Reproduction of Hydra: description, features

Different species of animals, preserved from ancient times to the present day, there are many. Among them there are primitive organisms that for more than six hundred million years continue to exist and reproduce - hydra.

Description and way of life

An ordinary inhabitant of reservoirs, a freshwater polyp called hydra, refers to coelenterate animals. It is a gelatinous semitransparent tube up to 1 cm long. One end, on which a unique sole is located, is attached to aquatic plants. On the other side of the body there is a corolla with a set of tentacles (from 6 to 12). They can stretch to a few centimeters in length and serve to search for prey, which hydra paralyzes with a stinging prick, pulls the tentacles to the oral cavity and swallows. The basis of nutrition consists of daphnia, larvae of mosquitoes, fish fry, cyclops. Depending on the color of the food eaten, the color of the translucent body of the hydra also changes.

Thanks to the contraction and relaxation of the integumentary-muscle cells, this organism can taper and thicken, stretch out to the sides and move slowly. Simply put, most of all on a moving and living an independent life the stomach resembles a freshwater hydra. Reproduction of it, in spite of this, occurs at rather high rates and in different ways.

Types of Hydra

Zoologists distinguish four types of these freshwater polyps. They are very different from each other. Large species with filiform tentacles several times the length of the body are called Pelmatohydra oligactis (long-stemmed hydra). Another species, with a body tapering to the sole, is called Hydra vulgaris or brown (ordinary). Hydra attennata (thin or gray) looks like an outwardly smooth tube with slightly longer tentacles than the body. The green hydra, called Chlorohydra viridissima, is so named because of its herbaceous color, which is given to it by unicellular algae supplying this organism with oxygen.

Features of reproduction

This simplest being can reproduce both sexually and asexually. In the summer, when the water warms up, the reproduction of the hydra occurs mainly by budding. Sexual cells are formed in the ectoderm of the hydra only in the autumn, with the onset of cold weather. By winter, adults die, leaving eggs, from which a new generation appears in spring.

Asexual reproduction

Under favorable conditions the hydra usually reproduces by budding. Initially, a small protrusion occurs on the wall of the body, which slowly turns into a small tubercle (kidney). Gradually it grows in size, stretching, and on it are formed tentacles, between which you can consider the oral opening. First, the young hydra connects with the mother's body with a thin stalk. After a while this young process is separated and begins an independent life. This process is very similar to how the plants develop kidney escape, so asexual reproduction of the hydra is called budding.

Sexual reproduction

When the cold comes or the conditions become not very favorable for the life of the hydra (the drying out of the reservoir or prolonged starvation), the formation of the sex cells takes place in the ectoderm. Eggs are formed in the outer layer of the lower part of the body, and in the special tubercles (male gonads), which are located closer to the oral cavity, spermatozoa develop. On each of them there is a long flagellum. With the help of it, the sperm can move in water to reach the egg and fertilize it. Since the sexual reproduction of the hydra occurs in the autumn, the embryo is covered with a protective shell and lies on the bottom of the reservoir for the whole winter, and only with the onset of spring begins to develop.

Sex cells

These freshwater polyps in most cases are dioecious (spermatozoa and ovules are formed on different individuals), hermaphroditism in hydra is extremely rare. With cooling in the ectoderm, the sex glands (gonads) are laid. Sex cells form in the body of the hydra from the intermediate cells and are divided into female (egg) and male (sperm). The egg looks like an amoeba and has a false leg. It grows very fast, absorbing the intermediate cells that are in the neighborhood. At the time of maturing, its diameter is from 0.5 to 1 mm. Reproduction of hydra with eggs is called sexual.

Spermatozoa are similar to flagellate protozoa. Leaving the body hydra and floating in the water with the help of the existing flagellum, they go in search of other individuals.

Fertilization

When the spermatozoon swims to the individual with the egg and penetrates inside, the nuclei of these two cells merge. After this process, the cell acquires a more rounded shape due to the fact that the pseudopods retract. A thick shell with outgrowths in the form of spines forms on its surface. Before the onset of winter, the hydra dies. The egg remains alive and falls into anabiosis, remaining at the bottom of the reservoir until spring. When the weather becomes warm, the overwintered cell under the protective shell continues its development and begins to divide, forming first the rudiments of the intestinal cavity, then the tentacles. Then the shell of the egg bursts, and a young hydra appears on the light.

Regeneration

Features of the reproduction of hydra include also an amazing ability to restore, as a result of which a new individual is regenerated. A whole body can form from a separate body piece, which is sometimes less than one-hundredth of a part of the whole volume.

It is necessary to cut the hydra into parts, as soon as the regeneration process starts, in which each piece gets its mouth, tentacles and sole. Even in the seventeenth century, scientists conducted experiments, when the method of splicing different halves of hydra even seven-headed organisms were obtained. Since that time, this freshwater polyp has received its name. This ability can be regarded as another way of breeding hydra.

What is dangerous hydra in an aquarium

For fish that have a size of more than four centimeters, hydras are not dangerous. They, rather, serve as a kind of indicator of how well the host feeds the fish. If food is given too much, it breaks up in water into smallest pieces, then you can see how quickly the hydra begin to grow in the aquarium. To deprive them of this food resource, it is necessary to reduce the amount of food.

In an aquarium where very tiny fish or fry live, the appearance and reproduction of hydra is quite dangerous. This can lead to various troubles. First of all fry will disappear, and the remaining fishes will constantly experience chemical burns, which are caused by hydra tentacles. In an aquarium this organism can get with live food, with plants brought from a natural pond, etc.

To combat the hydra, one should choose such methods that can not harm the fish inhabiting the aquarium. The easiest way is to use the hydra's love for the bright light. Although it remains a mystery how she perceives it in the absence of the organs of vision. It is necessary to obscure all the walls of the aquarium, except one, to which a glass is placed on the inside of the same size. During the day the hydras move closer to the light and are placed on the surface of this glass. After that, it remains only to carefully get it - and the fish are not threatened.

Due to the high capacity for reproduction in aquarium conditions, hydra can very quickly breed. This should be taken into account and closely monitored for their appearance in order to avoid troubles in time.