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. McCarthy and her team of University of Ulster scientists both in the laboratory and at Muck Island in Scotland.