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The role of coelenterates in nature and human life. The importance of coelenterates and marine coelenterates

Coelenterates are multicellular animals with ray (radial) symmetry. Their body consists of two layers of cells and has a sac-like, so-called intestinal cavity. Coelenterates are characterized by the presence of special stinging cells.

Radiation symmetry is a characteristic common feature sessile or sedentary animals. In this case, the animal can be equally in danger from any side, and food also comes from all sides. Therefore, the bodies of these animals are designed in such a way that the means of protection or catching prey are directed in different directions, like rays (or radii) from a single center.

Coelenterates are the most ancient and primitive multicellular animals. They evolved from primitive primordial multicellular organisms.

All coelenterates are aquatic animals, most of which live in the seas and oceans. They inhabit seas from the surface to extreme depths, from tropical waters to polar regions. A small number of species live in fresh waters. About 9,000 species of coelenterates are now known. Among them there are solitary and colonial animals.

A group of individuals that have similar adaptations for living in the same environment is called a life form of animals. Modern coelenterates are characterized by two life forms (two generations): an attached form - a polyp and a free-swimming form - a jellyfish.

Polyps (from the Greek polyp - “multipede”) - a life form, so named for its numerous tentacles. In rare cases (Fig. 36, A) polyps are single (for example, hydra and sea anemone), but more often they form colonies of up to several thousand individuals. In the form of a jellyfish (Fig. 36, B), coelenterates, as a rule, live solitarily.

Rice. 36. Schemes of the structure of coelenterates: A - polyp; B - jellyfish

In many coelenterates, both life forms (both generations) replace each other (alternate) during life cycle- from the birth of an organism to death. Some (hydra, coral polyps) do not have a free-swimming form - jellyfish. Others (some scyphoid jellyfish; see next paragraph) have lost their polyp form.

The body of coelenterates resembles a two-layer sac open at one end. The outer layer of cells is called ectoderm (from the Greek ectos - “outside” and dermis - “skin”), and the inner layer is called endoderm (from the Greek entos - “inside” and dermis - “skin”). The only body cavity of these animals, the intestinal cavity, communicates with the external environment through the oral opening (mouth). Through the mouth, food enters the intestinal cavity, and undigested residues are expelled through it.

In coelenterates, stinging cells are located on the tentacles. They serve both for catching prey and for defense. Coelenterates are predators. They feed on various small animals that “float” in the water column.

Coelenterates reproduce both asexually and sexually.

The importance of coelenterates

Coelenterates are of great importance in nature. Many fish feed on coral polyps and hide among the limestone, branched “forests” built by these animals. sea turtles and some fish eat jellyfish. The coelenterates themselves, being predators, influence marine animal communities by eating planktonic organisms, and large sea anemones and jellyfish also eat small fish. Humans use some coelenterates. Dead calcareous parts of coral reefs in some coastal countries are used for construction material and lime is produced by burning. Some types of jellyfish are edible. Black and red corals are used to make jewelry.

Some swimming jellyfish, sea anemones and corals can cause damage with their stinging cells. severe burns fishermen, divers and swimmers. Coral reefs impede shipping in some areas.

Freshwater hydra - single polyp

Habitat. External structure. Lifestyle. Movement. In the valleys with clean water(in the creeks of rivers, lakes and ponds) the freshwater hydra lives (Fig. 37). This is a small translucent animal about 1 cm long. The body of the hydra has a cylindrical shape. With its lower end (sole) it is attached to the stems and leaves aquatic plants, snags and stones. At the upper end of the body, around the mouth, there are 6-12 tentacles. Hydra, like other coelenterates, is characterized by radial symmetry. Hydra leads a sedentary lifestyle. Its body and tentacles can lengthen and shorten. In a calm state, the tentacles extend several centimeters. The animal slowly moves them from side to side, lying in wait for prey. If necessary, the hydra can move slowly. At the same time, it seems to be walking (tumbling), attaching itself to underwater objects alternately with the upper and lower ends of the body.

Rice. 37. Scheme of the structure of freshwater hydra: 1 - ectoderm; 2 - endoderm; 3 - mesoglea: 4 - sole; 5 - intestinal cavity; 6 - kidney; 7 - tentacle; 8 - mouth

The hydra's body looks like an oblong sac, the walls of which consist of two layers of cells - ectoderm and endoderm. Between them lies a thin gelatinous non-cellular layer - mesoglea, which serves as a support. The intestinal cavity of the hydra communicates with the external environment only through the mouth.

