Gastropods are the most numerous and diverse group of mollusks. It has about 90,000 species living in the seas, fresh waters, on land. Most of them have a one-piece shell.

One of the representatives of this class lives in lakes, ponds and river backwaters - a large pond snail about 5 cm in size.

External structure

In the pond snail, all three parts of the body are clearly distinguishable: head, leg and bag-shaped body. The top of the body is covered with a mantle. The pond snail has a spiral, twisted in 4-5 turns shell that protects the body of the animal. The shell is made of lime and topped with horn-like organic matter. In connection with the spiral shape of the shell, the body of the pond snail is asymmetric, since in the shell it is also curled into a spiral. The shell is connected to the body by a powerful muscle, the contraction of which draws the animal into the shell.

The leg of the pond snail is well developed, muscular, has a wide sole. The animal moves slowly sliding over plants or soil due to wave-like contraction of the leg muscles. The abundant mucus secreted by the skin glands of the foot facilitates smooth gliding.

Internal structure

Digestive system

In the mouth, on a special mobile outgrowth resembling a tongue, there is a grater with horny teeth. With their help, the pond snail scrapes off the soft parts of plants and microscopic algae deposits on underwater objects. There are in the throat salivary glands, the secret of which is processed food.

From the pharynx, food enters the stomach through the esophagus. The ducts of the liver flow into it. The stomach passes into the intestine, which makes several loops and ends with an anus at the front end of the body above the head.

Respiratory system

The body of the animal is covered with a mantle on the outside and closely adheres to the inner surface of the shell. Part of the mantle forms a kind of lung, numerous blood vessels develop in its walls, and gas exchange occurs here. The pond snail breathes atmospheric oxygen, so it often rises to the surface of the water and opens a round breathing hole on the right at the base of the shell. Next to the lung is the heart.

Circulatory system

The circulatory system is open, the blood is colorless. The heart consists of two sections - the atrium and ventricle, and blood vessels. Blood flows not only through the vessels, but also in the cavities between the organs. A large vessel, the aorta, departs from the heart. It branches into arteries. Then the blood enters the small cavities among the connective tissue. There, the blood gives off oxygen, is saturated with carbon dioxide, enters the veins and goes through them to the lung.

Here the veins branch into numerous small vessels - capillaries. The blood is enriched with oxygen and gets rid of carbon dioxide. Blood rich in oxygen is called arterial, and poor in oxygen and saturated with carbon dioxide is called venous. Then the blood is collected in the veins and enters the heart. It contracts 20-40 times per minute.

excretory system

Due to the asymmetry of the body, the pond snail retains only the left kidney.

At one end, it communicates through a wide ciliated funnel with the pericardial sac, where waste products accumulate, and at the other, it opens into the mantle cavity on the side of the anus.

Nervous system

Nervous system mollusks of scattered-nodular type. It consists of five pairs of nerve nodes (ganglia), interconnected by nerve bridges, and numerous nerves.

In connection with the twisting of the body, the nerve bridges between some nodes form a cross.

sense organs

On the head of a pond snail, there are organs of touch - tentacles, there are also tactile cells in the skin. The pond snail has one pair of tentacles. There are eyes - they are at the base of the tentacles. There are also organs of balance.

Reproduction. Development

Fertilization in the pond snail is internal. This animal is a hermaphrodite. The single gonad produces both sperm and eggs. They reproduce by eggs that are laid on aquatic plants or other objects. Fertilized eggs are covered with a common mucous membrane, securely attached to the substrate. Each animal lays about twenty clutches during the year.

After twenty days, tiny animals appear from the eggs. They grow rapidly, eating plant foods.

The pond snail becomes sexually mature at the end of the first year of its life. It is also interesting that when the reservoir (in which pond snails are found) dries up, not all mollusks die. Some secrete a dense film that closes the opening of the shell. In this state, the pond snail can live without water for about two weeks.

Well, we got to the most controversial aquarium snail, namely the pond snail. I know that 99% of aquarists not only dislike them, but hate them with fierce hatred for their voracity and fertility. However, it is still worth talking about the pond snail (more precisely, pond snails).

A bit of biology

Pond snails are a family of snails from the Pulmonata order, which, according to different classifications, includes from one (Lymnaea) to two (Aenigmomphiscola and Omphiscola) or several genera (Galba, Lymnaea, Myxas, Radix, Stagnicola), which differ mainly in the structure of the reproductive system. By appearance(by shells) representatives of these genera differ little from each other. In our review, we provide descriptions of the seven most common types of pond snails. middle lane Russia. To avoid confusion, we indicate their species names according to the traditional classification, according to which all pond snails belong to the same genus Lymnaea. However, in the description certain types information is provided on modern views on their taxonomy, along with their new names.

