Who among us has not read books about the colorful world of coral polyps in the shallow waters of tropical seas! But about the fact that a relative of these polyps lives in our overgrown stagnant reservoirs - hydra(Hydra) (though not very close), hardly anyone knows. And he is remarkable.
It is very difficult to find hydras in a body of water. They sit on plants, stones, pieces of wood in the water, but if you take any of these objects out of the water, you will see nothing but an inconspicuous slimy lump. You need to do it differently: collect plants from a densely overgrown pond, put them in a jar or aquarium with water and let everything calm down. After this, examine the contents through the glass. This is where you will see them. These are small creatures in the shape of a short, narrow cylinder, which is attached at the base to an underwater object and carries several flexible thread-like tentacles at the free end. There are hydras with variable thickness of the axial part of the body: it is thicker, and closer to the base it turns into a narrow stalk. This stalked or brown hydra (Hydra oligactis).
Hydra is extremely simple. Its body is a bag, at the free end of which a mouth opening opens, surrounded by tentacles. This bag consists of two layers of cells - outer and inner. The first one makes contact with the body external environment, the second assimilates the caught food. Food (primarily very small animals floating in the water column, such as crustaceans) is caught by the tentacles.
To catch crustaceans and other small animals, the hydra, like all representatives of cnidarians, has powerful weapon- batteries of stinging cells. There are especially many of them on the tentacles, which is why they sometimes look knotty. Inside each such 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.
So, hydra is on the hunt. Here it swims near its tentacles characteristic jumps daphnia. Suddenly she touched the hydra's tentacle, and something stopped her. And no matter how long you wait, the daphnia will no longer budge. Let us now select the victim from the hydra and examine it through a microscope. We will see many different stinging cells on the body of daphnia. Some of them, having pierced, injected poison into it, which is why it stopped moving, others wrapped themselves in several rings around the legs and bristles of the daphnia, and, finally, others simply stuck to the body - with them the hydra attracts prey to itself. The paralyzed victim is attached to the tentacle by microscopic “harpoons” (usually there are many of them and they different types). The tentacle bends, brings the prey to its mouth, and the hydra slowly swallows it. The body swells (the prey is often wider), and the process of digestion begins, carried out primarily inside the cells lining the intestinal cavity. Undigested food remains are expelled through the mouth.
On some hydras you can notice a kind of branching. Not far from the base, a second, small polyp emerges - this is a kidney. It will separate when it grows up and heal independent life. Hydras move slowly. They separate from the substrate on which they sit, turn their tentacles towards it and thus crawl or “walk” very slowly.
Hydra can reproduce both by budding and sexually. In the upper part of the hydra’s body there are small tubercles where sperm are formed, and in the lower part, closer to the point of attachment, there are large protrusions where eggs are formed.
Some hydras, such as the green hydra ( Hydra viridissima), have a bright green color, depending on the presence of unicellular algae in their body. Algae supply the hydra tissues with oxygen and some organic substances, and the hydra, in turn, provides them with nitrogen and phosphorus compounds necessary for plants.
One of the most remarkable abilities of hydras is the ability to rebuild their body from small pieces. The famous Danish writer Hans Scherfig, in his short book “The Pond,” written with extraordinary love for everything living on Earth, described the discovery of this ability of the hydra this way: “The twenty-fifth of September 1740 is a significant day in the history of zoology. On this day, the Swiss Abraham Tremblay cut freshwater polyp hydra into two parts. Both parts continued to live after the operation. From one piece, called Tremblay's "head", a new body grew, and from the other - a new "head". Fourteen days after the experiment, two new living organisms arose." Other experiments told by Scherfig in this book are also noteworthy: "The hydra is small, only two and a half centimeters. Such a small creature was divided into a hundred pieces - and from each piece a new hydra emerged. They split it in half and prevented the halves from growing together - they got two animals interconnected with each other. They dissected the hydra into bundles - a bunch-shaped colony of hydras was formed... When several hydras were cut and the individual parts were allowed to grow together, the result was absolutely monsters: organisms with two heads, several heads... And these monstrous, ugly forms continued to live... "Just like the mythical Lernaean hydra - a multi-headed snake with which Hercules fought and whose name this freshwater polyp received.
Hydra, although an inconspicuous and even inconspicuous inhabitant of our fresh waters, plays a noticeable role in reservoirs - in the thicket zone it significantly affects the number of small animals. In addition, the hydra gives general idea about the structure and way of life of primitive and ancient group animals - cnidarians.
