Tolstoy's relationship to Pierre. Pierre Bezukhov: character description

Shellfish- multicellular, three-layered animals with bilateral body symmetry, having a mantle (large fold of skin) surrounding the base of the body.

Type There are about 130 thousand species of mollusks.

Modern scientists distinguish in the type Mollusks classes : pit-tailed, groove-bellied, armored (chitons), monoplacophorans, bivalves, spatulate, gastropods (snails), cephalopods (octopuses, squids, cuttlefish).

Malacology(from the Greek malakion - mollusk and logos - word, doctrine) - a section of zoology that studies mollusks.

Conchology(conchiliology) (from the Greek konche, konchylion - shell and logos - word, doctrine) - a branch of zoology that studies shells (mainly mollusks).

Features of the external structure

have a soft body enclosed in a shell

have a bilaterally symmetrical body structure, i.e. folded according to the principle of mirror reflection - the left half of the body completely corresponds to the right half. However, in the process ontogeny Some species exhibit misalignment or uneven growth of organs, resulting in asymmetry. Asymmetry is especially pronounced among gastropods.

body has no segmentation. Consists of three sections: head, legs, torso.

The torso contains all the major internal organs.

have a mantle - an epithelial fold that completely or partially covers the body, connects it with external environment. The mantle complex of organs is located in the mantle cavity: the excretory tract of the reproductive system, the excretory tract of the digestive system, ctenidium, osphradium and hypobranchial gland. The complex also includes kidneys and pericardium.

the secondary cavity (in general) is represented by the cavity of the heart sac (pericardium) and the cavity gonads.

Features of the internal structure

Let's look at examples .

Aromorphoses, which contributed to the emergence of:

unsegmented body

the appearance of a complex fold - the mantle and mantle cavity

shell formation

Idiomatic adaptations, which contributed to biological progress:

appearance of the shell

the emergence of an apparatus for grinding food - the radula

the emergence of two forms of respiration - gill and pulmonary

high fertility

Let's look at a brief description of the external and internal structure For example Oysters.

Footnotes

1. Idiomatic adaptation– particular adaptation of organisms to a certain way of life in specific environmental conditions.

2. Aromorphosis– a progressive evolutionary change in structure, leading to a general increase in the level of organization of organisms.

3.Bilaterally symmetrical(bilateral) animals are multicellular animals in which the left side of the body mirrors the right half of the body.

4.Gonads- organs of animals that produce sex cells - gametes. Female gonads are ovaries, male gonads are testes. They produce sex hormones - androgens and estrogens.

5.Ctenidia– primary organs of gas exchange in mollusks.

6.Radula(grater) - a device used for scraping and grinding food from mollusks. Located in the oral cavity.

7.Hemocyanin– a respiratory pigment from the group of metalloproteins, contains copper and is an analogue of hemoglobin.

8.Filters– mollusks that use a passive method of feeding, in which organic particles and microorganisms enter the gill cavity through a siphon and are swallowed using two pairs of oral lobes located at the anterior end of the body.

9.Reduction in biology - reduction, simplification of structure or disappearance of organs due to the loss of their functions in the process of evolution.

10.Statocysts– mechanoreceptor organs of balance in invertebrates, which have the appearance of vesicles submerged under the body cover, or straps or flask-shaped protrusions of the cover (in jellyfish and sea urchins).

11.Osphradius– receptor organ of mollusks, formed by specialized sensitive epithelium.

12. Ontogenesis– individual development of the organism from fertilization (with sexual reproduction) or from the moment of separation from the maternal individual (with asexual reproduction) to death.

13. Segmentation in morphology: the same as metametry: the division of the body or individual organs into repeating segments (body parts).

14. Pericardium(pericardial sac) - the outer connective tissue membrane of the heart, normally separated from the epicardium by a gap filled with serous fluid - the pericardial cavity.

15. Hermaphrodite– an organism that has characteristics of male and female sex, including having both male and female genital organs.

16. Siphon- an organ of bivalve mollusks, which is an outgrowth of the siphonal (posterior) edge of the mantle.

17. Receptors(from Lat. receptor - receiving), in physiology - the endings of sensitive nerve fibers or specialized cells (retina of the eye, inner ear, etc.), transforming irritations perceived from the outside (exteroceptors) or from the internal environment of the body (interoceptors) into nervous excitation transmitted to the central nervous system.

18. Epithelium in animals and humans (epithelial tissue) - a layer of closely spaced cells covering the surface of the body (for example, skin), lining all its cavities and performing mainly protective, excretory and absorption functions. Most glands also consist of epithelium. In plants, cells lining the cavities of organs or their parts (for example, resin ducts in conifers).

More details:

Type Shellfish, or Soft-bodied, - a large group of unsegmented secondary animals, the body of which consists of a head, torso and legs. The body forms a leathery fold - mantle . She shapes sink . Between the trunk and the mantle is mantle cavity . About 130 thousand species belong to the phylum of mollusks.

General characteristics of the type

Some shellfish – bilaterally symmetrical animals. However, gastropods developed a twisted shell, and their body became secondary asymmetrical.

