Recent neurobiological studies on molluscs have concentrated on the analysis of relatively complex behaviour, whereas many localized reflex movements of the body do not form part of centrally determined neural programmes. The central ganglia, nerve trunks and neuron somata ofArmina californicahave been described with special reference to some of the smaller neurons in the pedal ganglia which are shown to control reproducible movements of the mantle, foot and oral veil. Similar movements are observed as part of normal behavioural responses.