All pond snails have a well-developed shell spirally twisted to the right (see how to determine the twist) by 2-7 turns (see photos and drawings). In different types of pond snails, it is of different sizes and shapes - from almost spherical to highly conical, with a more or less high curl, with a very extended last whorl. Most are light horn, horn, brownish horn, brownish brown, or black brown. Most often, it is thin-walled, slightly transparent and more matte, tower-shaped or ear-shaped; the mantle almost does not emerge from the mouth.
The body of pond snails is right-handed, thick, their head is wide, transversely cut; respiratory and genital opening on the right side. The visceral sac is in the form of a conical spiral. The tentacles are flat, triangular in shape, short and wide. The leg is rather long and massive. Its sole is elongated-oval. There is a short siphon formed by the outer edge of the mantle.
The pharynx of the pond snail is a muscular sac that passes into the esophagus, then into the goiter and stomach; the latter consists of a bilobed muscular section and an elongated pyloric section; a muscular stomach is characterized by a rough structure and contributes to the crushing of captured food; in the pyloric stomach and in the intestine leaving it, food is digested; the anus opens at the mouth of the shell.

When observing a pond snail in an aquarium, one can see how it sticks out the front part of the body from the shell and slowly slides along the glass walls. In this protruding part of the body, one can distinguish the head, clearly separated from the rest of the body by the neck interception, and the leg, a large muscular organ of movement of the pond snail, occupying the entire abdominal part of its body. On the head are triangular movable tentacles, at the base of which eyes sit; on the ventral side of the head in its front part, a mouth gap is placed. The movements of pond snails are of three types - sliding along surfaces with the help of a foot, ascent and immersion due to the pulmonary cavity, and sliding from below along the surface film of water.
The movement of the pond snail along underwater surfaces can be well traced when it crawls along the glass wall of the aquarium. It is caused by muscular contractions, undulating and evenly running along the sole; these movements have a fine adaptability, which allows the mollusk to move along thin twigs and leaves of aquatic plants.
Ascent to the surface and immersion to the bottom is carried out due to the filling and emptying of the lung cavity. With the expansion of the cavity, the cochlea floats to the surface without any push along a vertical line. For an emergency dive (for example, in case of danger), the pond snail pushes out the air in the lung cavity and falls sharply to the bottom. So, for example, if you prick the tender body of a mollusk floating on the surface, then the leg will immediately be drawn into the shell, and air bubbles will escape through the respiratory hole - the pond snail will throw out all its air ballast. After that, the mollusk will drop sharply to the bottom and will no longer be able to rise to the surface otherwise than by crawling along underwater surfaces, due to the loss of its air float.
The third way of movement is sliding along the lower surface of the water. When surfacing, the pond snail touches the surface tension film with the sole of the foot, then abundantly secretes mucus, straightens the leg, slightly arching the sole inward in the form of a boat and, contracting the muscles of the sole, slides over the surface tension film covered with a thin layer of mucus.

Like other lung snails, pond snails lack primary gills and breathe atmospheric air with the help of a lung, a specialized section of the mantle cavity, which is adjacent to a dense network of blood vessels. In order to renew the air in the lung cavity, they periodically rise to the surface of the water. Having risen to the surface, the pond snail opens its respiratory opening, which is located on the side of the body, near the edge of the shell, and air is drawn into the vast lung cavity. At this time, you can hear a characteristic squelching sound - the "voice of a mollusk" - this is the opening of the respiratory hole leading to the mantle cavity. In a calm state, the respiratory opening is closed by the muscular edge of the mantle.
The frequency of lifting for breathing depends on the temperature of the water. In well-heated water at a temperature of 18 ° -20 °, pond snails rise to the surface 7-9 times per hour. As the water temperature drops, they begin to rise to the surface less and less often and in autumn, long before the water body freezes at a temperature of 6 ° -8 ° C, due to a general drop in activity, they cease to rise to the surface at all. While photosynthesis of aquatic plants continues, pond snails consume oxygen bubbles on plants for respiration, and then stop filling the mantle cavity with air. At the same time, it either subsides or fills with water - a paradoxical, rare fact in nature, when the same organ alternately functions either as gills or as a lung.
In addition to breathing air or water, flowing in the cavity of the lung, the pond snail also lives due to skin breathing, which is carried out by the entire surface of the body washed by water; wherein great importance have eyelashes skin pond snail, the continuous movement of which contributes to the change of water washing the surface of the body of the mollusk.

Prudoviks are omnivores, but in nature they prefer plant foods. Slowly crawling, they scrape off algae raids from various objects submerged in water, for example, from the surface of the stems and leaves of higher aquatic plants. If algae become scarce, they also consume living plants - leaves and stems of aquatic plants, choosing the most tender of them, as well as plant detritus.
To scrape food, pond snails use a toothed grater - a horny plate that fits in the pharynx on a tongue-like elevation. The plate of the grater from the surface is seated with rows of cloves. The nature of the work of the grater is easy to observe in the aquarium, when the pond snail crawls along the glass and from time to time sticks the grater out of its mouth and runs it over the surface of the glass in order to scrape off the layer of green algae that has developed on it. Pond snails sometimes use animal food - they devour the corpses of tadpoles, newts, fish and mollusks, scraping them from the surface, small invertebrate animals.
Lifestyle. At the height of summer, pond snails stay near the surface of the reservoir, and sometimes even on the very surface of the water. To catch them, there is not even a need to use a net, they can easily be removed from underwater objects by hand.
When water bodies inhabited by pond snails, such as small lakes, ditches and puddles, dry out, not all mollusks die. On the onset adverse conditions molluscs secrete a dense film that closes the opening of the shell. Some can tolerate being out of the water for quite a long time.

