Class arachnids biology. Excretory and reproductive systems of arachnids What kind of breathing do arachnids have

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. Various parts of arachnoid warts secrete cobwebs different types. Spider threads vary in thickness, strength, stickiness. Various types The spider uses cobwebs to build a trapping net: 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. Internal structure 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. Out through the walls of the Malpighian vessels harmful products life, 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 spiders webs vary in shape. So, in a house spider living in a person’s housing, 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 - spider-cross; 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 rotting plant debris, small fungi, algae, invertebrates, suck plant sap; in human living quarters, 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 important role in biocenoses, are important for humans.

Lesson learned exercises

1. What are the signs external structure arachnids, distinguishing 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 internal organization 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?

Arachnoids, or arachnids, are one of the most ancient living creatures on Earth. Character traits the structures of arachnids are due to existence on land and a predatory lifestyle.

External structure

The external structure of arachnids is different. In spiders, the body is divided into sections:

• elongated cephalothorax;
• wide belly.

Between the two parts of the body is a narrow constriction. The cephalothorax is equipped with organs of vision and digestion. Spiders have several simple eyes (from 2 to 12) that provide a circular view.

On the sides of the mouth grow hard curved jaws - chelicerae . With them, the predator grabs its prey. Chelicerae are equipped with venom ducts that are injected into the body at the time of the bite. The first pair of limbs serves to protect during an attack.

The oral apparatus of arachnids is complemented by a second pair - leg tentacles . With them, the spider holds the victim while eating. They also function as organs of touch. The mouth tentacles are covered with many villi. The hairs sensitively pick up the slightest vibrations of the surface and air, help the spider to navigate in space, to feel the approach of other creatures.

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To the question: how many antennae a spider has, it is not difficult to answer. Arachnids do not have antennae.

On the sides of the cephalothorax are 4 pairs of limbs. The comb claws on the hind legs are designed for weaving webs.

It is visually easy to see what cover the spiders have on their bodies. They are protected by a strong chitinous shell. In the process of growth, it periodically changes during molting.

Rice. 1 Spider - cross

Internal structure

The peculiarity of the structure of arachnids is noticeable in the organization of the body cavity. It is a combination of primary and secondary cavity. The body is filled with hemolymph. The heart is located in the dorsal part of the abdomen and looks like a long tube. Blood vessels branch off from it. Circulatory system is not closed.

Spider blood is colorless.

Respiratory system presented:

• tracheae ;
• lung sacs .

Breathing is adapted to life on land. Spiders breathe with the help of trachea, which resemble two long tubes with numerous holes. They carry oxygen to the internal organs.

Digestive system comprises:

• mouth ;
• pharynx ;
• stomach ;
• anterior, middle and hindgut ;
• cesspools .

excretory system arachnids arranged in an unusual way. The excretory organs are two Malpighian vessels. These are tubes at one end that go into the internal cavity of the body, and at the other - into the intestines. Waste materials pass through the walls of blood vessels. The end products are brought out, and the liquid remains inside the body. Thus, the spiders retain moisture and can for a long time live in dry conditions.

Let's study what nervous system in arachnids. It is called nodal because main center forms 5 pairs of nerve nodes. A nerve chain runs along the abdomen.

IN sexual reproduction both males and females participate. Females are larger in size and often eat a partner. After fertilization, the female lays eggs and weaves a cocoon around them.

Rice. 2 Cocoon

The maximum number of eggs is 20 thousand.

After the appearance of the offspring, the mother looks after him for some time. The development of the young depends on the variety.

Web

Creation

Spiders have their own hunting equipment - a hunting net, in the form of a web. On the abdomen are arachnoid warts, equipped with special glands. A thin, but extremely strong thread is produced from them. The glands of arachnids produce a special substance that quickly hardens in the air. The web thread has different characteristics and purpose:

• non-adhesive, but strong for the network frame;
• adhesive and thin for mesh cells;
• soft for a cocoon with eggs and burrow walls.

Rice. 3 Web

Meaning

Spiders set their traps among the thickets and hide in a secluded place. When an insect enters the net, the vibrations of the threads inform the hunter about the prey. He tightly wraps the victim with a sticky substance and then injects a poisonous secret into it. This fluid acts like digestive juice. She softens the prey. After that, the predator sucks in the resulting slurry. This method of nutrition is called extraintestinal.