Mollusks are characterized by hard mineral shell , covering the body of the animal from the dorsal side. The shell, as a rule, consists of crystals of calcium carbonate. On top it is usually covered with a horn-like organic substance, and on the inside it is lined with a hard, shiny calcareous layer - mother of pearl . The shell can be solid, bivalve, or consisting of several plates (in chitons). Slowly moving and immobile mollusks have a highly developed shell. However, in some mollusks it is reduced (underdeveloped) or absent altogether. This happens when the mollusk lives in places where it is difficult for predators to reach (for example, when it burrows deep into the sand of the seabed or drills passages in the trunks of trees that have fallen into the sea). Molluscs that swim well have lost their shells.

Mollusc body consists of an unsegmented torso, head and legs. Head found in almost all mollusks. It contains a mouth opening, tentacles and eyes. Leg mollusk - a muscular unpaired outgrowth of the body. It is usually located on the ventral side and is used for crawling.

In bivalves, due to a sedentary lifestyle, the head is missing and the leg is partially or completely lost. In some species, the leg can turn into a swimming organ (for example, in cephalopods).

Internal structure. The body of the mollusk is surrounded by a fold of skin - mantle . The space formed between the walls of the body and the mantle is called mantle cavity . The mantle cavity contains the respiratory organs - gills. The external openings of the excretory organs, genitals and anus open there.

Mollusks have in general – secondary body cavity. It is well expressed in the embryonic state, and in adult animals it remains in the form of the pericardial sac and the cavity of the gonad. All spaces between organs are filled with connective tissue.

Digestion. The mouth opening leads into the pharynx. In the pharynx of representatives of many species there is grater (radula) - a special device in the form of a tape, lying on the ledge of the floor of the oral cavity. There are teeth on this tape. Using a grater, herbivorous mollusks scrape food from plants, and carnivorous mollusks, whose radula teeth are larger, hit and grab prey. In some predatory mollusks, salivary glands open into the oral cavity; the secretion of the salivary glands contains poison.

The pharynx passes into the esophagus, followed by the stomach, into which the liver ducts open. The stomach passes into the intestine, ending in the anus. In bivalves that feed on microscopic algae and small organic particles suspended in water, the structure of the oral apparatus is simplified: the pharynx, grater and salivary glands are lost.

Breath. In most mollusks, the respiratory organs are paired external gills - flat skin outgrowths lying in the mantle cavity. Land mollusks breathe using lung – modified mantle cavity.

Circulatory system. The heart of mollusks consists of one ventricle and two atria. Circulatory system open . Some mollusks have manganese or copper in their blood, the compounds of which play the same role as iron in the blood of higher animals - they ensure the transfer of oxygen.

Excretory organs presented paired buds , which at one end communicate with the cavity of the pericardial sac (remnants of the coelom), and at the other open into the mantle cavity.

Nervous system. The central nervous system consists of several pairs of ganglia (nodes) connected by nerve trunks, from which nerves extend to the periphery.

Sense organs. Mollusks have well-developed organs of touch, chemical sense and balance. Motile mollusks have organs of vision, and fast-swimming cephalopods have well-developed eyes.

Reproduction. Most shellfish dioecious . However, there is also hermaphrodites in which cross-fertilization occurs. Fertilization in mollusks is external (for example, oysters And toothless) and internal (y grape snail).

From a fertilized egg, a larva develops, leading a planktonic lifestyle (the so-called sailboat ), or a formed small mollusk.

Origin. There are several points of view on the origin of mollusks. Some zoologists believe that the ancestors of mollusks were flatworms. Others suggest that mollusks evolved from worms. Still others think that mollusks originate from ancestors common to annelids. Embryological data indicate the relationship of mollusks with annelids.

A typical mollusc larva (sailfish) is very similar to an annelid larva, bearing large lobes lined with cilia. The larva leads a planktonic lifestyle, then settles to the bottom and takes on the appearance of a typical gastropod.

The meaning of shellfish

Representatives of certain classes of mollusks are of great importance in many natural biocenoses. Aquatic mollusks are often the most abundant group in benthic ecosystems. The filtration method of feeding of bivalves leads to the fact that many of them precipitate mineral and organic particles, providing water purification. Fish, birds and animals eat shellfish.

Shellfish serve as food for people and are traditional objects of fishing and farming. (oysters, scallops, mussels, hearts, squid, Achatina, grape snail).

In the shells of sea mollusks pearl oysters A very beautiful pearl is formed. Sinks cowrie were used by the Aborigines as coins. Using fossil mollusk shells, geologists can accurately determine the age of sedimentary rocks.

Molluscs (soft-bodied) are animals with a soft body, not divided into segments, having a shell or its remains. Most mollusks have a head, a torso and a muscular leg. Under the shell there is a fold of skin - the mantle. The circulatory system is not closed. Most mollusks are dioecious, but some are hermaphrodites. Over 130 thousand species of mollusks are known.

The phylum Molluscs includes 7 classes: Lampshells, Monoplacophorans, Armorates, Spadepods, Gastropods, Bivalves and Cephalopods.

Class Gastropods (Gastropoda)

Gastropods (they are also called snails) are the most numerous and diverse class of mollusks. It has about 90 thousand species.

Habitat. In the lakes, ponds and river backwaters of our country you can meet one of the representatives of this class - big pond snail (5) about 5 cm long. In the forest floor, in damp meadows, in gardens and vegetable gardens, another species is found - naked slug (4) up to 12 cm long.