Prudoviki, like other pulmonary gastropods, are hermaphrodites. Eggs and spermatozoa develop in the same organism, in different parts of the same gland, but after leaving it, the paths of the genital ducts are separated, and the male and female genital openings near the mouth of the shell open separately.
A muscular copulatory organ protrudes from the male genital pore during copulation, while the female genital pore leads to an extensive seminal receptacle. In pond snails, mating is observed, with one individual playing the role of a female and the other a male, or both mollusks mutually fertilize each other. Sometimes chains of copulating pond snails are formed, with the extreme individuals playing the role of a female or male, and the middle ones - both.
Egg laying continues throughout the warm season, starting in early spring, and in the aquarium in winter. The eggs of pond snails in the laid state are connected by a common mucous membrane. In an ordinary pond snail (Lymnaea stagnalis), the clutch looks like a transparent gelatinous sausage with rounded ends, which mollusks lay on aquatic plants or other objects (video). In this species, the length of the roller reaches 45-55 mm with a width of 7-8 mm; eggs in it 110-120.
Large pond snails are especially prolific. According to observations in the aquarium, one pair of pond snails produced 68 clutches in 15 months, and in the other, 168 clutches in 13 months. The number of eggs in a clutch varies by species.
After 20 days, tiny snails come out of the eggs, already equipped with a shell, which grow quite quickly, eating plant foods.

Representatives of some species of pond snails living in the deep lakes of Switzerland have adapted to live at great depths. Under these conditions, they are no longer able to rise to the surface to capture atmospheric air, their lung cavity is filled with water, and gas exchange occurs directly through it. This is possible only in clean, oxygen-rich water. Such mollusks, as a rule, are smaller than their counterparts living in shallow water.
- The shape of the common pond snail shell depends on the place of existence of a particular individual. These mollusks are extremely variable; not only their size, color, shape, but also the thickness of the shell vary.
- Shells of all European species pond snails twisted to the right. Only as an exception are individuals with left-handed (leotropic) shells.
- The number of eggs in a clutch, as well as the size of the egg cord, varies widely. Sometimes in one clutch you can count up to 275 eggs.
- A large pond is quite demanding on the oxygen regime. At a high level of oxygen saturation (10–12 mg/l), mollusk populations are characterized by a high population density. Very rarely, L. stagnalis was found in oxygen-deficient water bodies.

Interestingly, pond snails can breed far before reaching their maximum age and size. For example, common pond snail it becomes sexually mature already at the end of the first year of its life, when it grows only to half its normal size.
- Pond snails can reproduce even being isolated from other individuals, so that copulation is not an act necessary for them to continue life, reproduction may well occur through self-fertilization.
- Pond snails are used in neurophysiology as model objects for studying the functioning of the nervous system of animals. The fact is that the nervous system of pond snails includes giant neurons. Placed in a nutrient medium, isolated pond snail neurons are able to stay alive for several weeks. The arrangement of giant neurons in the ganglia of the pond snail is fairly stable. This allows the identification of individual neurons and the study of their individual properties, which differ significantly from cell to cell. Irritation in the experiment of a single ganglion cell can cause a complex sequence of coordinated animal movements. This may indicate that giant mollusk neurons are capable of performing functions that in other animals are performed by large, complexly organized structures of many neurons.
- Snails have no hearing and voice, very poor eyesight, but their sense of smell is well developed - they are able to smell food at a distance of about two meters from them. The receptors are located on their horns.
- To improve digestion, the pond snail absorbs sand from the bottom of the reservoir
- Lifespan: 3-4 years.
- Max speed crawling - 20 cm / min.
- A large pond snail (L. stagnalis), when the reservoir dries up, releases a dense film that closes the shell opening. Some of the most adaptable forms of molluscs tolerate being out of water for quite a long time. So, an ordinary pond snail lives without water for up to two weeks.
- When water bodies freeze, mollusks do not die, freezing into ice, and come to life when thawed.
- Based on the results of recent joint research by scientists from the Pedagogical University of Tula and the Institute of Developmental Biology of the Russian Academy of Sciences, new, very Interesting Facts from the life of molluscs. As it turned out, snails have the ability to communicate with each other, transfer important information to each other, and even “give parental instructions” to larvae that have not yet been born, but are in the laid eggs. Although ordinary gastropod mollusks were chosen for the role of the test subjects - a coil and a large pond snail, scientists have an assumption that absolutely all representatives of the invertebrate world use this method of communication. At the first stage of the experiment, the experimental pond snails were divided into two groups. One of them was given food in the usual volumes, and the second was completely deprived of food for three days. Then water samples were taken from the containers in which the mollusks were kept, and from each container separately. As a result of the analysis, it was found that chemical composition differ significantly from each other. Then the caviar previously laid by the snails was placed in both containers. In the third, control container, they also placed caviar, but filled it clean water. All this was left for 10 days, after which the results were compared. As it turned out, in clean water, as well as in the one where well-fed snails lived, the larvae managed to reach the stage of full formation. The situation was completely different in the water where the hungry snails lived - the development of the larvae almost completely slowed down. This fact was commented on by Dr. biological sciences Elena Voronezhskaya, she said that parents seem to warn their children not to rush to develop and hatch, as they will not have anything to eat. In the course of further experiments, the following pattern was discovered: the longer the fasting period of adult snails, the more they released into the water a special substance that inhibited the development of larvae. This substance has received the name "RED-factor" from scientists, according to their assumptions, it is a lipoprotein.
- In a pond snail, most of the liver is located in the last turns of the spiral.
- One of the forms of the pond snail has adapted to life in hot springs near Baikal - the elongated pond snail (Lymnaea peregra)
- Biologists drew attention to the large size and yellow-orange color nerve cells the brain of a large pond snail, well adapted to a polluted environment. These cells are colored by pigments known as carotenoids. They can accumulate oxygen and, if it is not enough in the external environment, use the stored one.
- The blood of an ordinary pond snail is not red, like that of coils, but bluish, because it is colored with copper-containing hemocyanin.

