General characteristics of the type Mollusks presentation for a biology lesson (7th grade) on the topic. General characteristics of the type

1. What are the main features that characterize mollusks? Draw up and draw a diagram of the structure of a gastropod, and label it in the drawing.

The body of mollusks in most cases consists of a head, torso and muscular legs;

The torso is a skin-muscular bag surrounded by an extensive skin fold - the mantle;

Between the mantle and the body wall, a mantle cavity is formed, in which the respiratory organs, some sensory organs are located, the anus, ducts of the kidneys and gonads open into it;

The digestive system consists of the foregut, midgut and hindgut;

In the pharynx there is usually an organ that grinds food - a grater with horny teeth located on it;

The circulatory system is not closed (except for cephalopods); The movement of blood is ensured by a two-chambered heart;

There are organs of vision, balance, chemical sensitivity, and touch;

The respiratory organs of aquatic forms are gills, and those of terrestrial forms are lungs; represent a specialized area of the skin fold - the mantle.

2. What is the mantle? What is its meaning?

The mantle is a fold of tissue in mollusks surrounding the body. Between the mantle and the body, a mantle cavity is formed, in which some sensory organs are located and into which the anus, ducts of the kidneys and gonads open.

3. What is a sink? What are its functions? Which chemical substances form the bulk of the shell?

A shell is a protective formation covering the body of a mollusk. The shell is usually formed by secretions of the mantle. It can be solid, less often bicuspid or consisting of several plates. The outer layer of the shell is formed by an organic horn-like substance, the inner layer is formed by the thinnest plates of lime. The uneven reflection of light from these plates gives the inner surface of the shell a pearlescent shine. In some mollusks, the underdeveloped shell is buried under the skin or disappears completely (slugs, cephalopods).

4. Describe the body structure of bivalves.

The soft body of mollusks in most cases consists of a head, torso and legs. The mouth and sensory organs are located on the head. The body is a bag, its base is surrounded by an extensive fold of skin - the mantle. On the dorsal side, as a rule, there is a protective shell secreted by the mantle. The abdominal side, strongly thickened due to muscles, forms various shapes of legs: wide - crawling, wedge-shaped, fin-like - for swimming, rounded - suction, etc.

5. Discuss as a class the similarities and differences between different classes of mollusks.

In the process of settling across the planet, mollusks were divided into a number of groups, united into several classes. Among them are Gastropods, Bivalves and the most highly organized - Cephalopods.

6. Make a table " Comparative characteristics annelids and mollusks" (work in small groups).

7. What role do you think mollusks play in nature? Give examples of mollusks that live in your area.

Shellfish are important as a source of mother-of-pearl and pearls. The most prized pearls are the sea pearl mussel, found in the Red Sea, Indian and Pacific Oceans. Many marine bivalves are eaten, such as oysters, mussels, scallops, and squid. Bivalves are powerful natural water purifiers (biofilters). Feeding on organic substances suspended in water and tiny living organisms (plankton), they pass large amounts of water through the mantle cavity, purifying it.

8. Highlight the structural features of the body of mollusks associated with their way of life.

Key Features:

The body lacks segmentation, has bilateral symmetry (bivalves and cephalopods) or asymmetrical (gastropods);

The body of mollusks is enclosed in a shell, which protects the animal and provides support for the attachment of muscles; in gastropods the shell is solid in the form of a cap or spirally curled turret; in bivalves it consists of two valves connected by an elastic ligament; most cephalopods have lost the shell.

9. Make a detailed plan for the paragraph.

General characteristics of the external structure of representatives of the Mollusca type;

Structure of the nervous system;

The structure of the sense organs;

Structure of the circulatory system;

The structure of the respiratory organs;

The structure of the digestive system;

The structure of the excretory organs;

Meaning of shellfish;

Class Gastropods ( general characteristics class);

General characteristics of the class Bivalves;

Economic importance, representatives;

General characteristics of the class Cephalopods;

Structural features of representatives of this class;

Economic importance.

Habitat and external structure. Most mollusks live in the seas, a relatively small number live in brackish and fresh waters, even less on land. Many aquatic mollusks lead a bottom-dwelling lifestyle.

Some mollusks are bilaterally symmetrical animals. However, gastropods developed a twisted shell, and their body became asymmetrical for the second time.

