FUNCTIONAL MORPHOLOGY OF THE FEEDING PALPS OF SPIO SETOSA (POLYCHAETA: SPIONIDAE)
Dauer, D. M.
Department of Biological Sciences, Old Dominion University, Norfolk, Virginia, USA 23529
The functional morphology of the feeding palps of Spio setosa was studied by examining specimens collected from Delaware Bay, USA. Ciliary groups on the feeding palps of S. setosa include (1) frontal cilia lining the food groove that transport captured particles to the pharynx, (2) regular rows of cirri on the frontal surface adjacent to the food groove, and (3) widely scattered cirri on the lateral and abfrontal surface of the palp. Cirri are composed of closely spaced cilia that vary from less than 1 to 5-7 µm in length. Cirri on the palps of other spionid species studied to date are either much longer or are located on raised elevations (papillae) on the palp surface. S. setosa is a facultative suspension feeder that in flow orients the frontal surface of the palp directly into the current. Some facultative suspension-feeding spionids have ciliary groups that increase particle capture rate, including laterofrontal cirri (that deflect particles onto the food groove) and lateral cilia (that produce small-scale vortices in the vicinity of the food groove). The comparatively simple ciliary organization of the palps of S. setosa are speculated to be related to the magnitude of flow velocities encountered by this species. This species also increases the height of its tube above the sediment surface. Increased height above the sediment-water interface increases the proportion of fine-sized particles of higher nutritional quality.