself an inference from a certain, at first limited, group of facts, natural classification gives the right direction to further research, saving science from delusions and a waste of time.

Ticks (Acarina), small (from 0.1 to 30 mm) arthropods of the class of arachnids of the cheliceratic subtype. According to some zoologists, K. is a single order, which includes 3 suborders: hay mites (Opilioacarina), acariform K. (Acariformes) and ... ...

I Ticks (Acarina) are small (from 0.1 to 30 mm) arthropods of the class of arachnids of the cheliceratic subtype. According to some zoologists, K. is a single detachment, which includes 3 suborders: haymaker mites (Opilioacarina), acariform K. (Acariformes) ... ... Great Soviet Encyclopedia

Theoretical tour of the municipal stageXXVIIIAll-Russian Olympiad for Schoolchildren in Biology,

2011-12 academic year

10th-11th grades (maximum - 122.5 points)

Part I. The task includes 60 questions, for each of them 4 possible answers are offered. The maximum number of points that can be collected is 60 (1 point for each test task). For each question, choose only one answer that you think is the most complete and correct. Enter the index of the selected answer in the matrix of answers.

1. Among gastropods, viviparous are:

a) meadow; c) pond snail;

b) naked slug; d) grape snail.

2. In what organism is ATP synthesized outside the mitochondria?

a) mucor; c) amoeba;

b) Escherichia coli; d) chlamydomonas.

3. After doubling two pairs of chromosomes, the number of chromatids in them is equal to:

a) 2; b) 4; at 8; d) 16.

4. Which of the characteristics of a person has the broadest norm

reactions:

a) eye color; c) blood group;

b) the number of fingers; d) the vital capacity of the lungs.

5. In which group do all plants belong to the class Dicotyledonous?

a) cabbage, beans, wheat;

b) cherry, potato, tulip;

c) mustard, lettuce, apricot;

d) lily, rose, mint.

6. How is rubella transmitted?

a) food; c) transmission;

b) airborne; d) contact and household.

7. In what case is the composition of the RNA nucleotide indicated?

a) thymine-ribose-phosphate;

b) cytosine deoxyribose phosphate;

c) uracil-ribose-phosphate;

d) guanine deoxyribose phosphate.

8. What came first?

a) autotrophic nutrition; c) eukaryotic cell structure;

b) aerobic oxidation; d) sexual process.

9. Participates in the formation of the cytoskeleton:

a) endoplasmic reticulum; c) flagella;

b) microtubules; d) cell center.

10. Who is characterized by development with complete metamorphosis?

a) flies; c) lice;

b) bedbugs; d) cockroaches.

11. A similar internal structure has

a) mitochondria and chloroplasts;

b) the Golgi apparatus and lysosomes;

c) ribosomes and cell center;

d) lysosomes and endoplasmic reticulum.

12. In flowering plants, as a result of mitosis, the following are formed:

a) two sperm; c) disputes in microsporangia;

b) disputes in the megasporangia; d) haploid cells in microsporangia.

13. Groups of cells that stimulate the development of organs and tissues

the embryo is called:

a) by the organizers; c) inhibitors;

b) compensators; d) guides.

14. Splitting phenotype 3: 1 when crossing two plants

peas with smooth seeds indicate that both

parent individuals:

a) homologous; c) homozygous;

b) heterogametic; d) heterozygous.

15. Splitting in the second generation according to the phenotype 12: 3: 1 staining

wool is the result of interaction

16. Mammals inherited from animal-toothed lizards

a) four-chambered heart; c) hairline;

b) the structure of the dental system; d) feeding on animal food.

17. The adrenal medulla secretes a hormone

a) thyroxine; c) adrenaline;

b) insulin; d) glucagon.

18. The forebrain of a person is responsible for

a) pain and temperature sensitivity;

c) protective and digestive reflexes;

d) orienting reflexes to visual and sound stimuli.

19. Platelets are

a) the intercellular substance of the epithelial tissue;

b) specialized cells of epithelial tissue;

c) the intercellular substance of the connective tissue;

d) specialized cells of connective tissue.

