Active Uptake of Sodium by Softshell Turtles ( Trionyx spinifer )

Aquatic softshell turtles (Trionyx spinifer spinifer) show a net active uptake of sodium from solutions of this cation as dilute as S micromoles per liter. This probably occurs in the pharynx, a site of aquatic respiration. Inhibition of active sodium transport by low temperatures causes an extreme lowering of the sodium concentration in the plasma. Other fresh-water turtles may utilize this mechanism of ionic regulation. The ultrastructure of the pharyngeal villi is similar to that of frog skin and toad bladder.