We describe Notodendrodes hyalinosphaira, a large (up to 2.7 cm long), facultatively arborescent, agglutinated foraminifer. The species occurs abundantly, and apparently exclusively, in Explorers Cove, an embayment of western McMurdo Sound, Antarctica. The primary agglutinated test is an infaunal, unilocular sphere comprised of a single layer of principally quartz sand grains. Two secondary test features may be associated with the quartz sphere: (1) a thick cover of fine detrital material and/or (2) one, or rarely two, daisy-shaped appendages extending into the water column. These secondary test features in Notodendrodes hyalinosphaira apparently reflect trophic plasticity, ranging from infaunal uptake of dissolved nutrients to suspension feeding. Particle analysis reveals distinct size-class distributions for each test component, indicating a high degree of particle selection. The cell body (sarcode), which occupies approximately half of the quartz-sphere volume, is encased by a theca possessing a single aperture. Notodendrodes hyalinosphaira belongs to unilocular agglutinated foraminifera possessing certain structural similarities with allogromiids.