THE CELLULAR BASIS OF MOVEMENT COORDINATION IS CONSERVATIVE IN GASTROPODS DIFFERING IN FEEDING STRATEGIES

In herbivorous pulmonate molluscs, activity of the buccal central patt ern generator (CPG) for feeding is generally arrested during activatio n of CPG for defensive withdrawal. Using a series of neuromorphologica l methods including axon backfilling and immunocytochemistry we have i nvestigated both basommatophoran, fresh-water pulmonates (Lymnaea stag nalis, L. auricularia, Planorbarius corneus) and stylommatophoran, ter restrial ones (Bradibaena fruticum, Helix pomatia, H. lucorum, Limax c inereaniger, Succinea putris), and found that a pair of pleural-buccal projecting neurons, the right and left PIE cells, are responsible for this coordination. Opposite to the feeding-defence hierarchy in pulmo nates, defensive responses are inhibited during feeding arousal in a p redatory opisthobranch Clione limacina. In spite of this difference, t wo symmetric neurons similar to the pulmonate PIE cells have been foun d to occur in the pleural ganglia of C. limacina. Specific features in dicating the homology of the Clione PIE neurons to those of pulmonates are FMRFamide-like immunoreactivity and peculiar, indirect route of t he axon which traverses the ipsilateral pedal ganglion on its way to t he cerebral and buccal one. We conclude that homologous coordinating n eurons conserved in gastropod evolution may underlie defence/feeding d ominance in an opposite manner.