The calcareous foraminifer Cibicides refulgens is a conspicuous and abundant component of the epifaunal community living on the valves of the free-swimming Antarctic scallop, Adamussium colbecki. Examination of this association using light microscopy, scanning electron microscopy, radiotracer, and resin-casting/sectioning techniques, demonstrates that the foraminifer possesses a combination of morphological and physiological adaptations, unique among benthic calcareous foraminifera, which enhance its ability to acquire nutrients in an otherwise oligotrophic and seasonal environment. Three distinct modes of nutrition are employed: (1) grazing the algae and bacteria living upon the scallop shell surface, (2) suspension feeding through the use of a pseudopodial net deployed from a unique superstructure of agglutinated tubes which form an extension to the calcareous test, and (3) parasitism by eroding through the scallop's shell, and using free amino acids from the highly concentrated pool in the extrapallial cavity.