According to the method of feeding, the freshwater hydra is what. Freshwater polyp hydra
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.
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 in 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.
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 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 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 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 ones are formed. various cells ectoderm and endoderm. Hydra can restore enough most of your 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
U freshwater hydra there are 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.
In lakes, rivers or ponds with clean, clear water, attached animals that look like frayed twine are often found on the roots of duckweed, stems and leaves of other aquatic plants. This Hydras. Externally, Hydras look like small translucent brownish or greenish stems with a corolla tentacles at the free end of the body. Hydra is a freshwater polyp (“polyp” means “multipede”).
Hydras are radially symmetrical animals. Their body is in the form of a bag measuring from 1 to 3 cm (and the body usually does not exceed 5-7 mm in length, but the tentacles can stretch several centimeters). At one end of the body there is sole, used for attachment to underwater objects, on the opposite - oral hole, surrounded by long tentacles(5-12 tentacles). In our reservoirs, Hydra can be found from the beginning of June to the end of September.
Lifestyle. Hydras – predatory animals. They catch prey with the help of tentacles, on which they are located in huge numbers stinging cells. When you touch the tentacles, long threads containing strong toxins. Killed animals are pulled by tentacles to the mouth opening and swallowed. Hydra swallows small animals whole. If the victim is somewhat larger than the Hydra itself, it can also swallow it. At the same time, the predator’s mouth opens wide, and the walls of the body are greatly stretched. If the prey does not fit entirely into the gastric cavity, the Hydra swallows only one end of it, pushing the victim deeper and deeper as it is digested. Undigested food remains are also removed through the mouth. Hydras prefer daphnia (water fleas), but they can also eat other crustaceans, ciliates, various insect larvae and even small tadpoles and fry. A moderate daily diet is one daphnia.
Hydras usually lead a motionless lifestyle, but can crawl from place to place, sliding on their soles or tumbling over their heads. They always move in the direction of the light. When irritated, animals are able to shrink into a ball, which may also help them with bowel movements.
Body structure. The Hydra's body consists of two layers of cells. These are the so-called two-layer animals. The outer layer of cells is called ectoderm, and the inner layer – endoderm (endoderm). Between the ectoderm and endoderm there is a layer of structureless mass - mesoglea. Mesoglea sea jellyfish makes up up to 80% of body weight, and in Hydra the mesoglea is not large and is called supporting record.
Genus Hydra - Hydra
Inside the Hydra's body is gastric cavity (intestinal cavity), opening outward with one single hole ( oral hole).
IN endoderm are located epithelial-muscle and glandular cells. These cells line the intestinal cavity. The main function of the endoderm is digestive. Epithelial-muscle cells, with the help of flagella facing the intestinal cavity, push food particles, and with the help of pseudopods they capture them and pull them inside. Food is digested in these cells. Glandular cells produce enzymes that break down proteins. The digestive juice of these cells enters the intestinal cavity, where digestion processes also occur. Thus, Hydra has two types of digestion: intracavitary(extracellular), characteristic of other multicellular animals, and intracellular(characteristic of unicellular and lower multicellular organisms).
In the ectoderm Hydra has epithelial-muscular, nerve, stinging and intermediate cells. Epithelial-muscle (cover) cells cover the body of the Hydra. Each of them has a long process elongated parallel to the surface of the body, in the cytoplasm of which there are developed contractile fiber. The combination of such processes forms a layer of muscular formations. When the fibers of all epithelial muscle cells contract, the Hydra's body contracts. If the fibers contract on only one side of the body, then the Hydra bends in that direction. Thanks to the work of muscle fibers, Hydra can slowly move from place to place, alternately “stepping” with its sole and tentacles.
Stinging or nettle cells There are especially many tentacles in the ectoderm. Inside these cells is capsule with a poisonous liquid and a coiled tubular a thread. On the surface of stinging cells there is sensitive hair. These cells serve as Hydra's weapons of attack and defense. When prey or an enemy touches a sensitive hair, the stinging capsule instantly throws the thread out. The poisonous liquid, entering the thread, and then through the thread into the animal’s body, paralyzes or kills it. Stinging cells die after a single use and are replaced by new ones formed by intermediate cells.
