Toothless: structure and lifestyle. Laboratory work

"Bivalves"

INTRODUCTION

130 thousand species of various mollusks inhabit mainly the sea and fresh waters, although there are many of them on land. They most likely descended from common ancestors with annelids, and their primitive representatives still have similarities with them. Mollusks are bilaterally symmetrical, but their body is not segmented, unlike annelids and arthropods. The body of mollusks is divided into three sections: the head, trunk and leg.
Bivalve class.

Toothless and other bivalves.

Due to the fact that the features of the lifestyle and structure of the toothless should be considered in comparison with the large pond snail, knowledge testing is not carried out.

The teacher talks about the lifestyle of a typical representative of bivalves - toothless. To identify the nature of the structural features of its shell, it is necessary to organize laboratory work, which students perform according to the instructions.

Laboratory work. Toothless shell structure

Purpose: to find out the structural features of the toothless shell in connection with its protective role. Working process

Consider the shell of a toothless, determine its shape, color, front and rear ends.

Examine the horny layer of the shell, find the layers of its annual growth, count their number and determine the age of the toothless.

Examine the inner surface of the shell, find a trace! muscle attachments.

sketch appearance toothless shells, sign its main parts.

Answer the question; What is the importance of a shell in the life of a toothless?

The teacher checks the quality of the work, uses the knowledge gained by the students in the conversation, once again drawing the attention of the students to the shell, its outer layer, consisting of organic matter, and its protective value. Next, the teacher talks about the internal lime layer, which gives the sink strength. Reporting on the mother-of-pearl layer, he emphasizes its unequal development in bivalves. For example, in marine pearl mussels this layer is well developed, so they are of commercial importance. The teacher talks about the features of shell growth and notes the role of the mantle in this process. He invites students to answer the question: what is the difference between the toothless shell and the shell of a large pond snail?

When studying the systems of internal organs and the main processes of life, students should first be asked to recall the features of the internal structure of a large pond snail, and only then pay attention to the structure of the systems of internal organs of the toothless.

The teacher invites students to answer the question: how does a large pond snail breathe? Having received an answer, he talks about the respiration of toothless oxygen dissolved in water with the help of gills located in the mantle cavity. The teacher reports that the circulatory system of the toothless is similar to that of a large pond snail, and invites students to answer the questions: what are the structural features of the circulatory system of the toothless? What is the significance of this system in her life?

By revising nervous system the teacher should invite schoolchildren to remember its structure and significance in the life of a large pond snail, and on the basis of this knowledge, it is necessary to show the features of this toothless system using a table for this.

Toothless larva

1- appearance under a microscope; 2 - larvae on the fin of a fish.

To consolidate knowledge about the structure of the system of internal organs of toothless, the teacher should invite students to find them on a wet preparation.

You can get acquainted with the variety of bivalves, their main species (mi-day, oyster, etc.) using the tables from the book "Animal Life".

We recommend listening to a pre-prepared message from one of the students about the mussel. Then the teacher should talk about oysters, which for the sake of tasty meat bred on oyster jars. It is also advisable to draw the attention of schoolchildren to the shipworm, especially to its structure and negative role in economic activity human (damage to coastal structures).

When studying the class of bivalves, you can use the filmstrip "Variety of mollusks".

Chapter 2. TYPE OF SHELLS
130 thousand species of various molluscs inhabit mainly the sea and fresh waters, although there are many of them on land. They most likely descended from common ancestors with annelids, and their primitive representatives still have similarities with them. Mollusks are bilaterally symmetrical, but their body is not segmented, unlike annelids and arthropods. These are secondary cavitary animals, but in general they have been reduced to insignificant cavities in which the heart (pericardial sac, or pericardium) and sex glands lie.

The body of mollusks is divided into three sections: the head, trunk and leg. The head section in sessile forms can be reduced. Leg - a muscular outgrowth of the abdominal wall of the body, on which the mollusk crawls, in sessile and inactive forms it can also disappear. The body, as a rule, can grow on the dorsal side, forming, as it were, a hump - an visceral sac in which the organs of the mollusk are located, primarily the voluminous liver.

