The turtle features lungs that are desinged for rapid air exchange. The lungs of a turtle are highly elastic. This allows the turtles to hold their breath for a very long time. Without this important adaption turtles wouldn't be able to stay under water for nearly as long as they do. This is a functional adaption as the lungs do the work themselves without being told to. Unfotunatly there aren't too many more functional adaptations for the turtle.