External building. The pond snail has three distinct body parts. These are the head, leg and bag-like torso. The top of the body of the mollusk is covered with a special fold of skin - mantle . The naked slug has an elongated body, and the body and mantle are small.

The pond snail has a spiral shell, twisted in 4-5 turns, which protects the body of the animal. The shell is made of lime and is covered with a horn-like organic substance on top. Due to the spiral shape of the shell, the body of the pond snail is asymmetrical, since in the shell it is also curled into a spiral. The initial narrow and blind end of the shell is called top , and open and wide – mouth shells. The shell is connected to the body by a powerful muscle, the contraction of which pulls the snail inside the shell. In the naked slug, the shell was reduced (disappeared) in the process of evolution.

The leg of the pond snail and slug is muscular, well developed and has a wide sole . The characteristic way of movement of these animals is to slowly slide on their feet over plants or soil. The copious mucus secreted by the skin glands of the leg facilitates smooth gliding.

When crawling, the muscles of the cochlea's leg contract in waves from the anterior end of the sole to the posterior; the speed of such movement in terrestrial gastropods ranges from 4 to 12 cm per minute.

In gastropods that lead a swimming lifestyle, the legs turn into fins and blades. Among these mollusks there are walking, jumping and swimming individuals.

Digestive system. In the mouth, on a special movable outgrowth resembling a tongue, there is a grater ( radula ) with horny teeth. With their help, the pond snail and the slug scrape off their food: the pond snail scrapes off soft parts of plants and microscopic algae deposits on underwater objects, and the slug scrapes off leaves, stems, berries of various land plants and mushrooms. The pharynx contains salivary glands, the secretion of which processes food. From the pharynx, food enters the stomach through the esophagus. The liver ducts flow into it. The secretion of the liver dissolves carbohydrates, and food absorption also occurs in the liver. The stomach passes into the intestine, which makes several loops and ends with an anus at the front end of the body above the head (in a pond snail) or on the right side of the body (in a slug).

Respiratory system. In terrestrial and some freshwater mollusks, gills are replaced by an organ of air respiration - easy . The free edge of the mantle fuses with the body wall, leaving a small respiratory opening leading into the mantle cavity. Numerous blood vessels develop in the mantle, and the mantle cavity becomes the pulmonary cavity. This is how the lung is formed. Gas exchange occurs in the lung - saturating the blood with oxygen and releasing it from carbon dioxide.

To breathe, a pond snail living in water is forced to periodically rise to the surface of the reservoir and change the air in the lung cavity through the breathing hole.

Most aquatic gastropods breathe with feathers. gills . Due to the asymmetry of the body, underdevelopment of the organs on the right side of the body occurs. Therefore, in most gastropods, the right gill disappears and only the left one remains.

Circulatory system. The pond snail and slug have a heart consisting of an atrium, a ventricle and blood vessels. Circulatory system in gastropods open : blood flows not only through the vessels, but also in the cavities between the organs. departs from the heart aorta , it branches into arteries , after which the blood enters small cavities located among the connective tissue. There the blood gives off oxygen and is saturated with carbon dioxide. Next the blood flows through venous vessels into the lung, where the blood is enriched with oxygen and gets rid of carbon dioxide. Then the blood flows through the veins to the heart. The heart rate in gastropods is 20-40 times per minute.

Excretory system. Due to the asymmetry of the body, the pond snail and the slug retain only left kidney . At one end this kidney communicates with the pericardial sac (the remainder of the body cavity), where metabolic products are collected, the other opens into the mantle cavity on the side of the anus. The pericardium is a remnant of the coelom. Therefore, we can say that the excretory systems of mollusks and annelids are similar in structure.

Nervous system mollusks of the scattered-knot type. It consists of several large nerve ganglia, interconnected by nerve bridges, and numerous nerves. Due to the twisting of the body of gastropods, the nerve bridges between some nodes form a decussation.

Sense organs. On the head of both the pond snail and the slug there are organs of touch - tentacles. The pond snail has one pair, the slug has two. There are eyes. In a pond snail they are located at the base of the tentacles, and in a slug they are at the tops of the second pair of tentacles. The second pair of tentacles is the olfactory organ. In addition, gastropods also have balance organs.

Reproduction. Fertilization in pond snails and slugs internal . Both of these animals are hermaphrodites . The single reproductive hermaphroditic gland produces both sperm and eggs.

Fertilization in these mollusks is cross-fertilization: each of the mating individuals plays the role of both male and female, so the genetic material of different individuals is exchanged. From the fertilized eggs laid, small mollusks develop that look like adult animals.

Development. From the eggs of marine gastropods, a larva (sailfish) develops. The larva leads a planktonic lifestyle, then settles to the bottom and takes on the appearance of a typical gastropod.

Some marine gastropods (e.g. trumpeter) serve as commercial objects. Sea mollusk shells abalone They give a very beautiful mother of pearl. Sinks cowrie were used as coins. Grape snails are bred as edible animals.

Gastropods are distributed throughout the globe. Among them there are marine, freshwater, and terrestrial forms. The richest species are the coastal zones of subtropical seas and mountain forests of subtropics and temperate latitudes.

A characteristic feature of gastropods is their asymmetrical structure. This is the most numerous class of mollusks. The shell is solid, often spirally twisted. Slugs do not have shells. Many gastropods serve as food for fish and birds. Among gastropods there are pests of gardens and vegetable gardens .

