Lesson Class Arachnids (compendium and presentation). Topic: Type Arthropoda (Arthropoda)

distinguish at least 12 detachments, the most important of which are the detachments of Spiders, Scorpions, False Scorpions, Solpugs, Haymakers, Ticks.

Arachnids are distinguished by the fact that they lack antennae (antennales), and the mouth is surrounded by two pairs of peculiar limbs - chelicerae and mandibles, which in arachnids are called pedipalps. The body is divided into the cephalothorax and abdomen, but in ticks all sections are fused. walking legs four couples.

cross spiders these are ordinary representatives of the class Arachnida. cross spiders is the collective name of several species genus Araneus of the family Orb-weaving spiders of the order Spiders. Cross spiders are found in warm time years everywhere in the European part of Russia, in the Urals, in Western Siberia.

Cross spiders are predators that feed only on living insects. The spider-cross catches its prey with the help of a very complex, vertically located wheel-shaped trapping net(hence the name of the family - Orb-weaving spiders) . The spinning apparatus of spiders, which ensures the manufacture of such a complex structure, consists of external formations - arachnoid warts- and from the internal organs - spider glands. A drop of sticky liquid is released from the spider warts, which, when the spider moves, is drawn into the thinnest thread. These threads quickly thicken in the air, turning into a strong gossamer thread. The web is made up mainly of protein. fibroin. In terms of chemical composition, the web of spiders is close to the silk of silkworm caterpillars, but is more durable and elastic. The tensile load for the web is 40-261 kg per 1 sq mm of the thread section, and for silk it is only 33-43 kg per sq mm of the thread section.

To weave its trapping web, the Spider-cross first stretches especially strong threads in several places convenient for this, forming a supporting frame for the future network in the form of an irregular polygon. Then he moves along the upper horizontal thread to its middle and, going down from there, draws a strong vertical thread. Further from the middle of this thread, as from the center, the spider conducts radial threads in all directions, like the spokes of a wheel. This is the basis of the entire web. Then the spider starts spinning from the center spiral threads, attaching them to each radial thread with a drop of adhesive. In the middle of the web, where the spider itself then sits, the spiral threads are dry. Other spiral threads are sticky. Insects that fly onto the net stick to them with their wings and paws. The spider itself either hangs head down in the center of the web, or hides in

Class Arachnids Cross-spider

side under the leaf - there he has refuge. In this case, he stretches a strong signal thread.

When a fly or other insect enters the net, the spider, feeling the signal thread trembling, rushes out of its ambush. By thrusting the claws of the chelicera with poison into the victim, the spider kills the victim and secretes digestive juices into her body. After that, he entangles a fly or other insect with a web and leaves it for a while.

Under the influence of the secreted digestive juices, the internal organs of the victim are quickly digested. After some time, the spider returns to the victim and sucks out all the nutrients from it. From the insect in the web, only an empty chitinous cover remains.

Making a trapping net is a series of interconnected unconscious actions. The ability to do so is instinctive and inherited. This is easy to verify by following the behavior of young spiders: when they emerge from the eggs, no one teaches them how to weave a trapping net, the spiders immediately weave their web very skillfully.

In addition to the wheel-shaped trapping net, other types of spiders have nets in the form of a random weave of threads, nets in the form of a hammock or canopy, funnel-shaped nets and other types of trapping nets. The trapping web of spiders is a kind of adaptation outside the body.

I must say that not all types of spiders weave trapping nets. Some actively search for and catch prey, others lie in wait for it from an ambush. But all spiders have the ability to secrete webs, and all spiders are made from webs. egg cocoon and spermatic reticulum.

External structure. The body of the Spider-cross is divided into cephalothorax and abdomen, which connects to the cephalothorax with a thin movable stalk. There are 6 pairs of limbs on the cephalothorax.

First pair of limbs chelicerae, which surround the mouth and serve to capture and puncture prey. Chelicerae consist of two segments, the final segment has the form of curved claws. At the base of the chelicerae are poison glands, whose ducts open at the tips of the claws. With chelicerae, spiders pierce the covers of victims and inject poison into the wound. Spider venom has a nerve-paralytic effect. In some species, for example, Karakurt, near the so-called tropical black widow, the poison is so strong that it can kill

Class Arachnids Cross-spider

even large mammal(instantly!).

Second pair of cephalothoracic limbs pedipalps have the appearance of jointed limbs (they look like short legs sticking forward). The function of pedipalps is to feel and hold prey. In sexually mature males, the pedipalp is formed on the terminal segment copulatory apparatus, which the male fills with sperm before mating. During copulation, the male, using the copulatory apparatus, injects sperm into the female's seminal receptacle. The structure of the copulatory apparatus is species-specific (that is, each species has a different structure).

