LARGER AGGLUTINATED FORAMINIFERA OF MCMURDO SOUND, ANTARCTICA - ARE ASTRAMMINA-RARA AND NOTODENDRODES-ANTARCTIKOS ALLOGROMIIDS-INCOGNITO

Explorers Cove, an embayment on the oligotrophic western side of McMur do Sound, Antarctica, is noted for physical and biological similaritie s to the deep sea. This locality is an important site for foraminifera l biologists because large, deep-sea-like agglutinated taxa are abunda nt at depths accessible to SCUBA divers. Using microdissection methods , we found that many of the giant, single-chambered species from this locality display an allogromiid internal organization (i.e., a monotha lamous cell body encased by an organic wall or ''theca''). Another cha racteristic feature of these species is the presence of a distinct spa ce separating the cell body and agglutinated test. We used high voltag e transmission electron microscopy of thick sections to examine the th eca of Astrammina rara, a dominant Explorers Cove species possessing a simple spherical test morphology, and Notodendrodes antarctikos, a di stinctive arborescent species. We found that the simple gross morpholo gy of A. rara's agglutinated test belies the complex ultrastructure of its allogromiid-like theca, and that the complex dendritic morphology of N. antarctikos' agglutinated test contradicts the simple ultrastru cture of its theca. Additional field and laboratory observations on A. rara revealed that the agglutinated test can be a transient structure . Our observations raise questions regarding the taxonomy and phylogen y of unilocular agglutinated foraminifera and other primitive granulor eticuloseans. The results are also discussed in terms of test function in larger agglutinated foraminifera and the ecology of this important taxon.