The order Platyhelminthes is divided into 4 classes.
1. Turbellaria: Their bodies are flat like leaves. Cuticle is absent on the body. The epidermis is ciliated and rhabdite in nature. Suction is missing. Larval stage absent. They are known as Edewam. Such as Planaria (Dugesia tigrina).
2. Trematoda: They are cylindrical or flat like leaves. Cilia are absent on the body. The mouth has suckers or hooks. Larval stage present. They are known as Fluke. For example- liver worm (Fasciola hepatica).
3. Monogenia: These are small parasites. Their heads contain nerve cells and sensory organs. Alimentary canal is simple in nature. They are known as flatworms. Such as Planaria (Dugesia tigrina).
4. Cestoda: Their bodies are long and flattened like ribbons. Composed of 800-900 proglottid segments. Each segment has one or two sets of male or female reproductive organs. The mouth has suckers and curved hooks. Mouth opening and esophagus absent. They are known as tapeworms. For example, tapeworm (Taenia solium).