Toothless: structure and lifestyle. Toothless, common or river In a toothless, the shell consists of

Theme: Shellfish type

class Bivalve molluscs - Toothless and Perlovitsa

Target: to study the organization of the Bivalve molluscs class using the example of Toothless and Perlovitsa.

Tasks:

Study the classification of the type of Molluscs. Learn aromorphoses such as Molluscs. Everything should be written down in a notebook.

To study the organization of the Bivalve molluscs class using the example of Toothless and Perlovitsa. Complete notes in a notebook.

Consider wet preparations and a collection of different types of mollusc shells.

Examine the structure of the bivalve glochidia under a microscope.

Examine external and internal structure Toothless or Perlovitsy (dissection of molluscs).

In the album, sketch 3 pictures indicated in the printed manuals V (red check mark). You work with these manuals in the classroom, and they are stored in the laboratory assistant's department of biology and ecology. In this electronic tutorial, drawings for drawing are presented at the end of the file.

Know the answers to Control questions themes:

General characteristics of the Molluscs type. Classification of the type of Molluscs. Aromorphoses of the Shellfish type.

Features of the organization of mollusks of the class Bivalve molluscs.

Systematic position, lifestyle, body structure, reproduction, significance in nature and for humans Toothless and Perlovitsa.

Type Shellfish -Mollusca

The type is subdivided into the following subtypes and classes:

Subtype 1. Side effects... These are primitive molluscs with a prickly cuticle or with a shell consisting of eight plates. A head without eyes and tentacles. The nervous system consists of four longitudinal nerve trunks. Two classes:

Class 1. Armored, or Chitones (1 millennium century). The body of these mollusks is flattened, elliptical, with eight overlapping, like shingles, calcareous plates on the dorsal side. Length from 2 mm to 30 cm. The back and sides are covered with a mantle, and most of the lower surface is occupied by a flattened leg. There is a radula in the mouth (a kind of grater for scraping); the respiratory organs are the gills; nervous system with a periopharyngeal ring and two pairs of lateral nerve trunks connected by bridges (no ganglia). Diocese, external fertilization, development with metamorphosis, the larva is called trochophore. Chitons crawl over stones in the sea and are able to firmly attach to them. If you tear off the tunic from the stone, it curls up like a hedgehog, exposing the back plates for protection. Local residents of the tropical region collect chitons and eat them.

Class 2. Armless, or grooved belly (about 150 c.). These are the most primitive, deep-sea molluscs. The length of their worm-like body is usually about 2.5 cm, but in some forms it reaches 30 cm. The real leg is absent, there is no clearly defined head. The body is covered with a spiked cuticle rather than a shell.

Type Shellfish - Mollusca

Subtype 2. Conch... These are mollusks with a calcareous shell, solid, or divided into two lateral valves. The nervous system is of a scattered-nodular type; there are tentacles and eyes on the head. Five classes:

Class 3. Monoplacophores(total 8 modern species, the first of which - Neopilina- described recently - in 1952). This is a group of ancient, saucer-like molluscs with a segmented, worm-like body, each segment of which has its own gills, kidneys, and other organs. Sink in the form of a cap. They live at great ocean depths.

Class 4. Shovellegs, or Ladies (50th century). Sea creatures; live almost completely buried in the bottom silt. The conical shell is thin, elongated and somewhat curved, 5–8 cm long. A pointed leg protrudes from its wide mouth in the ground, and its narrow end with a hole at the top protrudes into the water. Shovellegs breathe with the help of a mantle, they have no gills. The head is missing. Disexual animals with external fertilization.

