On which segment is the genital opening of arachnids located? Arachnids

Question 1. What structural features are characteristic of representatives of the arachnid class?

Features of the structure of arachnids:

the body is divided into the cephalothorax and abdomen;

no antennae;

on the cephalothorax there are 4 pairs of walking legs; two more pairs of limbs are transformed into pedipalps, which serve to capture and hold prey, and chelicerae, tools for grinding and crushing food;

there are no limbs on the abdomen;

there is an external chitinous skeleton;

respiratory organs can be of two types and present together or separately: pulmonary sacs and trachea;

the excretory system is a pair of mostly branching Malpighian vessels - tubular tubules formed by invagination of the midgut;

the circulatory system is not closed;

the nervous system is formed by the ventral nerve cord; suprapharyngeal nerve ganglion, has more complex structure than in crustaceans;

eyes are simple.

Question 2. What parts does the spider’s body consist of? Scorpio?

The spider's body consists of an unsegmented cephalothorax and abdomen, connected by a thin stalk.

In the body of a scorpion, a cephalothorax and an abdomen, consisting of segments, are distinguished.

Question 3. How many limbs does a spider have? What are they called and what function do they perform?

The cephalothorax bears six pairs of limbs. Chelicerae are the first pair of limbs, consisting of 2–3 segments, ending in a claw, hook or stylet. Pedipalps (claws, claws) - the second pair of limbs - can perform several functions: organ of touch, lower jaw, walking legs, claws for grasping food; males can use them as a copulatory apparatus. Four last couples limbs - walking legs. Spiders' legs end in comb-shaped claws, which are necessary for making webs. The abdominal limbs are transformed into arachnoid warts.

Question 4. What sense organs does a spider have?

Mechanical tactile stimulation, which is very important for arachnids, is perceived by differently arranged sensitive hairs, which are especially numerous on the pedipalps. The organs of vision are represented by simple eyes; spiders most often have 8 eyes.

Question 5. How do arachnids develop?

The vast majority of arachnids have direct development. Only in ticks does development occur with metamorphosis. (Metamorphosis is a deep transformation of the structure of the body, during which the larva turns into an adult.) Arachnids are dioecious. There is sexual dimorphism. Arachnids developed (due to their land-based lifestyle) internal fertilization. The male uses his pedipalps to introduce sperm into the spermatheca of the female; the sperm fertilize the eggs in the uterus located in the abdomen. Most arachnids lay large, yolk-rich eggs protected by an arachnoid cocoon. Embryonic development occurs in the cocoon, upon completion of which small spiderlings emerge from the cocoon.

Question 6. Make a table " Comparative characteristics crustaceans and spiders” (work in small groups).

Comparative characteristics of crustaceans and spiders

Question 7. Describe medical significance ticks.

Most ticks of medical importance are blood-sucking. Animals that feed ticks are mammals, birds and reptiles.

Along with the host's blood, pathogens of various diseases enter the tick's body, which, when switching to another host, can be transmitted to it, which promotes the circulation of pathogens. The lifespan of ticks is quite long - from 6 months to 20-25 years.

Tick saliva has a local irritant and general toxic effect. Mass attacks mites can cause not only skin lesions, but also severe feverish conditions and nervous disorders. Particularly dangerous is the ability of ticks to carry pathogens.

The most important from a medical point of view are mites of the ixodid and argasid families, as well as the scabies mite of the acariform family.

Question 8. What is the essence of partially external digestion in spiders?

Digestion in spiders is partially extracavitary. Therefore, in a difficult digestive system, with many specialized departments, they have no need. The digestive system of spiders consists of a pharynx and a gut, which ends in the anus. The spider injects a secretion into the body of the killed prey. salivary glands, which has the ability to break down proteins. External (outside the spider’s body) digestion of food occurs into a liquid pulp, which is then absorbed by the spider.

The nervous system of any living organism receives information about the environment through the senses. The Arachnida class is no exception. In this article we will talk in more detail about all the sense organs of arachnids, their significance and location.

Sense organs of arachnids

Most main role touch plays a role. In spiders, this organ is presented in the form of hairs (trichobothria), which are located throughout the body. Most of them are on the pedipalps and walking legs. The structure of each hair is presented as follows:

the movable hair is attached to the bottom of the pit on the integument of the body;
in the fossa there is a group of sensitive cells to which the hair is connected.

