The biodiversity and biogeography of komokiaceans and other enigmatic foraminiferan-like protists in the deep Southern Ocean

Abstract

We present a survey of komokiaceans and other relatively large, stercomata-bearing testate protists, presumed to be foraminifera, based on extensive ship-board sorting of samples collected at 13 sites (depth range 1820–4930 m) in the Weddell Sea and two sites in the SE Atlantic (Cape and Aguilas basins, north of the Antarctic Convergence) during the ANDEEP III expedition. Thirty-nine species occurred in the Weddell Sea and a further 11 in the SE Atlantic basins. Of these 50 species, 35 are undescribed. We assign, with a greater or lesser degree of certainty, 26 and 13 species to the komokiacean families Komokiidae and Baculellidae, respectively, and another 2 to the Komokiacea incertae sedis. We include in the Baculellidae an undescribed species in which very fine hair-like fibres, similar to those seen in some species currently included in this family, arise from the segments that make up the chain-like test. A further 11 chain-like species lack these fibres and we therefore exclude them from the Komokiacea. A final group of species includes a mixture of different forms, some of which exhibit komokiacean-like features. These assemblages were most diverse at abyssal sites in the central Weddell Sea (27–30 species per site). Above 4000 m, 1–8 species were present at individual sites and only two species, Normanina conferta and Septuma brachyramosa, occurred at depths <2000 m. One of these, N. conferta, was the most widely distributed species, occurring at 11 stations south of the Antarctic convergence as well as the Aguilas Basin. Many (31–61%) of the Southern Ocean ANDEEP species are recognised in the North Atlantic and 6 were previously described from the central North Pacific. Our results suggest that some komokiacean and chain-like species are widely distributed at abyssal depths in the oceans. They also support other evidence that many undescribed komokiacean species exist and highlight some of the difficulties involved in defining the morphological limits of this difficult taxon.