Representatives of the Type Cavitary are multicellular animals with radial (radial) symmetry.
Their body consists of two layers of cells – outer (ectoderm) and inner (endoderm), between which the mesoglea is located.
Basically, coelenterates are predators. They have an intestinal cavity where food is digested. The cavity communicates with the environment through the mouth. There are no other holes (undigested residues are thrown out through the mouth).
The ectoderm is formed by epithelial-muscular, stinging, nerve, reproductive and intermediate (non-specialized) cells.
The endoderm is represented by digestive-muscular and glandular cells.
1. The epithelial-muscular (skin-muscular) cells perform the integumentary function, and also have muscular processes that provide the movement of the coelenterate.
2. Stinging cells have a capsule filled with poison that paralyzes the victim (neuroparalytic action). A stinging thread is immersed in the capsule. A sensitive hair is located on the cell surface. When this hair is touched, the stinging thread is thrown out and enters the victim’s body.
3. Nerve cells have long processes that together form a neural network. Such a nervous system is called diffuse.
4. Sex cells provide for sexual reproduction of coelenterates.
5. The glandular cells produce enzymes that digest food in the intestinal cavity (this is intracavitary digestion).
6. Digestive-muscle cells have flagella and pseudopods. Flagella move water with food particles, and the resulting pseudopods capture it. Further digestion occurs in the digestive vacuoles (this is intracellular digestion).
7. Non-specialized (intermediate) cells are able to transform into any type of cells and provide regeneration (restoration of lost parts) of coelenterates.
Cnidocil is a sensitive hair of the stinging cell of coelenterates.
Enzymes are biologically active substances that accelerate the processes taking place in the cell. Digestive enzymes speed up the digestion process.
Reproduction of coelenterates occurs sexually and asexually.
Asexual reproduction occurs by budding.
In the case of sexual reproduction, a new organism develops from a fertilized egg in the larval stage. Having attached to the bottom, the larva turns into a polyp. Polyps either form colonies or bud off free-living jellyfish. Here we can talk about the alternation of generations: an attached polyp and a free-living jellyfish.
The value of coelenterates
Coral polyps, coral polyps, form reefs, and sometimes entire islands – atolls – that represent specific ecosystems.
Lime rocks are formed from the dead corals. They are used in construction, in the decoration of dwellings.
Some coelenterates settle on mobile animals (sea anemone and hermit crab). Cancer moves the sea anemone, and sea anemone protects the cancer with its stinging cells.
In eastern countries, coelenterates (jellyfish) are used for food.
The poison of some jellyfish can be dangerous to humans, causes burns, and in severe cases, affecting the respiratory system, leads to death.