Sieve Plates and Habitat Adaptation in the Foraminifer Planulina ornata

Planulina ornata (d'Orbigny), a coarsely perforate species of foraminifera having a low trochospiral test, was recovered attached to phosphatic hardgrounds from the lower oxygen-minimum zone off Peru. Above the base of individual pores are calcified, perforate sieve plates, the largest so far described. Structure of the pores suggests a possible association with mitochondria and respiratory function. These large pores may facilitate extraction of the severely limited amount of oxygen from the ambient bottom waters at that locale.