The thread helps the spider move in space. With her help, he descends from a height, finds a way to his shelter.

A giant web has been discovered in Madagascar. It was woven by Darwin's spider. The diameter of a miracle is a network of 25 meters.

Spider thread in its appearance and properties resembles silk. Residents of tropical islands make small fishing nets from it. In the old days, cobwebs were applied to wounds instead of dressings.

What have we learned?

The body of arachnids consists of several connected parts. Distinctive features structures: oral limbs with poisonous ducts, extraintestinal digestion, the presence of arachnoid glands.

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excretory system. The excretory system is represented by the Malpighian vessels, which are a neoplasm in Arachnoidea, and the coxal glands, which correspond to the coelomoducts. Malpighian vessels - a pair of branching, blindly closed tubes at the ends, open at the border of the middle and posterior intestines.

They are of endodermal origin, that is, they belong to the middle intestine. Grains of guanine, the main excretory product of arachnids, accumulate in the epithelium and lumen of the Malpighian vessels. The coxal glands are formed by the sac-like part of mesodermal origin, the convoluted duct (labyrinth), the reservoir, and the external excretory duct. They are available in one or two pairs, open at the bases of the legs and rarely function in adult forms.

reproductive system. Arachnids have separate sexes. The sex glands are located in the abdomen and in the initial state of the pair. In some cases, there is a fusion of the right and left gonads. So, in a male scorpion, the testes are paired and each consists of two tubes connected by jumpers; in female scorpions, the ovary is one and consists of three tubes, of which the middle tube is obviously the result of the fusion of two medial tubes, similar to those of the male. In many spiders, harvestmen, and ticks, the paired gonads grow together at the ends into a ring. Paired oviducts and seminal ducts open with an unpaired genital opening, always on the second segment of the abdomen. The structure of the excretory part of the reproductive system and the copulatory adaptations of males are very diverse. Females usually have an extension of the oviducts - the uterus and seminal receptacles. In males, the copulatory organs are either associated with the genital opening, orserve as pedipalps (spiders) or chelicerae (some mites). In some cases, spermatophoric fertilization is carried out with the help of sperm packets.

Development. Most arachnids lay eggs, but there are also viviparous forms (scorpions, some ticks, etc.). Eggs are richyolk, due to which fragmentation is partial, superficial, all segments of the body and limbs are formed in embryonic development, and a small full-segment individual, similar to an adult, hatches from the egg. Post-embryonic development is direct, accompanied mainly by growth. Only in ticks, due to the small size of the eggs, a six-legged larva hatches and metamorphosis takes place. The study of the embryos of primitive arachnids allows us to better understand the structure of adults. So, in the embryo of scorpions, abdominal limbs are laid on all segments of the mesosome, from which the first pair then disappears, the second turns into genital covers, the third into ridge-shaped organs, and the remaining four pairs into lungs.

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 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, the blood returns to the heart from the mixed body cavity (myxocele), 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.

TO this class include arthropods adapted to living on land, breathing through the lungs and trachea. The class unites the detachments of spiders, ticks, scorpions, haymakers.

a brief description of

general characteristics

Structure and integument . For arachnids characteristic feature is a tendency to merge the segments of the body that form cephalothorax And abdomen. Scorpions have a fused cephalothorax and a segmented abdomen. In spiders, both the cephalothorax and the abdomen are continuous undivided sections of the body, between which there is a short stalk connecting these two sections. The maximum degree of fusion of body segments is observed in ticks, which have lost even the division of the body into the cephalothorax and abdomen. The body of ticks becomes whole without borders between segments and without constrictions.

The integument of arachnids is composed of cuticles, hypodermis And basement membrane. The outer layer of the cuticle is lipoprotein layer. This layer is very protects well from moisture loss during evaporation. In this regard, arachnids could become a real terrestrial group and settle in the most arid regions of the earth. The cuticle also contains proteins, tanned phenols And encrusting chitin, what gives the cuticle strength. The derivatives of the hypodermis are gossamer And poisonous glands.

