How hydra gets food. Hydra - class Hydrozoa: sensory organs, nervous and digestive systems, reproduction

In terms of its structure, the hydra is a very simple freshwater animal, which does not at all prevent it from demonstrating a high reproduction rate when placed in an aquarium. Hydras can harm small aquarium fish and fry.

Read straight away about how to deal with hydra in an aquarium >>>

Actually, a hydra is just a “stray stomach” equipped with tentacles, but this stomach can do a lot of things, even reproduce in two ways: asexually and sexually. Hydra is truly a monster. Long tentacles armed with special stinging capsules. A mouth that stretches so that it can swallow prey much larger than the hydra itself in size. Hydra is insatiable. She eats constantly. Eats countless amounts of prey, the weight of which exceeds its own. Hydra is omnivorous. Both daphnia and cyclops and beef are suitable for her food.

Photo 1. Hydra under a microscope. The tentacles appear knotty due to numerous stinging capsules. Hydra has as many as three capsules various types and in their structure are very similar to polar capsules , which indicates some relationship between these organisms, which are completely different from each other.

Drawing from V.A. Dogel ZOOLOGY OF INVERTEBRATES

In the fight for food, the hydra is ruthless. If two hydras suddenly grab the same prey, then neither will yield. Hydra never releases anything caught in its tentacles. The larger monster will begin to drag its competitor towards itself along with the victim. First, it will swallow the prey itself, and then the smaller hydra. Both the prey and the less fortunate second predator will fall into the super-capacious womb (it can stretch several times!). But the hydra is inedible! A little time will pass and the larger monster will simply spit out its smaller brother. Moreover, everything that the latter managed to eat himself will be completely taken away by the winner. The loser will see the light of God again, having been squeezed to the very last drop of anything edible. But very little time will pass and the pathetic lump of mucus will again spread its tentacles and again become a dangerous predator.

In essence, a freshwater polyp called a hydra is simply a wandering stomach armed with an apparatus for capturing food. It is an oblong bag, which is attached with the bottom (sole) to some underwater object. On the opposite side there are tentacles surrounding the mouth opening. This is the only visible hole in the hydra’s body: through it it swallows food and throws out undigested remains. The mouth leads into the internal cavity, which is the “organ” of digestion. Animals of this structure were previously classified as coelenterates. The currently valid name for this type is Cnidarians (Cnidaria)- These are very ancient and primitive organisms in their organization. If you cut the hydra crosswise into two parts, the hydra's womb will literally become bottomless. The mouth with tentacles will tirelessly continue to catch prey and swallow it. There will be no saturation, because everything that is swallowed will simply fall out on the other side. But the polyp will not die. In the end, from each part of a hydra cut in two, a completely full-fledged monster will grow. What is there in two, the hydra can be divided into a hundred parts, from each a new creature will grow. The hydras were dissected lengthwise with multiple cuts. The result was a bunch of hydras sitting on one sole.

Now you should understand what problems Hercules had to face in the fight against the Lernaean Hydra. No matter how much he chopped off her heads, each time more and more grew in their place. As always, there is some truth in any myth. But the hydra is not mythical, but quite real creature. This is a common inhabitant of our reservoirs. It can get into the aquarium along with live food, hand-frozen natural food (frozen bloodworms) and recklessly brought home aquatic plants from nature. And if suddenly this unique animal appears in your aquarium, then what should you do?

Photo 3. Hydras can reproduce sexually and asexually. The latter represents budding. This process of budding is precisely shown here: you can see how a small one (daughter organism) is formed on a large hydra (mother organism).

Firstly, you don’t have to do anything. For fish larger than 4 centimeters, hydra is not dangerous. It was only the mythical one that was big, and those from real life- small (the largest grow up to two centimeters, if you count their length together with straightened tentacles). In an aquarium, hydras feed on leftover food and can serve as a good indicator of whether the owner is feeding his fish correctly or not? If an excessive amount of food is given or it breaks up in the water into very small and numerous pieces that the fish no longer collect, then the hydras will breed extremely large. They will sit in close rows on all illuminated surfaces. They have such a weakness - they love light. Having seen the abundance of hydras, the owner of the aquarium must come to certain conclusions: either change the brand of food, or feed less, or get nurse fish. The main thing here is to deprive the hydras of an abundant food resource, then they will gradually disappear on their own.