20. The fitness of living organisms was explained by the initial

expediency

a) Charles Darwin; c) J.-B. Lamarck;

b) K. Linnaeus; d) A. Wallace.

21. The adaptability of organisms to constant environmental conditions

formed by natural selection

a) driving; c) disruptive (splitting);

b) stabilizing; d) balancing.

22. Biological factor of evolution, providing

the formation of the Pithecanthropus ability to make fire, was

a) the manifestation of care for the offspring;

b) opposition of the thumb;

c) an increase in brain volume;

d) group cooperation.

23. In the Cambrian, the most widespread

a) stegocephalic; c) shellfish;

b) trilobites; d) jawless fish.

24. Reverse transcription is typical for

a) unicellular fungi; c) prokaryotes;

b) protozoa; d) viruses.

25. From ancient seed ferns originated

a) modern ferns; c) lycopods;

26. Among vertebrates, only amphibians are characterized by

a) external fertilization;

b) development with transformation;

c) decreased metabolism;

d) inconsistent body temperature.

are available from

a) ants; c) bumblebees and wasps;

b) riders; d) May beetle.

28. The activity of the pituitary gland is under control

a) the hypothalamus; c) the adrenal cortex;

b) the thyroid gland; d) cerebral cortex.

29. Orientation reflexes refer to

a) unconditional, specific; c) unconditional, acquired;

b) conditional, acquired; d) individual, inherited.

30. Migration of individuals is referred to as the driving forces of evolution, since it

can lead to

a) increasing the diversity of the gene pool;

b) strengthening the struggle for existence;

c) strengthening the mutational process;

d) the emergence of adaptations.

31. Ability to develop new organisms from individual blastomeres

is lost in the embryo due to

a) cell differentiation;

b) the absence of the organizer;

c) the formation of endoderm;

d) the onset of a pause in cell division.

32. Splitting in the second generation according to the phenotype of 15: 1 seed color

wheat is the result

a) allelic genes by the type of incomplete dominance;

b) non-allelic genes by the type of complementarity;

c) allelic genes by the type of codominance;

d) non-allelic genes by the type of polymerization.

33. Reverse transcription is a synthesis process

a) RNA for DNA; c) protein on RNA;

b) DNA on RNA; d) protein for DNA.

are available from

a) toothless; c) pond snails;

b) grape snails; d) slugs.

35. A similar structure indicates the relationship of flat and round worms

systems

a) nervous; c) respiratory;

b) circulatory; d) digestive.

36. The activity of the thyroid gland is regulated

a) the adrenal medulla;

b) the cerebral cortex;

c) the adrenal cortex;

d) the pituitary gland.

37. In nature, for real populations, the following trait is characteristic

a) population waves;

b) the immutability of the gene pool;

c) free crossing of individuals;

d) the absence of the migration process.

38. The appearance of ferns on land occurred in

a) Permian; c) Devonian;

b) Cambrian; d) Carboniferous.

39. A predator-prey relationship is characteristic of a falcon

peregrine falcon and

a) a dove; c) the neck;

b) a kite; d) golden eagle.

40. The smallest genotypic similarity of individuals of one species is characteristic

for different

a) childbirth; c) subspecies;

b) families; d) populations.

41. Organisms maintain their integrity and exercise

various functions due to the ability

a) to reproduction;

b) to the metabolism and energy;

c) change its structure and function;

d) pass on their properties by inheritance.

42. The movement of the cytoplasm and its organelles is carried out with the help

a) channels of the endoplasmic reticulum;

b) microtubules and microfilaments;

c) cilia and flagella;

d) the cell center.

43. Sexual reproduction is based on

a) the fertilization process is mandatory;

b) the formation of germ cells;

c) exchange of genetic information;

d) participation in reproduction of two organisms is obligatory.

44. The ectoderm, located on the dorsal side of the embryo, is

organizer to form

a) muscle tissue; c) mesoderm;

b) the neural tube; d) endoderm.

45. Splitting in the second generation according to the phenotype 13: 3 coloration

plumage in chickens is the result of interaction

a) non-allelic genes of the epistasis type;

b) non-allelic genes by the type of polymerization;

c) allelic genes by the type of codominance;

d) allelic genes by the type of incomplete dominance.

