home Audience 2 The outer layer of the hydra. Hydroid class. Hydra cell types. Glandular cells of the endoderm

The outer layer of the hydra. Hydroid class. Hydra cell types. Glandular cells of the endoderm

Figure: Structure of freshwater hydra. Radial symmetry of Hydra

Habitat, structural features and vital functions of the freshwater hydra polyp

In lakes, rivers or ponds with clean, transparent water, a small translucent animal is found on the stems of aquatic plants - polyp hydra(“polyp” means “multi-legged”). This is an attached or sedentary coelenterate animal with numerous tentacles. The body of an ordinary hydra has an almost regular cylindrical shape. At one end is mouth, surrounded by a corolla of 5-12 thin long tentacles, the other end is elongated in the form of a stalk with sole at the end. Using the sole, the hydra is attached to various underwater objects. The body of the hydra, together with the stalk, is usually up to 7 mm long, but the tentacles can extend several centimeters.

Radial symmetry of Hydra

If you draw an imaginary axis along the body of the hydra, then its tentacles will diverge from this axis in all directions, like rays from a light source. Hanging down from some aquatic plant, the hydra constantly sways and slowly moves its tentacles, lying in wait for prey. Since the prey can appear from any direction, the tentacles arranged in a radial manner are best suited to this method of hunting.
Radiation symmetry is characteristic, as a rule, of animals leading an attached lifestyle.

Hydra intestinal cavity

The body of the hydra has the form of a sac, the walls of which consist of two layers of cells - the outer (ectoderm) and the inner (endoderm). Inside the body of the hydra there is intestinal cavity(hence the name of the type - coelenterates).

The outer layer of hydra cells is the ectoderm.

Figure: structure of the outer layer of cells - hydra ectoderm

The outer layer of hydra cells is called - ectoderm. Under a microscope, several types of cells are visible in the outer layer of the hydra - the ectoderm. Most of all here are skin-muscular. By touching their sides, these cells create the cover of the hydra. At the base of each such cell there is a contractile muscle fiber, which plays an important role in the movement of the animal. When everyone's fiber skin-muscular 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, the hydra can slowly move from place to place, alternately “stepping” with its sole and tentacles. This movement can be compared to a slow somersault over your head.
The outer layer contains and nerve cells. They have a star-shaped shape, as they are equipped with long processes.
The processes of neighboring nerve cells come into contact with each other and form nerve plexus, covering the entire body of the hydra. Some of the processes approach the skin-muscle cells.

Hydra irritability and reflexes

Hydra is able to sense touch, temperature changes, the appearance of various dissolved substances in water and other irritations. This causes her nerve cells to become excited. If you touch the hydra with a thin needle, then the excitement from irritation of one of the nerve cells is transmitted along the processes to other nerve cells, and from them to the skin-muscle cells. This causes muscle fibers to contract, and the hydra shrinks into a ball.

Picture: Hydra's irritability

In this example, we get acquainted with a complex phenomenon in the animal body - reflex. The reflex consists of three successive stages: perception of irritation, transfer of excitation from this irritation along the nerve cells and response body by any action. Due to the simplicity of the hydra's organization, its reflexes are very uniform. In the future we will become familiar with much more complex reflexes in more highly organized animals.

Hydra stinging cells

Pattern: Stringing or nettle cells of Hydra

The entire body of the hydra and especially its tentacles are seated with a large number stinging, or nettles cells. Each of these cells has a complex structure. In addition to the cytoplasm and nucleus, it contains a bubble-like stinging capsule, inside which a thin tube is folded - stinging thread. Sticking out of the cage sensitive hair. As soon as a crustacean, small fish or other small animal touches a sensitive hair, the stinging thread quickly straightens, its end is thrown out and pierces the victim. Through a channel passing inside the thread, poison enters the body of the prey from the stinging capsule, causing the death of small animals. As a rule, many stinging cells are fired at once. Then the hydra uses its tentacles to pull the prey to its mouth and swallows it. The stinging cells also serve the hydra for protection. Fish and aquatic insects do not eat hydras, which burn their enemies. The poison from the capsules is reminiscent of nettle poison in its effect on the body of large animals.

