One of the first groups of multicellular animals is the Intestinal type. Grade 7, which includes a course of zoology, examines in detail all the structural features of these amazing creatures. Let us once again recall what they are.
Intestinal Type: Biology
The name of the systematic unit, these animals received 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. Characterization of the type of intestinal also lies in the presence of specialized cells. But despite such a progressive structural feature, the body of these animals does not form real tissues.
Habitat and size
These first real multicellular animals can be found in fresh and salt ponds of various climatic zones. The type of Intestinal (grade 7 of a comprehensive school studies this topic in sufficient detail) is represented by small individuals with a diameter of several millimeters, and giant jellyfish with tentacles up to 15 meters long. Therefore, the nature of the reservoir where they live can be different. So, small freshwater hydras live in small puddles, and coral polyps form huge colonies in tropical seas.
Intestinal Type: General Description
The body of all the intestinal cavity consists of several types of cells, each of which performs a certain function, like the organs of more complex animals.
The main characteristic of the intestinal cavity is the presence 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 it touches the victim’s body, it unwinds and digs into it with force. As a result, it has a paralyzing effect. Then, using tentacles, representatives of this type place the victim in the intestinal cavity. And here begins the process of splitting organic matter. And it helps digestive and glandular cells.
The type of gastrointestinal is characterized by a high degree of regeneration. Scientists have proven that freshwater hydra can completely restore the body from 1/200 part. And perhaps this is due to the presence of intermediate cells. They actively divide, giving rise to all other types. Capillary and are capable of sexual reproduction due to the fusion of eggs and sperm.
Nerve cells are scattered throughout the body, interconnecting the body with the environment and combining it into a single whole. So, the movement of one of the representatives of the intestinal - hydra is very interesting. Due to the activity of skin-muscle cells, it, like an acrobat, moves from head to sole, making a real somersault.
Intestinal processes
The intestinal type is characterized by a more complex physiology compared to its predecessors - the simplest animals and sponges. Although there are common signs. For example, gas exchange still occurs through the covers, and there are no specialized structures for this.
Due to the presence of skin-muscle cells, jellyfish are capable of reactive movement. At the same time, their bell is reduced, the water is pushed out with force, causing a reverse push.
All coelenterates are predatory animals. With the help of tentacles, production through the oral opening enters the body. The efficiency of the splitting process is proved by the existence of two types of digestion simultaneously: cavitary and cellular.
For intestinal cavities, the presence of a response of their body to irritation - reflexes is characteristic. They arise in response to mechanical or chemical effects from the environment. And jellyfish have special sensitive formations that maintain the balance of the body and the perception of light.
Life cycle
The type of intestinal is also characterized by the fact that many of its species in the life cycle there is an alternation of generations. For example, the aurelia polyp reproduces in an exclusive asexual way by budding. Over time, the body of one of them is separated by transverse constrictions. As a result, small jellyfish appear. Visually, they resemble a stack of plates. In turn, they come off 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 the intestinal cavity contributes to a rapid increase in their number and more efficient resettlement.
Includes the type of entero-celiac classes, the polyps of which are not split off. They form colonies of bizarre forms. These are coral polyps. Alternation of generations does not occur in freshwater hydra. They reproduce in summer by budding, and in the fall proceed to sexual reproduction, after which they die. Fertilized ovules hibernate at the bottom of ponds. And in the spring of them young hydras develop.
Variety of intestinal
The intestinal type 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 the inhabitant of the warm tropical seas, which, thanks to its bright color, looks like a fantastic flower. Hence the second name of sea anemones - sea anemones. Among them there are predators and filtrators. And some types of sea anemones can enter into mutually beneficial cohabitation with hermit crabs.
The polyp has the ability to move and eat the remains of organic food arthropods. And cancer is reliably protected by stinging sea anemone cells. Interestingly, changing the sink from time to time, he transplantes the polyp there too. Cancer strokes the sea anemone with 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.
The value of intestinal 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, impaired functioning of the heart and respiratory organs. If assistance is not provided on time, a fatal outcome is possible.
Polyps and jellyfish are an important link in the food chain of aquatic inhabitants. And corals in many countries are used to make jewelry, souvenirs and building materials.
So, the type of Intestinal, the general characteristic of which was examined by us, is represented by two life forms. These 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.