Class Crustaceans. Laboratory work. Study of the external structure of crayfish
Checking the completion of laboratory work.The color of crayfish is greenish-black. The body is covered with a shell
, consisting of
chitin impregnated with calcium carbonate
.
The integument of the crayfish serves as an exoskeleton
, to which bundles
of striated muscles are attached from the inside.
The body of crayfish consists of two sections - the cephalothorax and abdomen.
At the anterior end of the cephalothorax there is a pair of long and a pair of short antennae - the organs of touch and smell.
The spherical eyes sit on long stalks.
Therefore, cancer can look in different directions at the same time. Each eye consists of many small eyes - facets.
At the anterior end of the body, the crayfish has three pairs of jaws:
a pair of upper jaws and two pairs of lower jaws.
The cancer uses them to tear its prey into small pieces.
There are three pairs of jaws on the cephalothorax .
They serve to bring food to the mouth
.
There are
5 pairs of walking legs.
With the help of the fourth pair, it moves along the bottom of the reservoir.
And the first pair has been turned into large claws.
With them, the cancer grabs prey and defends itself.
are located on the abdomen .
By sharply bending its abdomen, the crayfish pushes against the water with its tail fin, like an oar, and in case of danger can quickly swim backwards.
What structure do the limbs of crayfish have? (The limbs consist of numerous segments.)
— How does cancer move? Does cancer always move back?
- How will you evaluate your work when performing laboratory work? - 3.4.5. Write your points in the margins.
What substance causes the exoskeleton of cancer to harden?
Find this substance in the classroom. (Lime, chalk.)
The main element contained in lime is calcium. Therefore, if you want your hair and nails to be strong and your bones to be strong, then you need to eat foods containing calcium - cottage cheese, dairy products.
Students answer questions based on options.
1. How could limbs, covered with a solid hard chitinous case, bend?
The chitinous cover at the junction of adjacent segments is much less developed, which allows the limbs to bend in different directions. Based on the structure of the limbs, the entire type got its name - “Arthropods”.
2. How is the appearance of the head lobe related to the functions of the legs in crustaceans?
The capture of food in arthropods is carried out by the limbs. The jaws and mandibles are specialized for capturing food, pushing it into the mouth, and grinding it. This led to important consequences - to the formation of body parts, primarily the head! With the development of powerful muscles of the chewing limbs “accumulated” around the mouth, a powerful skeleton was also required for muscle attachment. In this regard, several anterior segments fuse to form a well-separated head capsule.
3. The cancer's head is motionless. How can he look in different directions at the same time without turning his head?
The spherical eyes sit on long stalks. Therefore, cancer can look in different directions at the same time. In case of danger, it hides its eyes in the recesses of its shell.
4. The chitinous cover is very strong and inextensible. How does the growth process of crustaceans occur?
Cancer periodically molts and sheds its integument. Until the new shell gets stronger (this takes about 1.5 weeks), the cancer is defenseless and cannot feed. At this time, he hides in shelters.
When molting, the crayfish does not sense the position of its own body for some time. Why?
Statocysts are depressions at the base of short antennae where a grain of sand is placed. In normal body position, these grains of sand press on the lower sensitive hairs underneath; If the body of a swimming crayfish turns upside down, the grains of sand move and press on other sensitive hairs, and then the crayfish feels that its body is out of its normal position. When a crayfish molts, grains of sand are also shed. Then the cancer itself inserts new grains of sand with its claws.
5. When catching crayfish, sometimes you come across individuals with one claw smaller than the other. How can such a phenomenon be explained?
Sometimes molting is very difficult for cancer: it, not being able to free its claw or walking leg from the old skin, breaks it off. But a damaged limb is capable of regeneration, which is why there are crayfish in which one claw is smaller than the other. Sometimes a cancer, when it is in danger, breaks off its claw with the help of its muscular effort.
6.
Where do crayfish spend the winter?
Where do crayfish spend the winter? An eternal question that worries thousands of Russian people. All cultured people need to know where crayfish spend the winter. So, crayfish are freshwater animals that live in the clean water of rivers, lakes and ponds. In winter, they do not change their place of residence, but simply descend much deeper, to where the water does not freeze. From late autumn to early spring, crayfish lead an inactive lifestyle, sitting in shelters for 20 hours a day, protecting their home, which is a long burrow, up to 35 cm. So there is no mystery at all regarding the place where crayfish spend the winter.
7.
Why do they turn red when they cook crayfish?
The coloring substances (pigments) contained in the skin of the crayfish are destroyed by boiling. Except for one red pigment. Therefore, when cooked, crayfish turn red.
Task 1. Study the external structure of crayfish. Prove the adaptability of his body to its environment.
1. Consider a crayfish. What sections is his body divided into? What is the strength of the cover and color? Explain the significance of such a cover in the life of a cancer.
The body is divided into segments and consists of several sections: lobe, thorax and abdomen or cephalothorax. The integument of the body contains a special solid substance - chitin.
