Flukes (Trematoda)

Flukes, the Trematoda, are flatworms that are all parasitic and have complex life cycles specialized for parasitism in animal tissues. In the major fluke taxon Digenea, which includes the human lung fluke, the worm passes through several juvenile stages that are parasitic in one, two or more intermediate hosts before reaching adulthood in a definitive host. Fossil trematode eggs have been found in Egyptian mummies and in the dried dung of a Pleistocene ground sloth, and larvae that parasitize molluscs can leave pits on the inside of a shell. They must also respire by diffusion, so in larger species the gut is highly branched to carry food to every part of the body.