EntranceThe diversity of mollusks and their significance in nature. The importance of mollusks in nature and human life
Mollusks are grouped into several classes: Gastropods (Gastropoda) , bivalve (Bivalvio) , Cephalopods (Cephalopoda).
The class Gastropods is divided into subclasses: Protozoabri (gills are located in front of the heart), Postopogabri (gills are located behind the heart) and pulmonate molluscs.
Interesting representatives of the anterior mollusks are rapana, cones, murex, tons, newts, etc. In the Black Sea, among the thickets of red phyllophora algae, rapana is found, which is a terrible predator for oysters and mussels. In the shallow waters of tropical seas, among corals and algae, live mollusks of the genus Cone. Their salivary glands produce poison, which is equivalent in effect to curare. Salivary glands of mollusks of the genus Ton produce a secretion containing sulfuric and aspartic acids. Sulfuric acid is used by mollusks to destroy the shells of their victims, while aspartic acid puts the victim into a state of stupor. Molluscs from the genus murex They are called purple because they have a gland that produces the coloring substance purple. The most turtle among gastropods is observed in
newts, or Charon (Charonia tritonis). This large predatory mollusk is the main natural enemy of the crown of thorns starfish. It devastates coral reefs due to mass reproduction.
Among the metastasiopod gastropods one can distinguish sea hares and sea angels. A characteristic feature of sea hares is their ability to secrete ink, which is a means of protection against predators. This secretion contains bromine and choline, which the mollusk receives from the red algae that it feeds on. The ink tends to reduce the mobility of predators. Sea angels is an example of a gastropod that has lost its shell and adapted to a predatory lifestyle in the water column. They have wing-shaped outgrowths of the legs, a developed fishing apparatus with oral appendages covered with sticky mucus, for hunting other pteropods.
A typical representative of pulmonary gastropods is regular stock carrier, or big (Lymnoea stogno/is), which lives in ponds, small lakes and rivers. This is one of the voracious inhabitants of fresh water bodies. It eats plants, animals and their remains. Although the stavkovik lives in water, it breathes oxygen from atmospheric air, which enters the lung. Common mollusks that live next to pond snails are coils, among which it stands out for its size horn coil. The herbivorous species of this group are grape snail, which has long been eaten in Western European countries, a huge African snail Achatina, which is a pest of citrus and bananas, a small freshwater snail physical, which often lives in aquariums.
Bivalve - This is a group of mollusks that have a symmetrical body with a well-developed trunk and legs, but without a head. This class includes more than 20,000 species that live only in water. Bivalves inhabit seas (mussels, oysters, scallops) and fresh water bodies (gillfishes, pearl mussels). Bivalves lead a benthic lifestyle and are found at different depths. Most of them are slowly crawling forms, some are immovably attached to the substrate. The turtle of these mollusks is bivalve, completely covering the body from the sides. The left and right shell valves are movably connected on the dorsal side by an elastic ligament formed by organic matter. The turtle closes due to the contraction of two, as in the gills, or another, as in the mids, closing muscles, which are attached to the inner sides of the opposite valves. The laterally flattened body consists of a torso surrounded by a mantle and a muscular wedge-shaped leg. A characteristic feature of bivalves is the absence of a head. The reduction of the chairman is associated with the absence of the pharynx, grater and salivary glands in the digestive system. A mouth surrounded by two pairs of oral lobes, located at the anterior end of the body. Nutrition occurs by filtration. The mantle, on the sides, completely covers the body of the mollusk, at its rear end it forms hollow tubular outgrowths - siphons. Through the lower (input) siphon, water enters the mantle cavity, and through the upper (outlet) siphon it leaves it. With water into the empty mantle
Internal structure of the edentulum: A - adductor muscle; B - anal opening; IN - outlet siphon; G - inlet siphon; D - gills; E - intestine; Eat - mantle; AND - gonad; From - nogo; AND - oral lobes; I - turtle; K - stomach; L - liver; M - kidneys N - pericardium; O - three-chambered heart
nutrients and oxygen are supplied to the nina. Most bivalves move using a wedge-shaped leg. The absence of a chairman, the simplification of the oral apparatus and the sedentary lifestyle of bivalves determined the poor development of the sense organs. Bivalves are mostly dioecious, but hermaphrodites are also known (for example, oysters). In most bivalves, development occurs with metamorphosis. A planktonic larva develops from a fertilized egg, which contributes to the spread of the species. In some freshwater bivalves (gillfishes, pearl mussels), a larva (glochidia) is formed, the development of which occurs in the skin of fish. A small mollusk forms from the larva and falls to the bottom through breaks in the skin.
