In favorable conditions, hydras can live for years, decades and centuries, without aging or losing fertility.

We meet hydras back in school: on the one hand, hydra was the name of the mythical monster that appears in one of the labors of Hercules, on the other hand, the same name is given to tiny coelenterates that live in freshwater bodies of water. Their body size is only 1-2 cm, outwardly they look like tubes with tentacles at one end; but despite small sizes and a sedentary lifestyle, they are still predators who, with the help of tentacles and the stinging cells in them, immobilize and grab prey - creatures even smaller than the hydras themselves.

Hydra Hydra vulgaris with budding clone. (Photo by Konrad Wothe/Minden Pictures/Corbis.)

Hydra company viridissima. (Photo by Albert Lleal/Minden Pictures/Corbis.)

However, they have one feature that is mentioned in any biology textbook. We're talking about extremely developed ability to regeneration: Hydra can restore any part of its body thanks to a huge supply of pluripotent stem cells. Such cells are capable of endlessly dividing and giving rise to all types of tissues, all varieties of other cells. But when stem cell in the process of differentiation it becomes muscle, or nervous, or something else, it stops dividing. And humans have such “omnipotent” stem cells only in the early stages embryonic development, and then their supply is quickly exhausted; instead of them, other, more specialized stem cells appear, which can also divide many times, but they already belong to some separate tissues. Hydra is luckier; with her, “almighty” stem cells remain for life.

But how long does a hydra live? If she is capable of constantly renewing herself, does it follow that she is immortal? It is known that even stem cells, which are present in adult humans and animals, gradually age and thereby contribute to the overall aging of the body. Could it be that hydra is unfamiliar with aging? James Whopal ( James W. Vaupel) from the Max Planck Institute for Demographic Research and his colleagues argue that this is so. In an article in a magazine PNAS The authors of the work describe the results of a long-term experiment with 2,256 hydras “in the leading roles.” The animals grew up in the laboratory and in almost ideal conditions: everyone had their own area, no shortage of food and regular, three times a week, replacement of water in the aquarium.

Aging is most easily noticed by increasing mortality (that is, a young population will die less often than an old one) and a decrease in fertility. However, over eight years of observation, nothing like this happened. The mortality rate was constant throughout and was approximately one case per 167 individuals per year, regardless of age. (Among the inhabitants of the laboratory there were 41-year-old specimens, which, however, were clones, that is, biologically they were much older, but as a separate individual they were observed only in the last few years.) Fertility - in addition to asexual self-cloning, hydras also have sexual reproduction- also remained constant for 80%. For the remaining 20%, it either increased or decreased, which was probably due to changes in living conditions - after all, even in the laboratory some factors remain unaccounted for.

Of course, in natural conditions, with predators, diseases and other environmental troubles, hydras are unlikely to fully enjoy eternal youth and immortality. However, by themselves, they obviously do not really age and, as a result, do not die. It is possible that there are other organisms on Earth with the same amazing property, but if we continue to try to unravel the biological mystery of aging - and its absence - hydra still remains the most convenient object of study.

Two years ago, the same James Whopal and his colleagues published in Nature an article that talked about the connection between aging and life expectancy. It turned out that in many species mortality does not change at all with age, and in some the likelihood of dying young is even higher. Hydra was also present in that work: according to calculations, even after 1,400 years, 5% of hydras in a laboratory aquarium will remain alive (the rest will simply die evenly over such a more than impressive period). As you can see, in general, the results with these coelenterates turned out to be so interesting that they have now made another separate article about them.

From this article you will learn everything about the structure of freshwater hydra, its lifestyle, nutrition, and reproduction.

External structure of the hydra

Polyp (meaning "many-legged") hydra is a tiny translucent creature that lives in clear clear waters slow-flowing rivers, lakes, ponds. This coelenterate animal leads a sedentary or sedentary lifestyle. The external structure of freshwater hydra is very simple. The body has an almost regular cylindrical shape. At one of its ends there is a mouth, which is surrounded by a crown of many long thin tentacles (from five to twelve). At the other end of the body there is a sole, with the help of which the animal is able to attach to various subjects under the water. The body length of freshwater hydra is up to 7 mm, but the tentacles can greatly stretch and reach a length of several centimeters.