The body of the mollusk is covered on the outside with a skin fold - the mantle. The mantle on the ventral side does not adhere tightly to the body, forming a mantle cavity from which the leg protrudes and in which the gills are located. It also opens the anus, the excretory openings of the kidneys and genital organs. In terrestrial forms, the gills are reduced, and such mollusks breathe through the walls of the mantle cavity, which turns into a lung.

The mantle also secretes a protective shell, mainly from calcium carbonate. Outside, the shell is covered with a leathery layer of organic matter, followed by the so-called porcelain-like layer, in which CaCO3 crystallizes in the form of prisms, and a mother-of-pearl layer, composed of tabular CaCO3 crystals, adjoins the mantle. Pearls shine beautifully and iridescent shimmers, for which since time immemorial it has been highly valued by man. Relatively rarely, any microscopic particle, falling between the mantle and the shell, is enveloped in a layer of mother-of-pearl and becomes a pearl. Pearls have long been considered one of the most precious stones- until the Japanese zoologist Mitsukur and then the industrialist Mikimoto guessed to artificially stimulate the formation of pearls in mollusks specially bred for this purpose. Such pearls are not inferior to natural ones (it is natural), but the price for it has fallen, supply has exceeded demand.

In lower mollusks, the shell may consist of 8 plates protecting the dorsal side, in others it is cap-shaped, twisted into a spiral or divided into two valves, movably articulated with it. Many mollusks, especially actively swimming ones, have lost their shells.

With rare exceptions, mollusks do not have jaws. To grind food, they have a radula (grater) - horny hook-shaped outgrowths of the walls of the pharynx.

Their circulatory system is open and consists of a heart composed of one or two ventricles and atria. Blood from the atria enters the ventricle and, by contractions, is driven into the main vessel - the port. The aorta divides into arteries that supply blood to the internal organs. In the end, blood enters the gaps - the gaps between tissues and organs, and from them - into the afferent gill vessels. Having given CO2 in the gills and receiving O2, the blood through the gill veins goes to the atria.

Thus, the heart of mollusks is more complex than that of crayfish and insects. Like in humans, it is divided into atria and ventricles. This principle in higher animals becomes the main one.

The nervous system of mollusks is simpler than that of arthropods. It consists of the peripharyngeal nerve ring and four trunks extending from it. In primitive forms, it all resembles an orthogon flatworms. This means that the ancestors of molluscs separated from the ancestors of annelids before they formed the ventral nerve chain. In most molluscs, the nervous system is scattered-nodal: paired clusters of nerve cells - ganglia, connected by nerves, serve the leg, internal organs, mantle.

Mollusks develop from larvae that are very similar to the trochophore of polychaete annelids.

Class laminabranchial, or bivalve

Bivalves (20 thousand species) inhabit sea and fresh waters. They are called lamellar-gill because in their highly organized representatives, pinnate ctenidia grow together into two-layer lattice plates lying in the mantle cavity. Russian name- shells.

The body of the mollusk is covered from the sides with a bivalve shell. The valves are connected on the dorsal side by an elastic ligament-ligament and a lock consisting of tooth-like protrusions on one valve and corresponding recesses on the other. The teeth of the castle, however, can disappear because the bivalve mollusks of our rivers are called toothless.

The normal state of the shell is open; a gap is formed between the valves on the ventral side. But the mollusk has one or two closing muscles attached to both valves. If disturbed, they contract, tightly closing the shell.

Like other mollusks, in bivalves, the shell grows from the edge and on its valves, like on a tree stump, traces of annual growths can be found. The largest mollusk is the giant tridacna of the coral reefs of the Pacific and Indian Oceans reaches 1.35 mi 250 kg of mass; Thin sheets of the mantle, hanging from the sides of the body, are adjacent to the shell, like the lining of a garment. Between them is the mantle cavity, in which lamellar gills and a leg lie. The leg of bivalves has the form of a keel or wedge (hence one of the names of the class - keeled) and serves mainly for digging sand or silt. They crawl very slowly, while others have become sessile. In such, the leg is reduced, like in mussels, or disappears altogether, like in oysters. Many of them grow to the bottom, secreting byssus from a special gland - a viscous sticky mucus that turns into silky threads in water. Such a life is not conducive to the development of "mind". And the head of the bivalves disappeared, leaving only the mouth opening at the front end of the body (another name for the class is headless).

