the tucuxi ("sotalia fluviatilis") in the amazon river is another species descended from oceanic dolphins; however, it does not perfectly fit the label of 'facultative' either, as it occurs only in fresh water. the tucuxi was until recently considered conspecific with the guiana dolphin ("sotalia guianensis"), which inhabits marine waters. it may also be true for the irrawaddy dolphin and the finless porpoise that, although the species may be found in both freshwater and marine environments, individual animals found in rivers may not be able to survive in the ocean, and vice versa. the tucuxi is currently classified as an oceanic dolphin (delphinidae).