Pseudobiceros

Pseudobiceros is a genus of flatworms. Like all flatworms, Pseudobiceros are hermaphrodites. This particular genus engages in penis fencing. When the "winner" touches its penis to the "skin" of the other, insemination occurs, and the "loser" has to bear the burden of motherhood.
Species.
according to the World Register of Marine Species, species include: