Garden snail (Cepaea hortensis). Common pond snail (Limnaea stagnalis)

Gastropods are the most numerous and diverse group shellfish It has about 90,000 species living in the seas, fresh water bodies, and 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 visible: the head, the leg and the bag-like body. The top of the body is covered with a mantle. The pond snail has a spiral shell, twisted in 4-5 turns, which protects the body of the animal. The shell is made of lime and is covered with a horn-like organic substance on top. Due to the spiral shape of the shell, the body of the pond snail is asymmetrical, 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 pulls the animal inside the shell.

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

Internal structure

Digestive system

In the mouth, on a special movable 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 pharynx salivary glands, the secretion of which processes food.

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

Respiratory system

The body of the animal is covered on the outside with a mantle and is closely adjacent to inner surface shells. 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 not closed, 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 organs. A large vessel departs from the heart - the aorta. It branches into arteries. The blood then enters small cavities among the connective tissue. There the blood gives up oxygen, is saturated with carbon dioxide, enters the veins and travels through them to the lungs.

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 blood poor in oxygen and rich in carbon dioxide is called venous. The blood then collects 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, through a wide ciliated funnel, it communicates 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

The nervous system of mollusks is of the scattered-nodular type. It consists of five pairs of nerve ganglia (ganglia), interconnected by nerve bridges, and numerous nerves.

Due to the twisting of the body, the nerve bridges between some nodes form a cross.

Sense organs

The pond snail's head contains 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 located at the base of the tentacles. There are also organs of balance.

Reproduction. Development

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

After about twenty days, tiny animals emerge from the eggs. They grow quickly, eating plant foods.

The pond fish 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 live) dries out, not all mollusks die. Some secrete a dense film that closes the opening of the shell. In this state, a pond snail can live without water for about two weeks.

The shell is spirally twisted, without a lid. In some species (slugs) the shell is reduced. The ganglia are concentrated in the head region, forming the peripharyngeal nerve ring. A nerve branch extends from the right parietal ganglion to the accessory azygos ganglion. Pulmonary molluscs have one atrium, one lung and one kidney.

rice. 1.
A - top view, B - side view: 1 - mouth, 2 - cerebral ganglion, 3 - pleural ganglion,
4 - parietal ganglion, 5 - visceral ganglion, 6 - liver, 7 - pericardium, 8 - lung, 9 - heart, 10 - kidney, 11 - stomach, 12 - gonad, 13 - mantle cavity, 14 - leg, 15 - head, 16 - anus, 17 - additional azygos ganglion.

(Fig. 2) is one of the largest terrestrial mollusks in Europe. The spherical-twisted shell has 4-4.5 whorls, reaches a height of 5 cm, a width of 4.5 cm. The shell is usually yellowish-brown in color with dark brown stripes running along it. The color and width of the stripes vary. On the head of a grape snail there are two pairs of tentacles, one of which contains eyes, the other serves as organs of smell and touch. It feeds on green parts of plants. By eating grapevine leaves and buds, it can cause harm to vineyards.

rice. 2. Grape
snail (Helix pomatia).

The grape snail is a bisexual animal. It has one hermaphrodite gland in which female and male gametes are formed. A hermaphroditic duct departs from the gland, into which the albuminous gland flows. After the confluence of the protein gland, the hermaphroditic duct expands, forming two gutters: a wide one for eggs and a narrow one for sperm. Next, each of the gutters is transformed into independent channels, respectively, the oviduct and the vas deferens. The oviduct drains into the uterus, the uterus into the vagina. In addition to the oviduct, the ducts of the spermatic receptacle and bags with calcareous needles flow into the uterus. The vagina opens with the genital opening in a special skin invagination - the genital atrium. The vas deferens passes into the ejaculatory canal, which penetrates the copulatory organ, which opens into the genital atrium. During mating, grape snails exchange spermatophores (packets of sperm), which are captured by the spermatheca. Fertilization will occur after mating. Eggs that enter the uterus are fertilized by foreign sperm coming from the spermatic receptacle. The formed eggs are laid in a burrow, which the parent first digs in the soil with its muscular leg.

