A New Higher-Level Taxonomy of Monothalamous Foraminifera

Monothalamous foraminifera are a highly diverse, paraphyletic assemblage of single-chambered lineages characterized by an organic or agglutinated test or lacking any external covering. Traditional morphology-based taxonomy divides them into the organic-walled Allogromiida and agglutinated Astrorhizida. Molecular systematics showed that this division is not justified as different wall types occur within the same lineages. Twenty years ago, based on molecular phylogenetic data, the monothalamids were classified into 13 lineages, called clades. Since then, the diversity of monothalamids from different habitats and regions has been extensively studied both genetically and morphologically, and many new species and genera have been described. Here, we analyzed 70 sequences of the 18S rRNA gene, representing 66 described species. We also analyzed 23 sequences of the COI gene for selected taxa. Based on molecular phylogenetic analyses and available morphological data, we establish a new formal higher-level taxonomy of monothalamous foraminifera. We introduce 5 new orders and distinguish 1 suborder and 34 families, of which 20 families are new. Our classification establishes a new taxonomic system that we hope will provide the foundation for organizing the vast diversity of monothalamous foraminifera revealed by recent studies.