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The structure of the freshwater hydra. Appearance, movement and nutrition of freshwater hydra. Inner layer of cells - hydra endoderm

The freshwater hydra is an amazing creature that is not easy to spot due to its microscopic size. Hydra belongs to the type of intestinal cavities.

The habitat of this small predator is rivers overgrown with vegetation, dams, lakes without strong currents. The easiest way to observe a freshwater polyp is through a magnifying glass.

It is enough to take water with duckweed from the reservoir and let it stand for a while: soon you will be able to see oblong "wires" of white or brown color 1-3 centimeters in size. This is how the hydra is depicted in the drawings. This is what a freshwater hydra looks like.

Structure

The body of the hydra has a tubular shape. It is represented by two types of cells - ectoderm and endoderm. Between them is the intercellular substance - mesoglea.

In the upper part of the body, you can see the mouth opening, framed by several tentacles.

On the opposite side of the "tube" is the sole. Thanks to the suction cup, attachment to stems, leaves and other surfaces occurs.

Hydra ectoderm

The ectoderm is the outer part of the body cells of an animal. These cells are essential for the life and development of the animal.

The ectoderm is made up of several types of cells. Among them:

  • skin-muscle cells they help the body move and squirm. When the cells contract, the animal shrinks or, on the contrary, stretches. A simple mechanism helps the hydra to move freely under the cover of water with the help of “tumbles” and “steps”;
  • stinging cells - they cover the walls of the body of the animal, but most of them are concentrated in the tentacles. As soon as small prey swims next to the hydra, it tries to touch it with its tentacles. At this moment, stinging cells release "hairs" with poison. Paralyzing the victim, the hydra draws it to the mouth opening and swallows it. This simple scheme allows you to easily get food. After such work, stinging cells self-destruct, and new ones appear in their place;
  • nerve cells. The outer shell of the body is represented by star-shaped cells. They are interconnected, forming a chain of nerve fibers. This is how the nervous system of the animal is formed;
  • sex cells actively grow in the autumn. They are egg (female) germ cells and spermatozoa. The eggs are located near the mouth opening. They grow rapidly, consuming nearby cells. Spermatozoa, after maturation, leave the body and swim in the water;
  • intermediate cells. they serve as a protective mechanism: when the animal's body is damaged, these invisible "defenders" begin to actively multiply and heal the wound.

Hydra endoderm

Endoderm helps hydra digest food. Cells line the digestive tract. They capture food particles, delivering it to the vacuoles. Digestive juice secreted by glandular cells processes useful substances necessary for the body.

What does a hydra breathe

Freshwater hydra breathes on the outer surface of the body, through which the oxygen necessary for its life functions enters.

In addition, vacuoles are also involved in the process of respiration.

Reproduction features

In the warm season, hydras reproduce by budding. This is an asexual way of reproduction. In this case, a growth forms on the body of the individual, which increases in size over time. From the "kidney" tentacles grow, and a mouth is formed.

In the process of budding, a new creature is separated from the body and goes into free swimming.

In the cold period of time, hydras reproduce only sexually. In the body of an animal, eggs and spermatozoa mature. Male cells, leaving the body, fertilize the eggs of other hydras.

After the function of reproduction, adults die, and the fruit of their creation is zygotes, covered with a dense "dome" in order to survive the harsh winter. In the spring, the zygote actively divides, grows, and then breaks through the shell and begins an independent life.

What does hydra eat

Hydra nutrition is characterized by a diet consisting of miniature inhabitants of reservoirs - ciliates, water fleas, planktonic crustaceans, insects, fish fry, worms.

If the victim is small, the hydra swallows it whole. If the prey is large, the predator is able to open its mouth wide, and significantly stretch the body.

Hydra regeneration

G Hydra has a unique ability: it does not age. Each cell of the animal is updated in a couple of weeks. Even having lost a part of the body, the polyp is able to grow exactly the same, restoring symmetry.

The hydra, cut in half, does not die: a new creature grows from each part.

The biological significance of freshwater hydra

Freshwater hydra is an indispensable element in the food chain. This unique animal plays an important role in the cleansing of water bodies, regulating the population of its other inhabitants.