In a number of European countries, grape snails are used as food.

rice. 3. Big
pond snail (Limnea stagnalis).

(Fig. 3) and small pond snail (L. truncatula)- frequently encountered inhabitants of our fresh water bodies. The head bears one pair of tentacles, at the base of which there are eyes. Hermaphrodites. During mating, just like in a snail, sperm are exchanged and eggs are fertilized by foreign sperm. They lay eggs in slimy cords that are attached to underwater plants and other objects. Development is direct, without larval stage. They breathe atmospheric oxygen, so they periodically rise to the surface of the water in order to take in a portion of air.

The size of the shell, its shape, the color of the leg and body are characterized by strong variability in the large pond snail. For example, the color of the body and legs can vary from blue-black to sandy yellow. The length of the shell of a large pond snail can reach 7 cm. Great pond snail omnivorous, feeds not only on plants and small animals, but can eat dead plant debris and animal corpses.

rice. 4.
A - Arion rufus,
B - limax maximus
(Limax maximus).

A collective group of terrestrial pulmonary mollusks with a partially or completely reduced shell (Fig. 4). On the head next to mouth opening there is a pair of labial tentacles, on top there are ocular tentacles bearing eyes. The narrowed portion of the body between the head and mantle is called the “neck.” At the bottom of the neck, a gland duct opens that secretes mucus. In addition to this gland, numerous mucous glands are scattered throughout the surface of the body, so the entire body of the slug is covered with mucus. The main purpose of mucus is to moisturize the skin. On the right side of the neck is the genital opening. The mantle looks like a flat thickening on the dorsal side of the body. Near the right edge of the mantle there is a respiratory opening leading to the pulmonary cavity. Near the respiratory opening on the right edge of the mantle, the anus and excretory pore open. Slugs are bisexual animals. During mating, male gametes are exchanged. Eggs are laid in moist, shaded areas.

Most slugs feed on plants, lichens or fungi. Predatory slugs feed on oligochaetes or other types of mollusks. Active at night, stay hidden during the day. Slugs settling in areas occupied by agricultural crops can cause significant damage to crop plantings. For example, the field slug (Agrolimax agrestis) eats sown grains and seedlings of winter wheat and rye, and the netted slug (Deroceras reticulatum) causes great damage to the harvest of tomatoes and cabbage.

Description of classes, subclasses and orders of the Mollusc type:

• Class Gastropoda

  • Subclass Pulmonary (Pulmonata)

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

Lifestyle and external structure. In ponds, lakes and quiet river backwaters, you can always find a large snail on aquatic plants - the large pond snail. On the outside, the pond snail's body is covered with 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 apex, 4-5 whorls and a large opening - the mouth.

The pond snail's body 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 pond snail's leg is muscular. When wave-like muscle contractions run along its sole, the mollusk moves. The pond snail's leg is located on the ventral side of the body, and therefore it is classified as a gastropod. In front, the body meets the head. A mouth is placed on the underside of the head, and two tentacles are located on its sides. The pond snail's tentacles are very sensitive: when you touch them, the mollusk quickly retracts its head and leg into the shell. There is an eye near the base of the tentacles on the head.

The body follows the shape of the shell, closely adhering to its inner surface. The outside of the body is covered with a mantle, with muscles and parenchyma located underneath it. Inside the body there remains a small cavity in which the internal organs are located.

Nutrition. Pond snail feeding aquatic plants. In his mouth is a muscular tongue covered with hard teeth. The pond fish from time to time sticks out its tongue and scrapes off the soft parts of plants with it, like a grater, which it swallows. Through the pharynx and esophagus, food enters the stomach and then into the intestines. The intestine bends in a loop inside the body and ends on its right side, near the edge of the mantle, with the anus. Next to the stomach in the body cavity lies a greyish-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 water, it breathes oxygen atmospheric air. To breathe, 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 - the lung. The walls of the lung are densely intertwined with blood vessels. This is where the blood is enriched with oxygen and carbon dioxide is released. Within an hour, the mollusk rises to breathe 7-9 times.

