The characteristic features of the structure of arachnids are due to adaptation to life on land. Their body most often consists of two sections - the cephalothorax and abdomen. Both departments are segmented in some species, fused in others. The structure and distribution of the limbs is characteristic. Antennae not developed. The front pair of limbs of the cephalothorax is located in front of the mouth and is called chelicerae. Usually these are powerful hooks used to capture and kill prey. The second pair of limbs are the mandibles, or pedipalps. In some species, they perform the function of oral limbs, in others they serve as locomotor organs. There are always 4 pairs of walking legs on the thoracic part of the cephalothorax. The abdomen often bears various paired appendages (arachnoid warts, organs of the external genital apparatus, etc.), which are considered as strongly altered limbs. There are no real limbs on the abdomen, they are reduced.
Arachnids are the first terrestrial animals that mastered land in the Silurian period and switched to air breathing. They lead a day or night lifestyle. They live in forests, meadows, pastures, in the sands of the desert. Some weave trapping nets, others attack prey. They feed on insects, but karakurts, scorpions and tarantulas bite humans, domestic animals (camels, horses), causing painful phenomena, sometimes fatal. Of particular danger are ticks - carriers of diseases from wild animals to humans and domestic animals (tularemia, plague, encephalitis). Scabies mites cause scabies in humans and mammals. To combat ticks, there are only chemical means, while biological ones are practically not developed. |
In connection with the terrestrial way of life, arachnids developed organs of atmospheric respiration. They are represented by either foliated lungs, or tracheae, or a combination of lungs and tracheas. Lungs in the amount of one or two pairs are located under the ventral covers of the abdomen. Each of them opens outwards with a slit-like opening, and inside it is blocked by plates in which blood circulates. Here it is saturated with oxygen and delivers it to the tissues.
The trachea is a system of branching air tubes. They begin with respiratory openings, or spiracles, leading to the main tracheal trunks. The latter branch and form ever smaller tubes through which air reaches the tissues. Thus, during tracheal breathing, oxygen is delivered to the tissues, bypassing the circulatory system. The circulatory system is better developed in species with pulmonary respiration. The heart is located in the dorsal part of the cephalothorax and is equipped with valves.
The excretory organs in some cases are represented by modified nephridia, opening at the base of the 1st-3rd pair of walking legs (coxal glands). They consist of a coelomic sac and a convoluted tubule, sometimes expanding and forming the bladder. More common is a special type of excretory organs - the so-called Malpighian vessels. In arachnids, this is one or more pairs of thin tubes located in the body cavity and opening into the intestine. The products of excretion enter them by osmosis and are excreted into the hindgut.
The nervous system, like that of all arthropods, consists of the brain (supraoesophageal ganglion), peripharyngeal ring and ventral nerve chain, the nodes of which often merge with each other. So, for example, in scorpions, all the ganglia of the thoracic segments are fused into one large knot, followed by a chain of 7 abdominal ganglia. In spiders, all the ganglia of the chain are merged into a single knot.
The eyes are simple, they can be from 2 to 12. Sensitive hairs on the limbs and the surface of the body perceive mechanical and tactile irritations. Small crevices in the cuticle contain chemical receptors.
Most arachnids lead a predatory lifestyle. A number of features of their structure are associated with this, in particular, the presence of poisonous glands (their secret kills prey), extraintestinal digestion (the secrets of special "salivary" glands and the liver are introduced into the body of the killed prey, quickly break down its proteins, which take the form of a liquid slurry), powerful muscles pharynx, acting as a pump that draws in semi-liquid food.
Poisonous glands in spiders open at the top of the pointed upper jaws, in scorpions - on the pointed last segment of the abdomen. Spider glands are especially developed in spiders. They are located on the underside of the abdomen in three pairs of arachnoid warts. The arachnoid apparatus of cross-spiders is especially complex (they distinguish six types of arachnoid glands that secrete the finest threads of various types of cobwebs - dry, wet, sticky, etc.). Spiders use the web to make trapping nets, a house, an egg cocoon, etc.
Arachnids have separate sexes. Sexual dimorphism is very pronounced. The male is usually much smaller than the female.
Class overview
Several orders belong to the class of arachnids. The most important of them: scorpions, saltpugs, spiders, ticks.
Order Scorpionida (scorpions)
Scorpions are medium-sized animals, usually 5-10 cm, some up to 20 cm. Three parts of the body - protosome (undivided cephalothorax), mesosome (wide anterior abdomen) and metasoma (narrow tail-like posterior abdomen) - are well expressed. The cephalothoracic shield is entire, it has a pair of larger median eyes and up to 5 pairs of small lateral ones. The abdomen adjoins the cephalothorax with a wide base, the pregenital (7th) segment is atrophied. The anterior part of the abdomen (mesosoma) is wider, its segments have isolated tergites and sternites; modified abdominal limbs are represented by a complete set: genital opercula on the eighth segment, ridge-like organs on the ninth, lung sacs on the tenth - thirteenth. The segments of the posterior section (metasoma) are narrow cylindrical; the tergite and sternite of each segment are fused into a single sclerite ring; the first metasomal segment is conical. The metasoma ends with a swollen caudal segment; a poisonous gland is placed in it, the duct of which opens at the end of a curved sharp sting. The scutes of the trunk and segments of the extremities are formed by a very hard cuticle, often with a ribbed or tuberculate sculpture.
In appearance, the most characteristic are large pedipalps with claws and a jointed flexible metasoma ("tail") with a poisonous apparatus at the end. The chelicerae are short and end in small claws. The coxae of the pedipalps and the two front pairs of legs have chewing processes directed towards the mouth. Walking legs 4 pairs. Respiration is carried out by leafy lungs.
Scorpions live in countries with a warm or hot climate, and are found in a wide variety of habitats, from humid forests and littoral sea coasts to barren rocky areas and sandy deserts. Some species are found in the mountains at an altitude of 3-4 thousand meters above sea level.
It is customary to distinguish between hygrophilous scorpion species living in humid areas and xerophilic scorpion species found in dry areas. But this division is largely arbitrary, since they are all active at night, and during the day they hide in shelters, under stones, under loose bark, in the burrows of other animals, or burrow into the soil, so that even in dry areas they find places where the air is sufficiently humid. . Differences in relation to temperature are more distinct. Most species are heat-loving, but some, living high in the mountains, as well as at the northern and southern borders of the scorpion range, tolerate cold winters well when inactive. Some species are found in caves, but they are random aliens here. Scorpions are frequent visitors to a person's home, but there are no real roommates of a person (synanthropes) among them.
The scorpion comes out hunting at night and is especially active in hot weather. It walks slowly with its "tail" raised, with half-bent pedipalps forward with slightly open claws. He moves by feeling, the main role is played by protruding tactile hairs (trichobothria) of the pedipalps. The scorpion is very sensitive to touching a moving object and either grabs it if it is a suitable prey, or retreats, assuming a threatening posture: it abruptly bends the “tail” over the cephalothorax and swings it from side to side. The prey is seized by the claws of the pedipalps and brought to the chelicerae. If it is small, then it is immediately kneaded by chelicerae and the contents are absorbed. If the prey resists, the scorpion stings it one or more times, immobilizing and killing with poison. Scorpions feed on live prey, hunting objects are very diverse: spiders, haymakers, centipedes, various insects and their larvae, cases of eating small lizards and even mice are known. Scorpions can starve for a very long time, they can be kept without food for several months, there are cases of starvation up to a year and a half. Most species probably go their entire lives without water, but some tropical rainforest dwellers drink water. When kept together in small cages, a scorpion often eats a fellow.
The breeding biology of scorpions is peculiar. Mating is preceded by a "nuptial walk". The male and the female grapple with claws and, raising their "tails" vertically, walk together for many hours and even days. Usually the male, backing away, entails a more passive female. Then copulation takes place. At the same time, individuals hide in some kind of shelter, which the male, without releasing the female, quickly clears with the help of his legs and "tail". Fertilization is spermatophoric. Individuals touch the ventral sides of the anterior abdomen, and the male introduces sperm bags into the female genital tract, and then secretes a special secret, which seals the female's genital opening. It is believed that when mating, scallops, the modified limbs of the ninth segment, play some role. They are equipped with numerous sense organs. At rest, the scallops are pressed to the abdomen; when mating, they protrude and oscillate. But they also bulge when the scorpion moves, and they are also credited with the role of organs of balance and some other functions.
