Common pond snail group. Large pond snail - molluscs - nature and animals. Type of circulatory system in a pond snail

Names: common pond snail, marsh pond snail, large pond snail, lake pond.

Area: Europe, Asia, North Africa, North America.

Description: pond snail, refers to lung molluscs. The largest of the pond snails living in Russia. In recent years, it has been divided into two types - Limnaea stagnalis And Limnaea fragilis.The appearance of the pond snail is very variable: depending on the conditions of existence, the color, thickness, shape of the mouth and whorl of the shell, and dimensions vary. The body of the pond snail can be divided into three main parts: the body, head and leg. The body repeats the shape of the shell, closely adhering to it. The shell is thin spiral (twisted in 4-5 turns), strongly elongated, with a large last turn. The shell consists of lime, covered with a layer of greenish-brown horn-like substance. The head is large, with flat triangular tentacles and eyes set at the inner edge of their bases. The tentacles are filiform. The mouth of the pond snail leads to the pharynx. It contains a muscular tongue covered with teeth (grater). From the pharynx, food enters the stomach, then into the intestines. The liver aids in the digestion of food. The intestine opens with an anus into the mantle cavity. The leg is narrow and long, muscular, occupies the entire ventral side of the body. The breathing hole is protected by a prominent blade. The circulatory system is open. The heart pumps blood into the vessels. Large vessels branch into small ones, from which blood enters the spaces between the organs.

Color: the color of the legs and body is from blue-black to sandy-yellow. The shell of the pond snail is brown.

Size: shell height 35-45 mm, width 23-27 mm.

Lifespan: up to 2 years.

Habitat: stagnant water bodies (ponds, lakes, river backwaters, canals, swamps) with abundant vegetation. It can live in slightly brackish water. There is also a pond snail in drying up reservoirs.

Enemies: fishes.

Food/food: the pond snail feeds on rotting remains of plants and animals. It deliberately swallows sand that remains in the stomach and helps grind hard food.

Behavior: the pond snail is almost always active. It crawls among thickets, scraping algae and small animals from the underside of leaves. The maximum crawling speed is 20 cm / min. It breathes air, the reserves of which are renewed, rising to the surface (6-9 times per hour). Pond snails, living in deep lakes at a considerable depth, breathe air dissolved in water, which is filled in the respiratory cavity. When the reservoir dries, it seals the mouth of the shell with a dense film. Can freeze into ice and then come to life when thawed.

Reproduction: the common pond snail is a hermaphrodite. Cross fertilization. It lays eggs enclosed in transparent slimy cords, which it attaches to underwater plants and objects. Lays 20-130 eggs.

Season/breeding period: during the whole year.

Incubation: about 20 days.

Offspring: development without a larval stage. Small pond snails with a thin shell emerge from the eggs.

Literature:
1. Brockhaus F.A., Efron I.A. encyclopedic Dictionary
2. M.V. Chertoprud. Fauna and ecology of gastropods in fresh waters near Moscow.
3. Virtual school "Bakai"
4. Great Soviet Encyclopedia

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CLASS Gastropoda mollusks

In gastropods, the body consists of a head, trunk and legs. The leg is a muscular abdominal part of the body, leaning on which the mollusk slowly glides.

Most gastropod molluscs have a spirally twisted shell (which is why they are also called snails), in which the animal can completely hide. At the bottom of the shell is a wide opening - the mouth through which the mollusk protrudes its head and leg when moving. Some terrestrial gastropods - slugs - do not have shells.

In the pharynx, gastropods have a muscular tongue covered with spines - the so-called grater. Using it, the mollusk scrapes plant tissues or scrapes off the plaque formed on underwater objects from various microorganisms.

