An intriguing, new planarian species from Tasmania, with a discussion on protandry in triclad flatworms (Platyhelminthes, Tricladida)

An account is given of an unusual new species of freshwater planarian from the Hartz Mountains in Tasmania, Australia, Romankenkius flaccidus Sluys, sp. nov. The species is characterized, among other features, by an asymmetrical penis papilla, an extremely large, elongated copulatory bursa, and by the absence of testes in animals with fully developed male and female copulatory apparatus. Instigated by the sexual cycle of this new species, the study opportunely reviews whether planarian flatworms generally are simultaneous or sequential—in particular protandrous—hermaphrodites. It is concluded that real protandry does not occur in triclads and that even less extreme cases of sexual segregation, such as complete reduction of the testes or the more or less complete separation of male and female functionality as present in some species, have only sparsely and convergently evolved within the group of the triclad flatworms.