Hydras are a valuable object of study for scientists in biology, medicine and science.

freshwater hydra- extremely unwanted settlers in the aquarium where they are kept shrimps. Unfavorable conditions can cause hydra breeding, a hydra regeneration from the smallest remains of her body makes her almost immortal and indestructible. But, nevertheless, there are effective methods of dealing with hydra.

What is a hydra?

Hydra(hydra) - freshwater polyp, ranging in size from 1 to 20 mm. Its body is a stem-leg, with which it attaches to any surfaces in the aquarium: glass, soil, snags, plants, and even snail egg laying. Inside the body of the hydra - the main organ that makes up its essence - the stomach. Why essence? Because her womb is insatiable. The long tentacles crowning the body of the hydra are in constant motion, capturing numerous small, sometimes invisible to the eye, living creatures from the water, bringing it to the mouth, which ends the body of the hydra.

In addition to the insatiable belly in the hydra, her ability to recover is frightening. Like , she can recreate herself from any piece of her body. For example, hydra can regenerate from cells left after rubbing it through mill gas (such a finely porous mesh). So rubbing it on the walls of the aquarium is useless.

The most common types of hydras in domestic reservoirs and aquariums:

- common hydra(Hydra vulgaris) - the body expands in the direction from the sole to the tentacles, which are twice as long as the body;

- hydra thin(Hydra attennata) - the body is thin, of uniform thickness, the tentacles are slightly longer than the body;

- hydra longstemmed(Hydra oligactis, Pelmatohydra) - the body is in the form of a long stem, and the tentacles exceed the body length by 2-5 times;

- hydra green(Hydra viridissima, Chlorohydra) is a small hydra with short tentacles, whose body color is provided by unicellular chlorella algae living in symbiosis with it (that is, inside it).

Hydra breed by budding (asexual variant) or by fertilization of an egg by a spermatozoon, as a result of which an “egg” is formed in the body of the hydra, which, after the death of an adult, waits in the wings in the ground or moss.

Generally hydra- an amazing creature. And if it were not for the obvious threat on her part to the small inhabitants of the aquarium, she could be admired. So, for example, scientists have been studying hydra for a long time, and new discoveries not only amaze them, but also make an invaluable contribution to the development of new medicines for humans. Thus, the hydramacin-1 protein was found in the body of the hydra, which has a wide spectrum of action against gram-positive and gram-negative pathogenic bacteria.

What does hydra eat?

Hydra hunts for small invertebrates: cyclops, daphnia, oligochaetes, rotifers, trematode larvae. In her death-bearing "paws" can please fish fry or young shrimp. The body and tentacles of the hydra are covered stinging cells, on the surface of which there is a sensitive hair. When it is irritated by a passing victim, a stinging thread is thrown out of the stinging cells, entangling the victim, piercing into it and letting out poison. Maybe hydra sting a snail crawling by or a shrimp swimming past. The ejection of the thread and the launch of the poison occur instantly and take about 3 ms in time. I myself have repeatedly seen how a shrimp that accidentally landed in a hydra colony bounced off like scalded. Numerous "shots" and, accordingly, large doses of poison can adversely affect adult shrimp or snails.

Where does the hydra come from in the aquarium?

There are many ways to bring hydra into an aquarium. With any object of natural origin, immersed in an aquarium, you can host this "infection". You will not even be able to establish the very fact of introducing eggs or microscopic hydras (remember, at the beginning of the article, their size is from 1 mm) with soil, snags, plants, live food, or even milligrams of water in which shrimp, snails or fish were purchased. Even with the apparent absence of hydras in the aquarium, they can be detected by examining any section of driftwood or stone under a microscope.

The impetus for their rapid reproduction, in fact, when hydra become visible to the aquarist, there is an overabundance of organic matter in the aquarium water. Personally, I found them in my aquarium after overfeeding. Then the wall closest to the lamp (I don’t have fluorescent lamps, but a table lamp) was covered with a “carpet” of hydras, which in appearance belong to the “thin hydra” species.

How to kill a hydra?

