Pond snails: description of freshwater mollusks. Large pond snail: characteristics, habitat, reproduction Species characteristics of the pond snail

Pond snails are gastropods.

The largest of domestic representatives pond snail family (Limnaeidae) - common pond snail (Limnaea stagnalis), having an elongated conical shell up to 55 mm high. U eared pond snail (L. auricularia) shell with a short curl, resembling an ear (height 26 mm). Marsh pond snail (L. palustris) similar to the common one, but its shell has the shape of a sharp cone with a small hole (shell height 32 mm). Sink egg-shaped pond snail(L. ovata) with a short whorl, and its last whorl with a wide ovoid opening (shell height 18 mm).

Pond fish live in freshwater bodies of water. The common pond snail is especially widespread. It stays near the surface of the water and is easy to catch. In the jar, it slowly crawls along the walls of the vessel. SlipperThis occurs due to the fact that the muscles of the sole of the wide leg contract in a wave-like manner.

Ponds: 1— ordinary; 2 - ear; 3 - swamp; 4 - ovoid

Pond snail structure: 1— oral lobes; 2— tentacles; 3— eyes; 4 - leg; 5— breathing hole

Pond snails can wander along the underside of the surface film of water, holding onto it with the help of their soles. At the same time, a ribbon of mucus remains behind them. It is believed that this movement is due to the surface tension of water.

The pond snail has air inside its respiratory cavity, which, like the swim bladder of a fish, supports it. If you give a slight push to a crawling snail, it will submerge in the water and float up again, like a cork. The cochlea can voluntarily compress the respiratory cavity and, due to a decrease in specific gravity sink to the bottom; when the cavity expands, it floats to the surface.

Pond fish are capable of staying underwater for very long for a long time. This is explained by the fact that the closed lungIn this cavity, air is used very rationally during breathing, and oxygen is gradually replaced by carbon dioxide. In addition, it is likely that respiration also occurs through the skin, using oxygen dissolved in water.

Pond snails feed on the leaves and stems of aquatic plants. Therefore, individuals of large species cannot be planted in decorative aquarium. In addition to plants, they eat small organisms (hydra, protozoa), fish eggs, meat and even the remains of dead fish and snails. So it is better to keep pond snails in a separate container.

When breeding, these snails lay eggs on aquatic plants and other objects. The masonry has the appearance of a transparent gelatinous sausage. In twenty daysThe eggs hatch into tiny snails, which, feeding on plant foods, grow quite quickly. This whole process can be observed in the aquarium.

All pond snails, like most gastropods, hermaphrodites.

Reproduction of pond snails

During the mating process, pond snails mutually fertilize each other, since they are bisexual creatures. Pond snail eggs are long, transparent, gelatinous cords that are attached to a variety of underwater objects. The eggs can even attach to another pond snail.

Caviar has complex structure– the egg cell is immersed in a mass of protein, and on top it is protected by a double shell. In turn, the eggs are in a mucous mass and are dressed in a special shell or cocoon. A cord extends from the inner part of the shell, the second end of which is attached to the outer shell of the egg, that is, it turns out that it is suspended from the wall of the cocoon. This complex structure of eggs is characteristic of many species of mollusks.

Thanks to this structure, the egg is provided with nutrients and protected from environmental influences. Inside the eggs, pond snails develop without the free-swimming larval stage. Most likely, this structure of eggs in pond snails is due to their connection with land ancestors, where such adaptations were more important than in water. The size of the clutch and the number of eggs in it can vary significantly. Sometimes there are up to 270 eggs in one cocoon.

Pond snails differ markedly from each other, and their size, color, thickness and shape of the shell can vary significantly. There are both large individuals and almost dwarf ones that have not matured due to poor nutrition or unfavorable conditions. external factors. In some individuals the shell consists of thick walls, while in others the shell is very thin and fragile, it breaks at the slightest impact. The curls and shape of the mouth vary greatly. The color of the body and legs can vary from sandy yellow to blue-black.

