Freshwater hydra: structure, reproduction, nutrition. Fighting hydra in the aquarium. The study of the morphological and physiological characteristics of the common hydra (hydra vulgaris) At what time of the year does the freshwater hydra die

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

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

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

Structure

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

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

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

Hydra ectoderm

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

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

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

Hydra endoderm

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

What does a hydra breathe

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

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

Reproduction features

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

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

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

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

What does hydra eat

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

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

Hydra regeneration

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

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

The biological significance of freshwater hydra

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

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

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

Freshwater hydras have a remarkable regenerative capacity. Instead of repairing damaged cells, they are constantly being replaced by stem cell division and, in part, 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 kingdom.

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

What is hydra

The freshwater hydra (Hydra) is a genus of small freshwater animals of the phylum Cnidaria and the class Hydrozoa. It is, in fact, 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 coloration comes from chlorella algae).

The structure of the hydra

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

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

The body of freshwater hydra consists of three layers:

• "outer shell" (ectodermal epidermis);
• "inner shell" (endodermal gastroderma);
• a gelatinous support matrix, the so-called mesogloe, 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 urticaria capsules that are ejected, releasing a paralyzing poison and, thus used to capture prey. These capsules do not regenerate, so they can only be dropped once. On each of the tentacles is from 2500 to 3500 nettle capsules.

Epithelial muscle cells form longitudinal muscle layers along the polypoid. By stimulating these cells, polyp can shrink quickly. There are also muscle cells in the endoderm, so named because of their function of absorbing nutrients. Unlike the muscle cells of the ectoderm, they are arranged in an annular pattern. This causes the polyp to stretch as the endoderm 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 the muscle cells in the endoderm, there are specialized gland cells that secrete digestive secretions.

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

Nervous system

The Hydra has a nerve network like all hollow animals (coelenterates), but it does not have focal points like the ganglia or the brain. Nonetheless accumulation sensory and nerve cells and their elongation on the mouths and stem. These animals respond to chemical, mechanical and electrical stimuli, as well as to light and temperature.

The hydra's nervous system is structurally simple compared to the more developed nervous systems of animals. neural 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 mainly feed on aquatic invertebrates. When feeding, they elongate their bodies to their maximum length and then slowly expand their tentacles. Despite their simple structure, tentacles are extraordinarily widened and can be up to five times their body length. 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 ejection process takes only about 3 microseconds), and the tentacles wrap around the prey.

Within a few minutes, the victim is drawn into the body cavity, after which digestion begins. Polyp can stretch a lot 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 expelled by contraction through the opening of the mouth.

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

Traffic

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

reproduction and longevity.

Hydra can reproduce both asexually and in the form of the germination of new polyps on the stem of the maternal polyp, by longitudinal and transverse division, and under certain circumstances. These circumstances are have not been fully explored but nutritional deficiencies play 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 in continuous self-renewal.

However, it appears that researchers still have a long way to go before they can understand how their work can be applied to reduce or eliminate 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.

Hydra is a genus of animals belonging to the Coelenterates. Their structure and activity are often considered on the example of a typical representative - freshwater hydra. Further, this particular species will be described, which lives in fresh water bodies with clean water, attaches to aquatic plants.

Usually the size of the hydra is less than 1 cm. The life form is a polyp, which suggests a cylindrical body shape with a sole at the bottom and a mouth opening on the upper side. The mouth is surrounded by tentacles (approximately 6-10), which can be extended in length exceeding the length of the body. The hydra leans in the water from side to side and with its tentacles catches small arthropods (daphnia, etc.), after which it sends them into the mouth.

For hydras, as well as for all coelenterates, it is characteristic radial (or radial) symmetry. If you look at not from above, then you can draw a lot of imaginary planes dividing the animal into two equal parts. Hydra does not care from which side food swims up to it, since it leads a motionless lifestyle, therefore, radial symmetry is more beneficial for it than bilateral symmetry (characteristic of most mobile animals).