2. Identify the body parts of the crayfish. Pay attention to the thickness of the chitinous cover in different places. Explain why it is not the same.
The hard shell of the crayfish prevents the animal from growing. Therefore, cancer periodically (2-3 times a year) changes - sheds old covers and acquires new ones.
3. Find the sense organs: antennae, eyes. Explain why cancer's eyes move.
There are two pairs of antennae. Cancer's eyes are complex. Each eye consists of many very small eyes directed in different directions - facets.
4. Referring to the picture in the textbook, find the crayfish’s jaws, mandibles and mouth opening.
5. Find the ventral horns of the crayfish. Note the difference in structure.
6. Look at the abdomen. Make sure it has segments. Count them. At the end of the abdomen, find the fin plates. Write about their role in the life of cancer.
The crayfish has limbs on its cephalothorax. If you turn it over on its back, then at the front end of the body you can find 3 pairs of jaws: a pair of upper jaws and two pairs of lower jaws. The cancer uses them to tear its prey into small pieces. The jaws are followed by three pairs of short jaws. They serve to bring food to the mouth.
7. Based on the features of the external structure of the crayfish, draw a conclusion about its habitat, methods of movement (on the bottom and water), nutrition, and protection from enemies.
Crayfish live on land and in water, move along the bottom with the help of walking legs, and swim with the help of a fin and abdominal legs. It feeds on mollusks, fins, and plants. Protects itself with powerful pincers.
Task 2. Fill out the table.
Adaptation of crayfish to an aquatic lifestyle Body parts and organs Adaptation to lifestyle Body covers: strength
coloring
the body is covered with a durable and dense chitinous shell, impregnated with calcium carbonate. Color: greenish-black Parts of the body that provide movement: along the bottom
in the water column
there are five pairs of walking legs. With the help of four pairs of these legs, the crayfish moves along the bottom of reservoirs. Sense organs in addition to the organs of touch, smell and vision, crayfish also have balance organs Respiratory system gills. They contain blood capillaries and gas exchange occurs.
Task 3. Fill out the diagram by writing down the names of the animals.
Crustaceans Free-living Parasites sea acorns Cyclops - serves as an intermediate host Aquatic life Land dwellers lobsters, lobsters, hermit crabs woodlice
Task 4. A. Color the internal organs of the crayfish (yellow - nervous system organs; green - digestive organs; black - gonads) and label them.
1. Yellow - organs of the nervous system. Periopharyngeal nerve ring and ventral nerve cord.
2. Green - digestive organs: stomach, liver, intestines.
3. Black - sex gland: ovary.
B. Color the internal organs of the crayfish (blue - respiratory organs, red - circulatory organs, brown - excretory organs) and write what they are called.
Task 5. In one clutch of a female daphnia there are approximately 60 eggs. After 15-20 days, young daphnia hatch from the eggs, which are soon able to lay eggs themselves. Count and record how many daphnia can theoretically appear from one female in three summer months.
There are approximately 90 days in 3 summer months
90:15=6 clutches in 3 months
Total: 6x60=360 eggs
Biology at the Lyceum
Copepods.
These include cyclops - very small crustaceans found in the same bodies of water as daphnia. The body of the Cyclops consists of a cephalothorax and a narrow abdomen. Two pairs of antennae are visible. With its long antennae, the Cyclops periodically makes a sharp swing and “soars” in the water column. The frightened crustacean makes a series of strokes and quickly swims away. The Cyclops has only one eye (because of this, they named him after the mythical one-eyed giant with whom the cunning Odysseus dealt). Cyclops do not have gills; they breathe over the entire surface of their body. It feeds on the same thing as daphnia - single-celled planktonic organisms. Cyclops serves as an intermediate host for some parasitic worms.
Isopods.
The order includes, in addition to other representatives, a small land animal -
woodlice . It lives in damp places, such as under stones, cellars and basements. Living in a ground-air environment, woodlice breathes atmospheric air with the help of modified gills - pockets that are located on the abdominal legs. Therefore, it can only live in a humid environment, and in dry air the woodlice dies. Freshwater bodies of water are inhabited by a small crustacean that vaguely resembles a wood lice - the water donkey
.
Multi-legged.
This order consists of small (up to several centimeters) crustaceans swimming on their sides, for which they are called
amphipods
. Using different legs, crustaceans can swim, walk along the bottom of reservoirs and along the wet soil of the banks, and also jump.
Barnacles.
Representatives of this order are small crustaceans that lead an attached lifestyle as adults, for example sea acorns and
barnacles . They live in the sea. Their entire body is covered with a calcareous shell-house. Most often, the shell is attached to stones, crab shells, the bottoms of ships, and the skin of whales. Barnacles catch their prey (small planktonic organisms) using long chest legs that protrude from the shell and quickly retract.