Key to families

1(4) The mouth of the shell, when the mollusk draws its head and leg into it, is closed by a thin cap attached to the leg.
2(3) On the curls of the shell there are dark longitudinal stripes (may be poorly visible due to the plaque covering the shell), the size is up to 45 mm;
3(2) Shell without dark stripes, one-color; the value is not more than 12 mm;
4(1) There is no lid at the mouth of the shell, so the compressed sole of the foot is visible on the mollusk hiding in it.
5(6) The coils of the shell are twisted in one plane;
6(5) The shell is twisted cone-shaped.
7(8) The shell is twisted to the right (if you take the shell so that the top is directed away from you, and the mouth towards you, then the mouth will be located to the right of the center line);
8(7) The shell is twisted to the left (the mouth is to the left of the center line); FAMILY POND (Lymnaeidae)

In pond snails, the shell is twisted spirally, in several turns, in the form of a turret. About 20 species are found in the USSR.

Common pond snail (Lymnaea stagnalis) The largest of our pond snails, the height of the shell is 45-55 mm, and in some individuals even up to 65 mm. It lives in stagnant water bodies - ponds, lakes, river backwaters with abundant vegetation. Here you can see how the pond snail, sticking its leg and head with tentacles out of the shell, slowly glides over the plants. Having reached the surface of the water, the pond snail spreads its leg wider and slides, hanging from below to the surface film of water. At the same time, at the mouth of the shell, on the side of the leg, a round breathing hole can be seen. In the middle of summer, the pond snail rises to the surface of the water 6-9 times within an hour. Distributed in Europe and North Asia to Kamchatka.

Ear pond snail (Lymnaea auricularia) This mollusk has a shell with a very wide mouth, shell height 25-40 mm, width 20-30 mm. Inhabits the surf zone of stagnant water bodies. Distributed in Europe and Asia (except the southeast).

COIL FAMILY (Plarmrbidae)

In 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 of water. In the USSR, there are 35 types of coils.

Coil horn (Planorbarius corneus) This mollusk has a shell diameter of up to 35 mm. It lives on plants in stagnant water bodies, in the same place as the common pond snail, but rarely rises to the surface of the water. Distributed in Europe and in Western Siberia to the Ob.

Coil bordered (Ptanorbis planorbis) The shell of the bordered coil is dark brown, 20 mm in diameter, with 5-6 whorls. On the last whorl from below there is a sharp protrusion - the keel. It lives in shallow water bodies and in the coastal part of large water bodies. Distributed in Europe and in Western Siberia to the Yenisei.

Coil twisted (Anisus vortex) The shell is yellow, up to 10 mm in diameter, with 6-7 whorls. The last whorl has a sharp, downwardly displaced keel. It lives in coastal thickets of stagnant water bodies, often floats on the surface of the water. Distributed in Europe and in Western Siberia to the Yenisei.

FAMILY PHYSIS (Physidae)

In physids, the shell is in the form of a turret, like in pond snails, but twisted to the left.

Fiza vesicular (Physa fontinalis) The shell is dull, pale yellow, 10-12 mm high, 5-6 mm wide, the height of the mouth is more than half the height of the shell. Lives on vegetation in various permanent reservoirs. Distributed in Europe and North Asia.

Aplexa sleepy (Aptexa hypnorum) The shell is shiny, golden-brown, 10-15 mm high, 5-6 mm wide (the height of the mouth is less than half the height of the shell). Lives only in temporary water bodies that dry up in summer. Distributed in Europe, Western Siberia and the south of the Far East.

FAMILY LUZHANKI (Viviparidae)

The mouth of the shell at rest is closed with a lid. Shells with dark longitudinal stripes. Luzhanok is also called viviparous, since they do not lay eggs, like other mollusks, but give birth to small, already shelled meadowsweet.

Marsh Luzhanka (Viviparus contectus) Sink height up to 43 mm. It lives in lakes, ponds, sometimes even in puddles with clear water. Stays on the bottom. Distributed in Europe and Western Siberia to the Ob.

BITINIA FAMILY (Bithyniidae)

As in meadow meadowsweet, the mouth of the shell is closed with a cap at rest, but the shells are one-colored, without stripes.

