The champion in this regard seems to be the recently discovered (1973) Fitzroy River turtle Rheodytes leukops ('white-eyed stream-diver'), which is confined to its namesake river in Queensland, Australia. It lives in shallow rapids where the water is highly oxygenated. One can detect the keen sense of discovery in the account by the scientists who found it, John Legler and John Cann: 'One of our vivid early impressions of Rheodytes was that adults of both sexes swam with a widely gaping cloacal orifice (up to 30mm in diameter). The orifice remains open when individuals are out of the water. We first became aware of the large cloacal bursae when a female was examined in bright sunlight; the carapace transmitted enough light to illuminate the coelomic cavity and produce a spectacular view internally for at least 100mm, via the cloaca, revealing a large sac lined with vascular, villose mucosa. . . . Water is pumped in and out of the bursae of captives and experimental animals at rates of 15 to 60 times per minute' (Legler and Cann 1980). Only dedicated herpetologists could characterize the vista up a turtle's gaping bunghole as a 'spectacular view.' But you can understand their enthusiasm--since the turtle's shell is only 260 millimeters long, a 100-millimeter-long bursa is relatively enormous. Up to 68 percent of the turtle's oxygen uptake is accomplished through the cloacal bursae, so it rarely needs to come to the surface to bask or breathe.