The ectoderm forms the covering of the animal’s body and consists of several types of cells (Fig. 38). The most numerous of them are epithelial-muscular. Due to the muscle fibers lying at the base of each cell, the hydra's body can contract, lengthen and bend.

Rice. 38. Section through the body of the hydra - ectoderm cells (1-4) and endoderm (5, 6): 1 - epithelial-muscle cells; 2 - intermediate cell; 3 - stinging cell; 4 - nerve cell; 5 - digestive-muscle cell; 6 - glandular cell; 7 - mesoglea

The ectoderm contains star-shaped nerve cells. The processes of neighboring nerve cells connect with each other, forming a nerve network that covers the entire body of the animal and represents the most primitive nervous system in animals.

If you touch the hydra or prick it with a needle, the animal will shrink. This happens because the signal received by even one cell will spread throughout the entire nerve network. Nerve cells “give command” to epithelial muscle cells. The muscle fibers contract, and then the entire body of the hydra shortens (Fig. 39). The response of the hydra body to such irritation is an example of an unconditioned reflex. Unconditioned reflexes characteristic of all multicellular animals.

Rice. 39. Stimulation of hydra nerve cells

The ectoderm also contains stinging cells that serve for attack and defense. They are mainly located on the tentacles of the hydra. Each stinging cell contains an oval capsule in which the stinging filament is coiled. If prey or an enemy touches the sensitive hair, which is located outside the stinging cell, in response to irritation the stinging thread is ejected and pierces the body of the victim (Fig. 40). Through the thread channel, a substance that can paralyze it enters the victim’s body.

Rice. 40. Diagram of the structure of a stinging cell: 1 - nucleus; 2 - stinging capsule; 3 - sensitive hair; 4 - stinging thread: coiled (left) and thrown out (right)

There are several types of stinging cells. The threads of some pierce the skin of animals and introduce poison into their bodies. The threads of others are wrapped around the prey. The threads of the third are very sticky and stick to the victim. Usually the hydra “shoots” several stinging cells.

The ectoderm also contains intermediate cells. From them other types of cells are formed.

Endoderm lines the entire intestinal cavity from the inside. The endoderm consists of digestive muscle and glandular cells. There are more digestive muscle cells than others. Their muscle fibers are capable of contraction. When they shorten, the hydra's body becomes thinner. Complex movements, for example the hydra's "tumbling" movement, occur due to contractions of the muscle fibers of the ectoderm and endoderm cells.

Nutrition. Each of the digestive-muscle cells of the endoderm has one to three flagella. Vibrating flagella create a current of water, which drives food particles towards the cells. The glandular cells present in the endoderm secrete digestive juice into the intestinal cavity, which liquefies and partially digests food.

Digestive muscle cells of the endoderm are capable of forming pseudopods, capturing and digesting small food particles in the digestive vacuoles. Thus, digestion in hydra and all coelenterates is intracellular and cavity.

Nutrients are distributed throughout the hydra's body. Undigested residues are removed through the mouth. Hydras feed on small invertebrate animals (often crustaceans - daphnia and cyclops), which they catch with their tentacles.

Breathing and excretion. Hydra breathes oxygen dissolved in water. She has no respiratory organs, and she absorbs oxygen over the entire surface of her body, releasing carbon dioxide outward. During the process of life, harmful substances are formed in cells and released into the water.

Reproduction and development. Hydra reproduces sexually and asexually. Asexual reproduction carried out by budding (Fig. 41). A protrusion forms on the body of the hydra - a kidney. It consists of two layers of cells - ectoderm and endoderm - and communicates through a common cavity with the maternal body. The kidney enlarges and grows in length. A mouth and small tentacles appear at its top, and a sole appears at the base. After this, the young hydra separates from the mother’s body, sinks to the bottom and begins an independent lifestyle. Often several buds form on the hydra’s body at once. Hydras most often reproduce asexually.

Rice. 41. Asexual reproduction of hydra (budding)

In autumn, with the approach of cold weather, hydras begin to reproduce sexually (Fig. 42). Sex cells are formed in the ectoderm from intermediate cells. Two types of tubercles appear on the body of the hydra. In some, sperm are formed, in others, eggs.

