The structure of the spider

The body of the spider-tarantula consists of the cephalothorax and abdomen, connected by a bridge. The exoskeleton covers the whole body of the spider from above with a rather stiff and dense shell. Almost all the muscles of the spider are attached to it, and even the exoskeleton protects the spider organism from loss of moisture and from external mechanical influences. It consists of an exoskeleton made of durable chitin.

The spider's cephalothorax contains the brain and the main muscles. Above the cephalothorax covers the carapace (solid shield). On the front of the carapace are 4 pairs of eyes, and to its depressed middle part are attached muscles. The sternum of the spider is in the lower part of the cephalothorax.

In the abdomen of the spider are the organs of the digestive and reproductive system. The abdomen ends with two-web cobweb appendages and an anal opening. The spider has 8 pairs of appendages. The first pair - chelicera, the second - pedipalps, then four pairs of walking legs, as well as cobweb appendages. Each pair has its own functions. Helicer - for protection from enemies, dragging food, digging holes, etc., pedipalps are organs of touch, walking legs speak for themselves, and with the help of cobweb appendages a spider can produce a web.

Internal structure of tarantula spiders

The brain is the center of the nervous system and is located in the lower part of the cephalothorax. The brain consists of a small upper and lower sub-esophagus. The upper brain "is responsible" for obtaining visual information, and the sub-esophagogastric is responsible for the motor functions.

On the front of the cephalothorax, spiders have four pairs of eyes. It should be noted that the eyesight of tarantulas is rather weak, therefore the main work on contacts with the environment is performed by touch. The organs of touch in this case are hairs, as well as lyroid and tarsal organs.

A feature of the digestive system of tarantulas is the so-called "external nutrition". The esophagus tube passes through the brain and connects to the sucking stomach, which connects to the true stomach with a small tube. To the true stomach is attached the intestine, which goes further to the abdomen, where there is a network of Malpighian tubules that perform the function of the kidneys. With the help of these tubules in the gut and the main digestive process occurs.

The system of respiration of tarantulas is represented by two pairs of book lungs. Lungs consist of the finest membranes, similar to book pages.

The circulatory system of spiders is unclosed, the vascular network along which the poisonous gray-blue hemolymph moves, has its endings in the tissues of the body. The "heart" of a tarantula is a long tubular organ encased in pericardium. Along the entire length of the "heart" are four pairs of holes - ostium, working as valves for the current of the hemolymph. Under the effect of contraction of the pericardium, the hemolymph moves through the anterior aorta - forward, backward - through the posterior aorta, and also sideways.

The reproductive system of male tarantulas consists of paired testes, a slit-like genital opening, an epigastric groove, and an epiginal pad. The copulatory organs of the male are located at the ends of the pedipalps, they are fully formed to the penultimate molt. In female tarantulas, it is represented by paired ovaries, a uterus, an oviduct opening, an epigene, a pocket-shaped seminal receptacle.

The structure of the spider

Outside structure. Spiders, unlike insects, do not have antennas (antennae) and jaws. The body is covered with an external skeleton (exoskeleton) and consists of two sections - the cephalothorax formed by the merged head and chest, and the abdomen. They are connected with each other by a narrow stalk. At the anterior end of the cephalothorax are simple eyes, the location of which serves as an important classification feature. Most spiders have four pairs. The cephalothorax carries six pairs of limbs. In front of the head are two downward-looking chelicers, each of which ends in a sharp claw. It opens the poisonous glands located in these extremities. The second pair - pedipalps, used as palps and grasping structures. In sexually mature males their ends are modified and used for mating. Between the bases of the pedipalp is a small mouth opening. All spiders, in contrast to insects, have four, not three pairs of walking legs. The last segment of each of them carries at least two claws, and some species have much more.

The cobweb glands open on the underside of the abdomen usually with six arachnoid warts. In front of them are located small breathing holes - spiracles, or stigmata.

Internal structure. Spiders feed on liquid tissues sucked from their victims, mainly insects. The digestive system of spiders consists of a specialized sucking stomach, another stomach with blind outgrowths and an intestine surrounded by the digestive gland ("liver") and opening at the end of the body with an anus.