Thanks to this tendency for pond snails to vary, a huge number of varieties of mollusks have formed within the species. Therefore, it can be difficult for even scientists to determine whether a particular individual is simply a variety or a new subspecies.

Species of pond snails

In our reservoirs, not only common pond snails are often found, but also another species - the long-eared pond snail. In addition, the marsh pond snail and the egg-shaped pond snail live in stagnant water.

By 6-7 months, small pond snails reach sexual maturity, and they live for about 2 years. An egg cocoon can contain from 4 to 25 eggs. Young individuals develop over 10-20 days.

Family representative freshwater mollusks group of gray-eyed people. It has an elongated, strongly pointed shell towards the apex, curled to the right, usually thin and translucent. The shell curls expand very quickly and the last one, the so-called belly, occupies the most significant part of the shell. Its color is pale yellowish.
The pond snail, like the reel, is one of the mollusks with pulmonary respiration and therefore from time to time floats to the surface to inhale atmospheric air. Its body is greenish-dark gray in color with yellow spots. The head is equipped with two triangular flat tentacles, at the base on the outer side of which there are eyes. The leg is shorter than the reel leg, but significantly wider. From the leg, the body inside the shell rises upward in a spiral and forms, closer to the opening of the shell, a kind of sac containing a mass of vessels and serving as a respiratory organ. On its right side there is an opening for air intake, which is closed by tightly locking muscles. The hole and the entire respiratory organ are easily visible when the animal, crawling along the plant, turns and often almost completely crawls out of the shell. This often happens when the pond snail, like a reel, crawls with its foot along the surface of the water, which it does in order to breathe atmospheric air.
Under the head there is a mouth opening, consisting of an upper jaw and two lateral sickle-shaped ones. Placed right here long tongue, which rake in algae. This is especially clearly visible when a pond snail crawls along the glass of an aquarium.
Pond snails are bisexual animals, and therefore they can be found mating 6-10 pieces together. Pond snails lay their eggs on the lower surface of floating leaves, on glass in an aquarium, and on various objects. The caviar is not connected in a flat cake shape, but in a worm-shaped or oval shape, similar to an icicle. From May to August they lay up to 20 such icicles, and each icicle contains 20-100 eggs. The eggs are transparent. The development of the embryo proceeds quickly, and after just a few days the embryo, covered with ciliated hairs, begins to rotate rapidly.
The snails hatch from their eggs no earlier than twenty, and sometimes even forty days, which, in all likelihood, depends on both the water temperature and the intensity of the lighting.
A remarkable phenomenon is sometimes observed with the gelatinous mass of eggs of these snails. It is covered with some kind of mold - small cilia with a pin-shaped thickening at the end, apparently, lily of the valley. These creatures apparently contribute to the destruction of this mass.
The snail reaches large sizes, and therefore is not entirely convenient for an aquarium. This inconvenience is increased by the fact that it grows so quickly and short time reaches large sizes.
Along with its rapid growth, this snail is distinguished by its gluttony, which preys on aquarium plants, with particular preference for plants that are at the same time soft and juicy. When young, the pond snail is not dangerous, since it is small and its appetite is insignificant.
Pond fish are capable of eating the corpses of their own brothers.
Also belongs to the same genus of pond snails Limnea stagnalis (common pond snail), even larger than the above.

CLASS Gastropoda Molluscs (Gastropoda)

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

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

In the pharynx of gastropods there is a muscular tongue covered with spines - the so-called grater. Using it, the mollusk scrapes out plant tissue or scrapes off plaque from various microorganisms that forms on underwater objects.

Family identification table

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 difficult to see due to plaque covering the shell), up to 45 mm in size;
3(2) Shell without dark stripes, single color; size no more than 12 mm;
4(1) There is no lid at the mouth of the shell, so the compressed sole of the foot of the mollusk hidden in it is visible.
5(6) The coils of the shell are twisted in one plane;
6(5) The shell is twisted in a cone shape.
7(8) The shell is twisted to the right (if you take the shell so that the apex 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); PRUDOVIKA FAMILY (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 pondweed (Lymnaea stagnalis) The largest of our pond snails, the shell height is 45-55 mm, and in some individuals even up to 65 mm. Inhabits stagnant bodies of water - ponds, lakes, river backwaters with abundant vegetation. Here you can see how a pond snail, sticking its leg and head with tentacles out of its shell, slowly slides along 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 the water. In this case, at the mouth of the shell, on the side of the leg, a round breathing hole can be seen. In mid-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.

