Concentric thin sculpture, moderately strong in the first part of the shell (« ring-like display » – de Folin) and weakening in the second part; septum hemispherical slightly to strongly flattened, without any appendage; peristome thick, sometimes forming a large apertural ring. Differs from auriculatum by the lack of the ear-like projection on the dextral side of the septum, which is typical in the latter. Operculum flat.

In the “smooth” Caecidae with hemispherical septa, subannulatum is often slender, and its septum is devoid of appendages. Possible specimen, subadult (aperture with a weak ring) trawled in the circalittoral of Almería, Andalucia. 2mm.