Microphallus piriformes is a parasitic trematode (fluke). It belongs to the Plagiorchiata, a large suborder of the digenean fluke order Plagiorchiida. M. piriformes is unusual among the flukes in having only one intermediate host rather than two, and no free-swimming cercarian stage.It is most notable, however, for modifying the behaviour of its intermediate host in a way that increases its chance of transmission to the primary host. This has been researched by Helen O.