The structure of a bivalve mollusk: 1 - the line along which the mantle is cut; 2 - closing muscle; 3 - mouth; 4 - leg; 5 - oral lobes; 6,7 - gills; 8 - mantle; 9 - inlet siphon; 10 - outlet siphon; 11 - hindgut; 12 - pericardium

Aquatic mollusks are often the dominant group of bottom biocenoses. M. is an important food item in the diet of commercial invertebrates, fish, and some whales. Edible meats (oysters, mussels, scallops, squid, Achatina, grape snail, etc.) are a traditional fishery object (about 1.5 million tons are mined annually in the world, according to other data - 5 million tons of various fish). ) and aquaculture (world production amounted to about 3.2 million tons in 1985). Diff. species of sea pearl mussels are the object of industrial breeding in the Persian Gulf, near the island. Sri Lanka, off the coast of Japan. Since ancient times, M. shells have been used as decorations, as money, in cult rituals, and in decorative and applied arts. Some M. become fouled; stone borers, shipworms can damage sea vessels, port vessels and other hydraulic engineering. structures; slugs, snails, etc. harm agriculture. cultures. Due to overfishing and habitat destruction, many species need protection, e.g. some tridacnae, cypriae, cones, etc. 19 species of M. in the Red Book of the USSR

Initial level of knowledge:

Response plan:

General characteristics of Mollusks.
The structure of gastropods using the example of the Greater pond snail
The structure of bivalve mollusks using the example of Toothless.
Variety of Mollusks
The importance of shellfish in nature and human life

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

General characteristics of the Mollusc type:

The body forms a skin fold - the mantle. Between the mantle and the body, a mantle cavity is formed, into which the anus, ducts of the kidneys and gonads open, as well as the respiratory organs and some sensory organs.

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 sections, each of which provides specific functions.

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

Digestive system consists of the foregut, midgut and hindgut. Digestive glands appeared, ensuring 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 extend 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 internal organs.

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

Excretory organs- kidneys, which are modified metanephridia.

Nervous system scattered-nodular type. Among the sense organs - organs of chemical sense and balance; many have eyes.

Reproduce mollusks only sexually. There are dioecious and hermaphrodite. Development is direct or with a larval stage.

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

The structure of gastropods using the example of the Greater pond snail

Animals of this class live in marine and fresh water bodies, many live on land. 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 lime layer.

The pond snail's body consists of three sections: head, body and legs. On the head there are 1–2 pairs of tentacles, well-developed eyes, which are often placed at the top of the tentacles; the leg is usually wide with a flat sole, the body is spirally twisted. The radula is located in the pharynx. This is a grater for scraping the soft parts of plants, consisting of horny teeth.

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

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

The structure of bivalve mollusks using the example of Toothless

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

The body is covered with a mantle, which hangs from the sides in the form of folds. On the dorsal side, the mantle fuses with the body of the mollusk. Often the free edges of the mantle grow together, leaving openings - siphons for the entry and exit of water from the mantle cavity. The outer epithelium of the mantle forms the shell valves. The outer layer of the shell consists of organic matter; the middle layer is formed from carbonated lime and has the greatest thickness. The inner layer is mother-of-pearl.

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

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

Nervous system bivalves are 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 closing 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 adductor muscle, 14 - anus, 16 - gills, 17 - gonad opening, 18 - midgut, 19 - gonad.

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

Reproduction. Most bivalves are dioecious. Testes and ovaries are paired. The reproductive 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 jagged spines on the edges. When a fish swims over the toothless one, the mollusk pushes the larvae through the excretory siphon into surrounding water. With the help of a byssal thread and spinous valves, the 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 for consolidation:

• What characteristics do bivalves and gastropods have in common?
• What is the difference between bivalves and gastropods?
• Why can a pond snail live in an aquarium with stagnant water, but a toothless one cannot?
• What control measures are most effective and safe against shellfish pests?

Literature:

1. Bilich G.L., Kryzhanovsky V.A. Biology. Full course. In 3 volumes - M.: LLC Publishing House "Onyx 21st century", 2002
2. Biology: A guide for applicants to universities. Volume 1. - M.: Novaya Volna Publishing House LLC: JSC " Publishing House ONYX", 2000.
3. Kamensky, A. A. Biology. Reference manual / A. A. Kamensky, A. S. Maklakova, N. Yu. Sarycheva // Complete course of preparation for exams, tests, testing. - M.: JSC "ROSMEN-PRESS", 2005. - 399 p.
4. Konstantinov V.M., Babenko V.G., Kuchmenko V.S. Biology: Animals: Textbook for 7th grade students secondary school/ Ed. V.M.Konstantinova, I.N. Ponoma-roar. – M.: Ventana-Graf, 2001.
5. Konstantinov, V. M. Biology: animals. Textbook for 7th grade general education schools /V. M. Konstantinov, V. G. Babenko, V. S. Kuchmenko. - M.: Ventana-Graf, 2001. - 304 p.
6. Latyushin, V.V. Biology. Animals: textbook. for 7th grade general education institutions / V.V. Laktyushin, V.A. Shapkin. - 5th ed., stereotype. - M.: Bustard, 2004. - 304 p.
7. Pimenov A.V., Goncharov O.V. Biology manual for applicants to universities: Electronic textbook. Scientific editor Gorokhovskaya E.A.
8. Pimenov A.V., Pimenova I.N. Zoology of invertebrates. Theory. Tasks. Answers: Saratov, OJSC publishing house "Lyceum", 2005.
9. Taylor D. Biology / D. Taylor, N. Green, W. Stout. - M.:Mir, 2004. - T.1. - 454s.
10. Chebyshev N.V., Kuznetsov S.V., Zaichikova S.G. Biology: a guide for applicants to universities. T.2. – M.: Publishing House LLC New wave", 1998.

