To whom does the toothless belong. Toothless is a mollusk with a fragile shell. Initial level of knowledge

Toothless (from Latin - anodonta) belongs to the genus of freshwater bivalve molluscs of the unionid family (Unionidae). Their natural habitat is sandy or muddy bottom in freshwater reservoirs. These mollusks are distributed in Europe, Asia and America.

Toothless is the best natural aquarium filter. It feeds on various kinds of microorganisms, thereby purifying the water. Therefore, toothless can be grown as food for some aquarium fish. Shellfish contain a lot of zinc, iodine and other substances necessary for the development of fish. Serve them to the inhabitants of the aquarium in a crushed form.

The length of the toothless shell is on average up to 10-12 cm, but some species reach 20-25 cm. The shell is oval, one end is rounded, the other is pointed. The shell valves are the same, without locking teeth, which is why they got their name, the walls are thin, outside they are painted, as a rule, in brown-green or yellowish-gray color, and inside they are covered with mother-of-pearl. The cusps are interconnected by a ligament, an elastic ligament that opens and closes the cusps when the closure muscles are weakened.

The mollusk moves with the help of a leg in the form of a muscular wedge, which it releases from the ventral side of the shell, while leaving deep furrows in the sand.

According to aquarists, in favorable conditions, toothless lives up to two years.

Types of toothless

There are more than 50 types of toothless. Among the most common are common or swan toothless (Anodonta cygnea), duck toothless (Anodonta anatina), narrow toothless (Pseudanodonta complanata).

The common toothless reaches a length of 20 cm, its wings are very thin and brittle. Duck toothless is usually up to 15 cm long. Narrow toothless is a rarer species and is distinguished by small flat shells.

Toothless are very sensitive to the quality of the water in the aquarium. They do not tolerate any chemistry and immediately die from it. They need large amounts of oxygen, which they breathe through their gills. Therefore, there must be plants in the aquarium, and additional forced aeration will also not hurt.

Toothless plows the sand when moving and can damage plants with a weak root system, so they need to be planted in pots.

Comfortable water temperature for a mollusk is up to 20-22? Before placing a toothless fish in an aquarium (both lake and pet store aquariums), you need to quarantine it and acclimatize it to its new environment. To do this, gradually, over 6-12 hours, aquarium water is added using a dropper. The term of adaptation is 3-7 days. In this case, the water must be aerated.

It is necessary to constantly monitor the condition of the toothless in the aquarium. Dead molluscs have shell flaps wide open.

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General characteristics of Mollusks.
The structure of gastropods on the example of the Great pond snail
The structure of bivalve mollusks on the example of Bezzubka.
Variety of Mollusks
The value of Mollusks in nature and human life

Number of species: about 130 thousand.
Habitat: fresh and salt water, many have adapted to life on land

General characteristics of the Mollusk type:

The trunk forms a skin fold - the mantle. A mantle cavity is formed between the mantle and the body, into which the anus, the ducts of the kidneys and gonads open, the respiratory organs, and some sensory organs are also located there.

There is a shell that performs the functions of an external or internal skeleton and protects mollusks. The outer layer of the shell is organic, the middle layer is calcareous, and the inner layer is mother-of-pearl. In some species of mollusks, the shell is reduced.

The segments merge into a small number of body regions, each providing a specific function.

The body cavity is mixed. The internal organs are immersed in the parenchyma, but there are cavities filled with fluid. The secondary cavity was partially reduced.

Digestive system consists of an anterior, middle and hindgut. Digestive glands arose, providing faster and more complete digestion of food. The ducts of the salivary glands open into the pharynx, and the ducts of the liver open into the midgut.

Circulatory system open, consists of the heart and blood vessels. Arteries depart from the ventricle of the heart, through which blood flows from the heart to all organs. Part of the way the blood passes not through the vessels, but through the cavities between the internal organs.

Respiratory system in most species they are represented by gills, in terrestrial representatives - by lungs. Gills and lungs are modified parts of the mantle, in which there are a lot of blood vessels.

excretory organs- kidneys, which are modified metanephridia.

Nervous system scattered-nodal type. Of the sense organs - the organs of chemical sense and balance, many have eyes.

breed shellfish only sexually. There are dioecious and hermaphrodites. Development is direct or with a larval stage.