Mollusks are characterized by a hard mineral shell that covers the animal’s body from the dorsal side. The shell consists of crystals of calcium carbonate. On top it is usually covered with a horn-like organic matter, and the inside is lined with a hard, shiny calcareous layer - mother-of-pearl. The shell can be solid, bivalve, or consisting of several plates (in marine mollusks, 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). Slugs and mollusks that swim well have lost their shells.

The body of mollusks consists of a trunk, head and legs (Fig. 70). Almost all mollusks have a head. It contains a mouth opening, tentacles and eyes. The leg is a muscular unpaired outgrowth of the body. It is located on the ventral side and is used for crawling.

Rice. 70. Various mollusks: A - gastropods: B - bivalve; B - cephalopod: 1 - leg; 2 - sink; 3 - tentacles

In bivalves, due to their sedentary lifestyle, the head is absent and the legs are reduced. In some species, the leg has become a swimming organ (for example, in cephalopods).

Internal structure. The body of the mollusk is surrounded by a fold of skin - the mantle. The space between the walls of the body and the mantle is called the mantle cavity. The openings of the excretory organs, genitals and anus open there. It contains the respiratory organs - gills. The secondary body cavity (coelom) is well defined in the embryonic state, and in adult animals it remains in the form of the pericardial sac and the cavity of the gonad. The spaces between organs are filled with connective tissue.

Digestion. The mouth opening leads into the pharynx. In the pharynx of many species there is a grater (radula) - a special device in the form of a ribbon lying on the protrusion of the floor of the oral cavity. There are teeth on this tape. Using a grater, herbivorous mollusks scrape food from plants, while carnivorous mollusks (which have larger grater teeth) grab prey. Some carnivorous mollusks have salivary glands that open into the oral cavity. The secretion (secreted substance) of the salivary glands contains poison.

The pharynx passes into the esophagus, followed by the stomach, into which the liver ducts open. The secretion of the liver dissolves carbohydrates, and food absorption also occurs in the liver. 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 aquatic mollusks, the respiratory organs are paired gills - flat skin outgrowths lying in the mantle cavity. Terrestrial mollusks breathe using the lung. It is a pocket (fold) of the mantle, which is filled with air and communicates with the external environment through the breathing hole.

Circulatory system. The heart of mollusks usually consists of three sections (one ventricle and two atria). The circulatory system is not closed. Some mollusks have manganese or copper in their blood. Their compounds play the same role as iron in the blood of higher animals - they ensure the transfer of oxygen.

The excretory organs are represented by paired kidneys, which at one end communicate with the cavity of the pericardial sac, which surrounds the heart, and at the other open into the mantle cavity. The pericardial sac is the remains of the coelom. Therefore, we can talk about the similarity of the excretory systems of mollusks and annelids.

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 visual organs. The eyes of fast-swimming cephalopods are especially well developed.

Reproduction. Most mollusks are dioecious. However, there are also hermaphrodites in whom cross-fertilization occurs. Fertilization in mollusks can be external (for example, in the oyster and toothless snail) and internal (in the grape snail).

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

Meaning. Representatives of some classes of mollusks play an important role 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 breeding (oysters, scallops, mussels, cockles, squid, Achatina, grape snail). Very beautiful pearls are formed in the shells of sea mollusks, pearl mussels. Aboriginal people used cowrie shells as coins. Geologists can use fossil mollusk shells to determine the age of sedimentary rocks.

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 annelids. Still others think that mollusks originate from ancestors common to annelids. Embryological data indicate the relationship of mollusks with annelids.

A typical mollusk 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.

Mollusks are non-segmented, bilaterally symmetrical soft-bodied animals (in gastropods the body is asymmetrical), having a shell, a mantle cavity, a reduced coelom, and an open circulatory system). Apparently, they descended from common ancestors with annelids, which had a poorly developed secondary body cavity, had ciliated integuments, and did not yet have the body divided into segments.

Exercises based on the material covered

Name the main methods of movement of mollusks.
Name the main similarities and differences between external and internal structure mollusks and annelids.
What traits do fast-swimming mollusks have?
What is the influence of a sedentary lifestyle on the organization of mollusks?
What is the role of mollusks in nature and in human life? Give examples.

General characteristics of mollusks.