46. ​​Modification of any plant organ is associated with

a) a change in its functions;

b) seasonal cooling;

c) underdevelopment of the growth cone;

d) the influence of specific stimulants.

47. The progressive trait of flowering plants is

a) the appearance of complex leaves;

b) the formation of a branched root system;

c) the formation of fruits;

d) reproduction by seeds.

48. The musculocutaneous sac is absent in

a) flat and round worms;

b) roundworms and molluscs;

c) molluscs and arthropods;

d) arthropods and annelids.

49. In reptiles, in connection with the transition to life in terrestrial

air environment for the first time

a) two ventricles and an atrium were formed in the heart;

b) a second circle of blood circulation appeared;

c) the belt of the forelimbs appeared;

d) cellular lungs have formed.

are

a) insects; c) crustaceans;

b) molluscs; d) annelids.

51. The activity of the adrenal glands is regulated directly

a) the pituitary gland; c) the thyroid gland;

b) the hypothalamus; d) the cerebral cortex.

52. Human medulla oblongata is responsible for

a) the change in the phases of sleep and wakefulness;

b) regulation of the constancy of the internal environment;

c) regulation of muscle tone and balance;

d) reflex implementation of inhalation and exhalation.

53. Under the influence of isolation as the driving force of evolution in

population occurs

a) an increase in the diversity of the gene pool;

b) strengthening the struggle for existence;

c) strengthening of the mutational process;

d) consolidation of its genetic difference.

54. Geographic speciation must be preceded by

a) saturation of the population with mutations;

b) resettlement of individuals over large areas;

c) the development of new living conditions by individuals;

d) the formation of a new population by hybridization.

a) in the Carboniferous; c) in the Triassic;

b) in chalk; d) in the Paleogene.

56. The relationship of the "predator - prey" type is characteristic of the mink and

a) foxes; c) ferret;

b) martens; d) muskrats.

57. Indicate the name of the scientist who was the first to try to prove that

spontaneous generation of life is impossible

a) L. Pasteur; c) F. Redy;

b) L. Spallanzani; d) J. Buffon.

58. Caring for offspring is most developed in

a) gophers; c) dolphins;

b) protein; d) kangaroo.

59. Atavism is not

a) multi-nipple; c) the formation of cervical ribs;

b) appendix; d) tails.

60. A substance that plays the role of a neurotransmitter in synapses is called

a) adrenaline; c) insulin;

b) norepinephrine; d) mucin.

PartII. You are offered test items with one answer out of four or five possible, but requiring multiple choice in advance. The maximum number of points that can be collected is 25 (1 point for each test task). Indicate the index of the answer that you consider the most complete and correct in the matrix of answers.

1. Blood circulation in vertebrates is carried out by:

I. Arteries;

II. Arteriolam;

III. Venam;

IV. Venulam;

V. Capillaries.

a) I, II, V; c) I, III, IV, V;

b) II, III, IV; d) I, II, III, IV, V.

2. For photosynthesis to proceed, the following conditions are required:

III. Carbon dioxide;

IV. Oxygen;

V. Mineral substances.

b) I, II, IV, V; d) I, II, III, V.

3. Representatives of the chordate type are characterized by:

I. Secondary body cavity;

II. Secondary mouth;

III. Bilateral symmetry;

IV. Three-layer;

V. Lack of internal skeleton.

a) I, II, III, IV; c) II, IV, V;

b) I, II, III, IV, V; d) I, III, IV, V.

4. Smooth muscle contains:

I. Actin, myosin, tropomyosin;

II. Actin only;

III. Myosin only;

IV. Actin and Troponin;

V. Uses A.T.F.

a) III, IV, V; c) I, II, III, IV;

b) I, V; d) II, III, IV, V.

5. What conditions of the primary atmosphere of the Earth contributed to the synthesis

organic compounds?

I. Availability of possible energy sources for the formation of chemical bonds;

II. The presence of a significant amount of O 2;

III. The presence of various microorganisms in the Earth's atmosphere;

IV. The presence of water vapor with an admixture of other gases in the almost complete absence of O 2.

a) I, II, III; c) II, III;

b) I, II, III, IV; d) I, IV.

