Monogenea

A Class of Parasites,

They are usually Ectoparasites on Fishes,with Direct life cycle ,and  mostly Hermaphrodites ,but Gyrodactylids are exceptional and they are Viviparous

They are very Host specific , their Infective larva is called Oncomiracidium

e.g. Gyrodactylus ,Dactylogyrus , Nitzschia ,Diclybothrium