The most characteristic features shellfish:

There is a skin fold - mantle;

Overall presented pericardial sac and gonadal cavity;

-lack of segmentation;

The body is divided into head, torso And leg;

-at most are present in the pharynx radula (grater)- apparatus for grinding food.

The Soft-bodied type includes the following classes: Gastropods, Bivalves, Cephalopods.

Class Gastropods

a brief description of

Gastropods, or snails, are the richest class of mollusks. Primarily gastropods are inhabitants of the sea, but many species have adapted to life in fresh water bodies and on land.

general characteristics

Rice. 1.Opened grape snail: 1 - labial tentacles; 2 - eye tentacle; 3 - pharynx; 4 - cerebral ganglion; 5 - lung; 6 - pulmonary vein; 7 - cut pulmonary opening; 8 - anus; 9 - opening of the ureter; 10 - rectum; 11 - ureter; 12 - atrium; 13 - ventricle of the heart; 14 - pericardium; 15 - kidney; 16 - stomach; 17 - liver; 18 - hermaphrodite gland; 19 - hermaphroditic duct; 20 - protein gland; 21 - seminal receptacle; 22 - seminal receptacle channel; 23 - oviduct; 24 - seed tube; 25 - bag of love arrows; 26 - finger-shaped glands; 27 - whip; 28 - penis; 29 - salivary glands

Digestive system. Mouth leads to oral cavity, which goes into muscular throat(Fig. 29). There is a muscular ridge in the pharynx - language, covered with a thin cuticle and bearing hard teeth arranged in transverse rows. Cuticle And teeth form radulu, or grater. One pair of ducts open into the pharynx salivary glands. In predatory gastropods that feed on other mollusks or echinoderms, the secretions of the salivary glands contain free sulfuric acid to dissolve shells. Behind the pharynx there is a rather long esophagus With goiter. At first midgut is formed stomach, into which the ducts flow liver. The liver can perform the functions of digestion, absorption and storage of fat and glycogen. Interestingly, in gastropods that eat hydroid polyps, their stinging cells are collected in the liver, retaining the ability to function. The stomach follows small intestine , turning into hindgut which ends anus above the head or somewhere on the right side of the body.

Respiratory system. Most gastropods breathe gills, which are formed as outgrowths into the mantle cavity. In terrestrial and secondary aquatic gastropods, part of the mantle cavity is separated and opens outwards with an independent opening. This isolated cavity is called pulmonary cavity.

Rice. 2.Longitudinal section through the pharynx of a grape snail: 1 - jaw; 2 - oral cavity; 3 - muscular wall of the pharynx; 4 - blood cavities of the tongue; 5 - radular cartilage; 6 - internal pharyngeal muscle; 7 - fold of pharyngeal epithelium; 8 - epithelium forming the radula; 9 - radular vagina; 10 - connective tissue of the radular vagina; 11 - muscle supporting the radular vagina; 12 - esophagus; 13 - buccal commissure; 14 - pharyngeal cavity; 15 - radula; 16 - language; 17 - cuticle

Excretory system presented a pair of buds, of which one left kidney is most often preserved. At one end, with the help of a ciliary funnel, the kidneys communicate with the pericardium. The opposite - they open into the mantle cavity.

Circulatory system not closed. Structure hearts depends on the systematic group. In the most primitive gastropods, the heart consists of ventricle And two atria. In this case, the ventricle is penetrated by the hindgut. With the development of asymmetry, the right atrium also changes: from blindly closed and reduced to complete disappearance. Thus, in most gastropods two-chambered heart and consists of ventricle And one, left, atrium. Blood more often colorless.

Rice. 3.Structure of the nervous system different types gastropods: 1 - visceral ganglion; 2 - buccal ganglion; 3 - cerebral ganglion; 4 - intestinal ganglion; 5 - pedal ganglion; 6 - pleural ganglion; 7 - parietal ganglion

Nervous system built according to scattered-nodal type(Fig. 3). Available 5 large clusters of ganglia. Cerebral ganglia located above the pharynx and innervate the eyes, statocysts (equilibrium organs), pharynx and head tentacles. Located in the leg pedal ganglia, innervating the muscles of the legs . Located next to the pedal ganglia pleural ganglia, which innervate the mantle. Parietal ganglia ctenidia (gills) and chemical sense organs are innervated. Located under the hindgut visceral ganglia, which innervate internal organs.

Sense organs. The organs of touch are the head tentacles and the edges of the mantle. The anterior pair of head tentacles acts as organs of taste and smell. All gastropods have one pair of eyes, located at the base or apex of the posterior pair of tentacles. The structure of the eyes varies from simple palpebral pits to optic vesicles with a lens and vitreous body.