6. In which cell organelles are proteins synthesized?

I. Chloroplasts; III. Mitochondria;

II. Ribosomes; IV. Endoplasmic reticulum.

b) I, II, IV; d) II, III, IV.

7. Where are ribosome subunits formed?

I. Cytoplasm;

III. Vacuoles;

IV. Nucleolus;

V. Golgi apparatus.

a) II, IV; c) I, II, III, IV;

b) I, II, III; d) I, III, IV, V.

8. What is the state of chromosomes at the beginning of cell division?

I. Spiralized; III. Bichromatid;

II. Despiralized; IV. Monochromatid.

a) I, II; c) I, IV;

b) I, II, III; d) II, III, IV.

9. List the main stages of aerobic dissimilation

I. Preparatory;

II. Glycolysis;

III. Fermentation;

IV. Breath;

V. Electron transport chain.

a) I, II, IV, V; c) I, IV, V;

b) II, III, IV, V; d) II, III, V.

10. What rays of the spectrum does chlorophyll absorb?

I. Red; III. Purple;

II. Green; IV. Blue.

a) I, II, III; c) I, II, III, IV;

b) I, III, IV; d) IV, V.

11. What is gastrulation?

I. Formation of a multicellular embryo;

II. The formation of germ layers;

III. Secondary cell formation;

IV. Formation of a multicellular embryo.

a) II, IV; c) II, III, IV;

12. What factors of anthropogenesis provided the development of bipedal locomotion?

I. The release of the upper limbs in the process of labor;

II. Mutation process;

III. Herd lifestyle;

IV. The driving form of natural selection;

V. Restriction of free crossing between individuals of different

populations.

a) II, IV, V; c) I, II, III, IV, V;

b) I, IV, V; d) II, IV, V.

13. Which muscles have received the greatest development in connection with

upright posture?

I. Occipital;

II. Dorsal;

III. Pectoral;

IV. Buttock;

V. Calf.

a) I, III, IV, V; c) III, IV, V;

b) I, II, IV, V; d) I, II, III, IV, V.

14. What substances are blood clotting factors

I. Thromboplastin;

II. Lipase;

III. Thyroxine;

IV. Fibrinogen;

V. Prothrombin.

a) I, IV; c) I, IV, V;

b) I, II, III; d) I, II, III, IV.

15. What organs does the autonomic nervous system innervate?

I. Heart;

II. Stomach;

III. Vessels;

V. Muscles of the arms.

a) I, II; c) I, II, III, V;

b) I, II, III; d) I, II, III, IV.

16. Bacteria cause diseases:

I. Relapsing fever;

II. Typhus;

III. Malaria;

IV. Tularemia;

V. Hepatitis.

a) II, IV; c) I, II, IV;

b) I, IV, V; d) II, III, IV, V.

17. If you cut off (cut off) the tip of the main root:

I. The root will die;

II. The whole plant will die;

III. The root will stop growing in length;

IV. The plant will survive but be weak;

V. Lateral and adventitious roots will begin to grow.

a) III, IV, V; c) I, IV, V;

b) III, V; d) II, IV, V.

18. Among arachnids, development with metamorphosis is typical for:

I. Spiders;

II. Ticks;

III. Solpug;

IV. Haymakers;

V. Scorpions.

a) II, III; c) I, IV;

b) II; d) I, II, III, V.

19. Animals leading an attached (sedentary) lifestyle, but

having free-swimming larvae are:

I. Corals;

III. Ascidians;

IV. Rotifers;

V. Barnacles.

a) I, II, III, IV; c) I, III, IV;

b) I, II, III, V; d) I, II, III, IV, V.

20. Chorda persists throughout life in

II. Sturgeon;

III. Sharks;

IV. Lampreys;

V. Lancelet.

a) I, II, III, IV; c) II, III, V;

b) III, IV, V; d) II, IV, V.

21. Each population is characterized by

I. Density;

II. Number;

III. The degree of isolation;

IV. Independent evolutionary destiny;

V. The nature of the spatial distribution.

a) I, II, V; c) II, V;

b) I, IV, V; d) II, III, IV.

