Osmoregulation in molluscs of the intertidal zone.

Abstract o 1. Gastropods ( Littorina littorea, Purpura lapillus, Patella vulgata ) and bivales ( Mytilus edulis, Scrobicularia plana, Glycymeris glycymeris ) of the littoral area behave as poikilosmotic animals when acclimated gradually to diluted media. However, when transferred directly to the more diluted medium, these molluscs react by a “shell-closing” mechanism, leading to a transitory hyperosmotic state in the blood and the perivisceral fluids. 2. In the euryhaline molluscs studied, osmoregulation is achieved by isosmotic regulation of the intracellular medium. Free amino acids and taurine play a significant part as osmotic effectors in this regulation, except in the case of the Polyphacophora Acanthochitona discrepans . 3. The part played by the amino-acid pool as well as the nature of the prominent amino acids at work in the regulation of the intra-cellular osmolarity varies from species to species; no single, general pattern emerges from our study.