Co-Activation of Antagonistic Motoneurons as a Mechanism of High-Speed Hydraulic Inflation of Prey Capture Appendages in the Pteropod Mollusk Clione limacina.

The predatory pteropod mollusk Clione limacina catches its prey by using specialized oral appendages called buccal cones. Eversion and elongation of buccal cones is a hydraulic phenomenon. In the cerebral ganglia, two groups of motoneurons have been identified that underlie functionally opposite movements of buccal cones: extrusion and retraction. We suggest that the remarkably rapid inflation of buccal cones (50 ms) is achieved through initial co-activation of antagonistic neurons, which presumably produces high pressure in the head hemocoel prior to buccal cone extrusion. The subsequent sudden inhibition of retractor motoneuron activity results in a very rapid and powerful inflation of the buccal cones. Cerebral interneurons that evoke co-activation are described.