Reproductive systems and development. Sex gland Always one. U dioecious gastropods it is represented ovary or testis. U hermaphrodite forms - hermaphroditic gland, in which they are formed and sperm, And eggs. Fertilization is internal, cross, but it also occurs external fertilization. Development with metamorphosis. Larva - sailboat

Class Gastropods- the most diverse and widespread group of mollusks.

There are about 90 thousand modern species of gastropods living in the seas (rapana, cones, murex), fresh water bodies (ponds, coils, meadows), as well as on land (slugs, grape snails).

External structure

Most gastropods have a spirally twisted shell. In some, the shell is underdeveloped or completely absent (for example, in naked slugs).

The body consists of three sections: heads, torso and legs.

On the head are one or two pairs of long soft tentacles and a pair of eyes.

The body contains internal organs.

The leg of gastropods is adapted for crawling and is a muscular outgrowth of the abdominal part of the body (hence the name of the class).

Common pondweed- lives in fresh water bodies and shallow rivers throughout Russia. It feeds on plant foods, scraping the soft tissues of plants with a grater.

Digestive system

In the oral cavity of gastropods there is a muscular tongue with chitinous teeth that form a “grater” (or radula). In herbivorous mollusks, the grater (radula) is used to scrape off plant food, in carnivorous mollusks it helps to retain prey.

The salivary glands usually open into the oral cavity.

The oral cavity passes into the pharynx, and then into the esophagus, which leads to the stomach and intestines. Channels flow into it digestive gland. Undigested food remains are thrown out through anal hole.

Nervous system

Nervous system ( the picture shows yellow ) consists of several pairs of well-developed nerve ganglia located in different parts bodies, and the nerves coming from them.

Gastropods have developed sensory organs, they are located mainly on the head: eyes, tentacles - organs of touch, organs of balance. Gastropods have well-developed olfactory organs - they can recognize odors.

Circulatory system

Gastropods have an open circulatory system consisting of a heart and blood vessels. The heart consists of two chambers: the ventricle and the atrium.

Respiration in mollusks living in water is carried out by gills, and in terrestrial ones - with the help of the lung.

In the mantle cavity, most aquatic gastropods have one or, less commonly, two gills.

In pond snails, coil snails, and grape snails, the mantle cavity acts as a lung. Oxygen from atmospheric air filling the “lung”, penetrates through the wall of the mantle into the blood vessels branched in it, and carbon dioxide from the blood vessels enters the cavity of the “lung” and comes out.

Excretory system

The excretory organs of mollusks are one or two kidneys.

Metabolic products that are unnecessary for the body come from the blood to the kidney, the duct from which opens into the mantle cavity.

The release of carbon dioxide from the blood and the enrichment of oxygen occurs in the respiratory organs (gills or lungs).

Reproduction

Shellfish breed only sexually.

Ponds, coils, slugs are hermaphrodites.

They usually lay fertilized eggs on plant leaves and various water objects or between lumps of soil. Small snails emerge from the eggs.

Many marine gastropods are dioecious animals; they develop from larval stage - swallowtail.

Meaning

Many shellfish serve as food for fish and birds. Terrestrial gastropods are eaten by amphibians, moles, and hedgehogs. Some species of gastropods are also eaten by humans.

Among the gastropods there are pests of gardens and vegetable gardens - slugs, grape snails, etc.

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Class Bivalve (elasmobranch) molluscs

Theory:

Bivalves Exclusively aquatic animals, they lead a mostly sedentary lifestyle. Most of them live in the seas (mussels, oysters, scallops), and only a small part lives in fresh water bodies (toothless, pearl barley, dreisena).

Characteristic feature of Bivalves - lack of head.

The shell of bivalve mollusks consists of two valves (hence the name of the class).

Representative - common toothless. Her body consists of a torso and legs covered with a mantle. It hangs from the sides in the form of two folds. The cavity between the folds and the body contains the leg and gill plates. The toothless fish, like all bivalves, has no head.

At the posterior end of the body, both folds of the mantle are pressed against each other, forming two siphons: lower (input) and upper (outlet). Through the lower siphon, water enters the mantle cavity and washes the gills, which ensures respiration.

Digestive system

Bivalve mollusks are characterized by a filtration feeding method. They have an inlet siphon, through which water with food particles suspended in it (protozoa, unicellular algae, remains of dead plants) enters the mantle cavity, where this suspension is filtered. Filtered food particles are directed to the mouth opening needle; then goes to esophagus, stomach, intestines and through anal hole enters the outlet siphon.
The toothless has a well developed digestive gland, the ducts of which flow into the stomach.

Bivalves breathe using gills.

Circulatory system

The circulatory system is not closed. It includes the heart and blood vessels.

Reproduction

Toothless is a dioecious animal. Fertilization occurs in the mantle cavity females, where sperm enter through the lower siphon along with water. Larvae develop from fertilized eggs in the gills of the mollusk.

Meaning

Bivalves are water filters, food for animals, used for human food (oysters, scallops, mussels), and producers of mother-of-pearl and natural pearls.

The shell of bivalve mollusks consists of three layers:

• thin outer - horny (organic);
• the thickest medium - porcelain-like (limestone);
• internal - mother-of-pearl.

The best varieties of mother-of-pearl are distinguished by the thick-walled shells of the sea pearl oyster, which lives in warm seas. When certain areas of the mantle are irritated by grains of sand or other objects, pearls form on the surface of the nacreous layer.