Scorpions are mostly viviparous, some species lay eggs in which the embryos are already developed, so that juveniles soon hatch. This phenomenon is called ovoviviparity. The development of embryos in the mother's body is long; from a few months to a year or more. In some species, the eggs are rich in yolk and the embryos develop in the egg membranes, in others there is almost no yolk and the embryos soon emerge into the lumen of the ovary. As they grow, numerous swellings of the ovary are formed, in which the embryos are placed. They feed on the secretions of special glandular appendages of the ovary. Embryos can be from 5-6 to several dozen, less often about a hundred. Baby scorpions are born wrapped in an embryonic membrane that sheds shortly after. They climb onto the mother's body and usually stay on it for 7-10 days. Scorpions of the first age do not actively feed, they are whitish, with a smooth cover and sparse hairs, the paws are devoid of claws and have suction cups at the end. Remaining on the body of the female, they molt, and after a while they leave the mother and begin to search for food on their own. After molting, the integuments harden and stain, claws appear on the paws. A scorpion becomes an adult in a year and a half, after birth, making 7 lines during this time. Life expectancy has not been precisely established, but it is usually at least several years. There are interesting cases of anomalies that occur in the embryonic development of scorpions, for example, doubling the "tail", and individuals: viable and grow to an adult state ("two-tailed scorpion" is mentioned by the already famous Roman scientist Pliny the Elder in his "Natural History", I century AD . e.).
Hard covers and a poisonous apparatus do not always save scorpions from enemies. Large predatory centipedes, salpugs, some spiders, praying mantises, lizards, and birds cope with them. There are species of monkeys that feast on scorpions, carefully removing the "tail". But the worst enemy of scorpions is man. Since ancient times, the scorpion has been the subject of disgust and mystical horror, and, perhaps, there is no other arthropod that would give rise to so many tales and legends. Scorpio appears both in the ancient myths of the Egyptians and Greeks, and in the prescriptions of medieval alchemists as a magical attribute of "transformation" - lead into gold, and in astrology, since the name of the scorpion is one of the zodiac constellations, and among Christians as a typical component of the "fauna" of the underworld. Curious are the assurances that scorpions can end their lives with "suicide": if you surround a scorpion with burning coals, then in order to avoid a painful death, it seems to kill itself with a sting. This opinion is untrue, but has a well-known basis. The fact is that the scorpion, like some other arthropods, under the influence of strong stimuli, can fall into a motionless state - a phenomenon of imaginary death (catalepsy, or thanatosis). Being surrounded by burning coals, the scorpion, of course, rushes about in search of a way out, assumes a threatening posture, waves its “tail”, and then suddenly becomes motionless. This picture is taken for "suicide". But after some time, such a scorpion "comes to life", unless it is baked from the heat.
Equally unreasonable is the rather widespread belief that a scorpion specifically seeks out a sleeping person at night to sting him. Where there are many scorpions, on hot nights, making their hunting walks, they often visit dwellings and can even climb onto the bed. If a sleeping person crushes a scorpion or touches it, then the scorpion can strike with its "tail", but, of course, there are no special searches for a person here.
A scorpion sting is a means of attack and defense. On small invertebrates, which usually serve as food for a scorpion, the poison acts almost instantly: the animal immediately stops moving. But larger centipedes and insects do not die immediately and live for a day or two after the injection; there are also insects that, apparently, are generally insensitive to the venom of scorpions. For small mammals, scorpion venom is mostly fatal. The poisonousness of different types of scorpions is very different. For a person, a scorpion sting is usually not fatal, but a number of cases are known with very serious consequences. When injected, pain appears, followed by swelling of the stung area. In severe poisoning, the tumor can take on a phlegmonous character. After the injection, general symptoms appear: weakness, drowsiness, convulsions, accelerated shallow breathing, pulse up to 140 per minute, chills, and sometimes a temperature reaction. Usually after a day or two these phenomena pass, but they can be delayed. Children are more susceptible to scorpion venom. Isolated cases of death have been described.
With scorpion injections, urgent measures must be taken. E. N. Pavlovsky recommends the immediate removal of the poison by suction and cauterization. The patient should be urgently taken to the hospital. The poison is destroyed by injecting a solution of potassium permanganate (1:1000) or bleach (1:60).
Most cases of scorpion stings are observed in Central Asia and Transcaucasia, where scorpions are common and numerous. About 700 species of scorpions are known, belonging to approximately 70 genera and 6 families.
Detachment Solpugida (solpugs, or phalanxes)
Their body is dissected more than that of scorpions: not only the abdomen, but also the cephalothorax is partially segmented. Chelicerae are adapted for grasping and killing prey. Pedipalps have the appearance of walking legs, as a result of which solpugs give the impression of ten-legged animals. Breathe through trachea.
Common in warm countries. Within our country, they are found in the Crimea, the Caucasus, Kazakhstan and Central Asia. Predators. When attacking a person, the salpuga bites through his skin and mechanically infects the wound with contaminated chelicerae. When bitten, acute pain is felt, the bitten place becomes inflamed and swollen. However, attempts to find poisonous glands ended in failure. The consequences of a bite are caused by the introduction of an infection.
Order Araneida (spiders)
The body consists of an undivided cephalothorax and an undivided abdomen. The cephalothorax is separated from the abdomen by a deep constriction. Chelicera claw-like; they open the duct of the poisonous gland. Pedipalps act as mouth limbs. Spiders breathe with lungs, and some species breathe with lungs and tracheae.
The order of spiders includes more than 15,000 species. Distributed almost everywhere. Spiders are predators. They feed on insects that they catch in their nets. Large tropical spider - tarantula - attacks birds. Most species are useful, as they exterminate insects. There are spiders whose bite is dangerous to humans.
Karakurt (Lathrodectus tredecimguttatus)- a small spider. The size of the female is 10-12 mm, the male is 3-4 mm. It has a velvety black body, decorated with reddish spots. It lives in the south of the Asian and European parts of the USSR in clay-solonetz and clay-sand steppes, as well as in wastelands, virgin lands and arable fields. The female builds a net on the ground among the stones. It feeds on insects, spiders, scorpions, etc. The poison of the karakurt is highly toxic. Horses, cows and camels often die from its bites. Sheep and pigs are immune to karakurt poison.
In humans, the bite of this spider causes severe intoxication. The bitten feels a burning pain that spreads from the injection site and covers the whole body in an hour. There is no swelling at the site of the bite. The patient is restless, feels a sense of fear, dizziness, headache. Cold sweat breaks out on the face. The skin is cold, bluish in color. Later, vomiting, trembling, bone pain appear. The patient tosses about in bed, at times falls into a state of stupor. Recovery comes slowly, in 2-3 weeks. Weakness remains for 1-2 months. In severe poisoning, death occurs within 1-2 days.
Order Acarina (ticks)
Includes small, sometimes even microscopic (from 0.1 to 10 mm) arachnids, usually with an undivided and unsegmented body; cephalothorax fused with abdomen; less often the abdomen is dissected. Chitin is leathery, easily extensible, but some parts of it are compacted (shields). The shape and nature of the location of the shields is important for taxonomy.
All ticks have six pairs of limbs. Two pairs (chelicerae and pedipalps) are transformed into piercing-sucking or gnawing-sucking mouthparts designed to pierce the host's skin and feed it with blood. The remaining four pairs (walking legs) consist of several segments (6-7), the first of which (basic, coxa or coxa) is fused to the body.
The digestive system of bloodsucking forms is highly branched, especially in females. The alimentary canal is characterized by the presence of blind outgrowths; they serve as a reservoir for ingested food. Excretory organs - Malpighian vessels. Respiratory organs - trachea. There is one pair of stigmata located either at the base of the chelicerae or at the base of the legs. The stigmas are located on a small shield (peritrema).