1. The body is not segmented.

2. Most have a sink.

3. The body is covered on the outside with a special fold of skin - the mantle.

4. Feeding: a) active (scraping, predation); b) passive (filtration)

5. Breathing: lungs (a special pocket of the mantle) or gills.

6. The circulatory system is not closed, they have a heart. Blood - hemolymph.

7. The nervous system is nodal. In sedentary people, the senses are poorly developed, while in active ones they are well developed.

Main aromorphoses:
1. Merger of segments into body parts (increasing the functional significance of organs).
2. Formation of nerve nodes in parts of the body.
3. The appearance of the heart, increasing the speed of blood circulation.
4. The appearance of digestive glands, more complete breakdown of food.

Comparative characteristics of the main classes of mollusks

Signs	Classes
Signs	Gastropods	Bivalve	Cephalopods
Habitat	Mainly land and fresh water bodies	Fresh waters and seas	Salty warm seas
Body symmetry	Asymmetrical	Bilaterally symmetrical	Bilaterally symmetrical
Body parts	Head, torso, leg	Torso, leg	Head, torso
Organs present on the head	1–2 pairs of tentacles, 1 pair of eyes at the base or at the ends of the upper pair of tentacles	No head	Tentacles formed from part of the leg that moved onto the head and surrounding the mouth; 2 large eyes
Sink	Single in the form of a curl or reduced	Made of two flaps with an elastic ligament on the dorsal side	Remains of a reduced shell under the skin or absent
Leg	Muscular, occupies the entire ventral side of the body	Muscular, wedge-shaped abdominal part of the body	Split into tentacles
Movement	Using your feet	Using the foot or (rarely) in a reactive manner (pushing water out of the mantle cavity)	Using tentacles (arms) and a reactive method (by pushing water out of the mantle cavity through a funnel)
Respiratory system	“Lung” is a cavity formed by the mantle between the bodies and part of the shell; marine species may have gills	Lamellar gills on the sides of the body	Gills
Nervous system	Parapharyngeal ganglia	3 pairs of ganglia	Ganglia forming the common peripharyngeal mass ("brain")
Excretory organs	1 pair of buds	1 pair of buds	1 or 2 pairs of buds
Reproduction and development	Usually dioecious, direct development	Most are dioecious, development with transformation (larva - glochidium)	Dioecious. The gonad is unpaired. Development is direct.

Meaning in nature and human life

In nature:

a) a link in food chains (for example: land mollusks serve as food for toads and moles);
b) bivalves filter water (one oyster filters about 10 liters of water per hour).

Interesting facts

The largest pearl, 24 cm in length and 14 cm in diameter, was found in a coral reef mollusk shell tridacni off the Philippine Islands. This mollusk has a shell length of up to 1.4 m, a weight of about 200 kg, and a body weight of about 30 kg. Unfortunately, pearls, unlike precious stones, are not eternal: 50–60 years after the pearl is removed from the mollusk, it begins to become covered with cracks. The maximum "life" of a pearl as jewelry does not exceed 150 years; this is due to the drying out of the organic layers inside it.

Byssus is produced mussels And pins. These are the threads that attach the shell to the substrate. According to their properties, these silky threads are yellowish or brownish in color, elastic, strong, with an unusual shine, and contain a protein substance close to fibroin in silk. The length of the byssal fibers reaches 30 cm. Beautiful lace and fabrics were made from the byssus. The first indications of the use of byssus threads for spinning and weaving date back to the 2nd and 3rd centuries. ADIn the 18th century V European countries Stockings, gloves, wallets, lace, as well as hats, jackets and dresses were made from “shell silk”. Naturally, products made from such an expensive material were highly valued: in Italy at the end of the 18th century. a pair of shell silk gloves cost 20 gold ducats.