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

COIL FAMILY (Plarmrbidae)

In coils, the shell turns are located in the same plane. The coils are not as mobile as pond snails and cannot be suspended from the surface film of water. There are 35 types of reels found in the USSR.

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

Coil edged (Ptanorbis planorbis) The edged coil has a dark brown shell, 20 mm in diameter, with 5-6 turns. On the last whorl below there is a sharp protrusion - the keel. Inhabits small reservoirs and the coastal parts of large reservoirs. Distributed in Europe and Western Siberia to the Yenisei.

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

PHYSIS FAMILY (Physidae)

Physids have a tower-shaped shell, like those of pond snails, but twisted to the left.

Physa vesicularis (Physa fontinalis) The shell is matte, pale yellow, 10-12 mm high, 5-6 mm wide, the height of the mouth is more than half the height of the shell. Inhabits vegetation in various permanent bodies of water. Distributed in Europe and Northern 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 bodies of water that dry up in summer. Distributed in Europe, Western Siberia and the south of the Far East.

LUZHANKA FAMILY (Viviparidae)

The mouth of the shell is closed by an operculum at rest. Shells with dark longitudinal stripes. Meadow mollusks are also called vivibearers, since they do not lay eggs like other mollusks, but give birth to small meadows that already have a shell.

Swamp meadow (Viviparus contectus) Sink up to 43 mm high. It lives in lakes, ponds, and sometimes even in puddles of clean water. Stays on the bottom. Distributed in Europe and Western Siberia to the Ob.

BITINI FAMILY (Bithyniidae)

Like the lawns, the mouth of the shell is closed by an operculum when at rest, but the shells are single-colored, without stripes.

Bitinia tentacular (Bithynia tentaculata) Sink up to 12 mm high. Inhabits stagnant and weakly flowing water bodies, on rocks, 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 mollusks have bare skin, many species stick to wet habitats. In addition, during the day the animals are usually motionless. In this case, the snails completely hide in the shell, sucking the sole of their feet to the substrate, and the slugs crawl under shelters - stones, leaves, between lumps of soil. But at night, and in rainy times and during the day, the mollusks crawl from place to place.

SNAILS

In land snails, the shell is twisted in a spiral. In some species the shell is elongated, so that its height is noticeably greater than its width; in other species, on the contrary, the shell is low and its width is greater than its height. While moving, the mollusk sticks its head and leg out of the shell. There are 4 forward-facing tentacles visible on the head. At the ends of the two longer tentacles there are dark balls - these are eyes. If you carefully touch the tentacles, the mollusk immediately retracts them, and if it is greatly 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 internal structure). We will consider only some of the largest and most widespread forms.

Common Yantarka (Succinea putris) It got its name from the amber-yellow color of its elongated, thin, fragile, almost transparent shell. Shell height 16-22 mm, width 8-11 mm. Shell with 3-4 whorls, the last whorl is strongly swollen and widened, the aperture is ovoid. The amberfish lives in damp places - in wet meadows, near bodies of water, it can often be seen on the floating leaves of aquatic plants, and sometimes it even submerges in water. Widely distributed throughout the USSR.

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

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

Cochlodina rocky (Cochlodina laminata) This species has an elongated, fusiform, slightly swollen, smooth, shiny, light horny shell, 15-17 mm high, 4 mm wide, with 10-12 whorls. Two lamellar curved protrusions are visible at the mouth. Lives in forests, on rocks, stumps, tree trunks. Distributed in the central zone of the European part of the USSR, north to Leningrad region, east to Kazan.