Hydra's mouth opens into intestinal cavity. This is where the digestion of food takes place. The rest of digestion is carried out in cells that absorb partially digested food from the intestinal cavity. Undigested residues are ejected through the mouth, since coelenterates do not have an anus.

The body of the hydra, like all coelenterates, consists of two layers of cells. The outer layer is called ectoderm, and the inner endoderm. Between them there is a small layer mesoglea- non-cellular gelatinous substance, which may contain various types of cells or processes of cells.

Hydra ectoderm

Hydra ectoderm is made up of several types of cells.

skin muscle cells the most numerous. They create the integuments of the animal, and are also responsible for changing the shape of the body (elongation or reduction, bending). Their processes contain muscle fibers that can contract (while their length decreases) and relax (their length increases). Thus, these cells play the role of not only covers, but also muscles. Hydra does not have real muscle cells and, accordingly, real muscle tissue.

The Hydra can move around using somersaults. She leans so hard that she reaches the support with her tentacles and stands on them, lifting the sole up. After that, the sole already leans and becomes on a support. Thus, the hydra makes a somersault and finds itself in a new place.

The hydra has nerve cells. These cells have a body and long processes that connect them to each other. Other processes are in contact with skin-muscle and some other cells. Thus, the whole body is enclosed in a nervous network. Hydras do not have an accumulation of nerve cells (ganglia, brain), however, even such a primitive nervous system allows them to have unconditioned reflexes. Hydras react to touch, the presence of a number of chemicals, temperature changes. So if you touch the hydra, it shrinks. This means that excitation from one nerve cell spreads to all the others, after which the nerve cells transmit a signal to the skin-muscle cells so that they begin to contract their muscle fibers.

Between the skin-muscle cells, the hydra has a lot of stinging cells. Especially a lot of them on the tentacles. These cells inside contain stinging capsules with stinging filaments. Outside, the cells have a sensitive hair, when touched, the stinging thread shoots out of its capsule and strikes the victim. In this case, poison is injected into a small animal, usually having a paralytic effect. With the help of stinging cells, the hydra not only catches its prey, but also defends itself from animals attacking it.

intermediate cells(located in the mesoglea rather than in the ectoderm) provide regeneration. If the hydra is damaged, then, thanks to the intermediate cells, new various cells of the ectoderm and endoderm are formed at the site of the wound. The Hydra can regenerate a fairly large portion of its body. Hence its name: in honor of the character of ancient Greek mythology, who grew new heads to replace the severed ones.

Hydra endoderm

The endoderm lines the intestinal cavity of the hydra. The main function of endoderm cells is to capture food particles (partially digested in the intestinal cavity) and their final digestion. At the same time, endoderm cells also have muscle fibers that can contract. These fibrils are directed towards the mesoglea. Flagella are directed towards the intestinal cavity, which scoop up food particles to the cell. The cell captures them the way amoeba do - forming pseudopods. Further, the food is in the digestive vacuoles.

The endoderm secretes a secret into the intestinal cavity - digestive juice. Thanks to him, the animal captured by the hydra breaks up into small particles.

Hydra breeding

The freshwater hydra has both sexual and asexual reproduction.

asexual reproduction carried out by budding. It occurs during a favorable period of the year (mainly in summer). A protrusion of the wall forms on the body of the hydra. This protrusion increases in size, after which tentacles form on it and a mouth erupts. Subsequently, the daughter individual is separated. Thus, freshwater hydras do not form colonies.

With the onset of cold weather (in autumn), the hydra transgresses to sexual reproduction. After sexual reproduction, hydras die, they cannot live in winter. During sexual reproduction in the body of the hydra, eggs and sperm are formed. The latter leave the body of one hydra, swim up to another and fertilize her eggs there. Zygotes are formed, which are covered with a dense shell that allows them to survive the winter. In the spring, the zygote begins to divide, and two germ layers are formed - the ectoderm and endoderm. When the temperature gets high enough, the young hydra breaks the shell and comes out.