Bithynia tentacle (Bithynia tentaculata) Sink height up to 12 mm. It lives in stagnant and weakly flowing water bodies, on stones, in silt and among plants. Distributed in Europe and Western Siberia.

Terrestrial gastropods

Terrestrial gastropods can be divided into two groups: snails, which have a shell, and slugs, which do not have a shell (in some species, a small remnant of the shell is hidden under the skin and is not visible from the outside). Since the skin of mollusks is naked, many species adhere to wet habitats. In addition, animals are usually motionless during the day. At the same time, snails completely hide in the shell, sticking their soles to the substrate, and slugs crawl under shelters - stones, leaves, between lumps of soil. But at night, and in rainy times and during the day, mollusks crawl from place to place.

snails

In land snails, the shell is spirally twisted. In some species, the shell is elongated, so that its height noticeably exceeds its width; in other species, on the contrary, the shell is low and its width is greater than its height. During movement, the mollusk protrudes its head and leg from the shell. There are 4 tentacles directed forward on the head. At the ends of two longer tentacles there are dark balls - these are the eyes. If you gently touch the tentacles, the mollusk immediately draws them in, and if it is strongly disturbed, it will completely hide in the shell. Several hundred species of snails are found in the USSR. Basically, these are very small species that are difficult to distinguish from each other (often only by their internal structure). We will consider only some of the largest and most widespread forms.

Amber ordinary (Succinea putris) It got its name for the amber-yellow color of the elongated, thin, fragile, almost transparent shell. Shell height 16-22 mm, width 8-11 mm. Shell with 3-4 whorls, last whorl strongly swollen and dilated, ovoid aperture. Amber lives in damp places - in wet meadows, near water bodies, it can often be seen on the floating leaves of aquatic plants, and sometimes it even plunges into water. Widespread throughout the USSR.

Cochlicopa slippery (Cochticopa lubrica) This is a small snail, with a smooth, shiny, elongated, conical shell, 6-7 mm high, 3 mm wide. It is quite common in damp places - in meadows, in grass, in moss, in fallen leaves of damp forests. Distributed throughout the USSR.

Iphigena swollen (Iphigena ventricosa) This snail has an elongated, fusiform, ribbed, reddish-horn shell, 17-18 mm high, 4-4.5 mm wide, with 11-12 whorls. A flat tooth-like protrusion protrudes from above into the mouth. It lives in forests, on the litter, on mossy tree trunks. Distributed in the Baltic States and the middle zone of the European part of the USSR.

Kochlodina rocky (Cochlodina laminata) In this species, the shell is elongated, fusiform, slightly swollen, smooth, shiny, light horn, 15-17 mm high, 4 mm wide, with 10-12 whorls. Two lamellar curved protrusions are visible at the mouth. It lives in forests, on rocks, stumps, tree trunks. Distributed in the middle zone of the European part of the USSR, north to the Leningrad region, east to Kazan.

bush snail (Bradybaena fruticum) The shell of this snail is spherical, almost smooth, 16-17 mm high, 18-20 mm wide, with 5-6 whorls. The color varies from grayish-white to reddish-horn, often a narrow brown band is visible on the last whorl of the shell. It lives in shrubs, deciduous forests, gardens, often the bush snail can be found on nettles and coltsfoot. Sometimes it climbs quite high on bushes, tree trunks and fences. Distributed in the European part of the USSR, in the Crimea and the North Caucasus.

garden snail (Cepea hortensis) The shell of the garden snail is kubariform, similar to the shell of a shrub snail, 15-16 mm high, 19-21 mm wide, with 4-5 whorls, dark spiral stripes are visible on all whorls. It lives in sparse bushes and forests, on stones and rocks. Distributed in the Baltics

hairy snail (Trichia hispida) In this small snail, the shell is covered with fine hairs (in older individuals, they can be erased). The shell is 5 mm high, 8-9 mm wide, grayish or reddish-brown in color, usually with a light stripe on the last whorl. It lives in bushes, on the ground in forest litter, under stones, deadwood. Distributed in the forest zone of the European part of the USSR, up to the Leningrad and Perm regions. It often causes harm to native, fruit and berry crops and ornamental plants, scraping leaf tissues so that only longitudinal thick veins remain from them.