Literature: Crayfish, mollusks. Ya. I. Starobogatov. Nature Leningrad region, 1988
Hydras are a genus of animals belonging to the Coelenterates. Their structure and life activity are often considered using the example of a typical representative - freshwater hydra. Next, we will describe this particular species, which lives in fresh water bodies with clean water, attaches to aquatic plants.
Typically, the size of a 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 (about 6-10), which can extend to a length exceeding the length of the body. The hydra bends from side to side in the water and with its tentacles catches small arthropods (daphnia, etc.), after which it sends them into its mouth.
Hydras, as well as all coelenterates, are characterized by radial (or ray) symmetry. If you look at it not from above, you can draw many imaginary planes dividing the animal into two equal parts. The hydra does not care from which side the food swims towards it, since it leads a stationary lifestyle, so radial symmetry is more advantageous to it than bilateral symmetry (characteristic of most mobile animals).
The hydra's mouth opens into intestinal cavity. Partial digestion of food occurs here. The rest of the digestion is carried out in the cells, which absorb partially digested food from the intestinal cavity. Undigested remains are expelled through the mouth, since coelenterates do not have an anus.
The body of hydra, like all coelenterates, consists of two layers of cells. The outer layer is called ectoderm, and internal - endoderm. Between them there is a small layer mesoglea- a noncellular gelatinous substance that may contain various types of cells or cell processes.
Hydra ectoderm
Hydra ectoderm consists of several types of cells.
Skin-muscle cells the most numerous. They create the integument of the animal, and are also responsible for changing the shape of the body (lengthening or decreasing, bending). Their processes contain muscle fibers that can contract (their length decreases) and relax (their length increases). Thus, these cells play the role of not only the integument, but also the muscles. Hydra does not have real muscle cells and therefore no real muscle tissue.
The hydra can move using somersaults. She bends down so much that her tentacles reach the support and stands on them, lifting her sole up. After this, the sole tilts and rests on the support. Thus, the hydra makes a somersault and ends up in a new place.
Hydra has nerve cells. These cells have a body and long processes with which they connect 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 a cluster of nerve cells (ganglia, brain), but even such a primitive nervous system allows them to have unconditioned reflexes. Hydras react to touch, the presence of a row chemical substances, temperature change. So if you touch a 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 stinging cells. There are especially many of them on the tentacles. These cells inside contain stinging capsules with stinging filaments. Outside the cells there is a sensitive hair, when touched, the stinging thread shoots out of its capsule and strikes the victim. In this case, a poison is injected into a small animal, usually having a paralytic effect. With the help of stinging cells, 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 at the site of the wound, new and different cells of the ectoderm and endoderm are formed. Hydra can restore quite a large part 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
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 fibers face the mesoglea. Flagella are directed towards the intestinal cavity, which rake food particles towards the cell. The cell captures them the way amoebas do - forming pseudopods. Next, the food ends up in the digestive vacuoles.
The endoderm secretes a secretion into the intestinal cavity - digestive juice. Thanks to it, the animal captured by the hydra disintegrates into small particles.
Hydra reproduction
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 breaks through. Subsequently, the daughter individual separates. Thus, freshwater hydras do not form colonies.
With the onset of cold weather (autumn), the hydra begins to sexual reproduction. After sexual reproduction, hydras die; they cannot live in winter. During sexual reproduction, eggs and sperm are formed in the body of the hydra. The latter leave the body of one hydra, swim up to another and fertilize its eggs there. Zygotes are formed, which are covered with a dense shell, allowing them to survive the winter. In the spring, the zygote begins to divide, and two germ layers are formed - ectoderm and endoderm. When the temperature gets high enough, the young hydra breaks the shell and comes out.
Hydra biology description internal structure photo lifestyle nutrition reproduction protection from enemies
Latin name Hydrida
To characterize the structure of a hydroid polyp, we can use as an example freshwater hydras, which retain very primitive organizational features.
External and internal structure
Hydras They have an elongated, sac-like body, capable of stretching quite strongly and shrinking almost into a spherical lump. A mouth is placed at one end; this end is called the oral or oral pole. The mouth is located on a small elevation - the oral cone, surrounded by tentacles that can stretch and shorten very strongly. When extended, the tentacles are several times the length of the hydra's body. The number of tentacles varies: there can be from 5 to 8, and some hydras have more. In Hydra, there is a central gastric section, which is somewhat more expanded, turning into a narrowed stalk ending in a sole. With the help of the sole, the hydra attaches to the stems and leaves of aquatic plants. The sole is located at the end of the body, which is called the aboral pole (opposite to the oral, or oral).
