GAMETOGENESIS IN AN ALLOGROMIID FORAMINIFER FROM MUDFLATS OF SAPELO ISLAND, GEORGIA, USA

The biodiversity of allogromiid Foraminifera (including naked, organic-walled, and monothalamous agglutinated taxa) is considerably higher than that recognized in most studies using traditional methods. The many mudflats associated with salt marshes of Sapelo Island, Georgia host an interesting array of mostly undescribed allogromiids in addition to other taxa. These Foraminifera are primarily associated with the thin surface layer of sediment that in turn overlies black, sulfidic mud. Different species of allogromiids inhabitat these mudflats which occur over a wide range of salinities extending from nearly marine to nearly freshwater. Among these various allogromiids is a small (<150 microns) translucent monothalamous foraminifer. Its test consists of a prominent agglutinated layer, consisting of clays and bioadhesive, which is underlain by an inner organic lining. Molecular analyses are employed to demonstrate the relationship of this species to other allogromiids. Gametogenesis is extremely common in populations present during the summer, thus facilitating both direct observation and ultrastructural preparations of most stages. Non-reproductive individuals appear golden-brown in color, reflecting a heavy diet of diatoms. Amazingly, such individuals appear completely stuffed with pennate diatoms, and the single nucleus occurs in a marginal position in the abapertural portion of the foraminifer. Centric diatoms are also ingested, but food vacuoles contain very little sediment indicating that this species does not routinely employ deposit feeding. Some foreign materials are egested at the onset of gametogenesis, but most are sequestered within a large, centrally-located vacuole. Gametogenesis occurs around this large vacuole and produces numerous flagellated gametes that are released directly into the surrounding seawater via the aperture. The occurrence of gametogenesis in so many contemporaneous individuals probably serves to increase reproductive success.