All arachnids have 4 pairs walking legs. The walking leg consists of seven segments: coxa, swivel, hips, cups, shins, pretarsus and paws armed with claws.

Arachnids have no antennae. On the front of the cephalothorax, the Cross-Spider has two rows of eight simple eyes. Other types of eyes may have three pairs, and even one pair.

Abdomen in spiders, it is not segmented and does not have true limbs. On the abdomen is a pair of lung sacs, two beams trachea and three couples arachnoid warts. The spider warts of the Spider-Spider consist of a huge number (about 1000) spider glands, which produce various types of cobwebs - dry, wet, sticky (at least seven varieties of the most different purposes). Different types of web perform different functions: one is for catching prey, another is for building a dwelling, the third is used in the manufacture of a cocoon. Young spiders also settle on cobwebs of a special property.

On the ventral side of the abdomen, closer to the junction of the abdomen with the cephalothorax, genital opening. In females, it is surrounded and partially covered by a chitinous plate. epigyna. The structure of the epigyne is species-specific.

Body covers. The body is covered with chitinous cuticle. The cuticle protects the body from external influences. The most superficial layer is called epicuticle and it is formed by fat-like substances, therefore the covers of spiders are not permeable to either water or gases. This allowed the spiders to colonize the most arid regions of the globe. The cuticle simultaneously performs the function

Class Arachnids Cross-spider

exoskeleton: Serves as a site for muscle attachment. Spiders molt periodically, i.e. shed the cuticle.

musculature arachnids consists of striated fibers that form powerful muscle bundles, i.e. the musculature is represented by separate bundles, and not by a bag like in worms.

body cavity. The body cavity of Arachnids is mixed - mixocoel.

Digestive system typical, consists of front, middle and rear intestines. The foregut is represented mouth, throat, short esophagus and stomach. The mouth is surrounded by chelicerae and pedipalps, with which spiders grab and hold prey. The pharynx is equipped with strong muscles for the absorption of food gruel. Ducts open into the foregut salivary glands, the secret of which effectively breaks down proteins. All spiders have the so-called extraintestinal digestion. This means that after killing the prey, digestive juices are introduced into the body of the victim and the food is digested outside the intestines, turning into a semi-liquid slurry, which is absorbed by the spider. In the stomach, and then in the middle intestine, food is absorbed. The midgut has long blind lateral protrusions, which increase the area of ​​absorption and serve as a place for temporary storage of food mass. This is where the ducts open. liver. It secretes digestive enzymes and also provides absorption nutrients. Intracellular digestion takes place in the liver cells. At the border of the middle and posterior sections, the excretory organs flow into the intestine - malpighian vessels. The hindgut ends anus located at the posterior end of the abdomen above the arachnoid warts.

Respiratory system . Some arachnid organs breathing are presented lung sacs, other's tracheal system, the third - both those and others at the same time. Some small arachnids, including some mites, have no respiratory organs; breathing is carried out through thin covers. The lung sacs are more ancient (from an evolutionary point of view) formations than the tracheal system. It is believed that the gill limbs of the aquatic ancestors of arachnids plunged into the body and formed cavities with lung leaflets. The tracheal system arose independently and later than the lung sacs, as organs more adapted to air breathing. The tracheae are deep protrusions of the cuticle into the body. The tracheal system is perfectly developed in insects.

Class Arachnids Cross-spider

In the Cross-Spider, the respiratory organs are represented by a pair lung sacs, forming leaf-like folds on the ventral side of the abdomen, and two bundles trachea that open spiracles also on the underside of the abdomen.

Circulatory system open, comprises hearts, located on the dorsal side of the abdomen, and several large blood vessels extending from it vessels. The heart has 3 pairs of ostia (holes). From the anterior end of the heart anterior aorta disintegrating into arteries. Terminal branches of arteries pour out hemolymph(this is the name of the blood in all arthropods) into the system cavities located between the internal organs. Hemolymph washes all internal organs, delivering nutrients and oxygen to them. Further, the hemolymph washes the lung sacs - gas exchange occurs, and from there it enters pericardium, and then through ostia- in the heart. The hemolymph of arachnids contains a blue respiratory pigment - hemocyanin, containing copper. Pouring into the secondary body cavity, the hemolymph mixes with the secondary cavity fluid, therefore they say that arthropods have a mixed body cavity - mixocell.

excretory system in arachnids is represented malpighian vessels, which open into the intestine between the midgut and hindgut. Malpighian vessels, or tubules, are blind protrusions of the intestine that provide absorption of metabolic products from the body cavity. In addition to Malpighian vessels, some arachnids also have coxal glands- paired saccular formations lying in the cephalothorax. Convoluted canals depart from the coxal glands, ending bladders and excretory ducts, which open at the base of the walking limbs (the first segment of the walking legs is called coxa, hence the name - coxal glands). The spider-cross has both coxal glands and malpighian vessels.

