These are common parasites of aquatic vertebrates and may cause minor pathology in large numbers.

Life Cycle

These are parasites of all classes of vertebrates. The cercariae encyst on aquatic vegetation or on the surface of aquatic invertebrates. The metacercariae have a tough cyst wall and are quite long-lived. They can build up in the environment and can produce quite heavy infections in hosts that consume large quantities of vegetation or invertebrates. Adults tend to live in the posterior portions of the digestive system of the definitive host, such as the colon, cecum or jejunum.


Cercariae possess eyespots and dense collections of cystogenous glands. The adult usually has the acetabulum located at the posterior of the body, but some groups are monostomes. The ovary is usually posterior to the testes.