SLUGS

Slugs have a naked body, devoid of a shell. In a calm state, slugs look like small slimy lumps, but when moving, their body is greatly stretched. Like snails, 4 tentacles directed forward are visible on the head. Two longer tentacles have eyes at the ends. A short neck is visible behind the head, passing into the back. Immediately behind the neck, an oval thickening is visible on the back, as if another layer of skin was superimposed on top. This is the so-called mantle, covering the respiratory organ - the lung. On the right side of the mantle, a rounded breathing hole is visible. As the name suggests, slugs produce a lot of mucus. It primarily protects the mollusks from drying out. In addition, mucus helps them to glide. A crawling slug always leaves a noticeable shiny slimy trail. In the middle zone of the European part of the USSR, 16 species of slugs live. Of these, we will consider the most common, widespread forms.

Key table of genera

1(2) The breathing hole is in front of the right edge of the mantle. When moving, the end of the leg protrudes slightly from under the back;
2(1) The breathing hole is located at the back of the right edge of the mantle. The leg does not protrude from under the back when moving.
3(4) Large slugs, over 100 mm long.
4(3) The size of the slugs does not exceed 50 mm.
5(6) Slime yellow;
6(5) The mucus is colorless, with irritation of the mollusk - milky white; GENUS ARION (Arion)

The body is thick, massive. The mantle is oval, rounded front and back. Breathing hole in front of the right edge of the mantle. When moving, the end of the leg protrudes slightly from under the back.

Arion brown (Arion subfuscus) Body length up to 80 mm. The mantle is about 1/3 of the body length. Coloring can be different, from brown to orange, more often rusty. The middle of the back is usually darker. It lives in deciduous, mixed and coniferous forests, occasionally found in old parks and cemeteries. A favorite food is cap mushrooms, in which the slug eats away large cavities. It can also feed on dead plant parts and animal carcasses. Distributed in the forest and forest-steppe zone of the European part of the USSR. In the Altai Territory, Eastern Siberia, the Amur basin and the Primorsky Territory, the brown Siberian Arion subspecies (Arion subfuscus sib ire us), which is distinguished by its monochrome black body color, lives. In warm, damp summers, this slug causes damage to vegetable gardens and fields located next to the forest.

Arion striped (Arion fasciatus) Body length up to 50 mm. The mantle occupies about 1/3 of the body length. The coloration is light - cream or yellowish-ash, the middle of the back and mantle is slightly darker. There are clearly defined dark stripes on the sides. It occurs more often in cultivated biotopes - vegetable gardens, fields, gardens, parks. Often causes significant damage to crops. Distributed in the northwestern and central regions of the European part of the USSR.

GENUS DEROCERAS (Deroceras)

Small slugs, quite slender and mobile. The skin is almost smooth, with weak grooves, without coarse wrinkles. Breathing hole in the back of the right edge of the mantle. The mucus is colorless, when the mollusk is irritated it is milky white.

slug reticulated (Deroceras reticulatum) Body length 25-35 mm. The mantle occupies about half the length of the body. The coloration is mostly cream or light coffee, with dark spots forming a grid-like pattern, especially noticeable on the mantle and back. The head and neck are also covered with small spots; tentacles are blackish. It lives in open places, avoiding forests and shrubs, more often on clay soils - meadows, fields, vegetable gardens, landfills, and in cities - in parks and gardens. Of all the slugs, the most dangerous pest of crops. In gardens, it willingly attacks cabbage, eating out large holes not only in the outer leaves, but also inside the head. In rainy years it damages winter seedlings. Widely distributed in the European part of the USSR.

field slug (Deroceras agreste) Body length 35-40 mm. The mantle occupies about 1/3 of the body length. Coloring from almost white to cream, without a dark pattern. It lives in open places - meadows, swamps, near roadside ditches, on forest edges, but, unlike the reticulated slug, avoids places with cultivated soil. Widely distributed throughout the USSR.