The circulatory system is not closed. It consists of the heart, arteries, veins and spaces (sinuses) between organs, washed with colorless blood (hemolymph). The heart is a pulsating tube with holes (ostia), stretching along the dorsal side of the body cavity. Unlike insects, it is not divided into several chambers.

Spiders, as already mentioned, breathe air. The organs of respiration are trachea and lungs, called pulmonary books. Each such book consists of a pouch, one of the walls of which is composed of numerous leaf-like folds resembling pages. They exchange oxygen and carbon dioxide between the blood and air. Outside the lungs open spiracles. The most primitive spiders have two pairs of pulmonary books, the more advanced ones have one or both replaced by tracheas penetrating the body.

The excretory system consists of a pair of coxal glands in the cephalothorax and the so-called. Malpighian vessels in the abdomen that open into the intestine.

The nervous system is similar to that of insects. It consists of the ventral trunk with branches that branch out to different organs and ganglia collected in the cephalothorax into a large sub-pharyngeal node, over which is the supra-pharyngeal - the "brain". On the pedipalps and walking legs there are sensory hairs.

Genital organs are represented by ovaries in females and testes in males. Their holes are located at the bottom of the abdomen.

INTERNAL STRUCTURE OF THE SPIDER.

Spiders are pretty close to insects, but at the same time they are clearly different from them. Their body is divided into two sections - the cephalothorax and the abdomen. The cephalothorax carries six pairs of limbs: four pairs of walking legs, a pair of tactile pedipalps similar to them, which have been mutated in males to participate in mating, and a pair of chelicers located in front of the mouth, armed with claws with ducts of poisonous glands immediately present. The digestive tract of spiders passes over the largest of their ganglia (the pharyngeal) and the main nerve trunks. A special sucking stomach drains the victim's liquid tissues. At the back it is connected to two blind gastric tubes, bent forward and reaching the poison glands; On the sides of these tubes four more pairs of blind outcrops go to the bases of the walking legs. They accumulate digestive juice. In the abdomen, the intestine passes, into which the ducts of the thin digestive ducts that form the "liver" flow. Excrement accumulates in a rectal (stericoral) sac and is discharged through the anus outwards. Malpighian vessels perform kidney function.