Rice. 42. Sexual reproduction hydra

There are hydras in which sperm and eggs are formed on different individuals. These are dioecious animals. In other species of hydras, both sperm and eggs are formed on the body of one organism. Such animals, combining the characteristics of both female and male genders, are called hermaphrodites.

Once in the water, the sperm swims with the help of a long flagellum and reaches the immobile eggs. Fertilization (the union of a sperm with an egg) occurs in the body of the mother's body. After this, a dense membrane is formed around the fertilized egg. A fertilized egg divides multiple times to form an embryo. In the fall, the hydra dies, and the shell-covered embryos sink to the bottom. In spring, embryo development continues. After the reservoir warms up, the membranes covering the embryos are destroyed and small hydras come out.

Regeneration. A damaged hydra easily restores lost body parts (Fig. 43) not only after it has been cut in half, but even if it has been dismembered into many parts. From each part a new small hydra is formed. This occurs due to the intensive division of intermediate cells, from which other types of cells arise. The ability of animals to restore damaged or lost body parts is called regeneration.

Rice. 43. Hydra regeneration

Hydra is a multicellular animal with a primitive structure. Her intestinal cavity looks like a solid bag. Nervous system consists of scattered stellate nerve cells that form the nerve network. Asexual reproduction occurs by budding. Hydra also reproduces sexually.

Exercises based on the material covered

List the main structural features of representatives of the phylum Coelenterata.
What is the significance Various types Hydra's cells?
Describe radial symmetry using the example of one of the representatives of the coelenterate phylum.
What kind of life do coelenterates lead?
How does a hydra move?
Describe the vital functions of coelenterates: nutrition, digestion, reproduction (using the example of hydra).
Explain, using a picture, the regeneration process of the hydra.
What is the significance of coelenterates?

Answer:

Coelenterates are the most ancient of the true multicellular animals. Over the long history of the development of this type, its representatives have managed to adapt very well to a wide variety of living conditions. They populated literally the entire ocean from its surface to the extreme depths; they can be found in the polar regions and in the tropics. Coelenterates settle on a wide variety of soils, some of them are able to withstand significant changes in the salinity of sea water, and some species have even penetrated into fresh waters. Almost everywhere they play very important role in the formation of communities of marine animals and plants - sea biocenoses.

In nature:
Coral reefs: In tropical seas, some species of colonial polyps form dense settlements in shallow water - coral reefs. Reef-forming corals often settle along the shores of islands, fringing them on all sides. If the seabed drops and the island submerges, the corals continue to grow upward and remain at the surface of the sea. Subsequently, from such ring-shaped reefs, islands - atolls - are formed, characteristic of tropical seas. Skeletons of reef-building corals are used to produce lime. Often on coral reefs organize underwater reserves where corals are protected as rare and valuable representatives of the animal world.

Sea anemones or sea anemones- lead a sedentary lifestyle, moving with the help of a muscular sole. The body has the shape of a pillar, with a mouth opening at the top surrounded by numerous tentacles. These underwater “flowers” grab prey with their tentacles, killing or stunning them with stinging cells, and then sending them into their mouths. Sometimes sea anemones attach to the body of other animals: to the shells of mollusks, to the shell of crayfish - and thus move faster. Such cohabitation and symbiosis turns out to be beneficial not only for sea anemones that have settled on the body of a crab or a shell occupied by a hermit crab and pick up scraps of prey from these crustaceans, but it is also beneficial for the animal on which it “rides”: its burning tentacles give repelling almost all predators.

For a person:
As corals grow, reefs, islands, and atolls are formed. They are thick deposits of limestone, which is used as a building material, as fertilizer, etc. Coral colonies with a thick calcareous skeleton create obstacles for navigation. Jewelry is made from red (noble) coral.
Some jellyfish are hunted in China and Japan, where they are eaten.

Question 25. Organization of sponges as the most primitive multicellular organisms.
Sponges are absolutely motionless, they have neither muscles nor nerve cells. Sponges are the most primitive group of multicellular animals, essentially a collection of cells that are not very connected to each other. Some of the sponges can, after being crushed into individual cells and passed through a fine sieve, form a body again. Sponge sizes vary from a few millimeters to several meters. Sponges reproduce sexually and asexually. During asexual reproduction, several cells form a bud, which separates from the adult sponge and, falling to the bottom, begins to grow further. During sexual reproduction, sperm are released into the water and enter the body of other sponges through the pores, like other small food. But inside another sponge, the sperm are not digested, but combine with the sex cells of the host, forming larvae, which emerge into the plankton and are carried by currents until they find a place to settle.