The most common mollusks belong to three classes: Gastropods, Bivalves, Cephalopods.

The structure of gastropods on the example of the Great pond snail

Animals of this class live in marine and fresh water bodies, many live on land. A characteristic feature is the asymmetry of the structure. The shell and body of gastropods are spirally twisted. The shell consists of two layers: a thin organic outer layer and a porcelain-like calcareous layer.

The body of a pond snail consists of three sections: head, trunk and legs. There are 1-2 pairs of tentacles on the head, well-developed eyes, which are often placed on the top of the tentacles; the leg is usually wide with a flat sole, the torso is spirally twisted. In the pharynx is the radula. This is a grater for scraping the soft parts of plants, consisting of horny cloves.

The respiratory organs in most gastropods are represented by gills. In terrestrial gastropods, the respiratory organ is the lung. A section of the mantle cavity in them is isolated and opens outwards with an independent opening. This is the so-called pulmonary cavity, in the walls of which numerous blood vessels are located. Blood is most often colorless, sometimes it contains a pigment containing copper and giving the blood of mollusks a blue color.

In the excretory system of a large pond snail, only one kidney is preserved. Large pond snail hermaphrodite, cross fertilization. Lays eggs in the form of slimy cords. Development is direct, without a larval stage. Young individuals develop from eggs.

The structure of bivalve mollusks on the example of Bezzubka

This class includes sedentary marine and freshwater molluscs, the body of which is enclosed in a shell consisting of two valves. A typical inhabitant of the bottom of fresh water bodies is toothless. On the dorsal side, the flaps are connected with an elastic ligament (ligament), or with a lock. The sashes are closed with the help of two muscles - contactors. There is no head. The body has only a torso and a leg. Bivalves move slowly, usually pushing their legs forward, and then pulling their whole body to it.

The body is covered with a mantle, which hangs from the sides in the form of folds. On the dorsal side, the mantle grows together with the body of the mollusk. Often, the free edges of the mantle grow together, leaving holes - siphons for the input and output of water from the mantle cavity. Shell shells are formed by the outer epithelium of the mantle. The outer layer of the shell is composed of organic matter; the middle layer is formed from carbonic lime and has the greatest thickness. The inner layer is mother-of-pearl.

Respiratory system- two lamellar gills. The gills, as well as the inner surface of the mantle, are equipped with cilia, the movement of which creates a current of water. The flow of water is also created by siphons.

Food particles that have entered the mantle cavity are glued together and sent to the mouth opening of the mollusk, located at the base of the leg. This way of feeding is called filtration, and animals are called filter feeders. The digestive system lacks a radula and salivary glands.

Nervous system bivalves is represented by three pairs of ganglia, which are connected by nerve cords - commissures. The sense organs are poorly developed, there are special cells that provide skin sensitivity, there are balance organs - statocysts, chemical sense organs.

Scheme of the internal structure of bivalve mollusks: 1 - mouth, 2 - anterior muscle, 3, 15, 20 - nerve nodes, 4 - stomach, 5 - liver, 6 - anterior aorta, 7 - external opening of the kidney, 8 - kidney, 9 - heart, 10 - pericardium, 11 - posterior aorta, 12 - hindgut, 13 posterior closing muscle, 14 - anus, 16 - gills, 17 - gonadal opening, 18 - midgut, 19 - gonad.

excretory organs represented by two kidneys. The ureters open into the mantle cavity.

reproduction. Most bivalves are dioecious. The testicles and ovaries are paired. The genital ducts open into the mantle cavity. Development occurs with metamorphosis. The larvae of freshwater mollusks (toothless and barley), called glochidia, have a bivalve shell with serrated spikes on the edges. When a fish swims over a toothless fish, the mollusk pushes the larvae through the excretory siphon into the surrounding water. With the help of a byssal thread and spiny valves, glochidia are attached to the skin of the fish. A small tumor forms around the larva, inside which the glochidium feeds at the expense of the host.

New concepts and terms: mantle, mantle cavity, radula, siphons (inlet, outlet), mixed body cavity, gills, biofilters, glochidia, pearl.

Questions to reinforce:

• What features unite bivalves and gastropods?
• What is the difference between bivalves and gastropods?
• Why can a pond snail live in an aquarium with stagnant water, but not toothless?
• What control measures are most effective and safe against mollusk pests?

