Parasitic flatworms (including flukes)

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Trematodea \Trem`a*to"de*a\, n. pl. [NL., from Gr. ? having holes, from ?, ?, a hole.] (Zo["o]l.) An extensive order of parasitic worms. They are found in the internal cavities of animals belonging to all classes. Many species are found, also, on the gills ...

Wikipedia Word definitions in Wikipedia
Trematoda is a class within the phylum Platyhelminthes . It includes two groups of parasitic flatworms , known as flukes . They are internal parasites of molluscs and vertebrates . Most trematodes have a complex life cycle with at least two hosts. The primary ...