Alimentary canal is absent in

Platyhelminthes includes three classes: Turbellaria, Trematoda and Cestoda.In turbellarians (e.g., Planaria) and trematodes (e.g., Fasciola), alimentary canal is incomplete with a single opening, the mouth, that serves for both digestion and egestion. In cestodes (e.g., Cestoda), digestive system completely absent. They absorb nutrients from the host through their body surface (tegument).