, (they can be downloaded from Google Play),
finder apps for iPhone and iPad: , (they can be downloaded from the AppStore),
pocket field qualifiers: ,
colored laminated identification tables: ,
determinant of the series "Encyclopedia of Nature of Russia": .

Photo 1. Common European toothless - Anodonta cygnea

Photo 2. Common European toothless - Anodonta cygnea

Rice. 1. Common European toothless - Anodonta cygnea

Toothless ordinary belongs to the subfamily Bezubok (Anodontinae) of the family Unionidae (Unionidae) of the class Bivalvia mollusks (Bivalvia). The subfamily toothless is characterized relatively thin shells, devoid of locking teeth.

Synonyms. Toothless common, or European, or swans - Anodonta cygnea (Linnaeus, 1758), = Anodonta mutabilis, = Mytilus cygneus Linnaeus, 1758, = Anodonta cellensis Schroter, 1779, = Mytilus zellensis Gmelin, 1791, = Anodonta ventricosa C. P25 , = Anodonta elongata nob. Potiez & Michaud, 1844.

Origin of name. The name of these mollusks, both Russian and Latin, is associated with the absence of locking teeth on the shell.

Appearance. Sink common toothless large, elongated-oval (its height is 0.5 length), slightly angular, relatively thin-walled, brittle. Growth lines clearly expressed, rough along their entire length, the epidermis between them is smooth, shiny, finely concentrically striated. Shells grey, olive brown or almost black colors. With a light coloration of the shell, radial rays are noticeable, which diverge from the top to the edges of the valves. Thickness shell valves is the same in the direction from the umbo to the ventral margin.

Dorsal and abdominal the edges the shells are straightened and parallel to each other (the shell diagram with the designation of sides and edges is shown in the description of the Bivalve class). The back edge creates a wide, blunt beak that connects to the top edge with a straight or concave line. crowns(apices) narrow, not protruding, lying from the anterior end of the shell for 0.25-0.3 of its length. Their sculpture is composed of 5-6 rows of weakly sinuous concentric folds, more or less straightened in the middle.

Ligament(ligament connecting the valves) long, wide, massive. Shield laterally constrained, protruding, pronounced, although the radial angles that separate it from the rest of the valves are indistinct. Shield inconspicuous.

Inner surface the sash is smooth, nacre thin, brittle, blue, irradiating. mantle line deep enough.

Toothless is a very variable species, forming in almost every large body of water, area, etc. various morphs, ecological races, varieties (see below - Features of taxonomy and other species).

Dimensions. The common toothless is the largest of our toothless, the length of the shell of an adult mollusk lies within 8-12 cm (the maximum mention is up to 20 cm), the height is 42-63 mm, the convexity is 26-46 mm.

Motion. Toothless movements are rather monotonous - they can dig into the sand with the help of rhythmic contractions of their legs, and also crawl along the bottom soil. Movement is carried out with slightly open sides, ventral side down, umbo up (the shell diagram with the designation of sides and edges is shown in the description of the class of Bivalves), into the gap between which the mollusk sticks out its leg, with the help of which it slowly crawls along the bottom. At the same time, characteristic deep furrows remain on sandy or silty soil, which are clearly visible in shallow water. The speed of movement is low - 20-30 cm per hour.

Breath. Like all bivalves, toothless mollusks breathe with gills, which are paired lobes on either side of the leg. In a calm state, when toothless is at the bottom, with the ventral side (half-open valves) down, water is sucked into the mantle cavity through the inlet (lower) siphon, washes the gills and is thrown out with force through the outlet (upper) siphon (a detailed description of the breathing process with illustrations and the scheme of water flows is given in the description of the Unionid family - Unionidae).

Nutrition. Toothless are filter feeders, their food is carried out simultaneously and in parallel with respiration - the water current drawn into the gill cavity carries with it small nutrient particles suspended in water - zoo- and phytoplankton, as well as detritus. The mollusk swallows them, driving them into its mouth opening with the help of soft outgrowths, which are called oral lobes and sit in the amount of two pairs at the front end.

