The eight species of Macoma examined fall into three feeding categories: two are deposit feeders, five are suspension feeders, and one feeds on the surface films of bacteria on sand grains. The type of particle which is found in the stomach depends on the behavior of the siphons, the quality or quantity of mucus secreted by the gills and labial palps, and, to some extent, on the sorting function of the labial palps. The labial palps act as supplementary filtering mechanisms. The stomach of M. secta, which ingests sand grains, is adapted to this diet by the enlargement of the gastric shield, but in the other species there is no obvious relationship between diet and stomach morphology.