A typical representative of bivalve mollusks is toothless, or gillyweeds. This mollusk lives at the bottom of reservoirs, half immersed in muddy soil. Its turtle reaches 10 cm in length. The front end of the animal is rounded, and the rear end is somewhat pointed. With the help of its leg, the toothless can slowly crawl along the bottom (from 20 to 30 cm per hour). If Toothless is disturbed, it quickly retracts its leg and, with the help of two muscles, closes the shell. The gillfish turtle, like the pond turtle, consists of limestone.
Edible mussel(Mytilis edulis) is a type of bivalve mollusk that has an elongated wedge-shaped shell and is capable of forming very strong bead threads, with the help of which they are attached to the substrate. Young mollusks can move well, but adults change their place of residence only under very unfavorable conditions. Mussels are wonderful filter feeders: in one hour, an adult can filter about three liters of water. Mussel meat is edible, it contains biologically active substances and is used for dietary nutrition.
Edible oyster(Ostrea edulis) is a species of bivalve molluscs that are found mainly in tropical seas. In temperate seas, they are found only where the water temperature in summer reaches 16 ° C. Unlike mussels, oysters grow with shells on stones and on the shells of other mollusks. The oyster turtle has asymmetrical valves with an uneven surface. The leg and bysus of the gland are reduced due to a sedentary lifestyle. In Ukraine, they are found in the Black Sea: in sheltered bays, on coastal rocks, and also in shallow waters. Oysters are very sensitive to the purity of the water and the sufficient amount of oxygen in it. According to their feeding method, they are water filterers - each individual can filter from 1 to 3 liters of water per hour.
Scallops is a group of mollusks that unites representatives of two families.
In the Black Sea there is only one type of scallop - Black Sea comb. These mollusks have a wide fan-shaped shell, painted in different colors. Unlike other sea mollusks, scallops lead a relatively active lifestyle. They move in short leaps. In this case, the shell valves open, and then quickly close and water is pushed out of the cavity of the mollusk with a strong stream, facilitating its movement. The scallop feeds by filtering the water.
Dracena, or trikutnitsa(Dreissena polymorpha) is a common species of freshwater mollusk. The body is small in size, up to 3.5-4 cm long, with a very characteristic triangular shell outline. Adult dracenas lead an attached lifestyle. They secrete a substance that turns into strong threads in the water, the so-called byssus, with which dreissena are attached to underwater objects. Dracena settlements have developed especially strongly in large reservoirs of the Dnieper, where they become overgrown with the remains of flooded trees and bushes, as well as hydraulic structures and pipelines, disrupting their work.
The largest of the bivalve mollusks is giant tridacna(Tridacna gigas), which can reach 1.5 m in length and weigh up to 300 kg. The real kingdom of the tradacna is the Great Barrier Reef off the coast of Eastern Australia.
Shipworms are called mollusks of the genus Teredo. These are small creatures up to 10 cm long, which with their small pointed turtle can make passages in wooden structures, making them unusable.
Cephalopods - a group of mollusks that have a symmetrical body with a well-developed head, body and tentacles. This is the most highly organized group of mollusks, which unites about 650 modern species. Cephalopods are exclusively marine organisms; they are more common in tropical and subtropical waters with high salinity (which is why they are not found in either the Black or Azov Seas). Cephalopods are carnivores that feed on crabs, fish and other animals. Squids and cuttlefish actively pursue their prey, and octopuses lie in wait for it. They can quickly change body color. This is explained by the presence in their skin of cells with various pigments, capable of stretching or shrinking under the influence of impulses from the central nervous system. The body of cephalopods consists of a head and a torso, covered with a mantle. The large head is well separated from the body, has eyes, tentacles surrounding the mouth opening, and a funnel. Octopuses have 8 identical ones, and squids and cuttlefish have 8 short and a pair of long (catching) tentacles. The tentacles usually have suction cups to hold prey. The turtle is absent in most modern cephalopod species or lies under the skin, like a cuttlefish. The mantle on the ventral side of the body forms a mantle cavity, which opens outwards with slit-like openings. The digestive system of cephalopods has hard horny jaws, a grater, and two pairs of salivary glands. The ink gland duct flows into the hindgut of many cephalopods, the secretion of which has a protective value. The circulatory system of cephalopods is almost closed. The high speed of blood movement in them is ensured by the work of a well-developed heart, consisting of a ventricle and two atria. The nervous system and the sensory organs associated with it have reached their highest development among mollusks. The nerve ganglia form a large napharyngeal cluster - the brain, which is protected by a cartilaginous capsule. The eyes are similar in structure to the eyes of vertebrates, and in terms of visual acuity they are not inferior to human eyes. Cephalopods are dioecious animals. They are characterized by direct development. They usually reproduce once in a lifetime. Some species (argonauts, octopuses) show care for their offspring.