Rice. 1. Organs of touch

Each vibration of the trichobothria accurately identifies all species mechanical movement. The organs of touch work so accurately that spiders easily detect the smallest vibrations of the web or air, while distinguishing the nature of the irritation.

Rice. 2. Spider hair

The lyre-shaped organs, located on the surface of the entire body, perform the function of chemical sense organs. They are presented in the form of cracks on the body, in the depths of which sensitive cells are located. These are the so-called olfactory organs. Taste-sensing cells are found on walking legs, tentacles, and the side of the pharynx. However, these animals distinguish odors only at close range.

Organs of vision of arachnids

Compared to crustaceans, arachnids have a simple structure of their visual organs. They are located in the front part of the cephalothorax and can be represented by three, four, or less often one pair of eyes. The visual organs of arachnids are presented differently in each order and species. For example, scorpions have larger middle eyes, and 2-5 pairs of smaller eyes on the sides. Spiders have four pairs of eyes arranged in two arcs. At the same time, the middle eyes of the anterior arch are larger than all other eyes.

Fig.3. Eye location

Arachnids do not see very well. For example, scorpions can distinguish their own kind only at a distance of 2-3 cm, and some types of spiders - at a distance of 20-30 cm.

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For some species arachnid vision plays a very important role. For example, jumping spiders with blackened eyes cease to distinguish females and perform characteristic mating season dance.

What have we learned?

Arachnids, like all animals, have sense organs. The most important role for their life is played by touch. The eyes have a simple structure; despite their number, arachnids see poorly.

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Answers to school textbooks

Features of the structure of arachnids:

The body is divided into a cephalothorax and abdomen;

There are no antennae;

There are 4 pairs of walking legs on the cephalothorax; two more pairs of limbs are transformed into pedipalps, which serve to capture and hold prey, and chelicerae, tools for grinding and crushing food;

There are no limbs on the abdomen;

There is an external chitinous skeleton;

The respiratory organs can be of two types and present together or separately: pulmonary sacs and trachea;

The excretory system is a pair of mostly branching Malpighian vessels - tubular tubules formed by invagination of the midgut;

The circulatory system is not closed;

The nervous system is formed by the ventral nerve cord; suprapharyngeal nerve ganglion, has a more complex structure than that of crustaceans;

The eyes are simple.

2. What parts does the spider’s body consist of?

The spider's body consists of an unsegmented cephalothorax and abdomen, connected by a thin stalk.

3. How many limbs does a spider have? What are they called and what function do they perform?

The cephalothorax bears six pairs of limbs. Chelicerae are the first pair of limbs, consisting of 2-3 segments, ending in a claw, hook or stylet. Pedipalps (maxillae, leg-tentacles) - the second pair of limbs - can perform several functions: organ of touch, lower jaw, walking legs, claws for grasping food; males can use them as a copulatory apparatus. The last four pairs of limbs are walking legs. Spiders' legs end in comb-shaped claws, which are necessary for making webs. The abdominal limbs are transformed into arachnoid warts.

4. What is the significance of chelicerae?

Chelicerae serve to grind and crush food. At the ends of the chelicerae, the duct of the poisonous (digestive) gland opens.

5. What sense organs does a spider have?

Mechanical, tactile irritations are perceived by differently arranged sensitive hairs, which are especially numerous on the pedipalps. The organs of vision are represented by simple eyes located on the dorsal surface of the cephalothorax. There are usually several pairs of them. Spiders most often have 8 eyes.

6. How does the spider’s digestive system work?

Digestion in spiders is partially extracavity. Therefore, they do not need a complex digestive system, with many specialized sections. The digestive system of spiders consists of a pharynx and a gut, which ends in the anus.

The spider injects the secretion of the salivary glands, which has the ability to break down proteins, into the body of the killed prey. External (outside the spider’s body) digestion of food occurs into a liquid pulp, which is then absorbed by the spider.

