One of the first groups of multicellular animals - type Coelenterates. Grade 7, which includes a zoology course, examines in detail all the structural features of these amazing creatures. Let's recap what they are.
Type Coelenterates: Biology
These animals received the name of the systematic unit due to the structure of the same name. It is called the intestinal cavity, and all representatives of the type have it: both polyps leading an attached lifestyle and actively moving jellyfish. A characteristic of the intestinal type also lies in the presence of specialized cells. But despite such a progressive structural feature, the body of these animals does not form true tissues.
Habitat and size
These first true multicellular animals can be found in fresh and s alt water bodies of various climatic zones. Type Intestinal (grade 7 of a comprehensive school studies this topic in some detail) is represented by both small individuals with a diameter of several millimeters and giant jellyfish with tentacles up to 15 meters long. That's whythe nature of the reservoir where they live can be different. So, small freshwater hydras live in small pools, and coral polyps form huge colonies in tropical seas.
Type Coelenterates: general characteristics
The body of all coelenterates consists of several types of cells, each of which performs a specific function, similar to the organs of more complex animals.
The main characteristic of coelenterates is the presence of stinging cells. They consist of a capsule in which a thread with a sharp end is twisted. On top of the cell is a sensitive hair. When it touches the body of the victim, it unwinds and digs 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 digestive and glandular cells help to carry it out.
Type Coelenterates is characterized by a high degree of regeneration. Scientists have proven that freshwater hydra can completely restore the body from 1/200 of a part. And perhaps this is due to the presence of intermediate cells. They actively divide, giving rise to all other types. Coelenterates are also capable of sexual reproduction due to the fusion of eggs and spermatozoa.
Nerve cells are scattered throughout the body, carrying out the relationship of the organism with the environment and uniting it into a single whole. So, the movement of one of the representatives of the coelenterates is very interesting.- hydras. Thanks to the activity of skin-muscle cells, she, like an acrobat, moves from her head to the sole, doing a real somersault.
Life processes of coelenterates
Type Coelenterates is characterized by a more complex physiology compared to its predecessors - protozoa and sponges. Although there are common signs. For example, gas exchange still occurs through the integument, and there are no specialized structures for this.
Due to the presence of skin-muscle cells, jellyfish are capable of jet propulsion. At the same time, their bell is reduced, the water is pushed out with force, causing a reverse push.
All coelenterates are carnivores. With the help of tentacles, prey enters the body through the mouth opening. The efficiency of the splitting process has been proven by the existence of two types of digestion simultaneously: abdominal and cellular.
For coelenterates, the presence of a response of their body to irritation - reflexes is characteristic. They arise in response to mechanical or chemical influences from the environment. And jellyfish have special sensitive formations that ensure the balance of the body and the perception of light.
Life cycle
Type Coelenterates is also characterized by the fact that in many of its species in the life cycle there is an alternation of generations. For example, the Aurelia polyp reproduces exclusively asexually by budding. With the passagetime, the body of one of them is separated by transverse constrictions. As a result of this, small jellyfish appear. Visually, they resemble a stack of plates. One by one, they come off the top and move to an independent and mobile lifestyle.
The alternation of sexual and asexual generations in the life cycle of coelenterates contributes to a rapid increase in their numbers and more efficient settlement.
Includes type Coelenterates whose polyps do not split off. They form colonies of bizarre shapes. These are coral polyps. There is no alternation of generations in freshwater hydra either. They reproduce in the summer by budding, and in the fall they switch to sexual reproduction, after which they die. Fertilized eggs overwinter at the bottom of water bodies. And in the spring, young hydras develop from them.
Variety of coelenterates
Type Coelenterates in nature is represented by two life forms: polyps and jellyfish. One of the most interesting representatives of the first group is sea anemone. This is an inhabitant of warm tropical seas, which, thanks to its bright color, looks like a fantastic flower. Hence the second name of anemones - sea anemones. Among them there are predators and filter feeders. And some species of anemones can enter into mutually beneficial cohabitation with hermit crabs.
Polyp has the ability to move around and eat the remains of organic food arthropods. And cancer is reliably protected by stinging anemone cells. Interestingly, by changing the shell from time to time, hetransplants a polyp there. Cancer strokes the sea anemone with claws, causing it to crawl into a new home on its own.
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.
The meaning of coelenterates in nature and human life
Many coelenterates can be dangerous to animals and humans. The action of their stinging cells causes burns. Their consequences for a person can be convulsions, headache, disorders of the heart and respiratory organs. If help is not provided in time, a fatal outcome is also possible.
Polyps and jellyfish are an important link in the food chain of aquatic life. And corals in many countries are used to make jewelry, souvenirs and building materials.
So, the type Coelenterates, the general characteristics of which we have considered, is represented by two life forms. These are polyps and jellyfish. These animals are characterized by radial symmetry, the presence of specialized cells and alternation of generations in the life cycle.
