Bouchet & Waren (1986) recognized three similar species in deep water of the Atlanto-Mediterranean area: Aclis wal¬ler! Jeffreys, 1867 described from off Shetland (140 m), Aclis attenuans Jeffreys, 1883 described from off Crete (70-120 fathoms = 128-219 m) and Aclis sarsi Dautzenberg & H. Fischer, 1912 described from off Norway (440 m). The Mediterranean A attenuans differs from the Atlantic A walleri in being smooth, without the axial riblets of A. walleri, in having a smaller (2-3 mm vs 4-5 mm high) and broader shell. Aclis sarsi differs from both in having only one protoconch whorl instead of more than two in the other two species
Bouchet & Waren further reported a single shell from the Canaries as probably representing a new species, but refrained from describing it as the specimen was not in good enough condition. It was stated as having "the same kind of apical whorls as A. sarsi but the shape is similar to A. attenuans". The SEAMOUNT 2 material contains additional shells of the same Canarian species but this (including the specimen figured by Bouchet & Waren) has a little more than two protoconch whorls and is therefore similar to Aclis attenuans and does not have the paucispiral protoconch of Aclis sarsi. Admittedly, the Canarian specimens are slightly larger (3.7 mm instead of usually less than 3 mm for Mediterranean specimens) and the protoconch is also slightly larger in proportion, but are here taken as a range extension of Aclis attenuans and new record to Canary Islands waters.