Class 5. Gastropods, or Snails (over 90 thousand). These animals, which include Slugs, Snails, Coils, Pond snails, are found everywhere: in small ponds and large lakes, in streams and rivers, on mountain tops, in forests and meadows, on the seabed and in the open ocean. The typical gastropod mollusk has sensory tentacles, two eyes and a mouth equipped with a radula on a well-separated head. They move with the help of large, mucus-covered legs. Many have a solid shell into which the entire body can be fully drawn. Sometimes the shell is reduced (slugs). A characteristic feature of the Gastropods is the asymmetry of the body: the body, like the shell, is spirally twisted. Due to the asymmetry of the body, the organs located on the right side of the body are reduced. Many terrestrial species breathe with the lungs (the pulmonary group), the rest with gills. Most are hermaphrodites, fertilization is external in the mantle cavity, eggs are laid in the form of slimy cords, their eggs emerge as a young mollusk.

Class 6. Bivalve, or Lamellar-gill (about 20 thousand century). This is well-known Scallops, Mussels, Pearl oysters, Oysters, Toothless, Perlovitsy... Their shells consist of two lateral valves. Many species live partially buried in the ground at the bottom of the reservoir, but most crawl. Mussels and Oysters firmly attached to stones using threads secreted by the mantle.

Type Shellfish - Mollusca

Class 7. Cephalopods(700 c.). These marine animals, which include Squid, Octopus, Nautilus and Cuttlefish are considered the most advanced of all molluscs. The large head has eyes and a mouth with horny jaws and a radula. The mouth is surrounded by 8 or 10 tentacles called arms. The tentacles of the cephalopods are a modified leg that has moved to the head. The tentacles carry disc-shaped suckers. The diameter of the suckers in some octopuses can reach 2 m (!). The sizes of the tentacles vary from a few centimeters to 8.5 m. The other part of the leg forms a funnel, which lies on the ventral side of the body. Through the funnel, the cephalopods forcefully eject water from the mantle cavity and move, thus, in jerks (reactive mode of movement). Have Cuttlefish and Squid the rudiment of the shell inside the body has been preserved; in octopuses, she disappeared without a trace. Have Korablikov, or Nautilusov, there is an external sink; it is coiled, like in snails, however, unlike them, it is divided inside by partitions into chambers. Cephalopods also have an ink gland that opens into the hind intestine: at the moment of danger or attack, the cephalopods release a drop of black secretion that can muddy a large number of water. All species are dioecious; fertilization is internal. From eggs surrounded by gelatinous capsules, adult-like miniature immature individuals hatch. In the Mesozoic era, there was a flourishing of cephalopods ( Belemnites, Ammonites). Have Belemnite the shell was greatly reduced to a small plate, the fossil remains of which are called the "devil's finger".

So, Molluscs have the following aromorphoses: 1. Segments merge into a small number of parts of the body (head, trunk, leg), each of which performs specific functions. 2. There was a further concentration of the nervous system - the formation of large nerve nodes in various parts of the body. 3. A heart appeared, which increased the blood circulation rate, which is significant

increased the intensity of metabolic processes. 4. The digestive glands appeared, which provided faster and more complete digestion of food. 5. A shell has formed, which serves as an external or internal skeleton and protects the soft body of mollusks.

Type Molluscs class Bivalve molluscs

Toothless and pearl barley

Toothless- genus Anodonta and Perlovitsa- genus Unio(type Molluscs, class Bivalve, or Lamellar gill molluscs, family Unionids) are mollusks widespread in fresh water bodies of temperate latitudes, which we call shells. Toothless prefer reservoirs with stagnant or slowly flowing water with a muddy bottom, and Perlovitsy prefer flowing reservoirs with a sandy bottom. Toothless are also more sensitive to chemical water pollution. For example, in our city on the Uy River, there are both kinds of mollusks: both Toothless and Perlovitsy, and on the Uvelka River there are many Perlovitsy, but Toothless are rare.

Sink. The bilaterally symmetrical body of these molluscs is enclosed in bivalve sink... Perlovitsa's shell is up to 15 cm long, somewhat elongated, more durable than that of Toothless. Shell valves Perlovitsa are connected on the dorsal side by special teeth and grooves - the so-called castle... The shell of the Toothless shell is up to 20 cm long, usually thin-walled, more rounded, without locking teeth (hence the name - Toothless), two shell valves are connected with the help of an elastic ligament ligament... The shell valves of these mollusks are closed with the help of two muscle-contactors.

