The pH of body fluids from marine intertidal invertebrates

The pH of the body fluids of 25 species of marine invertebrates from nine phyla was determined at temperatures to which these animals were acclimated. The gastrovascular fluid of several coelenterates and one species of flatworm was found to have pH values approximating to that of sea water. The coelomic fluid of nemertine, sipinculid, echiuroid, and annelid worms, as well as the heart fluid of several molluscs and the sternal sinus fluid of decapod crustaceans, were characterized by more alkaline pH values. Echinoderm polian vesicle fluid was characterized by slightly acidic pH values. The importance of the pH of the body to the respiratory physiology of marine invertebrates is discussed.