Habitat. The common toothless is found in a variety of water bodies, large and small, stagnant and fluid. Prefers lakes, reservoirs, ponds, oxbow lakes, canals and slowly flowing rivers. Keeps on organic-rich silty and sandy-silty soils. Normal feeding depth - 0.5-2 m

Spreading. The common toothless is one of the most widely distributed types of toothless. It is common in Central and Northern Europe, in the European part of Russia and the countries of the former USSR, as well as in Western Siberia, Western and Central Asia.

Features of taxonomy and other types. The common toothless is a rather variable species, forming various morphs, ecological races, and varieties in almost every large body of water, geographical region. According to various classifications, they are considered either subspecies of the common toothless, or separate species. This is:

• elongated or elongated toothless (Anodonta cygnea cellensis, = Anodonta cellensis Gm., = Anodonta zellensis) - the shell is long, its back part forms a narrow beak 12-16 cm long, lives in lakes and river oxbows,
• toothless fish (Anodonta cygnea piscinalis, = Anodonta piscinalis Nils.) - wide, angular, with a sharp posterior edge and almost straight dorsal, up to 110 cm long,
• toothless duck (Anodonta cygnea anatina, \u003d Anodonta anatina L.) - smaller, up to 8 cm long, resembling an ordinary and fish in shape.

Other descriptions. Catching a toothless fish is not a big deal, especially if the water is clear enough and the shells can be seen from the shore. For fishing, you need a net with a sufficiently strong rim, which can act like a rake, raking the ground and picking up mollusks released from sand and silt into the net.

The toothless shell consists of two convex valves, which, like strong shields, cover the delicate soft body of the mollusk, protecting it from adversity and danger. The valves are connected to each other by a hinge ligament-ligament (on the dorsal margin of the shell). The opposite edge is called the ventral. The blunt rounded edge of the shell is its anterior end; the rear end is sharper, elongated. From above, the shell is brown-green or brown-yellow; the color depends on the horny substance covering it from the outside. If you scrape the shell with a knife, it is easy to see that the dark stratum corneum comes off, and under it you can see a white substance - a porcelain layer. From the inside, the shell is lined with a brilliant layer of mother-of-pearl, which is easy to see when you find an empty shell of a dead shell.

Let's try to open tightly closed doors. This is not without difficulty, and the resulting gap immediately closes again. The valves are held by the work of strong closing muscles at the anterior and posterior ends of the shell. When opening the shell, the mantle of the animal is striking - a yellow mucous lining that covers the inside of the shell valves.

It is not difficult to observe the movements of the toothless by putting it in a vessel with water and leaving it alone for a while. After a while, the shell valves will slowly open, forming a gap through which a soft, yellowish, blunt process will stick out - the leg of the mollusk. With the help of this process, the mollusk can dig into the sand with its front end or slowly crawl along the bottom, leaving behind characteristic furrows in the sand. The speed of this movement, however, is very insignificant: hardly more than 20-30 cm per hour.

Toothless breathing can be observed on an excursion only if you manage to notice a mollusk half-burrowed in the sand in the shallow water, which remained undisturbed. Having put its rear end out of the ground, a calmly sitting animal opens two short tubes on it, formed by the edge of the mantle: an inlet siphon, with black fringed edges, through which water enters the gill cavity of the mollusk, washing the gills, and an excretory siphon, through which the waste water is displaced .

The flow of water is created by the beating of cilia covering the inner sides of the mantle and gills. Driven by cilia, water enters the mantle cavity to the mouth opening, is driven into it, enters the digestive system. Respiratory processes are carried out simultaneously with nutrition. If you open the valves of the caught toothless and insert wedges (from a stick or cork) between the valves, then in the open gap you can see delicate transversely striated brown-yellow gill plates, in pairs on each side of the body. The water entering through the siphon washes the gills, which absorb the oxygen dissolved in it and release carbon dioxide, which is removed with the flow of water through the excretory siphon.

On the tour, you can also observe some of the reproduction of toothless. Quite often there are mature females in which the gill plates are significantly swollen. These are females carrying embryos that develop in the cavity of the external gill. It is worth breaking through or cutting into such a gill, as a thick brown mass will come out of the hole, which seems fine-grained to the naked eye. It consists entirely of living toothless larvae, the so-called glochidia, which can only be seen through a microscope.

Species descriptions and illustrations are taken from computer identification of freshwater invertebrates in Russia(Bogolyubov A.S., Kravchenko M.V., Moscow, "Ecosystem", 2018) .

