The feeding mechanism of Zoophycos producers demonstrates non-selection by particle size or quality. The characteristic morphology and mode of Occurrence of Zoophycos and the presence of pellets with pyroclastic grains imply that the Zoophycos producers were surface deposit-feeders. They dwelt in a burrow within the sediment and ingested the grains with nutrient detritus on the sea floor around the burrow opening. Fecal pellets containing pyroclastic grains were compared with the overlying volcanic ash layers through the analyses of grain size and mineral composition based on samples from two horizons in the Upper Pliocene of Boso Peninsula, central Japan. Judging from the comparative analyses, no significant differences were found between the ash layer and the fecal pellets. This fact strongly suggests that the Zoophycos producers appear to indiscriminately ingest particles on the sediment surface. Environments of low nutrition input such as the deep sea, non-particle size and quality selection in Zoophycos producers may be the feeding strategy for the detritus-feeding burrow-dwellers. □ Zoophycos, surface deposit-feeding, Pliocene Shiramazu Formation, Boso peninsula, Japan.