The meaning of crustaceans
Crustaceans play a huge role in the food chains of aquatic biocenoses. Marine crustaceans form the basis of zooplankton and serve as food for many aquatic animals - from coelenterates to whales. Small crustaceans in the water column of seas and freshwater bodies provide food for many commercial fish. Among crustaceans there are many predators, parasites, and filter feeders that clean water from pollution. Some species of crustaceans parasitize fish, and some can be intermediate hosts of parasitic worms.
People use crustaceans for food; crabs, crayfish, lobsters, lobsters, shrimps, krill, etc. are fished for. The harvest of decapods in the world reaches almost 700 thousand tons per year. They are highly valued for their tasty and nutritious claw and belly meat.
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The variety of crustaceans and their significance
Most species of crustaceans are aquatic animals. Let's get acquainted with the representatives of lower cancers.
Lower crayfish
They are
small in size
(only a few centimeters), they
are devoid of chitinous cover
.
Most species live in the water column and are part of plankton
(organisms that inhabit the water column and
are not able to withstand transport by currents
).
Ocean-dwelling planktonic crustaceans are called krill
. Krill, thanks to the accumulation of a gigantic number of crustaceans, can even change the color of the water in the ocean.
The crustacean Artemia lives in very salty waters.
.
They are very rarely found in the open sea, most likely due to a lack of food and the presence of a large number of enemies. Adult crustaceans have three eyes and eleven pairs of legs
.
They have sizes up to 15 millimeters
. It feeds mainly on microscopic green algae. In fresh water, Artemia dies in about an hour.
In drying up fresh water bodies and puddles you can find shieldfish
.
They are about 2 – 3 cm
.
Some species reach 10 cm. The entire back of the animal is covered with a scute
, which is where they got their name.
They have 70 pairs of legs
.
Shchitni are one of the most ancient species
of animals currently existing on our planet.
They are found on all continents except Antarctica. Shields are predators
; they spend most of their time at the bottom, digging in the ground in search of food. They feed on invertebrate animals and even fish larvae.
Daphnia is found in large numbers in all fresh water bodies.
,
or water fleas
.
These are small crustaceans 2-3 mm
.
The body is covered with a shell
.
large antennas
on the head that daphnia use for movement.
A beak-like outgrowth
is also developed on the head .
At the posterior end there is a tail spine
.
Daphnia are filter feeders
.
By driving water through themselves, they filter out bacteria and single-celled algae. Daphnia are able to reproduce rapidly using parthenogenesis
. Daphnia is used as food for aquarium fish or insects kept in terrariums. They participate in water purification thanks to the filtration type of nutrition.
Cyclops crustaceans also live in our reservoirs.
.
They measure about 1 mm
and are barely visible
to the naked eye
.
They have an unpaired eye, which is where they got their name. They do not have a heart or blood vessels. The organs are washed by colorless hemolymph, which moves due to the pulsation of the intestines. Breathe with the entire surface of the body
.
Cyclops are predators
and feed on protozoa and small crustaceans. They themselves are food for many fish, fry, and tadpoles. They can serve as intermediate hosts for parasitic worms.
Some lower cancers lead a sedentary lifestyle
.
Sea acorns
have a calcareous shell and lead a sedentary lifestyle, attaching to the surface of rocks, stones, aquatic plants and animals.
sea ducks
- relatives of sea acorns.
They are distinguished by the presence of a long stalk
, with which they are attached to the surface.
They have a very interesting color and a calcareous shell about 5 cm in size.
They lead the same lifestyle as sea acorns. Sea ducks feed on plankton, protruding their legs from the opening of their shell like whiskers. In Portugal and Spain they are widely eaten and are an expensive delicacy.
Higher crayfish
- inhabitants
of sea and fresh waters
.
On land
, this class is inhabited by woodlice and some other crayfish, for example the “palm thief”.
Woodlice
They do not have a solid shell, so they can curl into a ball. They live in damp places: under stones, under a tree lying on the ground, in cellars and basements. They hide during the day and come out in search of food in the evening. They feed on plant debris.
Palm thief, or coconut crab
, lives in the tropics on the islands of the Indian and western Pacific oceans.
The palm thief is one of the largest terrestrial arthropods. Its length can reach 40 cm
and weight
– 4 kg
. It feeds on the fruits of tree-like tropical plants - pandans, as well as the contents of split coconuts. Coconut crab meat is eaten.
Under stones, rotting leaves, at the bottom of reservoirs you can see a small ( about 2 cm
) a yellowish crustacean quickly swimming on its side, bent in the shape of the letter “C”.
This is an amphipod
.
Amphipods are water orderlies
; they feed on carrion and rotting plants.
The most famous representatives of crustaceans are crayfish, shrimp, crabs, hermit crabs, lobsters and lobsters.
Narrow-toed crayfish is widespread in fresh water bodies.
.
about 20 cm
long and has highly elongated claws.
Lives up to 15 years. Prefers to live in warm, nutrient-rich water bodies. Omnivorous
- feeds on carrion and the remains of dead plants.
Broad-toed crayfish
has a wider body than the narrow-toed one.
