Mechanisms of Suspension Feeding in Bivalves: Resolution of Current Controversies by Means of Endoscopy

Controversy concerning the mechanism of suspension feeding in bivalves centers around whether particle capture and transport on the gills (ctenidia) is accomplished via mucociliary or hydrodynamic action. Evidence for and against these fundamentally different processes has been based on examinations of isolated feeding structures and dissected specimens, techniques that may produce artifactual data owing to the trauma associated with the procedures. In the present study, in vivo observations of the ctenidia of undisturbed bivalves, made with a fiber-optic endoscope and video image-analysis system, revealed that the two mechanisms are not mutually exclusive. Both mucociliary and hydrodynamic mechanisms function concurrenlty at different sites on the ctenidia, thereby minimizing particle loss and optimizing particle transport efficiently. The importanc of mucus in the normal feeding process of bivalves is confirmed. These findings refute results of previous studies that used surgically invasive techniques and emphasize the importance of making observations on morphologically intact specimens.