Hydra bothers many aquarists, or rather, the inhabitants of their aquariums. On the forum website the theme of "Hydra in the shrimp" has already been brought up three times. Having studied the reviews on the fight against hydra in the vast domestic and foreign Internet, I have collected the most effective (if you know more, supplement) methods for destroying hydra in an aquarium. After reading them, I think everyone will be able to choose the most appropriate method in his situation.

So. Of course, you always want to destroy uninvited guests without harming other inhabitants of the aquarium, primarily shrimp, fish and expensive snails. Therefore, salvation from hydras is mainly sought among biological methods.

Firstly, the hydra also has enemies that eat it. These are some fish: black molly, swordtails, from labyrinths - gourami, cockerels. They feed on hydra and large pond snails. And if the first option is not suitable for a shrimp because of the threat from fish to shrimp, especially young ones, then the option with a snail is very suitable, only you need to take snails from a trusted source, and not from a reservoir in order to avoid introducing another infection into the aquarium.

Interestingly, Wikipedia refers to creatures capable of eating and digesting hydra tissue as turbellarians, which include planaria. Hydras and planarians, like "Tamara and I go together", really often find themselves in the aquarium at the same time. But for planarians to eat hydras, aquarists are silent about such observations, although I have read about this more.

Hydra also serve as the main diet for the cladoceran crustacean Anchistropus emarginatus. Although his other relatives - daphnia - hydras themselves are not averse to swallowing.

VIDEO: hydra tries to eat daphnia:

Used to fight the hydra and its love of light. It is noticed that hydra is located closer to the light source, moving to that place with steps from foot to head and from head to foot. Inventive aquarists came up with a peculiar hydra trap. A piece of glass is tightly leaning against the wall of the aquarium, and a light source (lamp or lantern) is directed to that place in the dark. As a result, during the night the hydras move to a glass trap, which is then pulled out of the water and doused with boiling water. This remedy can rather be called control over the number of hydras, since this method does not give complete disposal of hydras.

Poorly tolerated hydra and elevated temperature. The method of heating the water in the aquarium is useful if it is possible to catch all the inhabitants of the aquarium valuable to you and transplant them into another container. The water temperature in the aquarium is brought to 42 ° C and kept for 20-30 minutes, turning off the external filter or removing the filler from the internal filter. Then the water is allowed to cool or diluted with hot settled cold water. After that, the living creatures are returned home. Most plants tolerate this procedure well.

Remove hydra and safe if dosages are observed 3% hydrogen peroxide. However, to achieve the desired effect, a solution of hydrogen peroxide at the rate of 40 ml per 100 liters of water must be infused daily for a week. Shrimps and fish tolerate this procedure well, but plants do not.

Of the radical measures - the use of chemistry. For the destruction of hydra, drugs are used, the active substance of which is fenbendazole: Panakur, Febtal, Flubenol, Flubentazole, Ptero Aquasan Planacid and many others. Such drugs are used in veterinary medicine for the treatment of helminthic invasions in animals, so you need to look for them in pet stores and veterinary pharmacies. However, you should pay attention to the fact that the composition of the drug does not include copper or other active substance in addition to fenbendazole, otherwise the shrimp will not survive such treatment. The preparations are available in powder or in tablets, which must be crushed into powder and try to dissolve as much as possible, you can use a brush, in a separate container with water collected from the aquarium. Fenbendazole dissolves poorly, so the resulting suspension, when poured into the aquarium, will give cloudy water and sediment on the ground and on objects in the aquarium. Undissolved particles of the medicine can eat up shrimp, but this is not scary. After 3 days, it is necessary to change the water by 30-50%. According to aquarists, this method is quite effective against hydras, but snails do not tolerate it well, and besides, biobalance in the aquarium may be disturbed after therapy.

When applying any of the above methods, it is necessary to pay special attention to the organic purity in the aquarium: do not overfeed the inhabitants, exclude feeding invertebrates with daphnia or brine shrimp, do water changes on time.

Added on 01/05/19: Dear fellow hobbyists, the author of this article did not test the effect of the preparations indicated in the article on shrimp that are sensitive to changes in water parameters (Sulawesi shrimp, Taiwan bee, Tigerbee). Based on this, the proportions indicated in the article, as well as the use of drugs itself, can be detrimental to your shrimp. As soon as the necessary and verified information on the use of the preparations given in the article in aquariums with Sulawesi, Taiwan bee, Tigerbee shrimp is collected, we will definitely make adjustments to the material presented.