In an aquarium where small fish live, and even more so where very tiny fry grow up, there is no place for hydras. In such a home pond they can cause a lot of trouble. If you don’t fight them, soon there will be no fry left at all, and small fish will suffer from chemical burns that the hydras will inflict on them with their stinging cells located in the tentacles. Inside each such stinging cell lies a large oval capsule with a sensitive hair sticking out, and in the capsule itself there is a thread twisted into a spiral, which is a thin tube through which paralyzing poison is supplied to the body of the caught victim. If any aquatic organism, for example, a daphnia or even a small fish, accidentally touches a tentacle, then whole batteries of stinging cells will come into action. The stinging threads ejected from the capsules paralyze and immobilize the victim. Like a variety of microscopic harpoons (penetranta cells), sticky Velcro (glutinanta cells) and entangling threads (volventa cells) they securely attach it to the tentacles. Smoothly curving, the tentacles will pull the helpless prey to the “dimensionless” throat. That is why such a primitively constructed creature, a simple lump of mucus, just a bag for digesting food with tentacles, is such a formidable predator.

The choice of means to combat hydra depends on the aquarium in which it has settled. If in a nursery, then neither chemical nor biological means of control can be used - there is a risk of ruining the still tender little ones. But you can use the hydra's love for light. The entire aquarium is shaded, and only one of the side windows is left illuminated. Another glass is leaned against this glass from the inside of the aquarium, such a size that it fits into the aquarium and covers most of the surface of the side wall. By the end of the day, all the hydras will move to the light and sit on this glass. All you have to do is carefully remove it and that’s it! Your fry are saved! How will the hydras end up on the illuminated wall? They don't have legs, but they can "walk". To do this, the hydra bends in the desired direction more and more until its tentacles touch the substrate on which it sits. Then, literally, she stands on her “head” (on tentacles, that is, she has no head at all in our understanding!) and the opposite end of her body, which is now on top (the one where her sole is located), begins bend towards the light. This is how the hydra, tumbling, moves towards the illuminated place. But this creature moves in this way only if it is in a hurry to get somewhere. Usually it just glides very slowly over the mucus secreted by the cells of the sole. But how and with what means the hydra perceives light in order to know where to move is an unanswered question, because it does not have a specialized organ of vision.

When the hydra is in a hurry, it moves using somersaults.

How else can you defeat the hydra? Chemical weapons! She really doesn’t like the presence of heavy metal salts in water, especially copper. So the usual copper-containing fish treatment products from the pet store will help here. For example, you can use Sera oodinopur.In addition, drugs to combat snails, which also usually contain copper, should also be effective -Sera snailpur. Therefore, if hydras have settled in your aquarium, then this is not only bad, but also good news: The water you use is free from heavy metal salts.
In the absence of the above and similar purchased products, you can use a homemade solution of copper sulfate in the fight against hydra. The technique described in the article about is suitable.

Photo 4. Hydras thrive on snags. Red parrots live in this aquarium. They are reluctant to pick up small particles of food from the bottom. That is why a lot of silt has accumulated on the snag, in which life boils, and hydras find abundant food.

There are also biological weapons to combat the hydra. If you have an aquarium with different peaceful fish average size, then get a couple more. These fish got their name because special structure their highly developed lips, which are perfectly suited for cleaning glass and stones in the aquarium from all kinds of fouling and remnants of uneaten food. The movements of the lips of these funny fish are very reminiscent of a kiss, especially when they, in conflict with each other, push with their wide open mouths, hence their name. These fish will quickly “kiss” all the hydras in the aquarium - clean!
Kissing gouramis eventually grow to a noticeable size - up to fifteen centimeters, therefore, if your aquarium is small, then to fight the hydra you should use other labyrinth fish: bettas, macropods, marble gouramis. They don't grow that big.