22. Similar organs developing in the course of evolution:

I. Fish gills and crayfish gills;

II. Butterfly wings and bird wings;

III. Pea tendrils and grape tendrils;

IV. Hair of mammals and feathers of birds;

V. Cactus spines and hawthorn spines.

a) I, III, IV, V; c) I, II, III, V;

b) I, II, IV, V; d) I, II, III, IV.

23. In the human body, hormonal functions are performed

connections:

I. Proteins and peptides;

II. Derivatives of nucleotides;

III. Cholesterol derivatives;

IV. Amino acid derivatives;

V. Derivatives of fatty acids.

a) III, IV, V; c) III, V;

b) I, III, IV, V; d) II.

24. Of the named polymers, insoluble polymers include:

II. Amylose;

III. Glycogen;

IV. Cellulose;

V. Amylopectin.

a) I, II, IV; c) II, IV, V;

b) I, II, III, IV; d) III, IV, V.

25. Predators, usually hunting from an ambush, include:

III. Jaguar;

IV. Cheetah;

V. Bear.

a) II, III, IV, V; c) I, II, III, V;

b) I, IV; d) II, III, V.

Part III. You are offered test tasks in the form of judgments, with each of which you must either agree or reject. In the matrix of answers, indicate the answer option "Yes" or "Not"... The maximum number of points you can score is 25.

1. Hepatic mosses are lower plants.
2. Gametes in mosses are formed as a result of meiosis.
3. Starch grains are leukoplasts with starch accumulated in them.
4. The hemolymph of insects performs the same functions as the blood of vertebrates.
5. In all invertebrates, fertilization is external.
6. The first crocodiles were land animals.
7. In the gastrointestinal tract, all proteins are completely digested.
8. With hard physical work, the body temperature can rise to 39 degrees.
9. Succession after deforestation is an example of secondary succession.
10. Gene drift can play the role of an evolutionary factor only in very small populations.
11. All hereditary diseases are associated with mutations in the chromosomes.
12. The largest molecules in living cells are DNA molecules.
13. In prokaryotes, translation and transcription processes occur simultaneously and in the same place.
14. Live birth is a characteristic feature of all mammals.
15. Genetic information in all living organisms is stored in DNA.
16. By the structure of the skull, you can determine whether the snake was venomous or not.
17. During the dormant period, the processes of vital activity in the seeds stop.
18. Pea antennae and cucumber antennae are similar organs.
19. The gallbladder does not belong to the glands, as it does not secrete enzymes.
20. The flagellum is an essential component of the bacterial cell.
21. Mossy are a dead-end branch of evolution.
22. All hormones are derived from amino acids, peptides or proteins.
23. The squirt of cartilaginous fish is the remnant of one of the gill slits.
24. Asexual reproduction of chlamydomonas occurs when unfavorable conditions occur.
25. The brain in vertebrates arises from the same layer of the embryo as the epidermis.

PartIV. You are offered test items that require matching between the contents of 1 and 2 columns. The maximum number of points you can score is 12.5. Fill in the task matrices in accordance with the requirements of the tasks.

1. Establish a correspondence between the structure and functions of the cell and the organelles for which they are characteristic (maximum - 2.5 points)

2. Establish a correspondence between the types of organisms and the directions of evolution along which their development is currently taking place (maximum - 2.5 points).

3. Establish a correspondence between the types of ecological relationships between organisms and organisms, reflecting these relationships (maximum - 2.5 points).

4. Establish the sequence (1-5) in which the DNA reduplication process takes place (maximum - 2.5 points)

A. Unwinding the spiral of the molecule.

B. The effect of enzymes on the molecule.

B. Separation of one strand from another part of the DNA molecule.

D. Attachment of complementary nucleotides to each DNA strand.

E. Formation of two DNA molecules from one.

5. Establish a correspondence between an organic compound (A – D) and the function it performs (1–5) (maximum - 2.5 points)

1. Component of the cell wall of fungi. A. Starch.

2. Component of the plant cell wall. B. Glycogen.

3. Component of the bacterial cell wall. B. Cellulose.

4. Reserve polysaccharide of plants. G. Murein.

5. Reserve mushroom polysaccharide. D. Khitin.

Tasks for the school stage of the All-Russian Olympiad for schoolchildren in biology 2010-2011y.

