WHOLE-BODY WITHDRAWAL CIRCUIT AND ITS INVOLVEMENT IN THE BEHAVIORAL HIERARCHY OF THE MOLLUSK CLIONE-LIMACINA

1. The behavioral repertoire of the holoplanktonic pteropod mollusk Cl ione limacina includes a few well-defined behaviors organized in a pri ority sequence. Whole body withdrawal takes precedence over slow swimm ing behavior, whereas feeding behavior is dominant over withdrawal. In this study a group of neurons is described in the pleural ganglia, wh ich controls whole body withdrawal behavior in Clione. Each pleural wi thdrawal (P1-W) neuron has a high threshold for spike generation and i s capable of inducing whole body withdrawal in a semi-intact preparati on: retraction of the body-tail, wings, and head. Each P1-W neuron pro jects axons into the main central nerves and innervates all major regi ons of the body. 2. Stimulation of P1-W neurons produces inhibitory in puts to swim motor neurons that terminate swimming activity in the pre paration. In turn: P1-W neurons receive inhibitory inputs from the cer ebral neurons involved in the control of feeding behavior in Clione, n eurons underlying extrusion of specialized prey capture appendages. Th us it appears that specific inhibitory connections between motor cente rs can explain the dominance of withdrawal behavior over slow swimming and feeding over withdrawal in Clione.