P.s. It is a pity that at the moment there are no veterinary clinics that aquarists could contact. Indeed, today every family has pets, and their owners, at least once, could use the services of a veterinary clinic. Imagine a competent veterinarian treating your aquarium pet - it's a pity that these are only dreams!

Hydra biology description internal structure photo lifestyle nutrition reproduction protection from enemies

Latin name Hydrida

To characterize the structure of a hydroid polyp, one can use as an example freshwater hydras, which retain very primitive features of organization.

External and internal structure

Hydra have an elongated, sac-like body that can stretch quite strongly and shrink almost into a spherical lump. A mouth is placed at one end; this end is called the mouth or oral pole. The mouth is located on a small elevation - the oral cone, surrounded by tentacles that can stretch and shorten very strongly. In the extended state, the tentacles are several times the length of the hydra's body. The number of tentacles is different: they can be from 5 to 8, and some hydras have more. In hydra, a central gastric, somewhat more expanded section is distinguished, turning into a narrowed stalk ending in a sole. With the help of the sole, the hydra is attached to the stems and leaves of aquatic plants. The sole is located at the end of the body, which is called the aboral pole (opposite to the mouth, or oral).

The wall of the body of the hydra consists of two layers of cells - ectoderm and endoderm, separated by a thin basal membrane, and limits the only cavity - the gastric cavity, which opens outward with a mouth opening.

In hydras and other hydroids, the ectoderm is in contact with the endoderm along the very edge of the mouth opening. In freshwater hydras, the gastric cavity continues into hollow tentacles inside, and their walls are also formed by ectoderm and endoderm.

The ectoderm and endoderm of the hydra consist of a large number of cells of various types. The main mass of cells of both the ectoderm and endoderm are epithelial-muscular cells. Their outer cylindrical part is similar to ordinary epithelial cells, and the base, adjacent to the basal membrane, is elongated spindle-shaped and represents two contractile muscular processes. In the ectoderm, the contractile muscular processes of these cells are elongated in the direction of the longitudinal axis of the hydra body. Their contractions cause shortening of the body and tentacles. In the endoderm, the muscular processes are elongated in an annular direction, across the axis of the body. Their contraction has the opposite effect: the body of the hydra and its tentacles narrow and lengthen at the same time. Thus, the muscle fibers of the epithelial-muscular cells of the ectoderm and endoderm, opposite in their action, make up the entire musculature of the hydra.

Among the epithelial-muscular cells, various stinging cells are located either singly or, more often, in groups. The same type of hydra, as a rule, has several types of stinging cells that perform different functions.

The most interesting are stinging cells with nettle properties, called penetrants. These cells throw out a long thread when stimulated, which pierces the body of the prey. The stinging cells are usually pear-shaped. A stinging capsule is placed inside the cell, covered with a lid on top. The wall of the capsule continues inward, forming a neck, which passes further into a hollow thread, coiled into a spiral and closed at the end. At the point of transition of the neck into the thread, there are three spines inside, folded together and forming a stylet. In addition, the neck and stinging thread are seated inside with small spines. On the surface of the stinging cell there is a special sensitive hair - knidocil, with the slightest irritation of which the stinging thread is ejected. First, the lid opens, the neck is twisted, and the stylet sticks into the cover of the victim, and the spikes that make up the stylet move apart and widen the hole. Through this hole, the eversible thread pierces the body. Inside the stinging capsule contains substances that have nettle properties and paralyze or kill prey. Once fired, a stinging thread cannot be used again by a hydroid. Such cells usually die and are replaced by new ones.

Another kind of stinging cells of hydra are volvents. They do not have nettle properties, and the threads they throw out serve to hold prey. They wrap around the hairs and bristles of crustaceans, etc. The third group of stinging cells are glutinants. They throw out sticky threads. These cells are important both in holding prey and in moving the hydra. The stinging cells are usually, especially on the tentacles, arranged in groups - "batteries".

