The Bucephaloidea are a superfamily

Taxonomic rank

In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...

 of trematode flatworm

Flatworm

The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...

s, belonging to the large group Digenea

Digenea

Digenea is a subclass within the Platyhelminthes consisting of parasitic flatworms with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults are particularly common in the digestive tract, but occur throughout the organ systems of all classes of vertebrates...

. They contain numerous endoparasites of mollusks and fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

. 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.

Most trematodes have several distinct developmental stages

Trematode lifecycle stages

Trematodes are small parasitic flatworms that use vertebrates as their definitive host, and molluscs as their intermediate host. In order to accomplish this, they have several varied lifecyle stages....

. The motile cercaria larva is released by the first intermediate host, typically a snail, and parasitizes a second intermediate host, where it encysts into a metacercaria. Finally, the adult flatworm typically inhabits the alimentary system or other body cavity of a fish.

Their direct child taxa are the Family Bucephalidae

Bucephalidae

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....

 and the Family Nuitrematidae.

Family Bucephalidae

Bucephalids are trematode parasites of fish, whose intermediate hosts 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...

. One 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.

Family Nuitrematidae

This family was described in 1975 by Kurochkin. It has many features similar to the bucephalids, but the body is sharply subdivided in two parts.