Slug smooth (Deroceras laeve) Body length up to 25 mm. The mantle occupies about half the length of the body. Coloring from reddish-brown to almost black, one-color. Very moisture-loving and cold-resistant. It lives in swamps, wet meadows, damp forests, on the banks of small overgrown reservoirs - here it can be found not only on soil and plants, but also on their underwater parts. Widely distributed throughout the USSR.

GENUS LIMAX (Limax)

Large slugs, more than 100 mm long. The coloration is spotted, sometimes the spots merge into dark stripes. A keel protrudes on the caudal part of the back. The body is wrinkled, the wrinkles are long, convex, with deep grooves between them.

Slug black (Limax cinereoniger) Body length 150-200 mm. The mantle occupies about 1/4 of the body length. The coloration is black or dark gray, the keel is light. Tentacles with black dots. Lives in deciduous and mixed forests, can also live in coniferous forests with good grass cover. It feeds mainly on fungi and lichens. Distributed in the Karelian Autonomous Soviet Socialist Republic, the Baltic States, Belarus, in the western and central regions of the RSFSR, east to Nizhny Novgorod.

Slug big (Limax maximus) Body length up to 130 mm. The mantle occupies about 1/3 of the body length. The coloration is variegated: on a yellowish, ash-gray or off-white background, 2-3 pairs of dark stripes or rows of dark spots. The tentacles are one-colored, without dark dots. It lives in cities - in parks, gardens, greenhouses, vegetable stores, where it can harm. Distributed in the northwestern and central regions of the European part of the USSR.

GENUS MALAKOLIMAX (Malacotimax)

Malacolimax gentle (Matacolimax tenellus) Body length up to 50 mm. The mantle occupies about 1/3 of the body length. The color is monochromatic, often yellow, greenish or grayish-yellow, sometimes orange-yellow. The head and tentacles are black or dark brown. The slime is yellow. It lives in deciduous forests, occasionally in coniferous ones. It feeds on cap mushrooms and lichens. Distributed in the northwestern, western and central regions of the European part of the USSR.

CLASS Bivalve mollusks (Bivalvia)

In bivalve mollusks, the shell consists of two halves connected on the dorsal side by an elastic ligament. On the ventral side, the halves of the shell can move slightly apart, and the leg of the mollusk protrudes through the gap formed. When moving, the mollusk pushes the silt or sand at the bottom with its foot, like a plow, catches the ground with its foot and pulls the body with the shell forward, again pushes the leg forward, pulls itself up again and thus crawls along the bottom with small steps. Some bivalves do not move, but sit in one place, attached to the substrate with special sticky threads. Bivalve molluscs do not have a head, so there is no grater. They feed on small planktonic organisms, which are sucked together with water through a siphon hole located at the rear end of the body. All bivalves live in water.

Dreissena river (Dreissena polymorpha) The shell of the river dreissena is greenish-yellow, with brown stripes, 30-50 mm long. The lower face, adjacent to the place of attachment, is flat, two lateral ones are convex. It lives in rivers, lakes and reservoirs.

FAMILY PERLOVITSA (Unionidae)

The shells of barley have an elongated oval shell. On each leaf, the most convex, prominent part is visible - the top. Concentrating around the top, arcuate lines pass on each leaf. Some of these arcs are sharper, darker - these are annual arcs, they can be used to approximately determine the age of the mollusk. There are 4 genera in the family. The most famous are barley and toothless.