Cephalopods are, without a doubt, the most aggressive and warlike inhabitants of the sea. Although they have plenty of enemies. But cephalopods don't give up without a fight. One of the most amazing protective devices that cephalopods acquired in the process of evolution is this miracle weapon - the ink bomb. Ink is produced by a special outgrowth of the rectum called the ink sac. It consists of two parts: ink is produced in one part, and ink is accumulated in the other. At the moment of danger, the entire contents of the bag are thrown away. But after a few minutes, the mollusk is again ready to repel any attack. But this does not exhaust all the possibilities of ink. In 1956, Dr. D. Hall published in the English magazine Nature interesting observations on the behavior of the squid. The zoologist put the squid in a tub and tried to catch it with his hand. When his fingers were already a few inches from the target, the squid suddenly darkened and, as it seemed to Hol, froze in place. The next moment, Hall grabbed... an ink model that fell apart in his hands. The deceiver was floating at the other end of the tub. What a subtle maneuver! The squid didn’t just leave its image in its place. No, it's a dress-up scene. First, it attracts the enemy's attention with a sharp change in color. Then he immediately replaces himself with another dark spot - the predator automatically fixes his gaze on it - and disappears from the scene, changing his “outfit”. Please note: the squid is now not black, but white.

Go ink Low-footed mollusks also have another amazing property. American scientist McGinity conducted a series of experiments on the Californian octopus and moray eel. And this is what he found: octopus ink, it turns out, paralyzes the olfactory nerves of predatory fish.

Dangerous Is cephalopod ink good for humans?

Let’s ask an underwater hunting expert like James Aldridge to answer this question. He writes: “I behaved so freely with the octopus that I received a stream of ink right in the face. And since I was without a mask, the liquid got into my eyes and blinded me. The world around me, however, did not darken as a result, but became colored. "A wonderful amber color. Everything around me seemed amber in color as long as the film of this ink remained before my eyes. This lasted for about ten minutes or so. This incident did not affect my vision."

However, octopuses and cuttlefish have another amazing adaptation that allows them to avoid meeting the enemy. It turns out that they have an exceptional ability to camouflage, so they can safely be called the “kings of camouflage.”

The ability of cephalopods to glow has long been known. The French naturalist Jean Baptiste Verani loved to come to the seashore when fishermen returned with their catch. One day, near Nice, he saw a crowd of people on the shore. A completely unusual creature was caught in the net. The body is thick - like a sac, like an octopus, but there are ten tentacles, and they are connected by a thin membrane. Verani lowered the bizarre captive into a bucket of sea water; “at that very moment,” he writes, “I was captivated by the amazing spectacle of sparkling spots that appeared on the skin of the animal. It was either the blue ray of sapphire that blinded me, or the opal ray of topaz, or both richly hued colors mixed in a magnificent radiance , surrounded the mollusk at night, and it seemed one of the most wonderful creations of nature." Thus, in 1834, Jean Baptiste Verani discovered the phenomenon of bioluminescence.

), freshwater bodies (toothless snails, pond snails, livebearers), less often - in a humid terrestrial environment (grape snail, slugs). Body sizes of adult mollusks different types vary significantly - from a few millimeters to 20 m. Most of them are sedentary animals, some lead an attached lifestyle (mussels, oysters), and only cephalopods are able to move quickly in a reactive manner.

The main characteristic features of the structure of mollusks are as follows: blowing:

The body lacks segmentation, has bilateral symmetry (bivalves and cephalopods) or asymmetrical (gastropods). The parts of the body are head with eyes located on it and 1-2 pairs of tentacles, torso, where most of the internal organs are located, and leg- the muscular abdominal part of the body used for movement. In bivalves, the head is reduced.
The body of the mollusk is enclosed sink, protecting the animal and providing support for muscle attachment. The outer layer of the shell is horny, the middle (porcelain) and inner (mother-of-pearl) are calcareous. Gastropods have a solid shell in the form of a cap or a spirally curled turret. In bivalves, it consists of two valves connected elastic ligament, “lock” teeth and closing muscles. Most cephalopods have lost their shells.
The body of the mollusk is covered with a fold of skin - mantle, the epithelium of which secretes the substance of the shell. Between the mantle and the body is formed mantle cavity, in which the gills, some sensory organs, anus, and the opening of the excretory organs are located.
Body cavity secondary (in general), however, it is greatly reduced and preserved only in the form of the pericardial cavity and the cavities of the gonads. The remaining space between the internal organs is filled with loose tissue - parenchyma.
The digestive system consists of three sections: the foregut, midgut and hindgut. Most mollusks (except bivalves) have a muscular tongue in the pharynx, covered with a horny plate with numerous denticles - grater With it they actively capture and crush plant and animal food. Ducts open into the pharynx salivary glands, and into the stomach - the duct of a special digestive gland - liver. Bivalves feed passively, filtering food suspension (algae, bacteria, detritus) through the gills, which enters the mantle cavity with water through the inlet siphon.
Circulatory system open and consists of hearts And vessels. The heart has a ventricle and 1-2 (less often 4) atria. In addition to the vessels, blood passes part of the way in the slit-like cavities between the organs.
Respiratory organs in aquatic mollusks - gills, for terrestrial - lung, representing a section of the mantle cavity. The wall of the lung contains a dense network of blood vessels through which gas exchange occurs. The lung opens outward with the respiratory opening - spiracle.
The excretory system is represented by 1-2 kidneys. They are modified metanephridia. The funnel of the kidney opens into the pericardial sac, and the excretory opening into the mantle cavity.
Nervous system scattered-node type: five pairs of large ganglia are located in vital organs (head, leg, mantle, respiratory organs and sac) and are connected by nerve trunks. Of the sense organs, the most developed are the organs of chemical sense, touch, balance, and in mobile predators - vision.
Reproduction occurs sexually. Most mollusks are dioecious animals, less often - hermaphrodites (pulmonary gastropods). In dioecious mollusks, fertilization is external, while in hermaphroditic mollusks, fertilization is internal, cross-fertilization. In freshwater and terrestrial pulmonary mollusks, as well as cephalopods, development is direct, in marine bivalves and gastropods - with incomplete metamorphosis, i.e., with a planktonic larval stage, which contributes to their settlement.

Molluscs, or soft-bodied mollusks, form a clearly limited type of animals, originating from annelids. Mollusks include mainly aquatic, less often terrestrial animals, characterized by the following characteristics.

The phylum Mollusca consists of large quantity very diverse forms - more than 100,000 species. These are soft-bodied, unsegmented animals with a true body cavity (coelom). They can range in size from a few millimeters to more than 20 m (as in the case of the giant squid Architheutis, the largest of the invertebrates). Among mollusks, several of the most interesting and valuable objects for neurobiological research have been found. As shown in Fig. 4.3 they evolved over 700 or 800 million years. Mollusks are divided into 7 classes.

1. Mollusks are bilaterally symmetrical animals, however, in some mollusks, due to a peculiar displacement of organs, the body becomes asymmetrical.

2. The body of mollusks is unsegmented; only a number of lower representatives show some signs of metamerism.

3. Mollusks are secondary cavity animals with a non-metameric residual coelom, represented in most forms by the pericardial sac (pericardium) and the gonad cavity. All spaces between organs are filled with connective tissue.

4. The body of mollusks, as a rule, consists of three sections - head, torso and legs. Very often the body grows onto the dorsal side in the form of an internal sac. The leg is a muscular unpaired outgrowth of the abdominal wall of the body, used for movement.

5. The base of the body is surrounded by a large fold of skin - the mantle. Between the mantle and the body there is a mantle cavity in which the gills, some sensory organs lie, and the openings of the hindgut, kidneys and reproductive apparatus open. All these formations, together with the kidneys and heart (located in close proximity to the mantle cavity) are called the mantle organ complex.

6. On the dorsal side of the body, as a rule, there is a protective shell secreted by the mantle, usually solid, less often bicuspid, or consisting of several plates.

7. Most mollusks are characterized by the presence in the throat of a special apparatus for grinding food - a grater (radula).

8. The circulatory system is characterized by the presence of a heart, consisting of a ventricle and atria; it is not closed, that is, part of its path the blood passes through a system of lacunae and sinuses that are not formed into vessels.

The respiratory organs are usually represented by primary gills - ctenidia. The latter, however, disappear in a number of forms or are replaced by respiratory organs of a different origin.

For excretion, the kidneys are used - modified coelomoducts, communicating at their internal ends with the pericardial sac.

9. The nervous system in primitive forms consists of a peripharyngeal ring and four longitudinal trunks; in higher forms, several pairs of ganglia are formed on the trunks as a result of the concentration of nerve cells. This type of nervous system is called scattered - nodal.

10. The development of mollusks is very similar to that of polychaete worms; in the majority, fragmentation is of a spiral type, deterministic. In the lower representatives, a trochophore emerges from the egg, in most of the rest - a modified trochophore larva - a swallowtail (veliger).