Species descriptions and illustrations are taken from computer identification of freshwater invertebrates in Russia(Bogolyubov A.S., Kravchenko M.V., Moscow, "Ecosystem", 2018) .

On the pages of our site you can also read entomology textbook: Introduction , Subject and tasks of entomology , Brief outline of the history of entomology , Basic principles of insect taxonomy , Insect structure , Nervous activity of insects , Insect reproduction , Insect development , Life cycles , Diapause , Protective devices and social lifestyle , Nutrition and feeding specialization of insects , Distribution insects, Insect population fluctuations, and educational book d.b.n. V.A. Krivokhatsky "Ant lion".

In the same reservoirs where the pond snail lives, you can also find another mollusk - toothless (lat. Anodonta). She lives at the bottom, burrowing halfway into the muddy ground. Its oval shell is about 10 cm long. The anterior end of the shell is rounded, while the posterior end is slightly pointed. The sink consists of two symmetrical wings - right and left. Mollusks that have a shell of two halves-shutters, like toothless, are called bivalve . Both flaps are interconnected by means of an elastic flexible ligament on the dorsal side. On the ventral side, they can open, and the leg of the mollusk protrudes into the resulting gap. Toothless has no head. The toothless leg, unlike the pond snail, does not have a wide flat sole, but in the form of a muscular wedge directed forward. When moving, the toothless pushes its leg forward and fixes it in the ground, and then pulls the body. Thus, the toothless takes, as it were, small steps, 1-2 cm each, moving only 20-30 cm in an hour. The disturbed toothless draws its leg into the shell and tightly closes the valves with the help of the closing muscles. When the muscles are relaxed, the flaps move apart from below under the action of a springy ligament.
The shell of the toothless, like the shell of the pond snail, consists of lime and is covered on the outside with a horn-like brown-green substance. The inner surface of the shell is covered with light mother-of-pearl shimmering in different colors of the rainbow. In toothless, the mother-of-pearl layer is poorly developed, and in some other mollusks, for example, barley and pearl oysters, it is much thicker. In a pearl oyster, mother-of-pearl can surround a grain of sand that accidentally got inside, and then a shiny ball is formed - a pearl.
The body of the toothless is located in the dorsal part of the shell. Two folds of the mantle depart from it, tightly adhering to the flaps. Between them, a mantle cavity is formed, in which the gills are placed on both sides, and in the middle - the leg.

In a live, undisturbed toothless, in the back of the sash, two small holes are visible - siphons. They lead to the mantle cavity. The gills and inner sides of the mantle folds are covered with cilia. They move continuously and draw water through the lower siphon. Water passes through the entire mantle cavity and exits through the upper siphon. Along with water, various small organisms living in it are brought in - protozoa, crustaceans. With a stream of water, they are brought to the mouth, located near the base of the leg, and from the mouth then enter the digestive system.
The current of water, which brings food to the toothless, also provides breathing. Oxygen enters the gills from the water, and carbon dioxide is released into the water.
The circulatory and excretory systems of the toothless have a similar structure to those of the common pond snail.
The nervous system is the same as that of a pond snail. There are three pairs of nerve nodes interconnected by jumpers. There are no special sense organs.

Toothless have separate sexes, but males do not differ in appearance from females. The eggs develop in the mantle cavity, on the gills. The larvae emerging from the eggs are released through the upper siphon into the water. Here they can be attached with sticky threads or teeth on the shell to the skin of the fish. A tumor forms on the body of the fish, inside which the mollusk continues to develop. After some time, the ripened mollusk breaks the skin of the fish and falls to the bottom. Thanks to this method of development, toothless can spread very widely.

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The leg mobility of bivalve mollusks is very high, it is provided by coordinated contractions of muscle groups with different orientations (oblique, longitudinal, transverse). In addition, there are several pairs of muscles that connect the leg to the inner surface of the shell.

The places of attachment of these muscles - imprints - are often clearly visible near the dorsal edge of the shell. As already mentioned, in many species there is a byssal gland in the leg, which secretes strong byssal filaments, with the help of which the mollusk is attached to the substrate.

