Allogromiids are classically defined as a group of monothalamous, soft-walled foraminiferans. Recent morphological, cytological, and molecular studies, however, challenge this view, showing that the soft-walled allogromiids are closely related to naked athalamids and unilocular agglutinated foraminiferans. To establish the phylogenetic relationships among these three groups we obtained partial small-subunit ribosomal DNA sequences of 50 species and undetermined morphotypes, and compared them to other foraminiferal taxa. Phylogenetic analyses of our data show that allogromiids, athalamids and astrorhizids comprise an assemblage of 13 lineages branching together at the base of the foraminiferal tree. Among these lineages, two are represented by a single species and four comprise similar genera, while the remaining seven are heterogeneous groups composed of several species having different types of wall structure and different test morphologies. All lineages are relatively well supported, yet the relationships among them are not resolved. In view of our data, we propose to revise the definition of allogromiids to include all naked and testate unilocular granuloreticuloseans that diverged early in the evolution of Foraminifera.
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