Zoologist Egon Heiss and his colleagues made the discovery while studying the feeding habits of this turtle, a freshwater species found in southern Canada and the eastern US. They realised that the turtles would only consume their food after dragging it into the water.

Upon investigation, they found out that this was because the turtle's tongue was covered with bud-like cells called papillae that draws in oxygen from the water that passes over them.

"We knew that an organ for aquatic respiration must be present somewhere but finally discovered it accidentally," says Mr Heiss.

Some freshwater turtles cannot breathe underwater, while others breathe through their skin. Other species use specialised cavities in their rear, called cloacal bursae, that draws in water and extracts the oxygen.

"Musk turtles, however, lack cloacal bursae and their skin is relatively thick and lacks a well developed capillary network," Mr Heiss said. So it is the large papillae in the throats that enabled them to remain underwater for months.

Adults spend much of their lives underwater, but juveniles surface onto land from time to time to find food.

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