While the news number for 07/25/18 was being made up. Scientists of the Federal Research Center for Comprehensive Study of the Arctic RAS (FICKIA RAS) and the Northern Arctic federal university(Arkhangelsk) created a genetic catalog of pond snails. For pond snails, their taxonomy was unclear, and we applied the molecular genetic method to Old World pond snails, examining material from about 40 countries. We conducted a revision, during which we showed that pond snails are divided into 10 genera, including a genus new to science and two species of pond snails discovered in remote high-mountainous regions of the Tibetan plateau. The genus is named Tibetoradix, and the species are Makhrov's pond snail (Radixmakhrovi) and the Tibetan Kozlov's pond snail (Tibetoradixkozlovi) in honor of the outstanding modern Russian ichthyologist Alexander Makhrov, as well as the traveler and explorer of the Central and East Asia Pyotr Kozlov, who lived in XIX-XX centuries.. It turned out that 35 species of pond snails live in Europe, Asia and Africa. "Before, grades ranged from three, ten or more"

And as usual, for those too lazy to read

In ponds, lakes and quiet backwaters of rivers on aquatic plants, you can always find a large gastropod snail - common pond snail.

Structure

The body of the pond snail (Fig. 58) is enclosed in a shell spirally twisted in 4-5 turns, which has a sharp top and a large opening - the mouth. The shell of wine consists of lime, covered with a layer of greenish-brown horn-like substance and reaches a height of 45-55 mm. It serves as protection for the soft body of the pond.

In the body of a pond snail, three main parts can be distinguished: the torso, head and leg, but there are no sharp boundaries between them. Only the head, leg and front part of the body can protrude from the shell through the mouth. The leg is muscular and occupies the entire ventral side of the body. Molluskshaving legs like those of a pond snail are called gastropods.

The sole of the foot secretes mucus, with the help of which the foot slides over underwater objects or even over the surface film of water, hanging from below, the pond snail moves smoothly forward.

The body repeats the shape of the shell, closely adjacent to it. In the front part of the body is covered by a special fold - the mantle. The mantle (skin fold) and the shell, twisted in a spiral, form the cover of the pond snail. The space between the body and the mantle is called the mantle cavity, through which communication with external environment. In front, the body passes into the head. A mouth is placed on the underside of the head, and two sensitive tentacles are placed on its sides. When touched, the pond snail quickly draws its head and leg into the shell. Near the bases of the tentacles is on the eye.

Digestive system

The common pond snail is a herbivore. The mouth leads to the throat. A muscular tongue covered with teeth is placed in it - this is the so-called grater. With it, the pond snail scrapes off plaque from organic matterformed on underwater objects, or scrapes the soft parts of plants. In the pharynx, food is processed by the secretions of the salivary glands. From the pharynx, food enters the stomach, then into the intestines. Digestion of food is also facilitated by a special digestive gland - the liver. The intestine ends with an anus located above the head.

Respiratory system

Although the pond snail lives in water, it breathes atmospheric air. For breathing, it rises to the surface of the water and opens a round breathing hole at the edge of the shell (Fig. 58), through which atmospheric air enters. It leads into the cavity - the lung, formed by the mantle and penetrated by a network of blood capillaries. In the lung, the blood is enriched with oxygen and carbon dioxide is released.

Circulatory system

The circulatory system of the pond snail (Fig. 58) is represented by a two-chamber heart, consisting of an atrium and a ventricle, and blood vessels.

Arterial blood enters from the lung into the atrium, then into the ventricle, and from it moves through the vessels to all organs of the body and pours out between them. Such a circulatory system is called open. Having given up oxygen and enriched with carbon dioxide, the blood is collected in the venous blood vessels and enters the lung, where gas exchange again takes place. Oxygenated blood travels through the vessels to the heart. It is more difficult to ensure the movement of blood in an open circulatory system than in a closed one, since the movement of blood slows down in the spaces between the organs. The voluminous two-chambered heart serves as a pump that pumps blood.

excretory system

The excretory system of the common pond snail (Fig. 58) includes one kidney with a ureter that breaks off near the anus.