Unlike the narrow-clawed crayfish, it is sensitive to water pollution
. In the 20th century there was a sharp decline in their numbers. All crayfish are eaten.
Lobster
– large animals, reaching a length of
80 cm
.
They have very large claws
. Otherwise they resemble crayfish. They have a fairly long life expectancy. Males live about 30 years, and females - about 50. In cooking, lobster is considered a delicacy.
Lobsters
similar to lobsters, but have small and thin claws.
The body and antennae are covered with spines
. They live in warm seas. They live on the bottom, hiding among stones, corals and plants. The meat is considered a delicacy.
Hermit crabs
empty mollusk shells
as shelter They live in shallow seas. Only three pairs of walking legs protrude from the shell. The abdomen loses segmentation
.
Hermit crabs are predators and corpse eaters
.
They feed on mollusks, echinoderms, other crustaceans, and the remains of dead fish. They are able to enter into symbiosis with sea anemones
, which protect them from enemies and eat the remains of their food.
Crabs
have
a small head and abdomen
. They live in seas, fresh water bodies and on land.
Shrimps
widespread in the seas of the whole world, many species have mastered fresh waters.
The size of adult individuals of different species varies from 2 to 30 cm.
They are a delicacy.
parasitic species among crustaceans
, which live on the skin and gills of fish, the skin of marine mammals, and in the body of other crustaceans.
Thus, small crustaceans called carp lice
.
The meaning of crustaceans
very large in nature.
Small lower crustaceans are part of plankton, which feeds a large number of aquatic animals, often very large ones, such as whales, whale and basking sharks. Thus, crustaceans are the most important link in food chains
.
In fish hatcheries, crustaceans are bred as fish food.
.
Large bottom crustaceans are orderlies of reservoirs
, eating dead animals and dead plants.
Many crustaceans - crayfish, shrimp, crabs, lobsters and lobsters - are used as food
. Their meat has high nutritional value and contains many proteins, fats and microelements necessary for humans.
But there is also a negative role
: some crustaceans can be carriers of various infections; sessile forms of crustaceans (barnacles) cover the bases of ships with a continuous cover and slow down their speed. Therefore, the bottoms of ships are coated with special paints containing toxic substances. Some are intermediate hosts of parasitic worms (for example, the Cyclops crustacean).
Text of the book “Biology. Diversity of living organisms. 7th grade"
Type Shellfish
Molluscs, or soft-bodied mollusks, form a separate type of invertebrate animals, originating from ancient unspecialized polychaete annelids. The number of species reaches 130 thousand.
The structure of mollusks.
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
.
The mantle seems to hang from the dorsal side of the body; between it and the body wall a mantle cavity is formed,
in which the respiratory organs, some sensory organs are located, and into which the anus, ducts of the kidneys and gonads open.
On the dorsal side, as a rule, there is a protective shell secreted by the mantle ,
usually 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
).
The abdominal side, strongly thickened due to muscles, forms various shapes of legs: wide - crawling, wedge-shaped, fin-like - for swimming, rounded - suction, etc.
Grape snail
Prosobranch mollusk
Digestive and respiratory systems
Eyeless deep sea octopus
Nervous system
mollusks of the scattered-knot type; it consists of a peripharyngeal nerve ring, in which the suprapharyngeal nerve ganglion (“brain”) receives the greatest development, and nerve trunks extending from it, connecting the nerve ganglia of different parts of the body.
From the senses
– organs of chemical sense and balance are found in all representatives; many species have eyes.
Circulatory system
characterized by the presence of a heart consisting of a ventricle and one or two atria and vessels. It is not closed, and part of the way the blood passes through the cavities between the internal organs.
Respiratory system
in most species they are represented by gills, and in terrestrial representatives - by lungs.
Digestive system.
The pharynx usually contains an organ that grinds food -
a grater
with horny teeth located on it.
As a rule, the grater is used to scrape off plant food and only in rare cases (among predators) to actively capture it. of the digestive gland
,
which combines the functions of the liver and pancreas,
open into the stomach The intestine opens into the mantle cavity through the anus. Excretory organs
are represented by kidneys, the ducts of which open into the mantle cavity.
Mollusks are predominantly dioecious animals. In hermaphroditic forms, cross-fertilization occurs.
The meaning of shellfish.
Some - very few - mollusks are important as a source of mother-of-pearl and pearls.
The formation of pearls occurs as follows: a grain of sand enters the mantle cavity, which is then covered over a long period of time with layers of nacre, similar to the inner, nacreous layer of a shell. The most prized pearls are the sea pearl mussel,
found in the Red Sea, Indian and Pacific oceans. Currently, to obtain pearls in large quantities, special sea farms are organized, where a grain of sand is artificially placed into the mantle cavity of pearl oysters, stimulating the formation of pearls.
Many marine bivalves have been eaten, apparently since time immemorial, for example oysters, mussels, scallops;
Squids,
cephalopods
, are also edible.