Circulation. Next to the lung is the 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 turn into thin capillaries, from which blood flows into the space between the organs. Thus, the circulatory system of the mollusk is not closed. The blood is then collected in a vessel that approaches the lung. Here it is enriched with oxygen and flows through the vessel into the atrium, and from there into the ventricle. Pond snail blood is colorless.

Selection. The pond snail has only one excretory organ - the kidney. Its structure is quite complex, but general outline resembles the structure of the excretory organs of an earthworm.

Nervous system. Main part nervous system The pond snail is a peripharyngeal cluster of nerve ganglia. Nerves extend from them to all organs of the mollusk.

Reproduction. Pond fish are hermaphrodites. They lay masses of eggs enclosed in transparent slimy cords that attach to underwater plants. The eggs hatch into small mollusks with a thin shell.

Other gastropods. Among the large number of species gastropods marine ones are especially famous, thanks to 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 and is eaten in some countries.

Common pondweed– lat. Limnaea stagnalis, a member of the phylum Mollusca, belongs to the class Gastropods. A feature of the common pond snail, like all representatives of the pond snail family, is its peculiar swimming in water. A special organ (leg) is directed upward during movement, protruding slightly on the surface of the water. To prevent the common pond snail from drowning while moving, the middle of the leg bends down, thus acquiring the shape of a boat, while the animal’s shell is directed down to the bottom. Scientists do not yet understand this peculiar movement.

Structure

The snail's eyes are located at the base of the second pair of tentacles. The common pond snail breathes through one lung, which is a modified mantle cavity. The air in the lungs, in a calm state of the mollusk, prevents it from falling to the bottom. But if at this time you touch an ordinary pond snail, it instantly releases air from the respiratory tract and instantly falls down. It also has one kidney and one atrium. The shell of the common pond snail has the shape of a twisted spiral.

Animal characteristics:

Dimensions: clam length 5 – 7 cm.

Color: The common pond snail has variable colors, ranging from dark blue to yellow. The shell has a thin translucent structure.

Food and habitat

Common pond snails are omnivores; they can feed on both plant and animal foods, mainly algae, aquatic plants, uruti leaves, etc. Common pond snails are widely distributed throughout to the globe, mainly on ponds, rivers, lakes, etc. They live at shallow depths.

After starting a new aquarium, novice aquarists are often faced with the problem of contamination and the appearance of unwanted algae. There are many ways to clean an aquarium tank, the best of which, perhaps, is biological, that is, adding natural cleaners to the fish. Often, fish owners resort to the help of pond snails. They not only help fight pollution, but are also interesting in terms of observing their behavior.

Description, types

The pond snail (lat. Lymnaeidae) is a snail belonging to the genus of pulmonate mollusks. As the name implies, it lives in fresh water bodies with stagnant water or water with a very slow flow.

Did you know? Snails belong to the most ancient animals on Earth. According to scientists, they appeared over 500 million years ago.

The body of the mollusk is divided into three parts: head, torso and leg. The pond snail has a finely spiraled shell with five to six whorls, mostly twisted to the right. Left-handed ones are found among the inhabitants of New Zealand and the Sandwich Islands. The shell opening is large, rounded at the front. The shape of the shell depends on the current of the body of water where the snail lives. Its dimensions range from 1 to 6 cm in height and from 0.3 to 3.5 cm in width. The body is tightly attached to the shell. The head of this mollusk is large. It has flat, triangular-shaped tentacles with eyes on their inner edge. The hole through which the pond snail breathes is protected in the form of a prominent blade. The color of the snail depends on the living conditions. The shell is usually brown. The head and body can be colored from black with a blue tint to yellow with brownish.
In nature, the pond snail is represented by many species living in the Northern Hemisphere, in Eurasia, North Africa, North America. Some of its representatives can be found in geysers, sulfurous, slightly salty and salty waters. They can be found even at an altitude of 5.5 thousand meters in Tibet and at a depth of 250 m.

Did you know?The snail's tiny brain is divided into four sections and is quite efficient. Scientists claim that these mollusks have the ability to make independent decisions. After conducting more detailed studies of two neurons that are responsible for the feeling of hunger and the decision to go for food, they decided to use this data to work with simple algorithms in robotics.