Two shell valves of the Toothless and Perlovitsa shells are connected to each other on the dorsal side, and on the abdominal side, a muscular outgrowth of the abdominal wall of the body is inserted into the resulting gap - leg... Toothless and Perlovitsy, slightly opening the shell valves and sticking out a wedge-shaped leg from there, slowly crawl along the bottom of the reservoir, leaving a trace drawn by their foot. The speed of movement is no more than 20-30 cm per hour.

Pay attention again to the shell of the molluscs: at the shell they distinguish front end- wider and more rounded, and rear the end- narrower, sharper. The most convex part of the sash is called navel... Both navels right and left sash form the apex of the shell. The sink has three layers. Outer conchiolinic- dirty greenish color, formed by organic matter conchiolin... If you scrape it, then the middle opens - porcelain layer white... The inner surface of the shell valves is covered with pearlescent layer. The porcelain and nacreous layers are composed of calcium carbonate crystals. Thin plates of the mother-of-pearl layer, when reflected by light rays, give a kind of pearlescent shine. Pay

Type Molluscs class Bivalve molluscs

attention to the curved lines on the surface of the shell, parallel to its apex. it annual the lines gain... With the growth of the mollusk, it grows and

sink. The top of the shell is the oldest part of it. The age of the mollusk can be determined by the number of annual lines.

Body Toothless and Perlovitsa consists of torso and legs, and the head is not isolated. The body is covered with a skin fold called mantle... The mantle hangs down from the sides of the body in the form of folds. On the dorsal side, the mantle grows together with the body of the mollusk. At the posterior end of the body, the free edges of the mantle grow together, leaving holes - siphons to enter ( branchial siphon) and output ( cloacal siphon) water from the mantle cavity. Shell valves are formed by the outer epithelium of the mantle. Between the mantle and the body is mantle cavity, into which the anus, ducts of the kidneys and gonads open, the respiratory organs of Toothless and Perlovitsa (gills), some sense organs are also located there.

Musculature in molluscs it is well developed and consists of muscle bundles, although muscle fibers are of a smooth type. The muscle bundles are especially strongly developed in the animal's leg. Also, Toothless and Perlovitsa have two well-developed closing muscles that hold the shell valves.

Body cavity. Internal organs are located inside the body in parenchyma, but there are cavities filled with fluid (like Ascaris has a primary body cavity). Secondary body cavity - the whole- partially reduced, in the remains of the coelom is the heart (in pericardium) and gonads. Thus, the body cavity in molluscs is formed by the remains of the primary cavity and a highly reduced coelom. Such a cavity is called mixed cavity, or mixsocel.

Digestive system in Toothless and Perlovitsa, it consists of the anterior, middle and hind gut. The anterior gut is presented mouth hole, oral cavity and by the throat... Please note: the mouth opening is located at the base of the leg (!), It is surrounded by mouth lobes triangular shape. Food particles - various organic residues that have fallen into the mantle cavity with a stream of water through the gill inlet siphon, stick together into lumps and are sent to the mouth of the mollusk. This way of eating is called filtration, and the animals Toothless and Perlovitsa, respectively, are filter feeders. In the digestive system of Toothless and Perlovitsa, there is no radula and salivary glands, characteristic of other mollusks. Food from oral cavity Fall into esophagus opening in stomach. Middle intestine makes a few bends at the base of the leg, then goes into hind gut which ends anus... Shellfish have a digestive gland - liver... The liver of Toothless and Perlovitsa is very extensive, it surrounds the stomach on all sides.

Type Molluscs class Bivalve molluscs

Nervous system in bivalve molluscs and in Toothless and Perlovitsa scattered-knot type... It is represented by three pairs ganglia(nerve nodes) that are connected commissars(nerve cords). The first pair of ganglia ( head) is located near the esophagus, the second ( foot) in - leg and third ( internal) - under the posterior muscle-closure of the shell. Nerves extend from the nodes to various organs. The sense organs of Toothless and Perlovitsa are poorly developed: there are special receptors(nerve endings) that provide skin sensitivity; there are organs of balance - statocysts; around the mouth and in the mouth - chemical sense organs... Toothless and Perlovitsa have no eyes.

