What does common hydra eat? Hydra - class Hydrozoa: sensory organs, nervous and digestive systems, reproduction

Hydra. Obelia. The structure of the hydra. Hydroid polyps

They live in marine and rarely in fresh water bodies. Hydroids are the most simply organized coelenterates: a gastric cavity without septa, nervous system without ganglia, the gonads develop in the ectoderm. Often form colonies. Many have a change of generations in their life cycle: sexual (hydroid jellyfish) and asexual (polyps) (see. Coelenterates).

Hydra sp.(Fig. 1) - a single freshwater polyp. The length of the hydra's body is about 1 cm, its lower part - the sole - serves to attach to the substrate; on the opposite side there is a mouth opening, around which 6-12 tentacles are located.

Like all coelenterates, hydra cells are arranged in two layers. The outer layer is called ectoderm, the inner layer is called endoderm. Between these layers is the basal plate. In the ectoderm there are the following types cells: epithelial-muscular, stinging, nervous, intermediate (interstitial). Any other ectoderm cells can be formed from small undifferentiated interstitial cells, including germ cells during the reproductive period. At the base of the epithelial-muscle cells are muscle fibers located along the axis of the body. When they contract, the hydra's body shortens. Nerve cells are stellate in shape and located on the basement membrane. Connected by their long processes, they form a primitive nervous system of the diffuse type. The response to irritation is reflexive in nature.

rice. 1.
1 - mouth, 2 - sole, 3 - gastric cavity, 4 - ectoderm,
5 - endoderm, 6 - stinging cells, 7 - interstitial
cells, 8 - epithelial-muscular ectoderm cell,
9 - nerve cell, 10 - epithelial-muscular
endoderm cell, 11 - glandular cell.

The ectoderm contains three types of stinging cells: penetrants, volventes and glutinants. The penetrant cell is pear-shaped, has a sensitive hair - cnidocil, inside the cell there is a stinging capsule, which contains a spirally twisted stinging thread. The capsule cavity is filled with toxic liquid. At the end of the stinging thread there are three spines. Touching the cnidocil causes the release of a stinging thread. In this case, the spines are first pierced into the body of the victim, then the venom of the stinging capsule is injected through the thread channel. The poison has a painful and paralyzing effect.

The other two types of stinging cells perform additional function retention of prey. Volvents shoot trapping threads that entangle the victim's body. Glutinants release sticky threads. After the threads shoot out, the stinging cells die. New cells are formed from interstitial ones.

Hydra feeds on small animals: crustaceans, insect larvae, fish fry, etc. The prey, paralyzed and immobilized with the help of stinging cells, is sent to the gastric cavity. Digestion of food is cavity and intracellular, undigested residues are excreted through the mouth.

The gastric cavity is lined with endoderm cells: epithelial-muscular and glandular. At the base of the epithelial-muscular cells of the endoderm there are muscle fibers located in the transverse direction relative to the axis of the body; when they contract, the body of the hydra narrows. The area of ​​the epithelial-muscle cell facing the gastric cavity carries from 1 to 3 flagella and is capable of forming pseudopods to capture food particles. In addition to epithelial-muscular cells, there are glandular cells that secrete digestive enzymes into the intestinal cavity.

rice. 2.
1 - maternal individual,
2 - daughter individual (bud).

Hydra reproduces asexually (budding) and sexually. Asexual reproduction occurs in the spring-summer season. The buds are usually formed in the middle areas of the body (Fig. 2). After some time, young hydras separate from the mother’s body and begin to lead an independent life.

Sexual reproduction occurs in autumn. During sexual reproduction, germ cells develop in the ectoderm. Sperm are formed in areas of the body close to the mouth, eggs - closer to the sole. Hydras can be either dioecious or hermaphroditic.

After fertilization, the zygote is covered with dense membranes, and an egg is formed. The hydra dies, and a new hydra develops from the egg the following spring. Direct development without larvae.

Hydra has a high ability to regenerate. This animal is able to recover even from a small severed part of the body. Interstitial cells are responsible for regeneration processes. The vital activity and regeneration of hydra were first studied by R. Tremblay.

Obelia sp.- a colony of marine hydroid polyps (Fig. 3). The colony has the appearance of a bush and consists of individuals of two types: hydranthus and blastostyles. The ectoderm of the colony members secretes a skeletal organic shell - the periderm, which performs the functions of support and protection.

Most of the colony's individuals are hydrants. The structure of a hydrant resembles that of a hydra. Unlike hydra: 1) the mouth is located on the oral stalk, 2) the oral stalk is surrounded by many tentacles, 3) the gastric cavity continues in the common “stem” of the colony. Food captured by one polyp is distributed among members of one colony through the branched channels of the common digestive cavity.

rice. 3.
1 - colony of polyps, 2 - hydroid jellyfish,
3 - egg, 4 - planula,
5 - young polyp with a kidney.