Nautiluses, or boats - a series of cephalopods, representatives of which have a spirally twisted shell with a diameter of up to 30 cm, which is divided into 35-38 separate chambers. The mollusk itself lives in the front chamber itself, while others are filled with gas and act as a hydrostatic apparatus. The mouth is surrounded by numerous (about 90) tentacles. These are the most primitive of modern cephalopods. Nautiluses feed on small crabs or fish. Distributed in the Indian Ocean and western Pacific Ocean. The most famous of the species is Nautilus pompilius.
Cuttlefish- a series of cephalopods that have an internal limestone shell (sepion) in the form of a wide plate that occupies almost the entire dorsal side of the body. It is very durable, which allows the cuttlefish to withstand high pressure. Cuttlefish belong to benthic forms. Unlike squids, their body is flattened from top to bottom. They live in the coastal waters of tropical and subtropical seas. character
Another feature of cuttlefish is their retractile tentacles, which are located in pockets on the head at rest and when moving. But if necessary, they can be instantly thrown away. The most famous animals of this series are common cuttlefish(lives in the Mediterranean), broad-armed cuttlefish(this is the largest of the cuttlefish that lives in the Pacific Ocean) and pharaoh cuttlefish(there are numerous species of cuttlefish in the Indian Ocean).
Squid - a series of cephalopods that have 10 tentacles: 4 pairs of arms and a pair of tentacles with chitinous rings. The turtle is vestigial in the form of an internal chitinous plate. This group contains the largest and most mobile cephalopods with developed fins (for example, giant squids of the genus Architeuthis can reach 20 m). Squid have a streamlined torpedo-shaped body, which allows them to move at high speed with their “tail” forward, the main method of movement is reactive. A cartilaginous “arrow” runs along the squid’s body, which supports it. The coloration is varied; some deep-sea species of squid have a transparent body. Squids are consumed as food, so they are one of the objects of industrial fishing. The most famous animals from this series are common squid, Antarctic squid(up to 3.5 m long), winged squid(capable of flight over water).
Octopuses- a series of cephalopods that have 8 tentacles. These tentacles do not have chitinous rings, and therefore, unlike squids, claws and hooks never form on them. The body of octopuses is bag-shaped, without swimmers. The turtle is residual in the form of a cartilaginous inner plate. There are about 200 species belonging to the Octopus series. Most octopuses live near the bottom, hiding during the day in caves, cracks, under stones, and going out to hunt at night. They feed on crabs, lobsters, fish and shellfish. Octopus saliva contains poison that paralyzes and partially dissolves the hard shells of crayfish. This poison is also dangerous for humans (especially in the black-tailed octopus, which is called the “blue death”). Octopuses are characterized by caring for their offspring. The most famous of the mollusks of this series is common octopus, sand octopus, giant octopus, Arctic octopus, Argonaut octopus(lives in a shell, like a nautilus, which is why it is called the “paper boat”).
The body is clearly divided into a head with eyes, tentacles and mouth, a leg and a torso. The turtle is whole, spirally twisted, 4-7 cm long.
Living conditions: fresh water bodies, coastal areas.
Movement - on the abdominal side due to contraction of the leg muscles.
Diet - feeds on plants, small animals and animal corpses, from which it scrapes layers of tissue using the radula. The intestine bends in a loop and ends with the anus in the front of the mantle.
Transport of substances is carried out by an unlocked circulatory system. Colorless blood flows through the vessels and between parenchyma cells. Blood movement is ensured by the contraction of a two-chambered heart (20-30 beats per minute).
The secretion of substances is one kidney, the ducts of which open into the mantle cavity.
Response to stimuli - the nervous system has a well-defined main ganglion. There are eyes, an organ of balance (in the leg), organs of touch and organs of chemical sense, with the help of which the quality of water is recognized. In case of danger, it quickly hides in the shell.
Reproduction is hermaphrodite. Internal cross fertilization. The eggs are covered with mucus and are laid on the surface of underwater plants. The larval stage continues in the egg; the young mollusk emerges in a fully formed state.
Class Bivalves (toothless).
