Costs and benefits of opisthobranch swimming and neurobehavioral mechanisms

Abstract

After opisthobrancli molluscs dislodge from the substrate during onset of swimming, the ensuing flexio'n or undulatory motions are usually not well oriented with respect to predators, prey or suitable substrate. Swimming motions are effective in launching animals off the substrate and elevating them into the water column where they are primarily transported passively by ambient waves and tidal currents. Both active swimming and passive transport on ambient currents may provide escape from predators, search for food and mates, and dispersal to new and potentially adaptive locations. However, loss of contact with the substrate and launching into the water column may also bring a high cost in terms of exposure to diverse risks. I illustrate several forms of opisthobranch swimming and describe . their mechanisms and roles. In addition, adaptations of some opisthobranchs to reduce the risks of exposure to predators during swimming are suggested. These adaptations include small size, transparency or inconspicuous color to reduce pré dation while swimming, and neurobehavioral mechanisms of rheotaxis and geomagnetic sensitivity.