Hydra epithelial muscle cells functions. What is a freshwater hydra? Structure and nervous system. External and internal structure

The first to see and describe the hydra was the naturalist A. Levenguk, who invented the microscope. This scientist was the most significant naturalist of the 17th-18th centuries.

While examining aquatic plants with his primitive microscope, Leeuwenhoek noticed a strange creature that had hands “in the form of horns.” The scientist even observed the budding of these creatures and saw their stinging cells.

The structure of freshwater hydra

Hydra belongs to the coelenterate animals. Its body is tube-shaped; in the front part there is a mouth opening, which is surrounded by a corolla consisting of 5-12 tentacles.

Under the tentacles, the hydra's body narrows and a neck is formed, which separates the body from the head. The back of the body is tapered into a stalk or stalk, with a sole at the end. When the hydra is well-fed, its body length does not exceed 8 millimeters, and if the hydra is hungry, the body is much longer.

Like all representatives of the coelenterates, the body of the hydra is formed by two layers of cells.

The outer layer consists of a variety of cells: some cells are used to kill prey, other cells have contractility, and others secrete mucus. And in the outer layer there are nerve cells that form a network covering the body of the guide.

Hydra is one of the few representatives of coelenterates that lives in fresh water, and most of these creatures live in the seas. The habitat of hydras is a variety of bodies of water: lakes, ponds, ditches, river backwaters. They settle on aquatic plants and the roots of duckweed, which covers the entire bottom of the reservoir with a carpet. If the water is clean and transparent, then hydras settle on the rocks near the shore, sometimes forming a velvet carpet. Hydras love light, so they prefer shallow places near the banks. These creatures can discern the direction of light and move towards its source. If hydras live in an aquarium, they always move to the illuminated part of it.

If you place aquatic plants in a vessel with water, you can see hydras crawling along their leaves and the walls of the vessel. There is an adhesive substance on the sole of the hydra, which helps it firmly attach to aquatic plants, stones and the walls of the aquarium; it is quite difficult to tear the hydra from its place. Occasionally, the hydra moves in search of food; this can be observed in aquariums, when a mark remains on the stack in the place where the hydra was sitting. In a few days, these creatures move no more than 2-3 centimeters. While moving, the hydra attaches itself to the glass with a tentacle, tears off the sole and drags it to a new place. When the sole is attached to the surface, the hydra levels out and rests on its tentacle again, taking a step forward.

This method of movement is similar to the movement of moth butterfly caterpillars, which are often called “land surveyors.” But the track pulls the back end towards the front and then moves the front end again. And the hydra turns over its head every time it moves. This is how the hydra moves quite quickly, but there is another, slower way of moving - when the hydra slides on its sole. Some individuals can detach from the substrate and swim in the water. They straighten their tentacles and sink to the bottom. And the hydras rise upward with the help of a gas bubble that forms on the sole.

How do freshwater hydras feed?

Hydras are predatory creatures; they feed on ciliates, cyclops, small crustaceans - daphnia and other small living creatures. They sometimes eat larger prey, such as small worms or mosquito larvae. Hydras can even cause damage to fish ponds as they eat newly hatched fish.

How hydra hunts can be easily observed in an aquarium. She spreads her tentacles widely, which form a net, while she hangs with her tentacles down. If you observe a hydra, you will notice that its body, slowly swaying, describes a circle with its front part. A prey swimming past is touched by the tentacles, tries to free itself, but becomes silent as the stinging cells paralyze it. The hydra pulls the prey to its mouth and begins to eat.

If the hunt is successful, the hydra swells from the number of crustaceans eaten, and their eyes are visible through its body. Hydra can eat prey that is larger than itself. The hydra's mouth can open wide and its body can stretch significantly. Sometimes a part of the victim sticks out of the hydra’s mouth, which did not fit inside.

Reproduction of freshwater hydra

If there is enough food, hydras multiply quickly. Reproduction occurs by budding. The process of growth of a bud from a tiny tubercle to a fully formed individual takes several days. Often several buds form on the hydra’s body until the young individual separates from the mother hydra. Thus, asexual reproduction occurs in hydras.

In autumn, when the water temperature drops, hydras can also reproduce sexually. On the body of the hydra, gonads form in the form of swellings. In some swellings, male reproductive cells are formed, and in others, egg cells. Male reproductive cells float freely in water and penetrate into the body cavity of hydras, fertilizing immobile eggs. When eggs are formed, the hydra usually dies. Under favorable conditions, young individuals emerge from the eggs.

Regeneration in freshwater hydra

Hydras exhibit an amazing ability to regenerate. If a hydra is cut in half, new tentacles will quickly grow in the lower part, and a sole will grow on the upper part.

In the 17th century, the Dutch scientist Tremblay conducted interesting experiments with hydras, as a result of which he was not only able to grow new hydras from pieces, but also to fuse different halves of hydras, obtain seven-headed polyps and turn their bodies inside out. When a seven-headed polyp similar to the hydra from Ancient Greece was obtained, these polyps began to be called hydra.