Grade 11

PartI. You are offered test tasks that require you to choose only one answer out of four possible. The maximum number of points that can be collected is 30 (1 point for each test task). The index of the answer, which you consider the most complete and correct, indicate in the matrix of answers.

In favorable spore conditions, bacteria:
a) divides, forming 3 - 6 new disputes;
b) merges with another dispute with subsequent division;
c) dies;
d) grows into a new bacterial cell. +

There are no membranous nuclei in algae cells:
a) green;
b) red;
c) brown;
d) blue-green. +

Most of the cells in the embryo sac of flowering plants have:
a) haploid set of chromosomes; +
b) diploid set of chromosomes;
c) triploid set of chromosomes;
d) tetraploid set of chromosomes.

A person consumes cauliflower organ (s):
a) a modified apical kidney;
b) thickened turnip stem;
c) a modified inflorescence ; +
d) lateral modified kidneys.

Root cones are very thickened:
a) adventitious roots; +
b) root hairs;
c) main roots;
d) air tubers.

The tsetse fly is a carrier of trypanosomes that cause in humans:
a) sleeping sickness; +
b) eastern ulcer;
c) malaria;
d) coccidiosis.

The development of larvae from eggs laid by roundworms occurs:
a) at a temperature of 37 ° C, high concentration of CO 2, for two weeks;
b) at a temperature of 20-30 o C, a high concentration of CO 2, within two weeks;
c) at a temperature of 37 ° C, high concentration of O 2, within a week;
d) at a temperature of 20-30 o C, high concentration of O 2, for two weeks. +

Unlike roundworms, annelids have developed:
a) the digestive system;
b) the excretory system;
c) circulatory system; +
d) the nervous system.

The worker bees are:
a) females who laid eggs and started caring for their offspring;
b) females whose sex glands are not developed; +
c) young females capable of laying eggs in a year;
d) males that have developed from unfertilized eggs.

The complication of the circulatory system corresponds to the evolution of chordates among the following animals:
a) toad - rabbit - crocodile - shark;
b) shark - frog - crocodile - rabbit; +
c) shark - crocodile - frog - rabbit;
d) crocodile - shark - toad - dog.

Cellulose that has entered the human gastrointestinal tract:
a) is not cleaved due to the absence of a specific enzyme;
b) is partially broken down by bacteria in the large intestine ; +
c) it is cleaved by salivary α-amylase;
d) is cleaved by pancreatic α-amylase.

What is the reaction of the environment in the duodenum:
a) slightly acidic;
b) neutral;
c) slightly alkaline; +
d) alkaline.

Viral diseases do not include:
a) measles;
b) tick-borne encephalitis;
c) rubella;
d) diphtheria. +

The food chain is:
a) the sequence of organisms in a natural community, each element of which is food for the next; +
b) the sequential passage of food through various sections of the digestive tract;
c) dependence of plants on herbivores, and their, in turn, on predators;
d) the totality of all food connections in the ecosystem.

Continuous human intervention is required for existence:
a) freshwater ecosystems;
b) natural ecosystems of the land;
c) ecosystems of the World Ocean;
d) agrocenoses. +

Under natural conditions, the natural carriers of the plague pathogen are:
a) birds;
b) rodents; +
c) ungulates;
d) a person.

In the vast forests of the North, so-called concentrated felling using heavy equipment is often carried out, which leads to:
a) to the replacement of forest ecosystems with swamp ones; +
b) to desertification or complete destruction of ecosystems;
c) to an increase in the share of tree species that are more valuable from the point of view of the economy;
d) to the process of converting organic residues in the soil into humus.

Two breeds of dogs, for example, lapdog and German shepherd, are animals:
a) one type, but with different external characteristics; +
b) two species, one genus and one family;
c) two species, two genera, but one family;
d) one species, but living in different environmental conditions.

The first terrestrial vertebrates evolved from fish:
a) ray-finned;
b) cross-finned; +
c) whole-headed;
d) lungs.