The nervous system is characterized by the fusion of all the ganglia of the nerve chain and the brain into a common mass. The sense organs are represented mainly by the organs of touch and smell. The eyes may be missing.
Ticks are dioecious. The genital opening is located between the bases of one or another pair of legs. Females are larger than males. A six-legged larva emerges from the fertilized eggs laid by the female. She molts and turns into an eight-legged nymph. Unlike the adult tick, the nymph has an underdeveloped reproductive apparatus; there is usually no external genital opening. There may be several nymphal stages. At the last molt, the nymph turns into a sexually mature form - an imago.
Life cycle. Development, unlike other arachnids, occurs with metamorphosis, including egg, larva, nymph and adult (sexually mature form). The larva has three pairs of legs and breathes through the surface of the body. After molting, she turns into a nymph. The nymph has four pairs of legs, breathes with the help of trachea (stigmas appear), but does not have a genital opening. There may be several nymphal stages. The nymph after molting turns into an imago. Most mites of medical importance are blood-sucking. Animals - hosts of ticks are mammals, birds and reptiles.
There are one-, two- and three-host ticks. In single-hosts, all stages of development pass on the same host. With a two-host type of development, the larva and nymph feed on one host, and the imaginal form on the other. In three-host ticks (taiga tick), each stage is looking for a new host. In the latter case, development can be extended over a long period, for example, in the taiga tick up to 5 years.
Together with the blood of the host, pathogens of various diseases penetrate into the body of the flare, which, when switching to another host, can be transmitted to it, which contributes to the circulation of pathogens. The life span of ticks is quite long - from 6 months to 20-25 years.
From the point of view of medicine, ticks of the Ixodes and Argas families, as well as the scabies mite of the Acariform family, are of the greatest importance from the point of view of medicine.
Ixodid ticks (Ixodidae)
They are of interest as a natural reservoir and carriers of a number of serious diseases: tick-borne encephalitis, tick-borne typhus, tularemia, hemorrhagic fevers, etc.They have large sizes of 4-5 mm. Females sucking blood reach 10 mm or more. The male has a shield on its back that covers the entire dorsal surface. In females, nymphs, and larvae, the scutellum occupies only the anterior part of the body; on the rest of the surface, the chitin is thin and easily extensible. This is important, since the female absorbs a large amount of blood during feeding, 200-400 times her mass in a hungry state. The oral apparatus is located terminally at the anterior end of the body. It consists of a massive base of pedipalps, on which four-segmented palps are located on the sides and a proboscis in the middle. Its lower part is the hypostome - an outgrowth of the base. The posterior side of the hypostome is equipped with sharp teeth directed backwards. On top of the hypostome are cases containing two-segmented chelicerae. The terminal segment of the chelicera bears large, sharp teeth and is movably connected to the previous one. When the tick pierces the skin of the victim and spreads the mobile segments of the chelicera to the sides, it is impossible to remove its oral apparatus from the skin. After saturation, the tick reduces the chelicerae and releases the oral apparatus.
The eggs are laid in the soil. In the process of development, a larva, one generation of nymphs and an imaginal form are formed. The change of stages occurs only after bloodsucking. Among ixodid ticks there are one-, two- and three-host ticks. Larval stages usually feed on small vertebrates (rodents, insectivores), adult forms - on large animals (cattle, deer) and humans. Having drunk blood, the females lay eggs, after which they die.
The main direction of prevention is protection from bites (special clothing, repellents).
Argas mites (Argasidae)
carriers of pathogens of some vector-borne diseases in humans and animals. Species of the genus Ornithodorus are of the greatest importance.Ornithodorus tick (Ornithodorus papillipes) - a settlement tick - a blood-sucking tick, a carrier of pathogens of tick-borne relapsing fever (tick-borne recurrence). The body is dark gray, up to 8.5 mm long. Unlike Ixodes, they do not have shields. The lateral edges in the middle part of the body are almost parallel to each other, the presence of a marginal welt is characteristic. The chitinous cover of hungry ticks lies in folds. The totality of the oral organs and the integument adjacent to them forms the so-called "head". It is relatively small, located in the anterior part of the body on the ventral side and is not visible from the dorsal side. There are no eyes. On the midline of the body, behind the first pair of legs, is the genital opening, and a little behind the middle of the body is the anus.
The ornitodorus tick is common in the south of Kazakhstan, in Central Asia, Iran and India. It lives in natural (caves) or artificial (dwellings) shelters, and each species is associated with a specific type of shelter (rodent burrow, cave with bats, porcupines, etc.). It is found in human dwellings, in stables, pigsties and other outbuildings. It hides like bedbugs in the crevices and cracks of adobe walls. It feeds on blood, attacking humans or animals. Sucking blood lasts 30-40 minutes, after which the tick returns to the cracks in the walls.
In the process of development, males go through the larval stage and 3 nymphal stages, while females have 4 or 5 nymphal stages. Life expectancy is exceptionally long - 20-25 years. In the absence of hosts, the tick is able to live for 10-11 years without food. When covering the cracks with clay, the immured tick remains alive for more than a year.
Body broadly oval, dimensions 0.3-0.4 x 0.2-0.3 mm. A notch runs across the oval body, delimiting the cephalothorax from the abdomen. On the surface of the body there are many short spines and long setae. The legs are greatly shortened, which is associated with an intradermal lifestyle. Two pairs of legs are located on the sides of the mouth apparatus, two are assigned to the posterior end of the body. There are no eyes. Breathing occurs through the surface of the body.
The entire period of development from egg laying to the sexually mature form lasts 9-12 days. An adult tick lives for approximately 1.5 months.
Ticks can affect any area of the skin, but are most often found on the back of the hands, in the interdigital spaces, armpits, and perineum. The passages are visible on the skin in the form of straight or winding lines of a whitish-dirty color.
Prevention. Isolation and treatment of people with scabies; disinsection of clothing and items they used; fight against scabies of farm animals, keeping the body and home clean.
- Class Arachnoidea (arachnids)
Sexually mature males in the way of life and appearance in most species are very different from females. In many species, the males are brightly colored. They are usually smaller, have proportionately more elongated legs, a different arrangement of pedipalps, and also differ from females in much greater mobility. Sexual maturity of males occurs earlier than that of females. The average maturity of males is 1.5 years, in females it occurs no earlier than 2 years (in some species, the difference is even more divergent in time - 1.5 and 3 years, respectively), therefore, in fact, it seems impossible to "closely related" crossing of spiders that emerged from one cocoon, in natural conditions. However, this is possible in captivity when growing males and females by artificially creating for them different temperature and humidity conditions and feeding regimes from an early age.
A mature male before mating weaves the so-called sperm - web, which, as a rule, has a triangular or quadrangular shape, on the lower side of which he releases a drop of sperm. The sperm is captured by the copulatory apparatus, after which the male proceeds to search for the female. At this time, his behavior is directly opposite to that of the previous period of life. He leads a vagrant lifestyle, is highly active and can be seen moving even in the daytime, covering rather significant distances in search of a female (7-9 km per night ( Shillington et al. 1997).
The detection of the female occurs mainly due to touch (vision in no way affects this process: spiders with smeared eyes easily find females) by the odorous trail left by her on the substrate or web at the hole (for example, the female Aphonopelma hentzi at the entrance to the hole weaves a ball from the web). In the first variant, if the female is not ready to mate, she swiftly attacks the male, spreading her chelicerae and preparing to grab him. In this case, the male is forced to hastily retreat, otherwise he may not be perceived as a potential partner, but risks turning into a “hearty dinner”, or losing one or more limbs. Unlike other species of spiders, which are characterized by complex mating behavior, consisting in the performance of peculiar "wedding dances", for example, species of families Araneidae, Salticidae, Lycosidae, or in offering to a female of recently killed prey (in Pisauridae), courtship of tarantulas is relatively simpler.
Having found the female, the male cautiously moves inside the hole. When meeting with a female, two scenarios are possible.