Photo 5. Following the red parrots, the hydras were placed in an aquarium marble gourami. In just one day they “licked” the snag clean! There was no trace left of the hydras, and the deposits of silt from the snags had disappeared.

As you can see, unlike the mythical hydra, freshwater hydra can be easily gotten rid of. You won't need to perform the second labor of Hercules for this. But before you destroy the hydras, watch them. After all, this is true most interesting creatures. Their ability to change the shape of their body, to stretch and contract unimaginably, is worth something.

In the middle of the 18th century, when entertainment with a microscope became fashionable in select society, the naturalist Abraham Tremblay's Memoirs on the History of a Kind of Freshwater Polyps with Horn-shaped Arms, published by the naturalist Abraham Tremblay, became a real bestseller.
Hydras are a very fragment that has survived to this day. ancient life. Despite all their amazing primitiveness, these creatures have been living in this world for at least six hundred million years!

In our reservoirs you can find several species of hydra, which zoologists currently classify as three various kinds. Long-stemmed hydra (Pelmatohydra oligactis)- large, with a bunch of very long thread-like tentacles, 2-5 times the length of its body. Common or brown hydra (Hydra vulgaris)- tentacles approximately doubled longer than body, and the body itself, like the previous species, narrows closer to the sole. Thin or gray hydra (Hydra attennata)- on a “skinny stomach” the body of this hydra looks like a thin tube of uniform thickness, and the tentacles are only slightly longer than the body. Green hydra (Chlorohydra viridissima) with short but numerous tentacles, grassy green in color. This green color occurs due to the presence in the body of the hydra of green unicellular algae - zoochlorella, which supply the hydra with oxygen, and they themselves find a very comfortable environment in the body of the hydra, rich in nitrogen and phosphorus salts.
Read additional materials about hydra and see photos of hydra on aquarium glass at.

When writing this article, materials from the following books were used:
1. A.A. Yakhontov. "Zoology for the teacher", vol. 1, Moscow, "Enlightenment", 1968
2. Ya.I. Starobogatov. "Crayfish, mollusks", Lenizdat, 1988
3. N.F. Zolotnitsky. "Amateur's Aquarium", Moscow, "TERRA", 1993
4. V.A. Dogel "Zoology of invertebrates", Moscow, " Soviet science", 1959

Vladimir Kovalev

Updated 04/21/2016

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The common hydra lives in freshwater bodies of water, attaches itself on one side of its body to aquatic plants and underwater objects, leads a sedentary lifestyle, and feeds on small arthropods (daphnia, cyclops, etc.). Hydra is typical representative coelenterates and has characteristic features their structures.

External structure of the hydra

The hydra's body size is about 1 cm, excluding the length of the tentacles. The body has a cylindrical shape. On one side there is mouth opening surrounded by tentacles. On the other side - sole, they attach the animal to objects.

The number of tentacles can vary (from 4 to 12).

Hydra has life form single polyp(i.e., it does not form colonies, since during asexual reproduction the daughter individuals are completely separated from the mother; hydra also does not form jellyfish). Asexual reproduction occurs budding. At the same time, a new small hydra grows in the lower half of the hydra’s body.

Hydra is capable of changing its body shape within certain limits. It can bend, bend, shorten and lengthen, and extend its tentacles.

Internal structure of the hydra

Like all coelenterates internal structure The body of the hydra is a two-layer sac, forming a closed (there is only a mouth opening) intestinal cavity. The outer layer of cells is called ectoderm, internal - endoderm. Between them there is a gelatinous substance mesoglea, which mainly performs support function. The ectoderm and endoderm contain several types of cells.

Mostly in the ectoderm epithelial muscle cells. At the base of these cells (closer to the mesoglea) there are muscle fibers, the contraction and relaxation of which ensures the movement of the hydra.