The inner layer of cells is the hydra endoderm

Figure: structure of the inner layer of cells - hydra endoderm

Inner layer of cells - endoderm A. The cells of the inner layer - the endoderm - have contractile muscle fibers, but the main role of these cells is to digest food. They secrete digestive juice into the intestinal cavity, under the influence of which the hydra’s prey softens and breaks down into small particles. Some of the cells of the inner layer are equipped with several long flagella (as in flagellated protozoa). The flagella are in constant motion and sweep particles towards the cells. The cells of the inner layer are capable of releasing pseudopods (like those of an amoeba) and capturing food with them. Further digestion occurs inside the cell, in vacuoles (like in protozoa). Undigested food remains are thrown out through the mouth.
The hydra has no special respiratory organs; oxygen dissolved in water penetrates the hydra through the entire surface of its body.

Hydra regeneration

The outer layer of the hydra's body also contains very small round cells with large nuclei. These cells are called intermediate. They play a very important role in the life of the hydra. With any damage to the body, intermediate cells located near the wounds begin to grow rapidly. From them, skin-muscle, nerve and other cells are formed, and the wounded area quickly heals.
If you cut a hydra crosswise, tentacles grow on one of its halves and a mouth appears, and a stalk appears on the other. You get two hydras.
The process of restoring lost or damaged body parts is called regeneration. Hydra has a highly developed ability to regenerate.
Regeneration, to one degree or another, is also characteristic of other animals and humans. Thus, in earthworms it is possible to regenerate a whole organism from their parts; in amphibians (frogs, newts) entire limbs, various parts of the eye, tail and internal organs can be restored. When a person is cut, the skin is restored.

Hydra reproduction

Asexual reproduction of hydra by budding

Figure: Hydra asexual reproduction by budding

Hydra reproduces asexually and sexually. In summer, a small tubercle appears on the hydra’s body - a protrusion of the wall of its body. This tubercle grows and stretches out. Tentacles appear at its end, and a mouth breaks out between them. This is how the young hydra develops, which at first remains connected to the mother with the help of a stalk. Outwardly, all this resembles the development of a plant shoot from a bud (hence the name of this phenomenon - budding). When the little hydra grows up, it separates from the mother’s body and begins to live independently.

Hydra sexual reproduction

By autumn, with the onset of unfavorable conditions, hydras die, but before that, sex cells develop in their body. There are two types of germ cells: ovoid, or female, and spermatozoa, or male reproductive cells. Sperm are similar to flagellated protozoa. They leave the hydra's body and swim using a long flagellum.

Figure: Hydra sexual reproduction

The hydra egg cell is similar to an amoeba and has pseudopods. The sperm swims up to the hydra with the egg cell and penetrates inside it, and the nuclei of both sex cells merge. Happening fertilization. After this, the pseudopods are retracted, the cell is rounded, and a thick shell is formed on its surface - a egg. At the end of autumn, the hydra dies, but the egg remains alive and falls to the bottom. In the spring, the fertilized egg begins to divide, the resulting cells are arranged in two layers. From them a small hydra develops, which, with the onset of warm weather, comes out through a break in the egg shell.
Thus, the multicellular animal hydra at the beginning of its life consists of one cell - an egg.

In ancient Greek myth, the Hydra was a multi-headed monster that grew two instead of a severed head. As it turns out, the real animal, named after this mythical beast, has biological immortality.

Freshwater hydras have remarkable regenerative abilities. Instead of repairing damaged cells, they are constantly replaced by stem cell division and partial differentiation.

Within five days, the hydra is almost completely renewed, which completely eliminates the aging process. The ability to replace even nerve cells is still considered unique in the animal world.

More one feature freshwater hydra is that a new individual can grow from separate parts. That is, if a hydra is divided into parts, then 1/200 of the mass of an adult hydra is enough for a new individual to grow from it.

What is hydra

Freshwater hydra (Hydra) is a genus of small freshwater animals of the phylum Cnidaria and class Hydrozoa. It is essentially a solitary, sedentary freshwater polyp that lives in temperate and tropical regions.

