Sea Snakes: An Unusual Salt Gland under the Tongue

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Abstract
The posterior sublingual gland of sea snakes is a salt gland. It secretes a fluid surpassing seawater in sodium chloride concentration. The gland lies on the ventrolateral surfaces of the tongue sheath and empties through multiple ducts into the sheath. Fluid is expelled from the sheath when the tongue is extended. For freshly captured Pelamis, the plasma concentrations of sodium, chloride, and potassium were 210, 167, and 8 millimoles per liter, respectively. Injections of sodium chloride led to a rise in its concentration in the plasma and to an increase in the rate and concentration of fluid secreted by the sublingual gland. The ultrastructure of this gland is similar to that of other reptilian salt glands. However, the gland is not homologous with any other salt gland. The sublingual gland in Pelamis is larger than that in Laticauda, and the rate of electrolyte excretion from the larger gland is greater.