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 potent iometry on pooled samples. Ionized calcium showed major variations ass ociated with the moult cycle. Titres were low and relatively stable in intermoult and early premoult, then progressively increased during mi d and late premoult to reach maximal values just at exuviation, and ra pidly fell down during the postmoult. The variations of the ionized fr action showed a close correlation with those of the calcaemia ( = tota l fraction), suggesting the presence of efficient haemolymphatic calci um-buffering mechanisms which are discussed in connection with the spe cific calcium turnover in Orchestia.