(Aranei),
a group of arachnids, including mites, scorpions, haymakers, etc. Spiders for a number of signs are close to insects, but clearly differ from them, and these groups are related only by a very distant relationship. A well-known characteristic feature of many spiders is the ability to weave a complexly arranged hawk net (net) from a silk-like substance secreted by the arachnid glands. Some spiders, such as the black weaver spider (black widow) and tropical bird-eaters, can inflict very painful bites that are fatal, but most spiders, although biting, are not dangerous to humans. The name of the class Arachnoidea comes from the Greek. arachne is a spider. In ancient Greek mythology Arachnaya was a girl who was so skilled as a weaver that, summoning the goddess Athena to the very patroness of this craft, she weft a better fabric than she. The disgruntled goddess turned the rival into a spider, announcing that from now on Arachna and all her family will be spinning and weaving until the end of the century. In total it is known approx. 30 000 species of spiders. The length of their torso is from 0.1 to 5 cm. The main food is the liquid tissues of insects, which spiders catch, rushing from ambush or using cobwebs. Spiders are found on almost all inhabited latitudes and altitude marks: they were found on the slopes of Mount Everest at 6700 m above sea level and caught (juveniles) 600 m from the surface of the earth. Some species live in water. Having settled, the juveniles of a number of small species are taken to the ends of grass and other towering objects and, raising their abdomen, begins to secrete the arachnoid thread, which is picked up by a stream of air and, reaching a sufficient length, carries away the animal. Such years occur in certain seasons and are especially noticeable in the "Indian summer", when in the air you can see whole "carpets-planes" from dozens of interwoven cobwebs. This unique way of settling allows spiders to cover huge distances and to reach even the islands lost in the ocean.
Web and the construction of a net. The ability to secrete a spider thread is a characteristic feature of almost all spiders. Material for it is formed in the special glands located in the back of the abdomen, and the so-called. arachnoid warts. Some spiders produce threads of different (up to six) types and use each of them for quite specific purposes. When the spider moves, it continuously allocates a web, which, like a mountaineer, a safety rope, from time to time attaches to the surfaces it passes through. That's why the disturbed spider almost always can, with his legs tucked, fall off the support and, hanging on an extensible thread, descend it to the ground. When the net gets prey, the spider usually flies its web and only then kills with poisonous claws (chelicera) and sucks. Probably the most interesting feature of spiders is the construction of a network of trapping nets. Their forms are very diverse and often very beautiful. Not all spiders use their web for catching insects, but each species weaves it in a specific way, and the resulting design may well serve as a taxonomic feature. The most beautiful, so-called. wheel-shaped, a spider-circle spiders of the family of cross-arms (Araneidae). First the spider climbs to a high place, usually near a path or other open space, and secrets a very light thread that is picked up by the wind and, accidentally hitting a nearby branch or other support, wraps around it. The spider moves on this thread to a new point, along the way reinforcing the web with an additional secret. In a similar way, another two or three relatively thick "cables" are laid, constituting a closed frame, inside which the proper construction will be located. Usually the net is oriented more or less vertically, but some types of spiders build horizontal networks. Between the sides of the frame stretch filaments, radii, connecting in the center, like spokes in the wheel hub. Now, starting near this place, the spider moves to the periphery in a spiral, leaving behind itself a thread attached to the radii, the distance between the turns of which is determined by the swing of its limbs. While the web is not yet sticky, but after reaching the outer frame, the spider is again spiraling, but with denser spirals, it returns to the center, this time forming a thread, which, unlike the previous ones, is covered with droplets of sticky secretion. As this helix is ​​actually laid, the thread of the first non-stick spiral is bitten and discarded. Obviously, it served only as a kind of construction forest. When the net is ready, the spider moves to their center or to a nearby shelter and waits for a flying insect to stick to the web. Usually the whole structure works one night, and by the morning it is in many places torn. One of the most beautiful networks weaves the usual appearance of Argiope aurantia, a large spider with a black and golden pattern on the body. For its extensive spiked tent, a zigzag filament that runs vertically through the center of the structure is characteristic. The form of the trapping network of other species is completely different. For example, in representatives of the genus Frontinella, it resembles a cup on a saucer. In funnel spiders (the Agelenidae family) the net is similar to the net, and spiders of the Gnaphosidae family build tubular shelters from the web under rocks and other objects, where they hide between the outlets for hunting. An unusual wheel-like network of golden threads builds the view of Nephila clavipes. For this large spider, common in the southern United States, are characterized by legs with tufts of hairs. The ability of spiders to secrete a silk-like thread repeatedly led to attempts to use them like silkworms, but these experiments had no success. The main difficulty is that spiders need to be fed live insects, and for a fairly quick one kilogram fiber it takes more than 1.3 million. spiders! At one time cobwebs were made by crosshairs of optical instruments, for example theodolites, leveling and telescopes. Many spiders do not build networks at all and just hunt prey from ambush. This is typical of representatives of such families as spiders-wolves (Lycosidae), spiders-horses (Salticidae) and ptichaeids-terafosides (Theraphosidae). Spiders-horses, for example, track down victims, using sharp sight, and overtake them with one jump.

SPOONING THE SPOKE NETWORK. From the middle of the upper thread the spider descends on the cobweb to the bottom. From the middle of this web, divided as a result into two "radiuses", it stretches the third "radius", the second end of which attaches to the upper thread, and continues such movements to the center and from it until it establishes all the "spokes" of the wheel-like network. Its "hub" it strengthens with several spiral turns.