Question 26. Reproduction and development of sponges.
Asexual reproduction of sponges:
1) fragmentation (as a result of damage by currents, surf, predators). The sponge regenerates lost fragments, which also form new sponge.
2) budding
3) formation of gemmules (formed in the mesochyl of a dying sponge around archaeocytes). A spongin membrane is formed. An encrustation of spicules may occur, covering the entire cell mass except for a small opening, the micropyle. The gemmule consists of a shell and archaeocysts, which, when rounded, become thesocytes. In the spring, thesocytes turn into pinacoderm, which, growing, comes out through the micropyle. The remaining thesocytes then move into the pinacoderm and form a new sponge.
Most often, sponges are hermaphrodites. One sponge releases sperm, which are carried by water currents to another sponge, inside which the eggs are fertilized. Oviparous birds hatch the zygote into the external environment. Live births occur. The embryos and larvae are lecithotrophic.
Sponges do not have reproductive organs (gonads). The germ cells lie in the mesochyl. Spermatozoa are formed from choanocytes immersed in the mesochyl and surrounded by a thin cell wall, and give rise to the spermatocyst. Eggs are formed from archaeocytes or from modified choanocytes. The egg accumulates the yolk by phagocytosing the surrounding feeding cells, or “nanny” cells. The egg and nurse cells are enclosed in a follicle with cell walls. The germ cells are evenly distributed throughout the mesochyl.
During the breeding season, the wall of the spermatocyst is destroyed, the sperm enter the efferent canals (or the atrium) and are thrown out through the osculum. Currents of water carry sperm into the aquifer system of another sponge and enter the choanoderma, where they are phagocytosed by choanocysts. The choanocyte loses its flagellum and collar and becomes a carrier cell that carries the sperm to the egg. The egg either phagocytoses the carrier cell or takes over the sperm nucleus. Sperm do not have an acrosome.
Larvae of the embryo:
1) coeloblastula - a hollow ball consisting of one layer of flagellar cells. With the transition of some cells into the cavity, the coeloblastula becomes steroblastula.
2) amphiblastula - a hollow ball of two types of cells (flagellated and flagellated with granular cytoplasm). While in the mother's body, the flagella are directed inside the sponge, but then it turns inside out.
3) parenchymula - the larva is already steroblastula.
4) trichymella - steroblastula with a belt of flagellated cells at the equator.
The larva attaches to the substrate and develops into a sponge.

Question 27. The meaning of sponges
TYPE OF SPONGE (Spongia, or Porifera)

Sponges are multicellular aquatic, mainly marine, animals immovably attached to the bottom and underwater objects. No symmetry
or there is an indistinct radial symmetry. Organs and tissues are not expressed, although the body is built from a variety of cells that perform many
functions, and intercellular substance. The internal cavities are lined with choanocytes - special flagellated collar cells. There is no nervous system.
The body is penetrated by numerous pores and canals extending from them, communicating with cavities lined with choanocytes. There is a continuous flow of water through the body of the sponge. Almost all have complex mineral or organic skeletons.
There are about 5,000 species of sponges in the modern fauna.
Sponges reach their greatest species diversity in tropical and subtropical zones of the world's oceans, although in the arctic and subarctic
There are a lot of them in the waters. Most sponges are inhabitants of shallow depths (up to 500 m). The number of deep-sea sponges is small, although they were found at the bottom of the deepest abyssal depressions (up to 11 km). Sponges settle mainly on rocky soils, which is due to the way they feed. . Most deep-sea sponges have a flint skeleton
- strong, but fragile, in shallow-water sponges - massive or elastic
(horny sponges). By filtering huge amounts of water through the body, sponges are
powerful biofilters. By doing this, they help purify water from mechanical
and organic pollution.
Sponges often cohabit with other organisms, and in some cases this
cohabitation has the character of simple commensalism (tenancy), in others
takes on the character of a mutually beneficial symbiosis. So, colonies of sea sponges
serve as a place of settlement for a large number of different organisms - annelids,
crustaceans, darters (echinoderms), etc. In turn, sponges often
settle on other animals, including mobile ones, for example on the shell
crabs, shells gastropods and so on. For some, especially
freshwater sponges, characterized by intracellular symbiosis with unicellular
green algae (zoochlorella), which serve as additional
source of oxygen. If the algae develops excessively, it is partially
digested by sponge cells.
Peculiar environmental group represent drilling sponges (genus Cliona).
Settled on a calcareous substrate (mollusk shells, coral colonies,
calcareous rocks, etc.), they form passages in it that open outward
small holes. Outgrowths of the sponge's body protrude through these holes,
bearing osculums. The mechanism of action of drilling jaws on the substrate is still
unclear Apparently, a significant role is played in the dissolution of lime.
carbon dioxide released by the sponge.
Practical significance There are not many sponges. IN southern countries there is a fishery
toilet sponges with a horny skeleton used for washing and
various technical purposes. They are caught in the Mediterranean and Red Seas,
Gulf of Mexico, Caribbean Sea, Indian Ocean, off the coast of Australia.
Fishing for glass sponges (mainly Eupectella) used in
as decorations and souvenirs, it also exists off the coast of Japan.

