These are parasites of all classes of vertebrates. Those with adults in the liver can cause serious pathology.
Adults live in the intestine, liver, bile duct or gall bladder of the definitive host. The egg is embryonated when laid but must be eaten by a snail for hatching to occur. (It is common that parasites which pass to the next host by ingestion are already developed when released.) Sporocysts and then rediae are produced. The cercariae that are released contact a fish second intermediate host and encyst under the scales, to await ingestion by the next definitive host.
The adult body is usually spinose and the redia does not possess appendages. There is no cirrus or cirrus sac, just a common genital pore.