Radiation symmetry

Let's take a closer look external structure hydra. The table will help you remember their purpose.

The body of the hydra, like many other animals leading an attached lifestyle, is characterized by What is it? If you imagine a hydra and draw an imaginary axis along its body, then the animal’s tentacles will diverge from the axis in all directions, like the rays of the sun.

The structure of the hydra's body is dictated by its lifestyle. It attaches itself to an underwater object with its sole, hangs down and begins to sway, exploring the surrounding space with the help of tentacles. The animal is hunting. Since the hydra lies in wait for prey, which can appear from any direction, the symmetrical radial arrangement of the tentacles is optimal.

Intestinal cavity

Let's look at the internal structure of the hydra in more detail. The hydra's body looks like an oblong sac. Its walls consist of two layers of cells, between which there is an intercellular substance (mesoglea). Thus, there is an intestinal (gastric) cavity inside the body. Food enters it through the mouth opening. It is interesting that the hydra, which is in this moment does not eat, there is practically no mouth. The ectoderm cells close and grow together in the same way as on the rest of the body surface. Therefore, every time before eating, the hydra has to break through its mouth again.

The structure of the freshwater hydra allows it to change its place of residence. There is a narrow opening on the sole of the animal - the aboral pore. Through it, liquid and a small bubble of gas can be released from the intestinal cavity. With the help of this mechanism, the hydra is able to detach from the substrate and float to the surface of the water. In this simple way, with the help of currents, it spreads throughout the reservoir.

Ectoderm

The internal structure of the hydra is represented by ectoderm and endoderm. The ectoderm is called the body-forming hydra. If you look at an animal under a microscope, you can see that the ectoderm includes several types of cells: stinging, intermediate and epithelial-muscular.

The most large group- skin-muscle cells. They touch each other with their sides and form the surface of the animal’s body. Each such cell has a base - a contractile muscle fiber. This mechanism provides the ability to move.

When all fibers contract, the animal’s body contracts, lengthens, and bends. And if the contraction occurs on only one side of the body, then the hydra bends. Thanks to this work of cells, the animal can move in two ways - “tumbling” and “stepping”.

Also in the outer layer are star-shaped nerve cells. They have long processes, with the help of which they come into contact with each other, forming a single network - nerve plexus, entwining the entire body of the hydra. Nerve cells also connect with skin and muscle cells.

Between the epithelial-muscle cells there are groups of small, round-shaped intermediate cells with large nuclei and a small amount of cytoplasm. If the hydra's body is damaged, the intermediate cells begin to grow and divide. They can turn into any

Stinging cells

The structure of hydra cells is very interesting; the stinging (nettle) cells with which the entire body of the animal, especially the tentacles, are strewn deserve special mention. have a complex structure. In addition to the nucleus and cytoplasm, the cell contains a bubble-shaped stinging chamber, inside which there is a thin stinging thread rolled into a tube.

A sensitive hair emerges from the cell. If prey or an enemy touches this hair, the stinging thread sharply straightens and is thrown out. The sharp tip pierces the victim’s body, and poison flows through the channel running inside the thread, which can kill a small animal.

Typically, many stinging cells are triggered. The hydra grabs prey with its tentacles, pulls it to its mouth and swallows it. The poison secreted by the stinging cells also serves for protection. Larger predators do not touch the painfully stinging hydras. The venom of the hydra is similar in effect to the poison of nettles.

Stinging cells can also be divided into several types. Some threads inject poison, others wrap around the victim, and others stick to it. After triggering, the stinging cell dies, and a new one is formed from the intermediate one.

Endoderm

The structure of hydra also implies the presence of such a structure as the inner layer of cells, endoderm. These cells also have muscle contractile fibers. Their main purpose is to digest food. Endoderm cells secrete digestive juices directly into the intestinal cavity. Under its influence, the prey is split into particles. Some endoderm cells have long flagella that are constantly in motion. Their role is to pull food particles towards the cells, which in turn release pseudopods and capture food.