Shells and pearls are used to make jewelry, buttons and other products.

Some mollusks, such as the shipworm, so named for its body shape, harm wooden structures in water.

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Class Cephalopods

Theory:

Cephalopods- a small group of highly organized animals, distinguished by the most perfect structure and complex behavior among other mollusks.

Their name - “Cephalopods” - is explained by the fact that the leg of these mollusks has turned into tentacles (usually 8-10 of them), located on the head around the mouth opening.

Cephalopods live in seas and oceans with a high salt content (they are not found in the Black, Azov and Caspian Seas, the water of which is desalinated by the rivers flowing into them).

Most cephalopods are free-swimming molluscs. Only a few live at the bottom.

Modern cephalopods include cuttlefish, squid, and octopuses. Their body sizes range from a few centimeters to 5 m, and the inhabitants of greater depths reach 13 m or more (with elongated tentacles).

External structure

The body of a cephalopod bilaterally symmetrical. It is usually divided by an interception into a body and a large head, and the leg is modified into a funnel located on the ventral side - a muscular conical tube (siphon) and long muscular tentacles with suction cups located around the mouth (octopuses have 8 tentacles, cuttlefish and squid have 10, nautilus have about 40). Swimming is aided by the pulsating ejection of water from the mantle cavity through the siphon - jet motion.

The body of most cephalopods lacks an external shell; there is only an underdeveloped internal shell. But octopuses don’t have shells at all. The disappearance of the shell is associated with the high speed of movement of these animals (the speed of some squids can exceed 50 km/h).

Mollusks are one of the most ancient invertebrate animals. They are distinguished by the presence of a secondary body cavity and rather complex internal organs. Many of them have a calcareous shell, which protects their body quite well from the attacks of numerous enemies.

This is not often remembered, but many species of this type lead a predatory lifestyle. The developed salivary gland helps them in this. By the way, what is the salivary gland in mollusks? This generalizing concept refers to a fairly wide range of specific organs located in the pharynx and oral cavity. They are intended for the secretion of various substances, the characteristics of which can be very different from our understanding of the word “saliva”.

As a rule, mollusks have one or two pairs of such glands, which in some species reach very impressive sizes. In most predatory species, the secretion they secrete contains from 2.18 to 4.25% chemically pure sulfuric acid. It helps both fight off predators and hunt their relatives (sulfuric acid perfectly dissolves their calcareous shells). This is what the salivary gland is in mollusks.

Other natural value

Many species of slugs, as well as the vine snail, cause enormous damage to agriculture around the world. At the same time, it is the mollusks that play vital role in global water purification, since organic matter filtered from it is used to feed them. In many countries, large ones are bred on sea farms, as they are valuable food product, which contains a lot of protein. These representatives and oysters) are even used in dietary nutrition.

IN former USSR 19 representatives of this ancient type were considered rare and endangered. Despite the diversity of mollusks, they should be treated with care, as they are extremely important for the proper functioning of many natural biotopes.

In general, mollusks are often distinguished by their most important practical significance for humans. For example, the pearl mussel is bred en masse in many coastal countries, since this species is a supplier of natural pearls. Some shellfish are of great value for medicine, the chemical and processing industries.

Want to know Interesting Facts about shellfish? IN Antique period and the Middle Ages, inconspicuous cephalopods were sometimes the basis of the well-being of entire states, since the most valuable purple was obtained from them, which was used to dye the royal robes and robes of the nobility!

Shellfish type

In total, it has more than 130,000 species (yes, the variety of mollusks is incredible). Clams by total number Second only to arthropods, they are the second most common living organisms on the planet. Most of them live in water, and only a relatively small number of species choose land as their place of residence.

general characteristics

Almost all animals that are part of this type are distinguished by several specific features. Here is the accepted one today general characteristics shellfish:

• Firstly, three layers. Their organ system is formed from ectoderm, endoderm and mesoderm.
• The symmetry is of a bilateral type, caused by a significant displacement of most of their organs.
• The body is unsegmented, in most cases protected by a relatively strong calcareous shell.
• There is a fold of skin (mantle) that envelops their entire body.
• A well-defined muscular outgrowth (leg) is used for movement.
• The coelomic cavity is very poorly defined.
• There are almost all the same organ systems (in a simplified version, of course) as in higher animals.

Thus, the general characteristics of mollusks indicate that we have before us quite developed, but still primitive animals. It is not surprising that many scientists consider mollusks to be the main ancestors of large quantity living organisms on our planet. For clarity, we present a table that describes in more detail the characteristics of the two most common classes.

Detailed characteristics

The body is still symmetrical, although this is not observed in bivalves. The division of the body into segments was preserved only in very primitive species. The secondary body cavity is represented by a bursa surrounding the heart muscle and genitals. The entire space between the organs is completely filled with parenchyma.

The majority of the body can be divided into the following sections:

• Head.
• Torso.
• A muscular leg through which movement is carried out.

In all bivalve species the head is completely reduced. The leg refers to a massive muscular process that develops from the base of the abdominal wall. At the very base of the body, the skin forms a large fold, a mantle. Between it and the body there is a fairly large cavity in which the following organs are located: gills, as well as the conclusions of the reproductive and excretory systems. It is the mantle that secretes those substances that, when reacting with water, form a durable shell.