Bivalves feed like sponges by filtering water through their mantle cavity. The epithelium of the walls of the mantle cavity and gills is composed of ciliary cells. Coordinated strokes of the cilia create a current of water. Fresh water with food particles like microscopic algae enters through the inlet siphon formed by the petals of the mantle, makes a circle through the mantle cavity and is discharged through the outlet siphon. At this time, she gives oxygen, is saturated carbon dioxide, and food particles, previously glued with mucus, enter the oral opening, captured by the oral lobes. A medium-sized oyster passes up to 10 liters of water through its mantle cavity in 1 hour. Reproducing in abundance, shells become a powerful factor in cleaning water bodies.

Some stone-boring molluscs with sharp edges of shells can drill into hard soils and soft stone minks and moves. Others drill Wood, of which the most famous and dangerous shipworm is the teredo.

Teredo does not look like a mollusk, it is worm-shaped, at the rear end there are two long siphons, at the front end there is a tiny shell, the valves of which have turned into a drill. Teredo drills wood with it and swallows sawdust. It also has symbiont bacteria that break down cellulose. (Some of its symbionts can assimilate nitrogen dissolved in water.) As a result, the tree turns into a kind of sponge, exuded by passages. We have teredo found in the Black, Azov and Far Eastern seas.

The circulatory system of bivalves is also open. She has a curious feature: the heart, consisting of a ventricle and two atria, is, as it were, superimposed on the intestines.

Schematic section through the mantle cavity of a bivalve

1- sink; 2 - cut through the anterior closing muscle; 3 - section through the posterior closing muscle; 4 - the edge of the mantle; 5 - leg; 6-inlet siphon; 7 - outlet siphon (arrows show the movement of water flow); 8-gills; 9 - oral lobes.

Teredo shipworm (in wood)

Unionid freshwater shells

The excretory organs of bivalves, like the nervous system, are typical of mollusks - usually three pairs of ganglia connected by nerves. Although they do not have a head, they sometimes have eyes, along the edge of the mantle, on siphons, even on the gills.

Fertilization in shells is external, but sometimes the eggs remain on the gills of the mother, are fertilized by sperm brought into the mantle cavity, and develop further (gill pregnancy). Their larva is similar to a trochophore.

There are superorders of primary branchial bivalves, in which the gills are pinnate ctenidia, and real lamellar gills - their vast majority. Of the latter, we note a detachment of freshwater shells - unionids, with glochidia larvae, which include not only toothless and barley, but also river pearls of our northern rivers. They give good mother-of-pearl and pearls, but their reserves are rapaciously undermined - after all, pearl mussels grow slowly, reaching a length of 10 cm or more in 50 years.

The highly valued oysters and mussels belong to the second detachment - mytilides; they have already begun to be artificially bred, growing the settling larvae on the tiles. The most important producers of pearls - sea pearl oysters of the Pacific and Indian oceans - belong to the same order.

The order of pectinids - scallops includes large, commercial scallops. They are able to swim quickly by flapping their wings. Throwing water out of the mantle cavity, the mollusk moves in a jet way.

The largest detachment of bivalves is veins er ida. It includes the giant tridacna, the cockles of our southern seas (their shells often form shell beaches) and the same teredo. Some have infiltrated fresh water. Such is Dreissena - a small sessile shell that multiplied in abundance in the rivers, lakes and reservoirs of Europe. Growing in huge (up to 10,000 ind./m2) numbers, mussels clog drains, pipes, and water intakes, causing great harm. They do not have glochidia, and they spread upstream, growing to the bottoms of ships.

Many representatives of this order living in the seas are excellent food for fish, seabirds and even walruses. In general, bivalves play an important role in the life of the seas and oceans.

Chapter 3
Bivalve mollusks have a shell consisting of two valves joined at the dorsal side. The muscles that close the shell flaps are so powerful that even a person must make an effort to open a large shell. The shell consists of three layers: outer horny, middle, the hardest - porcelain and mother-of-pearl, lining the shell from the inside.

