Phylliroe bucephala is a parasitic species of pelagic nudibranch, a marine gastropod mollusc in the family Phylliroidae.

This species of nudibranch is transparent with its guts visible through the laterally flattened body.

It has a tail and two long smooth rhinophores.

It feeds on jellyfish and plankton as an adult.

The juveniles parasitize Zanclea medusae.