The kidney has a direct connection with the circulatory system and absorbs from the blood final products breakdown of proteins.

Nervous system

The nervous system of the pond snail is of the nodal type and includes a near-pharyngeal nerve ring formed by two nodes and four pairs of nodes with nerves extending from them. material from the site

sense organs

The pond snail has organs of vision under the tentacles - eyes, organs of touch - tentacles and organs of balance - small whitish bubbles lying on the surface of the nerve node of the legs. In these bubbles in a liquid medium are small bodies, changing the position of which allows you to maintain the balance of the body.

reproduction

Reproduction is sexual. Common pond snails are hermaphrodites. Fertilization is internal.

During the copulation of two individuals, mutual fertilization takes place, that is, the exchange of male gametes - spermatozoa. After that, the individuals disperse and lay fertilized eggs tied into gelatinous cords. They attach themselves to underwater plants.

From the zygote develop small pond snails with a thin shell.

Position in systematics (classification)

The common pond snail is one of the species of the most numerous class among mollusks - Gastropods.

On this page, material on the topics:

  • Message about the pond snail briefly

  • Does the common pond snail secrete mucus

  • Type of circulatory system in a pond snail

  • Adaptation of mollusks to the habitat common pond snail

  • Grater at the pond

Questions about this item:

  • The small pond snail is similar to the common pond snail, only the shell size is smaller (see appendix fig. 25). The small pond snail lives in temporary reservoirs - puddles, ditches, swampy meadows, sometimes even on moist soil near the water's edge. In a word, there are many places where a temporary resident is found.

    It feeds, like its relative, on algae and microorganisms.

    The small pond snail is distributed throughout Europe and Northern Asia, like the common pond snail.

    gastropods;

    coil family;

    horn coil.

    Coils (Planorbis) belong to the class of gastropods (Gastropoda), to the order of pulmonary (Pulmonata), to the family of coils (Planorbidae).


    The coil can be distinguished at a glance due to its extremely characteristic
    shell, curled in one plane in the form of a spiral cord.
    The horn coil (P. corneus L.) attracts the most attention, the largest among the others (shell diameter 30 mm, height 12 mm), reddish-brown. This coil is found everywhere in both pond and lake waters.
    The movements of the coils resemble the movements of pond snails. Crawling, snails expose their dark soft body far from the shell and move along underwater objects with the help of their wide flat legs. On the head there is a pair of thin tentacles, at the base of which the eyes are placed. Coils, just like pond snails, can wander along the surface of water bodies, being suspended from a film of surface tension of a liquid.
    Coils breathe atmospheric air, taking it into the lung cavity formed by the walls of the mantle. The respiratory opening leading to the indicated cavity opens on the side of the body, near the edge of the shell. It opens when the coil rises to the surface of the water for a supply of air. With a lack of air, the coil uses a special leathery outgrowth, which is placed on the body near the pulmonary opening and plays the role of a primitive gill. In addition, the coil, in all likelihood, breathes directly through the skin.
    Nutrition. Coils feed on plant foods, eating parts of plants that are scraped off with a grater. Especially willingly, these snails eat green plaque from small algae, which forms on the walls of the aquarium. Outside, through the glass, it is not difficult to observe how the animal works with its grater, raking up plaque like a spatula. It is very possible that coils can also eat animal food. At least in captivity, they willingly pounce on raw meat.
    Reproduction. Coils reproduce by laying eggs on the leaves of aquatic plants and other underwater objects. The masonry of the horn coil is constantly found on excursions and is so characteristic that it can be easily distinguished: it has the appearance of a flat gelatinous plate of oval yellowish or light brown color and contains several dozen round pinkish transparent eggs. After two weeks or more (depending on the temperature of the water), tiny snails hatch from the eggs, which grow quite quickly. The caviar of coils, like other snails, is readily eaten by fish and exterminated by them in large numbers. Like the pond snail, coils are hermaphrodites.
    The behavior of the coils during the drying of the reservoirs in which they occur is interesting. They burrow into moist silt, like the large horn coil (P. corneus). Sometimes this coil remains on the surface of the soil, sticking to the silt with its mouth, if moisture remains in it, or it releases a dense, water-insoluble film, which closes the shell opening. In the latter case, the body of the mollusk gradually shrinks, eventually occupying a third of the shell, and the weight of the soft parts drops by 40-50%. In this state, the mollusk can survive out of water for up to three months (marginal coil P. marginatus P. planorbis).

    The body of the coil, like that of pond snails, is divided into three parts: head, torso and leg (see appendix fig. 26). The leg is a muscular abdominal part of the body, leaning on which the mollusk slowly glides. At the coils, the turns of the shell are located in the same plane. Coils are not as mobile as pond snails, and cannot be suspended from the surface film.

