The Neural Basis of Escape Swimming Behaviour in the Squat Lobster Galathea Strigosa Ii. the Motor Programme and Sensory Feedback Interactions

1. A motor programme underlying backward swimming in the squat lobster Galathea strigosa is described. Swimming is accomplished by repeated flexions and extensions of the abdomen. This investigation indicates that the behaviour is generated centrally, possibly in the suboesophageal or thoracic nervous system, and is probably homologous with non-giant escape behaviour in crayfish. 2. The effects of sensory feedback on the swimming rhythm have been investigated in free-swimming and restrained preparations. Proprioceptive feedback, probably originating in the abdominal muscle receptor organs, is involved in the maintenance of high frequency swimming. 3. During swimming, the walking legs and unmodified male swimmerets are rhythmically active in phase with abdominal flexion. Swimmeret 'flicking' in the male is effected by high frequency spiking in a single phasic swimmeret motor neurone. The results suggest that, when active, the central pattern generator for swimming dominates other neural oscillators for rhythmic limb movements.