One of the first groups of multicellular animals -type of the intestines. Grade 7, which includes a course of zoology, examines in detail all the features of the structure of these amazing creatures. Let's once again remember what they are.
The name of the systematic unit is these animalsthanks to the structure of the same name. It is called the intestinal cavity, and it has all the representatives of the type: polyps, leading the attached way of life, and actively moving jellyfish. The characteristic of the type of coelenterates is also the presence of specialized cells. But despite such a progressive feature of the structure, the body of these animals does not form real tissues.
These first true multicellular animalscan be found in fresh and salt water bodies of various climatic zones. Type The intestinal (7th grade of the general education school studies this topic in sufficient detail) is represented by small individuals with a diameter of several millimeters, and jellyfish-giants with a tentacle length of up to 15 meters. Therefore, the nature of the reservoir, where they live, can be different. So, small freshwater hydra inhabit small puddles, and coral polyps form huge colonies in the tropical seas.
The body of all coelenterates consists of cells of several types, each of which performs a certain function, like the organs of more complex animals.
The main characteristic of coelenterates ispresence of stinging cells. They consist of a capsule, in which a thread with a sharp end is twisted. A sensitive hair is located on top of the cell. When he touches the victim's body, he unwinds and bites into it with force. As a result, it has a paralyzing effect. Further, with the help of tentacles, representatives of this type place the victim in the intestinal cavity. And here begins the process of splitting organic substances. And it helps to carry out digestive and glandular cells.
Type of the intestinal is characterized by highdegree of regeneration. Scientists have proven that the freshwater hydra can completely restore the body from the 1/200 part. And perhaps this is due to the presence of intermediate cells. They actively share, giving rise to all other types. They are able to coelenterate and to sexual reproduction due to the fusion of eggs and spermatozoa.
Nerve cells are scattered throughout the body,realizing the relationship of the organism with the environment and integrating it into a single whole. So, very interesting is the movement of one of the representatives of coelenterates - hydra. Due to the activity of the skin-muscle cells, she, like an acrobat, moves from head to sole, making a real somersault.
Type of the intestinal is characterized by morecomplex physiology in comparison with its predecessors - the simplest animals and sponges. Although there are common signs. For example, gas exchange still occurs through coverlets, and specialized structures for this are absent.
Due to the presence of skin-muscle cells, jellyfish are capable of reactive movement. At the same time, their bell is shortened, water is pushed out with force, causing a backward thrust.
All coelenterates are predatory animals.With the help of tentacles, extraction through the mouth opens into the body. The efficiency of the cleavage process is proved by the existence of two types of digestion simultaneously: cavitary and cellular.
For coelenterates, there is a responsethe reaction of their body to irritation - reflexes. They arise in response to mechanical or chemical effects from the environment. And jellyfish have special sensitive formations, ensuring the balance of the body and the perception of light.
Type of the intestinal canal is also characterized by,that many of its species in the life cycle observed alternation of generations. For example, the aurelia polyp propagates by an exclusive asexual pathway by means of budding. Over time, the body of one of them is divided by transverse constrictions. As a result, small jellyfish appear. Visually they resemble a stack of plates. In turn, they break away from above and move on to an independent and mobile way of life.
The alternation of sexual and asexual generations in the life cycle of coelenterates facilitates a rapid increase in their number and a more efficient resettlement.
Includes type of Guttural classes, polypswhich do not split off. They form colonies of bizarre forms. It's coral polyps. There is no alternation of generations between the freshwater hydra. They reproduce in the summer by budding, and in the autumn they pass to sexual reproduction, after which they perish. Fertilized ovules winter at the bottom of water bodies. And in the spring of them young hydras develop.
Type of the intestinal in nature is represented by twolife forms: polyps and jellyfish. One of the most interesting representatives of the first group is actinia. It is an inhabitant of the warm tropical seas, which, due to its bright color, looks like a fantastic flower. Hence the second name of sea anemones - sea anemones. Among them are predators and filtrators. And some species of actinia can enter into mutually beneficial cohabitation with hermit crabs.
Polyp has the ability to move and eatremnants of organic food of arthropods. And the cancer is safely protected by the stinging cells of anemia. It is interesting that, changing the shell from time to time, he transplants polyp. Cancer strokes the actinium of the claws, as a result of which it independently creeps into a new dwelling.
And colonies of coral polyps form huge clusters. For example, the Great Barrier Reef stretches along the coast of Australia for a distance of about 2 thousand km.
Many coelenterates can be dangerous foranimals and humans. The action of their stinging cells causes burns. Their consequences for a person may be convulsions, headache, disruption of the heart and respiratory organs. If you do not provide assistance in time, a fatal outcome is possible.
Polyps and jellyfish are an important link in the feeding chain of aquatic inhabitants. Corals in many countries are used for making jewelry, souvenirs and building materials.
So, the type of the intestinal cavity, a general characteristicwhich we considered, is represented by two life forms. They are polyps and jellyfish. These animals are characterized by radiation symmetry, the presence of specialized cells and the alternation of generations in the life cycle.