Nervous system. Like all Arthropods, Arachnids nervous system - ladder type. But in Arachnids, there was a further concentration of the nervous system. A pair of supraesophageal nerve ganglia is called the "brain" in arachnids. It innervates (governs) the eyes, chelicerae and pedipalps. All cephalothoracic nerve ganglia of the nerve chain merged into one large nerve ganglion located under the esophagus. All abdominal nerve ganglia of the nerve chain also merged into one large abdominal ganglion.

From all senses highest value for spiders has touch. Numerous tactile hairs - trichobothria- scattered in large numbers over the surface of the body, especially on the pedipalps and walking legs.

Class Arachnids Cross-spider

Each hair is movably attached to the bottom of a special hole in the integument and is connected to a group of sensitive cells located at its base. The hair perceives the slightest vibrations of the air or the web, sensitively reacting to what is happening, while the spider is able to distinguish the nature of the irritating factor by the intensity of the vibrations. Tactile hairs are specialized: some register chemical stimuli, others - mechanical, others - air pressure, fourth - perceive sound signals.

The organs of vision are represented simple eyes found in most arachnids. Spiders usually have 8 eyes. Spiders are myopic, their eyes perceive only light and shadow, the outlines of objects, but details and color are not available to them. There are organs of balance - statocysts.

Reproduction and development. arachnids separate sexes. Fertilization internal. Most arachnids lay eggs, but live births have been observed in some arachnids. Development without metamorphosis.

The Cross-Spider has a well-defined sexual dimorphism: the female has a large abdomen, while mature males develop on pedipalps copulatory organs. In each species of spider, the copulatory organs of the male approach the epigyne of the female like a key to a lock, and the structure of the copulatory organs of the male and the epigyne of the female is species-specific.

Cross-spiders mate in late summer. Sexually mature males of trapping nets do not weave. They wander in search of the webs of females. Having found the trapping net of a sexually mature female, the male somewhere aside on the ground, or on some twig, or on a leaf weaves a small spermatic reticulum in the form of a hammock. On this mesh, the male from his genital opening, which is located on the ventral side of the abdomen closer to the junction of the abdomen with the cephalothorax, squeezes out a drop sperm. Then he sucks this drop into the pedipalps (like a syringe) and proceeds to seduce the female. The spider's eyesight is weak, so the male needs to be very careful so that the female does not mistake him for prey. To do this, the male, having caught some insect, wraps it in a web and presents this kind of gift to the female. Hiding behind this gift as a shield, the male very slowly and very carefully approaches his lady. Like all women, the spider is very curious. While she is looking at the presented gift, the male quickly climbs onto the female, puts his pedipalps with sperm on the female's genital opening and

Class Arachnids Cross-spider

performs copulation. The female at this moment is good-natured and relaxed. But, immediately after mating, the male must hastily leave, since the behavior of the spider after copulation changes dramatically: it becomes aggressive and very active. Therefore, slow males are often killed by the female and eaten. (Well, after mating, the male will still die. From an evolutionary point of view, the male is no longer needed: he has fulfilled his biological function.) This happens in almost all species of spiders. Therefore, in studies, females are most often found, while males are rare.

After copulation, the female continues to feed actively. In autumn, a female from a special web makes cocoon in which it lays several hundred eggs. She hides the cocoon in some secluded place, for example, under the bark of a tree, under a stone, in the cracks of a fence, etc., and the female herself dies. Cross-spider eggs overwinter. In the spring, young spiders emerge from the eggs, which begin an independent life. Shedding several times, the spiders grow and reach sexual maturity by the end of summer and start breeding.

Meaning. The role of spiders in nature is great. They act as consumers of the second order in the structure of the ecosystem (i.e., consumers of organic matter). They destroy many harmful insects. They are food for insectivorous birds, toads, shrews, snakes.

Questions for self-control

Name the classification of the phylum Arthropoda.

What is the systematic position of the Spider-cross?

Where do cross spiders live?

What body shape do cross spiders have?

What is the body of a spider covered with?

What body cavity is characteristic of a spider?

What is the structure of the digestive system of a spider?

What are the digestive characteristics of spiders?

What structure does circulatory system spider?

How does a spider breathe?

What is the structure of the excretory system of a spider?

What is the structure of the nervous system of a spider?

What is the structure of the reproductive system of a spider?

How does the cross-spider reproduce?

What is the importance of spiders?

Class Arachnids Cross-spider

Rice. Spider-cross: 1 - female, 2 - male and wheel-shaped trapping net.

Rice. Spider-cross weaves a trapping web

Class Arachnids Cross-spider

Rice. Internal structure Spider-cross.

