Abstract

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 to be morphologically simplistic, but they 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 on small subunit ribosomal DNA (SSU rDNA) sequences by others has delineated 13 genetic clades, most of which unite taxa that do not share a common general morphology. Here, we present ultrastructural and molecular results on an undescribed allogromiid, Niveus flexilis nov. gen., nov. sp., collected from low-salinity marshes along coastal Georgia, USA. Partial SSU phylogenetic analyses indicate that this taxon is a member of Clade E Allogromiid Foraminifera.

This taxon is small (<300 μm), generally ovate in shape, and has a single aperture. The flexible test is composed of a thin (<0.5 μm), 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 (3–8 μm), 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 (1.5 μm) of endoplasmic reticulum overlain by a layer of vesicles of unknown function. 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, particularly Psammophaga spp. Ultrastructural data for additional Clade E taxa are necessary to identify fine morphological characters that may be synapomorphies for this group.

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