Bivalves are powerful natural water purifiers (biofilters). Feeding on organic matter suspended in water and tiny living organisms (plankton), they pass large amounts of water through the mantle cavity. It is estimated that mussels
inhabiting 1 m2 of the bottom, they can filter up to 280 m3 of water per day.
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.
Pearl formation
Class Gastropods
Gastropods, or Snails, are the richest class of mollusks, including about 90 thousand species.
The body shape of gastropods is varied. The head is clearly separated from the body, bears 1–2 pairs of tentacles and a pair of eyes. The leg is well developed and usually has a wide crawling sole. The body forms an outgrowth in the form of a large internal sac. A characteristic feature of all gastropods is the asymmetry of the structure, resulting from the formation of a spirally twisted shell.
The sizes of gastropods range from 2–3 mm to several centimeters ( grape snail, slug, pond snail
).
Most gastropods are marine animals. Some representatives of this class, in the course of evolution, adapted to life in fresh water bodies, while others switched to terrestrial existence. In the seas, gastropods are found at various depths, on land - in a wide variety of climatic conditions. They are tolerant of high and low temperatures, partly due to their ability to hibernate: in the north in winter, in the south in summer and often in winter.
The food of gastropods is varied; Among them there are many herbivorous inhabitants of water bodies and land, and there are a large number of predators that feed on worms, crustaceans or other mollusks.
Land mollusk
Large pond fish
Tropical lung clam
Pelican foot clam
True parasites are found only in one of the subclasses of gastropods. Most of them parasitize on the skin or in the body cavity of echinoderms (starfish, sea urchins, etc.). The parasitic lifestyle led to significant changes and simplification of their organization: the loss of the shell, legs, mantle, up to the complete disappearance of the digestive, nervous and other systems.
The economic importance of gastropods is low. Slugs
and
grape snails
are agricultural pests.
But in some countries, especially in France, grape snails are considered a delicacy and are specially bred. whelms
are also eaten .
Shells of species with a well-developed mother-of-pearl layer are used to make jewelry. In the old days, special shells - cowries - served as bargaining chips in southern countries. A number of gastropod species are the first intermediate hosts of parasitic flatworms, which are also dangerous to humans. Two genera of tropical mollusks - Cone
and
Terebra
- have poisonous glands and can seriously “sting” a careless person who picks them up.
Sea mollusk shells
Internal structure of the cochlea
Class Bivalves
A characteristic feature of bivalve shells is a bivalve shell, the valves of which are connected on the dorsal side by an elastic ligament and a lock consisting of tooth-like projections on one valve and corresponding recesses on the other. Most representatives have a pair of mantle outgrowths transformed into large lamellar gills.
The body is oblong, laterally flattened, bilaterally symmetrical. Consists of a torso and legs. At the front end of the body there is a mouth, at the rear there is an anus. Between them, on the ventral side of the body, a leg protrudes. In a few bivalves, the leg is equipped with a flat crawling sole, while in all others it is strongly flattened laterally and pointed along the free edge, forming something like a keel. Such a leg is used not so much for crawling as for digging sand or silt, in which bivalves often live.
The body is covered with a mantle, surrounding the bivalves with two large mantle folds, between which a mantle cavity is formed, where the leg and gills are located. The pallial folds of the anterior, ventral and posterior sides usually end in a free edge, on which small tentacles and even ocelli can sometimes develop.
Both shell valves are formed by the outer epithelium of the mantle folds. The valves cover the body from the sides and are equally developed in most bivalves.
Bivalves reach significant sizes. Thus, some species inhabiting the coastal zones of the Indian and Pacific oceans have a shell with a diameter of 135 cm, their body weight can reach 250 kg (giant tridacna).
In the reservoirs of the central zone you can find toothless, pearl barley,
as
well as river pearl mussel.
Marine bivalves – mussels, oysters, scallops
They are considered a delicacy in many countries around the world.
Some stone-cutting mollusks can use the sharp edges of their shells to drill holes and passages in hard soils and soft stones. Others drill into wood, the most famous and dangerous of which is the shipworm, teredo.
Veneris bivalve mollusk
Freshwater pearl mussel
Bivalve shells
Internal structure of toothless
Teredo
does not look like a mollusk, it is worm-shaped, at the rear end there are two long siphons, at the front there is a small shell, the valves of which have turned into a drill.
Teredo drills wood with it and absorbs sawdust. It also has symbiont bacteria that break down cellulose. As a result, the tree, worn out by tunnels, turns into something like a sponge. In our country, teredo
is found in the Black, Azov and Far Eastern seas.
Many bivalves that live in the seas are excellent food for fish, seabirds and even walruses. In general, bivalves play an important role in the life of the seas and oceans.
Class Cephalopods*
In the modern fauna, about 700 species are described, living in the seas, free-swimming and (less often) crawling, very mobile, large (up to 18 m in length) predators such as octopus, squid, cuttlefish
etc. There are also smaller (about 1 cm) forms.