1 - poisonous glands; 2 - throat; 3 - blind outgrowths of the intestine; 4 - malpighian vessels; 5 - heart; 6 - lung sac; 7 - ovary; 8 - oviduct; 9 - spider glands; 10 - pericardium; 11 - ostia in the heart.

OVERVIEW OF THE CLASS ARCHITECATES FROM THE TYPE Arthropoda

Arachnids or arachnids are a collection of all terrestrial chelicerae. There are about 60 thousand species of them, very different in appearance. The branch of zoology devoted to the study of arachnids is called arachnology.

They distinguish from 9-13 orders of modern arachnids and several fossil orders. 6 squads generally accepted: scorpions, ticks, salpugs, false scorpions, haymakers and spiders.

Arachnids are descended from aquatic arthropods from the class Racoscorpion, which gradually came to life on land. The morpho-physiological adaptations of arachnids to life on land are not yet sufficiently perfect, therefore arachnids, as a rule, prefer such terrestrial biotopes that are less prone to drying out, some are nocturnal.

Cross spiders are a genus of the class of arachnids with about 2 thousand species. They are widespread and are typical representatives of their class.

Crosses live in forests, gardens, meadows. Weave a web between branches, on buildings, etc. They feed on small insects.

The size of representatives of cross-spiders is from 1.5 to 4 cm in females and about 1 cm in males.

The chitinous cuticle of cross spiders is quite thin. The body is subdivided into a small, slightly elongated, non-segmented cephalothorax and a large, in comparison with it, non-segmented, rounded abdomen. A lighter pattern in the form of a cross is formed on top of the abdomen. Hence the name of these spiders.

There are four pairs of walking legs on the cephalothorax. In front of them are chelicerae (jaws) and pedipalps (mandibles). With the help of the first, the cross-spider kills the victim. Their terminal segments are transformed into claws, in which ducts of poisonous glands open. The poison has a paralyzing effect. Pedipalps are used to hold the victim, turn it over, and they also have many organs of touch.

At the end of the abdomen there are six arachnoid warts (three pairs). They open the ducts of the spider glands, which can be about 1000. Cross spiders secrete various types of webs. Some are sticky, others are more durable. When released, the web hardens in air, turning into a fairly strong thread. Spiders weave trapping nets, shelters, cocoons from the web, bind the victim with it. The trapping web of the spider-cross consists of a strong polygonal base and radial supports and sticky concentric circles. From the central part of the network, a thread departs to the spider's shelter. The oscillations of the web when the victim hits it are transmitted along this thread to the spider, and it crawls out of the shelter.

The spider-cross injects into the victim not only poison, but also digestive juices, which break down its tissues, turning it into a liquid slurry. Extraintestinal digestion lasts about an hour. The spider can only eat liquid food, which is completely digested inside it. digestive system. The suction of food occurs due to the muscular pharynx. There is a stomach, a branched midgut, into which the ducts of the liver open. Here, nutrients are absorbed into the hemolymph (arthropod blood mixed with lymph). Undigested residues go into the hindgut and are excreted through the anus.

The circulatory system is characteristic of all arthropods: open. On the dorsal side of the abdomen there is a tubular heart. From the heart, the hemolymph is pushed through the vessels to the front of the body, then it pours into the spaces between the organs and flows in the abdominal direction, where it is enriched with oxygen. After that, the hemolymph is again collected in the vessels and sent to the heart.

The respiratory system of the spider-cross consists of a pair of lung sacs and trachea. The lungs are located in the anterior part of the abdomen, contain many leaf-like folds, in which a lot of hemolymph flows. Tracheas are thin bundles of tubes that run through the body. They do not need hemolymph as an intermediary for the transfer of oxygen.

In cross-spiders, the excretory organs are represented by malpighian vessels, whose ducts open into the extension of the hindgut (cloaca), and coxal glands, the ducts of which open at the base of the first pair of walking legs.

In the ventral nerve chain in cross-spiders, the ventral ganglia merge. There are 8 simple eyes, which, like all arachnids, see poorly. The organs of touch, represented by sensitive hairs, are well developed. There are organs of smell and chemical sense.

Spider-spiders have pronounced sexual dimorphism. Females are larger and kill males after fertilization. The sex glands are paired, their common duct opens on the abdomen. The male delivers his sexual products to the female with the help of pedipalps. After fertilization, the female spins a cocoon using a soft silky web. Then it lays eggs in a cocoon, in which small spiders develop, i.e., the development of cross-spiders is direct.

Sections: Biology

Class: 7

Goals and objectives of the lesson

Educational:

• Formation of knowledge about the structural features and life processes of the spider-cross in connection with the ground-air habitat.

Educational:

• Education of observation.
• Formation of motivation to work with additional literature.
• Education of work culture.