GENUS OF PERLOVITSA (Unio) Barley shells have a thick-walled shell, the tops of the valves protrude upwards. If you look at the shell from the end, then the place of fastening of the valves - the ligament - will be in the recess.

Barley ordinary (Unio pktorum) The shell of the common barley is long, narrow, up to 145 mm, with almost parallel dorsal and ventral margins. The color in young individuals is yellow-green, in old ones it is greenish-brown. It lives in lakes and rivers, in places with a slow current, on sandy, not very silted ground. Distributed in the European part of the USSR, except for the north and northeast.

Barley swollen (Unio tumidus) This species has a shorter shell, up to 110 mm, with non-parallel edges. The habitats and distribution are the same as those of the common barley.

GENUS OF TOothless (Anadonta) In toothless, the shell is thin-walled, the tops of the valves do not protrude much. If you look at the sink from the end, then the place of fastening of the valves is not deepened. Some species have a large keel on the upper edge of the valve. The shape of the shell is very variable in individuals of the same species living in different water bodies.

GENUS PEA (Pisidium) In peas, the top of the shell valves is shifted to the side, the shell is short-oval. The size of the peas does not exceed 11 mm.

River pea (Pisidium amnicum) The shell diameter of the river pea is 10-11 mm. It lives in the backwaters of rivers and lakes, on silty-sandy soil. Distributed in the European part of the USSR and in Siberia to the Lena.

Pond snails (Lymnaea stagnalis) belong to the class of gastropods, a subclass of true snails and a detachment of pulmonary mollusks (Pulmonata). Currently, there are about 120 species. The pond snail and other species of this family are very variable: the configuration, size, and thickness of the shell, and the color of the legs and torso of these organisms vary. They live in fresh water rivers, lakes and ponds. Ponds are equipped with a solid shell with a sharp top, twisted in 4 - 5 turns, and a large mouth, from which the head and leg protrude. The head is equipped with a mouth, two tentacles and two eyes. The body of the pond snail is a large spiral sac covered with a mantle and shell, and located above the leg. Bilateral symmetry is broken in the pond snail due to the turbospiral shape of the shell, which led to the asymmetry of the organs located in the mantle cavity (one atrium, one kidney, half of the liver). On the ventral side of the pond snail is a massive muscular leg with a wide sole, which serves to move it.

Structure

Pond snails, like other lung snails, lack primary gills. They breathe with the help of the lung, which is a specialized section of the mantle cavity, enriched with a large number of blood vessels. Pond snails periodically rise to the surface of the water surface to fill the lung with atmospheric air through a round breathing hole located at the base of the shell, since they can stay under water for no more than an hour. In addition, pond snails are able to breathe the entire surface of the body. In clean reservoirs, in oxygen-enriched water, mollusks can live at a depth and not rise for a new portion of oxygen. They get their oxygen from the water that fills the lung, which functions like a gill. Inhabited in such conditions, mollusks are smaller than those that live in shallow water. The heart is located next to the lung and consists of an atrium and a ventricle. Pond snails have an open circulatory system with colorless blood. The excretory organ is one kidney.

The nervous system is a near-pharyngeal nerve ring formed by nerve nodes, from which nerves extend to all organs. The tentacles are equipped with tactile receptors and chemical sense organs (taste and smell). There are also organs of balance.

The digestive system of the pond snail consists of the esophagus, sac-like stomach, liver, intestines and ends with the anus. The oral cavity of the pond snail passes into a muscular pharynx, in which a grater tongue (radula) is located, covered with rows of hard teeth. With a radula, the pond snail scrapes off particles of plants and small animals and eats them.

Pond snails feed mainly on plant foods. Their diet includes both living plants and decomposed ones. In addition, they eat bacteria and animal food (flies that have fallen into the water, fish eggs).

Mollusks, or soft-bodied, live in the sea, in fresh waters and on 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 is composed 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, the pond snail's digestive system 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 general terms it 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 damp places and feed on 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.