A remarkable new monothalamid (Rhizaria, Foraminifera) from the shoreline of Livingston Island, Antarctica

In this study, we describe a novel monothalamous Foraminifera, discovered in shoreline sediment samples from the Southern Ocean. The individuals, approximately 75 μm in diameter, are relatively small for Foraminifera, mostly spherical, with an organic-walled test. Notably, these Foraminifera exhibit a unique behavior in culture: they surround themselves in planktonic diatoms, enabling them to float in the water column. This floating behavior is unusual for Foraminifera, which are often larger and possess a thick test made of calcite or agglutinated particles. We hypothesize that the small size of the organism, its lightweight organic test, and the habit of surrounding itself with centric diatoms may enable the floating behavior observed in culture and potentially aid dispersal in nature. Phylogenetic analysis of the 18S rDNA barcoding fragment places this undescribed organism as an independent lineage among monothalamid Foraminifera. We erect the novel genus Pensilisphaera with its type species Pensilisphaera antarcticaensis.