In the space enclosed between the mantle sheets and the body - in the mantle cavity - there are gills, oral lobes, some sensory organs and openings of the hindgut, kidneys and sex glands. The mouth opening is placed in a recess behind the anterior adductor. The gills occupy the posterior part of the mantle cavity. In primary gills they are bipinnate; in septum-gills, they are modified into a plate with holes lying horizontally. In true laminabranchs, in particular the toothless, the gills are more complicated.

Take a sheet of paper and fold it in half lengthwise. The place of the inflection will correspond to the axis of the gills on which they are suspended. Then fold each half again parallel to the first fold so that you get an "accordion"; each half of the "accordion" will correspond to the half-gills - external and internal. Each gill plate consists of rows of individual threads (filaments), and each thread, respectively, forms a descending and ascending knee.

In toothless, between adjacent threads and between the knees formed by them, there are connections ("bridges"); each semi-gill is thus a latticed, intricately perforated two-layer plate. The mantle cavity and gills are constantly washed by the current of water. This current is generated mainly by the work of microscopic cilia of the epithelium covering the inner surface of the mantle, gills, oral lobes and body walls. Water enters the mantle cavity through the lower (inlet, respiratory) siphon and first enters its large, lower part - the respiratory chamber; then it is filtered through the cracks in the gills and goes into the upper part of the mantle cavity - the exhalation chamber, from where it is brought out through the upper (excretory, anal) siphon.

The suction of water through the lower siphon occurs due to the difference in hydrostatic pressure in the supra-gill and sub-gill chambers. In toothless, like in many other bivalve mollusks, water enters through the posterior end and is excreted through it; such a current can be called circular or return. However, cases are known when water enters through the front end of the body, and is excreted through the back; such a current is called through. In addition to the ciliary epithelium, the muscles of the gills, mantle and siphons also take part in water exchange.

The flow of water entering the mantle cavity carries particles of suspension with it. This current is easy to detect if you put the toothless in a vessel of water so that the water slightly covers the shell. Having allowed the mollusk to calm down, it is necessary to pour some powder into the water at the back end of the shell, which remains suspended in the water (ink, carmine, dry grated algae). Then it is easy to see that the powder grains are sucked through the lower siphon into the shell and after a while are thrown out through the upper one. From time to time, toothless, often without any external irritation, slams the valves with force and throws out jets of water, renewing all the water in the mantle cavity at once.

Soon the flaps open again and the normal slow circulation of water resumes. The water entering the mantle cavity provides the mollusk not only with oxygen for respiration, but also with food. Since bivalve mollusks lack a head and associated organs - pharynx, salivary glands, organs for capturing and chewing food, most of these animals, in particular toothless, feed by a filtration method, that is, filtering and consuming organic particles suspended in water, as well as unicellular algae, bacteria and very small invertebrates.

With the help of a complex ciliary mechanism of the gills and oral lobes, the shells first "roughly" filter out all edible particles, and then separate the inedible mineral mixture and organic lumps that are too large for them. The mucus secreted by the corresponding cells envelops the sorted food particles, which are sent to the food grooves; located near the toothless along the ventral edge of the semi-gills or at their base. Through these grooves, again with the help of cilia, the edible mixture is transported to the oral lobes, where the particles are finally sorted, after which they are sent to the mouth and swallowed.

Despite this rigorous two-stage selection, grains of sand are commonly found in the stomachs of bivalves. They play the same role as small stones in the goiter of chicken birds, which deliberately swallow them: they contribute to grinding and grinding the food bolus. Those particles that have been sorted out as unsuitable for nutrition enter the mantle cavity and are removed with the output current in the form of so-called pseudofeces. As we have already found out, representatives of the superorder and primary gills (walnuts, Portlandian nuculans, bathyspinules, etc.) have the most simply arranged bipinnate gills - ctenidia.

The oral lobes are very strongly developed; each of them consists of two leaves and is equipped with a long appendage, very mobile and retractable. When the animal is active, these appendages protrude between the valves in the posterior abdomen and collect organic particles (detritus) from the bottom. A groove runs along the ventral, or inner, side of the appendages - a channel for transporting the collected material. Further, this material enters a narrow slit-like space between the leaves of the oral lobe. The surfaces of the sheets facing one another are provided with clearly defined transverse folds, on which the incoming detritus is sorted. Ctenidia are used only for respiration.