Abdomen of arachnids. Excretory and reproductive systems of arachnids. Features of the nervous system
Like any other living creatures, spiders are distinguished by various abilities, among which the ability to breathe stands out. Of course, the respiratory system of arachnids is significantly different from the breathing of other mammals, not to mention humans.
Respiratory system of spiders
It is worth noting that the respiration characteristic of spiders is not entirely clear even to specialists, since the process of oxygen and carbon dioxide exchange in these representatives of arachnids is quite interesting and difficult.
The main difference between the respiratory system of spiders and insects is that the breathing of spiders is directly related to the participation of blood in this process. The respiratory system of any insect is a rather complex system of a complex of tubes that permeate its body from all sides. In this case, the tubes form the trachea and are in close contact with the tissues.
The respiratory system of arachnids is a complex of five different systems, and their number depends on the taxonometric group. Much depends here, of course, also on the type of spider, since their large species have the most advanced respiratory system.
Trachea of arachnids
The trachea of spiders permeate the body of representatives of the class around the entire perimeter, thus forming the basis that the breath of spiders has. The tracheal tubes end near the tissues, which ensures their contact with each other. However, this contact is not close enough to supply oxygen to the respiratory system of spiders and remove carbon dioxide from it, as happens in the body of ordinary insects.
Accordingly, the breathing of spiders with the help of a tubular trachea occurs in a slightly different way. Usually there are no more than one or less often two holes in the tubular trachea, and they are displayed on the underside of the abdomen next to the appendages.
Thus, breathing is carried out, which is inherent specifically for arachnids.
Respiratory system. The respiratory organs of the cross are a pair of leaf-folded lungs and tubular tracheae. The lungs are located at the base of the abdomen on the sides of the genital opening, where there are two transverse slits - stigmas of the lungs.
The stigma leads to the lung cavity, on the wall of which there are a number of flat pockets that diverge in a fan-like fashion. The pockets are connected with jumpers and do not fall off, so that air freely penetrates between them. Blood circulates in the cavities of the pockets, the exchange of gases occurs through their thin cuticular walls.
The tracheal system consists of two non-branching tubes, which are directed forward from a common pocket, which opens with an inconspicuous transverse slit in front of the arachnoid warts.
excretory system. There are two types of excretory organs: Malpighian vessels and coxal glands. In addition, the excretory function is performed by special cells (nephrocytes and guanocytes) lying in the body cavity. The Malpighian vessels are represented by four branching tubes blindly closed at the ends, which flow into the rectal bladder along its sides at the border of the middle and posterior intestines. Malpighian vessels are lined with squamous epithelium, in the cells of which grains of guanine, the main excretion product, are formed. The coxal glands, which in arachnids are the remains of the coelomoduct system, are located at the base of the first pair of legs. In an adult spider, they do not function.
poison glands. Poisonous glands are located in the anterior part of the cephalothorax at the base of the chelicerae. This is a pair of rather large cylindrical glands that enter the cavity of the main segments of the chelicerae. The outer lining of the gland is formed by a spirally curled ribbon-like muscle, during the contraction of which the poison is poured out through a thin duct that opens at the end of the claw-like segment of the chelicerae.
Spinning apparatus. The spinning apparatus is represented by three pairs of spider warts and spider glands. At rest, spider warts, together with the anal tubercle, form a common closed group. At the tops of the warts there are numerous arachnoid tubes through which a secret is secreted - a web that hardens when it comes into contact with air. Spider glands fill the lower part of the female's abdominal cavity.
Their structure and size are not the same; distinguish tubular, ampulloidal, dendritic and pear-shaped glands. The latter are especially numerous and connected in bundles according to the number of warts (Plate X). The role of various glands and warts is different, the tubular glands secrete a web for the egg cocoon, the ampullic glands for building a network, the pear-shaped glands for braiding prey; arboreal secrete a sticky secret that covers the network.
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A feature of the Arachnida class is extraintestinal digestion. In addition, these animals have excretory organs that save water. Read more about the digestive and excretory systems of arachnids in this article.
Digestive system
The digestive system of arachnids includes the intestine, which consists of three sections: front, middle and back.
Anterior section presented in the form of a pharynx, which, narrowing, passes into a sucking stomach. Inside, the entire intestine is covered with a cuticle. The stomach itself is designed so that it is possible to suck out the contents of the victim. At the base of the pharynx, near the mouth opening, there are excretory channels, the so-called salivary glands.
middle department , located in the cephalothorax, has 5 pairs of glandular blind outgrowths. Their function, like the salivary glands, is to dissolve proteins. The secretion of these glands is injected into the victim, where extra-intestinal digestion takes place. The insides of the prey turn into a liquid slurry, which is absorbed through the stomach. In the abdominal region, the midgut is curved. Here, branching glandular appendages or the so-called liver open into it.
The main function of the liver is intracellular digestion and absorption of nutrients. In this place, food is finally digested under the influence of special enzymes.
Back department presented in the form of a rectum. On the border between the middle and posterior sections, the organs of excretion open - the Malpighian vessels. Residues from digestion and the secretion of the excretory vessels accumulate in the rectal bladder. Further, the waste is excreted through the rectum through the anal tubercle.