In the ectoderm there are small undifferentiated cells, the so-called interstitial cells, due to which many types of cells develop, mainly stinging and sex cells. Interstitial cells are often located in groups at the base of epithelial-muscular cells.

The perception of stimuli in hydra is associated with the presence in the ectoderm of sensitive cells that serve as receptors. These are narrow, tall cells with a hair on the outside. Deeper, in the ectoderm, closer to the base of the skin-muscle cells, there are nerve cells equipped with processes, with the help of which they contact each other, as well as with receptor cells and contractile fibers of the skin-muscle cells. Nerve cells are scattered in the depths of the ectoderm, forming with their processes a plexus in the form of a mesh, and this plexus is denser on the perioral cone, at the base of the tentacles and on the sole.

The ectoderm also contains glandular cells that secrete adhesive substances. They are concentrated on the sole and on the tentacles, helping the hydra to temporarily attach to the substrate.

Thus, in the ectoderm of the hydra there are cells of the following types: epithelial-muscular, stinging, interstitial, nervous, sensitive, glandular.

The endoderm has less differentiation of cellular elements. If the main functions of the ectoderm are protective and motor, then the main function of the endoderm is digestive. In accordance with this, most of the endoderm cells consist of epithelial-muscular cells. These cells are equipped with 2-5 flagella (usually two), and are also able to form pseudopodia on the surface, capture them, and then digest food particles. In addition to these cells, the endoderm contains special glandular cells that secrete digestive enzymes. In the endoderm there are also nerve and sensory cells, but in much smaller numbers than in the ectoderm.

Thus, several types of cells are also represented in the endoderm: epithelial-muscular, glandular, nervous, and sensitive.

Hydras do not always remain attached to the substrate, they can move from one place to another in a very peculiar way. Most often, hydras move “walking”, like moth caterpillars: the hydra tilts its oral pole to the object on which it sits, sticks to it with its tentacles, then the sole comes off the substrate, pulls up to the oral end and reattaches. Sometimes the hydra, having attached its tentacles to the substrate, raises the stem with the sole up and immediately brings it to the opposite side, as if “tumbling”.

Hydra Power

Hydras are predators, they sometimes feed on rather large prey: crustaceans, insect larvae, worms, etc. With the help of stinging cells, they capture, paralyze and kill prey. Then the victim is pulled by tentacles to a highly extensible mouth opening and moves into the gastric cavity. In this case, the gastric part of the body swells strongly.

Digestion of food in hydra, unlike sponges, only partially occurs intracellularly. This is due to the transition to predation and the capture of rather large prey. The secret of the glandular cells of the endoderm is secreted into the gastric cavity, under the influence of which the food softens and turns into gruel. Small food particles are then captured by the digestive cells of the endoderm, and the digestion process is completed intracellularly. Thus, for the first time in hydroids, intracellular or cavitary digestion occurs, which occurs simultaneously with more primitive intracellular digestion.

Protection from enemies

Hydra nettle cells not only infect prey, but also protect the hydra from enemies, causing burns to predators attacking it. And yet there are animals that feed on hydras. Such, for example, are some ciliary worms and especially Microstomum lineare, some gastropod molluscs (pond snails), Corethra mosquito larvae, etc.

Hydra's ability to regenerate is very high. Experiments conducted by Tremblay as early as 1740 showed that pieces of the hydra's body, cut into several dozen pieces, regenerate into a whole hydra. However, a high regenerative capacity is characteristic not only of hydras, but also of many other intestinal cavities.

reproduction

Hydras reproduce in two ways - asexual and sexual.

Asexual reproduction of hydras occurs by budding. Under natural conditions, hydra budding occurs throughout the summer period. Under laboratory conditions, hydra budding is observed with fairly intensive nutrition and a temperature of 16-20 ° C. Small swellings form on the body of the hydra - buds, which are a protrusion of the ectoderm and endoderm. In them, due to multiplying cells, further growth of the ectoderm and endoderm occurs. The kidney increases in size, its cavity communicates with the gastric cavity of the mother. At the free, outer end of the kidney, tentacles and a mouth opening finally form.

Soon, the formed young hydra is separated from the mother.