Circulatory system open, comprises hearts and blood vessels. The heart is in the pericardial sac pericardium and consists of two atria and one ventricle... Move away from the ventricle arteries - vessels 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 internal organs... Then the blood flows through the venous vessels to the gills, gas exchange takes place and the oxygen-rich blood returns to the heart.

Respiratory system... On both sides of the leg in the mantle cavity (i.e. between the body and the mantle), Bezzubka and Perlovitsa have two lamellar gills... The gills, as well as the inner surface of the mantle, are equipped with cilia, the movement of which creates the flow of water. Through the lower (inlet, or gill) siphon, water enters the mantle cavity. Water is removed through the outlet (cloacal) siphon located on top. The gills are penetrated by a dense network of blood capillaries, where gas exchange takes place. Along with the flow of water through the inlet siphon, food particles also enter the mantle cavity.

Excretory organs at Toothless and Perlovitsa - NSglasses, which are modified metanephridia (so-called kidney metanephridial type). Each kidney is composed of numerous tubules. The tubule begins with a funnel in the pericardial sac (in the coelomic cavity), and the other end of the tubule opens into the mantle cavity. The kidneys are located under the heart.

Reproduction. Toothless and Perlovitsa dioecious, although there are no external sex differences. Testes and ovaries(male and female sex glands) are paired. The reproductive ducts from the gonads open into the mantle cavity. Fertilization at Toothless and Perlovitsa outward in the mantle cavity. Here, on the female's gills, eggs are attached, which are fertilized by spermatozoa that penetrate into the mantle cavity with a stream of water through the gill (introductory) siphon. After a while, the larvae of Toothless and Perlovits emerge from the eggs, which are called glochidia. Glochidia have a bivalve shell with serrated spines at the edges and a sticky byssus thread. When a fish swims over Toothless or Perlovitsa, adult mollusks push the larvae through the outlet siphon into the surrounding water. With a byssus thread and

Type Molluscs class Bivalve molluscs

Meaning. Toothless and Perlovitsy are an element of the biological diversity of fresh water bodies, they are an integral part of the food chain. In places where these molluscs are especially abundant, they become powerful natural water purifiers (biofilters). In some regions, people collect Toothless and Perlovits for feed. poultry... In the old days, beautiful mother-of-pearl buttons were made from Perlovits shells.

Questions for self-control

Name aromorphoses like Molluscs.

What is the classification of the type of Molluscs?

What is the systematic position of Toothless, Perlovitsa?

Where do Toothless and Perlovitsy live?

What is the difference between Toothless and Perlovitsa shells?

What is the body structure of Toothless, Perlovitsa?

What is the body of Toothless, Perlovitsy covered with?

What body cavity is typical for Toothless, Perlovitsa?

What is the structure of the digestive system of Toothless, Perlovitsa?

What is the structure of the circulatory system of Bezzubka, Perlovitsa?

How does Toothless breathe, Perlovitsa?

What is the structure of the excretory system of Bezzubka, Perlovitsa?

What is the structure of the nervous system of Toothless, Perlovitsa?

What is the structure of the reproductive system of Toothless, Perlovitsa?

How does Toothbrush reproduce, Perlovitsa?

What is the meaning of Toothless, Perlovitsa?

Type Molluscs class Bivalve molluscs

Rice. Pearl barley: A - common pearl barley; B - swollen pearl barley, or wedge-shaped; B - thick pearl barley.

Rice. Toothless.

Rice. Glochidia is the larva of Toothless and Perlovitsa.

Type Molluscs class Bivalve molluscs

Rice. The structure of Toothless.