In the second scenario, the female, as a rule, does not initially show any interest in the male. In this case, the male lowers the cephalothorax and raises the abdomen, stretching forward the spaced front legs and pedipalps, backing away in the direction of the exit from the hole, thereby attracting the attention of the female and, as it were, inviting her to follow him. From time to time he stops and moves his front legs and pedipalps now to the right, then to the left, trembling with his whole body so that the female's interest in him does not weaken until they leave the hole and come to the surface. Here, having space for safe movement, he feels more confident.
The male periodically carefully approaches the female, quickly touches her with the tips of the front pair of legs and pedipalps or “drums” on the substrate. He usually repeats this procedure several times with slight interruptions until he is convinced that the behavior of the female does not pose a danger to him, and she will not harm him (to date, studies have not been carried out regarding the presence of features characteristic of the mating behavior of various species tarantulas).
If the female is still passive, the male will slowly approach her, bringing his front paws between her pedipalps and chelicerae, which the female usually pushes apart when ready to mate. Then he, as it were, rests against them with his tibial hooks in order to take a stable position and tilts back her cephalothorax, “stroking” the lower surface of the base of the abdomen.
If the female expresses her readiness to mate (which is also often expressed in frequent "drum" sound emitted by kicking the feet on the substrate), he unfolds the embolus of one of the pedipalps and introduces it into the gonoporelocated in epigastric groove. The male performs the same action with the second pedipalp. This is actually the very moment of copulation, which lasts literally a few seconds, after which the male, as a rule, quickly runs away, since usually the female immediately begins to pursue him. Contrary to popular belief that a female often eats her partner after mating, in most cases this does not happen (in fact, cases of eating females by males are known), if there is enough space for him to retire a considerable distance, and the male is able to after some time to fertilize several more females. Often also a female mates with different males in one season.
fertilization egg-stealing takes place in uterus with which they communicate seminal receptacles, and after a certain period copulation(from 1 to 8 months), the duration of which is directly dependent on various conditions (season, temperature, humidity, food availability) and the specific type of tarantula, the female lays eggs, braiding them in cocoon. This whole process takes place in the living chamber of the burrow, which turns into a nest. The cocoon, as a rule, consists of two parts, fastened by the edges. First, the main part is woven, then the masonry is laid on it, which is then woven with the covering part. Some species ( Avicularia spp., Theraphosa blondi) weave their “protective hairs” into the walls of the cocoon to protect it from possible enemies.
Interestingly, for several species of tarantulas, the facts of laying are known after mating one after another of several (one or two) cocoons with a time difference, as a rule, no more than a month: Hysterocrates spp.., Stromatopelma spp., Holothele spp., Psalmopoeus spp.., Tapinauchenius spp.., Metriopelma spp.., Pterinochilus spp..
(Rick West, 2002, oral communication), Ephebopus murinus and E. cyanognathus
(Alex Huyer, 2002, oral communication), Poecilotheria regalis
(Jan Evenow, 2002, oral communication). At the same time, the percentage of unfertilized eggs increases significantly in repeated clutches. The number of eggs laid by a female varies from species to species and is related to her size, age, and other factors. Record number of eggs known for the species Lasiodora parahybana and is approximately 2500 pieces! On the contrary, in small species it does not exceed 30-60. Incubation periods are also different - from 0.8 to 4 months. Interestingly, arboreal species generally have shorter life spans than terrestrial species (see table).
Unlike most other spiders, the female tarantula guards her clutch and cares for the cocoon, periodically turning it over with the help of chelicerae and pedipalps and moving it depending on changes in humidity and temperature conditions. This is associated with certain difficulties with the artificial incubation of spider eggs at home, which is often advisable, since it is not uncommon for females to eat laid cocoons, both as a result of stress caused by anxiety, and "for unknown reasons." For this purpose, collectors from the USA, Germany, England and Australia have developed an incubator, and some fanciers, taking cocoons from females, take over their “motherly” functions by turning the cocoon by hand several times a day (see also Breeding). №
View
Duration* of incubation
A source of information
1.
Acanthoscurria musculosa
83
Eugeniy Rogov, 2003
2.
Aphonopelma anax
68
John Hoke, 2001
3.
Aphonopelma caniceps
64
McKee 1986
4.
Aphonopelma chalcodes
94
Schultz & Schultz
5.
Aphonopelma hentzi
76
McKee 1986
56
Baerg, 1958
6.
Aphonopelma seemanni
86
McKee 1986
7.
Avicularia avicularia
52
McKee 1986
39, 40,45
Garrick Odell, 2003
51
Stradling, 1994
8.
Avicularia metallica
68
Todd Gearhart, 1996
9.
Avicularia sp. (ex. Peru)
37
Emil Morozov, 1999
59
Denis A. Ivashov, 2005
10.
Avicularia versicolor
29
Thomas Schumm, 2001
46
Mikhail F. Bagaturov, 2004
35
Todd Gearhart, 2001
11.
Brachypelma albopilosum
72
McKee 1986
75, 77
Schultz & Schultz
12.
Brachypelma auratum
76
McKee 1986
13.
Brachypelma emilia
92
Schultz & Schultz
14.
Brachypelma smithi
91
McKee 1986
66
Todd Gearhart, 2001
15.
Brachypelma vagans
69
McKee 1986
71
Todd Gearhart, 2002
16.
Ceratogyrus behuanicus
20
Phil&Tracy, 2001
17.
Ceratogyrus darlingi
38
Thomas Ezendam, 1996
18.
Cyclosternum fasciatum
52
McKee 1986
19.
Chilobrachys fimbriatus
73
V. Sejna, 2004
20.
Encyocratella olivacea
28
V. Kumar, 2004
21.
Eucratoscelus constrictus
25
Rick C. West, 2000
22
Eucratoscelus pachypus
101
Richard C. Gallon, 2003
23.
Eupalaestrus campestratus
49
Todd Gearhart, 1999
24.
Eupalaestrus weijenberghi
76
Costa&Perez-Miles, 2002
25.
Grammostola aureostriata
29
Todd Gearhart, 2000
26.
Grammostola burzaquensis
50-55
Ibarra-Grasso, 1961
27.
Grammostola iheringi
67
McKee 1986
28.
Grammostola rosea
54
McKee 1986
29.
haplopelma lividum
56
Rhys A. Bridgida, 2000
60
John Hoke, 2001
52
Mikhail Bagaturov, 2002
30.
Haplopelma minax
30
John Hoke, 2001
31.
Haplopelma sp. "longipedum"
73
Todd Gearhart, 2002
32
Heterothele villosella
67
Amanda Weigand 2004
33
Heteroscodra maculata
39
Graeme Wright, 2005
34
Holothele Incei
36, 22
Benoit, 2005
35.
Hysterocrates skepticus
40
Todd Gearhart, 1998
36.
Hysterocrates gigas
37, 52
Mike Jope 2000
89
Chris Sainsburry 2002
37.
Lasiodora cristata
62
Dirk Eckardt, 2000
38.
Lasiodora difficilis
68
Todd Gearhart, 2002
39.
Lasiodora parahybana
106
Dirk Eckardt, 2000
85
Eugeniy Rogov, 2002
40.
Megaphobema robustum
51
Dirk Eckardt, 2001
41.
Nhandu coloratovillosus
59
Mikhail Bagaturov, 2004
42.
Oligoxystre argentinense
37-41
Costa&Perez-Miles, 2002
43.
Pachistopelma rufonigrum
36,40
S. Dias & A. Brescovit, 2003
44
Pamphobeteus sp. plateyomma
122
Thomas (Germany), 2005
45.
Phlogiellus inermis
40
John Hoke, 2001
46.
Phlogius crassipes
38
Steve Nunn, 2001
47.
Phlogius stirlingi
44
Steve Nunn, 2001
48
Phormictopus cancerides
40
Gabe Motuz, 2005
49
Phormictopus sp. "platus"
61
V. Vakhrushev, 2005
50.
Plesiopelma longisteriale
49
F.Costa&F.Perez-Miles, 1992
51.
Poecilotheria ornata
66
Todd Gearhart, 2001
52.
Poecilotheria regalis
43
Todd Gearhart, 2002
77
Chris Sainsburry 2005
53.
Psalmopoeus cambridgei
46
Alexey Sergeev, 2001
54.
