Promachoteuthis sloani is a species of squid from the northern Atlantic Ocean. It is known from only three specimens and very little is understood of its biology. P. sloani is characterised by several morphological features: nuchal fusion is absent between the head and mantle, the arms generally bear 3–4 series of suckers, and papillae are present on the tentacles.
The holotype is an immature female of 58 mm mantle length (ML) in near-perfect condition. It was caught by R/V G.O. SARS in 2004 at 53°05′N 36°46′W / 53.083°N 36.767°W / 53.083; -36.767. The paratype, also an immature female, is larger at 102 mm ML. It was caught by R/V Walther Herwig in 1973 at 46°00′N 15°49′W / 46.000°N 15.817°W / 46.000; -15.817. Both were trawled in nets that fished to depths greater than 2,650 m.