The body has bilateral symmetry, distributed over the torso and leg. The shell consists of two valves connected to each other by an elastic ligament and closing muscles; thanks to their contraction, the valves quickly close. In the dorsal part there are inlet and outlet siphons. Through the first, water enters the mantle cavity, and through the second, it is discharged out.
Conditions of existence - lives at the bottom of fresh water bodies, plunging into sand and silt.
Movement - with the help of its legs, it goes deep into sand or silt and moves at a speed of 20-30 cm / hour.
Diet - feeds on small organisms and their remains enter the mantle cavity along with water through the inlet siphon. In the mantle cavity there is a mouth with two blades, through which water and food particles enter the intestines. The intestine forms several loops and ends with the anus in the mantle cavity.
Respiration - breathes oxygen dissolved in water, which it absorbs through gills located in the mantle cavity.
Transport of substances is an open circulatory system with a three-chambered heart.
Excretion of substances – two kidneys.
Response to stimuli - the nervous system consists of three pairs of nerve ganglia located near the mouth, the posterior adductor muscle and in the leg. This placement of the nerve ganglia ensures instant closure of the edentulous valves in case of danger. Along the edges of the mantle there are tactile receptors and chemoreceptors, and at the leg there are balance organs.
Class Cephalopods.
The body is divided into a head, torso and tentacles (branched legs). The body is covered with a mantle, under which, on the dorsal side, there are remains of a shell (only the nautilus has an external shell). Tentacles surround the mouth. Body sizes can reach 2.5 m (giant squid).
Living conditions are exclusively marine animals. They swim with the help of tentacles and in a reactive way - they draw water into the mantle cavity and sharply push it out through the funnel. Some squids can reach speeds of up to 40 km/h.
Food: predators. They catch prey with tentacles, kill it with a chitinous beak and eat it.
Breathing is the same as in bivalves.
Transport of substances – the circulatory system has well-developed capillaries and is practically closed.
Excretion of substances - kidneys.
Reaction to stimuli - they are distinguished by complex forms of behavior, capable of learning and easy formation of conditioned reflexes. The nerve ganglia merge into the brain, surrounded by a cartilaginous membrane. They have large, complexly constructed eyes. They have a delicate sense of smell. A protective form of behavior in some is the release of an ink cloud from a special cavity when an enemy approaches.
Reproduction: dioecious animals. Fertilization is internal. Direct development - the larva has all the organs of an adult, but sometimes differs in body shape. Characteristic concern for one's offspring.
Shellless. Southern Epimenia
The phylum of mollusks is divided into 7 classes: unshelled, monoplacophoran, armored, spadepod, bivalves, gastropod and cephalopod.
Shellless (Aplacophora) molluscs have a worm-like body up to 30 cm long, entirely covered by a mantle, and no shell. On the ventral side they have a groove with a ridge - the vestige of a leg. Nephridia are absent. This group of mollusks are hermaphrodites.
One of the two subclasses - grooved-bellied mollusks - live in the seas at a depth of 15 m to 4 km. They burrow into the mud or live on corals. 250-300 species.
Monoplacophora are marine, predominantly fossil forms. The head and leg can be pulled into the shell by muscles. They breathe with 5-6 pairs of feathery gills. The heart consists of 2 ventricles and 4 atria. The nervous system includes four longitudinal nerve trunks connected by a peripharyngeal ring.
The heyday of monoplacophorans was from the Cambrian to the Devonian. To date, 1 genus with 8 species has been preserved.
The class of armored mollusks (Polyplacophora) includes about 1000 species of marine bottom animals, found in all seas, mainly in shallow waters. Shellfish live on rocks and rocks and feed on algae and detritus. Some of them are consumed by humans as food.
The oblong body, 0.5-30 cm long, is divided into a head, torso and leg, with which armored mollusks stick to the substrate. The dorsal side of the body is covered with a shell consisting of eight scutes. The respiratory organs are gills, the heart consists of two atria and one ventricle. The sense organs include eyes, located on the dorsal surface of the body, and organs of touch. Most shell mollusks are dioecious with external fertilization; develop with metamorphosis.
The body of spadefoot (Scaphopoda) molluscs is enclosed in a tusk-like shell. Body length is 0.4-25 cm. There are holes at the ends of the shell; through the front of them, spadefoots can extend their head and leg outward. Above the base of the head there are hunting tentacles that serve for touching and capturing food (mainly foraminifera). These mollusks are dioecious; external fertilization. A floating larva emerges from the egg.
About 600 species lead a burrowing lifestyle in the seas at various depths (up to 6 km).