Bivalve mollusks live at the bottom of water bodies and are able to move with the help of a muscular leg, which they attach to the substrate and pull the rest of the body. The speed of movement, of course, is small - up to 30 cm / h.

Bivalves breathe by drawing water through the inlet siphon (a tube formed by the edge of the mantle) into the gill cavity and releasing it through the outlet siphon. According to the type of food, all bivalve mollusks are filter feeders, and they absorb food simultaneously with respiration.

Shellfish: common barley

Pearl barley, similar to toothless, has a more elongated and thick greenish shell. It has industrial significance: mother-of-pearl buttons are made from its shells.

Peas and balls are smaller bivalves, their shell length does not exceed 1.5 cm. In peas, the top of the shell is shifted to the posterior end, and in balls it is located in the center of the shell.

Mollusks: A - horny sharovka; B - river pea

Lesson "Origin, features of the structure and life of mollusks"

Lesson objectives:

Acquaintance with the features of the structure and life of mollusks; the origin of mollusks, the diversity of species, the environment of life.

Develop writing skills holding comparative analysis between systematic groups of living organisms.

Promote development environmental education, respect for nature, feelings of empathy, the need to come to the rescue.

Equipment: multimedia projector, shellfish collection

Lesson plan:

Parts-blocks of the lesson ( summary teacher and student activities)	Temporary implementation
Organizational moment: greeting, announcement of the topic of the lesson.	2 minutes
Lecture material using presentations (slides). Work with text	7 minutes 2 minutes
Consolidation of the studied material: Repetition of the main features inherent in the type of mollusk, Work on questions (express survey), Carrying out a comparative analysis of the complexity of the organization between the types of annelids and mollusks using the table.	4 minutes 2 minutes 5 minutes 4 minutes
Summing up the lesson	4 minutes

Lesson script.

The lesson “The origin and structural features of mollusks” is the first lesson in the study of the topic “Mollusks”. The main function of this lesson is to form general idea about this group of animals: about the origin, about the features of morphology and anatomy, which will make it possible to make the transition to a detailed, more in-depth study of the classes of molluscs each separately. In accordance with the didactic purpose, this lesson belongs to the type of lesson for learning new material. To activate mental activity and to quickly connect students to work, to awaken their interest in the topic under study, it is necessary to invite students to listen to an excerpt from M.E. Saltykov-Shchedrin “Karas-idealist”, and give the children the opportunity to try to guess which group of animals will be discussed in the lesson.

I. The teacher announces the topic and objectives of the lesson

II. Learning new material.

Introductory speech of the teacher

Guys, today we will begin our acquaintance with a very unusual group of living organisms, but what are their names, I want you to guess for yourself. Please listen to a short fragment from M.E. Saltykov-Shchedrin "Karas-idealist". “The crucian lies, buried in the silt, and selects microscopic shells from there for the sake of its food and argues: Yes, and it (the shell) is arranged in such a way that it is impossible to swallow it. Pull the water with your snout, but in your goiter you are already apparently invisibly teeming with shells. Have you guessed which animals in Everyday life we call shells?

lecture material. At the stage of studying new material (comprehension), the teacher reads lecture material, using a presentation, for a more visual representation of the animal's organ systems, while students briefly note the main features of the structure of the mollusk. This method of work will make it possible to activate all information channels that form the three main systems of perception - visual, auditory, kinesthetic.

1.2 Common features type, origin of molluscs.

Mollusks, or soft-bodied, form a separate type of invertebrates, characteristic feature which is the presence of a skin fold - a mantle, originating from ancient non-specialized polychaete worms. The number of species reaches 130 thousand, seven classes are distinguished, we will get acquainted with only three of them: gastropods, bivalves, cephalopods.

External building.

The body of mollusks in most cases consists of a head, torso and legs. The sense organs are located on the head. The trunk is a skin-muscular sac, its base is surrounded by an extensive skin fold-mantle. Between the mantle and the wall of the body, a mantle cavity is formed, in which the respiratory organs, some sensory organs are located, and where the anus, ducts of the kidneys and gonads open.