Each species is distinguished by the characteristic color of the shell, body, leg, as well as the shape and thickness of the shell walls, the shape of the helix and the mouth.

We invite you to take a closer look at the most famous species:

1. The common prudovik is a big one. The largest in our area and the most famous representative of the family. The shell is elongated, conical, 4.5-6 cm long and 2-3.5 cm wide. It is twisted in a spiral with 4-5 turns, which quickly expand, forming a large hole. Its color is brown, the walls are thin and translucent; The body of the mollusk is greenish-gray. The species is widespread, found throughout the Northern Hemisphere in various freshwater bodies.
   
2. This species has an elongated, pointed at the top and durable shell. The curls twist to the right and have six to seven turns. The shell is thin, almost transparent, pale yellow in color. Its dimensions are small: length - 1-1.2 cm, width - 0.3-0.5 cm. The body and mantle of this pond snail are light gray. There are dark spots on the mantle. The species is distributed throughout Russia, living in ponds, swamps, and puddles. Can live along the banks of drying up reservoirs.
   
3. Ushkovy. It is named so because the mouth of the shell is very similar in appearance to a human ear. Its shell is small - 2.5-3.5 cm in height and 2.5 cm in width. Has thin walls. Painted in a gray-yellow tint. Has up to four turns. The last turn is very large. The body is colored green-gray or yellow-green with numerous inclusions. The mantle can be plain - light gray, or spotted. The eared pond snail lives in various reservoirs, lives on plants, snags, and stones.
   
4. Ovoid or oval. Like the eared pond snail, the egg-shaped shell curl makes up a third of the mouth. The sink has thin walls and is therefore very fragile. U adult it is 2-2.7 cm in height and 1.4-1.5 cm in width. The shape of the mouth is ovoid. The shell is painted light pink, shiny and almost transparent. The body is light gray or light olive in color. The mantle is also light gray. Habitat The habitats of the ovoid pond snail are lakes and quiet rivers. It can live both in the coastal zone and in the depths.
5. The marsh pond snail has a shell height of 3.2 cm and a width of 1 cm. In appearance, this species is similar to the common pond snail, but differs from it in that its shell has the shape of a sharp cone with a small hole. It is dark brown in color. In addition, the marsh one is smaller than usual: the height of the shell is 2-3 cm, the width is 1 cm. There are six to seven whorls on the shell. Its walls are thick. The body is greenish-gray in color. The mantle is light. Lives in small bodies of water - swamps, puddles, streams, ponds.
   
6. Frilled or frilled. It got its name due to the fact that its shell is completely or partially covered by a mantle. The shell of the raincoat is shiny and smooth. It can be colorless, yellowish or yellowish-horny. It is small in size, its height is 1.9 cm, width is 1.2 cm. It has 2.5-4.5 curls. The last one is very big. The shape of the shell resembles a ball. The mouth is oval and large. The body is colored olive with gray color with numerous inclusions. The mantle is yellow-brown or yellow-green with large light spots. Lives in lakes quiet rivers, in shallow water.

Habitat in nature

In nature, common pond snails eat mainly plants. However, their diet may also include animal food (flies, fish eggs, etc.) and bacteria. They breathe as they crawl out of the water to the surface. They need to carry out six to nine such lifts per day. Those snails that live at great depths are able to subsist on air dissolved in water. They draw water into the pulmonary cavity. Pond snails can swim - they turn their soles up and give it a slightly concave shape.

Did you know? Snails have no hearing or 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 themselves. Receptors are located on their horns.

Under natural conditions, these snails can rarely be found idle; usually they are “in a hurry” somewhere, busy with something - for example, scraping algae from stones. Maximum speed which they can develop is 20 cm per minute.
It is interesting that these mollusks are able to survive when the reservoir dries out, sealing the shell with a thick film, as well as when the pond is covered with ice - after it thaws, they come to life and continue their life activities. The average lifespan of an aquarium pond snail is two years. wildlife- nine month.