The shell of bivalve mollusks consists of two valves that cover the body of the mollusk from the sides. From the back, the valves are connected to each other by an elastic bridge - a ligament, and from the inside - by muscles. The thickened dorsal edge of the valves bears projections that form a lock. The shell has dimensions from several millimeters to tens of centimeters. The giant tridacna grows up to 1.5 m in length, and the weight of this animal can exceed 200 kg. Tridacna can live up to a hundred years.
Bivalve mollusks have no head - this is the result of adaptation to a sedentary lifestyle. For the same reason, the sense organs are poorly developed: there are organs of touch, balance (statocysts), and chemoreceptors (osphradia on the gills). Some have eyes. On the ventral side of the body there is a leg that serves for attachment to the substrate. Respiratory organs - double-pinnate gills (in primitive forms) or gill plates. The heart consists of a ventricle and two atria.
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The class has been known since the Cambrian. About 150 families and 20,000 species. Bivalve molluscs, found in marine and fresh waters, feed on plankton and detritus, filtering water through siphons at the back of the shell. Some drill into hard rock and wood (using the sharp teeth of a shell or dissolving the rock with the acid released). The shipworm damages the bottoms of ships and piers by boring long passages into them. Some bivalves (oysters, mussels, scallops) are eaten.
The shells of gastropods (Gastropoda) mollusks are twisted into a spiral and are distinguished by a wide variety of shapes. In some mollusks, the shell is immersed inside the body or is absent altogether. On the head there are a pair of tentacles with eyes. During evolution, gastropods have lost bilateral symmetry. In many species, symmetrical organs located on the right side of the body were reduced. Some species have a kind of lung - a cavity filled with air or water with oxygen dissolved in it. There are both hermaphrodites and dioecious forms.
Various species of the class live on land (from alpine highlands and tundra to tropical forests and deserts) and in water. Land snails, which live for several years, endure the winter in hibernating burrows clogged with mucus. Aquatic forms crawl along the bottom; some are part of the plankton, moving with the help of a modified fin or keel leg. A typical freshwater representative is the pond snail. The shells of the porcelain cowrie snail were used in many countries as coins, and red and violet dyes - purple - were extracted from murex. Slugs are agricultural pests. The grape snail is consumed by humans as food. About 40,000 (according to some sources, more than one hundred thousand) species are divided into three subclasses: prosobranchial, opisthobranchial and pulmonate. Extinct gastropods have been known since the Cambrian or even Proterozoic; 15,000 species.
The class Cephalopoda is the most highly organized group of mollusks. The head is clearly separated. Part of the leg has evolved into 8 or 10 tentacles ("arms") surrounding the mouth. At the end of the tentacles, with which the animal grabs prey, there are suction cups, often equipped with horny hooks. The mouth contains powerful horny jaws, reminiscent of a parrot's beak. With its help, cephalopods tear food apart, and the teeth of the radula grind it into pulp. The fact is that the brain of these mollusks surrounds the esophagus on all sides, preventing them from swallowing large pieces of food.
Remains of the shell are sometimes preserved under the skin in the form of a horny plate; the external shell was found mainly in extinct forms. The only modern cephalopods that still retain an external spiral shell are nautiluses. The circulatory system is well developed; blood has a blue color due to hemocyanin, which is part of red blood cells. Cephalopods breathe with gills; some are capable of staying on land for a long time (several hours or even days) thanks to the water stored in the mantle cavity.
At the entrance to the mantle cavity there is a funnel (siphon), which is the second part of the modified leg. Thanks to the reactive force arising from the water thrown back from it, the animal moves forward with the rear end of its body. Muscle contractions occur with a very high frequency, which ensures uniform movement. This is achieved, in particular, by the high conductivity of the nerves - in some squids their thickness reaches 18 mm. The squid has a recorded speed of 55 km/h. Cephalopods can also swim, helping themselves with their tentacles. Some squids, pushing water out of a siphon at the surface of the sea, can rise several meters into the air.
The organs of vision are perfect. Eyes, similar to humans, have a lens and a retina; in giant squids their size exceeds 40 cm. There are also miniature thermolocators on their fins. Sensitive organs of smell (or taste) are concentrated on the inner surface of the tentacles and on the suckers. The developed organs correspond to a large brain.
For passive protection from enemies, autotomy is used (cephalopods “throw away” the tentacles by which the enemy grabbed them) and ink curtains, possibly poisonous, are sprayed to the side. In addition, special cells scattered throughout the skin - chromatophores and iridiocysts - allow you to change body color, “adjusting” to the environment. Some cephalopods are capable of luminescence.