Psalmopoeus irminia
76
Guy Tansley 2005
55.
Pterinochilus chordatus
23, 38
Mike Jope 2000
56.
Pterinochilus murinus
26, 37
Mike Jope 2000
22, 23, 25
Phil Messenger, 2000
57.
Stromatopelma calceatum
47
Eugeniy Rogov, 2002
58.
Stromatopelma c. griseipes
53
Celerier, 1981
59
Thrigmopoeus truculentus
79, 85, 74
J.-M. Verdez & F. Cleton, 2002
60.
Tapinauchenius plumipes
48
John Hoke, 2001
61.
Theraphosa blondi
66
Todd Gearhart, 1999
62.
Vitalius roseus
56
Dirk Eckardt, 2000
The size of babies born varies widely from 3-5 mm (for example, Cyclosternum spp.. ) up to 1.5 cm in the span of the legs of the goliath tarantula Theraphosa blondi. Newborn spiders of arboreal species, as a rule, are larger than those born in terrestrial tarantulas, and their number is usually noticeably smaller (as a rule, does not exceed 250 pieces). 
Young spiders are very mobile and, at the slightest danger, hide, run away to the nearest shelter or quickly burrow into the soil. This behavior has been noted for both terrestrial and arboreal species.
Hatching of juveniles from eggs of the same clutch occurs more or less at the same time. Before hatching, small spines form at the bases of the pedipalps of the embryo - "egg teeth", with the help of which he breaks the shell of the egg and appears "into the light." Before the so-called postembryonic molting, which usually occurs inside the cocoon, the hatched spider has very thin covers, its appendages are not dissected, it cannot eat and lives off the yolk sac remaining in the intestine. This life stage is called "prelarva"(according to another classification - 1st stage nymph). After the next molt (3-5 weeks), the prelarva passes into the stage "larvae" (nymphs 2nd stage), also not yet feeding, but slightly more mobile and already having primitive claws on the legs and developed chelicerae ( Vachon, 1957). With next ( postembryonic) young spiders are formed by molting, which, becoming more active and able to feed on their own, come out of the cocoon and at first, as a rule, stick together, and then scatter in different directions, starting an independent life. Usually, after the release of juveniles from the cocoon, the mother no longer takes care of her, but an interesting feature of the biology of species of the genus Hysterocrates sp. from the island of Sao Tome, which lies in the fact that young spiders live with the female for up to six months after leaving the cocoon. At the same time, the female shows real concern for her children, not noted by any other member of the tarantula family, actively protecting them from any possible danger and getting food for them. Similar facts are known for Haplopelma schmidti (E. Rybaltovsky), as well as tarantulas Pamphobeteus spp.. (various sources). The biology and lifestyle of young spiders are generally similar to those of adult spiders. They equip shelters for themselves, actively hunt for food objects that are suitable in size. The number of links during life is different, depending on the size of the spider and its gender (for males, their number is always less), within 9 - 15 per life. The overall lifespan of female tarantulas is also very different.
Arboreal, even such large spiders as Poecilotheria spp.. , as well as tarantulas of the genus Pterinochilus live no more than 7 - 14 years. Large terrestrial, and especially American spiders, live in captivity up to 20 years, and according to individual reports, even to a more respectable age (for example, the age of the female Brachypelma emilia who lived at S. A. Shults and M. J. Schultz, was estimated at least 35 years).
The life expectancy of males is significantly less and, in the general case, is limited to 3-3.5 years. The fact is that males, as mentioned above, mature earlier than females (1.5-2.5 years), and, as a rule, the average lifespan of male tarantulas of the last age (after the last molt) is five to six months. However, for individual specimens of a number of species, much longer periods are known. Yes, according to Dr. Claudio Lipari, the life limits of males of the last age of the Brazilian Grammostola pulchra amounted to at least 27 months, and one copy lived with him for more than four years. Other centenarians among last-age male tarantulas reported Luciana Rosa, the following: Grammostola rosea- 18 months, Megaphobema velvetosoma
- 9 months, Poecilotheria formosa- 11 months, Poecilotheria ornata- 13 months Poecilotheria rufilata
- 17 months. According to the Moscow collector Igor Arkhangelsky male of last age Brachypelma vagans lived in captivity 24 months(however, the last few months it was fed artificially), and another individual of the same species lived 20 months. According to a Canadian scientist Rika Vesta adult male tarantula Phormictopus cancerides
lived at Allana McKee, having lost the upper segments of the pedipalps after molting, 27 months, and the male Brachypelma albopilosum
at the very Rika Vesta - 30 months after maturity and died during the second molt (personal communication). The following facts of longevity among male tarantulas have been noted Lasiodora parahybana
: 3 years Jeff Lee, 2 years 6 months Joey Reid and 2 years 3 months Jim Hitchiner. Also the male of the species Grammostola rosea lived 2 years 5 months Jay Staples. It should be true to say that such cases are known only when keeping tarantulas in captivity. Regarding the onset of puberty in tarantulas, there is the following, often conflicting information. Male tarantulas of the genus Avicularia reach sexual maturity by 2.5 years, females - by 3 years ( Stradling 1978, 1994). Baerg (Baerg, 1928, 1958) reports that males Aphonopelma spp.. reach sexual maturity at 10-13 years, females - at 10-12 years. tarantulas Grammostola burzaquensis
become sexually mature at 6 years of age Ibarra Grasso, 1961), Acanthoscurria sternalis
- at 4-6 years old ( Galiano 1984, 1992). The information given by these authors most likely relates to observations in nature. At the same time, it should be taken into account that in captivity, the timing of the onset of puberty of tarantulas is generally reduced, and often quite significantly. In conclusion, I would like to note that tarantulas in captivity actually have no natural enemies. Watch an interesting clip about it. Such kind as Scolopendra gigantea, individual specimens of which reach 40 cm in length, are able to cope with a spider of considerable size. Also members of the genus Ethmostigmus from Australia are known as predators of tarantulas of the local fauna. However, scorpions Isometrus, Liocheles, Lychas, Hemilychas
as probably and some urodacus, are not averse to having a snack with a juvenile tarantula, and scorpions from the genus Isometroides generally known to specialize in eating spiders, and can be found regularly in old burrows belonging to tarantulas ( S. Nunn, 2006). In addition to those listed as natural enemies of tarantulas, large spiders are noted in nature. Lycosidae, and for Australia also a spider Latrodectus hasselti, in the nets of which the remains of adult male tarantulas were regularly found. And, of course, among invertebrates, the main enemy of tarantulas, like other spiders, is ants. Considering the natural enemies of tarantulas, one cannot help but dwell on some vertebrates. Australian arachnologist Stephen Nunn repeatedly observed as the largest frog in Australia Litoria infrafrenata(white-lipped tree frog) caught and ate mature males. Similarly, the American aga toad introduced in Australia ( Bufo marinus), which is one of the natural enemies of therafozid in Central America, eats the latter and in Australia. In this regard, the fact of being in a hole with a female and 180 young tarantulas of the species Selenocosmia sp.. a medium-sized toad-aga, which probably "ate" young tarantulas ( S. Nunn, 2006). The development cycle from egg to adult is 20-21 days on average. These flies, called humpback flies, can be confused with other flies - well known to many fruit flies. However, Drosophila are extremely rare in terrariums of tarantulas and are distinguished by the red color of their eyes. I would also like to note that, in addition to the previously mentioned species of frogs, representatives of a small group of Diptera insects are also found in spider burrows. They lay their eggs directly on the host spider itself or in the soil of its burrow. In this case, the larvae concentrate in the region of the mouth of the tarantula or in the substrate and feed on organic residues. Interestingly, for three South American tarantula species, Theraphosa blondi, Megaphobema robustum
and Pamphobeteus vespertinus
characterized by their specific types of Diptera. In home terrariums, as a rule, there are representatives of two groups of winged insects - humpback flies of the family Phoridae(recently widespread among collectors around the world) and the so-called "pot flies". Gobat flies of the family Phoridae they look more pointed and humpbacked compared to the "potted ones", they fly very rarely - only when they are disturbed, mainly moving along the substrate in characteristic jerks. You can get rid of them by replacing the substrate and disinfecting the terrarium of the tarantula, transplanting it into a new container. Drying the substrate also helps, with the obligatory provision of a container of water for drinking to the tarantula. In general, they are perfectly safe for healthy spiders, but may cause them anxiety. At the same time, these problems, as a rule, do not arise if the terrarium is well ventilated and a ventilation mesh is used, through which the penetration of Diptera is impossible. However, it should be taken into account that the humpback larvae can penetrate into cocoons, which are shed by tarantulas, and eat eggs and developing larvae, as well as develop on weakened and sick individuals. Adults can also be carriers of various diseases, incl. carry nematode eggs. Finally, I note that in terrariums with tarantulas, representatives of invertebrates brought in, usually with a substrate, are occasionally found - springtails and wood lice, which also do not harm them. At the same time, some collectors specially populate terrariums with tarantulas with the culture of tropical woodlice. Trichorhina tomentosa
, because they feed on the waste products of spiders and destroy excess organic residues in the substrate. What do you need to know about tarantulas, what difficulties arise when keeping and handling them, and what conditions need to be created so that they not only feel good at home, but also multiply?
