Trematode life cycle stages

Trematodes are covered by a tegument, that protects the organism from the environment by providing secretory and absorptive functions.

Miracidia will then grow and develop within the intermediate host into a sac-like structure known as a sporocyst or into rediae, either of which may give rise to free-swimming, motile cercariae larvae.

[1] While the details vary with each species, the general life cycle stages are: The egg is found in the faeces, sputum, or urine of the definitive host.

[5] 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.

[citation needed] The larval form of the parasite develops within the germinal cells of the sporocyst or redia.

Species of family Syncoeliidae have mesocercariae or metacercariae that are not encysted and can be free floating, but details of the early stages of the life cycles of these marine parasites are not known.

[9]: 32–33  Metacercariae of certain species, such as Copiatestes filiferum, have long filamentous structures termed byssal filaments,[10][11] 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.

Not all trematodes follow the typical sequence of eggs, miracidia, sporocysts, rediae, cercariae, and adults.