There are at least 5 species of the genus in Europe, including:

Hydra vulgaris (common freshwater species).
Hydra viridissima (also called Chlorohydra viridissima or green hydra, the green coloring comes from chlorella algae).

Hydra structure

Hydra has a tubular, radially symmetrical body up to 10 mm long, elongated, sticky leg at one end, called the basal disc. Omental cells in the basal disc secrete a sticky fluid, which explains its adhesive properties.

At the other end is a mouth opening surrounded by one to twelve thin mobile tentacles. Every tentacle dressed in highly specialized stinging cells. Upon contact with prey, these cells release neurotoxins that paralyze the prey.

The body of the freshwater hydra consists of three layers:

“outer shell” (ectodermal epidermis);
“inner lining” (endodermal gastroderma);
gelatinous supporting matrix called mesogloya, which is separated from the nerve cells.

The ectoderm and endoderm contain nerve cells. In the ectoderm, there are sensory or receptor cells that receive stimuli from the environment, such as the movement of water or chemical stimuli.

There are also ectodermal nettle capsules that are expelled, releasing paralyzing poison and, Thus, serve to capture prey. These capsules do not regenerate, so they can only be discarded once. Each tentacle contains from 2500 to 3500 nettle capsules.

Epithelial muscle cells form longitudinal muscle layers along the polypoid. By stimulating these cells, polyp may shrink quickly. The endoderm also contains muscle cells, they are called so because of their function, the absorption of nutrients. Unlike ectoderm muscle cells, they are arranged in a ring-like manner. This causes the polyp to stretch as the endodermal muscle cells contract.

The endodermal gastrodermis surrounds the so-called gastrointestinal cavity. Because the this cavity contains both the digestive tract and the vascular system, it is called the gastrovascular system. For this purpose, in addition to muscle cells in the endoderm, there are specialized gland cells that secrete digestive secretions.

In addition, the ectoderm also contains replacement cells, as well as endoderm, which can be transformed into other cells or produced, for example, sperm and eggs (most polyps are hermaphrodites).

Nervous system

Hydra has a nervous network, like all hollow animals (coelenterates), but it does not have coordination centers such as ganglia or a brain. Nevertheless there is an accumulation sensory and nerve cells and their extension on the mouths and stem. These animals respond to chemical, mechanical and electrical stimuli, as well as light and temperature.

The nervous system of hydra is structurally simple compared to the more developed nervous systems of animals. Nerve networks connect sensory photoreceptors and touch-sensitive nerve cells located on the body wall and tentacles.

Respiration and excretion occur by diffusion throughout the epidermis.

Feeding

Hydras primarily feed on aquatic invertebrates. When feeding, they extend their body to its maximum length and then slowly extend their tentacles. Despite their simple structure, tentacles unusually expand and can be five times the length of the body. Once fully extended, the tentacles slowly maneuver in anticipation of contact with a suitable prey animal. Upon contact, the stinging cells on the tentacle sting the victim (the ejection process takes only about 3 microseconds), and the tentacles themselves wrap around the prey.

Within a few minutes, the victim is drawn into the body cavity, after which digestion begins. Polyp can stretch significantly its body wall to digest prey more than twice the size of the hydra. After two or three days, the indigestible remains of the victim are removed by contraction through the opening of the mouth.

The food of freshwater hydra consists of small crustaceans, water fleas, insect larvae, water moths, plankton and other small aquatic animals.

Movement

The hydra moves from place to place, stretching its body and clinging to an object alternately with one or the other end of the body. Polyps migrate about 2 cm per day. By forming a gas bubble on its leg, which provides buoyancy, the hydra can also move towards the surface.

Reproduction and lifespan.

Hydra can reproduce both asexually and in the form of germination of new polyps on the stalk of the mother polyp, by longitudinal and transverse division and under certain circumstances. These circumstances are still have not been fully studied, but lack of nutrition plays an important role. These animals can be male, female or even hermaphrodite. Sexual reproduction is initiated by the formation of germ cells in the wall of the animal.

Conclusion

The unlimited lifespan of the hydra attracts the attention of natural scientists. Hydra stem cells have the ability to perpetual self-renewal. The transcription factor has been identified as a critical factor for continuous self-renewal.