The body contours of a flying squirrel, a marsupial flying squirrel, and a woolly wing are very similar. This is a consequence:
a) divergences;
b) convergence; +
c) parallelism;
d) random coincidence.

The number of chromosomes during sexual reproduction in each generation would double if the process did not form during evolution:
a) mitosis;
b) meiosis; +
c) fertilization;
d) pollination.

With parthenogenesis, the body develops from:
a) zygotes;
b) a vegetative cell;
c) somatic cells;
d) unfertilized egg . +

A molecule serves as a matrix for translation:
a) tRNA;
b) DNA;
c) rRNA;
d) mRNA. +

Circular DNA is characteristic of:
a) mushroom kernels;
b) bacterial cells; +
c) animal nuclei;
d) plant nuclei.

Magnesium ions are part of:
a) vacuoles;
b) amino acids;
c) chlorophyll; +
d) cytoplasm.

In the process of photosynthesis, the source of oxygen (by-product) is:
a) ATP
b) glucose;
c) water; +
d) carbon dioxide.

Of the plant cell components, the tobacco mosaic virus infects:
a) mitochondria;
b) chloroplasts; +
c) the core;
d) vacuoles.

In chloroplasts of plant cells, light-harvesting complexes are located
a) on the outer membrane;
b) on the inner membrane;
c) on the thylakoid membrane; +
d) in the stroma.

In second generation marriages between Caucasian and Negroid people, there are usually no people with white skin color. It's connected with:
a) incomplete dominance of the skin pigmentation gene;
b) polymerization of skin pigmentation genes; +
c) epigenomic heredity;
d) non-chromosomal heredity.

PartII. You are offered test items with one answer out of four possible, but requiring multiple prior choice. Indicate the index of the answer that you consider the most complete and correct in the matrix of answers. The maximum number of points that can be scored is 20 (2 points for each test task).

Bacteria cause disease:
I... relapsing fever. +
II... typhus. +
III... malaria.
IV... tularemia. +
V... hepatitis.
a) II, IV;
b) I, IV, V;
c) I, II, IV; +
d) II, III, IV, V.

Roots can perform functions:
I... kidney formation. +
II... leaf formation.
III... vegetative propagation. +
IV... absorption of water and minerals. +
V... synthesis of hormones, amino acids and alkaloids. +
a) II, III, IV;
b) I, II, IV, V;
c) I, III, IV, V; +
d) I, II, III, IV.

If you cut off (trim) the tip of the main root:
I... the root will die.
II... the whole plant will die.
III... the root will stop growing in length. +
IV... the plant will survive but be weak.
V... lateral and adventitious roots will begin to grow. +
a) III, IV, V;
b) III, V; +
c) I, IV, V;
d) II, IV, V.

Among arachnids, development with metamorphosis is characteristic of:
I... spiders.
II... ticks. +
III... solpug.
IV... haymakers.
V... scorpions.
a) II; +
b) II, III;
c) I, IV;
d) I, II, III, V.

Chorda persists throughout life:
I... perch.
II... sturgeon. +
III... sharks.
IV... lampreys. +
V... lancelet. +
a) I, II, III, IV;
b) III, IV, V;
c) II, III, V;
d) II, IV, V. +

Spawns only once in a lifetime:
I... stellate sturgeon.
II... sardine.
III... pink salmon. +
IV... rudd.
V... river eel. +
a) II, III, V;
b) III, V; +
c) I, III, V;
d) I, II, III, V.

In the renal glomerulus, the following are normally practically not filtered:
I... water.
II... glucose.
III... urea.
IV... hemoglobin. +
V... plasma albumin. +
a) I, II, III;
b) I, III, IV, V;
c) II, IV, V;
d) IV, V. +

Each population is characterized by:
I... density. +
II... number. +
III... degree of isolation.
IV... independent evolutionary destiny.
V... the nature of the spatial distribution. +
a) I, II, V; +
b) I, IV, V;
c) II, V;
d) II, III, IV.