The body of cephalopods is bilaterally symmetrical, with a sharp division into the head and trunk. The shell in primitive forms is external, multi-chambered, while in higher representatives it is internal and underdeveloped.
One part of the leg is turned into tentacles,
which are located on the head and surround the mouth opening, equipped with oral jaws curved like a beak.
The other part of the leg forms a funnel
.
Higher cephalopods have only eight tentacles. These are wide at the base, tapering towards the end, muscular outgrowths with a longitudinal groove on the inner side facing the mouth. This side of the tentacles is lined with numerous large disc-shaped suckers
,
allowing the animal to stick unusually firmly to the bottom and embrace prey.
Some species, in addition to eight tentacles, have two much longer hunting tentacles, expanded at the end. There are two large eyes on the sides of the head. Cephalopods live in the seas and oceans both in the water column and near the bottom; deep-sea forms are known.
Argonaut
Internal structure of an octopus
Many octopuses
and
cuttlefish
change color depending on the background they are in front of. This is achieved by compressing or stretching special cells under the skin under the control of the nervous system.
A special adaptation of cephalopods is the ink gland,
the duct of which opens into the hindgut.
suddenly disturbed octopus, squid
or
cuttlefish
releases its secretions from the funnel - a black or brown cloud that hides the animal from the attacking enemy. This “ink” is poisonous and paralyzes the olfactory nerves of predatory fish. In the eternal darkness of the deep sea, some cuttlefish and squid, instead of “ink,” shoot out a cloud of brightly glowing symbiotic bacteria, blinding the enemy. They also have luminous organs in their skin of different colors (light blue, purple-red) that can “turn on” and “turn off.” In structure they resemble eyes.
Humans use some species of cephalopods, mainly squids,
for food.
Questions and tasks
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.
2. What is the mantle? What is its meaning?
3. What is a sink? What are its functions? What chemicals form the bulk of the shell?
4. Describe the body structure of bivalves.
5. Discuss as a class the similarities and differences between different classes of mollusks.
6. Make a table “Comparative characteristics of 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.
8. Highlight the structural features of the body of mollusks associated with their way of life.
9. Make a detailed plan for the paragraph.
Laboratory work
Complete work No. 11 on p. 17–18 (Laboratory work).
Work with computer
Refer to the electronic application. Study the material and complete the assigned tasks.
Internet links
1. https://www.krugosvet.ru/enc/nauka_i_tehnika/biologiya/MOLLYUSKI.html (Overview of representatives of the type)
2. https://www.sbio.info/list.php?c=orgmolusk (General characteristics, taxonomy)
3. https://www.zooeco.com/0-dom/0-dom-moll.html (Type Review)
The body of most mollusks consists of a head, torso, and legs. It is usually covered with a shell. The mantle is a fold of skin that limits the mantle cavity, in which the gills are located and where the ducts of the sex glands, kidneys and anus open. The nervous system of the scattered-nodular type reaches its greatest development in cephalopods, which are characterized by complex behavior. Bivalves and cephalopods are exclusively aquatic animals. Gastropods are found both in aquatic environments and on land.
Phylum Arthropods
Arthropods are the richest phylum of animals in groups, including over 1.5 million species. These include a variety of aquatic and land forms with articulated limbs and a segmented body.
Arthropods are bilaterally symmetrical animals, their body in most cases consists of three sections - the head, thorax and abdomen and is covered with a continuous chitinized cuticle, which breaks up into harder scutes and membranous sections connecting them.
The first arthropods arose in the sea and descended from ancient free-living primitive polychaete worms.
The phylum unites a number of classes, among which the most famous are Crustaceans, Arachnids
and
Insects.
Sidewalk spider
Class Crustaceans
Crustaceans, the most ancient of arthropods, make up a significant part of the aquatic fauna. At least 30–35 thousand species are known.
Representatives of the class are combined into two large groups: lower ( daphnia, cyclops
) and higher (
crayfish, crab, shrimp
) crustaceans.
Crustaceans differ from other arthropods in some characteristic features. Firstly, this is the simultaneous presence of two pairs of antennae:
short -
antennules
and long -
antennas.
Secondly, only in crustaceans the limbs in many cases retain their primitive structure.
The structure of crustaceans.
As a rule, crustaceans have three body parts: head, chest and abdomen.
In some, such as crayfish, the head and thoracic regions are fused and form a monolithic cephalothorax.
The cephalothoracic limbs of crayfish are very diverse and often perform different functions. In many cases, they are organs of movement (swimming, moving on a solid substrate). In a large number of forms, the legs of one to three anterior thoracic segments take part in supporting food and crushing it.
The broad-toed crayfish hides under stones during the day and leaves the shelter in the evening in search of food.
Lobster decorated
In crayfish, the first two pairs of limbs are transformed into antennae. Then follows a pair of upper and two pairs of lower jaws, followed by three pairs of maxillae, forming the oral apparatus. Crayfish have five pairs of walking legs, the first of which ends with claws, which are used for capturing food and also for defense.