The body wall of the hydra consists of two layers of cells - ectoderm and endoderm, separated by a thin basal membrane, and limits a single cavity - the gastric cavity, which opens outwards with the oral opening.
In hydras and other hydroids, the ectoderm is in contact with the endoderm along the very edge of the mouth opening. In freshwater hydras, the gastric cavity continues into the tentacles, which are hollow inside, and their walls are also formed by ectoderm and endoderm.
Hydra ectoderm and endoderm consist of large number cells of various types. Main mass The cells of both ectoderm and endoderm are epithelial-muscle cells. Their outer cylindrical part is similar to ordinary epithelial cells, and the base adjacent to the basal membrane is elongated fusiform and consists of two contractile muscular processes. In the ectoderm, the contractile muscular processes of these cells are elongated in the direction of the longitudinal axis of the hydra's body. Their contractions cause shortening of the body and tentacles. In the endoderm, the muscular processes are elongated in a circular direction, across the axis of the body. Their contraction has the opposite effect: the body of the hydra and its tentacles narrow and at the same time lengthen. Thus, the muscle fibers of the epithelial-muscle cells of the ectoderm and endoderm, opposite in their action, make up the entire hydra musculature.
Among the epithelial-muscular cells, various stinging cells are located either singly or, more often, in groups. The same type of hydra, as a rule, has several types of stinging cells that perform different functions.
The most interesting are stinging cells with nettle-like properties, called penetrants. When stimulated, these cells release a long filament that pierces the body of the prey. The stinging cells are usually pear-shaped. A stinging capsule is placed inside the cage, covered with a lid on top. The wall of the capsule continues inward, forming a neck, which then passes into a hollow filament, coiled and closed at the end. At the junction of the neck and the filament, there are three spines inside, folded together and forming a stylet. In addition, the neck and stinging thread are lined with small spines on the inside. On the surface of the stinging cell there is a special sensitive hair - the cnidocil, at the slightest irritation of which the stinging thread is ejected. First, the cap opens, the neck is unscrewed, and the stiletto is pierced into the victim’s cover, and the spikes that make up the stiletto move apart and widen the hole. Through this hole, the twisting thread is pierced into the body. Inside the stinging capsule there are substances that have nettle properties and paralyze or kill prey. Once fired, the stinging thread cannot be used again by the hydroid. Such cells usually die and are replaced by new ones.
Another kind of stinging cells of hydras are volventa. They do not have nettle properties, and the threads they throw out serve to hold prey. They wrap around the hairs and bristles of crustaceans, etc. The third group of stinging cells are glutinants. They throw out sticky threads. These cells are important both in retaining prey and in moving the hydra. Stinging cells are usually located, especially on the tentacles, in groups called “batteries”.
The ectoderm contains small undifferentiated cells, the so-called interstitial, through which many types of cells develop, mainly stinging and reproductive cells. Interstitial cells are often located in groups at the base of epithelial muscle cells.
The perception of irritations in hydra is associated with the presence of sensitive cells in the ectoderm that serve as receptors. These are narrow, tall cells with a hair on the outside. Deeper, in the ectoderm, closer to the base of the skin-muscle cells, there are nerve cells equipped with processes through which they contact each other, as well as with receptor cells and contractile fibers of the skin-muscle cells. Nerve cells are located scatteredly in the depths of the ectoderm, forming with their processes a plexus in the form of a mesh, and this plexus is denser on the perioral cone, at the base of the tentacles and on the sole.
The ectoderm also contains glandular cells that secrete adhesive substances. They concentrate on the sole and on the tentacles, helping the hydra temporarily attach to the substrate.
Thus, in the ectoderm of the hydra there are cells of the following types: epithelial-muscular, stinging, interstitial, nervous, sensory, glandular.
The endoderm has less differentiation of cellular elements. If the main functions of the ectoderm are protective and motor, then the main function of the endoderm is digestive. In accordance with this, most of the endoderm cells consist of epithelial-muscle cells. These cells are equipped with 2-5 flagella (usually two), and are also capable of forming pseudopodia on the surface, capturing them, and then digesting food particles. In addition to these cells, the endoderm contains special glandular cells that secrete digestive enzymes. The endoderm also contains nerve and sensory cells, but in much smaller quantities than in the ectoderm.