Predators, usually ambush predators, include:
I... Wolf.
II... Lynx. +
III... jaguar. +
IV... cheetah.
V... bear. +
a) II, III, IV, V;
b) I, IV;
c) I, II, III, V;
d) II, III, V. +

Of these animals, the tundra biocenosis includes:
I... squirrel.
II... ferret.
III... arctic fox. +
IV... lemming. +
V... green toad.
a) I, II, III, IV;
b) II, III, IV, V;
c) III, IV; +
d) III, IV, V.

Part 3.You are offered test tasks in the form of judgments, with each of which you must either agree or reject. In the matrix of answers, indicate the answer option "yes" or "no".Maximum points you can score25 (1 point for each test task).

Liver mosses are lower plants.

Gametes in mosses are formed as a result of meiosis.

Starch grains are leukoplasts with starch accumulated in them. +

After fertilization, the ovules turn into seeds, and the ovary into a fruit.

In all invertebrates, fertilization is external.

The hemolymph of insects performs the same functions as the blood of vertebrates.

All representatives of the order of reptiles have a three-chambered heart.

Domestic animals tend to have larger brains than their wild ancestors.

The first crocodiles were land reptiles. +

Live birth is a characteristic feature of all mammals.

Unlike most mammals, humans are characterized by the presence of seven cervical vertebrae and two occipital condyles.

In the human gastrointestinal tract, all proteins are completely digested.

Hypervitaminosis is known only for fat-soluble vitamins. +

The human brain uses about twice as much energy per gram of weight as that of a rat.

With hard physical work, the body temperature can rise to 39 degrees. +

Viral infections are usually fought with antibiotics.

Nutrient cycling can be studied by introducing radioactive markers into natural or artificial ecosystems. +

Succulents easily tolerate dehydration.

Succession after deforestation is an example of secondary succession. +

Gene drift can play the role of an evolutionary factor only in very small populations. +

Genetic information in all living organisms is stored in the form of DNA.

One codon corresponds to each amino acid.

In prokaryotes, translation and transcription processes occur simultaneously and in the same place. +

The largest molecules in living cells are DNA molecules. +

All hereditary diseases are associated with mutations in the chromosomes.

Part 4.You are offered test tasks that require matching. Fill in the answer matrices according to the requirements of the assignments.The maximum number of points that can be collected is 10 (by2,5 scoreafor each test task).

Establish in what sequence (1 - 5) the process of DNA reduplication takes place.

Establish a correspondence between an organic compound (A - D) and the function it performs (1 - 5).

3. Establish a correspondence between the classes of gastropods and bivalve molluscs.

4. Establish a correspondence between the families Rosaceae and Moths.

Matrix of answers to the Olympiads for schoolchildren in biology.
2010/2011 account year. Grade 11

Exercise 1. [ 3 0 points]

Task 2. [ 2 0 points]

Task 3.

Task 4. [ 10 points]

Sequence
Processes

3.

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 solid, but it is followed by a long 12-segment one, like in Gigantostraca, the abdomen, which is 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 mites. 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. Representatives of some orders (scorpions, false scorpions) have pedipalps turned into powerful long pincers, while 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.

Spider spider warts 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 look like legs.

Veils 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 Chelitzerovs to become a real land group and populate the most arid 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 intestine 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" opens into the anterior colon. 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 middle intestine to the bases of the limbs; similar protrusions are found in ticks, haymakers and other arachnids. In the abdominal part of the middle intestine, 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 a mesodermal nature, lying in two (less often in one) segments of the cephalothorax. They are well developed in embryos even 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 shows a pronounced 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 chelicerae, of the acron appendages - 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 ganglion mass in the cephalothorax on the ventral side, giving nerves to the 2nd-6th 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.

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 between females and produce a "love dance" characteristic of the mating period.

Respiratory system Arachnids are diverse. In some, these are the pulmonary sacs, in others - the trachea, in others, 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 (solpugi, 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 breathing 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, therefore, corresponds 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 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.

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 part 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 retain their isolation 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 merge together at the anterior end of the abdomen 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 seminal receptacles.

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 advanced forms, by copulation. The spermatophore is a sac secreted by the male, which contains a portion of the 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 more segments than in adult animals. So, in the embryos of spiders, the abdomen consists of 12 segments, similar to adult crustaceans and scorpions, and on the 4-5 front ones there are rudiments of legs. 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

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