VOLUME REGULATION AND NITROGEN METABOLISM IN THE MURICID GASTROPOD THAIS HAEMASTOMA

Ammonia and primary amine excretion and concentrations of intracellular ninhydrin-positive substance (NPS) and free amino acids (FAA) were measured in Thais haemastoma acclimated to salinities between 5 and 35%o and over 14 days following direct transfer from 10 to 3O%o or from 30 to lO%o. There was no trend in excretion rates with acclimation salinity. Intracellular NPS and FAA levels were directly related to acclimation salinity, with amino acids constituting over 90% of the NPS at salinities greater than 10%o. The intracellular free amino acid pool of T. haemastoma was not dominated by any single amino acid but glycine, alanine, aspartate, taurine, proline, and glutamate (in decreasing order) each contributed more than 5% of the FAA. Alanine and glycine were the major intracellular osmotic effectors during both the high and low salinity transfers. Taurine levels did not change in the hyperosmotic transfer, but taurine was lost from the foot over the course of the hyposmotic transfer, suggesting that it behaves as a passive osmolyte. Snails are capable of taking up exogenous ammonia from seawater during a 10to 30%o transfer, suggesting that ammonia is being used as an aminating source.