7. What do arachnids eat?

8. Describe the respiratory organs of spiders.

The respiratory organs in some species are the lung sacs (scorpions), in others - the trachea (salpugi, false scorpions, some ticks), in others - the lungs and trachea at the same time (spiders). The lung is a special cavity that develops on the abdomen. Tracheas are invaginations of the outer integument in the form of tubes that penetrate the body and carry oxygen to all tissues and organs.

Some small arachnids (for example, some ticks) do not have respiratory organs, and respiration occurs through the thin integument of the body.

9. How do arachnids develop?

10. What is the significance of arachnids in nature and for humans?

Spider mites damage crop plants by sucking their juices, thereby reducing their yield.

Granary mites, multiplying in huge quantities in grain, make it unsuitable for human consumption.

Most soil mites feed on decaying organic substances, which contributes to their processing and soil formation.

The respiratory organs of Arachnida are diverse. In some, these are pulmonary sacs, in others, in tracheas, in others, both at the same time. Only pulmonary sacs are found in scorpions, flagipes, and primitive spiders. In scorpions, on the abdominal surface of the 3rd - 6th segments of the anterior abdomen there are 4 pairs of narrow slits - spiracles, which lead to the pulmonary sacs (Fig. 389). Numerous leaf-shaped folds, parallel to each other, protrude into the cavity of the sac, between which narrow slit-like spaces remain; air penetrates through the respiratory slit into the latter, and hemolymph circulates in the pulmonary leaves. Flaglegs and lower spiders have only two pairs of pulmonary sacs. In most other arachnids (salpugs, harvestmen, pseudoscorpions, some ticks) the respiratory organs are represented by tracheas (Fig. 399, Fig. 400). On the 1st - 2nd segments of the abdomen (in salpugs on the 1st segment of the chest) there are paired respiratory openings, or stigmas. From each stigma, a bundle of long, thin, air-bearing tubes of ectodermal origin, blindly closed at the ends, extends into the body (formed as deep invaginations of the outer epithelium). In false scorpions and ticks, these tubes, or tracheae, are simple and do not branch; in harvestmen they form side branches.

Finally, in the order of spiders both genera respiratory organs meet together. Lower spiders have only lungs; among 2 pairs they are located on the underside of the abdomen. In other spiders, only one anterior pair of lungs is preserved, and behind the latter there is a pair of tracheal bundles (Fig. 400), opening outward with two stigmata. Finally, one family of spiders (Caponiidae) has no lungs at all, and the only respiratory organs are 2 pairs of tracheas (Fig. 400).

The lungs and trachea of arachnids arose independently of each other. The lung sacs are undoubtedly more ancient organs. It is believed that the development of the lungs in the process of evolution was associated with modification of the abdominal gill limbs, which were possessed by the aquatic ancestors of arachnids and which were similar to the gill-bearing abdominal legs of horseshoe crabs. Each such limb protruded into the body. In this case, a cavity was formed for the pulmonary leaves (Fig. 401). The lateral edges of the leg are fused to the body almost along its entire length, except for the area where the respiratory slit is preserved.

The abdominal wall of the pulmonary sac corresponds, therefore, to the former limb itself, the anterior section of this wall corresponds to the base of the leg, and the pulmonary leaves originate from the gill plates located on the posterior side of the abdominal legs of the ancestors. This interpretation is supported by the development of the pulmonary sacs. The first folded rudiments of the pulmonary plates appear on the posterior wall of the corresponding rudimentary legs before the limb deepens and turns into the lower wall of the lung. Tracheas arose independently of them and later as organs more adapted to air breathing. Some small arachnids, including some ticks, do not have respiratory organs and breathe through thin integuments.

Class Arachnida, unlike crustaceans, live primarily on land, breathing using tracheas and lungs. The class includes three orders, in whose representatives one can trace the process of fusion of body parts. Thus, in the order of spiders, the body is divided into the cephalothorax and abdomen; in scorpions, it consists of the cephalothorax, protomothorax, and posterior abdomen; in mites, all sections are fused into one shield.

General characteristics of arachnids: absence of antennae, four pairs of walking legs, tracheal or pulmonary respiration, permanent perioral appendages - upper tentacles and legs. The cephalothorax contains four pairs of simple eyes, mouthparts, and limbs (walking legs). The most common are spiders and mites.