Intermediate cells small, round, with large nuclei and a small amount of cytoplasm. When the Hydra's body is damaged, they begin to rapidly grow and divide. Epithelial-muscular, nerve, germ and other cells can be formed from intermediate cells.
Nerve cells scattered under the integumentary epithelial-muscular cells, and they are stellate in shape. The processes of nerve cells communicate with each other, forming a nerve plexus that thickens around the mouth and on the sole.
Genus Hydra - Hydra
This type of nervous system is called diffuse- the most primitive in the animal world. Some of the nerve processes approach the skin-muscle cells. The processes are capable of perceiving various irritations (light, heat, mechanical influences), as a result of which excitation develops in the nerve cells, which is transmitted through them to all parts of the body and animal and causes an appropriate response.
Thus, Hydra and other Coelenterates have real fabrics, although little differentiated - ectoderm and endoderm. The nervous system appears.
Hydra does not have special respiratory organs. Oxygen dissolved in water penetrates the hydra through the entire surface of the body. Hydra also has no excretory organs. The end products of metabolism are excreted through the ectoderm. Sense organs are not developed. The sense of touch is carried out over the entire surface of the body, the tentacles (sensitive hairs) are especially sensitive, throwing out stinging threads that kill or paralyze prey.
Reproduction. How does Hydra reproduce? asexual, so sexual way. During the summer it reproduces asexually - budding. In the middle part of the Hydra's body there is a budding belt on which tubercles are formed ( kidneys). The bud grows, a mouth and tentacles form at its apex, after which the bud thins out at the base, separates from the body of the mother and begins to live independently. This resembles the development of a plant shoot from a bud - hence the name of this method of propagation.
In autumn, with the approach of cold weather, sex cells are formed from intermediate cells in the ectoderm of Hydra - spermatozoa And eggs. Stalked Hydras dioecious, and their fertilization cross. The egg cells are located closer to the base of the Hydra and are similar to an amoeba, and the sperm are similar to flagellated protozoa and develop in tubercles located closer to the mouth opening. The sperm has a long flagellum, with which it swims in water and reaches the eggs, and then merges with them. Fertilization occurs inside the body of the mother. The fertilized egg begins to divide, becomes covered with a dense double shell, sinks to the bottom and overwinters there. In late autumn, Hydras die. And in the spring, a new generation develops from overwintered eggs.
Regeneration. When the body is damaged, cells located near the wound begin to grow and divide, and the wound quickly closes (heals). This process is called regeneration. Regeneration occurs in many animals, and humans also have it. But not a single animal can compare with Hydra in this matter. Perhaps the hydra got its name precisely for this property (see the second labor of Hercules).
Lernaean Hydra (Second Labor of Hercules)
After the first feat, King Eurystheus sent Hercules to kill the Lernaean hydra. It was a monster with the body of a snake and nine heads of a dragon. The hydra lived in a swamp near the city of Lerna and, crawling out of its lair, destroyed entire herds and devastated the entire surrounding area. The fight with the nine-headed hydra was dangerous because one of its heads was immortal. Hercules set off on a journey to Lerna with his friend Iolaus. Arriving at a swamp near the city of Lerna, Hercules left Iolaus with his chariot in a nearby grove, and he himself went to look for the hydra. He found her in a cave surrounded by a swamp. Having heated his arrows red-hot, Hercules began to shoot them one after another into the hydra. The arrows of Hercules enraged the Hydra. She crawled out, wriggling a body covered with shiny scales, from the darkness of the cave, rose menacingly on her huge tail and was about to rush at the hero, but the son of Zeus stepped on her torso with his foot and pressed her to the ground. The hydra wrapped its tail around the legs of Hercules and tried to knock him down. Like an unshakable rock, stood The hero, with swings of his heavy club, knocked down the heads of the hydra one after another. The club whistled in the air like a whirlwind; The hydra's heads flew off, but the hydra was still alive. Then Hercules noticed that in the hydra, in place of each knocked-down head, two new ones grew. Help for the hydra also appeared. A monstrous cancer crawled out of the swamp and dug its claws into Hercules’ leg. Then the hero called Iolaus for help. Iolaus killed the monstrous cancer, set fire to part of the nearby grove and, with burning tree trunks, burned the hydra's necks, from which Hercules knocked off the heads with his club. The hydra has stopped growing new heads. She resisted the son of Zeus weaker and weaker. Finally, the immortal head flew off the hydra. The monstrous hydra was defeated and fell dead to the ground. The victor Hercules buried her immortal head deeply and piled a huge rock on it so that it could not come out into the light again.
