# Microphallus piriformes > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Microphallus_piriformes > Markdown URL: https://mediated.wiki/source/Microphallus_piriformes.md > Source: https://en.wikipedia.org/wiki/Microphallus_piriformes > Source revision: 1245152165 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) ***Microphallus piriformes*** is a [parasitic](/source/Parasite) [trematode](/source/Trematode) (fluke). It belongs to the [Xiphidiata](/source/Xiphidiata), a large [suborder](/source/Suborder) of the [digenean](/source/Digenea) fluke [order](/source/Order_(biology)) [Plagiorchiida](/source/Plagiorchiida). *M. piriformes* is unusual among the flukes in having only one [intermediate host](/source/Intermediate_host) rather than two, and no free-swimming [cercarian](/source/Cercaria) stage.[1] It is most notable, however, for modifying the [behaviour](/source/Behaviour) of its intermediate host in a way that increases its chance of transmission to the [primary host](/source/Primary_host). This has been researched by [Helen O. McCarthy](/source/Helen_O._McCarthy) and her team of [University of Ulster](/source/University_of_Ulster) scientists both in the [laboratory](/source/Laboratory) and at [Muck Island](/source/Muck,_Scotland) in [Scotland](/source/Scotland).[1] ## Ecology The [life cycle](/source/Biological_life_cycle) of *M. piriformes* requires two hosts: the [rough periwinkle](/source/Rough_periwinkle) *Littorina saxatilis* (a [littoral](/source/Littoral) [snail](/source/Snail)) and the [herring gull](/source/European_herring_gull) *Larus argentatus* (and perhaps other members of the herring gull complex). The immature flukes live in the snail, and the adult flukes live in the [bird](/source/Bird).[1] Normally, rough periwinkles are rarely eaten by herring gulls. This is due to two reasons: First, the birds forage in the snails' rocky shore [habitat](/source/Habitat) mainly during the breeding season (which lasts about 4 months each summer) but not at other times. Second, [periwinkles](/source/Common_periwinkle) move with the [tides](/source/Tide) to stay at the water line. Thus, even when the gulls forage in periwinkle habitat, the snails tend to stay out of easy reach of the birds.[1] It is not precisely known how the snails are infected; probably they eat the eggs directly from the gulls' [feces](/source/Feces). The eggs hatch into a [miracidium](/source/Miracidium) stage, which develops into multiple [sporocysts](/source/Trematode_lifecycle_stages). Rather than further developing into a cercaria which leaves the snail to infect the second intermediate host as usual for trematodes, they directly develop into [encysted](/source/Cyst) [metacercariae](/source/Metacercaria) in the snail. Infection [castrates](/source/Castrate) the periwinkles; [brooding](/source/Avian_incubation) *L. saxatilis* generally move only to avoid being left above water by the tide while non-brooding (including castrated) periwinkles are more active.[1] As soon as the flukes have reached the metacercarian stage, they alter the periwinkles' behaviour: Rather than moving to stay near the water line, the infected snails develop a pronounced tendency to move upwards. This becomes most pronounced shortly before [high tide](/source/High_tide), and thus the periwinkles carrying mature metacercariae are left a considerable distance above water when the tide recedes. This makes them far more accessible to the foraging gulls than uninfected [conspecifics](/source/Conspecific), which will often move up when the tide is highest to feed on [algae](/source/Alga) which they cannot otherwise access, but return underwater as soon as the tide recedes to avoid [desiccation](/source/Desiccation).[1] Once the snails are eaten by herring gulls, the metacercariae hatch into mature flukes. These mate and produce eggs which are shed with the bird's feces. Their adult lifespan is a mere two weeks; several [generations](/source/Generation) are thus produced each summer. It is unknown whether *M. piriformes* spends the winter as resting eggs in the habitat, or as sporocysts in already-infected periwinkles. In any case, snails harboring metacercariae generally die of desiccation before winter if they are not eaten.[1] ## See also Other [parasites](/source/Parasite) that modify intermediate host behavior to facilitate transmission: - *[Dicrocoelium dendriticum](/source/Dicrocoelium_dendriticum)*, a fluke - *[Corynosoma constrictum](/source/Corynosoma_constrictum)*, a [thorny-headed worm](/source/Thorny-headed_worm) - *[Gynaecotyla adunca](/source/Gynaecotyla_adunca)*, a fluke - *[Hymenolepis diminuta](/source/Hymenolepis_diminuta)*, a [tapeworm](/source/Tapeworm) - *[Polymorphus paradoxus](/source/Polymorphus_paradoxus)*, a thorny-headed worm ## Footnotes 1. McCarthy *et al.* (2000) ## References - (2000): A transmissible trematode affects the direction and rhythm of movement in a marine gastropod. *Animal Behaviour* **59**(6): 1161–1166. [doi:10.1006/anbe.2000.1414](https://doi.org/10.1006/anbe.2000.1414) (HTML abstract) --- Adapted from the Wikipedia article [Microphallus piriformes](https://en.wikipedia.org/wiki/Microphallus_piriformes) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Microphallus_piriformes?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.