A variety of spiders.   We have already mentioned spider-spiders and spiders, not building networks. Let's consider in more detail their various types.
Terafosides. One of the most interesting American spiders is the Dugesiella hentzi. This is a large animal, the span of its legs reaches 15 cm. The body color is dark brown, so that in general the animal is, to put it mildly, unattractive. It's accepted to be afraid, but this spider is relatively harmless: its bite is no worse than a bee. It is common in the south-west of the USA and leads a more or less nocturnal lifestyle. The main enemy of this species is a wasp from the genus Pepsis, whose name translates from English as "a large blue tarantula hawk". She paralyzes the spider with a sting and pulls it into her mink for feeding the larva. The bites of some tropical terafosides are very toxic even to humans. Representatives of this family often live up to 20 years.
The kenyzides.   In some areas of the US there are interesting spiders from the family Ctenizidae. They are different in size and reach a length of 2.5 cm; the color of the massive body is dark. These spiders are digging in the ground of the mink and lining their walls with cobwebs. A characteristic feature of such shelters is a tightly fitting door, which is very difficult to open when the spider holds it from the inside. It is established that in this case the animal can withstand a pulling force equal to almost a pound: for man it is equivalent to 10 tons. From time to time, the kenyzides emerge from the mink for hunting. Their main enemy is one of the types of wasps, able to open the door of their lair or attacking spiders when they are outside.
Real bird-eaters (Aviculariidae).   This family includes the world's largest spiders, attacking the tropics even on chicks. The length of their torso reaches 5 cm, and the span of the legs is 18 cm.
Spiders are the "archers".   Representatives of the genus Mastophora probably use the most unusual way of catching prey. First, the spider pulls a strong thread between the branches of a web, usually over a stream where small midges curl. Approximately in the middle of it, he attaches a hunting string with a heavy sticky lump on the end and holds it with the front leg. When an insect flies nearby, he wags this thread like a lasso, trying to hook the victim.
Spiders are excavators.   Representatives of the genus Atypus weave from the web a tight, closed at the ends tubule with a diameter of approx. 2.5 cm, which comes out of their mink and lies on the ground, usually under a tree, lasting for a distance of about 30 cm. The spider hides inside the tube and, when an incautious insect sits on it, grabs it right through the arachnoid wall.
Spider-boaters (Thomisidae). These spiders are also called spiders-crabs for their external resemblance to the latter. They are medium-sized, often brightly colored and usually hide in flowers, where they hunt for insects that flew past nectar, such as bees.
Water spiders.   In the US, relatively large spiders of the genus Dolomedes are common, who can run on the surface of standing water and even dive under water, holding on to plants. These spiders feed on insects, fish fry and tadpoles. In Europe, a silverback spider inhabits under water in places where the current is weak or nonexistent, most of the life. Probably, this is the most unusual spider in the world, given that he, like all members of his class, breathes atmospheric air. In spring, it goes under the water and stretches there between the plants a horizontal network of cobwebs with very small cells. Then, rising to the surface, he expose the end of the abdomen, covered with non-wetted hairs. Between them, air is collected, which the spider, in the form of a bubble held by its feet, drags it into the depths and shakes it off under its net. That does not allow bubbles to float and after multiple such voyages arches a bell the size of a thimble and even more, propped from the inside by an air chamber. The spider hides inside it, inaccessible to most enemies, immediately lays eggs, takes out the young and winters. The bells of the male and female living separately are connected to each other by a bridge of cobwebs.
Poisonous spiders. Spiders are afraid to be afraid. Indeed, almost all of them are armed with poisonous claws, but for humans only a few species are dangerous. In the United States, one must beware of two of them - the "brown hermit" (Loxosceles reclusa) and the "black widow" (Latrodectus mactans). The length of the first is only 0.6 cm. This spider lives in the Midwest, often in dwellings, where it hides behind furniture. On the spot of his painful bite a sore is formed, which can never completely overgrow. Spider "black widow" is found almost throughout the US. The bite of this species causes severe pain and can lead to death due to a neurotoxin injected into the wound. The female body is brilliantly black with bright red spots. On the underside of the abdomen, there is usually a red pattern in the form of an hourglass. The male is much smaller than the female, but is similar in color. The name "black widow" is explained by the fact that the female often eats the partner after mating, which, incidentally, is quite common among spiders. This species is non-aggressive, and spiders usually try to hide from a person, but if you take them in your hands, they often bite.
The structure of the spider.
Outside structure.   Spiders, unlike insects, do not have antennas (antennae) and jaws. The body is covered with an external skeleton (exoskeleton) and consists of two sections - the cephalothorax formed by the merged head and chest, and the abdomen. They are connected with each other by a narrow stalk. At the anterior end of the cephalothorax are simple eyes, the location of which serves as an important classification feature. Most spiders have four pairs. The cephalothorax carries six pairs of limbs. In front of the head are two downward-looking chelicers, each of which ends in a sharp claw. It opens the poisonous glands located in these extremities. The second pair - pedipalps, used as palps and grasping structures. In sexually mature males their ends are modified and used for mating. Between the bases of the pedipalp is a small mouth opening. All spiders, in contrast to insects, have four, not three pairs of walking legs. The last segment of each of them carries at least two claws, and some species have much more. The cobweb glands open on the underside of the abdomen usually with six arachnoid warts. In front of them are located small breathing holes - spiracles, or stigmata.