Sexual reproduction of hydras in nature is usually observed in autumn, and in laboratory conditions it can be observed with malnutrition and temperatures below 15-16 ° C. Some hydras are dioecious (Relmatohydra oligactis), others are hermaphrodites (Chlorohydra viridissima).

Sex glands - gonads - arise in hydra in the form of tubercles in the ectoderm. In hermaphroditic forms, male and female gonads are formed in different places. The testes develop closer to the oral pole, while the ovaries develop closer to the aboral. The testicles produce a large number of motile spermatozoa. Only one egg matures in the female gonad. In hermaphroditic forms, the maturation of spermatozoa precedes the maturation of eggs, which ensures cross-fertilization and excludes the possibility of self-fertilization. The eggs are fertilized in the body of the mother. A fertilized egg puts on a shell and hibernates in this state. Hydras, after the development of reproductive products, as a rule, die, and in the spring a new generation of hydras comes out of the eggs.

Thus, in freshwater hydras, under natural conditions, there is a seasonal change in the forms of reproduction: throughout the summer, hydras intensively bud, and in the fall (for central Russia - in the second half of August), with a decrease in temperature in water bodies and a decrease in the amount of food, they stop breeding. budding and proceed to sexual reproduction. In winter, hydras die, and only fertilized eggs overwinter, from which young hydras emerge in spring.

The hydra also includes the freshwater polyp Polypodium hydriforme. The early stages of development of this polyp take place in the eggs of sterlets and cause great harm to them. Several types of hydra are found in our reservoirs: stalked hydra (Pelmatohydra oligactis), common hydra (Hydra vulgaris), green hydra (Chlorohydra viridissima) and some others.

To the class hydroid include invertebrate aquatic cnidarians. In their life cycle, two forms are often present, replacing each other: a polyp and a jellyfish. Hydroids can gather in colonies, but single individuals are not uncommon. Traces of hydroids are found even in the Precambrian layers, however, due to the extreme fragility of their bodies, the search is very difficult.

A bright representative of hydroid - freshwater hydra, single polyp. Its body has a sole, a stalk, and long tentacles relative to the stalk. She moves like a rhythmic gymnast - with every step she makes a bridge and somersaults over her "head". Hydra is widely used in laboratory experiments, its ability to regenerate and high activity of stem cells, which provides "eternal youth" to the polyp, prompted German scientists to search for and study the "immortality gene".

Hydra cell types

1. Epithelial-muscular cells form the outer covers, that is, they are the basis ectoderm. The function of these cells is to shorten the body of the hydra or make it longer, for this they have a muscle fiber.

2. Digestive-muscular cells are located in endoderm. They are adapted to phagocytosis, capture and mix food particles that have entered the gastric cavity, for which each cell is equipped with several flagella. In general, flagella and pseudopods help food to penetrate from the intestinal cavity into the cytoplasm of hydra cells. Thus, her digestion goes in two ways: intracavitary (for this there is a set of enzymes) and intracellular.

3. stinging cells located primarily on the tentacles. They are multifunctional. Firstly, the hydra defends itself with their help - a fish that wants to eat the hydra is burned with poison and throws it away. Secondly, the hydra paralyzes the prey captured by the tentacles. The stinging cell contains a capsule with a poisonous stinging thread, a sensitive hair is located outside, which, after irritation, gives a signal to “shoot”. The life of a stinging cell is fleeting: after a “shot” with a thread, it dies.

4. Nerve cells, together with processes similar to stars, lie in ectoderm, under a layer of epithelial-muscular cells. Their greatest concentration is at the sole and tentacles. With any impact, the hydra reacts, which is an unconditioned reflex. The polyp also has such a property as irritability. Recall also that the “umbrella” of a jellyfish is bordered by a cluster of nerve cells, and ganglia are located in the body.

5. glandular cells secrete a sticky substance. They are located in endoderm and aid in the digestion of food.

6. intermediate cells- round, very small and undifferentiated - lie in ectoderm. These stem cells divide endlessly, are capable of transforming into any other, somatic (except for epithelial-muscular) or sex cells, and ensure the regeneration of hydra. There are hydras that do not have intermediate cells (hence, stinging, nervous and sexual), capable of asexual reproduction.