Developing:

• Develop students' cognitive processes.
• To develop the concepts of "relationship of structure and function", "adaptability of the structure of the body to the way of life."
• Ability to compare, compare, draw conclusions, independently work with a textbook.

Equipment

• Table "Type of arthropods. Class Arachnids. Cross-spider".
• Video "Class Arachnids".
• Table "Type of arthropods. Class crustaceans. Crayfish".
• Multimedia. Presentation
• Television.
• Video recorder.

Lesson Plan

I. Organization of the lesson.

Greeting, checking absent in the lesson, school supplies from students.

II. Updating the knowledge, skills and abilities of students.

Programmed survey of students on the topic: "Type of arthropods. Class Crustaceans"

Match definitions and terms.

Mutual verification of students' work using a sample of correct answers on the screen through a projector prepared by the teacher using multimedia (slide 1).

III. Learning new material.

Tell me, what type of animals did we start acquaintance with?

Name the characteristics of the arthropod type.

We continue our acquaintance with the type of arthropods. Pay attention to the screen. I suggest you solve riddles. Who is it? (slide 2).

Not for fish, but for setting up nets? (spider)

On a shelf in a corner, is a sieve hanging not twisted by hand? (web)

As you already understood, the lesson will focus on spiders and cobwebs.

The topic of our lesson:"Class arachnids. Lifestyle and external structure of the spider - cross"

The explanation of the new material is accompanied by multimedia (slide 3).

"Ugh! Spider!" - the man cries out, and now the crunch of the calf of this animal crushed by the foot is already heard. A person experiences an inexplicable disgust, and sometimes fear when meeting with spiders. Spiders are familiar to everyone, and at the same time how little we know about this amazing, interesting and diverse group of animals (slide 4).

Acquaintance with representatives of arachnids (student presentation). (slide 5-8).

Communication of the objectives of the lesson.

Teacher: Today in the lesson we will get acquainted with the main features of the arachnid class using the example of a spider - a cross.

The Latin name for spiders is Arachnida. Where did the name of spiders come from? (slide 9).

The legend is told by the teacher against the background of slow music.

The ancient Greek myth about Arachne, the daughter of a craftsman, who studied weaving with the goddess Athena, is known. She began to boast of the art of the weaver and even challenged Athena herself to a competition. Enraged, Athena turned the craftswoman into a spider. According to legend, when classifying spiders, they received the name Arachnida.

The spider is an interesting animal in many ways. What is the structure of a spider? To answer this question, let's look at the table. A typical representative is the spider - cross. Why? (slide 10)

Habitat and features external structure spider-cross(slide 11)

To clarify the habitat and features of the external structure of the cross-spider, let's turn to the textbook. On page 121 you will find the answers to the questions you have been asked.

Independent work with the textbook page 121.

• Prepare answers to questions (the questions are on the tables of the children):
• How many body parts does a spider have? What are their names?
• How many pairs of walking legs does a spider have? What part of the body are they attached to? Pay attention to sensitive hairs and nails on the limbs.
• Why are spiders classified as arthropods?
• What organs can be seen on the head of a spider? Do spiders have antennae? How many eyes and what types of eyes does a spider have?
• Is it possible to see the segmentation of the abdomen in a spider? Are there limbs on the abdomen?

Work with students on questions. Evaluation of responses.

Generalization of the teacher (story according to the table "Type Arthropods. Class Arachnids. Spider - cross")

We have described the structural features of the spider - cross, and now we will depict the external structure of the spider in a notebook.

Independent work in notebooks page 25 fig.19. "Scheme of the external structure of the cross-spider".

Examination independent work according to the reference picture (slide 12).

Picture 1

Based on the diagram, we conclude that:

Spiders are eight-legged arthropods with 2 body parts: a fused abdomen and cephalothorax, 8 simple eyes, no antennae.

What are the differences and similarities in the external structure of cancer and spider - cross. (slide 13-14)

II part of the study of new material

P h i s c u l t m i n t k a

Features of the internal structure of the spider - cross in comparison with crayfish.

Hunting and feeding of a spider - a cross.

Teacher: Spiders survive where others die - in the highlands, caves. Why?

They can go several weeks without food.

There are 2 distinctive features in spiders:

1. They all spin a web
2. Poisonous.

What is a web and why is it needed? (student's message)

Look at the screen. Pay attention to how the spider kills the victim? (watching a movie)

Filling out the scheme in students' notebooks page 25 scheme 14.

Features of the digestive system of the spider - cross: (slide 15)

Figure 2

Conclusion by students: nutrition begins outside the body under the influence of poison and saliva. Spiders feed on liquid, partially digested food.

How does crayfish eat? What is the difference between the digestive system of a cancer and the digestive system of a spider?

