IN-VIVO STUDIES OF SUSPENSION-FEEDING PROCESSES IN THE EASTERN OYSTER, CRASSOSTREA-VIRGINICA (GMELIN)

Suspension-feeding processes in the eastern oyster Crassostrea virgini ca (Gmelin, 1791) were examined, in vivo, with an endoscope linked to a video image-analysis system. We found that many of the previously pu blished concepts of particle transport and processing in this species, obtained using surgically altered specimens or isolated organs, are i ncomplete or inaccurate. In particular, our observations demonstrate t hat (1) captured particles are transported along the gills by both muc ociliary (marginal grooves) and hydrodynamic (basal tracts) processes; (2) the labial palps accept material from the gills both in mucus-bou nd particle strings (transported in marginal grooves), and suspended i n particle slurries (transported in basal tracts); (3) the labial palp s reduce the cohesive integrity of the mucous strings and disperse and sort the entrapped particles; (4) particles are ingested in the form of a slurry; and (5) ciliary activity on the labial palps is independe nt of that on the lips, allowing the oyster to filter particles from s uspension and produce pseudofeces without ingesting any particulate ma tter. Because many ostreids have the same plicate gill structure, we b elieve that our conclusions are applicable to other oyster species. In addition, the present observations are consistent with other endoscop ic examinations recently made on bivalves in different families. We co nclude that accepted theories of particle handling in suspension-feedi ng bivalve mollusks must be modified to accommodate observations made with the endoscope.