The ventral side, strongly thickened due to the muscles, forms various forms of legs: wide - crawling, wedge-shaped - for swimming, rounded - suction, etc.

On the dorsal side, as a rule, there is a shell, more often whole, less often bivalve or consisting of several plates. In some mollusks, the shell is under the skin or disappears altogether. The outer layer of the shell is formed by an organic horn-like substance, the inner layer is formed by the thinnest lime plates, the uneven reflection of light from which gives the inner surface of the shell a pearly sheen /

1.3. Internal structure.

1.3.1. Nervous system.

The nervous system of mollusks is scattered-nodular type: it consists of a peripharyngeal nerve ring, in which the supraesophageal ganglion is most developed, and nerve trunks extending from it, connecting the nerve ganglia of different parts of the body.

1.3.2. Sense organs.

The sense organs are represented by organs chemical feeling and balance, many species have eyes.

1.3.3. Respiratory system. In most species, the respiratory organs are represented by gills, terrestrial mollusks, and also some types of aquatic gastropods have a lung - a special pocket of the mantle, the walls of which are densely braided with vessels.

1.3.4. Circulatory system.

It is characterized by the presence of a heart, consisting of a ventricle and one or two atria, and blood vessels. Blood from the heart enters the vessels, then the blood enters the spaces between the organs, into the unformed system of lacunae and sinuses, washes them, then reassembles into the vessels, flows to the lungs, and from there enters the heart.

1.3.5. Organs digestive system.

The digestive system is represented by the pharynx, in which there is an organ that grinds food - a grater (radula) with horny teeth located on it. The grater is used for scraping plant food and only in rare cases for its active capture. Through the esophagus, food enters the stomach, where the ducts of the digestive gland open, which combines the functions of the liver and pancreas. The intestine is differentiated into the small intestine and the hindgut. The hindgut opens with powder into the mantle cavity. Gastropods and cephalopods have salivary glands.

1.3.6. excretory organs.

The excretory organ is represented by the kidneys, the ducts of which open into the mantle cavity.

2. Working with text. self form working with text will motivate interest in self-search activities

Source of pearls and mother-of-pearl (sea pearl).

Eating (oysters, mussels, scallops).

Natural water purifiers (bivalves).

At the end of the lesson, the teacher asks a question

Tell me, which of the meanings of shellfish do you consider the most important? Explain the answer?

III. Consolidation. Since this type of lesson is the study of new material, which is associated with the acquisition of new knowledge, taking into account the repetition of previously studied material, so that the work is not monotonous and tedious, it is worth varying the tasks, but so that their content simultaneously corresponds to the achievement of the goal, by repeating fundamentals topic being studied. First, the children are offered a task with illustrated drawings, where they can independently, from memory, determine the organs and parts of the body of the mollusk, and then, by repeating the slides, check the correctness of their answers and the possibility of correcting the mistakes made. The second task is a list of questions presented on a multimedia screen, after which the teacher proposes to conduct a mutual check on the pop-up answers, and only after that the number of correct answers should be analyzed using the dichotomy method. The third task is analytical in nature, where, using the data in the table, students should not only see the complications in the organization of the structure of mollusks in relation to annelids, but also draw a conclusion based on these data that in the evolutionary development plan this is a more highly organized group of animals. To activate the work of children and arouse interest, consolidation should be carried out in a non-standard form. The teacher offers the children a journey that they can take based on their knowledge. In addition, the goal for which children will have to go on a “swimming” also carries an educational burden, thanks to which the foundations of environmental education are laid, the desire to come to the rescue, and the development of a sense of empathy.

Determine the main features of the Mollusk type. (Guys, on your table are samples of schematic representations of organ systems of mollusks. Try to describe them correctly). Structural features characteristic of mollusks: a soft body, the presence of a mantle, a scattered-nodular nervous system, a differentiated intestine, the presence of a specialized organ that grinds food - a grater, digestive glands open type circulatory system, the presence of a heart divided into chambers, an excretory organ - the kidneys.

What do you see as the features of the external structure of mollusks?

What is a mantle?

Is there body segmentation in mollusks?

What type of circulatory system? Why?