7. sex cells develop in ectoderm. The egg cell of freshwater hydra is equipped with pseudopods, with which it captures neighboring cells along with their nutrients. Found among hydras hermaphroditism when eggs and sperm are formed in the same individual, but at different times.

Other features of freshwater hydra

1. Hydras do not have a respiratory system; they breathe the entire surface of the body.

2. The circulatory system is not formed.

3. Hydra feed on larvae of aquatic insects, various small invertebrates, crustaceans (daphnia, cyclops). Undigested food residues, like other coelenterates, are removed back through the mouth opening.

4. Hydra is capable of regeneration for which intermediate cells are responsible. Even cut into fragments, the hydra completes the necessary organs and turns into several new individuals.

The body of the hydra has the form of 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 serving as a support.

The ectoderm forms the covering of the animal's body and consists of several types of cells: epithelial-muscular, intermediate and stinging.

The most numerous of them are epithelial-muscular.

ectoderm

epithelial muscle cell

at the expense muscle fibers, lying at the base of each cell, the body of the hydra can contract, lengthen and bend.

Between the epithelial-muscular cells are groups of small, rounded cells with large nuclei and a small amount of cytoplasm, called intermediate.

When the body of the hydra is damaged, they begin to grow intensively and divide. They can turn into other types of hydra body cells, except for epithelial-muscular ones.

In the ectoderm are stinging cells used 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 thread is coiled.

The structure of a stinging cell with a coiled stinging filament

If the prey or the enemy touches the sensitive hair, which is located outside the stinging cell, in response to irritation, the stinging thread is thrown out and pierces the victim's body.

The structure of the stinging cell with ejected stinging thread

Through the channel of the thread, a substance capable of paralyzing the victim enters the body of the victim.

There are several types of stinging cells. The threads of some pierce the skin of animals and inject poison into their bodies. The threads of others wrap around prey. The threads of the third are very sticky and stick to the victim. Usually the hydra "shoots" several stinging cells. After the shot, the stinging cell dies. New stinging cells are formed from intermediate.

The structure of the inner layer of cells

The endoderm lines the entire intestinal cavity from the inside. Its composition includes digestive-muscular and glandular cells.

Endoderm

Digestive system

There are more digestive-muscular cells than others. Muscular fibers they are capable of contraction. When they shorten, the hydra's body becomes thinner. Complex movements (movement by "tumbling") occur due to contractions of the muscle fibers of the cells of the ectoderm and endoderm.

Each of the digestive-muscular cells of the endoderm has 1-3 flagella. wavering flagella create a current of water, with which food particles are adjusted to the cells. Digestive-muscular cells of the endoderm are able to form pseudopods, capture and digest small food particles in the digestive vacuoles.

The structure of the digestive muscle cell

Glandular cells in the endoderm secrete digestive juice into the intestinal cavity, which liquefies and partially digests food.

The structure of the yellow cell

Prey is captured by tentacles with the help of stinging cells, the poison of which quickly paralyzes small victims. With coordinated movements of the tentacles, the prey is brought to the mouth, and then, with the help of contractions of the body, the hydra is "put on" the victim. Digestion begins in the intestinal cavity ( abdominal digestion), ends inside the digestive vacuoles of the epithelial-muscular cells of the endoderm ( intracellular digestion). Nutrients are distributed throughout the hydra's body.

When the remains of the prey that cannot be digested and the waste products of cellular metabolism are in the digestive cavity, it contracts and is emptied.

Breath

Hydra breathes oxygen dissolved in water. She has no respiratory organs, and she absorbs oxygen with the entire surface of the body.

Circulatory system

Is absent.

Selection

The release of carbon dioxide and other unnecessary substances formed in the process of life is carried out from the cells of the outer layer directly into the water, and from the cells of the inner layer - into the intestinal cavity, then out.

Nervous system

Under the skin-muscle cells are stellate cells. These are nerve cells (1). They are interconnected and form a nervous network (2).

