The correct option is B Cestoda
Platyhelminthes are a phylum of invertebrate which can be free-living or parasites. They have bilateral symmetry and the body is not segmented. Cestoda and Trematoda are parasitic while Turbellaria contains the free-living worms. Cestodes are parasitic worms which live in the digestive tracts of vertebrates as adults. They live in the bodies of other animals in the juvenile stage. These are endoparasites which live inside the body of the host organism.
Thus, the correct answer is option C.