Convergent evolution of sublingual salt glands in the marine file snake and the true sea snakes

Abstract

1. The posterior sublingual gland of the little file snake (Acrochordus grnulatus) is a salt gland. It secretes a fluid as concentrated as 600 mM Na and 20 mM K. Cl is the anion; mean values during active secretion are 432–553 mM. 2. The location and structure of the little file snake salt gland are extremely similar to those of sea snake salt glands. This similarity is believed to have originated independently by convergent evolution since the file snakes (Acrochordidae) are not closely related to the true sea snakes (Hydrophiidae). 3. Maximum rates of electrolyte excretion from the little file snake salt gland (50–60 μmoles Cl/100 g hr) are higher than those of some sea snakes. 4. The little file snake occurs in both fresh water and marine habitats. Fasting sea water adapted snakes lose less than 0.5% of their body weight per day in 100% sea water.