Paper No. 2
Presentation Time: 1:30 PM-5:30 PM
COMPARISON OF CELLULAR FINE STRUCTURE OF SELECTED "CLADE E" ALLOGROMIID FORAMINIFERS FROM COASTAL GEORGIA, USA
The allogromiids (sensu lato) represent a seemingly inconspicuous taxonomic group of Foraminifera because of their limited presence in the fossil record and apparent absence in sediments. It has been proposed that extant allogromiids represent modern descendants of taxa that compose the evolutionary base of the foraminiferal clade. Historically, allogromids have been considered primitive' in the foraminiferal lineage because of their morphological simplicity, organic test, or lack of test all together. Although allogromiids appear morphologically simplistic, they in fact have diverse, intricate shell architectures at the fine structural level. 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. Of particular interest, the Clade E allogromiids, appear to be conspicuously abundant along coastal Georgia salt marshes, mudflats and tidal channels, yet their diversity at this location and their phylogenetic cohesiveness have not been adequately assessed. Other workers have shown that they share a molecular affinity in phylogenetic reconstructions based on SSU sequences, however the resolution of Clade E is problematic in that the clade becomes less cohesive as more taxa are added to the analyses. To date, no known gross morphological characteristics unite all members of this clade defined by SSU rDNA sequences. Here we compare gross morphology and the fine structure of the test, wall and cell body for selected Clade E allogromiids from coastal Georgia USA: Psammophaga sp., Niveus flexilis, the 2005 Gam Foram', Fusiform' and Fruitcake'. Our results show that certain features of the wall are consistent throughout the group whereas certain features of the cell body differ. Ultimately it is hoped that test architecture, features of the cell body and mode of reproduction (if observed) at the fine structural level can be used in conjunction with molecular data to enhance the resolution of Clade E.