If we talk about the real Hydra, then its ability to regenerate is even more incredible! A new animal can grow from 1/200 of a Hydra; in fact, a whole organism is restored from the pulp. Therefore, Hydra regeneration is often called an additional method of reproduction.
Meaning. Hydras are a favorite subject for studying regeneration processes. In nature, Hydra is an element of biological diversity. In the structure of the ecosystem, Hydra, as a predatory animal, acts as a second-order consumer. No animal simply wants to feed on Hydra itself.
Questions for self-control.
Name the systematic position of Hydra.
Where does Hydra live?
What body structure does Hydra have?
How does Hydra eat?
How does Hydra excrete waste products?
How does Hydra reproduce?
What is the significance of Hydra in nature?
Genus Hydra - Hydra
Rice. The structure of Hydra.
A - longitudinal section (1 - tentacles, 2 - ectoderm, 3 - endoderm, 4 - gastric cavity, 5 - mouth, 6 - testis, 7 - ovary and developing zygote).
B - cross-section (1 - ectoderm, 2 - endoderm, 3 - gastric cavity, 4, 5 - stinging cells, 6 - nerve cell, 7 - glandular cell, 8 - supporting plate).
B - nervous system. G - epithelial muscle cell. D - stinging cells (1 - in a dormant state, 2 - with a discarded thread; the nuclei are painted black).
Genus Hydra - Hydra
Rice. Reproduction of Hydra.
From left to right: Hydra with male gonads, Hydra with female gonads, Hydra during budding.
Rice. Hydra movement.
Hydras move, attaching to the substrate either with the sole or with a mouth cone with tentacles.
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 a single life form 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. They give rise to other types of cells, 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.
Figure: Structure of freshwater hydra. Radial symmetry of Hydra
Habitat, structural features and vital functions of the freshwater hydra polyp
In lakes, rivers or ponds with clean, transparent water, a small translucent animal is found on the stems of aquatic plants - polyp hydra(“polyp” means “multi-legged”). This is an attached or sedentary coelenterate animal 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. Using 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 extend several centimeters.
Radial symmetry of Hydra
If you draw an imaginary axis 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 tentacles arranged in a radial manner are best suited to this method of hunting.
Radiation symmetry is characteristic, as a rule, of animals leading an attached lifestyle.
Hydra intestinal cavity
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: structure of the outer layer of cells - hydra ectoderm
The outer layer of hydra cells is called - ectoderm. Under a microscope, several types of cells are visible in the outer layer of the hydra - the ectoderm. Most of all here are skin-muscular. By touching their sides, these cells create the cover of the hydra. At the base of each such cell there is a contractile muscle fiber that plays important role when the animal moves. When everyone's fiber skin-muscular cells contract, the hydra's body contracts. If the fibers contract on only one side of the body, then the hydra bends in that direction. Thanks to the work of muscle fibers, the hydra can slowly move from place to place, alternately “stepping” with its sole and tentacles. This movement can be compared to a slow somersault over your head.
The outer layer contains and 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. Some of the processes approach the skin-muscle cells.