What are the structural features of the nervous system?

What are the respiratory organs

Has there been a complication of the structure of the digestive system in comparison with the rings?

2 task from teredo (the mollusk began to undermine the bottom of the travelers' ship, in order to continue the further journey, the children must complete the task).

Express survey.

3 task from the sea pearl.

Analyze between themselves two systematic groups of animals: molluscs and annelids, enter the data in the table.

1. What complications in the organization of mollusks do we observe in comparison with annelids.

2. Consider why mollusks are a “dead end branch of evolution”?

IV. Generalization and analysis of the studied material.

Mollusks, for the most part, are aquatic animals with a skin fold-mantle, a scattered-nodal nervous system, an open circulatory system, a multi-chambered heart, a differentiated intestine, the presence of digestive glands, a kidney as an excretory organ, respiratory organs - gills and lungs.

To form a sense of kindness, respect for nature, development logical thinking a letter “comes” to the children - an appeal. The letter consists of syllables that are interconnected by arrows, if you go in the direction indicated by them, then the text of the message will be formed: “Love and protect us”. With the question “How do you guys understand these words, what do they mean to you?”, the teacher tries to get the guys to think more deeply about the meaning of this phrase so that it does not remain just a set of words, but causes emotional experiences.

V. Summing up. When summing up the lesson, you can use a democratic approach and invite the guys to evaluate the work of their comrades, and then the work of the whole class as a whole.

Guys, let's evaluate your work in the lesson, what do you think, which of your comrades deserves an excellent rating? Explain the answer.

Announcement homework pp. 134-135 retelling.

Abstract on the topic "Variety of molluscs".

Reflection.

• 
  What new did you learn at the lesson today?
• 
  How do you rate your work in class?

To choose from the three proposed options is excellent - the sun is radiant, good - the sun with a cloud, satisfactory - a cloud.

Laboratory work. The external structure of various mollusks

In the type of molluscs, three main classes are distinguished: Gastropods (ponds, coils, slugs), Bivalves (barley, toothless, oysters, mussels), Cephalopods (squids, octopuses, cuttlefish). The soft body of most mollusks belonging to the classes of gastropods and bivalves is enclosed in a shell. The body outside is completely or partially covered with a special fold of skin - a mantle. The mantle secretes substances from which the shell is formed. Mollusks live in water bodies and on land.

Purpose: to get acquainted with the external structure of various mollusks, to identify their similarities and differences.

Equipment: toothless shells, pearl barley, pond snail, coils, scalpel, hydrochloric acid, pipette.

Safety engineering. Use lab aprons while working. Be careful when working with a scalpel. Be especially careful when working with hydrochloric acid - it can burn your skin or ruin clothing. Never use chemicals without reading their instructions.

WORKING PROCESS

1. Consider the shells of toothless and barley. Locate the anterior (wide, rounded) and posterior (narrow) ends of the shell. Find the highest outer part shell (top) and note the concentric circles around it. They display the alternation of periods of slow and rapid growth(annual growth). How many annual growths did you count at the sink

Scrape off the outer layer with a scalpel anywhere on the shell. Be careful when working with a scalpel, hold it so as not to cut yourself. Under top layer there is a porcelain layer. Drop as shown in Fig. 3, on the porcelain layer with hydrochloric acid. Be careful when working with acid, do not drip on skin or clothing. Describe your observations.

Rice. 3 Bubbling indicates the presence of calcium carbonate in the sink

2. Examine the inside of the shell and establish how the toothless shell differs from the barley shell.

Sketch the shell and make captions.

3. Consider pond snail shells and coils. Find the mouth and curl. Count how many turns in the coil of the pond snail shell and coil. _________________________________________________

Are all curls the same? _________________

What is the similarity between the shell of a pond snail and a coil? _________________________________

What is their difference?__________________________________

Sketch the shell of a pond snail. Make signatures for it.

findings

1. Insert missing words.

Mollusks are highly organized invertebrates. The body is soft, in most species it consists of _____, ______, ________. From the dorsal side and from the sides it is covered with a fold of skin __________. Between the mantle and the body of the mollusk, a __________ cavity is formed. Many species have a well-developed hard calcareous _______. Some of them still have remnants.