Cephalopods can grow to gigantic sizes - 18 m or more (their weight can reach several tons). There are numerous stories about giant octopuses (krakens) supposedly dragging sea vessels to the bottom.
All cephalopods are dioecious. Male octopuses transfer sperm into the mantle cavity of the female with a special tentacle - the hectocotylus. Often it breaks away from the body and swims on its own in search of a female. The female usually incubates the eggs, sometimes building nests.
Cephalopods live in the seas (up to a depth of 5 km), preferring warm bodies of water. Some forms live among coastal rocks, others - at great depths. Some swim in the water column, others crawl along the bottom. Almost all are predators, feeding on fish, crustaceans, and other mollusks; prey is caught with tentacles, killing it with the secretion of poisonous glands. Many cephalopods (squid, cuttlefish, octopuses) are consumed by humans. The class is divided into two subclasses: quadribranchs (extinct ammonites and the only extant genus of nautiluses) and bibranchs (cuttlefish, squids, octopuses and extinct belemnites). About 600 modern species.
>>Diversity, meaning and general features of mollusks
§ 20. Diversity, meaning and general features of mollusks
Topic: Diversity of mollusks, their role in nature
System of concepts:Molluscs, Gastropods, Bivalves, Cephalopods,radial symmetry, pearls, link in the food chain, intermediate host, filter feeders.
Educational tasks:
Educational:expand students' knowledge about the diversity of mollusks,reveal the significance of mollusks in nature and human life.
Developmental: development of cognitive interest and curiosity, development of skills and abilities to work with additional literature, development of the ability to highlight the main thing, structure, systematize the studied material, draw conclusions, development of thinking, attention, verbal intelligence.
Educational: the formation of a scientific and materialistic worldview, the implementation of moral, aesthetic, labor and environmental education.
Lesson type: learning new material
Lesson type: lesson presentation
Teaching methods:verbal: explanation, conversation, story, student performance; visual: viewing a presentation, demonstrating natural inanimate objects and visual aids.
Means of education:ICT tools: computer, multimedia installation, presentation in PowerPoint; didactic handouts: cards with text for group work;natural: collections of mollusks; visual: pictures and photographs depicting mollusks, drawings from the textbook (V.B. Zakharov, N.I. Sonin “Biology. Diversity of living organisms. Grade 7”).
During the classes:
I. Class organization.Hello, dear guys. (Children's answers) I am glad to welcome you. Let's check the general readiness for the lesson: the availability of textbooks and supplies. Who is on class duty? Please name the missing students. (Children's answers)
II. Updating of basic concepts, introduction to the topic
1. What types of animals have we met this year? (Children's answers: -Type: coelenterates, flatworms, roundworms, annelids, mollusks.)
2. What types of body symmetry do animals have? (Children's answers: Radiation symmetry (hydra); bilateral symmetry (flatworms, white planaria))
3. Which of these types are the most highly organized? (Children's answers: shellfish)
Over the past millions of years, mollusks have populated the entire Earth. In terms of the number of species, they occupy second place after insects. There are about 130 thousand species of living mollusks and about 50 thousand extinct species. There are a lot of shellfish. And a person in his life has information only about a certain amount of them.
Why does a person need to have knowledge about mollusks? (Children's answers: to use them in their practical activities, to protect them, etc.)
Slide 1 So, the topic of the lesson:The diversity of mollusks and their role in nature.
Today in class we will:
- Let's get acquainted with the diversity of mollusks in nature;
- Let's consider the role of mollusks in human economic activity;
- We will prove the need to protect shellfish;
- Let's learn to generalize, compare, and draw conclusions.
III. Learning new material.
We will begin our study of a new topic with a short excerpt from M.E. Saltykov-Shchedrin’s fairy tale “The Idealist Crucian.”
“The crucian carp lies buried in the mud, and selects microscopic shells from there for the sake of its food and reasons: Yes, it (the shell) is designed in such a way that it is impossible to swallow it. Draw up the water with your snout, and your crop is apparently teeming with shells.” Tell me, what animals in everyday life do we call shells? (Children's answer: mollusks.)
What do we already know about mollusks?
(Children's answers: origin of mollusks; external and internal structure of mollusks; reproduction of mollusks; features of life activity.)