Only higher crayfish have abdominal limbs. They often perform not a motor function, but some other function: respiratory, copulatory organs, etc.
Crustaceans have a hard covering, the basis of which is chitin.
- a special organic substance. The chitinous cover is almost inextensible. This interferes with the growth of young crayfish. Therefore, like all arthropods, crayfish molt periodically. A new one is formed under the old cover. The old chitinous cover bursts and is shed. Cancer is growing quickly. As the chitin becomes saturated with lime, growth slows and then stops completely until the next molt. From the inside, muscles are attached to the chitinous cover, and it plays the role of an exoskeleton.
Nervous system
crayfish resembles that of annelids. It consists of the suprapharyngeal nerve ganglion - the brain, the subpharyngeal ganglion, the peripharyngeal nerve ring and a pair of abdominal nerve trunks with nodes in each segment.
1. First pair of antennae 2. Second pair of antennae 3. Upper jaws 4. Lower jaws 5. Mandibles 6. Walking legs 7. Abdominal limbs
central nervous system
Sense organs.
The sense of touch is associated with certain areas of the body, namely with part of the hairs and setae on the surface of the antennules, antennae and other limbs.
Balance organs are relatively rare in crustaceans. However, in most decapods
at the base of the antennules there is a small vesicle - a statocyst, lined with sensitive epithelium and communicating with the external environment.
Small grains of sand easily fall into it, playing the role of “hearing pebbles” - statoliths.
When molting, they are removed, and the animals gain a new supply of sand grains, plunging their heads into the sand.
Most crayfish have a pair of complex ( faceted)
) eye.
Each such eye consists of many small eyes - facets
(crayfish have more than 3 thousand of them), closely spaced and separated from each other only by thin layers of black pigment. The eye, in turn, consists of a complex light-refracting apparatus and a group of sensitive cells from which nerve endings arise, giving rise to the optic nerve. Compound eyes often sit on special movable outgrowths of the head - stalks.
Circulatory system
in crustaceans, like in other arthropods, it is not closed: partly the hemolymph - the fluid that performs the functions of blood - moves inside the vessels, partly - in parts of the body cavity not limited by special walls -
the sinuses.
Organ of balance
Structure of the eye
Internal structure of cancer
Respiratory system
in crayfish it is a skin gill, closely associated with the limbs. These are lamellar or branched thin-walled outgrowths of the skin that extend from the bases of the legs.
In woodlice
on the lamellar abdominal legs there are deep branching invaginations of the skin. The limb cavity is filled with hemolymph, washing the invaginations. Air enters the invagination and diffuses into the surrounding hemolymph. These organs resemble tracheas, the respiratory organs of typical land arthropods.
Digestive system
looks like a straight or slightly bent tube.
In crayfish, after the esophagus, a large expansion is formed - the stomach. It is divided into two sections - chewing and glandular. The intestine sometimes looks like a simple tube, but more often it forms lateral protrusions, the walls of which are rich in glands. These outgrowths not only secrete digestive enzymes, but also digest liquid food gruel. In crayfish,
a large two-lobed “liver” consists of many small tubes that gather on each side into one duct that flows into the intestine.
Some parasitic crayfish have no intestine at all.
Food for crayfish most often consists of various smaller animals or already decomposing organic remains.
Excretory system
represented by paired
green glands
.
Each of them consists of a terminal sac and a convoluted tubule with glandular walls extending from it.
It opens outward, sometimes forming a noticeable expansion in front of it - the bladder. Reproductive system.
Most crayfish are dioecious, often with clearly defined
sexual dimorphism
,
i.e., with external differences between males and females.
Lifestyle and meaning.
Crustaceans inhabit mainly seas and freshwater bodies of various types, including underground ones. There are planktonic and benthic forms. Some crayfish lead a sedentary lifestyle. There are many known parasites.
Circulatory system
Excretory system
woodlouse
Lower crayfish usually live in the water column and are part of the plankton. They are important, being an essential part of the diet of many fish and cetaceans. Cyclops
– intermediate hosts of parasitic worms – tapeworm and guinea worm.
The most primitive forms live in very salty bodies of water ( artemia
) or drying up reservoirs and puddles (
shchitni
).
Daphnia
crustaceans, well known to aquarists - are found in large numbers in all fresh water bodies.
Some lower crustaceans switched to a sedentary lifestyle, for example, the sea acorn
and
the sea duck.
Their mobile larva forms a bivalve shell and, attaching to underwater objects, builds a limestone house.
Higher crayfish are inhabitants of sea and fresh waters. Woodlice from this class live on land
and some other crayfish (
"palm thief").
People eat crayfish, crabs, and lobsters Many necrophagous crayfish have sanitary significance, cleaning water bodies from animal corpses. Freshwater crayfish and crabs in the countries of the Far East are intermediate hosts for the parasitic flatworm, the pulmonary fluke.
