The abyssal Pacific Clarion Clipperton Zone (CCZ) hosts vast, commercially valuable seafloor deposits of polymetallic nodules. Foraminifera (testate protists) dominate benthic communities in this region. Here, we present a taxonomic survey, combining morphological and genetic data and focussing on mainly meiofauna-sized Foraminifera from the eastern CCZ. Sequences obtained from >100 specimens, the majority photographically documented, were analysed phylogenetically. Most were single-chambered Monothalamea (‘monothalamids’), a high percentage of them squatters inhabiting empty tests of mainly multi-chambered Foraminifera. The first sequences for the monothalamid genus Storthosphaera were obtained, while specimens assigned to Gloiogullmia, Hippocrepinella and Vanhoeffenella yielded new sequences. Among multichambered taxa, high-throughput Illumina sequencing (HTS) revealed a second haplotype of the calcareous rotaliid Oridorsalis umbonatus, possibly representing a distinct species. Additional HTS sequences were obtained from the rotaliids Nuttallides umbonifer and Globocassidulina subglobosa, confirming their wide distributions. We also obtained the first sequences for Cribrostomoides subglobosa, showing that it branches separately from other members of this genus. The fact that many sequences did not correspond to known morphospecies reflects the scarcity of reference barcodes for deep-sea Foraminifera, particularly the poorly known but highly diverse monothalamids. We recommend using HTS of single specimens to reveal further unknown species. Despite extensive research, much remains to be learnt about the true scale of foraminiferal biodiversity in the CCZ.
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