The central pattern generator for swimming in the pteropod mollusk Clione limacina consists of at least four pedal interneurons, two each controlling parapodial upstroke and downstroke. The two sets of antagonistic interneurons are linked by reciprocal monosynaptic inhibitory synapses, and all exhibit apparently strong postinhibitory rebound. This simple neuronal network produces reverberating alternate cyclic activity in the absence of tonic drive or apparent feedback modulation.