Digestion continues inside the cell and is therefore called intracellular. Food is processed in vacuoles, and undigested remains are thrown out through the mouth. Breathing and excretion occurs through the entire surface of the body. Let's look again cellular structure hydra. The table will help you do this clearly.

Reflexes

The structure of the hydra is such that it is able to sense temperature changes, chemical composition water, as well as touch and other irritants. The nerve cells of an animal are capable of being excited. For example, if you touch it with the tip of a needle, the signal from the nerve cells that sensed the touch will be transmitted to the rest, and from the nerve cells to the epithelial-muscular cells. The skin-muscle cells will react and contract, the hydra will shrink into a ball.

Such a reaction is bright. It is a complex phenomenon consisting of successive stages - perception of the stimulus, transfer of excitation and response. The structure of the hydra is very simple, therefore the reflexes are monotonous.

Regeneration

The cellular structure of the hydra allows this tiny animal to regenerate. As mentioned above, intermediate cells located on the surface of the body can transform into any other type.

With any damage to the body, the intermediate cells begin to divide, grow very quickly and replace the missing parts. The wound is healing. The regenerative abilities of the hydra are so high that if you cut it in half, one part will grow new tentacles and a mouth, and the other will grow a stem and sole.

Asexual reproduction

Hydra can reproduce both asexually and sexually. Under favorable conditions in summer time A small tubercle appears on the animal’s body, the wall protrudes. Over time, the tubercle grows and stretches. Tentacles appear at its end and a mouth breaks through.

Thus, a young hydra appears, connected to the mother’s body by a stalk. This process is called budding because it is similar to the development of a new shoot in plants. When a young hydra is ready to live on its own, it buds off. The daughter and mother organisms attach to the substrate with tentacles and stretch into different sides until they separate.

Sexual reproduction

When it starts to get cold and creates unfavourable conditions, the turn of sexual reproduction begins. In the fall, hydras begin to form sex cells, male and female, from the intermediate ones, that is, egg cells and sperm. The egg cells of hydras are similar to amoebas. They are large and strewn with pseudopods. Sperm are similar to the simplest flagellates; they are able to swim with the help of a flagellum and leave the body of the hydra.

After the sperm penetrates the egg cell, their nuclei fuse and fertilization occurs. The pseudopods of the fertilized egg retract, it becomes rounded, and the shell becomes thicker. An egg is formed.

All hydras die in the fall, with the onset of cold weather. The mother's body disintegrates, but the egg remains alive and overwinters. In the spring it begins to actively divide, the cells are arranged in two layers. With the coming warm weather the small hydra breaks through the shell of the egg and begins independent life.

In lakes, rivers or ponds with clean, clear water, attached animals that look like frayed twine are often found on the roots of duckweed, stems and leaves of other aquatic plants. This Hydras. Externally, Hydras look like small translucent brownish or greenish stems with a corolla tentacles at the free end of the body. Hydra is a freshwater polyp (“polyp” means “multipede”).

Hydras are radially symmetrical animals. Their body is in the form of a bag measuring from 1 to 3 cm (and the body usually does not exceed 5-7 mm in length, but the tentacles can stretch several centimeters). At one end of the body there is sole, used for attachment to underwater objects, on the opposite - oral hole, surrounded by long tentacles(5-12 tentacles). In our reservoirs, Hydra can be found from the beginning of June to the end of September.

Lifestyle. Hydras – predatory animals. They catch prey with the help of tentacles, on which they are located in huge numbers stinging cells. When you touch the tentacles, long threads containing strong toxins. Killed animals are pulled by tentacles to the mouth opening and swallowed. Hydra swallows small animals whole. If the victim is somewhat larger than the Hydra itself, it can also swallow it. At the same time, the predator’s mouth opens wide, and the walls of the body are greatly stretched. If the prey does not fit entirely into the gastric cavity, the Hydra swallows only one end of it, pushing the victim deeper and deeper as it is digested. Undigested food remains are also removed through the mouth. Hydras prefer daphnia (water fleas), but they can also eat other crustaceans, ciliates, various insect larvae and even small tadpoles and fry. A moderate daily diet is one daphnia.

