The main characteristics of Platyhelminthes include:
1. Flat: Their bodies are flat and have no body cavity.
2. No fixed skeleton: Except for a few species with calcium or siliceous bone plates, most flatworms do not have a hard skeleton, and the body wall is composed of muscles and epidermal cells.
3. Single longitudinal nervous system: Unlike the central nervous system of other animals, platyhelminthes have a single longitudinal nerve cord on which ganglia and neurons are distributed.
4. Original digestion: Platyhelminthes lack a digestive tract. After food enters the mouth through the mouth, it is digested into nutrients that the cells can absorb, and the remaining waste is excreted from the mouth.
5. Diverse lifestyles: There are many types of Platyhelminthes. Some are free-swimming and parasitic on other organisms, and some species are attached to objects such as rocks or aquatic plants.
In short, the main characteristics of Platyhelminthes are flat bodies, lack of fixed bones, single longitudinal nervous system, primitive digestion and diverse lifestyles.