Coelenterates settle on a wide variety of soils, some of them are able to withstand significant changes in the salinity of sea water, and some species have even penetrated into fresh waters. Almost everywhere they play a very important role in the formation of communities of marine animals and plants - sea biocenoses.

The biological importance of coelenterates is great in food chains in the World Ocean. They are especially important in absorbing suspended organic matter and purifying sea water. The role of coral polyps in the calcium cycle in the biosphere and the formation of sedimentary rocks is great.

Coelenterates are commercial objects. Salted jellyfish are used as food. Their fishery is of local importance, mainly in Japan and China. The main commercial interest is from corals, from which jewelry and art objects are made. In addition, collecting coral polyps is now popular. Coral branches are sold as souvenirs. Red and black corals are especially prized. Jewelry is made from them. Coral limestones are an excellent building material. In addition, lime is obtained from them. Some hydroid polyps are harvested for biological purposes. active substances for medicine.

Coral polyps take part in the formation of the relief of the earth's surface. Other animals (echinoderms, mollusks, worms, fish - website note) settle in their “thickets” or on their surface. The skeleton of corals forms deposits of lime. Reefs make it difficult for ships to pass. Different kinds jellyfish, which are poisonous animals (crossfish, Portuguese man-of-war), can pose a danger to humans. The poison is the products of the activity of stinging cells. In China, some scyphoid jellyfish are hunted as food.

Marine coelenterates

With the exception of a few freshwater species, coelenterates live in the seas.

Coral polyps (Anthozoa) are colonial (less often solitary) marine organisms. The body ranges in length from a few millimeters to one meter and has six-ray or eight-ray symmetry. Due to the fact that fertilization in corals is internal, the planula larva develops in the intestinal cavity of the polyp, which forms eggs. There is no jellyfish stage. The oral opening is connected to the intestinal cavity by the pharynx. Polyps of one colony have a common intestinal cavity, and food obtained by one of the polyps becomes the property of the entire colony. About 6,000 species of coral polyps live in all seas with fairly high salinity; There are about 150 species in the northern and Far Eastern seas of Russia.

Some anemones without skeletons (sea anemones) provide a good example of symbiosis. They coexist with hermit crabs, living on their shells. The cancer feeds on the remains of the sea anemone's prey, and in return transfers it from place to place - to places more favorable for hunting. Another sea anemone is symbiotic with a clownfish. The bright fish, immune to the poison of the tentacles, lures enemies, and the sea anemone grabs them and eats them. Something goes to the clown too. Some sea anemones live (in aquariums) up to 50–80 years.

Some colonial polyps (such as madrepore corals) surround themselves with a massive calcareous skeleton. When a polyp dies, its skeleton remains. Colonies of polyps, growing over thousands of years, form coral reefs and entire islands. The largest of them, the Great Barrier Reef, stretches along the eastern coast of Australia for 2,300 km; its width ranges from 2 to 150 km. Reefs in their distribution areas (warm and salty waters with a temperature of 20–23 °C) are a serious obstacle to navigation. Coral branches are used as decorations.

Hydroid. Photo: Derek Keats

Coral reefs are unique ecosystems in which a huge number of other animals find shelter: mollusks, worms, echinoderms, fish. During the Ice Age, coral reefs fringed many islands. Then the sea level began to rise, and the polyps average speed centimeter per year they built up their reefs. Gradually, the island itself disappeared under water, and in its place a shallow lagoon surrounded by reefs formed. The wind brought plant seeds to them. Then animals appeared and the island turned into a coral atoll.

