From our article you will learn what a hydra is. This representative of the intestinal cavity is characterized by more complex processes of life in comparison with the first multicellular organisms - sponges. What structural features is this related to? Let's figure it out together.
What is hydra in mythology
This biological species got its name because of similarities with the mythological hero - the Lernean hydra. According to legend, it was a snake-like monster with poisonous breathing. The body of the hydra had several heads. Nobody succeeded in defeating her - several new ones immediately grew in place of a cut head.
The Lernean hydra inhabited Lake Lerna, where it protected the entrance to the underworld of Hades. And only Hercules could chop off her immortal head. After he buried it in the ground and covered it with a heavy stone. This is the second feat of Hercules from the twelve.
Hydra: Biology
High ability to restore lost body parts or regeneration is also characteristic of freshwater hydra. This animal is a representative of the type of intestinal. So what is hydra? This is a single freshwater polyp that leads an exclusively attached lifestyle.
General characteristics of the intestinal
Like all gastrointestinal, hydra is an aquatic inhabitant. She prefers shallow puddles, lakes or rivers with a small current, which allow them to attach to plants or benthic objects.
The classes of intestinal are represented by hydroid, jellyfish and coral polyps. All their representatives are characterized by radial, or radial symmetry. This feature of the structure is associated with a sedentary lifestyle. In this case, an imaginary point can be placed in the center of the animal’s body, from which rays can be drawn in all directions.
All coelenterates are multicellular animals, but they do not form tissues. Their body is represented by two layers of specialized cells. The intestinal cavity is located inside, in which food is digested. Different classes of gastrointestinal differ in lifestyle:
- Hydroids attach to the substrate with the sole and are single.
- Coral polyps are also immobile, but form colonies, which include hundreds of thousands of individuals.
- Jellyfish actively swim in the water column. At the same time, their bell is reduced and the water is pushed out with force. Such a movement is called reactive.
Body structure
The body of a freshwater hydra has the appearance of a stalk. Its base is called the sole. With its help, the animal is attached to underwater objects. At the opposite end of the body is a mouth opening surrounded by tentacles. It leads into the intestinal cavity.
The walls of the hydra body are made up of two layers of cells. The outer one is called ectoderm. It consists of skin-muscle, nerve, intermediate and stinging cells. The inner layer, or endoderm, is formed by their other types - digestive and glandular. Between the layers of the body is a layer of intercellular substance, which has the form of a plate.
Cell types and vital processes
Since neither tissues nor organs are formed in the hydra body, all physiological processes are carried out using specialized cells. So, epithelial-muscular provide movement. Yes, despite the attached lifestyle, hydroids are capable of moving. At the same time, the epithelial-muscle cells of one side of the body contract first, the animal "bends", stands on the tentacles and again lowers to the sole. Such a movement is called walking.
Between the epithelial-muscular there are stellate nerve cells. With their help, the animal perceives irritations from the environment and in a certain way responds to them. For example, if you touch the hydra with a needle, it contracts.
Ectoderm also contains intermediate cells. They are capable of amazing transformations. If necessary, cells of any type are formed from them. They determine the high level of regeneration of these animals. It is known that hydra can fully recover from 1/200 of its part or a mushy state.
Sex cells are also formed from intermediate cells. This happens with the onset of autumn. In this case, the eggs and sperm merge, forming a zygote, and the mother's body dies. In spring, young individuals develop from them. In summer, hydra multiplies by budding - a small tubercle forms on its body, which increases in size, acquiring the features of an adult body. As it grows, it splits apart and goes on to independent existence.
Digestive cells are located in the endoderm of the intestinal cavity. They break down nutrients. And glandular cells secrete enzymes into the intestinal cavity, under the influence of which food breaks up into pieces. Thus, hydra is characterized by two types of digestion. They are called intracellular and abdominal.
Stinging cells
It is impossible to answer the question of what is hydra if you do not get acquainted with the characteristics of stinging cells. In nature, they are found only in intestinal animals. With their help, protection, defeat and retention of prey are carried out. Therefore, their main number is located on the tentacles.
The stinging cell consists of a capsule with a spirally twisted thread. On the surface of this structure is a sensitive hair. It is he who is touched by the prey passing by. As a result, the thread unwinds and forces itself into the victim’s body, paralyzing it.
According to the type of nutrition, intestinal cavities, hydra in particular, are heterotrophic predators. They feed on small aquatic invertebrates. For example, daphnia, cyclops, oligochaetes, rotifers, fleas, mosquito larvae and fish fry.
The value of the intestinal
The importance of hydra in nature is primarily that it plays the role of a biological filter. It purifies water from suspended particles that it eats. This is an important link in freshwater supply chains. Some branched crustaceans, turbellaria and fish, the size of which exceeds 4 cm, feed on hydrams. Malkov hydra itself affects the poison of stinging cells.
But scientists, when asked what hydra is, will probably answer that this is a well-known object of laboratory research. On these intestinal cavities, the features of the processes of regeneration, the physiology of lower multicellular, and budding are studied.
So, freshwater hydra is a representative of the Hydroid class of the type of Enterocavum . This is a multicellular bilayer animal with radiation symmetry, the body of which consists of several types of specialized cells.