1 - leading edge; 2 - abdominal edge; 3 - rear edge; 4 - dorsal, or hinge, edge; 5 - top of the head; 6 - external ligament; 7 - anterior closure muscle; 8 - posterior muscle-closure; 9 - front leg retractor; 10 - protractor; 11 - rear leg retractor; 12 - leg elevators; 13 - leg; 14 - right fold of the mantle; 15 - introductory (gill, respiratory) siphon; 16 - outlet (cloacal) siphon; 17 - cloacal chamber; 18-dorsal mantle canal; 19 - dorsal mantle opening; 20 - mouth opening; 21 - mouth blades; 22 - left outer hemisp; 23 - left inner hemisp; 24- region of Keber's organ; 25 - the area of the pericardium; 26 - the line along which the left mantle fold is cut.

DRAWINGS TO BE PERFORMED IN THE ALBUM

(3 pictures in total)

Lesson topic: Type Shellfish- Mollusca.

Type: Molluscs

Genus: Toothless - Anodonta

Genus: Perlovitsa - Unio

Rice. 1. Toothless (Perlovitsa). External structure.

1-sink 6-top sink

2-leg 7-entry (gill) siphon

3-front end 8-lead (cloacal) siphon

4-back end 9-back side

5-ligament (ligament) 10-abdominal side

Lesson topic: Type Shellfish- Mollusca.

Type: Molluscs

Class: Lamellar gill, or Bivalve molluscs

Order: True lamellar-gill

Genus: Toothless - Anodonta

Genus: Perlovitsa - Unio

Rice. 2. Toothless (Perlovitsa). Internal structure.

1 - shell 11 - intestine

2-mantle 12-anus

3-leg 13-liver

4-entry siphon (gill) 14-heart

5-lead siphon (cloacal) 15-pericardium 6-posterior articular muscle 16-kidney 7-anterior closure 17-lead opening of the kidney

18-head ganglion muscle (cerebral)

8-mouth lobes 19-leg ganglion (pedal)

9-mouth 20-internal ganglion

10-stomach (visceral)

21 - sex gland (gonad)

Lesson topic: Type Shellfish- Mollusca.

Rice. 3. Glochidia is the larva of Toothless and Perlovitsa.

1 - muscle-closure; 2 - teeth; 3 - byssus thread.

Toothless and pearl barley

Toothless (Anodonta) and pearl barley (Unio) - large (up to 20 cm) bivalve molluscs. They can be found half-buried in the ground at the bottom of reservoirs.

It is not difficult to catch bivalve molluscs: if the water is clear enough, the shells can be seen from the shore. It should be borne in mind that it is necessary to move with caution in places where shellfish accumulate, as you can accidentally step on the shell and injure your leg. You can transport them even without water,lying down aquatic plants so as not to dry out and break.

1 - leading edge; 2 - abdominal edge; 3 - rear edge; 4 - dorsal, or hinge, edge; 5 - top of the head; 6 - external ligament; 7 - anterior closure muscle; 8 - posterior muscle-closure; 9 - front leg retractor; 10 - protractor; 11 - rear leg retractor; 12 - leg elevators;13 - leg; 14 - right fold of the mantle; 15 - introductory (breathing) siphon; 16 - outlet siphon; 17 — cloacal chamber; 18 — dorsal mantle canal; 19 - dorsal mantle opening; 20 - mouth opening; 21 - mouth blades; 22 - left outer hemisp; 23 - left internal semi-gill; 24 — region of Keber's organ; 25 - the area of the pericardium; 26 - the line along which the left mantle fold is cut. (From the book "The Life of Animals", vol. 2, 1988)

By placing the mollusk in a vessel with water and leaving it alone for a while, you can see how, after a while, the shell valves will slowly open and gradually the leg will begin to protrude. The mollusk can bury itself in the sand with its front end or slowly crawl along the bottom, leaving characteristic grooves behind it. According to Raikov and Rimsky-Korsakov (1956), the speed of movement is no more than 20-30 cm / hour.

In our reservoirs, it is very common European toothless (Anodonta cygnea). This species, depending on environmental conditions, is very variable and has different morphs.

