The correct option is D Cestoda
Turbellaria are one of the subdivisions of the phylum Platyhelminthes which are free-living, carnivorous flatworms.
Crustaceans are a very large group of arthropods of which a few are parasitic.
Oligochaeta is a class of animals in Annelids which contains earthworms and not all are parasitic.
Cestoda is the name given to a class of parasitic flatworms of the phylum Platyhelminthes, which include tapeworms.
Thus, the correct answer is option D.