    Coils live on plants in stagnant and slow-flowing reservoirs, in the same place as an ordinary pond snail, but rises to the surface of the water much less frequently.

    beauty family;

    larva of a beauty girl.

    On a sunny day, blue lights flash up and then go out over the river (see appendix fig. 27). It is flitted by graceful dragonflies. At some point, they resemble helicopters.

    The body is bronze-green, the wings of females are light smoky, those of males are almost entirely blue.

    All dragonflies, wherever they are, wherever they fly, need water. They lay their eggs in the water. And only in water their larvae can live. The larvae do not look like adult dragonflies. They just have the same eyes.

    Special mention must be made of the eyes of dragonflies. Each eye is made up of thousands of small eyes. Both eyes are large and protruding. Thanks to this, dragonflies can look in all directions at the same time. This is very handy for hunting. After all, dragonflies are predators. And their larvae, living in the water, too.

    Dragonflies hunt in the air - they grab insects on the fly. The larvae live in the water, and here they also get food for themselves. But they do not chase prey, but lie in wait for it. The larva sits motionless or crawls slowly along the bottom. And some tadpoles or some insects swim by. The larva does not seem to care about them, but how this tadpole or insect turns out to be close. Once! She instantly throws out her long arm and grabs the prey, quickly pulling it to her.

    "But insects don't have arms," ​​you say. And you will be right. Yes, of course they don't have hands. But there is a very long lower lip with hooks at the end. The lip folds like a hand at the elbow when you press the brush to your shoulder. And while the larva watches for prey, the lip is not visible. And when the prey is close, the larva instantly throws out its lip to its full length - as if shooting it - and grabs a tadpole or an insect.

    But there are moments when the larva needs to save itself. And here saves her speed. More precisely, the ability to move with lightning speed from place to place.

    Some predator rushed at the larva. Another second - and the larva was gone. But where is she? Just been here, and now in a completely different place. How did she get there? Very simple. Activated her "jet engine".

    It turns out that dragonfly larvae have a very interesting adaptation: a large muscular sac inside the body. The larva sucks water into it, and then throws it out with force. It turns out a water "shot". The water jet flies in one direction, and the larva itself in the opposite direction. Just like a rocket. This is how it turns out that the larva makes a lightning-fast jerk and slips out from under the very "nose" of the enemy.

    After flying a few meters, the larva slows down, sinks to the bottom or clings to some plant. And again it sits almost motionless, waiting for the time when it will be possible to throw out the "hand" and grab the prey. And if necessary, it will re-launch its "jet installation". True, not everyone has a "jet engine", but only the larvae of large dragonflies.

    A year later, the larvae of some dragonflies, after three years, the larvae of others climb out of some plant sticking out of the water to the surface. And this is where it happens small miracle: the skin of the larva bursts and a dragonfly appears from it. The most real and not at all like a larva.

    The dragonfly will shed its skin like a suit, and even pull out its legs, like out of stockings. He will sit for several hours, rest, spread his wings and go on his first flight.

    Some dragonflies fly far from their birthplace. But the time will come, and they will definitely return. Because they cannot live without a river or a lake, a pond or a swamp - without water, in a word. And the river, the pond, the lake also cannot live without these friends of theirs.

    Dragonfly eggs are laid in water or in the tissues of aquatic plants. The eggs hatch into larvae of an extremely characteristic shape, interesting in their biological features. These larvae are playing important role among other things live stuff freshwater excursions.
    Dragonfly larvae are found everywhere in stagnant and slowly flowing water. Most often they are on aquatic plants or at the bottom, where they sit motionless, sometimes move slowly. There are species that burrow into the silt.

    The larvae move either by swimming or crawling. Larvae from the group of buttercups swim differently than others. An important role in the movement is played by the expanded gill plates located at the posterior end of the abdomen, which serve as an excellent fin. Bending its long body, the larva beats the water with this fin and rapidly pushes forward, moving like a small fish.

    Dragonfly larvae feed exclusively on live prey, which they watch motionless for hours, sitting on aquatic plants or at the bottom. Their main food is daphnia, which are eaten by them in large quantities, especially by younger larvae. In addition to daphnia, dragonfly larvae willingly eat water donkeys. They are less willing to consume cyclops, perhaps due to the small size of the latter.
    The favorite food of dragonfly larvae are also mayfly larvae and mosquito larvae from the families of culicids and chironomids.
    They also eat the larvae of aquatic beetles, if only they are able to master them. However, they do not touch large larvae of swimmers, well-armed and no less predatory, even if they are planted in a common vessel with them.
    Dragonfly larvae do not chase their prey, but sit motionless on aquatic plants or on the bottom and guard the prey. When a daphnia or other animal suitable for food approaches, the larva, without moving from its place, throws out its mask with lightning speed and grabs its prey.

    For grasping prey, the larvae have a wonderful oral apparatus, which is aptly called "masks". This is nothing more than a modified lower lip, which looks like grasping tongs, sitting on a long lever - a handle. The lever is equipped with a hinge joint, thanks to which the whole device can be folded and, in a calm state, covers the underside of the head like a mask (hence the name). Noticing the prey with its large bulging eyes, the larva, without moving, aims at it and with a lightning movement throws its mask far forward, grabbing the prey with remarkable speed and accuracy. Captured prey is immediately devoured with strong gnawing jaws while the mask brings the prey to the mouth and holds it like a hand while eating.


