Polychaete larvae from several families are thought to be natural predators upon planktonic bivalve larvae. However, little direct evidence of interactions between these predators and prey is available. We conducted predator-prey experiments on laboratory roller tables for five putative predatory polychaete larvae, representing four families (metatroch-less larvae of the Polynoidae and metatrochophore larvae of the Spionidae, the Magelonidae, and the Phyllodocidae). D-hinge veliger larvae of the oyster Crassostrea gigas were offered as prey. Predation was monitored over a range of prey densities and in the presence and absence of background plankton. "Background plankton" are any naturally occurring plankton assemblages found in whole, unfiltered seawater at ambient concentrations. For all polychaete larvae examined, when natural C. gigas densities and background plankton were used, no predation was observed. Magelonids and phyllodocids did not consume any C. gigas larvae, regardless of conditions. Polynoid and spionid trochophores consumed C. gigas veligers at both the "natural" and unnaturally high prey densities in filtered seawater. The addition of background plankton eliminated the predation at all natural prey densities and significantly reduced the predation observed at high prey densities.