A minute new species of Saccammina (monothalamous Foraminifera; Protista) from the abyssal Pacific

Abstract. Saccammina minimus sp. nov., a spherical agglutinated organism presumed to be a foraminiferan, is described from the Kaplan Central site in the abyssal eastern Equatorial Pacific (5042 m water depth). The new species is minute in size (<100 μm diameter) with a test wall composed of a jumble of small mineral grains and a few relatively larger diatom fragments. Occasional specimens, often droplet-shaped rather than spherical, have a simple aperture. The new species is by far the most abundant organism in sieve fractions >32 μm of samples collected at the KC site. In six subcores (6.6 cm² surface area, 0–1 cm layer) from two cores obtained during a single deployment of a multiple corer, it represented 59% of all stained foraminifera in the samples. However, it had an extremely patchy small-scale distribution on a scale of centimetres; for example, 3, 285 and 1090 specimens were extracted from three subcores. A separate study has reported similar patterns among other minute indeterminate monothalamous foraminifera at the Kaplan East site (4032–4089 m water depth) located to the east, c. 1200 km from our study site. The reason for these very patchy distributions is not clear.