Bush snail (Bradybaena fruticum) This snail has a spherical shell, almost smooth, 16-17 mm high, 18-20 mm wide, with 5-6 whorls. The color can vary from grayish-white to reddish-horny, often with a narrow brown stripe visible on the last whorl of the shell. Lives in bushes deciduous forests, gardens, the bush snail can often be found on nettles and coltsfoot. Sometimes she climbs quite high on bushes, tree trunks and fences. Distributed in the European part of the USSR, Crimea and the North Caucasus.

Garden snail (Cepaea hortensis) The garden snail has a cube-shaped shell, similar to the shell of a bush snail, 15-16 mm high, 19-21 mm wide, with 4-5 whorls, dark spiral stripes are visible on all whorls. Lives in sparse bushes and forests, on stones and cliffs. Distributed in the Baltic states

Hairy snail (Trichia hispida) This small snail has a shell covered with fine hairs (in older specimens they may 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 the forest floor, under stones, and dead wood. Distributed in the forest zone of the European part of the USSR, up to the Leningrad and Perm regions. Often causes damage to garden, fruit and berry crops and ornamental plants, scraping out the leaf tissues so that only thick longitudinal veins remain.

SLUGS

Slugs have a naked body, without a shell. In a calm state, slugs look like small mucous lumps, but when they move, their body stretches greatly. Like snails, 4 tentacles pointing forward are visible on the head. There are eyes at the ends of the two longer tentacles. A short neck is visible behind the head, extending into the back. Immediately behind the neck, an oval thickening is visible on the back, as if another layer of skin was placed on top. This is the so-called mantle, covering the respiratory organ - the lung. A rounded respiratory opening is visible on the right side of the mantle. As the name suggests, slugs produce a lot of mucus. It primarily protects the shellfish from drying out. In addition, mucus helps them when sliding. A crawling slug always leaves a noticeable shiny slimy trail. In the central zone of the European part of the USSR there are 16 species of slugs. Of these, we will consider the most common, widespread forms.

Determinative table of childbirth

1(2) The breathing hole is located in the front part 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 slugs does not exceed 50 mm.
5(6) Slime yellow;
6(5) The mucus is colorless, and when the mollusk is irritated, it becomes milky white; KIND OF ARION (Arion)

The body is thick and massive. The mantle is oval, rounded at the front and back. Breathing hole in the front part 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. The color can vary, from brown to orange, most often rusty. The middle of the back is usually darker. Lives in deciduous, mixed and coniferous forests, occasionally found in old parks and cemeteries. Favorite food is cap mushrooms, in which the slug eats out large cavities. It can also feed on dead parts of plants and animal corpses. Distributed in forest and forest-steppe zone European part of the USSR. In the Altai region, Eastern Siberia, the Amur basin and the Primorsky Territory, the subspecies Arion subfuscus sib ire us lives, characterized by a monochromatic black body color. In warm, damp summers, this slug causes damage to vegetable gardens and fields located near the forest.

Arion striped (Arion fasciatus) Body length up to 50 mm. The mantle occupies about 1/3 of the body length. The color is light - cream or yellowish-ashy, the middle of the back and mantle is slightly darker. There are clearly demarcated dark stripes on the sides. It is found more often in cultural biotopes - vegetable gardens, fields, orchards, parks. Often causes significant damage to agricultural 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 faint grooves, without rough wrinkles. Breathing hole at the back of the right edge of the mantle. The mucus is colorless, and when the mollusk is irritated it is milky white.

Reticulated slug (Deroceras reticulatum) Body length 25-35 mm. The mantle occupies about half the length of the body. The coloring 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 bushes, 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 agricultural crops. In vegetable gardens it readily attacks cabbage, eating large holes not only in the outer leaves, but also inside the head of cabbage. IN rainy years damages winter crop 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. The color ranges 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, it 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. Color ranges from reddish-brown to almost black, monochromatic. 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 color is spotty, 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 color 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 mushrooms 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.

