Costs and Benefits of Opisthobranch Swimming and Neurobehavioral Mechanisms

After opisthobranch molluscs dislodge from the substrate duringonset of swimming, the ensuing flexion or undulatory motionsare usually not well oriented with respect to predators, preyor suitable substrate. Swimming motions are effective in launchinganimals off the substrate and elevating them into the watercolumn where they are primarily transported passively by ambientwaves and tidal currents. Both active swimming and passive transporton ambient currents may provide escape from predators, searchfor food and mates, and dispersal to new and potentially adaptivelocations. However, loss of contact with the substrate and launchinginto the water column may also bring a high cost in terms ofexposure to diverse risks. I illustrate several forms of opisthobranchswimming and describe their mechanisms and roles. In addition,adaptations of some opisthobranchs to reduce the risks of exposureto predators during swimming are suggested. These adaptationsinclude small size, transparency or inconspicuous color to reducepredation while swimming, and neurobehavioral mechanisms ofrheotaxis and geomagnetic sensitivity.