The toothless feed occurs simultaneously with its breathing. The water flowing through the siphon into the gill cavity and washing the gills carries small living organisms with it. The mollusk swallows them, driving them into its mouth opening with the help of two pairs of mouth lobes located at the front end of the body.

Quite often, mature individuals are found in water bodies, in which the gill plates are strongly swollen. These are females carrying larvae (glochidia) in the cavity of the external gill.

The developed glochidia emerge from the gill cavity of the female and are thrown out with a stream of water from the outlet siphon. Soon they attach to the skin of various fish, overgrow with epithelium and end up on the host's body. There they live for several weeks, makinghis further development then fall to the bottom in the form of tiny, already formed molluscs, capable of independent life.

Perlovitsy: A - common pearl barley; B - swollen pearl barley, or wedge-shaped; V - thick pearl barley

Very similar to a toothless river pearl barley (Unio pictorum), but it is distinguished by a more elongated and thick-walled shell and the presence of teeth near the hinge ligament (the toothless does not have these teeth - hence its name). Perlovitsa lives mainly in reservoirs with sandy soil, while toothless usually settles in stagnant waters with muddy bottom.

Pearl buttons used to be made from pearl shells. There were attempts to make buttons from toothless shells, but because of the thin shells of the mollusk, this material turned out to be very fragile.

Pearl barley grows slowly. Their age can be determined by the number of stripes on the shell valves (like rings on a tree cut, each stripe indicates an annual growth).

For pearl barley, a low aquarium with large area bottom (the so-called trough aquarium). At the bottom should be placed washed sand with a layer of 5-10 cm. Plants are not needed for molluscs. But for decoration, you can take a few bushes of plants (better - elodea or hornwort) from the "native" reservoir.

If you don't have an aquarium, you can use any other vessel, but sand is a must. The lower the water level in the tank, the better the oxygen regime.

Habitat and structure of the toothless

Pattern: toothless shell

Pattern: structure of the toothless

In the same reservoirs where the pond snail lives, you can find another mollusk - the toothless. Toothless 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, the posterior end is slightly pointed. The shell consists of two symmetrical valves - right and left. Molluscs with a shell of two halves-valves, like a toothless, are called bivalve... Both valves are connected to each other 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. The toothless has no head. The leg of the toothless, in contrast to the pond snail, is not with a wide flat sole, but in the form of a muscular, forward-directed wedge. When moving, the toothless pushes the leg forward and fixes it in the ground, and then tightens 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 pulls its leg into the shell and tightly closes the valves with the help of the locking muscles. When the muscles are relaxed, the flaps are moved 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 sink is covered with a light, iridescent different colors rainbow mother-of-pearl. In the toothless, the nacreous layer is poorly developed, and in some other mollusks, for example, the pearl barley and pearl mussel, it is much thicker. These shells are used for making buttons. In a pearl oyster, mother-of-pearl can surround a grain of sand that has accidentally got inside, and then a shiny ball is formed - pearl.

The body of the toothless tooth is located in the dorsal part of the shell. Two folds of the mantle extend from it, tightly fitting to the valves. A mantle cavity is formed between them, in which gills are placed on both sides, and in the middle is a leg.

Toothless food

In a living, undisturbed toothless, in the back of the valve, two small holes are visible - siphons... They lead to the mantle cavity. Gills and inner sides mantle folds are covered with cilia. They move continuously and draw in water through the bottom siphon. Water flows through the entire mantle cavity and out through the upper siphon. Together with the water, various small organisms living in it are brought in - protozoa, crustaceans. With the current of water, they are brought to the mouth located near the base of the leg, and from the mouth they then enter the digestive system.

Toothless breath

The flow of water, which brings food to the toothless, also provides respiration. Oxygen enters the gills from the water, and carbon dioxide is released into the water.

The circulatory and excretory systems of the edentulous

Nervous system of the edentulous

The nervous system of the edentulous is the same as that of the pond snail. There are three pairs of nerve nodes connected by jumpers. There are no special senses.

Breeding toothless

>> Toothless

§ 19. Toothless

Habitat and structure of the toothless.