Spider habitat

What is the habitat of spiders? Why? (slide 16)

Respiratory organs: 1) lungs: bags, 2) trachea. Gas exchange takes place in them. They breathe oxygen in the air.

Name the respiratory organs of cancer.

The circulatory system of spiders (slide 17)

What is the circulatory system of cancer?

The circulatory system of spiders is open, the heart is in the form of a tube, the liquid is hemolymph.

Organs of excretion of spiders (slide 18)

Name the excretory organs of cancer.

In a spider, the excretory organs are the Malpighian vessels.

spider nervous system

What is the nervous system of cancer?

In a spider, the nervous system consists of: cephalothoracic ganglion + nerves.

Reproductive system (slide 19)

In spiders, the female sex glands are the ovaries. The male sex glands are the testes.

Independent work with the textbook.

How does the reproduction and development of spiders occur? How Do Crayfish Reproduce?

Conclusion: spiders are characterized by sexual dimorphism. Internal fertilization in connection with life on land, the laying of eggs by the female in a cocoon woven from cobwebs, the appearance of spiderlings in the spring of next year.

IV. Lesson summary

Let's summarize what we learned and learned in the lesson. To do this, let's run a test.

Mutual verification of students' work using a sample of correct answers on the screen through multimedia (slide 20).

V. D/z

Homework instruction. Recording from the board in diaries. Mutual check about D / z (slide 21).

• paragraph 25, pages 120 - 124,
• Message (further reading) - "5",
• Task 2 p.126 - "4",
• Task 4 p. 126 - "3".

Literature

1. Biology. Animals. Textbook for grade 7 / V.N. Konstantinov, V.S. Kuchmenko and N. Ponomareva. - "Ventana - Count", 2005.
2. Biology. Handbook for the teacher. Moscow 1995.
3. Journal "Biology at school", No. 6 Moscow "School - press", 1995.
4. Teacher's book "I'm going to biology lesson", Moscow, 1999.

The cross-spider can be found in the forest, park, on the window frames of village houses and cottages. Most of the time, the spider sits in the center of its trapping web of sticky thread - cobwebs.

The body of the spider consists of two sections: a small elongated cephalothorax and a larger spherical abdomen. The abdomen is separated from the cephalothorax by a narrow constriction. Four pairs of walking legs are located on the sides of the cephalothorax. The body is covered with a light, strong and rather elastic chitinous cover.

The spider periodically molts, shedding its chitinous cover. During this time it grows. At the front end of the cephalothorax there are four pairs of eyes, and below a pair of hook-shaped hard jaws - chelicerae. With them, the spider grabs its prey.

There is a canal inside the chelicerae. Through the channel, the poison from the poisonous glands located at their base enters the body of the victim. Next to the chelicerae are short, covered with sensitive hairs, the organs of touch - the leg tentacles.

At the lower end of the abdomen there are three pairs of arachnoid warts that produce cobwebs - these are modified abdominal legs.

The liquid released from the spider webs instantly hardens in the air and turns into a strong cobweb thread. Various parts of arachnoid warts secrete cobwebs different types. Spider threads vary in thickness, strength, stickiness. different types The spider uses cobwebs to build a trapping net: at its base, more durable and non-sticky threads, and concentric threads are thinner and stickier. The spider uses the web to strengthen the walls of its shelters and to make cocoons for its eggs.

Internal structure

Digestive system

The digestive system of a spider consists of a mouth, pharynx, esophagus, stomach, intestines (anterior, middle and posterior). In the midgut, long blind outgrowths increase its volume and absorption surface.

Undigested residues are brought out through the anus. The spider cannot eat solid food. Having caught prey (any insect), with the help of a web, he kills it with poison and lets digestive juices into his body. Under their influence, the contents of the caught insect liquefies, and the spider sucks it up. Only an empty chitinous shell remains from the victim. This type of digestion is called extraintestinal.

Circulatory system

The spider's circulatory system is not closed. The heart looks like a long tube located on the dorsal side of the abdomen.

Blood vessels branch off from the heart.

A spider has a body cavity mixed nature- in the course of development, it occurs when the primary and secondary cavities of the body are connected. Hemolymph circulates in the body.

Respiratory system

The respiratory organs of the spider are the lungs and trachea. Lungs, or lung sacs, are located below, in front of the abdomen. These lungs evolved from the gills of the distant ancestors of aquatic spiders.

The spider-cross has two pairs of non-branching tracheas - long tubes that deliver oxygen to organs and tissues. They are located in the back of the abdomen.

Nervous system

The nervous system of a spider consists of the cephalothoracic ganglion and numerous nerves extending from it.

excretory system

The excretory system is represented by two long tubules - Malpighian vessels. With one end, the Malpighian vessels blindly end in the body of the spider, with the other they open into the posterior intestine. Out through the walls of the Malpighian vessels harmful products life, which are then brought out. Water is absorbed in the intestines. Thus, spiders conserve water, so they can live in dry places.