Nervous system and irritability of hydra

If you touch the hydra (2), then excitation (electrical impulses) occurs in the nerve cells, which instantly spreads throughout the entire nervous network (3) and causes contraction of the skin-muscle cells and the entire body of the hydra shortens (4). The response of the hydra organism to such irritation is unconditioned reflex.

sex cells

With the approach of cold weather in autumn, germ cells form from intermediate cells in the hydra ectoderm.

There are two types of germ cells: egg, or female germ cells, and sperm, or male germ cells.

The eggs are closer to the base of the hydra, the spermatozoa develop in tubercles located closer to the mouth.

egg cell Hydra looks like an amoeba. It is equipped with pseudopods and grows rapidly, absorbing adjacent intermediate cells.

Hydra egg cell structure

Hydra sperm structure

spermatozoa in appearance they resemble flagellated protozoa. They leave the body of the hydra and swim with the help of a long flagellum.

Fertilization. reproduction

The spermatozoon swims up to the hydra with the egg cell and penetrates into it, and the nuclei of both germ cells merge. After that, the pseudopods are retracted, the cell is rounded, a thick shell is released on its surface - an egg is formed. When the hydra dies and collapses, the egg remains alive and falls to the bottom. With the onset of warm weather, a living cell inside the protective shell begins to divide, the resulting cells are arranged in two layers. A small hydra develops from them, which comes out through a rupture of the egg shell. Thus, the multicellular animal hydra at the beginning of its life consists of only one cell - the egg. This suggests that the ancestors of the hydra were single-celled animals.

Hydra asexual reproduction

Under favorable conditions, hydra reproduces asexually. A kidney forms on the body of the animal (usually in the lower third of the body), it grows, then tentacles form and the mouth breaks through. The young hydra buds from the mother's organism (while the maternal and daughter polyps are attached with tentacles to the substrate and pulled in different directions) and leads an independent lifestyle. In autumn, the hydra switches to sexual reproduction. On the body, in the ectoderm, gonads are laid - sex glands, and germ cells develop from intermediate cells in them. With the formation of gonadal hydra, a medusoid nodule is formed. This suggests that the Hydra gonads are greatly simplified sporosacs, the last stage in the transformation of the lost medusoid generation into an organ. Most species of hydra are dioecious, hermaphroditism is less common. Hydra eggs grow rapidly, phagocytizing surrounding cells. Mature eggs reach a diameter of 0.5-1 mm. Fertilization occurs in the body of the hydra: through a special hole in the gonad, the sperm enters the egg and merges with it. The zygote undergoes complete uniform crushing, as a result of which a coeloblastula is formed. Then, as a result of mixed delamination (a combination of immigration and delamination), gastrulation occurs. Around the embryo, a dense protective shell (embryotheca) with spiny outgrowths is formed. At the gastrula stage, the embryos fall into anabiosis. Adult hydras die, and the embryos sink to the bottom and hibernate. In the spring, development continues, in the parenchyma of the endoderm, an intestinal cavity is formed by divergence of cells, then the rudiments of tentacles are formed, and a young hydra emerges from under the shell. Thus, unlike most marine hydroids, the hydra does not have free-swimming larvae, its development is direct.

Regeneration

Hydra has a very high ability to regenerate. When cut across into several parts, each part restores the "head" and "leg", retaining the original polarity - the mouth and tentacles develop on the side that was closer to the oral end of the body, and the stalk and sole - on the aboral side of the fragment. The whole organism can be restored from separate small pieces of the body (less than 1/100 of the volume), from pieces of tentacles, and also from a suspension of cells. At the same time, the regeneration process itself is not accompanied by an increase in cell divisions and is a typical example of morphallaxis.

Movement

In a calm state, the tentacles are extended by several centimeters. The animal slowly moves them from side to side, lying in wait for prey. If necessary, the hydra can move slowly.

"Walking" mode of locomotion

"Walking" method of movement of the hydra

Curving its body (1) and attaching its tentacles to the surface of an object (substrate), the hydra pulls the sole (2) to the front end of the body. Then the walking movement of the hydra is repeated (3.4).

"Tumbling" way of movement

"Tumbling" way to move the hydra

In another case, it seems to be somersaulting over its head, alternately attaching to objects either with tentacles or with a sole (1-5).