Hydra is a genus of freshwater sedentary coelenterates from the class of hydroids

In ancient mythology, the hydra was a horrible monster with several heads that quickly grew if they were chopped off. Modern representatives of coelenterates are much smaller and are absolutely safe for humans. But they got their name precisely because of their good ability to regenerate. They are able to completely restore the body from its microscopic part. How are these amazing animals arranged?

Habitat

Hydra is a representative of the type of the intestinal, which includes about 10 thousand modern species. It is a small polyp, the size of which is about 2 cm, which lives by attaching to the support. As a substrate, he prefers algae or the bottom of fresh water bodies, in which there is no current.

Symmetry of the body

The body of the hydra has a cylindrical shape. Its lower part is called the sole. At the opposite end of the body are the tentacles.

Hydra is an organism that has radiation symmetry. If an imaginary axis is drawn from the oral opening to the sole, the tentacles will disperse like rays.

Intestinal cavity

The name of the type of these multicellular animals was obtained due to the presence of an intestinal cavity within the cylindrical body. The food enters through the oral opening. Here, too, is its digestion. The walls of the body of coelenterates consist of two layers of the body: the outer and the inner. Between them is a layer of intercellular substance, which looks like a thin plate.

Ectoderm

The outer layer of the coelenterates body is called the ectoderm. Let us consider which hydra cells form it. First of all, it is skin-muscular. Due to their contractions, the body of the hydra is capable of shrinking and tilting to the sides. Between them are nerve cells that have a stellate shape - neurons. Connecting with their processes, they form a plexus. Thanks to this structure, the whole organism is interconnected with the environment.

Which hydra cells are capable of division? First of all, intermediate. On the functions performed, they can be compared with the structures of the educational tissue of plants. These are non-specialized formations, in the division of which cells of all other types are formed. Their presence causes a high level of regeneration of polyps - the ability to restore lost or damaged parts of the body.

"Business card" hydra

Hydra is a polyp, which, like all coelenterates, has stinging cells. Since their presence is characteristic only of this type of animal, stinging cells are the "visiting card" of polyps and jellyfish.

Its components are a capsule with a sensitive hair and a spirally twisted thread. It contains substances that paralyze the victim. When single-celled, fish fry or small mollusks touch a sensitive hair, the thread unwinds and digs into the victim's body. In this case, the cell itself dies. It can no longer fulfill its function. The division of hydra cells , in particular, intermediate cells, ensures the continuous appearance of new stinging cells.

Endoderma

The internal layer of the body is dominated by digestive and glandular cells. Due to their action organic substances are cleaved. They have flagella, by means of which a constant flow of water is created and food particles appear inside specialized vacuoles. In them, the process of digestion of food is completed.

Features of life processes

In spite of the fact that the hydra is an organism, leading an attached way of life, it is capable of movement. It resembles an acrobat in a circus. First, the hydra leans to the side, then as it were, "rises on its head," resting on the substrate with tentacles. Then again falls on the sole. On a level surface, the hydra can slide.

The process of breathing is carried out through the covers. For this, the hydra uses oxygen dissolved in water.

Nerve cells are capable of perceiving irritation from the environment, transforming it into a nerve impulse, and carrying it through all parts of the body. These are the first multicellular animals capable of performing simple reflexes. If you touch the polyp with a sharp needle, his whole body will shrink. This simple protective reflex is the response of the body to irritation.

Which hydra cells are capable of division can also be considered using the example of polyp propagation. During the summer, the hydra propagates vegetatively by budding. First, a small protrusion forms on her body. Then this kidney grows, eventually separates from the mother's body and begins an independent existence. In autumn, due to a decrease in water temperature and a shortage of nutrients, budding ceases. Hydra goes on to sexual reproduction. Among them there are also dioecious individuals and hermaphrodites - organisms that are capable of forming both male and female sex cells. Hydra is characterized by external fertilization. Male germ cells of spermatozoa go into the water and connect with the eggs, which remain connected with the mother's body. As a result, zygotes are formed, covered with dense membranes. After that, adults die. Eggs sink to the bottom, where they winter. With the onset of the warm season, young polyps come out of them.

There is no circulatory system. Isolation occurs through the cells of the outer layer, and from the inner one they first enter the intestinal cavity, from which they exit through the oral opening.

Intensive division of the hydra determines their ability to regenerate. Experienced, it was proved that the polyp is able to completely recover from any part of the body: tentacles, soles, a collection of cells, and also from suspended matter.

Freshwater polyp (hydra) is an organism, the study of regeneration of which was the beginning of a new science - experimental zoology. This animal was first described in his scientific works by the inventor of the microscope Antoni van Leeuwenhoek, and the systematic name given to this species was given by Carl Linnaeus. With it is connected the story of the exploits of Hercules. According to ancient mythology, he defeated the many-headed Lernaean hydra. She also had in mind a scientist, since she also had the ability to regenerate. At the place of the severed head, a new one immediately grew. Our hero buried him in the ground, having committed one of twelve feats.

Some species are able to form a symbiosis with unicellular green algae by zoochlorella. It is proved that such a polyp can exist for several months without food.

Hydra is a typical representative of the type of the intestinal cavity, the characteristic feature of which is the presence of two body layers, specialized cells and a cavity in which the digestion process takes place.