Hydra has several varieties stinging cells. Most of them are on the tentacles, where they are located in groups (batteries). The stinging cell contains a capsule with a coiled thread. On the surface of the cell, a sensitive hair “looks” out. When the hydra's victims swim by and touch the hairs, a stinging thread shoots out of the cage. In some stinging cells, the threads pierce the arthropod's cover, in others they inject poison inside, in others they stick to the victim.

Among the ectoderm cells, Hydra has nerve cells . Each cell has many processes. Connecting with their help, nerve cells form the hydra nervous system. Such a nervous system is called diffuse. Signals from one cell are transmitted across the network to others. Some processes of nerve cells contact epithelial muscle cells and cause them to contract when necessary.

Hydras have intermediate cells. From them other types of cells are formed, except epithelial-muscular and digestive-muscular. All these cells provide the hydra with a high ability to regenerate, that is, restore lost parts of the body.

In the body of the hydra in the fall they are formed germ cells. Either sperm or eggs develop in the tubercles on her body.

The endoderm consists of digestive muscle and glandular cells.

U digestive muscle cell on the side facing the mesoglea there is a muscle fiber, like epithelial muscle cells. On the other side, facing the intestinal cavity, the cell has flagella (like euglena) and forms pseudopods (like amoeba). The digestive cell scoops up food particles with flagella and captures them with pseudopods. After this, a digestive vacuole is formed inside the cell. The nutrients obtained after digestion are used not only by the cell itself, but are also transported to other types of cells through special tubules.

Glandular cells secrete a digestive secretion into the intestinal cavity, which ensures the breakdown of prey and its partial digestion. In coelenterates, cavity and intracellular digestion are combined.

Hydra - simplest organism from the order Coelenterates. This freshwater polyp lives in almost every body of water. It is a translucent gelatinous body, similar to a independently moving stomach, where the hydra digests food.

How does hydra feed?

The size of this simplest organism rarely exceeds 2 cm. Externally, the hydra resembles a mucous tube of greenish or brown color. Its color depends on the food eaten. With one end of its body it attaches to plants, stones or snags in the water, and with the other it catches prey. They are mainly small invertebrates - daphnia, cyclops, naidid oligochaetes. Sometimes small crustaceans, as well as fish fry, serve as food.

The mouth opening of the hydra is surrounded by tentacles, of which there are from six to twenty pieces. They are in constant movement. As soon as the victim touches them, located in the tentacles, they immediately throw out a pointed thread containing poison. Plunging into an approaching animal, it paralyzes it and, pulling it with tentacles, brings it to its mouth. At the same time, it seems that its body is, as it were, put on the victim, which thus ends up in the intestines, where the digestion of food by the hydra begins. The stinging capsule with poison can only be used once, after which it is replaced with a new one.

The structure of the digestive system

The hydra's body is very similar to a two-layer sac, which is called ectoderm, and the inner one is called endoderm. Between them is a structureless substance called mesoglea.

The composition of the inner layer, where the hydra digests food, consists mainly of glandular and digestive cells. The former secrete digestive juice into the intestinal cavity, under the influence of which the eaten food liquefies and breaks down into small particles. Other cells in the inner layer grab these pieces and pull them inside.

Thus, the digestion process begins in the intestinal cavity and ends inside the endoderm cells. All food remains that cannot be digested are thrown out through the mouth.

How does it happen in Hydra?

The digestive cells of the inner layer have from 1 to 3 flagella at the end, with the help of which fine particles food is drawn in and digested. The absence of a transport system in the hydra body complicates the task of providing ectoderm cells with nutrients, given that the mesoglea is quite dense. This problem is solved thanks to the existing outgrowths on the cells of both layers. They cross by connecting through gap junctions. Organic molecules in the form of amino acids and monosaccharides, passing through them, they provide nutrition to the ectoderm.

When cellular metabolic waste remains where the hydra digests food, it contracts, resulting in emptying.

Freshwater hydra is amazing creature, which is not easy to detect due to its microscopic size. Hydra belongs to the phylum of coelenterates.