There is a unique case when an amateur Jay Stotsky small arboreal male Poecilotheria regalis successfully molted twice! at the last age, with an interval between molts in 18 months. At the same time, the pedipalps and one chelicera lost during the first molt fully recovered after the second molt!
The only creatures that hunt tarantulas in nature are hawk wasps from the family pompilidae, of which species of genera are well studied pepsis and Hemipepsis(the largest reach 10 cm in length), paralyzing the spider, laying an egg on its abdomen, the hatched larva from which, during its further development, feeds on such a kind of “canned food” ( Dr. F. Punzo, 1999, S. Nunn, 2002, 2006).
In the vast majority of "pot flies" found in the terrariums of tarantulas, are species of mosquitoes of the families Fungivoridae and Sciaridae, and start in the containers of tarantulas with insufficient ventilation due to prolonged waterlogging of the substrate and its subsequent decay, as well as decomposition of food debris and spider feces, as well as plant remains, under high humidity conditions, resulting in the formation of a fungal microculture, which feed on their larvae .
Fans of growing flowers in greenhouses regularly encounter these insects. They are also sometimes found in the potted culture of indoor plants, from which, apparently, they got their name. They are smaller in size, thinner than diptera families. Phoridae, with dark wings and actively fly.
Latin name Arachoidea
General characteristics of arachnids
External structure
As in typical chelicerae, the body of the vast majority of arachnids consists of a fused cephalothorax, bearing six pairs of limbs, and an abdomen. The abdomen, unlike horseshoe crabs, does not carry real limbs. There are only their rudiments or limbs, turned into special organs.
Antennae, or antennules, are absent. The eyes are simple. The first pair of limbs of the cephalothorax is located in front of the mouth. These are short chelicerae, consisting of 2-3 segments, ending in a claw, hook or stylet. Chelicerae are homologous to the second antennae of crustaceans. Behind the mouth is the second pair of limbs - pedipalps. Their bases have chewing processes, and the remaining segments can serve as tentacles. Pedipalps can turn into walking legs or food capture organs - powerful pincers (scorpions, false scorpions). All arachnids are characterized by feeding on liquid food, so the anterior part of the digestive system is a sucking apparatus.
In connection with the emergence on land, arachnids transformed some of the organ systems of the primary aquatic chelicerae and new ones arose. Some groups have both old and newly acquired organs at the same time. So, the respiratory organs in arachnids are the lungs, located in pairs on the abdominal segments. Their origin and development prove that they are modified gill peduncles of aquatic chelicerae. The new respiratory organs of arachnids are tracheas - blind protrusions of the outer integument.
The excretory organs are also dual in nature. They are represented by coxal glands, which are more ancient in origin (coeloducts) and newly emerged Malpighian vessels.
The differences between representatives of the arachnid orders lie in the degree of segmentation of the body, primarily the abdomen, and in the specialization of the cephalothoracic limbs, adapted to perform various functions. The body is most strongly segmented in scorpions. It consists of a small fused cephalothorax and abdomen, represented by 12 segments, of which 6 wider ones make up the anterior abdomen, or mesosome, and the remaining 6 narrower ones make up the posterior abdomen, or metasome. Attention should be paid to the similarity in the dismemberment of the body in scorpions and in extinct gigantic crustacean scorpions. In both, the metasome is represented by six segments. In other groups of arachnids, the posterior part of the abdomen, the metasome, is reduced, and the abdomen is shortened. In terms of the degree of dissection of the abdomen, scorpions are similar to scorpions and pseudoscorpions, in which, however, the abdomen is not externally divided into anterior and posterior belly. Salpugs are in some respects even more dissected animals than scorpions. In addition to the segmented abdomen, which has 10 segments, the salpugs have two free thoracic segments that are not part of the fused head. The segmented abdomen of harvestmen also consists of 10 segments, which are not separated by a deep constriction from the cephalothorax, as in real spiders. In arthropod spiders (four-lungs), the abdomen consists of 11 segments, and in higher spiders it consists of 6, while the abdominal segments completely merge. In ticks, the number of abdominal segments is reduced to 7, and in some - to 4-2. At the same time, in most ticks, not only all segments of the abdomen have merged, but it is also impossible to distinguish the main sections - the cephalothorax and abdomen, which form one whole in them. Thus, it is obvious that the evolution of various orders of arachnids proceeded in the direction of a decrease in the number of abdominal segments and their fusion, a decrease in the degree of general dissection of the body.
In representatives of various orders, the chelicerae and pedipalps underwent the greatest changes, and the four pairs of walking legs remain the least changed, turning into an articulated leg ending in a paw with claws.
In scorpions, false scorpions and harvestmen, chelicerae end in small claws. They play the role of the upper jaws, and, in addition, the animals hold their prey with them. In salpugs, chelicerae have turned into powerful claws adapted to seizing and killing prey. In real spiders, the chelicerae are claw-shaped and consist of two segments. The main segment is very strongly swollen, and the second has a claw-like shape. Near its pointed end, a duct of a poisonous gland opens, located at the base of the chelicera. In a calm state, this segment is applied to the main segment and partially enters a special groove. With two chelicerae, the spiders seize and kill the prey, letting the secret of the poisonous gland into the wound. Finally, in mites, chelicerae and pedipalps form piercing-sucking (dog ticks, etc.) or gnawing-sucking (scabies mites, barn mites, etc.) mouthparts.
The second pair of limbs - pedipalps - in solpugs differ little from walking legs, and in scorpions and false scorpions they turned into grasping organs - claws. In female spiders, pedipalps play the role of jaws, since they have a chewing plate at the base, and at the same time they are oral tentacles. Male spiders have a swelling on the last segment of the pedipalps, which is a device for fertilizing females. During the breeding season, a special pear-shaped appendage with an elongated end develops on this segment, on which there is an opening leading to a narrow canal, ending inside this organ with an expanded ampulla. With the help of this device, male spiders collect sperm inside the ampoule and, when mating, inject it into the female's genital opening.
Abdominal limbs, as such, are absent in all arachnids. However, some of them have survived in a heavily modified form. The rudiments of the abdominal limbs are located only on the mesosome (anterior six segments). The most complete set of them is preserved in scorpions. They have on the first segment of the abdomen, on which the genital opening is located in all arachnids, there are small genital caps, and on the second segment there are special comb-like appendages of unknown purpose. On the next four segments, there are a pair of lung sacs. Four-lung spiders and flagellates have two pairs of lungs on the first two segments of the abdomen; in two-lung spiders, one pair of lungs (on the first segment), and on the second, tracheae develop instead of lungs (they are not connected with the limbs). All spiders on the third and fourth segments develop arachnoid warts - the transformed abdominal limbs of these segments. In some groups of small arachnids (some of the mites), rudiments of the abdominal limbs are preserved on the first three segments, the so-called coxal organs.