Hydras usually lead a motionless lifestyle, but can crawl from place to place, sliding on their soles or tumbling over their heads. They always move in the direction of the light. When irritated, animals are able to shrink into a ball, which may also help them with bowel movements.

Body structure. The Hydra's body consists of two layers of cells. These are the so-called two-layer animals. The outer layer of cells is called ectoderm, and the inner layer – endoderm (endoderm). Between the ectoderm and endoderm there is a layer of structureless mass - mesoglea. Mesoglea sea ​​jellyfish makes up up to 80% of body weight, and in Hydra the mesoglea is not large and is called supporting record.

Genus Hydra - Hydra

Inside the Hydra's body is gastric cavity (intestinal cavity), opening outward with one single hole ( oral hole).

IN endoderm are located epithelial-muscle and glandular cells. These cells line the intestinal cavity. The main function of the endoderm is digestive. Epithelial-muscle cells, with the help of flagella facing the intestinal cavity, push food particles, and with the help of pseudopods they capture them and pull them inside. Food is digested in these cells. Glandular cells produce enzymes that break down proteins. The digestive juice of these cells enters the intestinal cavity, where digestion processes also occur. Thus, Hydra has two types of digestion: intracavitary(extracellular), characteristic of other multicellular animals, and intracellular(characteristic of unicellular and lower multicellular organisms).

In the ectoderm Hydra has epithelial-muscular, nerve, stinging and intermediate cells. Epithelial-muscle (cover) cells cover the body of the Hydra. Each of them has a long process elongated parallel to the surface of the body, in the cytoplasm of which there are developed contractile fiber. The combination of such processes forms a layer of muscular formations. When the fibers of all epithelial muscle cells contract, the Hydra's body contracts. If the fibers contract on only one side of the body, then the Hydra bends in that direction. Thanks to the work of muscle fibers, Hydra can slowly move from place to place, alternately “stepping” with its sole and tentacles.

Stinging or nettle cells There are especially many tentacles in the ectoderm. Inside these cells is capsule with a poisonous liquid and a coiled tubular a thread. On the surface of stinging cells there is sensitive hair. These cells serve as Hydra's weapons of attack and defense. When prey or an enemy touches a sensitive hair, the stinging capsule instantly throws the thread out. The poisonous liquid, entering the thread, and then through the thread into the animal’s body, paralyzes or kills it. Stinging cells die after a single use and are replaced by new ones formed by intermediate cells.

Intermediate cells small, round, with large nuclei and a small amount of cytoplasm. When the Hydra's body is damaged, they begin to rapidly grow and divide. Epithelial-muscular, nerve, germ and other cells can be formed from intermediate cells.

Nerve cells scattered under the integumentary epithelial-muscular cells, and they are stellate in shape. The processes of nerve cells communicate with each other, forming a nerve plexus that thickens around the mouth and on the sole.

Genus Hydra - Hydra

This type of nervous system is called diffuse- the most primitive in the animal world. Some of the nerve processes approach the skin-muscle cells. The processes are capable of perceiving various irritations (light, heat, mechanical influences), as a result of which excitation develops in the nerve cells, which is transmitted through them to all parts of the body and animal and causes an appropriate response.

Thus, Hydra and other Coelenterates have real fabrics, although little differentiated - ectoderm and endoderm. Appears nervous system.

Hydra does not have special respiratory organs. Oxygen dissolved in water penetrates the hydra through the entire surface of the body. Hydra also has no excretory organs. The end products of metabolism are excreted through the ectoderm. Sense organs are not developed. The sense of touch is carried out over the entire surface of the body, the tentacles (sensitive hairs) are especially sensitive, throwing out stinging threads that kill or paralyze prey.

Reproduction. How does Hydra reproduce? asexual, so sexual way. During the summer it reproduces asexually - budding. In the middle part of the Hydra's body there is a budding belt on which tubercles are formed ( kidneys). The bud grows, a mouth and tentacles form at its apex, after which the bud thins out at the base, separates from the body of the mother and begins to live independently. This resembles the development of a plant shoot from a bud - hence the name of this method of propagation.

