Trematode

The Trematodes are a class of flatworms in the phylum Platyhelminthes. They are called flukes, and are internal parasites of molluscs and vertebrates. Most trematodes have a complex life cycle with at least two hosts. The primary host, where the flukes sexually reproduce, is a vertebrate. The intermediate host, which is the agent of dispersal, is usually a snail.

Trematoda
Botulus microporus, a giant digenean parasite from the intestine of a lancetfish
Scientific classification
Kingdom:	Animalia
Phylum:	Platyhelminthes
Class:	Trematoda Rudolphi, 1808
Subclasses
Aspidogastrea Digenea

The trematodes or flukes are estimated to include 18,000^[1] to 24,000^[2] species.