The paper describes Hyperammina micaceus sp. nov., a distinctive new deep-water agglutinated foraminiferan from the Porcupine Abyssal Plain (PAP), northeast Atlantic (4850 m water depth). The new species is tiny (<1 mm long and 20–30 μm wide), with an oval proloculus which merges smoothly into the long, tubular part of the test. The test wall is composed of a single layer of plate-like mineral grains. Hyperammina micaceus occurs in most of the PAP cores collected between 1989 and 2002 and represents up to 4% (in one sample 18%) of the live foraminiferal assemblage in the 0–1 cm layer (>63 μm size fraction). It tends to be more common in samples collected during the late spring and summer (May to September), prior to the spring bloom, than in samples obtained during the autumn (October) and the earlier part of the year (March, April), before the spring bloom. Live specimens are concentrated in the 0–0.5 cm sediment layer but are uncommon in the overlying phytodetrital deposits and virtually absent below 1 cm depth.