EFFECTS OF HYPERGRAVITY ON STATOCYST DEVELOPMENT IN EMBRYONIC APLYSIA-CALIFORNICA

Aplysia californica is a marine gastropod mollusc with bilaterally pai red statocysts as gravity-receptor organs. Data from three experiments in which embryonic Aplysia californica were exposed to 2 X g are disc ussed. The experimental groups were exposed to excess gravity until ha tching (9-12 day), whereas control groups were maintained at normal gr avity. Body diameter was measured before exposure to 2 X g. Statocyst, statolith and body diameter were each determined for samples of 20 em bryos from each group on successive days. Exposure to excess gravity l ed to an increase in body size. Statocyst size was not affected by exp osure to 2 X g. Statolith size decreased with treatment as indicated b y smaller statolith-to-body ratios observed in the 2 X g group in all three experiments. Mean statolith diameter was significantly smaller f or the 2 x g group in Experiment 1 but not in Experiments 2 and 3. Def ective statocysts, characterized by very small or no statoliths, were found in the 2 X g group in Experiments 1 and 2.