The pond fish is an unpretentious aquarium inhabitant. The main conditions for its maintenance are the water temperature not lower than 22°C, its moderate hardness and weak light - preferably fluorescent with minimal power.
With more warm water snails will reproduce more often and actively, and this is not desirable for home aquariums. The size of the aquarium is not important. Rocky soil is suitable. It can be pebbles or coarse sand.

No special cleaning is required for shellfish. All you need is standard procedures that every aquarist should follow:

• weekly water change by 30%;
• aeration;
• filtration.

Nutrition, mineral supplements

Every aquarium owner planning to place a pond snail in it will be interested in the question of what it eats and where to get food for it. There will be no problems with this, since he can eat what the fish haven’t eaten, their excrement, and rotten plants. A person can prepare a salad for him from finely chopped greens, cabbage, zucchini, pumpkin, tomatoes, and other vegetables and fruits.
You should be careful when introducing pond snails into an aquarium, since upon reaching adulthood they can be very voracious and eat most of the underwater vegetation. Occasionally, snails will need to be fed with mineral supplements. The main thing for them is calcium, so you can add crushed eggshells, chalk, and sepia to them.

Important! You should not plant pond snails in a tank where soft and succulent underwater plants grow. This threatens the death of the latter. These snails cannot handle only algae with hard, dense leaves.

Compatibility with other aquarium inhabitants

Diseases

Snails rarely get sick. But they themselves serve as a source of infectious diseases for other aquarium inhabitants. Moreover, the danger lies in the fact that usually the presence of infection in the body of a mollusk does not affect its appearance, so it is not always possible to immediately determine whether it is dangerous for fish or not. The most common disease in the small pond snail is fungal infection - its shell becomes covered with a white coating.
Treatment will consist of baths with the addition of solutions of salt or potassium permanganate. Also, if a clam does not consume the required amount of vitamins and minerals, the walls of its shell may become thin and damaged. If you observe this problem, it is worth feeding the snail with substances containing calcium. Small cracks will disappear on their own after some time after starting treatment. But the deep ones will need to be “glued together” with a special preparation sold in zoological stores.

Breeding

Pond snails reach sexual maturity at six to eight months. Since they have no sexual differences, representatives of the pond snail family reproduce by laying eggs, usually from 20 to 130 per clutch. This process can occur in them several times a year, and over the course of its entire life, one individual is capable of producing offspring about five hundred times. Mollusks lay eggs on the leaves of plants. Incubation occurs within 14-20 days. The eggs hatch into babies with a thin shell. Thus, pond snails, in addition to being very voracious, are also fertile. Therefore, aquarists do not have a question about breeding them. More often, another problem arises - how to prevent their frequent reproduction and overpopulation of the aquarium. If the task is to breed these mollusks, then the reproduction process can be stimulated by raising the water temperature by a couple of degrees.

Did you know? The largest sea snail is considered to be the giant Australian whelk, whose shell reaches 91 cm and weighs 18 kg. The tiger Achatina is recognized as the largest land mollusk - with a shell 27.5 cm high and a body weight of about 1 kg.

It is not necessary to add snails to the aquarium yourself. They can appear unexpectedly - their eggs are carried along with underwater plants. In this case, the owner needs to organize their proper maintenance and ensure that the number of individuals does not exceed the capabilities of the aquarium tank. If it is possible to control their reproduction, then the presence of pond snails will definitely benefit the fish’s home - they can help get rid of unfriendly algae settling on the decor, walls and plants, and keep their place of residence clean. Mollusks are indispensable cleaners for spawning aquariums. An overpopulation of snails threatens oxygen deficiency, which is why, first of all, the fish will suffer. Thus, it is possible, but not advisable, to keep pond snails in an aquarium. On the one hand, they are able to clean the tank, get into places where the human hand cannot reach, and get rid of unnecessary algae. In addition, they do not require special care and nutrition. On the other hand, these snails can cause serious damage to underwater plants and, as a result, to the beauty of the aquarium. They are often added to an aquarium without live algae by beginners. Experienced aquarists prefer to deal with snails of other species.