Shell Movements of the Freshwater Mussel, Hyridella australis Lam. (Lamellibranchiata)

Abstract

An analysis of about 4,500 hours of shell movement tracings of the freshwater mussel, Hyridella australis Lam., is presented. Nine series of experiments have been conducted, representing variations in light and temperature conditions. It has been found that, as well as shell movements, shell position or degree of openness must be considered. The shells may be closed (phase 1), completely open (phase 3), or stationary, intermediate between the two (phase 2), for the validity of which position mathematical proof has been found. The characteristics of each phase have been outlined. Temperature, within the range 17 to 27°C shows no well-definded influence on shell movements or the degree of openness. The influence of light, especially in regard to phase 2, is discussed. A diurnal light rhythm is associated with a diurnal feeding rhythm; under continuous illumination the shells tend to remain apart but in phase 2, darkness suppresses shell movements and feeding. The shell movements during ovulation are discussed.