The Trematodes, also called flatworms or flukes, are members of the Helminths. The Helminths also include the Cestodes and Nematodes.

Trematodes are characteristically non-segmented flat, round to oval worms that are no more than a few centimeters long. They parasitize mollusk and vertebrates. It is in the vertebrates, the definitive host, that they will sexually reproduce. While in the mollusk, the intermediate host, asexual reproduction will take place. The presence of this intermediate host is therefore crucial for the lifecycle of the parasite and each Trematode has a unique mollusk intermediate host.

Physically, in addition to the shape and size previously mentioned, they will have two suckers (one in close proximity to the mouth and the other on the underside of the parasite). Internal organs can be elucidated and reveal male and female organs as most of them are hermaphrodites.

The Trematodes include over 18,000 species with only a small per cent known to parasitize humans. The following are a list of the most clinically common Trematodes in humans. Click on each for a clinical/laboratory description of each Trematode.