A NEW ALLOGROMIID FORAMINIFER FROM COASTAL GEORGIA, USA: FINE STRUCTURE AND GAMETOGENESIS

Allogromiids (sensu lato) occupy diverse habitats including marine, brackish, freshwater and terrestrial environments, serve a suite of trophic functions within their communities and are modern descendents of the earliest diverging foraminiferal lineages. Allogromiids appear morphologically simplistic, but have diverse, intricate shell architectures at the fine structural level. They are not well known from the fossil record and are sometimes difficult to recognize in modern systems. Recent molecular work (SSU rDNA) by others has delineated thirteen genetic clades, most of which unite taxa that do not share a common general morphology. The ultimate goal of this research is to examine and compare test architecture at the fine structural level, features of the cell body, mode of reproduction (if observed) and molecular genetics from representatives from a single allogromiid clade (Clade E). Here, we present our results on an undescribed Clade E allogromiid (“Rod and Gun White Allo”) collected from low-salinity marshes.

This taxon is small (<300 microns), generally ovate in shape and has a single aperture. The flexible test is composed of a thin, outer agglutinated layer of fine clay particles predominantly arranged parallel to the shell surface. The outer surface of the test is crenulated and irregular. The agglutinated layer is underlain by a thick inner organic lining (IOL) which is in direct contact with the cell membrane. The IOL contains numerous small electron dense particles along with long, fine fibers generally arranged parallel to the outer surface of the shell. Small vesicles lie just beneath the plasma membrane and appear to release test construction materials at the base of the IOL. The nuclear membrane is surrounded by a thick layer of endoplasmic reticulum overlain by a layer of vesicles of unknown function. Sexually reproducing gamonts release many small biflagellated gametes through the aperture directly into surrounding seawater. Fine cytological examination of the test suggests that this new allogromiid shares a similar constructional theme with other Clade E allogromiids examined to date (Psammophaga sp. and another undescribed Clade E allogromiid). Ultrastructural data for additional Clade E taxa are necessary to identify fine morphological characters that would reflect the phylogenetic relationships of this group.