In autumn, with the approach of cold weather, sex cells are formed from intermediate cells in the ectoderm of Hydra - spermatozoa And eggs. Stalked Hydras dioecious, and their fertilization cross. The egg cells are located closer to the base of the Hydra and are similar to an amoeba, and the sperm are similar to flagellated protozoa and develop in tubercles located closer to the mouth opening. The sperm has a long flagellum, with which it swims in water and reaches the eggs, and then merges with them. Fertilization occurs inside the body of the mother. The fertilized egg begins to divide, becomes covered with a dense double shell, sinks to the bottom and overwinters there. Late autumn The hydras are dying. And in the spring, a new generation develops from overwintered eggs.

Regeneration. When the body is damaged, cells located near the wound begin to grow and divide, and the wound quickly closes (heals). This process is called regeneration. Regeneration occurs in many animals, and humans also have it. But not a single animal can compare with Hydra in this matter. Perhaps the hydra got its name precisely for this property (see the second labor of Hercules).

Lernaean Hydra (Second Labor of Hercules)

After the first feat, King Eurystheus sent Hercules to kill the Lernaean hydra. It was a monster with the body of a snake and nine heads of a dragon. The hydra lived in a swamp near the city of Lerna and, crawling out of its lair, destroyed entire herds and devastated the entire surrounding area. The fight with the nine-headed hydra was dangerous because one of its heads was immortal. Hercules set off on a journey to Lerna with his friend Iolaus. Arriving at a swamp near the city of Lerna, Hercules left Iolaus with his chariot in a nearby grove, and he himself went to look for the hydra. He found her in a cave surrounded by a swamp. Having heated his arrows red-hot, Hercules began to shoot them one after another into the hydra. The arrows of Hercules enraged the Hydra. She crawled out, wriggling a body covered with shiny scales, from the darkness of the cave, rose menacingly on her huge tail and was about to rush at the hero, but the son of Zeus stepped on her torso with his foot and pressed her to the ground. The hydra wrapped its tail around the legs of Hercules and tried to knock him down. Like an unshakable rock, stood The hero, with swings of his heavy club, knocked down the heads of the hydra one after another. The club whistled in the air like a whirlwind; The hydra's heads flew off, but the hydra was still alive. Then Hercules noticed that in the hydra, in place of each knocked-down head, two new ones grew. Help for the hydra also appeared. A monstrous cancer crawled out of the swamp and dug its claws into Hercules’ leg. Then the hero called Iolaus for help. Iolaus killed the monstrous cancer, set fire to part of the nearby grove and, with burning tree trunks, burned the hydra's necks, from which Hercules knocked off the heads with his club. The hydra has stopped growing new heads. She resisted the son of Zeus weaker and weaker. Finally, the immortal head flew off the hydra. The monstrous hydra was defeated and fell dead to the ground. The victor Hercules buried her immortal head deeply and piled a huge rock on it so that it could not come out into the light again.

If we talk about the real Hydra, then its ability to regenerate is even more incredible! A new animal can grow from 1/200 of a Hydra; in fact, a whole organism is restored from the pulp. Therefore, Hydra regeneration is often called an additional method of reproduction.

Meaning. Hydras are a favorite subject for studying regeneration processes. In nature, Hydra is an element of biological diversity. In the structure of the ecosystem, Hydra, as a predatory animal, acts as a second-order consumer. No animal simply wants to feed on Hydra itself.

Questions for self-control.

Name the systematic position of Hydra.

Where does Hydra live?

What body structure does Hydra have?

How does Hydra eat?

How does Hydra excrete waste products?

How does Hydra reproduce?

What is the significance of Hydra in nature?

Genus Hydra - Hydra

Rice. The structure of Hydra.

A - longitudinal section (1 - tentacles, 2 - ectoderm, 3 - endoderm, 4 - gastric cavity, 5 - mouth, 6 - testis, 7 - ovary and developing zygote).