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

GENUS MALACOLIMAX (Malacotimax)

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

CLASS Bivalve molluscs (Bivalvia)

In bivalves, 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 resulting gap. When moving, the mollusk pushes the silt or sand at the bottom with its foot, like a plow, hooks its foot into the ground and pulls the body with the shell forward, again pushes the leg forward, pulls itself up again and thus crawls along the bottom in small steps. Some bivalves do not move, but sit in one place, attached to the substrate with special adhesive threads. Bivalve mollusks do not have a head, so they do not have a grater. They feed on small planktonic organisms, which are sucked in along with water through a siphon opening 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 edge adjacent to the place of attachment is flat, the two lateral edges are convex. Lives in rivers, lakes and reservoirs.

PERLOVITSA FAMILY (Unionidae)

Pearl barley has an elongated oval shell. On each valve, the most convex, protruding part is visible - the apex. Concentrating around the apex, arched lines run along each valve. Some of these arcs are sharper, darker - these are annual arcs, from which you can approximately determine the age of the mollusk. There are 4 genera in the family. The most famous are pearl barley and toothless.

GENUS OF PERLOVITSA (Unio) Pearl barley has a thick-walled shell, the tops of the valves protrude upward. If you look at the shell from the end, the place where the valves are held together - the ligament - will be in the recess.

Common pearl barley (Unio pktorum) The common pearl barley has a long, narrow shell, up to 145 mm, with almost parallel dorsal and ventral edges. The color of young individuals is yellow-green, and that of older ones is greenish-brown. It lives in lakes and rivers, in places with slow flows, on sandy, not very silted soil. Distributed in the European part of the USSR, except in the north and northeast.

Pearl 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 pearl barley.

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

GENUS OF 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 diameter of the river pea shell is 10-11 mm. It lives in river backwaters and lakes, on silt-sandy soil. Distributed in the European part of the USSR and in Siberia to the Lena.

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

Structure

The body of the pond snail (Fig. 58) is enclosed in a spirally twisted shell of 4-5 turns, which has a sharp apex and a large opening - the mouth. The shell 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 fish.

Three main parts can be distinguished in the body of a pond snail: the body, 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. Mollusks that have legs like those of a pond snail are called gastropods.

The sole of the foot secretes mucus, with the help of which the foot glides over underwater objects or even over a surface film of water, suspended from below, the pond fish smoothly moves forward.

The body follows the shape of the shell, fitting closely to it. In the front part of the body is covered by a special fold - the mantle. The mantle (fold of skin) 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 meets the head. A mouth is placed on the underside of the head, and two sensitive tentacles are located on its sides. When touched, the pond snail quickly pulls its head and leg into the shell. There is an eye near the base of the tentacles.

Digestive system

The common pond snail is a herbivore. The mouth leads to the throat. It contains a muscular tongue covered with teeth - this is the so-called grater. With it, the pond snail scrapes off deposits of organic matter that form on underwater objects, or scrapes the soft parts of plants. In the pharynx, food is processed by secretions 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 the anus, located above the head.

Respiratory system

Although the pond snail lives in water, it breathes atmospheric air. To breathe, 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-chambered heart, consisting of an atrium and a ventricle, and blood vessels.

Arterial blood flows from the lung to the atrium, then to the ventricle, and from there it moves through the vessels to all organs of the body and flows between them. Such a circulatory system is called open. Having given up oxygen and enriched carbon dioxide, the blood collects in the venous blood vessels and enters the lung, where gas exchange occurs again. Oxygenated blood moves through the vessels to the heart. Ensure blood flow in an open circuit circulatory system more difficult than in a closed one, since in the spaces between organs the movement of blood slows down. 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 comes off near the anus.

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

Nervous system

The nervous system of the pond snail is of a nodal type and includes a peripharyngeal 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 vesicles lying on the surface of the nerve ganglion of the legs. In these bubbles in a liquid environment there 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 copulation of two individuals, mutual fertilization occurs, that is, the exchange of male gametes - sperm. After this, the individuals disperse and lay fertilized eggs tied into gelatinous cords. They attach to underwater plants.

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