Internal structure. Spiders They feed on liquid tissues sucked from their victims, mainly insects. The digestive system of spiders consists of a specialized sucking stomach, another stomach with blind outgrowths and an intestine surrounded by the digestive gland ("liver") and opening at the end of the body with an anus. The circulatory system is not closed. It consists of the heart, arteries, veins and spaces (sinuses) between organs, washed with colorless blood (hemolymph). The heart is a pulsating tube with holes (ostia), stretching along the dorsal side of the body cavity. Unlike insects, it is not divided into several chambers. Spiders, as already mentioned, breathe air. The organs of respiration are trachea and lungs, called pulmonary books. Each such book consists of a pouch, one of the walls of which is composed of numerous leaf-like folds resembling pages. They exchange oxygen and carbon dioxide between the blood and air. Outside the lungs open spiracles. The most primitive spiders have two pairs of pulmonary books, the more advanced ones have one or both replaced by tracheas penetrating the body. The excretory system consists of a pair of coxal glands in the cephalothorax and the so-called. Malpighian vessels in the abdomen that open into the intestine. The nervous system is similar to that of insects. It consists of the ventral trunk with branches that branch out to different organs and ganglia collected in the cephalothorax into a large subacute node, over which is the supra-pharyngeal "brain". On the pedipalps and walking legs there are sensory hairs. Genital organs are represented by ovaries in females and testes in males. Their holes are located at the bottom of the abdomen.

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INTERNAL STRUCTURE OF THE SPIDER. Spiders are quite close to insects, but at the same time clearly differ from them. Their body is divided into two sections - the cephalothorax and the abdomen. The cephalothorax carries six pairs of limbs: four pairs of walking legs, a pair of tactile pedipalps similar to them, which have been mutated in males to participate in mating, and a pair of chelicers located in front of the mouth, armed with claws with ducts of poisonous glands immediately present. The digestive tract of spiders passes over the largest of their ganglia (the pharyngeal) and the main nerve trunks. A special sucking stomach drains the victim's liquid tissues. At the back it is connected to two blind gastric tubes, bent forward and reaching the poison glands; On the sides of these tubes four more pairs of blind outcrops go to the bases of the walking legs. They accumulate digestive juice. In the abdomen, the intestine passes, into which the ducts of the thin digestive ducts that form the "liver" flow. Excrement accumulates in a rectal (stericoral) sac and is discharged through the anus outwards. Malpighian vessels perform kidney function.

Reproduction.   Fertilization in spiders is a very complicated process. After mating, the female often eats the male. Eggs are deposited in the arachnoid cocoon, which the female carries with it or attaches to a solid object, for example, a plant. In some spiders, including the above-mentioned species of Argiope aurantia, these cocoons are well visible in trees, especially in winter after the fall of the leaves. Hatching eggs from the eggs soon begin to weave their own trap networks or settle through the air, attaching themselves to volatile cobwebs.
See also Insects.