DEPOSIT-FEEDING IN SELECTED DEEP-SEA AND SHALLOW-WATER BENTHIC FORAMINIFERA

Ultrastructural evidence for deposit feeding in two deep-sea foraminif era, Globobulimina pacifica and Uvigerina peregrina, is presented and compared with results on Ammonia beccarii, a common nearshore dweller. In all three taxa, food vacuoles are common in the last chamber and c ontain numerous aggregates of sediment and organic detritus. Within ag gregates, bacteria are often found surrounded by a sheath of sediment particles generally bound by bacterial exopolymers. In actively-feedin g individuals of A. beccarii, food vacuoles along the distal edge of t he cytoplast contain live bacteria associated with sediment aggregates as well. Bacteria do not occur in the cell's interior, although hollo w sheaths of sediment and detritus do persist. This indicates that the digestion of bacteria may occur very near the distal margin of the cy toplast in this species. Likewise, sediment aggregates both with and w ithout bacteria occur in food vacuoles of the deep-sea species examine d. All three species ingest relatively large volumes of organic detrit us associated with sediments, although the role of this material in th e diet of foraminifera is uncertain. These results suggest that the de ep-sea and shallow-water species examined feed on bacteria by deposit feeding and ingest bacterial cells, in addition to relatively large vo lumes of associated sediment and organic detritus.