Jellyfish

Not all coelenterates live at the bottom; many of them are able to swim in the water column. These include jellyfish. The body of the jellyfish is gelatinous, similar in shape to an umbrella. There is a mouth in the middle of its lower side. Tentacles are located along the edges of the body. The jellyfish moves in the water, sharply contracting its umbrella. In this case, the water is thrown out, and the jellyfish receives a jet push and moves with its convex side forward.

Like all coelenterates, jellyfish are predators. They kill prey with stinging cells. If you come into contact with a jellyfish while swimming, you can get quite sensitive burns. In the Black Sea, you should beware of the cornerota jellyfish, whose translucent whitish umbrella reaches the size of a soccer ball and has bright purple or blue edges. Another Black Sea jellyfish, the flat pink aurelia, is completely harmless. Jellyfish can reach quite large sizes. At the very large jellyfish- cyanea, living in the Arctic seas, the umbrella sometimes exceeds 2 m in diameter, and the tentacles extend almost 30 m.

Purple or horse anemone - Actinia equine (L.) is a beautiful, flower-like animal, a representative of the coelenterates. The height of the purple sea anemone is 2-3 cm and is almost equal to its width. There are 192 tentacles arranged in six rows on the oral disk of the sea anemone. Sea anemones are painted bright red and are very beautiful. In a calm manner top part bordered by a crown of delicate, slightly colored tentacles.

In the coastal waters of Crimea and other areas of the Black Sea, it settles near the shores on stones and shells. It is found from the water's edge to a depth of 30 m. Firmly attached with its sole to the ground, this active predator with its numerous tentacles catches prey swimming nearby - small crustaceans, mollusk larvae and other small animals. Having caught prey, the sea anemone transfers it with its tentacles to the center of the corolla, where the mouth opening is located. Well-fed sea anemones do not straighten their tentacles and can remain in a “compressed” state for a long time.

Reproduction begins in spring and ends by summer. Anemones are dioecious, although cases of hermaphroditism occur. Fertilization can be either internal or external. The purple sea anemone is characterized by viviparity. The juveniles develop in the female's body cavity, from which small sea anemones emerge.
Although the sea anemone leads an attached lifestyle, it can move slowly if necessary. The forward movement is carried out using a dense sole. Part of it, separating from the substrate, is pushed forward and secured, after which the rest of the sole is pulled up.

Some people with high individual susceptibility may feel a burn when coming into contact with sea anemones, but it is mild and does not pose a danger to swimmers.

The importance of coelenterates in nature

Coelenterates live almost everywhere: the surface and depths of the oceans, freshwater bodies, various soils, polar regions and the tropics.

Coelenterates:

participate in the formation of sea biocenoses;
increase the biological productivity of water bodies;
absorb in large quantities suspended organic matter and purified sea water For example, the freshwater hydra is a natural filtrate, purifying the water from organic particles, the coral sea anemone polyp feeds on bacteria, algae, and protozoa in the water, performing the function of a filtrate.

Coelenterates are a necessary link in food chains in the World Ocean. They regulate the number of fish and crustaceans. Coral polyps take part in the calcium cycle in nature and also form sedimentary rocks.

In nature, you can observe amazing symbioses of coelenterates with other organisms.

Example 1

“Cohabitation” of a hermit crab and an adamsia sea anemone. The sea anemone uses the crayfish for movement, receiving food particles from the sand agitated by the crayfish, as well as its food remains. In the person of Adamsia, the hermit crab receives reliable protection from enemies. When changing houses, the crayfish transfers the sea anemone to a new location. Often hermit crabs take Adamsia from their relatives.

Example 2

Symbiosis of sea anemones and clown fish, or amphiprions. The fish clean the sea anemone from food debris and debris and take care of it. The sea anemone eats what is left of the clown fish's prey.

Small shrimps can act as parasites and cleaners. They hide from their enemies in the tentacles of sea anemones. Jellyfish have complex relationships with other organisms in nature.

For example, the body of golden jellyfish is inhabited by the algae zooxanthella, which gives the jellyfish a yellowish color. The algae use the waste products of the jellyfish as food, and the jellyfish also provides uniform lighting. What benefits algae bring to jellyfish is not completely clear.

Example 3

The larvae of jellyfish cunoctantus and jellyfish kunina attach to the umbrella of other jellyfish, where they reproduce by budding. These jellyfish take food directly from the host’s stomach with their tentacles.