B - cross-section (1 - ectoderm, 2 - endoderm, 3 - gastric cavity, 4, 5 - stinging cells, 6 - nerve cell, 7 - glandular cell, 8 - supporting plate).

B - nervous system. G - epithelial muscle cell. D - stinging cells (1 - in a dormant state, 2 - with a discarded thread; the nuclei are painted black).

Genus Hydra - Hydra

Rice. Hydra breeding.

From left to right: Hydra with male gonads, Hydra with female gonads, Hydra during budding.

Rice. Hydra movement.

Hydras move, attaching to the substrate either with the sole or with a mouth cone with tentacles.

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

A bright representative of hydroids - 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 each 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, providing “eternal youth” to the polyp, prompted German scientists to search 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 hydra's body or make it longer; for this they have muscle fibers.

2. Digestive-muscular cells are located in endoderm. They are adapted to phagocytosis, capture and mix food particles that enter the gastric cavity, for which each cell is equipped with several flagella. In general, flagella and pseudopods help food penetrate from the intestinal cavity into the cytoplasm of hydra cells. Thus, her digestion occurs 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 prey captured by its tentacles. The stinging cell contains a capsule with a poisonous stinging thread; on the outside there is a sensitive hair, which, after irritation, gives a signal to “shoot”. The life of a stinging cell is short-lived: after being “shot” by a thread, it dies.

4. Nerve cells, together with shoots similar to stars, lie in ectoderm, under a layer of epithelial-muscle cells. Their greatest concentration is at the sole and tentacles. When exposed to any impact, the hydra reacts, which is an unconditional reflex. The polyp also has such a property as irritability. Let us also remember that the “umbrella” of a jellyfish is bordered by a cluster of nerve cells, and the body contains ganglia.

5. Glandular cells release a sticky substance. They are located in endoderm and promote food digestion.

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 epithelial-muscular) or reproductive cells, and ensure the regeneration of the hydra. There are hydras that do not have intermediate cells (hence, stinging, nerve and reproductive cells), capable of asexual reproduction.

7. Sex cells develop into ectoderm. The egg cell of the freshwater hydra is equipped with pseudopods, with which it captures neighboring cells along with their nutrients. Among the hydras there is 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 over the entire surface of the body.

2. Circulatory system not formed.

3. Hydras eat larvae of aquatic insects, various small invertebrates, and crustaceans (daphnia, cyclops). Undigested food remains, like other coelenterates, are removed back through the mouth.

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

The body shape of the hydra is tubular. The mouth opening of these animals is covered with tentacles. Hydras live in water, and with their stinging tentacles they kill and bring prey to their mouths.

   Type - Coelenterates
   Class - Hydroid
   Genus/Species - Hydra vulgaris, H.oligactis, etc.

   Basic data:
DIMENSIONS
Length: 6-15 mm.

REPRODUCTION
Vegetative: has a budding character. A bud appears on the body of the mother, from which the daughter gradually develops.
Sexual: Most species of hydra are dioecious. The gonads contain cells from which eggs develop. Sperm cells develop in the testis.

LIFESTYLE
Habits: live in fresh and brackish waters.
Food: plankton, fish fry, ciliates.
Lifespan: no data.

RELATED SPECIES
The phylum Coelenterata includes more than 9,000 species, some of them (15-20) live only in fresh waters.

   Freshwater hydras are one of the smallest predators. Despite this, they are able to provide themselves with food. Hydras have a tubular body shape. Using their soles, they attach themselves to underwater plants or rocks and move their tentacles in search of prey. Green hydras contain photosynthetic algae.

FOOD

   Hydra is a predatory animal that lives in water. It feeds on small organisms living in water, for example, ciliates, oligochaete worms, planktonic crustaceans, water fleas, insects and their larvae, and fish fry. A hydra that hunts attaches itself to an aquatic plant, branch or leaf and hangs on it. Her tentacles are very wide open. They constantly make circular searching movements. If one of them touches the victim, others rush towards it. Hydra paralyzes prey with stinging cell venom. The hydra uses its tentacles to pull its paralyzed prey towards its mouth. She swallows small animals whole. If the prey is larger than the hydra, the predator opens its mouth wide and the walls of its body stretch. If such prey is so large that it does not fit into the gastric cavity, then the hydra swallows only part of it and, to the extent of digestion, pushes the victim deeper and deeper.