2. Set the age of the toothless by the number of annual growths on the shell. __________________

3. What is the porcelain layer of toothless and barley shells formed from? ______________________

4. How do the shells of the pond snail and coil differ from the shells of the toothless and barley? ____________

Problem tasks

1. What, in your opinion, are the advantages and disadvantages of shells that contain mollusks? ______ ______________________________________

2. Why are fossil mollusks more common than fossil worms? _______________________

Chapter 4
1. Write the names of the bivalve body parts. What functions do they perform?

2.

3. Fill in the table


4. Bivalves

Using initial letters, write the names of the molluscs (horizontally).

Answer options: mussel, oyster, tridacna, toothless, barley

5. Test tasks on the topic "Mollusks"

1. In terms of the number of species, the Mollusca type is second only to the type:

a) Arthropods;

b) the simplest;

c) Intestinal;

d) annelids.

2. Species of mollusks are known:

a) about 1 million;

b) over 13 thousand;

c) over 130 thousand;

d) about 1300.

3. With the help of the lungs breathes:

a) cuttlefish;

b) pond snail;

c) toothless;

d) squid.

4. An active predator is:

a) a pond snail;

b) toothless;

c) coil;

d) squid.

5. Active, mobile lifestyle leads:

a) an octopus

b) toothless;

c) barley;

6. The filter is:

a) rapana;

b) pond snail;

c) cuttlefish;

d) toothless.

7. Select from the list below:

1 - gastropods; 2 - cephalopods; 3 - bivalves:

a) squid;

c) oyster;

d) octopus;

e) coil;

e) pea;

g) ball;

h) toothless;

i) rapana;

j) a pond.

8. In an hour, one oyster can filter.

>>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, 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, is not wide flat sole, but in the form of a muscular, forward-pointing wedge. 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. Inner surface 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. These shells are used to make buttons. 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.

Nutrition.

In a live, undisturbed toothless, the doors are slightly ajar in the back part and 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 38 . 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.

Breath.

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.

Circulatory and excretory system toothless have a similar structure to those of 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 discharged 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.

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

Biology: Animals: Proc. for 7 cells. avg. school / B. E. Bykhovsky, E. V. Kozlova, A. S. Monchadsky and others; Under. ed. M. A. Kozlova. - 23rd ed. - M.: Education, 2003. - 256 p.: ill.

Lesson content lesson summary support frame lesson presentation accelerative methods interactive technologies Practice tasks and exercises self-examination workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures graphics, tables, schemes humor, anecdotes, jokes, comics parables, sayings, crossword puzzles, quotes Add-ons abstracts articles chips for inquisitive cheat sheets textbooks basic and additional glossary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in the textbook elements of innovation in the lesson replacing obsolete knowledge with new ones Only for teachers perfect lessons calendar plan for the year guidelines discussion programs Integrated Lessons

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. She feeds different kind 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, 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. Toothless narrow - more rare view 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 large number of oxygen 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.

Nutrition

Habitat and structure of toothless

Pattern: toothless shell

Figure: toothless structure

In the same reservoirs where the pond snail lives, you can also find another mollusk - 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, 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. These shells are used to make buttons. In a pearl oyster, mother-of-pearl can surround a grain of sand that accidentally got inside, and then a shiny ball is formed - 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.

Toothless food

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.

Toothless breath

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.

Circulatory and excretory systems of toothless

The nervous system of the toothless

The nervous system of the toothless is the same as that of the pond snail. There are three pairs of nerve nodes interconnected by jumpers. There are no special sense organs.

Toothless breeding

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 discharged 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.

Presented in domestic reservoirs. This species lives mainly on sandy and muddy bottoms. Let's take a closer look at the structure of the toothless shell, find out what lifestyle this mollusk leads.

Structure

Considering the structure of the toothless shell, the outer and inner layers, it is worth noting that such a mollusk is extremely similar to another common mollusk in our reservoirs - barley. The shape of the shells of these species is almost identical. However, toothless are more massive, and also have a fine structure of the outer shell. In addition, these creatures do not contain teeth on inside shells, forming a kind of castle, like a barley. Hence the name - toothless.

