sentences:  These are "O. tetrapis" (Central Africa, except the Congo River Basin), "O. osborni" (Congo River Basin), and a third possibly unnamed species (West Africa).Uncertainty exists for the population in Nigeria (between "O. tetrapis" and the possibly unnamed West African species) as it has not been studied.A fourth clade was found in a study of captives in 2013, but where members of this clade live in the wild is unclear.