The correct option is
B SchistosomaThe
platyhelminths are parasitic and non-parasitic flatworms.
Cestoda, Trematoda are parasitic while Turbellaria contains free-living worms. Schistosoma which are commonly known as blood-flukes, are parasitic flatworms responsible for a number of infections in humans termed schistosomiasis. Adult flatworms parasitize blood capillaries of either the mesenteries or plexus of the bladder.
So, the correct answer is option B.