Questions and tasks
1. On the basis of what characteristics are various animals grouped into the phylum Arthropods?
2. What structural features are characteristic of crustaceans? Make and sketch a diagram of the structure of cancer.
3. What inorganic substances make up the shell of crustaceans?
4. Name the functions of the abdominal limbs of crayfish.
5. Make a table “Comparative characteristics of annelids and crustaceans” (work in small groups).
6. What is the biological meaning of such a phenomenon in crustaceans as molting?
7. Make a detailed plan for the paragraph.
Laboratory work
Complete work No. 12 on p. 18–19 (Laboratory work).
Work with computer
Refer to the electronic application. Study the material and complete the assigned tasks.
Internet links
1. https://sbio.info/page.php?id:=125 (General characteristics of crustaceans, taxonomy)
2. https://www.rakoobraz.ru/ (Structure, fossil crustaceans)
The phylum Arthropods unites bilaterally symmetrical animals with a segmented body, jointed limbs and a hard cover, the basis of which is chitin. Arthropods are characterized by molting - the replacement of the old cover with a new one.
Crustaceans are mainly aquatic animals. The body consists of a head, thorax (or cephalothorax) and abdomen. The crayfish has five pairs of walking legs on its cephalothorax; the abdominal legs are involved in movement (swimming) and sexual reproduction. Respiratory organs - gills. The eyes are complex. The circulatory system is not closed. The secretion is carried out by green glands. Lower crayfish are the food source for many aquatic animals. Higher crayfish are orderlies of reservoirs; many species are used by humans for food.
Branchiopods and Cephalocaridae
Branchiopods include the most primitive crustaceans. They have their own characteristic features:
- homonomic body segmentation;
- the head is not fused with the thoracic segments;
- thoracic limbs are leaf-shaped, perform the functions of movement, food capture and breathing;
- compound eyes and an unpaired ocellus in the nauplius larva;
- the abdominal section has no limbs and ends with a fork.
The order Lampshells are the most primitive representatives of the gill-breathers. They live in salty reservoirs, in Arctic lakes, and in temporary drying up reservoirs. Representatives of the unshelled species are biofiltrates; they feed on small organic particles and unicellular algae. Artemia crustaceans are common in salt waters and serve as food for small fish.
Cephalocarids are small crustaceans, up to 3 mm long, that live in sea mud. They occupy an intermediate position between branchiopods and copepods. A primitive feature is the position of the antennae located behind the mouth, the similarity of the last two head legs with the thoracic legs.
Finished works on a similar topic
- Course work Diversity of crustaceans 450 rub.
- Abstract Diversity of crustaceans 220 rub.
- Test work: Variety of crustaceans 240 rub.
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Laboratory work in biology grade 7
4.Look at the head. Find the mouth; paired nostrils; behind the nostrils on the sides
heads - eyes. Count the number of eyelids (using a dissecting needle). On
Locate the auditory openings at the back end of the head. Find and look through a magnifying glass (on
upper surface of the head along the midline) unpaired parietal eye.
5. What features of the lizard’s external structure indicate its terrestrial existence?
LABORATORY WORK No. 10.
Topic: Study of representatives of the bird class
.
Target:
find in the external structure of the bird features of adaptation to flight.
Equipment
: living object - living bird.
ClassBirds.
Representative: any bird.
Progress
TASKS:
1. Consider the appearance of the bird. Establish what sections the body bird consists of.
Pay attention to the characteristic features of the bird’s external structure:
feather cover, spindle-shaped body shape, the presence of a feather tail.
2.Look at the bird's head. What organs are located on it? What does it matter?
movable neck?
3.Look at the forelimbs of the bird? What type do they have? Which organs
Do terrestrial vertebrates correspond to the wings of birds? Find the departments in the wing,
characteristic of the forelimbs of vertebrates.
4.Look at the bird's legs. What are they covered with? How many toes are there on your feet?
How do they end?
5.Look at the spread wings and tail. Please note the large
flying surface, lightness and strength of these organs. Are they the same
different wing and tail feathers in appearance.
6. Pay attention to the tiled arrangement of the outer feathers.
Compare with the arrangement of scales on the body of a fish. What is the significance of this
feather arrangement?
7.Is there a difference in the appearance of flight feathers, tail feathers and cover feathers?
What is this connected with?
LABORATORY WORK No. 11.
Topic: Study of representatives of the class mammals
.
Target:
reveal the features of the external structure of mammals.
Equipment
: living objects – pets: rabbit, cat, dog and others
animals.
ClassMammals.
Representative: domestic rabbit.
Progress
TASKS:
1. Consider the appearance of the mammal. Determine what parts the body consists of
a rabbit.
Pay attention to the characteristic features of the external structure of the rabbit:
hair, elongated body shape, presence of a tail.
2. Describe the structure and significance of hair (long hair - spine, short -
undercoat) due to their functional significance.
Note when shedding occurs and how the hairline changes.
3. Find the vibrissae. What are they? Where are they located? What is their
meaning?
What derivatives of the epidermis, besides hair, are there in mammals?