Reproduction. Development

Fertilization in spiders is internal. The female cross spider is larger than the male. The male carries the spermatozoa into the female genital opening with the help of special outgrowths located on the front legs.

She lays her eggs in a cocoon woven from a thin silky cobweb. The cocoon weaves in various secluded places: under the bark of stumps, under stones. By winter, the female cross spider dies, and the eggs hibernate in a warm cocoon. In the spring, young spiders come out of them. In autumn, they release cobwebs, and on them, like on parachutes, they are carried by the wind over long distances - spiders are resettled.

Representatives of arachnids are eight-legged land arthropods, in which the body is divided into two sections - the cephalothorax and abdomen, connected by a thin constriction or fused. Arachnids do not have antennae. Six pairs of limbs are located on the cephalothorax - two front pairs (mouth organs), which serve to capture and grind food, and four pairs of walking legs. There are no legs on the abdomen. Their respiratory organs are lungs and trachea. The eyes of arachnids are simple. Arachnids are dioecious animals. The class Arachnida includes more than 60 thousand species. The body length of various representatives of this class is from 0.1 mm to 17 cm. They are widely distributed throughout the globe. Most of them are land animals. Among ticks and spiders there are secondary water forms.

The biology of arachnids can be considered using the example of a spider-cross.

External structure and lifestyle. The cross-spider (so named for the cross-shaped pattern on the dorsal side of the body) can be found in the forest, garden, park, on the window frames of village houses and cottages. Most of the time, the spider sits in the center of its trapping web of sticky thread - cobwebs.

The body of the spider consists of two sections: a small elongated cephalothorax and a larger spherical abdomen (Fig. 90). The abdomen is separated from the cephalothorax by a narrow constriction. At the anterior end of the cephalothorax, there are four pairs of eyes above, and below, a pair of hook-shaped hard jaws - a chelicerae. With them, the spider grabs its prey. There is a canal inside the chelicerae. Through the channel, poison from the poisonous glands located at their base enters the body of the victim. Next to the chelicerae are short, covered with sensitive hairs, the organs of touch - the leg tentacles. Four pairs of walking legs are located on the sides of the cephalothorax. The body is covered with a light, strong and rather elastic chitinous cover. Like crayfish, spiders periodically molt, dropping their chitinous cover. At this time they are growing.

Rice. 90. The external structure of the spider: 1 - leg tentacle; 2 - leg; 3 - eye; 4 - cephalothorax; 5 - abdomen

At the lower end of the abdomen there are three pairs of arachnoid warts that produce cobwebs (Fig. 91) - these are modified abdominal legs.

Rice. 91. Trapping nets of various types of spiders (A) and the structure (with magnification) of the spider web (B)

The liquid released from the spider web warts instantly hardens in the air and turns into a strong spider web. Different parts of spider warts secrete different types of webs. Spider threads vary in thickness, strength, stickiness. The spider uses various types of webs to build a trapping web: at its base, the threads are stronger and not sticky, and the concentric threads are thinner and stickier. Spiders use the web to strengthen the walls of their shelters and to make cocoons for their eggs.

Digestive system the spider consists of a mouth, pharynx, esophagus, stomach, intestines (Fig. 92). In the midgut, long blind outgrowths increase its volume and absorption surface. Undigested residues are brought out through the anus. The cross spider cannot eat solid food. Having caught prey, such as some kind of insect, with the help of a web, he kills him with poison and lets digestive juices into his body. Under their influence, the contents of the caught insect liquefies, and the spider sucks it out. Only an empty chitinous shell remains from the victim. This type of digestion is called extraintestinal.

Rice. 92. The internal structure of the spider-cross: 1 - poisonous gland; 2 - mouth and esophagus; 3 - stomach; 4 - heart; 5 - lung sac; 6 "- sex gland; 7 - trachea; 8 - spider gland; 9 - intestine; 10 - Malpighian vessels; 11 - outgrowths of the intestine

Respiratory system. The respiratory organs of the spider are the lungs and trachea. Lungs, or lung bags, are located below, in front of the abdomen. These lungs evolved from the gills of distant ancestors of aquatic spiders. The spider-cross has two pairs of non-branching tracheas - long tubes that deliver oxygen to organs and tissues. They are located in the back of the abdomen.

Circulatory system spiders are open. The heart looks like a long tube located on the dorsal side of the abdomen. Blood vessels branch off from the heart.

In a spider, as in crustaceans, the body cavity is of a mixed nature - in the course of development it arises when the primary and secondary cavities of the forehead are connected. Hemolymph circulates in the body.

excretory system It is represented by two long tubes - Malpighian vessels.

