Members of the family Bucephalidae are trematode flatworms with no oral sucker, using instead a rhynchus as an adhesive organ at their anterior end. Many are common parasites of freshwater fish.

The name "Bucephalus" meaning "ox head" was originally applied to the genus Bucephalus

Bucephalus (trematode)

Bucephalus is the genus name for many trematode flatworms that are parasites of molluscs and fish. Like other Bucephalidae, they are found in fish both as adults and as metacercariae. In marine and freshwater teleosts, they live as parasites inside the digestive tract, especially the...

because of the horn-like appearance of the forked tail (furcae) of its cercaria larva. By what Manter calls a "curious circumstance", horns are also suggested by the long tentacles of adult worms.

They typically occur in teleost fishes as sexually reproducing adults. In their intermediate hosts, which include mollusks and at least one amphibian

Amphibian

Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

, they occur as asexually reproducing stages.

The characteristic feature is an anterior rhyncus or holdfast that is separate from the digestive system. They also differ from other digeneans in the configuration of the digestive systems and genitalia. The intestine is simple and saccular; they have no acetabulum.