When the paths of man and mollusk first crossed is now almost impossible to establish. However, excavations of sites and burials of ancient people indicate that this was a very long time ago. Thus, in North America, in the state of Minnesota, during the construction of a railway, the skeleton of an Ice Age girl was found, on whose neck hung a shell from the distant southern seas. In 1876, in France, also during the construction of the railway, an ancient burial place was found. Along with the people were weapons, tools, household items and...a necklace made of sea shells.
It can be assumed that mollusks and their shells played an important role in the fate of humanity. Slide 2 In general, there are several classes in the Phylum Mollusca. Which? (Children's answers: Gastropods, Bivalves, Cephalopods). Let's get acquainted with some of them and determine their meaning.
Now you should make a table in your notebook “The value of shellfish”, consisting of two columns. (Table on the board. Children make a table in a notebook.)
You need to divide into 4 groups. Each group receives a small text ( see Appendix 1) . Get to know him within 5 minutes. Next, the text is read to the class and answers to the questions are given:
What kind of mollusks are we talking about?
What is their economic importance? (Guys work in groups)
I think everyone is ready to perform. I ask a representative from the first group to come forward.
Slide 3 First group text:
The secret of the strange actions was revealed very simply: it was the first stage in preparing the festive table - after all, it is impossible to chew unbeaten octopus meat. And people spare no effort to get a tasty morsel! Octopus is a delicious dish!
Indeed, there are octopus dishes; their recipe came to us from Ancient Troy.
Stuff the octopus head with spices and finely chopped tentacles, and then bake in the oven like a big pie. It’s very tasty, in our menu it’s called Trojan-style octopus.
And in ancient Sparta black soup was famous! A preparation that required special care! They took the cuttlefish, gutted it, but did not touch the ink sac, so they boiled it with it. The ink gave the stew not only a black color, but also a unique flavor that was highly valued.
Slide 4 -What other shellfish are used for cooking? (Children's answers: mussels, oysters, squid, grape snails.)
Yes, indeed, they contain a lot of vitamins A, B, C, D. Many believe that oysters have a special taste due to the presence of iodine in their body, which is also very useful, especially for people with thyroid disease. Don't forget to fill out the table.
Now I ask the second group to speak.
Text of the second group:
Slide 5
Guys, here's an additional question for you: How do you think cypre shells are used now? (Children's answer: as collectible exhibits.)
Yes, cypres have very valuable shells. Thus, a specimen of the Cyprea fultoni species was sold in New York to a collector from Italy for 24 thousand dollars.
I ask the representative of the third group to come out. Don't forget to fill out the table.
Text of the third group:
Slide 6
Slide 7 Guys, additional question: 1. What kind of jewelry do you think can be made from pearls? In your opinion, are only pearl oysters producing pearls?
(Children's answers: no, there are other bivalves, only their pearls are less valuable)
The last group left to perform.
Text of the fourth group:
Slide 8
Guys, an additional question: Those of you who were at sea, did you bring a rapana shell as a souvenir? (Children's answers: yes or no)
And now you are invited to look at a unique collection of shells collected from all over the world. They can also be used as souvenirs. (Children look at collections of shellfish)
Slide 9 The largest, the queen of all shells, is the tridacna, weighing up to 500 kg, with a diameter of 1.5 meters.
And now you are invited to go to a hypermarket, where there are many products made from these animals.
Grocery department:Here you will be offered a variety of shellfish, frozen, canned, and dried.
Jewelry department:Here you will see earrings, pendants, beads and other jewelry made from pearls
Maintenance department:Here you can buy paint and slate made from shellfish.
Scallop shells are used as tiles to cover house roofs. Write it down in the table. Such roofs shimmer in different colors of the rainbow, withstand different weather changes, are very durable and do not require repairs.
There is a purple dye made from a sea snail called murex. Write it down in the table. It does not fade for hundreds of years. This dye was used to dye the fabrics of Roman emperors, and was used to make blush and ink.
Are there any shellfish that are harmful to humans? (Children's answers: there is, for example, a grape snail, which causes harm to fruit-growing farms). Right. For example, a shipworm damages the wooden floors of ships. There are shellfish that are dangerous to humans. The Cone family contains mollusks with very beautiful cone-shaped shells. But these mollusks are poisonous. Their poison has a paralytic effect. There is an opinion that cones are more dangerous than sharks. So, in the Pacific Ocean, on average, one person per year dies from sharks, and two or three from cones.
And now I will return to our question at the beginning of the lesson:
Why does a person need to have knowledge about mollusks?
So, your answer options. (Children's answers to the question:
1.To understand their diversity
2.Understand their role in nature.
3. Know their application in human life.
4.Learn to appreciate shellfish.