With one end, the Malpighian vessels blindly end in the body of the spider, with the other they open into the posterior intestine. Through the walls of the Malpighian vessels, harmful waste products come out, which are then brought out. Water is absorbed in the intestines. In this way, spiders conserve water, so they can live in dry places.

Nervous system The spider consists of the cephalothoracic ganglion and numerous nerves extending from it.

Reproduction. Fertilization in spiders is internal. The male carries the spermatozoa into the female genital opening with the help of special outgrowths located on the front legs. The female, some time after fertilization, lays eggs, braids them with cobwebs and forms a cocoon (Fig. 93).

Rice. 93. Female spider with a cocoon (A) and the resettlement of spiders (B)

The eggs develop into small spiders. In autumn, they release cobwebs, and on them, like on parachutes, they are carried by the wind over long distances - spiders are resettled.

Variety of arachnids. In addition to the cross-spider, about 20 thousand more species belong to the order Spiders (Fig. 94). A significant number of spiders build trapping webs from the web. Y different web spiders differ in shape. So, in a house spider living in a person’s housing, the trapping net resembles a funnel, in a poisonous, deadly for humans karakurt, the trapping net resembles a rare hut. Among spiders there are also those that do not build trapping webs. For example, side-walker spiders sit in ambush on flowers and wait for small insects arriving there. These spiders are usually brightly colored. Jumping spiders are able to jump and thus catch insects.

Rice. 94. Various spiders: 1 - cross-spider; 2 - karakurt; 3 - spider regiment; 4 - crab spider; 5 - tarantula

Wolf spiders roam everywhere looking for prey. And some spiders sit in minks in ambush and attack insects crawling nearby. These include a large spider that lives in southern Russia - a tarantula. The bites of this spider are painful for humans, but not fatal. The Haymakers include very long-legged arachnids (about 3,500 species) (Fig. 95, 2). Their cephalothorax is indistinctly separated from the abdomen, the chelicerae are weak (therefore, haymakers feed on small prey), the eyes are located in the form of a “turret” on top of the cephalothorax. Harvestmen are capable of self-mutilation: when a predator grabs a haymaker by the leg, he discards this limb, and he runs away. Moreover, the severed leg continues to bend and unbend - “mow”.

Scorpions are well represented in the subtropics and deserts by small animals 4-6 cm long (Fig. 95, 3). Large scorpions up to 15 cm long live in the tropics. The body of a scorpion, like that of a spider, consists of a cephalothorax and abdomen. The abdomen has a fixed and wide anterior part and a narrow, long movable posterior part. At the end of the abdomen there is a swelling (the poisonous gland is located there) with a sharp hook. With it, the scorpion kills its prey and defends itself from enemies. For a person, the injection of a large scorpion with a poisonous sting is very painful, and can lead to death. The chelicerae and tentacles of scorpions are claw-shaped. However, chelicerae claws are small, while leg tentacle claws are very large and resemble those of crayfish and crabs. In total, there are about 750 species of scorpions.

Rice. 95. Various representatives of arachnids: 1 - tick; 2 - haymaker; 3 - scorpion; 4 - phalanx

Ticks. There are more than 20 thousand species of ticks. The length of their body usually does not exceed 1 mm, very rarely - up to 5 mm (Fig. 95, 1 and 96).

Unlike other arachnids, ticks do not have a body divided into cephalothorax and abdomen. Ticks that feed on solid food (microscopic fungi, algae, etc.) have gnawing jaws, while those that feed on liquid food form a piercing-sucking proboscis. Ticks live in the soil, among fallen leaves, on plants, in water, and even in human homes. They feed on decaying plant remains, small mushrooms, algae, invertebrates, suck plant sap; in living quarters of people, microscopic mites feed on dry organic residues contained in dust.

Rice. 96. Ixodid tick

The meaning of arachnids. Arachnids play a big role in nature. Known among them are both herbivores and predators that eat other animals. Arachnids, in turn, feed on many animals: predatory insects, birds, animals. Soil mites are involved in soil formation. Some ticks are carriers of serious diseases of animals and humans.

Arachnids are the first terrestrial arthropods that have mastered almost all habitat conditions. Their body consists of the cephalothorax and abdomen. They are well adapted to life in the ground-air environment: they have dense chitinous covers, they have pulmonary and tracheal breathing; save water, play an important role in biocenoses, have importance for a person.

Lesson learned exercises

1. What are the signs of the external structure of arachnids that distinguish them from other representatives of arthropods
2. Using the example of a spider-cross, tell about the methods of obtaining and digesting food. How are these processes related to the internal organization of the animal?
3. Give a description of the structure and activity of the main organ systems, confirming the more complex organization of arachnids compared to annelids.
4. What is the importance of arachnids (spiders, ticks, scorpions) in nature and human life?