Osmotic Balance in a Marine Pulmonate,Amphibola crenata

Abstract

The pulmonate mud-snail Amphibola crenata is an osmoconformer in 25%-125% sea water, its haemolymph being slightly hyperosmotic and hyperionic to the medium. It maintains its haemolymph markedly hyperosmotic in media below 25% sea water and in freshwater, in which it survives for a week or longer. On exposure to dilute or concentrated media, water which enters or leaves the tissues preferentially enters or leaves the cells. Regulation of cell volume towards initial values is accomplished within 5 days. Measurements of changes in cell volume, and of distribution of tissue water between the intracellular and extracellular compartments, in snails moved from 100% sea water into dilute or concentrated media, and in snails moved back to 100% sea water, indicate that mechanisms of cell volume regulation are minimal in ca 60-65% sea water. Changes in the concentration of tissue free amino acids are in accord with current theories of mechanisms of isosmotic intracellular regulation. The results are discussed in the light of the taxonomic, evolutionary and ecological status of Amphibola as a shore-living, primitive, marine representative of a predominantly terrestrial and freshwater group of gastropod molluscs.

The Ins and Outs of Urea: Identification of Putative DUR3-like Urea Transporters in the Oligohaline Nerite Snail Theodoxus fluviatilis and Their Expression under Changing Salinities

“…In general, all groups keep the osmolality of their body fluids close to the level of their environment (osmoconformers) to reduce the necessity of energy-consuming osmoregulatory processes. However, oligohaline snails are able to hyperregulate their internal osmolality under very low-salinity conditions [26][27][28][29].…”