However, it appears that the researchers still have a long way to go before they can understand how their findings could be applied to reducing or eliminating human aging.

Application of these animals for needs humans are limited by the fact that freshwater hydras cannot live in dirty water, so they are used as indicators of water pollution.

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. The mesoglea in sea jellyfish makes up up to 80% of the body weight, while 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. The nervous system appears.

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. In late autumn, Hydras die. 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.

One of the typical representatives of the order of coelenterates is freshwater hydra. These creatures live in clean bodies of water and attach themselves to plants or soil. They were first seen by the Dutch inventor of the microscope and famous naturalist A. Leeuwenhoek. The scientist even managed to witness the budding of a hydra and examine its cells. Later, Carl Linnaeus gave the genus a scientific name, referring to the ancient Greek myths about the Lernaean Hydra.

Hydras live in clean bodies of water and attach to plants or soil.

Structural features

This aquatic inhabitant is distinguished by its miniature size. On average, the body length is from 1 mm to 2 cm, but it can be a little more. The creature has a cylindrical body. In front there is a mouth with tentacles around (their number can reach up to twelve pieces). At the back there is a sole, with the help of which the animal moves and attaches to something.

There is a narrow pore on the sole through which liquid and gas bubbles from the intestinal cavity pass. Together with the bubble, the creature detaches from the selected support and floats up. At the same time, his head is located in the thick of the water. Hydra has a simple structure, its body consists of two layers. Oddly enough, when the creature is hungry, its body looks longer.

Hydras are one of the few coelenterates that live in fresh water. Most of these creatures inhabit the sea area . Freshwater species may have the following habitats:

ponds;
lakes;
river factories;
ditches.

If the water is clear and clean, these creatures prefer to be close to the shore, creating a kind of carpet. Another reason why animals prefer shallow areas is the love of light. Freshwater creatures are very good at distinguishing the direction of light and moving closer to its source. If you put them in an aquarium, they will definitely swim to the most illuminated part.

Interestingly, unicellular algae (zoochlorella) may be present in the endodermis of this creature. This is reflected in the appearance of the animal - it acquires a light green color.

Nutrition process

This miniature creature is a real predator. It is very interesting to find out what freshwater hydra eats. The water is home to many small animals: cyclops, ciliates, and crustaceans. They serve as food for this creature. Sometimes it can eat larger prey, such as small worms or mosquito larvae. In addition, these coelenterates cause great damage to fish ponds, because caviar becomes one of the things that hydra feeds on.

In the aquarium you can watch in all its glory how this animal hunts. The hydra hangs with its tentacles down and at the same time arranges them in the form of a network. Her torso sways slightly and describes a circle. Prey swimming nearby touches the tentacles and tries to escape, but suddenly stops moving. The stinging cells paralyze her. Then the coelenterate creature pulls it to its mouth and eats it.

If the animal has eaten well, it swells. This creature can devour victims, which exceeds it in size. Its mouth can open very wide, sometimes part of the prey’s body can be clearly seen from it. After such a spectacle, there is no doubt that the freshwater hydra is a predator in its feeding method.

Reproduction method

If the creature has enough food, reproduction occurs very quickly by budding. In a few days, a tiny bud grows into a fully formed individual. Often several such buds appear on the hydra’s body, which are then separated from the mother’s body. This process is called asexual reproduction.

In autumn, when the water becomes colder, freshwater creatures can reproduce sexually. This process works as follows:

Gonads appear on the body of the individual. Some of them produce male cells, while others produce eggs.
Male reproductive cells move in water and enter the body cavity of hydras, fertilizing the eggs.
When eggs are formed, the hydra most often dies, and new individuals are born from the eggs.

On average, the body length of a hydra is from 1 mm to 2 cm, but it can be a little more.

Nervous system and breathing

In one of the layers of the body of this creature there is a scattered nervous system, and in the other there is a small number of nerve cells. In total, there are 5 thousand neurons in the animal’s body. The animal has nerve plexuses near the mouth, on the sole and on the tentacles.