The blastostyle has the form of a stalk and does not have a mouth or tentacles. Jellyfish bud from the blastostyle. Jellyfish break away from the blastostyle, float in the water column and grow. The shape of the hydroid jellyfish can be compared to the shape of an umbrella. Between the ectoderm and endoderm there is a gelatinous layer - mesoglea. On the concave side of the body, in the center, on the oral stalk there is a mouth. Numerous tentacles hang along the edge of the umbrella, serving for catching prey (small crustaceans, larvae of invertebrates and fish). The number of tentacles is a multiple of four. Food from the mouth enters the stomach; four straight radial canals extend from the stomach, encircling the edge of the jellyfish's umbrella. The method of movement of the jellyfish is “reactive”; this is facilitated by the fold of ectoderm along the edge of the umbrella, called the “sail”. The nervous system is of a diffuse type, but there are clusters nerve cells along the edge of the umbrella.

Four gonads are formed in the ectoderm on the concave surface of the body under the radial canals. Sex cells form in the gonads.

From the fertilized egg, a parenchymal larva develops, corresponding to a similar sponge larva. The parenchymula then transforms into a two-layer planula larva. The planula, after swimming with the help of cilia, settles to the bottom and turns into a new polyp. This polyp forms a new colony by budding.

For life cycle obelia is characterized by alternation of asexual and sexual generations. The asexual generation is represented by polyps, the sexual generation by jellyfish.

Description of other classes of the type Coelenterates.

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 strange creature, who 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 the 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 caterpillar 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 bud growth 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. At 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 a hydra was obtained from Ancient Greece, these polyps came to be called hydra.

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 exactly this type, 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 in the water from side to side 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 radial) 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 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 shortening, 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 chemicals, 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, 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.

At least five species of hydra live in Europe, including Hydra vulgaris (brown or common hydra) and Hydra Viridissima (green hydra).The first descriptions were given by naturalist A. Levenguk. sea ​​water preferable for most species, but freshwater hydra prefers ponds, lakes and rivers. Hydras live in bodies of water with minimal current. They attach to rocks, plants or the bottom.

Important! These animals are light-loving and strive for the sun, crawling onto the rocks closer to the shore.

The structure of freshwater hydra

The body of the animal has the shape of a radially symmetrical tube: there is an opening in front, which is used as a mouth, it is surrounded by a corolla of 5-12 tentacles. Each one is “wrapped” in highly specialized caustic cells. Upon contact with the victim, they produce neurotoxins, performing the functions of obtaining food. Under them there is a small narrowing - the neck. It separates the head and torso. The rear end of the animal tapers into a stalk, which is also called a “stalk.” It ends with a sole (basal disc). The leg serves as a support for the body, with its help the hydra can attach to other surfaces. The basal sole contains omental cells that secrete a sticky fluid. To move, the animal sticks to the adjacent support with its tentacles and releases the leg, moving it further, and so on until it reaches the target. It can also glide on the basal disc or swim briefly.

Important! If the hydra has eaten, its body length will be about 5-8 mm, and if not, it will be much longer. Therefore, it can only be examined in detail under a microscope.

The hydra's body consists of 2 layers of cells:

• ectoderm;
• endoderm.

Between them passes a layer of mesoglea (intercellular substance). On the outer layer there is different cells: some are intended for paralysis during hunting and protection, others for secreting mucus, others for movement, etc.

Important! Breathing and excretion of metabolic products occur in the hydra over the entire surface of the body. Oxygen is supplied through the skin.

Hydra has several simple reflexes.It can respond to mechanical stress, temperature, light, chemical compounds and other irritants.

Cellular composition of the body

It consists of six types of cells that perform separate functions:

• Epithelial-muscular. Provides the ability to move.
• Ferrous. Produce enzymes necessary for digestion.
• Interstitial. Intermediate type. They can become cells of other species if necessary.
• Nervous. Responsible for reflexes. They are found throughout the body, connecting into a network.
• Stinging. Contains a paralyzing agent. They exist for protection and nutrition.
• Genital. Almost all hydras are dioecious, but there are also hermaphroditic individuals. Both eggs and sperm are formed from i-cells.

Freshwater hydra nutrition

Hydra is a predatory animal. She eats small crustaceans (cyclops, daphnia), and also feeds on mosquito larvae and small worms. The hunting behavior of the bucket hydra is quite interesting: it hangs head down and spreads its tentacles. At the same time, her body swings very slowly in a circle. When the prey is caught by the tentacles, the stinging cells strike it and immobilize it. The hydra lifts it with its tentacles to its mouth and absorbs it.

Important! Hydra is capable of absorbing prey that is larger than itself due to the significantly stretchable walls of its body.

Reproduction methods

Hydra can reproduce both by budding and sexually. If living conditions are good, the animal will choose the asexual path. The budding process of this animal occurs very quickly if the individual is well fed. The growth of a bud from the size of a small tubercle to a full-fledged individual that sits on the mother’s body takes place in a few days. In this case, even if there is a new hydra that has not separated on the mother’s body, new buds can form. The sexual method usually takes place in the fall, if the water becomes colder. Characteristic swellings form on the surface of the body - gonads with eggs. Male reproductive cells simply float in the water, and then penetrate the eggs, and fertilization occurs. After the eggs are formed, the hydra dies, and they go down to the bottom and hibernate. In the spring they continue to develop and grow.

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 a typical representative of 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, mainly performing a supporting 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. Obtained after digestion nutrients 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.