    Breath. Dragonfly larvae breathe with tracheal gills. In lute-type larvae, the gill apparatus is located at the posterior end of the abdomen in the form of three thin, expanded plates pierced by a mass of tracheal tubes. Shortly before the adult dragonfly hatches, the larvae also begin to breathe atmospheric air with the help of spiracles that open on their upper side of the chest. This explains why adult larvae often sit on aquatic plants, exposing the front end of their body out of the water.

    Luke-type larvae have the ability to discard gill plates if they are infringed. This is easy to verify by experience: put the larva in the water and squeeze the gill plate with the tip of tweezers. This phenomenon is called self-mutilation (autotomy) and is well known in many animals (spiders, lizards, etc.). For this reason, it is necessary to catch larvae from the water that lack 1 - 2, and sometimes all 3 tail plates. In the latter case, breathing takes place, in all likelihood, through a thin skin that covers the body. The torn off plate is restored again after some time, due to which it is possible to observe larvae with gill plates of unequal length. It should be noted that in Calopteryx one of the plates is always shorter than the other two, which is not an accidental circumstance, but a generic feature.

    Dragonflies reproduce using eggs that the females lay in the water. The clutches of different species are very diverse. Dragonflies such as yoke and buttercups drill their eggs into the tissues of aquatic plants. In this regard, their eggs also have a characteristic oblong shape, and the stuck end is pointed. In the place where the egg is stuck, a trace remains on the surface of the plant, which then takes the form of a dark spot or scar.
    Since the eggs of different species of dragonflies are placed on the plant in a certain order, peculiar, sometimes very characteristic patterns are formed.

    The suborder of dragonflies is homoptera;

    Lutka family; sunflower-bride.

    A very slender, elegant, graceful dragonfly (see appendix fig. 28). The body is green, metallic-shiny. In females, the sides, breasts are yellow, and in males with a bluish-gray bloom.

    There are no significant differences between dragonflies, and all descriptions of dragonflies and their larvae are the same, so in the previous chapter you can find all descriptions of both larvae and adults.

    Mayfly Squad;

    Mayfly ordinary.

    Quiet summer evenings when the sun's rays are no longer burning, some insects that look like butterflies, but with two or three long threads on their tails, swarm in the air near the banks of rivers, lakes and ponds (see appendix fig. 29). They either soar up, then freeze, stabilizing the fall with long tail threads, then, spreading their wide wings, slowly sink down. So they swirl over the shore, like a dense fog or cloud about ten meters high and about a hundred meters long. These swarms rush over the water like a storm. You will not see such an exceptional phenomenon every day, only in July-August it is repeated several times.

    This is dancing, carrying out the mating flight, mayflies. Their wings and they themselves are so tender that it is simply amazing how they do not break during the flight. You involuntarily think that they will not live long. And this opinion is true: many mayflies live only one day. Therefore, they are called mayflies, and their scientific name comes from the Greek word "ephemeron" - fleeting.

    After the mating flight, the females lay their eggs in the water and die. With such short life they don't eat anything.

    Mayfly larvae develop in water. The larvae live longer, two to three years. And unlike an adult, they eat very well. And they feed on algae, decaying organic matter, small invertebrates and molt up to twenty-five times during development. Many fish feed on the larvae of mayflies, and various birds eat adult mayflies.

    On examination, the quick, sharp movements of the larvae are primarily striking. When disturbed, it takes off headlong and swims very briskly, with three feathery caudal filaments, richly pubescent with hairs (Cloon, Siphlurus), serving as fins. The legs serve mainly for attachment to aquatic plants. The quick movements of the mayflies probably serve as a defense against their many enemies, who actively hunt for these tender larvae. The color of the larvae, in general, greenish, matching the color of the aquatic plants among which they huddle, probably also plays a protective role.

    The respiration of larvae is easy to observe during excursions. It is of considerable interest as a good example of tracheal-gill respiration. The gills look like thin delicate plates that are placed in rows on both sides of the abdomen (Cloeon, Siphlurus). These delicate tracheal leaves are constantly moving, which can be perfectly seen in a larva sitting in water even without the help of a magnifying glass. Most often, these movements are uneven, jerky: like a wave runs through the leaves, which then remain motionless for some time until a new wave. The physiological significance of this movement is quite clear: in this way, the flow of water washing the gill plates increases, and the exchange of gases accelerates. The larvae's need for oxygen is generally very high, therefore, in aquariums, the larvae die at the slightest damage to the water.
    The food of the larvae is very diverse. The free-swimming, stagnant water forms most commonly encountered on excursions are peaceful herbivores, feeding on microscopic green algae (Cloeon, Siphlurus). Other species lead a predatory lifestyle and actively hunt for small aquatic animals. The food of many species of mayflies is still not well understood.

