Neurons controlling foot and mantle movements inArmina californica

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Abstract
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 of Armina californica have 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. With the exception of one pair, the motor fields of all pedal neurons studied were ipsilateral, and only one neuron in the right pleural ganglion was found to give bilateral responses of the mantle and foot. Most pedal neurons had a functional homologue in the opposite ganglion, which could vary slightly in its topographical position with respect to its partner. Neural homologues often shared common sensory or interneuron inputs resulting from external stimuli applied to the mantle or foot, but no monosynaptic and only two polysynaptic pathways were found between pairs of pedal neurons at this level. The activity of synergistic neurons, or those driving incompatible movements must be integrated through higher‐order interneurons elsewhere in the ganglia.