Colonial polyps form coral reefs in shallow waters in tropical seas. Islands of tropical seas - atolls - are formed from ring-shaped reefs. Symbiont algae live in coral polyps.

The importance of coelenterates in human life

Representatives of coelenterates are commercial objects. Salted jellyfish Rhopilema verrucosa and Rhopilema esculenta are used as food (fishing occurs mainly in China and Japan). The poisonous tentacles of jellyfish are first removed, then they are salted and dried. Dried jellyfish are used in salads, fried with the addition of cinnamon, pepper, nutmeg, and boiled.

All kinds of art and jewelry are made from coral polyps. Coral branches are used as souvenirs. The most valuable are black and red corals; expensive jewelry is made from them. Nowadays, coral collecting is becoming popular.

Coral limestone is good building material, lime is obtained from it. In medicine, hydroid polyps and jellyfish are used

for the purpose of obtaining biologically active substances;
as laboratory animals when conducting experiments.

Note 1

Based on the ability of jellyfish to foretell the onset of a storm, the Jellyfish Ear device was created to indicate the approach of a storm, earthquake or storm.

Underwater reserves are often created on coral reefs. Present and Negative influence coelenterates, for example,

coral polyps form reefs that prevent free movement ships;
The venom of some jellyfish is dangerous for humans, for example, the venom of stinging cells Portuguese man-of-war, living in tropical seas, causes not only severe burns, but also disturbances in the rhythm of breathing, heart function, and severe pain; cyanea and sea wasp are dangerous for residents of the northern regions;
jellyfish and polyps eat fish fry, causing damage to fisheries.

Environment-formers of biocenoses of coral reefs and atolls.

Formers of calcareous rocks.

They gave rise to the first three-layered animals.

They are a link in the food chain of aquatic biocenoses,

Some people eat (aurelium and rapilleme) and use them as decorations.

Some are poisonous and dangerous to humans and animals (jellyfish cross, cornet, etc.).

New concepts and terms: radial symmetry, ectoderm, endoderm, mesoglea, intestinal cavity, ganglion, stinging cells, diffuse nervous system, cavity digestion, statocyst, rhopalia, budding, regeneration, planula, jet propulsion

Questions for consolidation:

What are the differences between Unicellular and Multicellular animals? Why are they combined into one kingdom?
What are the advantages of Multicellular animals over Unicellular animals? What are the disadvantages?
How does the hydra reflex work? Can the release of a stinging thread be attributed to reflexes? Explain your answer.
What types of digestion do coelenterates have, and by what cells are they carried out?
What cells are characteristic only of coelenterates, what are the features of their structure and function?
What life forms are found in coelenterates, and how do generations alternate?
Why are corals sometimes mistaken for plants and called “sea flowers”? In what fundamental differences Coral polyps from a plant organism.

Type Flatworms

Initial level of knowledge:

Response Plan:

general characteristics Flatworms

External and internal structure Flatworms

Reproduction of Flatworms

Classification of Flatworms, variety of species

Peculiarities of the structure and development of worms of the Ciliate class using the example of the Milk planaria

Features of the structure and development of worms of the class Flukes using the example of the Liver fluke

Features of the structure and development of worms of the Tapeworm class using the example of the Bull tapeworm and others.

General characteristics of flatworms

Number of species: about 25 thousand.

Habitat: They live everywhere in humid environments, including the tissues and organs of other animals.

Structure: Flatworms are the first multicellular animals in which, during the course of evolution, bilateral symmetry, three-layer structure, and real organs and tissues appeared.

Bilateral (two-sided) symmetry means that an imaginary axis of symmetry can be drawn through the animal’s body, with the right side of the body being a mirror image of the left.

During embryonic development in three-layered animals, three layers of cells are laid down: the outer one is the ectoderm, the middle one is the mesoderm, and the inner one is the endoderm. From each layer certain organs and tissues develop:

the skin (epithelium) and the nervous system are formed from the ectoderm;

from the mesoderm - muscle and connective tissue, reproductive tissue, excretory system;

from endoderm - digestive system.

In flatworms, the body is flattened in the dorso-abdominal direction, there is no body cavity, the space between internal organs filled with mesoderm cells (parenchyma).

The digestive system includes the mouth, pharynx and intestines. Absorption of food and excretion of undigested residues occurs through the mouth. Tapeworms have a completely absent digestive system; they absorb nutrients over the entire surface of the body, being in the intestines of the host.