The shell can be either completely solid or consist of two valves or several plates. The composition of this shell includes a lot of carbon dioxide (of course, in a bound state - CaCO 3), as well as conchiolin, a special organic substance that is synthesized by the body of the mollusk. However, in many species of mollusks the shell is completely or partially reduced. The slugs have only a microscopic-sized plate left from it.

Characteristics of the digestive system

Gastropods

There is a mouth at the front end of the head. The main organ in it is a powerful muscular tongue, which is covered with a particularly strong chitinous grater (radula). With its help, snails scrape off algae or other organic matter from all accessible surfaces. In predatory species (we'll talk about them below), the tongue has degenerated into a flexible and hard proboscis, which is intended for opening the shells of other mollusks.

In Cones (they will also be discussed separately), individual segments of the radula protrude beyond the oral cavity and form a kind of harpoon. With their help, these representatives of mollusks literally throw their poison at the victim. In some predatory gastropods, the tongue has turned into a special “drill”, with which they literally drill holes in the shell of their prey for injecting poison.

Bivalve

In their case, everything is much simpler. They simply lie motionless on the bottom (or hang, tightly attached to the substrate), filtering hundreds of liters of water with organic matter dissolved in it through their body. The filtered particles go directly into the large stomach.

Respiratory system

Most species breathe through gills. There are “front” and “rear” views. In the former, the gills are located in the front of the body and their apex is directed forward. Accordingly, in the second case the top looks back. Some have lost their gills in the truest sense of the word. These large mollusks breathe directly through their skin.

To do this, they developed a special skin organ of an adaptive type. In land species and secondary aquatic mollusks (their ancestors returned to the water again), part of the mantle is wrapped, forming a kind of lung, the walls of which are densely penetrated with blood vessels. To breathe, such snails rise to the surface of the water and collect air using a special spiracle. The heart, located not far from the simplest “structure,” consists of one atrium and a ventricle.

The main classes included in the type

How is the type of mollusk divided? The classes of mollusks (there are eight in total) are “crowned” by the three most numerous:

• Gastropods (Gastropoda). This includes thousands of species of snails of all sizes, mainly hallmark which is low speed movement and well-developed muscular legs.
• Bivalves (Bivalvia). Sink with two doors. As a rule, all species included in the class are sedentary and sedentary. They can move both with the help of a muscular leg and by means of jet propulsion, throwing out water under pressure.
• Cephalopods (Cephalopoda). Mobile mollusks have shells either completely absent or in their infancy.

What else is included in the phylum molluscs? The classes of mollusks are quite diverse: in addition to all of the above, there are also Spade-footed, Armored and Pit-tailed, Grooved-bellied and Monoplacophora. All of them are living and well.

What fossils does this type of mollusk contain? Classes of mollusks that are already extinct:

• Rostroconchia.
• Tentaculitis.

By the way, the same Monoplacophorans were considered completely extinct until 1952, but at that time the ship “Galatea” with a research expedition on board caught several new organisms that were classified as a new species Neopilina galatheae. As you can see, the name of this species of mollusks was given by the name of the research vessel that discovered them. However, this is not uncommon in scientific practice: species are much more often designated in honor of the researcher who discovered them.

So it is possible that all subsequent years and new research missions will be able to enrich the type of mollusks: classes of mollusks that are now considered extinct may well survive somewhere in the bottomless depths of the world's oceans.

No matter how strange it may sound, one of the most dangerous and incredible predators on our planet are... seemingly harmless gastropods. For example, cone snails (lat. Conidae), the poison of which is so unusual that modern pharmacists use it in the manufacture of certain types of rare medicines. By the way, the name of mollusks of this family is completely justified. Their shape is indeed most similar to a truncated cone.

They can be persistent hunters, being extremely ruthless in dealing with floodplain prey. Of course, the role of the latter is often played by colonial, sedentary species of animals, since it is simply impossible for snails to keep up with other snails. The prey itself can be tens of times larger than the hunter. Want to know more interesting facts about shellfish? Yes please!

About snail hunting methods

Most often, the insidious mollusk uses its most powerful organ, a strong muscular leg. It can attach to prey with the equivalent of 20kg of force! This is quite enough for a predatory snail. For example, a “caught” oyster opens in less than an hour with only ten kilograms of force! In a word, the life of mollusks is much more dangerous than is commonly thought...

Other species of gastropods prefer not to press anything at all, carefully drilling into the shell of their prey using a special proboscis. But this process cannot be called simple and fast, even if one wants to. So, with a shell thickness of only 0.1 mm, drilling can take up to 13 hours! Yes, this method of “hunting” is only suitable for snails...

Dissolution!

To dissolve someone else's shell and its owner, the mollusk uses sulfuric acid (you already know what the salivary gland is in mollusks). This makes destruction much easier and faster. After the hole is made, the predator begins to slowly eat its prey from the “package”, using its proboscis for this. To some extent, this organ can safely be considered an analogue of our hand, since it is directly involved in capturing and holding prey. In addition, this manipulator can often extend so that it exceeds the length of the hunter’s body.

This is how snails can get their prey even from deep crevices and large shells. We remind you once again that it is from the proboscis that a strong poison is injected into the victim’s body, the basis of which is chemically pure sulfuric acid (released from the “harmless” salivary glands). In a word, from now on you know exactly what the salivary gland is in mollusks and why they need it.