Limbs. head limbs, except two pairs of jaws in arachnids missing. Jaws or, as a rule, refer to the limbs of the cephalothorax. The cephalothorax of arachnids bears 6 pairs of limbs What is a hallmark of this class. The two front pairs are fitted

to capture and crush food - chelicerae And pedipalps(Fig. 1). Chelicerae, which look like short claws, are located in front of the mouth. In spiders, chelicerae end in a claw, near the top of which there is a hole venom gland. Second pair - pedipalps, on the main segment have chewing outgrowth, with which food is crushed and kneaded. In some species, the pedipalps turn into powerful claws(like scorpions) or like walking legs and in some forms of spiders at the end of the pedipalp may be aggregative organ. The remaining 4 pairs of limbs of the cephalothorax perform the function of movement - this walking legs. During embryonic development, a large number of limbs are laid on the abdomen, but in adult chelicerates, the abdomen is devoid of typical limbs. If the abdominal limbs are preserved in the adult state, then they are usually modified in the genital lids, tactile appendages (scorpions), lung sacs or spider warts.

Rice. 1. Mouth organs of the cross spider: 1 - terminal claw-shaped segment of the chelicera; 2 - basal segment of helicerae; 3 - pedipalp; 4 - chewing outgrowth of the main segment of the pedi-palp; 5 - the main segment of the walking leg

Digestive system(Fig. 2) has features associated with a peculiar way of eating arachnids - extraintestinal, or external, digestion. Arachnids cannot take solid food pieces. Digestive enzymes are injected into the victim's body and turn its contents into a liquid slurry that is absorbed. Due to this throat has strong muscles And serves as a kind of pump that draws in semi-liquid food. midgut most arachnids have lateral blind-closed protrusions to increase the suction surface. Ducts open into the intestines in the abdomen steam liver. The liver performs not only digestive functions, releasing digestive enzymes, but also an absorption function. Intracellular digestion takes place in the liver cells. hindgut ends anus.

Respiratory system arachnids represented lung sacs And tracheae. However, some species have lung sacs only(scorpions, primitive spiders). In others, the respiratory organs are only tracheae

Rice. 2.Spider organization scheme: 1 - eyes; 2 - poisonous gland; 3 - chelicera; 4 - brain; 5 - mouth; 6 - subpharyngeal nerve node; 7 - glandular outgrowth of the intestine; 8 - bases of walking legs; 9 - lung; 10 - pulmonary opening - spiracle; 11 - oviduct; 12 - ovary; 13 - spider glands; 14 - arachnoid warts; 15 - anus; 16 - Malpighian vessels; 17 - os-ti; 18 - ducts of the liver; 19 - heart; 20 - pharynx connected with the body wall by muscles

(salpugs, haymakers, some ticks). In spiders, two types of respiratory organs occur simultaneously. Eat four-legged spiders who have 2 pairs of lung sacs and no trachea; bilung spiders- one pair of lung sacs and a pair of tracheal bundles and lungless spiders- only trachea. Some small spiders and some mites have no respiratory organs and respiration is carried out through the thin integuments of the body.

Circulatory system like all arthropods open. Hemolymph contains a respiratory enzyme hemocyanin.

Rice. 3.The structure of the heart in arachnids. A - scorpion; B - spider; B - tick; G - haymaker: 1 - aorta (arrows show ostia)

The structure of the heart depends on the degree of segmentation - the more segments, the more ostia (Fig. 3). In ticks that lack segmentation, the heart may completely disappear.

excretory system in adult arachnids is represented a pair of branching Malpighian vessels, opening at the border of the middle and hind intestines into the digestive system.

Nervous system arachnids, like circulatory, depends on the segmentation of the body. The least concentrated nerve chain in scorpions. In arachnids, the brain, unlike crustaceans and insects, consists of two sections - anterior and posterior, the middle region of the brain is absent, since arachnids do not have head limbs, antennules or antennae, which this region should control. There is a large ganglionic mass in the cephalothorax And ganglia of the abdominal chain. With a decrease in segmentation, the ventral chain disappears. So, in spiders, the entire abdominal chain merges into holothoracic ganglion. And in haymakers and ticks, the brain and cephalothoracic ganglion form a continuous ganglionic ring around the esophagus.

sense organs mainly represented special hairs, which are located on pedipalps, legs and trunk And react to air vibrations. On the pedipalps are also located sensory organs that perceive mechanical And tactile stimuli. organs of vision presented with simple eyes. The number of eyes can be 12, 8, 6, rarely 2.

Development . Most arachnids lays eggs, but also observed live birth. Development direct, but ticks have metamorphosis.