Hydra does not divide neurons into groups. The cells perceive irritation and send a signal to the muscles. The nervous system of an individual contains electrical and chemical synapses, as well as opsin proteins. Speaking about what the hydra breathes, it is worth mentioning that the process of excretion and respiration occurs over the surface of the entire body.

Regeneration and growth

The cells of a freshwater polyp are in the process of constant renewal. In the middle of the body they divide, and then move to the tentacles and sole, where they die. If there are too many dividing cells, they move to the lower region of the body.

This animal has an amazing ability to regenerate. If you cut his torso crosswise, each part will be restored to its previous form.

The cells of a freshwater polyp are in the process of constant renewal.

Lifespan

In the 19th century there was a lot of talk about the immortality of animals. Some researchers tried to prove this hypothesis, while others wanted to refute it. In 1917, after a four-year experiment, the theory was proven by D. Martinez, as a result of which the hydra officially became an ever-living creature.

Immortality is associated with an incredible ability to regenerate. The death of animals in winter is associated with unfavorable factors and lack of food.

Freshwater hydras are entertaining creatures. Four species of these animals are found throughout Russia and they are all similar to each other. The most common are ordinary and stalked hydras. When you go for a swim in the river, you can find a whole carpet of these green creatures on its bank.

Microscopic structure. Both cell layers of the hydra consist predominantly of so-called epithelial-muscle cells. Each of these cells has its own epithelial part and a contractile process. The epithelial part of the cell faces either outward (in the ectoderm) or toward the gastric cavity (in the endoderm).

Contractile processes extend from the base of the cell adjacent to the supporting plate - the mesoglea. Inside the contractile process are muscle fibers. The contractile processes of ectoderm cells are located parallel to the axis of the body and the axes of the tentacles, i.e., along the body of the hydra; their contraction causes shortening of the body and tentacles. The contractile processes of endoderm cells are located across the body in a circular direction; their contraction causes a narrowing of the hydra body. On the free surface of endoderm cells there are flagella, most often 2, and sometimes pseudopodia may appear.

In addition to epithelial-muscle cells, the ectoderm and endoderm contain sensory, nerve and glandular cells.

The former occupy the same position as epithelial-muscle cells, i.e., one pole extends to the surface of the body or to the digestive cavity, the other to the supporting plate.

Hydra . I - in a calm state; II - contracted after irritation

The second lie at the base of the epithelial-muscle cells, near their contractile processes adjacent to the supporting plate. Nerve cells are connected by processes into a primitive nervous system of the diffuse type. Nerve cells are especially numerous around the mouth, on the tentacles and on the sole.

Microscopic structure of hydra . I - incision through the body wall; II - diffuse nervous system (connections of nerve cell processes with each other are visible); III - separate epithelial-muscular cell ectoderm:

1—stinging cells, 2—epithelial-muscular cells of the ectoderm, 3—epithelial-muscular cells of the endoderm, 4—glandular cells of the endoderm, 5—flagellate and pseudopodial outgrowths of endoderm cells, 6—interstitial cells, 7—sensitive cells of the ectoderm, 8—sensitive ectoderm cells, 9—nerve cells of the ectoderm (nerve cells of the endoderm are not shown), 9 (III)—cell body, 10—contractile processes with contractile fibril inside them (11)

Glandular cells of the ectoderm are located mainly on the sole and tentacles; their sticky secretions on the sole serve to attach the hydra to the substrate, and on the tentacles they play a role in moving the animal (see below). The glandular cells of the endoderm are located near the mouth; their secretion has digestive value.

The ectoderm also contains stinging cells, i.e. cells containing stinging capsules (see above), they are especially numerous on the tentacles. Hydra has four types of stinging cells: the largest pear-shaped ones are penetrants, the small pear-shaped ones are volventes, the large cylindrical ones are glutinants, or streptolins, and the small cylindrical ones are stereolins. The effects of these types of capsules vary; Some of them, with their sharp threads, can pierce the wall of the enemy’s or victim’s body and introduce a toxic substance into the wound and thereby paralyze it, while others only entangle the victim with threads.

Finally, the hydra has undifferentiated so-called interstitial cells, from which various cellular elements of the hydra develop, in particular germ cells.