Excretory organs – protonephridia. They consist of thin branching tubules, at one end of which there are star-shaped fiery cells embedded in the parenchyma. A bunch of cilia (flickering flame) extends inside these cells, the movement of which resembles the flickering of a flame (hence the name of the cells). Flame cells capture liquid decay products from the parenchyma, and cilia drive them into the tubule. The tubules open on the surface of the body as an excretory pore, through which waste products are removed from the body.

Nervous system of the scalene type (orthogonal). It is formed by a large head paired nerve ganglion (ganglion) and six nerve trunks extending from it: two on the ventral side, two on the dorsal and two on the sides. The nerve trunks are connected to each other by jumpers. Nerves extend from the ganglion and trunks to organs and skin.

Reproduction and development:

Flatworms are hermaphrodites. Sex cells mature in the sex glands (gonads). A hermaphrodite has both male glands - testes, and female glands - ovaries. Fertilization is internal, usually cross-fertilization, i.e. worms exchange seminal fluid.

Class Ciliated Worms

Milk planaria, a small aquatic animal, the adult is ~25 mm long and ~6 mm wide, with a flat, milky white body. At the front end of the body there are two eyes that distinguish light from darkness, as well as a pair of tentacles (chemical sense organs) necessary for searching for food. Planarians move, on the one hand, thanks to the work of the cilia covering their skin, and on the other hand, thanks to the contraction of the muscles of the skin-muscular sac. The space between the muscles and internal organs is filled with parenchyma, in which there are intermediate cells responsible for regeneration and asexual reproduction.

Planarians are predators that feed on small animals. The mouth is located on the ventral side, closer to the middle of the body, from it comes a muscular pharynx, from which three branches of a closed intestine extend. Having captured the victim, the planaria sucks out its contents with its throat. Digestion occurs in the intestines under the action of enzymes (intestinal), and intestinal cells are able to capture and digest pieces of food (intracellular digestion). Undigested food remains are removed through the mouth.

Reproduction and development. Ciliated animals are hermaphrodites. Cross fertilization. Fertilized eggs fall into a cocoon, which the worm lays on underwater objects. Development is direct.

Class Flukes

The fluke feeds on blood and liver cells, sucking food through the oral sucker with the help of a muscular pharynx and esophagus, from there the food enters the branched, blindly closed intestine.

Rice. Development of the liver fluke:

Class Tapeworms

Bull tapeworm – tapeworm, reaches a length from 4 to 12 meters. The body includes a head with suckers, a neck and a strobila - a band of segments. The youngest segments are located at the neck, the oldest are sacs filled with eggs, located at the posterior end, where they come off one by one.

Reproduction and development. The bovine tapeworm is a hermaphrodite: each of its segments has one ovary and many testes. Both cross-fertilization and self-fertilization are observed. The posterior segments, filled with mature eggs, open and are excreted with feces. Large cattle(intermediate host) can swallow eggs along with grass; in the stomach, microscopic larvae with six hooks emerge from the eggs, which enter the blood through the intestinal wall and are carried throughout the animal’s body and carried into the muscles. Here the six-hooked larva grows and turns into a finna - a vesicle, inside which is the head of the tapeworm with a neck. A person can become infected with finches by eating undercooked or undercooked meat from an infected animal. In the human stomach, a head emerges from the finca and attaches to the intestinal wall. New segments bud from the neck - the worm grows. Bull tapeworm secretes toxic substances, which cause intestinal disorders and anemia in humans.

Development pork tapeworm has a similar character, its intermediate host, in addition to pigs and wild boars, can also be humans, then finches develop in its muscles.

The development of the wide tapeworm is accompanied by a change of two intermediate hosts: the first is a crustacean (Cyclops), the second is a fish that has eaten the crustacean. The definitive host may be a person or a predator that eats the infected fish.

New concepts and terms: mesoderm, skin-muscle sac, tegument, hypodermis, reduction, protonephridia (flame cells), orthogon, strobila, ganglion, gonads, hermaphrodite, direct and indirect development, final and intermediate host, miracidium, cercaria, finna, segment, armed and unarmed tapeworm.

Type Roundworms

Initial level of knowledge:

Response Plan:

General characteristics of Roundworms

Body structure of human roundworm

Reproduction and development of human roundworm

Classification of Roundworms, variety of species

The significance of Roundworms in nature and human life

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