Integrative taxonomy of new genera and species of giant foraminifera (Rhizaria: Foraminifera: Xenophyophoroidea) from the abyssal northwest Pacific reveals novel morphological complexity

Abstract Xenophyophores are megafauna-sized deep-sea monothalamid foraminifera. Based on micro-computed tomography, light microscopy, and scanning electron microscopy, we describe five new species from two abyssal northwest Pacific sites. Frutexia perplexa gen. & sp. nov. has an unusual bush-like test. Platyzona fasciata gen. & sp. nov. comprises plates with prominent concentric zones. Fluxaphilia mollis gen. & sp. nov. has a complex test comprising thin plates. Two species have homogeneous, ‘muddy’ tests with novel morphological features. In Monolithammina corynodes gen & sp. nov. and Monolithammina sp., the upper exposed and lower buried parts have distinctly different morphologies and internal structures, and the distal extremities are ramified by fine channels terminating in tiny surface apertures. Homogammina fictilis sp. nov. also features fine channels and tiny apertures, in addition to larger internal voids. Our molecular phylogeny revealed two large clades, one comprising 13 species, including Fluxaphilia mollis and P. fasciata (the Fluxaphilia complex), and the other comprising seven species, including Frutexia perplexa (the Frutexia complex). Monolithammina corynodes branches as sister to the Frutexia complex. However, our phylogeny failed to recover reliable phylogenetic relationships within these groupings or more deeply within the Xenophyophoroidea. This study enhances knowledge of the taxonomic and genetic diversity of xenophyophores and their morphological complexity.