In order to study the internal structure of the hydra's body, it is killed, painted, and using special instruments, longitudinal and transverse sections are made through its body, as well as thin sections of individual parts of the animal's body. Examining such sections under a microscope, you can notice that the body of the hydra does not consist of one cell, like that of the common amoeba, green euglena or slipper ciliate, but of many. Animals whose body consists of a large number of cells are called multicellular. This means that hydra is a multicellular animal.

Hydra cells form body walls, which consist of two layers: outer and inner. Between these layers there is a thin transparent supporting membrane separating them. The outer layer, or ectoderm, is also called the cutaneous or integumentary layer. The inner layer, or endoderm, is also called the digestive layer.

External structure

The body of the freshwater hydra has the shape of a long sac. Usually it is attached at one end of its cylindrical body to an aquatic plant, underwater rock or other object. The end of the freshwater hydra's body, with which it attaches to underwater objects, is called the sole. At the opposite, free end of the body there are from 6 to 12 thin, hair-like tentacles. In an extended position, the tentacles can exceed the length of the hydra’s body, reaching 25 cm.

Most invertebrate animals are characterized by a certain symmetry of the body, that is, the correct arrangement of body parts and some organs relative to the body axis. The symmetry of the body of a particular invertebrate animal is closely related to its lifestyle. Freshwater hydra and most other coelenterates are characterized by ray (radial) symmetry of the body. Through the body of such animals, when dividing them into two identical halves, many planes of symmetry can be drawn. Radiation symmetry of the body is possible only in animals living in water.

• Type: Cnidaria = Coelenterates, cnidarians
• Subphylum: Medusozoa = Jellyfish-producing
• Class: Hydrozoa Owen, 1843 = Hydrozoans, hydroids
• Subclass: Hydroidea = Hydroids
• Squad: Hydrida = Hydras
• Genus: Hydra = Hydras

Genus: Hydra = Hydras

Hydras are characterized by a primitive diffuse nervous system, formed in the ectoderm by nerve cells in the form of a scattered nerve plexus. The endoderm contains only individual nerve cells, but in total Hydra has about 5,000 neurons. Nerve plexuses are located on the sole, around the mouth and on the tentacles. There is evidence that hydra has a perioral nerve ring similar to that of the umbrella of hydromedusas. Although the hydra does not have a clear division into sensory, intercalary and motor neurons, it nevertheless has sensory and ganglion nerve cells. The bodies of sensitive cells are located across the epithelial layer; they have a stationary flagellum surrounded by a collar of microvilli, which protrudes into the external environment and is able to perceive irritation. The processes of ganglion cells are located at the base of the epithelial-muscular cells and do not extend into the external environment. Hydra is the most primitive animal, in whose nerve cells light-sensitive opsin proteins are found, which in Hydra and humans have a common origin. In general, the presence of a nervous system in the hydra allows it to carry out simple reflexes. Thus, hydra reacts to mechanical irritation, temperature, lighting, the presence of certain chemicals in water and a number of other environmental factors.

Stinging cells are formed from intermediate cells only in the torso area. There are about 55,000 stinging cells in Hydra and they are the most numerous of all cell types. Each stinging cell has a stinging capsule, which is filled with a poisonous substance, and a stinging thread is screwed inside the capsule. On the surface of the cell, only a sensitive hair rips, and when irritated, a thread is immediately thrown out and hits the victim. After the thread is fired, the stinging cell dies, and in its place new ones are formed from intermediate cells.

Hydra has four types of stinging cells. When hydras hunt, the first to shoot are the desmonemas (volvents): their spiral stinging threads entangle the outgrowths of the prey’s body and ensure its retention. When the victim tries to jerk free, the vibration caused by them triggers stenoteles (penetrants), which have a higher threshold of irritation. And the spines present at the base of their stinging threads are anchored in the body of the prey, and poison is injected into its body through the hollow stinging thread. Large glutinants (their stinging thread has spines, but, like volventas, does not have a hole at the top) are apparently mainly used for protection. Small glutinants are used only when the hydra moves to firmly attach its tentacles to the substrate. Their firing is blocked by extracts from the tissues of Hydra victims.

On the tentacles of the hydra there is the largest number of stinging cells, which form stinging batteries here. The stinging battery usually includes one large epithelial-muscular cell in which the stinging cells are immersed. In the center of the battery there is a large penetrant, around it there are smaller volvents and glutinants. Cnidocytes are connected by desmosomes to the muscle fibers of the epithelial muscle cell.

Ultra-high-speed filming of the firing of the Hydra penetrant showed that the entire firing process takes about 3 ms. Moreover, in the initial phase of firing, the speed reaches 2 m/s, and the acceleration is about 40,000 g; which appears to be one of the fastest cellular processes known in nature. In the early phase of nematocyst firing, the speed of this process is 9-18 m/s, and the acceleration ranges from 1,000,000 to 5,000,000 g, which allows a nematocyst weighing about 1 ng to develop a pressure of the order of magnitude at the tips of the spines (the diameter of which is about 15 nm 7 hPa, which is comparable to the pressure of a bullet on a target and allows it to pierce the fairly thick cuticle of victims...

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.