Hydra is a genus of freshwater animals of the hydroid class of the intestinal type. Hydra was first described by A. Leeuwenhoek. In the reservoirs of Ukraine and Russia, the following species of this genus are common: common hydra, green, thin, long-stemmed. A typical representative of the genus looks like a single attached polyp 1 mm to 2 cm long.

Hydras live in fresh water bodies with stagnant water or a slow current. They lead an attached lifestyle. The substrate to which the hydra is attached is the bottom of the reservoir or aquatic plants.

The external structure of the hydra . The body has a cylindrical shape, on its upper edge there is a mouth opening surrounded by tentacles (from 5 to 12 in different species). In some forms, the body can be conditionally divided into a trunk and a stalk. At the posterior edge of the stalk there is a sole, thanks to which the organism is attached to the substrate, and sometimes moves. Characterized by radial symmetry.

The internal structure of the hydra . The body is a bag consisting of two layers of cells (ectoderm and endoderm). They are separated by a layer of connective tissue - mesoglea. There is a single intestinal (gastric) cavity, which forms outgrowths extending into each of the tentacles. The mouth opens into the intestinal cavity.

Food. It feeds on small invertebrates (cyclops, cladocerans - daphnia, oligochaetes). The poison of stinging cells paralyzes the prey, then, with the movements of the tentacles, the prey is absorbed through the mouth opening and enters the body cavity. At the initial stage, cavity digestion occurs in the intestinal cavity, then intracellular - inside the digestive vacuoles of endoderm cells. There is no excretory system, undigested food residues are removed through the mouth. The transport of nutrients from the endoderm to the ectoderm occurs through the formation of special outgrowths in the cells of both layers, tightly interconnected.

The vast majority of cells in the composition of hydra tissues are epithelial-muscular. They form the epithelial cover of the body. The processes of these ectoderm cells make up the longitudinal muscles of the hydra. In the endoderm, cells of this type carry flagella for mixing food in the intestinal cavity, and digestive vacuoles are also formed in them.

Hydra tissues also contain small interstitial progenitor cells that can, if necessary, transform into cells of any type. Characterized by specialized glandular cells in the endoderm, which secrete digestive enzymes into the gastric cavity. The function of the stinging cells of the ectoderm is the release of toxic substances to defeat the victim. In large numbers, these cells are concentrated on the tentacles.

The body of the animal also has a primitive diffuse nervous system. Nerve cells are scattered throughout the ectoderm, in the endoderm - single elements. Accumulations of nerve cells are noted in the area of ​​​​the mouth, soles, and on the tentacles. Hydra can form simple reflexes, in particular, reactions to light, temperature, irritation, exposure to dissolved chemicals, etc. Breathing is carried out through the entire surface of the body.

reproduction . Hydra reproduction occurs both asexually (budding) and sexually. Most species of hydras are dioecious, rare forms are hermaphrodites. When the sex cells merge in the body of the hydra, zygotes are formed. Then the adults die, and the embryos hibernate at the gastrula stage. In spring, the embryo turns into a young individual. Thus, the development of the hydra is direct.

Hydras play an essential role in natural food chains. In science, in recent years, hydra has been a model object for studying the processes of regeneration and morphogenesis.

Figure: The structure of a freshwater hydra. Radiation symmetry of the hydra

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

In lakes, rivers or ponds with clean, clear water, a small translucent animal is found on the stems of aquatic plants - polyp hydra("polyp" means "many-legged"). This is an attached or inactive intestinal cavities 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. With the help of 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 stretch several centimeters.

Radiation symmetry of the hydra

If an imaginary axis is drawn 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 radiating tentacles are best suited for this method of hunting.
Radiation symmetry is typical, as a rule, for animals leading an attached lifestyle.

Intestinal cavity of hydra

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

The outer layer of hydra cells is called - ectoderm. Under a microscope, in the outer layer of the hydra - the ectoderm - several types of cells are visible. Most of all here are skin-muscular. Touching the sides, these cells create a cover of the hydra. At the base of each such cell there is a contractile muscle fiber that plays an important role in the movement of the animal. When the fiber of all skin-muscular cells are reduced, the body of the hydra is compressed. If the fibers contract only on one side of the body, then the hydra bends down in this direction. Thanks to the work of muscle fibers, the hydra can slowly move from place to place, alternately "stepping" either with the sole or with the tentacles. Such a movement can be compared to a slow somersault over the head.
The outer layer contains 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. Part of the processes approaches the skin-muscle cells.