LIFESTYLE

   Hydras live alone. However, in places that are particularly rich in food, several hydras hunt at once. This happens because the water current brings a lot of food to a certain place. Hydras of the Nuiga genus prefer fresh water. These animals were discovered by the researcher who invented the microscope, A. Leeuwenhoek (1632-1723). Another scientist, G. Tremblay, discovered that hydras easily restore lost body parts. An inconspicuous tubular body, crowned with tentacles that grow around the mouth opening, and a sole at the end of the body are the main features of the hydra's appearance. The gastric cavity of this animal is continuous. The tentacles are hollow. The body walls consist of two layers of cells. There are glandular cells located in the middle part of the hydra's body. Different kinds very similar to each other. They differ mainly in color (and, as a consequence, different colors talk about some structural feature). Bright green hydras have symbiotic algae living in their bodies. Hydras react to light and swim towards it. These animals are sedentary. They spend most of their lives in an attached state, waiting for prey. With the sole, like a suction cup, hydras are firmly attached to plants.

REPRODUCTION

   Hydras reproduce in two ways - sexual and vegetative. Vegetative propagation is represented by budding. When suitable external conditions Several buds develop on the hydra's body. At the very beginning, the bud looks like a small mound, later miniature tentacles appear at its outer end. The tentacles grow and stinging cells appear on them. The lower part of the body of the daughter individual becomes thinner, the hydra's mouth opens, the young individual branches off and begins an independent life. These animals reproduce by budding in warm time of the year. With the onset of autumn, hydras begin sexual reproduction. Sex cells are formed in the gonads. The gonad cracks and an egg emerges. Around the same time, sperm are formed in the testes of other hydras. They also leave the gonad and swim in the water. One of them fertilizes the egg. An embryo develops in the egg. Protected by a double shell, it overwinters at the bottom. In the spring, a fully formed hydra emerges from the egg.
  

DID YOU KNOW THAT...

• Hydra does not age, since every cell in its body is renewed after a few weeks. This animal lives only in the warm season. With the beginning of winter, all adult hydras die. Only their eggs, protected by a strong double shell - the embryotheca, can survive the winter.
• Hydras easily restore their lost limbs. The scientist G. Tremblay (1710-1784), as a result of his numerous experiments, obtained a seven-headed polyp, from which severed heads grew back. He looked like mythical creature- Lernaean Hydra defeated by the hero ancient Greece- Hercules.
• During constant movements in the water, the hydra performs quite original acrobatic tricks.

  

CHARACTERISTIC FEATURES OF HYDRA

   Tentacles: the mouth opening is surrounded by a corolla with 5-12 tentacles with stinging cells. With their help, the animal paralyzes its prey and pulls it into its mouth. A hydra that hunts attaches itself to a hard surface and, spreading its tentacles widely, makes circular searching movements with them.
   Body: body shape is tubular. At the anterior end is a mouth opening surrounded by tentacles. The aboral pore is located in the middle of the sole. The hydra wall consists of two layers of cells. Digestive processes take place in the midsection of the body.
   Mouth opening: covered with a corolla of tentacles. With its tentacles, the hydra pulls the animal into its mouth and swallows it.
   Leg: The rear end of the hydra is narrowed - this is a leg that has a sole at the end.
   Gonads: are formed in the ectoderm and have the appearance of tubercles. Sex cells accumulate in them.
   Dome: length about 13 mm. This is for self-defense. The hydra rises and forms a dense dome.
   Bud: vegetative propagation Hydra has a budding character. Several buds may appear on the body at the same time. The buds are growing quickly.

PLACES OF ACCOMMODATION
Freshwater hydras live in fresh and brackish waters. They inhabit rivers, lakes, swamps and other bodies of water. The most common species are the common and brown hydra.
PRESERVATION
Each species of genus living on certain territory. These days they are not in danger of extinction.