VARIATIONS IN HEMOLYMPH IONIZED CALCIUM CONCENTRATIONS IN THE CRUSTACEAN ORCHESTIA-CAVIMANA DURING A MOLT CYCLE

Measurements of ionized calcium concentration in the haemolymph of the semi-terrestrial crustacean Orchestia cavimana were taken during the 14 successive moulting stages by ion-selective electrode direct potentiometry on pooled samples. Ionized calcium showed major variations associated with the moult cycle. Titres were low and relatively stable in intermoult and early premoult, then progressively increased during mid and late premoult to reach maximal values just at exuviation, and rapidly fell down during the postmoult. The variations of the ionized fraction showed a close correlation with those of the calcaemia ( = total fraction), suggesting the presence of efficient haemolymphatic calcium-buffering mechanisms which are discussed in connection with the specific calcium turnover in Orchestia.