Integuments and skin glands
The body of arachnids is covered with a chitinous cuticle, which is secreted by a layer of flat cells of the hypodermis. In most forms, chitin is poorly developed and the covers are so thin that they shrink when dried. Only in some arachnids (scorpions) the chitinous cover is denser, as it contains calcium carbonate.
Skin (hypodermal) formations include various glands: poisonous, arachnoid, odorous glands of harvestmen, frontal and anal glands of flagellates, etc. Not all arachnids are poisonous. Poison glands are present only in scorpions, spiders, parts of pseudoscorpions and some ticks. In scorpions, the posterior abdomen ends in a curved tail needle. At the base of this needle is a pair of saccular glands that secrete a poisonous secret. At the very end of the needle, the openings of the ducts of these glands are placed. Scorpions use this device in a peculiar way. Grasping the prey with pedipalp claws, the scorpion bends the posterior abdomen onto its back and strikes the victim with a needle, from which it releases poison into the wound. In spiders, the venom glands are located at the base of the cholicerae, and their ducts open on the claw of the chelicerae.
Spider glands are present mainly in representatives of the order of spiders. So, in a female cross-spider (Araneus diadematus), up to 1000 spider glands of various structures are placed in the abdomen. Their ducts open with tiny holes at the ends of special chitinous cones, which are located on the spider web warts and partly on the abdomen near them. Most spiders have 3 pairs of arachnoid warts, but only two of them are formed from the ventral legs. In some tropical spiders, they are multi-segmented.
Spider glands are also found in pseudoscorpions and spider mites, but they are located in the chelicerae of the former and in the pedipalps of the latter.
Digestive system
The digestive system consists of three main sections - the anterior, middle and hindgut.
The foregut with its glands is an organ adapted to liquefy and absorb food. In spiders, the mouth leads into the pharynx, followed by a thin esophagus, which flows into a sucking stomach, actuated by muscles extending from it to the dorsal integuments of the cephalothorax. These three sections (pharynx, esophagus, sucking stomach) are parts of the anterior ectodermic gut and are lined from the inside with chitin. The ducts of the salivary glands open into the pharynx, secreting a secret that dissolves proteins. Having pierced the covers of prey, the spider lets saliva into the wound, which dissolves the tissues of the victim, and then sucks out semi-liquid food. From the sucking stomach begins the endodermic midgut, in which the digestion and absorption of food takes place.
The middle intestine, located in the cephalothorax, forms five pairs of blind glandular outgrowths, going forward to the head end and the bases of the walking legs. Blind outgrowths of the midgut are very characteristic of many arachnids: ticks, harvestmen, etc. They increase the capacity of the intestine and its suction capacity. In the abdomen, into the middle intestine, the ducts of a highly developed paired liver flow. The liver is a derivative of the midgut. It consists of many thin tubes, not only secreting digestive enzymes, but also capable of digesting and absorbing nutrients. Intracellular digestion can occur in liver cells. Further, the middle intestine forms an expanded section, the so-called rectal sac or cloaca, into which the excretory organs open - the Malpighian vessels. From the rectal sac comes the ectodermic posterior (rectum) intestine, ending in the anus.
The digestive system of other arachnids varies in detail, but is generally similar.
Respiratory system
In connection with the terrestrial way of life, arachnids breathe atmospheric air. Respiratory organs in arachnids can be lungs and tracheas. At the same time, it is curious that some arachnids (scorpions, flagellated and four-lung spiders) have only lungs, others (false scorpions, salpugs, haymakers, partly mites) have only tracheae, and finally, the third (most spiders) have both lungs and trachea.
Four pairs of lungs in scorpions are located on the 3rd-6th segments of the anterior abdomen. From the ventral side, 4 pairs of slit-like holes - stigmas leading to the lungs are clearly visible. The arachnid lung is a sac-like organ lying on the underside of the abdominal segments. The stigma leads to the lung cavity, which in the anterior part of the lung sac is blocked by plates lying one above the other, which are outgrowths of the lung wall. Between them there are narrow cavities into which air enters. Blood circulates inside the pulmonary plates, and thus there is an exchange of gases between the blood and the air that fills the lungs. Most spiders have one pair of lungs (two-lung spiders), some have two pairs (four-lung spiders).
Comparison of the structure of the lung with the structure of the abdominal limbs and gills of horseshoe crabs indicates their great similarity. The position of the lungs on the underside of the abdomen, where the abdominal limbs should have been, enhances this resemblance. The data of comparative anatomy and embryology fully support the assumption that the lungs of arachnids were formed from the gill legs of fossil merostomes. The transformation of an abdominal limb with gills into a lung can be imagined as follows. In the abdominal wall of the body, to which the gills were attached, a depression formed, and the lamellar limb adhered to the integument from the sides. The cavity formed in this way communicated with the external environment in the rear part by a narrow, slit-like opening. From the gill filaments, attached only by a wide base to the limb, pulmonary plates with their rather complex structure were formed.
In most arachnids, the respiratory organs are tracheae (solpugs, haymakers, etc.), and in two-lung spiders, tracheae exist along with lungs. Tracheae begin with spiracles (stigmas), usually on the underside of the abdomen. The spiracle can be from one unpaired (in some spiders) to three pairs (in salpugs). The spider's spiracle is located on the abdomen just in front of the arachnoid warts. It leads to two pairs of tracheal tubes, lined from the inside with a thin layer of chitin, which in some arachnids (salpugs, haymakers and some spiders) forms spiral thread-like thickenings that do not allow the tubes to subside.
In salpugs, harvestmen and other arachnids, in which the tracheas are the only respiratory organs, they form a very complex system of branching tubes that penetrate into all parts of the body and limbs. Some small arachnids lack special respiratory organs; they breathe through the entire surface of the body (a number of types of ticks, etc.).
Circulatory system
The circulatory system of arachnids exhibits a metameric structure. In scorpions and most flagellates, the heart is long, tubular, bearing seven pairs of ostia. In spiders, the number of pairs of ostia is reduced to five or even two. In other arachnids, the heart is shorter, while in ticks it is a small bubble.
Arterial vessels depart from the heart forward, backward and to the sides, and the degree of development and branching of the arterial vessels is very different and is directly dependent on the structure of the respiratory organs. Scorpions, which have lungs localized in a certain place, and spiders, whose tracheas are little branched, have the most highly developed system of arterial vessels. In salpugs, haymakers, and other forms breathing through tracheae, the system of blood vessels is poorly developed, and sometimes absent. This is explained by the fact that with a sufficiently strong branching of the trachea, the exchange of gases occurs directly between the trachea and tissues of the animal, and the blood almost does not take part in the transport of gases. This is a very interesting example of a correlation in the development of various organ systems, which is even more pronounced in insects.
The degree of development of the circulatory system also depends on the size of the animal. In ticks, it is the least developed: some ticks have only a bubble-shaped heart, while others do not have it.
excretory system
The main organs of excretion in arachnids are completely new organs associated with the intestines - the Malpighian vessels. They are one or two pairs of thin tubes, more or less branched and located on the abdomen. These tubules are protrusions of the midgut, that is, they are of endodermal origin. Malpighian vessels, blindly closed at the free end, open into the rectal bladder, or cloaca, the last section of the midgut. Guanine, the main excretory product of arachnids, accumulates in their lumens.
Along with the malpighian vessels, arachnids also have other excretory organs - the coxal glands. There may be one or two pairs. They open outward most often at the base of the first and third pair of walking legs. In a typical case, the coxal glands consist of a coelomic sac, a nephridial canal, sometimes expanding and forming a bladder, and an excretory opening. These organs are apparently homologous to the coelomoducts of annelids and correspond to the coxal glands of horseshoe crabs. In adult arachnids, the coxal glands are usually reduced and do not function, being replaced by the Malpighian vessels.
Nervous system and sense organs
The nervous system of arachnids is represented by the abdominal nerve chain typical of all arthropods. Arachnids are characterized by a significant concentration and fusion of groups of nerve ganglia. The smallest degree of convergence and fusion of ganglia is observed in scorpions. They have a paired supraesophageal ganglion (brain) connected by connectives to the cephalothoracic ganglionic mass that innervates the limbs (2-6 pairs). This is followed by the seven ganglia of the ventral nerve cord. In salpugs, flagellates, and pseudoscorpions, only one of the abdominal ganglia remains free, while the rest join the common ganglionic mass. In spiders, all the ganglia of the ventral nerve cord form a single subpharyngeal node. In ticks, a fusion of the subpharyngeal node is also observed with the brain.
