Hysteromorpha triloba , a strigeid trematode is a strange looking and generally small parasite found in the digestive tracts of fish-eating vertebrates. The first intermediate host is a snail (e.g., Gyraulus hirsutus), and the second intermediate hosts are fishes of the families Cyprinidae (Abramis sp., Hyborhynchus notatus, Idus idus, Leuciscus sp., and Tinca tinca), Poeciliidae (Poecilia vivipara), and Siluridae (Ameiurus sp.). In the fish intermediate hosts, metacercaria encyst in the musculature (forming white cysts) and the parasite is passed on to the definite host when infected fish are eaten. Definitive hosts include herons, egrets, pelicans, and cormorants.
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Contributed by Jessica Light.