The habitat of this small predator— rivers, dams, and lakes overgrown with vegetation 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 a pond and let it stand for a while: soon you will be able to see elongated “wires” of white or brown color, 1-3 centimeters in size. This is exactly how the hydra is depicted in the drawings. This is exactly what a freshwater hydra looks like.

Structure

The hydra's body is tubular in shape. It is represented by two types of cells - ectoderm and endoderm. Between them there is an intercellular substance - mesoglea.

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

On the opposite side of the “tube” there is a sole. Thanks to the suction cup, it attaches to stems, leaves and other surfaces.

Hydra ectoderm

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

The ectoderm consists of several types of cells. Among them:

• skin-muscle cells - they help the body move and wriggle. When the cells contract, the animal contracts or, on the contrary, stretches. A simple mechanism helps the hydra move unhindered under the cover of water using “somersaults” and “steps”;
• stinging cells - they cover the walls of the animal's body, but most of them are concentrated in the tentacles. As soon as small prey swims near the hydra, it tries to touch it with its tentacles. At this moment, the stinging cells release “hairs” containing poison. Paralyzing the victim, the hydra attracts it to its mouth and swallows it. This simple scheme allows you to easily obtain food. After such work, the stinging cells self-destruct, and new ones appear in their place;
• nerve cells. The outer shell of the body is composed of star-shaped cells. They are connected to each other, forming a chain of nerve fibers. This is how the nervous system of an animal is formed;
• germ cells are actively growing in autumn period. They are egg (female) reproductive cells and sperm. The eggs are located near the mouth opening. They grow quickly, consuming nearby cells. Sperm after maturation leave the body and float in water;
• intermediate cells - they serve defense mechanism: when an animal’s body is damaged, these invisible “defenders” begin to actively multiply and heal the wound.

Hydra endoderm

The endoderm helps the hydra digest food. Cells line digestive tract. They capture food particles, delivering them to the vacuoles. The digestive juice secreted by the glandular cells processes the beneficial substances necessary for the body.

What does hydra breathe?

Freshwater hydra breathes through the outer surface of the body, through which the oxygen necessary for its life is supplied.

In addition, vacuoles also participate in the respiration process.

Features of reproduction

In the warm season, hydras reproduce by budding. This is an asexual method of reproduction. In this case, a growth forms on the body of the individual, which increases in size over time. Tentacles grow from the “bud” and a mouth is formed.

During the budding process, a new creature separates from the body and goes free swimming.

IN cold period Since then, hydras reproduce only sexually. Eggs and sperm mature in the animal's body. Male cells, having left the body, fertilize the eggs of other hydras.

After the reproductive function, adult individuals die, and the fruit of their creation becomes 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 membrane and begins an independent life.

What does hydra eat?

The hydra's diet is characterized by a diet consisting of miniature inhabitants of reservoirs - ciliates, water fleas, planktonic crustaceans, insects, fish fry, and worms.

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

Regeneration of Hydra vulgaris

G Hydra has unique ability: She doesn't age. Each cell of the animal is renewed in a couple of weeks. Even having lost a part of the body, the polyp is able to grow exactly the same one, restoring symmetry.

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

Biological significance of freshwater hydra

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

Hydras are a valuable research object for scientists in the biological, medical and scientific fields.

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 type 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);
• a gelatinous support 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 environment, such as water movement or chemical irritants.

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, absorption nutrients. Unlike ectoderm muscle cells, they are arranged in a ring. This causes the polyp to stretch as the endodermal muscle cells contract.

The endodermal gastrodermis surrounds the so-called gastrointestinal cavity. Because this cavity contains both the digestive tract and 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 produce, 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 hydra's nervous system is structurally simple compared to more developed ones. nervous systems 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 lengthen their body to maximum length, and then slowly expand their tentacles. Despite their simple structure, tentacles expand unusually and can be five times larger longer bodies. 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 researchers have yet to go long haul, before they can understand how the results of their work can 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.