Of the sense organs are the organs of touch and vision. The organs of touch are the hairs that cover the limbs, especially the pedipalps. The eyes of arachnids are simple (not compound), usually several pairs. Spiders have 8 eyes located on the head in two rows.
Sex organs and reproduction
Arachnids are dioecious, and sexual dimorphism is quite pronounced (in spiders and ticks). In spiders, males are often much smaller than females, and their pedipalps are turned into a copulatory apparatus.
The genital organs of all arachnids consist of paired glands or of unpaired, but bearing traces of fusion of paired glands. Females have an unpaired gland in the form of a "frame with crossbars" and paired oviducts. Males have paired testicles with characteristic crossbars and a copulatory apparatus.
The female spiders have paired seminiferous sacs that open as independent openings in front of the unpaired genital opening on the first abdominal segment. In addition, each of them communicates through a special channel with the uterus, formed by the fusion of the final sections of the oviducts.
With the help of a process of the copulatory apparatus of the pedipalps, the spiders inject sperm into the female spermatic receptors through their external openings. From there, the sperm travels to the uterus, where fertilization takes place.
With the help of ticks, partnerogenesis is characteristic. Some species of scorpions are viviparous, and the development of fertilized eggs occurs in the ovaries. Newborn scorpions do not leave their mother, and she carries them on her back for some time.
Development
The development of fertilized eggs in most arachnids is direct. Only in ticks, due to the small size of eggs, development takes place with metamorphosis. Eggs in most cases are rich in yolk, and crushing is either superficial (spiders, haymakers, salpugs, mites) or discoidal (oviparous scorniopes).
In viviparous scorpions, embryos that develop in the mother's ovary consume protein substances secreted by the female's organs. Therefore, despite the small supply of yolk in the eggs of viviparous scorpions, they are characterized by complete crushing.
During embryonic development, more segments are laid in arachnids than in adult forms. On the abdominal segments, the rudiments of the abdominal limbs appear, which are further reduced or transformed into other organs.
Classification
Phylogeny of arachnids
A number of facts have been cited above, on the basis of which one can imagine the origin of arachnids and the phylogenetic relationships between the orders of this class.
Undoubtedly, the relationship of terrestrial chelicerae - arachnids with aquatic chelicerae - crustaceans, and through them with a very ancient and even more primitive group - trilobites. Thus, the evolution of this branch of arthropods went from the most homonomous forms in terms of segmentation, as evidenced by trilobites, to more and more heteronomous animals.
Of the sciencelike, the most primitive and ancient group are scorpions, the study of which provides a lot for understanding the evolution of arachnids. Within the class, the evolution of certain groups led to a greater or lesser fusion of the abdominal segments, to a greater development of the tracheal system, replacing the more ancient respiratory organs - the lungs, and finally, to the development of special adaptations characteristic of representatives of individual orders.
Among the true spiders, the four-lunged spiders are undoubtedly the more primitive group. Two pairs of lungs, the absence of tracheae, the presence of two pairs of coxal glands, and some of them have an articulated abdomen - all these features indicate their greater primitiveness compared to the group of two-lung spiders.
Gallery
Instead of external fertilization, which was characteristic of the distant aquatic ancestors of arachnids, they developed internal fertilization, accompanied in primitive cases by spermatophoric insemination or, in more advanced forms, by copulation.
The spermatophore is a sac secreted by the male, which contains a portion of seminal fluid, thus protected from drying out during exposure to air. In pseudoscorpions and in many ticks, the male leaves the spermatophore on the ground, and the female captures it with the external genitalia. At the same time, both individuals perform a "nuptial 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 no spermatophores. In some cases, parts of the body that are not directly connected with the reproductive system serve for copulation, for example, the modified terminal segments of the pedipalps in male spiders (Fig. 405).
Most arachnids lay eggs. However, many scorpions, false scorpions, and some ticks have live births. Eggs are mostly large, rich in yolk.
Various types of cleavage occur in arachnids, but superficial cleavage occurs in most cases. Later, due to the differentiation of the blastoderm, the germinal streak is formed. Its surface layer is formed by the ectoderm, the deeper layers are the mesoderm, and the deepest layer adjacent to the yolk is the endoderm. The rest of the embryo is dressed only in ectoderm. The formation of the body of the embryo occurs mainly due to the embryonic streak.
In further development, it should be noted that segmentation is more pronounced in embryos, and the body consists of a greater number of segments than in adult animals. So, in the embryos of spiders, the abdomen consists of 12 segments, similar to adult racoscorpions and scorpions, and there are rudiments of legs on 4 - 5 anterior segments (Fig. 406). With further development, all abdominal segments merge, forming a whole abdomen.
In scorpions, the limbs are laid on 6 segments of the anterior abdomen (Fig. 406). The anterior pair of them gives genital caps, the second - comb organs, and the development of other pairs is associated with the formation of lungs.
All this indicates that the class Arachnida originated from ancestors with rich segmentation and with limbs developed not only on the cephalothorax, but also on the abdomen (pro-belly). Almost all arachnids have direct development, but mites have metamorphosis.
About 25 thousand species of arachnids are known. These arthropods are adapted to living on land. They are characterized by respiratory organs. As a typical representative of the class Arachnids, consider the cross-spider.
The external structure and nutrition of arachnids
In spiders, the segments of the body merge, forming the cephalothorax and abdomen, separated by interception.
The body of arachnids is covered chitinized cuticle and the underlying tissue (hypoderm), which has a cellular structure. Its derivatives are spider and poisonous glands. The poisonous glands of the cross spider are located at the base of the upper jaws.
A distinctive feature of arachnids is the presence six pairs of limbs. Of these, the first two pairs - the upper jaws and leg tentacles - are adapted to capture and grind food. The remaining four pairs perform the functions of movement - these are walking legs.
During embryonic development, a large number of limbs are laid on the abdomen, but later they are transformed into spider warts, opening the ducts of the spider glands. Hardening in air, the secretions of these glands turn into cobwebs, from which the spider builds a trapping web.
After the insect has got into the net, the spider wraps it in cobwebs, sticks the claws of the upper jaws into it and injects poison. It then leaves its prey and hides for cover. The secret of poisonous glands not only kills insects, but acts as digestive juice. After about an hour, the spider returns to its prey and sucks out semi-liquid, partially digested food. From the killed insect, one chitinous cover remains.
Respiratory system in the cross-spider, it is represented by lung sacs and tracheae. lung bags and the tracheae of arachnids open outward through special openings on the lateral parts of the segments. In the lung sacs there are numerous leaf-like folds in which blood capillaries pass.
Trachea They are a system of branched tubules that go directly to all organs, where tissue gas exchange takes place.
Circulatory system arachnids consists of a heart located on the dorsal side of the abdomen and a vessel through which blood moves from the heart to the front of the body. Since the circulatory system is not closed, blood returns to the heart from the mixed body cavity (myxocoel), where it washes the lung sacs and trachea and is enriched with oxygen.
excretory system The spider-cross consists of several pairs of tubes (Malpighian vessels) located in the body cavity. Of these, waste products enter the posterior intestine.
Nervous system arachnids are characterized by the fusion of nerve nodes with each other. In spiders, the entire nerve chain merges into one cephalothoracic ganglion. The organ of touch is the hairs that cover the limbs. The organ of vision is 4 pairs of simple eyes.
Reproduction of arachnids
All arachnids are dioecious. The female cross-spider lays eggs in autumn in a cocoon woven from a silky web, which she attaches in secluded places (under stones, stumps, etc.). By winter, the female dies, and spiders emerge from the eggs that have overwintered in a warm cocoon in the spring.
Other spiders also take care of their offspring. For example, a female tarantula carries her young on her back. Some spiders, having laid their eggs in a web cocoon, often carry it with them.