Irritability and Hydra Reflexes

Hydra is able to feel touch, temperature changes, the appearance of various dissolved substances in the water, and other irritations. From this, her nerve cells are excited. If you touch the hydra with a thin needle, then the excitation from irritation of one of the nerve cells is transmitted through the processes to other nerve cells, and from them to the skin-muscle cells. This causes a contraction of the muscle fibers, and the hydra shrinks into a ball.

Pattern: Hydra's irritability

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

Hydra stinging cells

Pattern: string or nettle cells of hydra

The entire body of the hydra, and especially its tentacles, are covered with a large number of stinging, or nettles cells. Each of these cells has a complex structure. In addition to the cytoplasm and the nucleus, it contains a bubble-shaped stinging capsule, inside which a thin tube is folded - stinging thread. Sticking out of the cage sensitive hair. As soon as a crustacean, fish fry or other small animal touches a sensitive hair, the stinging thread quickly straightens, its end throws itself out and pierces the victim. Through the 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, it fires many stinging cells at once. Then the hydra pulls the prey to the mouth with tentacles and swallows. The stinging cells also serve the hydra for defense. Fish and aquatic insects do not eat hydras that burn enemies. The poison from the capsules in its effect on the body of large animals resembles nettle poison.

Inner layer of cells - hydra endoderm

Figure: the 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 the digestion of food. They secrete digestive juice into the intestinal cavity, under the influence of which the extraction of hydra softens and breaks up 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 scoop particles up to the cells. The cells of the inner layer are capable of releasing prolegs (like in an amoeba) and capturing food with them. Further digestion occurs inside the cell, in vacuoles (as in protozoa). Undigested food remains are thrown out through the mouth.
The hydra does not have special respiratory organs; oxygen dissolved in water penetrates into the hydra through the entire surface of its body.

Hydra Regeneration

In the outer layer of the body of the hydra there are also very small rounded 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 intensively. Skin-muscular, nerve and other cells are formed from them, and the wounded area quickly overgrows.
If you cut the hydra across, then 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. The hydra has a highly developed ability to regenerate.
Regeneration to one degree or another is also characteristic of other animals and humans. So, in earthworms, the regeneration of the whole organism from their parts is possible, in amphibians (frogs, newts) whole limbs, different parts of the eye, tail and internal organs can be restored. In humans, when cut, the skin is restored.

Hydra breeding

Hydra asexual reproduction by budding

Figure: Hydra asexual reproduction by budding

Hydra reproduces asexually and sexually. In summer, a small tubercle appears on the body of the hydra - a protrusion of the wall of its body. This tubercle grows, stretches. Tentacles appear at its end, and a mouth erupts between them. This is how a young hydra develops, which at first remains connected to the mother with the help of a stem. 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 on its own.

Hydra sexual reproduction

By autumn, with the onset of adverse conditions, hydras die, but before that, germ cells develop in their body. There are two types of germ cells: egg, or female, and spermatozoa, or male sex cells. Spermatozoa are similar to flagellar protozoa. They leave the body of the hydra and swim with the help of a long flagellum.

Figure: Hydra sexual reproduction

The hydra egg cell is similar to an amoeba, has pseudopods. The spermatozoon swims up to the hydra with the egg cell and penetrates into it, and the nuclei of both germ cells merge. going on fertilization. After that, the pseudopods are retracted, the cell is rounded, a thick shell is released 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, a fertilized egg begins to divide, the resulting cells are arranged in two layers. A small hydra develops from them, which, with the onset of warm weather, comes out through a rupture of the egg shell.
Thus, a multicellular animal hydra at the beginning of its life consists of one cell - an egg.