    The phenomena of reproduction in mayflies are of great interest and have long attracted the attention of observers. Unfortunately, these phenomena on excursions have to be seen only by chance. As mentioned above, females drop their eggs into the water. The eggs hatch into larvae, which grow and molt many times (the Cloeon has more than 20 molts), and the rudiments of wings gradually form in them. When the larva completes its development, a winged insect hatches. At the same time, the larva floats to the surface of the reservoir, the covers on its back burst, and in a few seconds an adult mayfly emerges from the skin, which flies into the air. Since the process of hatching in larvae is often carried out simultaneously, the surface of those reservoirs where larvae are found in large numbers presents a wonderful sight during hatching, which has been described more than once in the literature: the surface of the water seems to boil from a multitude of hatching insects, and clouds of mayflies, like snow flakes hovering in the air. However, the winged insects that hatch from the larvae do not represent the final stage of development. They are called subimago and after a short period of time (from several hours to 1-2 days) they molt again, thus turning into imago (the only case among winged moulting insects). Sometimes on an excursion you can watch how a winged mayfly sits on some plant or even on a person and immediately sheds its skin.

    Detachment ticks;

    hydrachnida family;

    The vast majority of ticks are very small animals, no more than one millimeter, only a few are larger, for example, our tick.

    Mollusks, or soft-bodied, live in the sea, in fresh waters and on dry land. The body of mollusks, as a rule, is covered with a shell, under which there is a skin fold - the mantle. The space between the organs is filled with parenchyma. About 100,000 species of molluscs are known. We will get acquainted with representatives of three classes: gastropods, bivalves and cephalopods.

    lifestyle and external structure. In ponds, lakes and quiet backwaters of rivers on aquatic plants you can always find a large snail - a large pond snail. Outside, the body of the pond snail is dressed in a protective spirally twisted shell about 4 cm long. The shell consists of lime covered with a layer of greenish-brown horn-like organic matter. The shell has a sharp top, 4-5 whorls and a large opening - the mouth.

    The body of a pond snail consists of three main parts: head, torso and legs. Only the leg and head of the animal can protrude from the shell through the mouth. The leg of the pond snail is muscular. When undulating muscle contractions run along its sole, the mollusk moves. The leg of the pond snail is located on the ventral side of the body, and therefore it is classified as a class of gastropods. In front, the body passes into the head. A mouth is placed on the underside of the head, and two tentacles are located on its sides. The tentacles of the pond snail are very sensitive: when touched, the mollusk quickly draws its head and leg into the shell. Near the base of the tentacles on the head is an eye.

    The body repeats the shape of the shell, closely adhering to its inner surface. Outside, the body is covered with a mantle, under it there are muscles and parenchyma. A small cavity remains inside the body, in which the internal organs are located.

    Nutrition. The pond snail feeds on aquatic plants. In his mouth is placed a muscular tongue, covered with hard teeth. From time to time, the pond snail sticks out its tongue and scrapes with it, like a grater, the soft parts of plants, which it swallows. Through the pharynx and esophagus, food enters the stomach and then into the intestine. The gut loops inside the body and ends on its right side, near the edge of the mantle, with an anus. Next to the stomach in the body cavity lies a grayish-brown organ - the liver. Liver cells produce digestive juice, which flows through a special duct into the stomach. Thus, digestive system the pond snail is even more complex than that of the earthworm.

    Breath. Despite the fact that the pond snail lives in the water, it breathes oxygen from the atmospheric air. For breathing, it rises to the surface of the water and opens a round breathing hole on the right side of the body at the edge of the shell. It leads to a special pocket of the mantle - a lung. The walls of the lung are densely woven with blood vessels. This is where the blood is enriched with oxygen and carbon dioxide is released. Within an hour, the mollusk rises for breathing 7-9 times.

    Circulation. Next to the lung is a muscular heart, consisting of two chambers - the atrium and the ventricle. Their walls alternately contract (20-30 times per minute), pushing blood into the vessels. Large vessels pass into the thinnest capillaries, from which blood exits into the space between the organs. Thus, the circulatory system of the mollusk is not closed. Then the blood is collected in a vessel suitable for the lung. Here it is enriched with oxygen and enters the atrium through the vessel, and from there into the ventricle. The blood of the pond snail is colorless.

    Selection. The pond snail has only one excretory organ - the kidney. Its structure is rather complicated, but in in general terms resembles the structure of the excretory organs of an earthworm.

    Nervous system. The main part of the nervous system of the pond snail is the peripharyngeal accumulation of nerve nodes. Nerves depart from them to all organs of the mollusk.

    Reproduction. Prudoviks are hermaphrodites. They lay masses of eggs enclosed in transparent, slimy cords that are attached to underwater plants. Eggs hatch into small mollusks with thin shells.

    Other gastropods. Among a large number of species of gastropods, marine mollusks are especially famous, thanks to their beautiful shells. Slugs live on land, so called because of the abundant mucus they secrete. They don't have shells. Slugs live in wet places and eat plants. Many slugs eat mushrooms, some are found in fields and gardens, causing damage to cultivated plants.

    The grape snail is widely known, which is eaten in some countries.