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.

References

1. Littlewood D.T.J. & Bray R.A. 2000. The Digenea, in Interrelationships of the Platyhelminthes. Systematics Association Special Volume #60, pp168–185. ISBN 978-0-7484-0903-7
2. Poulin, Robert; Morand, Serge (17 January 2005). Parasite biodiversity. Smithsonian. p. 216. ISBN 978-1-58834-170-9.