Spider Squad

A typical representative of the order of spiders is cross spider. It can be found in forests, parks, on estates, in houses, where they weave large trapping nets from cobwebs. The spider has the first pair of mouthparts - the upper jaws, equipped with sharp, downward-curved claws.

At the end of the claws, the excretory ducts of the poisonous glands open. The spider's jaws are used to kill prey and for protection. The second pair of mouthparts are the tentacles, with which the spider probes and turns the victim while eating.

Four pairs of jointed walking legs are covered with sensitive hairs. The abdomen of arachnids is larger than the cephalothorax. At the posterior end of the abdomen of spiders there are arachnoid warts into which the arachnoid glands open. The substance secreted by the glands hardens in air, forming spider threads. Some glands secrete a cobweb that is strong and non-sticky, used to form the skeleton of a trapping net. Other glands secrete small sticky threads with which the spider builds a trapping web. The third glands secrete a soft, silky web used by the female to weave a cocoon.

The spider entangles the victim in the trapping net with a sticky web, plunges the claws of the upper jaws into the prey and injects into it a poisonous liquid that dissolves soft tissues and acts as digestive juice. Leaving the victim shrouded in web, the spider moves aside, waiting for its contents to be digested. After some time, the spider absorbs the partially digested food. This is how spiders partially digest food outside the body.

The spider's respiratory organs are represented by pulmonary sacs communicating with environment. In addition to them, the spider has tracheas in its abdomen - two bundles of respiratory tubes that open outward with a common respiratory opening.

The spider's circulatory system is basically the same as that of a crayfish.

The role of excretory organs is performed by the Malpighian vessels; the spider has one pair of them, but they branch. The hemolymph (blood mixed with lymph) of the spider washes these vessels and metabolic products exit through the gaps, then enter the intestine and are then excreted out.

The nervous system is formed by the subpharyngeal node, the brain, from which nerves extend to various organs.

Spiders have numerous and varied sense organs: organs of touch (hairs on the spider’s body and on the legs), smell and taste (on the legs and legs), taste organs are also present on the lateral parts of the pharynx; organs of vision (eight simple eyes). Some spiders are able to distinguish color, especially those. which look for prey on plant flowers (crab spiders).

Spiders are dioecious animals. Females are larger than males. In autumn, the female weaves a cocoon from a web and lays eggs in it. The eggs overwinter in it, and in the spring spiders hatch from them. Most spiders are beneficial: many small mammals, birds, lizards, and some insects feed on them. Among the spiders there are also poisonous ones - tarantula and karakurt. They are very dangerous for humans and pets.

Squad of pincers

In most representatives of the mite order, the body does not have a clear division into segments or sections. There are a lot of ticks. Some of them live in the soil, others - in plants, animals and humans.

Unlike spiders, flares have an indirect development. The egg hatches into a six-legged larva, which after the first molt develops a fourth pair of legs. After several molts, the larva turns into an adult.

Red spider mite settles on the leaves of cotton and other valuable plants. It reduces cotton yields and causes plant death.

Flour mite settles in onions and grains. By eating away the embryo of the future plant in the grain, it causes the death of the seeds. It causes damage food products in warehouses. for example, various cereals, baked goods, sunflower seeds. Cleanliness and ventilation of the premises where food is stored is one of the main measures to combat flour mites.

Scabies mite (scabies itching) causes a disease such as scabies in humans. Females of this type of mite penetrate into the more delicate areas of human skin and gnaw passages in it. This is where they lay their eggs. Young flares emerge from them, again gnawing passages in the skin. Keeping your hands clean prevents this dangerous disease.

Scorpion squad

Scorpios live in countries with warm and hot climates, and are found in the most various places habitat: from rain forests And sea coasts to barren rocky areas and sandy deserts. Scorpions often settle in human dwellings.

Scorpions are mostly viviparous; some species lay eggs in which the embryos are already developed, so that the young hatch soon. This phenomenon is called ovoviviparity. Scorpio becomes an adult a year and a half after birth, making 7 molts during this time.

The scorpion sting is a means of attack and defense. On small invertebrates that usually serve as food for the scorpion, the poison acts almost instantly: the animal immediately stops moving. For small mammals Scorpions' venom is mostly fatal. For humans, a scorpion sting is usually not fatal, but there are a number of cases with very serious consequences and even death.