Looking at what a toothless shell looks like, external structure shell, it should be noted that the latter is formed from two keratinized halves tightly adjacent to each other. In front of the sink has an extension. It narrows in the back. In a live, freshly caught mollusk, the valves are always securely closed, which is a protective reflex against predators.

To consider internal structure toothless shells, will have to be cut internal muscles that keep the shell closed. In the natural environment, the shell opens by contraction of a strong horn-shaped ligament that runs along the entire dorsal part of the body of the mollusk. While toothless is alive, her protective shell most time remains closed. When the animal dies, the muscles relax and the valves open voluntarily.

What is a toothless shell?

It should be noted that the structure of the shell of toothless and pond snails, as well as the same pearl barley, is almost identical. The outer shell of the mollusk is, in fact, a keratinized calcareous layer, covered with a brownish, petrified silty coating. If a piece of shell is placed in a solution of hydrochloric acid, gas bubbles will begin to actively stand out from the material. This indicates the organic structure of the outer shell of the mollusk.

Studying the toothless structure, you can see that inside the shell there is a mother-of-pearl layer, which looks like thin plates overlapping each other. The shell surfaces here have an attractive iridescent sheen.

In general, the keratinized part of the body of the mollusk consists of three layers. The outer part of the shell is formed by a keratinized calcareous layer. From the inside, the toothless carapace is lined with a porcelain and mother-of-pearl layer.

soft tissues

Exploring what the toothless are, the structure of the mollusk, one should talk about the internal, mantle cavity of such an animal. Opening the shell flaps, one can see folded skin structures that are located on both sides of the body. The edges of such soft tissues smoothly pass into the shell and are connected to the keratinized structures with strong ligaments.

The structure of the toothless external is represented by structures that are sufficiently resistant to mechanical stress. In its turn, inner part clam is extremely soft. For this reason, such animals are also called soft-bodied. In the mantle, folded cavity are the internal organs. To see them, it is enough to unscrew the soft tissues.

The shell valves in the posterior part of the body of the mollusk do not fit together tightly. There is a small gap through which fresh water enters the sink. The liquid is filtered out by the digestive organs of the toothless and brought out through a special upper opening on the body. The movement of water in the mantle cavity is supported by the rhythmic fluctuations of the so-called ciliated cilia that cover the internal organs of the mollusk.

Breathing and nervous system

In the mantle cavity of the mollusk there are gills. They can be distinguished from other soft tissues by their characteristic brown tint. Each inner side of the shell contains a pair of gills. The water that enters the sink brings toothless not only nutrients but also oxygen.

As for the nervous system, in toothless it is primitive and consists of several pairs of nerve nodes. With the help of nerve fibers located in soft tissues, the mollusk perceives stimuli and responds to them. So, when touching an open shell, its valves will instinctively close.

Reproduction features

Toothless are heterogeneous creatures. Outwardly, females are no different from males. During the mating season, molluscs concentrate in a certain area of ​​the reservoir. The males release the seed into the water. Spermatozoa enter the body of females through a special siphon, after which the fertilization of eggs begins. The latter develop into larvae. Through the same siphon, not yet fully formed individuals are thrown out.

Lifestyle

Toothless, the structure of which was described above, lead. Such molluscs feed passively. Toothless filter out primitive organisms and plant particles from the water. The latter enter the mantle cavity through the oral lobes - small leathery folds located in the front of the body. The movement of shimmering eyelashes useful material are driven into the digestive organs.

To follow the toothless and behavior in the natural environment, it is enough to place the mollusk in an aquarium that has a sandy bottom. After some time has passed, you can notice the separation of the shell valves. A leathery fold will look out through the gap formed, thanks to which the animal moves along the bottom. By itself, toothless leaves shallow grooves on the surface of the sand. Within an hour, the mollusk is able to cover a distance of no more than 30-40 centimeters.

Finally

As you can see, toothless are typical representatives primitive bivalves. Such animals massively settle in ponds and rivers, because they do not have natural enemies. Unlike the same oysters and mussels, toothless are not eaten by humans.