In the same reservoirs where the pond snail lives, you can find another clam- toothless 37 ... 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, the posterior end is slightly pointed. The shell consists of two symmetrical valves - right and left. Molluscs with a shell of two halves-valves, like a toothless, are called bivalve... Both valves are connected to each other 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. The toothless has no head. The leg of the toothless, in contrast to the pond snail, is not with a wide flat sole, but in the form of a muscular, forward-directed wedge. When moving, the toothless pushes the leg forward and fixes it in the ground, and then tightens 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 pulls its leg into the shell and tightly closes the valves with the help of the locking muscles. When the muscles are relaxed, the flaps are moved 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 sink is covered with light mother-of-pearl, iridescent in various colors of the rainbow. In the toothless, the nacreous layer is poorly developed, and in some other mollusks, for example, the pearl barley and pearl mussel, it is much thicker. These shells are used for making buttons. In a pearl oyster, mother-of-pearl can surround a grain of sand that has accidentally got inside, and then a shiny ball is formed - a pearl.

Nutrition.

In a living, undisturbed toothless, in the back of the valve, two small openings 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 in water through the lower siphon 38. Water flows through the entire mantle cavity and out through the upper siphon. Together with the water, various small organisms living in it are brought in - protozoa, crustaceans. With the current of water, they are brought to the mouth located near the base of the leg, and from the mouth they then enter the digestive system.

Breath.

The flow of water, which brings food to the toothless, also provides respiration. Oxygen enters the gills from the water, and carbon dioxide is released into the water.

The circulatory and excretory systems of the edentulous have a similar structure to those of common pond snail.

The nervous system is the same as that of the pond snail. There are three pairs of nerve nodes connected by jumpers. There are no special senses.

Toothless are dioecious, but males do not differ externally from females. Eggs develop in the mantle cavity, on the gills. The larvae that emerged from the eggs are removed through the upper siphon into the water. Here they can be attached with sticky threads or scalloped teeth to the skin of the fish. A tumor forms on the body of the fish, inside of which the mollusk continues to develop. After a while, the ripe shellfish breaks the skin of the fish and falls to the bottom. Thanks to this method of development, toothless can spread very widely.

1. What are the features external structure and toothless movement in relation to the habitat?
2. What is the difference between toothless and pond snail nutrition?
3. How does a toothless breathe in connection with its adaptation to life in water? 4. Find the words in italics in § 19 and explain their meaning.

Biology: Animals: Textbook. for 7 cl. wednesday shk. / B. E. Bykhovsky, E. V. Kozlova, A. S. Monchadsky and others; Under. ed. M.A.Kozlova. - 23rd ed. - M .: Education, 2003 .-- 256 p.: Ill.

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Toothless (from Latin - anodonta) belongs to the genus of freshwater bivalve mollusks of the Unionidae family. Their natural habitat is a sandy or silty bottom in freshwater bodies. These mollusks are widespread in Europe, Asia and America.

Toothless is the best natural filter for your aquarium. She eats different kinds microorganisms, thereby purifying the water. Therefore, the 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. They are served 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, the outside is painted, as a rule, brown-green or yellowish-gray, and the inside is covered with mother-of-pearl. The leaves are interconnected by a ligament - an elastic ligament that opens and closes the leaves when the closing 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 grooves in the sand.

According to aquarists, in favorable conditions the 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 tooth reaches a length of 20 cm; its valves 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 a lot of oxygen, which they breathe through their gills. Therefore, there must be plants in the aquarium, and additional forced aeration will not hurt either.

Toothless plows the sand while moving and is capable of damaging plants with a weak root system, so they need to be planted in pots.

Comfortable water temperature for the mollusk is up to 20-22? С. Before placing a toothless in an aquarium (both lake and one grown in aquariums in pet stores), you need to keep it in quarantine and acclimate to a new environment for it. To do this, gradually, over 6-12 hours, add aquarium water... The adaptation period 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. In dead molluscs, the shell valves are wide open.

Nutrition

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