Thus, the endoderm also contains several types of cells: epithelial-muscular, glandular, nervous, sensory.
Hydras do not remain attached to the substrate all the time; they can move from one place to another in a very unique way. Most often, hydras move “walking”, like the caterpillars of moths: the hydra bends with its oral pole towards the object on which it sits, sticks to it with its tentacles, then the sole comes off the substrate, is pulled up to the oral end and is attached again. Sometimes the hydra, having attached itself to the substrate with tentacles, lifts the stalk with the sole upward and immediately carries it to the opposite side, as if “tumbling.”
Hydra Power
Hydras are predators; they sometimes feed on quite large prey: crustaceans, insect larvae, worms, etc. With the help of stinging cells, they capture, paralyze and kill prey. Then the victim is pulled with tentacles to the highly distensible mouth opening and moves into the gastric cavity. In this case, the gastric region of the body becomes greatly inflated.
Digestion of food in hydra, unlike sponges, only partially occurs intracellularly. This is associated with the transition to predation and the capture of fairly large prey. The secretion of glandular cells of the endoderm is secreted into the gastric cavity, under the influence of which the food softens and turns into mush. Small food particles are then captured by the digestive cells of the endoderm, and the digestion process is completed intracellularly. Thus, in hydroids, intracellular or cavity digestion first occurs, which occurs simultaneously with the more primitive intracellular digestion.
Protection from enemies
The nettle cells of the hydra not only infect prey, but also protect the hydra from enemies, causing burns to predators attacking it. And yet there are animals that feed on hydras. These are, for example, some ciliated worms and especially Microstomum lineare, some gastropods (pond worms), Corethra mosquito larvae, etc.
The hydra's ability to regenerate is very high. Experiments carried out by Tremblay back in 1740 showed that pieces of the body of a hydra, cut into several dozen pieces, regenerate into a whole hydra. However, high regenerative ability is characteristic not only of hydras, but also of many other coelenterates.
Reproduction
Hydras reproduce in two ways - asexual and sexual.
Asexual reproduction of hydras occurs by budding. IN natural conditions hydra budding occurs throughout the summer. In laboratory conditions, budding of hydras is observed with sufficiently intense nutrition and a temperature of 16-20 ° C. Small swellings are formed on the body of the hydra - buds, which are protrusions of the ectoderm and endoderm outward. In them, due to the multiplying cells, further growth of the ectoderm and endoderm occurs. The kidney increases in size, its cavity communicates with the gastric cavity of the mother. At the free, outer end of the bud, tentacles and a mouth opening are finally formed.
Soon the matured young hydra separates from the mother.
Sexual reproduction of hydras in nature is usually observed in the fall, and in laboratory conditions it can be observed with insufficient nutrition and a drop in temperature below 15-16 ° C. Some hydras are dioecious (Pelmatohydra oligactis), others are hermaphrodites (Chlorohydra viridissima).
Sex glands - gonads - appear in hydras in the form of tubercles in the ectoderm. In hermaphrodite forms, male and female gonads are formed in various places. The testes develop closer to the oral pole, and the ovaries develop closer to the aboral pole. It is formed in the testes a large number of motile sperm. Only one egg matures in the female gonad. In hermaphrodite forms, the maturation of sperm precedes the maturation of eggs, which ensures cross-fertilization and eliminates the possibility of self-fertilization. The eggs are fertilized in the mother's body. The fertilized egg is covered with a shell and spends the winter in this state. Hydras, as a rule, die after the development of sexual products, and in the spring a new generation of hydras emerges from the eggs.
Thus, in freshwater hydras under natural conditions, there is a seasonal change in forms of reproduction: throughout the summer, hydras bud intensively, and in the fall (for middle zone Russia - in the second half of August), with a decrease in temperature in reservoirs and a decrease in the amount of food, they stop reproducing by budding and switch to sexual reproduction. In winter, hydras die, and only fertilized eggs overwinter, from which young hydras emerge in the spring.
The freshwater polyp Polipodium hydriforme also belongs to the order Hydra. The early stages of development of this polyp take place in the eggs of sterlets and cause them great harm. Several types of hydra are found in our reservoirs: stalked hydra (Pelmatohydra oligactis), common hydra (Hydra vulgaris), green hydra (Chlorohydra viridissima) and some others.
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 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-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 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 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.