In controlled laboratory experiments using a wide array of exotic sediments of known characteristics (glass and plastic beads) we studied the mechanical, evolutionarily-fixed component of particle selection for ingestion in 5 surface and 6 subsurface deposit feeders, from 3 phyla (Annelida, Mollusca and Arthropoda). Three species were nonselective within all or part of the 3-324 μm particle size range tested, while the remaining 8 species exhibited unimodal patterns of size selection, peaking near 6 μm. In addition, the surface deposit feeders displayed a strong preference for particles of low specific gravity. Particle selection in tube construction by the polychaetes followed similar but weaker trends. Initial particle gathering into the mantle cavities of the bivalves by inertial suction or adhesion to mucus-covered appendages appeared nonselective.