Fig.1. Digestive system (green)
excretory system
What is the excretory system of arachnids, it was said earlier - this is malpighian vessels. They are excretory tubes, which are immersed in the hemolymph with one blind end, and with the other open - in the intestine. Thus, metabolic products can be excreted through the walls of these vessels from the hemolymph and excreted through the intestines.
Fig.2. Malpighian vessels (9)
The excretion product is guanine. It, like uric acid, is slightly soluble, therefore it is removed in the form of crystals. At the same time, moisture losses are insignificant, and this is important for arachnids that have adapted to life on land.
Rice. 3. The structure of arachnids
In addition to the Malpighian vessels, young individuals also have coxal glands - paired sac-like formations. However, in adults, they completely or partially atrophy.
What have we learned?
The digestive system is adapted for extraintestinal digestion. For this, special enzymes are produced in the body of the spider, which are introduced into the body of the victim. The digestive organs themselves are equipped with a reinforced muscular system in order to be able to absorb the dissolved contents of the prey. The excretory organs are Malpighian vessels, which help to save excess moisture, and metabolic products are excreted through the intestines.
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Representatives of arthropods is a class of arachnids. The most famous of them are ticks, scorpions and spiders. In this article, you will study the external structure of arachnids, get acquainted with the features of the nervous system and sensory organs of arachnids.
Arachnids are everywhere. There are groups that live in the tropics and subtropics. Scorpions are found in the temperate zone, and some types of ticks and spiders can live in polar conditions.
External structure
The body of an animal consists of two sections:
- cephalothorax;
- abdomen.
There are two pairs of mouthparts on the cephalothorax: leg tentacles and chelicerae. The first pair of limbs are chelicerae, at the ends they have claws. It is on them that there are ducts of poisonous glands, with the help of which the animal defends itself and kills its prey.
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The second pair of limbs covered with bristles are the tentacles. They are also the organ of smell and touch.
The next 4 pairs are walking legs. At the ends they have claws and are also covered with bristles. As a result, we get 6 pairs of limbs.
The abdomen is covered with a soft shell. There are no limbs on it, and in some spiders they are modified into arachnoid warts. On top of the warts, the ducts of the glands that form the cobweb open. On the abdomen there are exits of the organs of respiration, digestion and reproduction.
Fig.1. External structure
Most arachnids have no muscles in their limbs. They move due to the influence of hemolymph pressure. Some species of scorpions have a muscle that can bend two joints at once.
The cover of the body is complexly organized and is formed by a single-layer epithelium, which forms a chitinous membrane. To protect against damage, as well as excess water loss, chitin is covered with a wax-like film. Many species have hairs on the surface of the body that perform a protective function and are sensory organs.
Features of the nervous system
Diverse in structure and the nervous system of arachnids. Outwardly, it is a solid abdominal chain, but there are a number of features:
- In the brain there is no department responsible for the work of antennules in crustaceans and insects;
- The anterior and posterior sections regulate the work of the eyes of arachnids, as well as the chelicerae;
- Ganglia in most cases are concentrated, forming a ganglionic mass.
Fig.2. Nervous system (blue color)
sense organs
The sense of touch for spiders is of great importance, the presence of hairs on the body is proof of this. Each individual hair is attached to the bottom of a special hole that connects it to sensitive cells.
Sensitive hairs are able to capture the slightest fluctuations in the air or cobwebs. Depending on the intensity of the vibrations, spiders distinguish the nature of the irritation.
The lyre-shaped organs, located throughout the body, are responsible for the chemical senses.
The organs of vision are the eyes, which have a simple structure. Answer the question: "How many eyes do arachnids have?" difficult, as it all depends on the type. In general, their number varies from 2 to 12. Despite the number of pairs of eyes, the eyesight of this class is poor and they see at a short distance.
Fig.3. The layout of the eyes in different species
What have we learned?
Arachnids in appearance belong to the type of arthropods. This class has adapted to the terrestrial habitat and is distributed everywhere. The body of the animal consists of two sections, on which there are 6 pairs of limbs. Touch plays an important role among the sense organs.
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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 this is the collective name of several biological species of the genus Araneus of the family Orb-weaving spiders of the order Spiders. Cross-spiders are found in the warm season 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 a very complex, vertical 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 a 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 webs. 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 nets.
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 a 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 gossamer warts. The spider warts of the Spider-Spider consist of a huge number (about 1000) gossamer 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, sexual hole. 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
outdoor skeleton: 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 ensures the absorption of 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 anal hole located at the posterior end of the abdomen above the arachnoid warts.
Respiratory system. Some arachnids have respiratory organs pulmonary bags, 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, consists of 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 out 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 urinary bubbles and output 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 have a 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.
Of all the sense organs, the most important for spiders is 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 fluctuations in 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.
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.
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 copulative bodies. 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
Meaning. The role of spiders in nature is great. They act as second-order consumers in the ecosystem structure (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 is the structure of the circulatory system of a 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. The internal structure of the 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.