Hydra irritability and reflexes
Hydra is able to sense touch, temperature changes, the appearance of various dissolved substances in water and other irritations. This causes her nerve cells to become excited. If you touch the hydra with a thin needle, then the excitement from irritation of one of the nerve cells is transmitted along the processes to other nerve cells, and from them to the skin-muscle cells. This causes muscle fibers to contract, and the hydra shrinks into a ball.
Picture: Hydra's irritability
In this example, we get acquainted with a complex phenomenon in the animal body - reflex. The reflex consists of three successive stages: perception of irritation, transfer of excitation from this irritation along the nerve cells and response body by any action. Due to the simplicity of the hydra's organization, its reflexes are very uniform. In the future we will become familiar with much more complex reflexes in more highly organized animals.
Hydra stinging cells
Pattern: Stringing or nettle cells of Hydra
The entire body of the hydra and especially its tentacles are seated with a large number stinging, or nettles cells. Each of these cells has a complex structure. In addition to the cytoplasm and nucleus, it contains a bubble-like stinging capsule, inside which a thin tube is folded - stinging thread. Sticking out of the cage sensitive hair. As soon as a crustacean, small fish or other small animal touches a sensitive hair, the stinging thread quickly straightens, its end is thrown out and pierces the victim. Through a 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, many stinging cells are fired at once. Then the hydra uses its tentacles to pull the prey to its mouth and swallows it. The stinging cells also serve the hydra for protection. Fish and aquatic insects do not eat hydras, which burn their enemies. The poison from the capsules is reminiscent of nettle poison in its effect on the body of large animals.
The inner layer of cells is the hydra endoderm
Figure: 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 to digest food. They secrete digestive juice into the intestinal cavity, under the influence of which the hydra’s prey softens and breaks down 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 sweep particles towards the cells. The cells of the inner layer are capable of releasing pseudopods (like those of an amoeba) and capturing food with them. Further digestion occurs inside the cell, in vacuoles (like in protozoa). Undigested food remains are thrown out through the mouth.
The hydra has no special respiratory organs; oxygen dissolved in water penetrates the hydra through the entire surface of its body.
Hydra regeneration
The outer layer of the hydra's body also contains very small round 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 rapidly. From them, skin-muscle, nerve and other cells are formed, and the wounded area quickly heals.
If you cut a hydra crosswise, 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. Hydra has a highly developed ability to regenerate.
Regeneration, to one degree or another, is also characteristic of other animals and humans. Thus, in earthworms it is possible to regenerate a whole organism from their parts; in amphibians (frogs, newts) entire limbs, different parts of the eye, tail and internal organs. When a person is cut, the skin is restored.
Hydra reproduction
Asexual reproduction of hydra by budding
Figure: Hydra asexual reproduction by budding
Hydra reproduces asexually and sexually. In summer, a small tubercle appears on the hydra’s body - a protrusion of the wall of its body. This tubercle grows and stretches out. Tentacles appear at its end, and a mouth breaks out between them. This is how the young hydra develops, which at first remains connected to the mother with the help of a stalk. 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 independently.
Hydra sexual reproduction
By autumn, with the onset of unfavorable conditions, hydras die, but before that, sex cells develop in their body. There are two types of germ cells: ovoid, or female, and spermatozoa, or male reproductive cells. Sperm are similar to flagellated protozoa. They leave the hydra's body and swim using a long flagellum.
Drawing: sexual reproduction hydra
The hydra egg cell is similar to an amoeba and has pseudopods. The sperm swims up to the hydra with the egg cell and penetrates inside it, and the nuclei of both sex cells merge. Happening fertilization. After this, the pseudopods are retracted, the cell is rounded, and a thick shell is formed 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, the fertilized egg begins to divide, the resulting cells are arranged in two layers. From them a small hydra develops, which with the onset warm weather comes out through a break in the egg shell.
Thus, the multicellular animal hydra at the beginning of its life consists of one cell - an egg.