Optimal option: 1+3+4+2
We will confirm your answers with entries in the table. Let's check that it's filled out correctly using the slide
Slide 10 Table 1
Name of the mollusk | Economic importance |
Octopuses Oysters Cyprus Pearl mussels Murex Cones Grape snail Scallop Shipworm (horned worm) | Food product Food product Cowrie money Natural pearls Paint purple Dangerous for humans Food product harmful to fruit growing farms Sinks for covering roofs Damages wooden parts of underwater structures |
IV. Consolidation of the studied material.
Slide 12 And now I want to invite you to correlate mollusks with their economic importance using a slide. Work in your notebooks backwards. table 2
Answers: 1 –A, B, D, Z
2 – B, D
3 – E
4 – I
5 – F
6 – B
(The guys work individually in notebooks on the reverse side, then do a mutual check using Slide 13 give a rating10 points – “5”, 9.8 points – “4”, 7-5 points – “3”. Then they talk through the mistakes made together with the teacher.)
Let's try to summarize the lesson and give grades. The assessment consists of 2 points: performance in groups to fill out the table and completion of the control task. (Grading)
So, our lesson comes to an end.
V. Homework
At home you will study the material from the textbook “Type of Molluscs”, prepare for the test and complete any creative task on the topic “Shellfish”: crossword puzzle, drawing, puzzles, etc..
Thank you for your active work in class. I really liked you, you worked well in class. Goodbye.
Annex 1
First group text:
The most mysterious, most fantastic cephalopods live on the seabed. Among them are octopuses.
But first, a little history! Europeans who came to Ceylon at the beginning of the 20th century were perplexed on the eve of major holidays. All the housewives on the beach, it seemed to them, were doing their laundry. When the Europeans took a closer look, they saw that it was not the laundry that was being knocked out, but some strange objects. Big-headed monsters were pulled out of baskets by their long tentacles, thrown onto stones and beaten with rolling pins. “I swear by Neptune,” the Europeans exclaimed, “they are fighting off the octopuses.”
The secret of the strange actions was revealed very simply: it was the first stage in preparing the festive table - after all, it is impossible to chew unbeaten octopus meat. And people spare no effort to get a tasty morsel! Octopus is a delicious dish! Indeed, there are octopus dishes; their recipe came to us from Ancient Troy. Stuff the octopus head with spices and finely chopped tentacles, and then bake in the oven like a big pie. It’s very tasty, in our menu it’s called Trojan-style octopus. And in ancient Sparta black soup was famous! A preparation that required special care! They took the cuttlefish, gutted it, but did not touch the ink sac, so they boiled it with it. The ink gave the stew not only a black color, but also a unique flavor that was highly valued.
Text of the second group:
Among gastropods, the most famous are various types of cypres. Cypra shells, the so-called cowries, were once used as money in Japan, China and other countries. The sinks have a smooth surface, round shape and great strength. Cowries were also used in Rus' under the names of grass snakes, weevils, and snake heads. This happened during the so-called coinless period (12-14 centuries). They are still found during excavations in the Novgorod and Pskov regions. Today the value of cowries as money has disappeared almost everywhere. However, among small, secluded African tribes it is still preserved.
Text of the third group:
There are pearl mussels. These are real wizards who are able to make amazing jewelry from a small grain of sand caught between the flaps of its shell. Their pearlescent glands secrete liquid, which envelops the grain of sand and hardens. In ancient times, people believed that on long nights, when the shell of a pearl oyster opens slightly, a drop of moonlight penetrates and a pearl grows from it. In reality, this is not a drop of moonlight, but a simple grain of sand.
Nowadays pearls are used to make jewelry.
The best pearls are produced by shells of the genera Pteria and Pinctada, which live off the coast of Sri Lanka. They are called real pearl oysters.
Text of the fourth group:
The Black Sea is home to a predatory mollusk called rapana. His shells are sold as souvenirs in all Black Sea cities and most of us are familiar with them. But few people know that rapana appeared in the Black Sea only fifty years ago. Until 1974, she lived in the Sea of Japan and the Yellow Sea and on the Japanese Pacific coast. How could rapana move from the Sea of Japan to the Black Sea? One can only guess about this. Most likely, rapana larvae attached to the bottom of some ship sailing from the Sea of Japan to the Black Sea. They took root there well, they just chopped them up, because... The water in the Black Sea is less salty than in the Japanese Sea. Rapana hunts mussels and oysters. If you put an empty shell to your ear, you can hear the sound of the sea...