e of
Clinostomum phalacrocoracis in fish 's
Kunstformen der Natur (1904): The tail's furcae (forked structures) give the impression of horns, hence the genus name
Bucephalus meaning "ox head". While the details vary with each
species, the general life cycle stages are:
Egg The egg is found in the faeces, sputum, or urine of the definitive host. Depending on the species, it will either be non-embryonated (immature) or embryonated (ready to hatch). The eggs of all trematodes (except
schistosomes) are
operculated. Some eggs are eaten by the intermediate host (snail) or they are hatched in their habitat (water).
Miracidium Miracidia hatch from eggs either in the environment or in the intermediate host. They do not have a mouth; therefore they cannot eat and need to find a host quickly if they hatch in the environment. Energy is needed to develop into a sporocyst. The first intermediate host can differ for different trematodes.
Sporocyst Sporocysts are elongated sacs that produce either more sporocysts or rediae. This is where larvae can develop. •
Mother sporocyst: These have loose plates (cilia) and migrate to gonads. •
Daughter sporocyst: These are an asexual production of cercariae; they absorb nutrients while having no mouth.
Redia (plural: rediae) After the sporocyst the larva forms. The first development from it forms the redia. They have a mouth which allows them to have an advantage to their competitors because they can just consume them and will either produce more rediae or start to form cercariae.
Parasite competition in snail hosts Co-infections of different parasite species within the same host could occur and cause competition between the rediae and sporocysts. Not all trematode species have a redia stage; some may just have a sporocyst stage depending on the life cycle. The rediae are dominant over sporocysts because they have mouths and are able to either eat their competitors' food or their competitors.
Cercaria (plural: cercariae) The larval form of the parasite develops within the germinal cells of the sporocyst or redia. A cercaria has a tapering head with large penetration glands. Bony and cartilaginous fish are the definitive hosts within at least the gills, oral cavity or skin, and crustaceans like
krill and
copepods can be paratenic or possibly intermediate hosts. Metacercariae of certain species, such as
Copiatestes filiferum, have long filamentous structures termed byssal filaments, which in
C. filiferum have been reported to foul the feet of
white-faced storm petrels and cause snagging-related mortality in this accidental host after the metacercariae dry out and form hardened connections between the legs.
Cercaria is also used as a genus of trematodes, when adult forms are not known. The usage dates back to Müller, in 1773.
Adult The fully developed mature stage. As an adult, it is capable of sexual reproduction. ==Deviations from the typical life cycle==