Massive occurrence of a new soft-walled monothalamous foraminifer, Bathyallogromia brandtae n.sp., in the hadal Aleutian trench

Large numbers of spherical, organic-walled, monothalamous foraminifera were observed and isolated from the fine-sized sediment fraction collected at hadal depths in the Aleutian trench. The foraminifer was one of the few living species found among diatom frustules that make up most of this sediment fraction. Morphologically, the species resembles the genus Bathyallogromia described from the Weddell Sea and subsequently found in the abyssal Arctic Ocean, and other high latitude areas but never in such massive abundance. Molecular phylogenetic analyses based on partial 18S rRNA gene sequences confirmed its generic identification as a new species within the Bathyallogromia clade that is described here as Bathyallogromia brandtae sp.nov. Our study offers new evidence that deep-sea monothalamous foraminifera can proliferate in extreme hadal settings and have biogeographic distributions that are more restricted than is commonly assumed.