Tornus unisulcatus: Shell minute, semitransparent, glossy, with a very depressed spire; last whorl marked by a single deep spiral groove just below the periphery, and a second, shallow one round the umbilicus.There are about two whorls, more or less circular in section, marked by prosocline growth lines (or low costae) as well as by the spiral grooves. The base of the shell is concave and lets the whole underside of the spire be seen. The outer lip has a deep notch at the end of the deep spiral groove. Up to 0.4mm high, 0.99 mm broad; last whorl occupies 90% of shell height, aperture 75%.
The body of the animal has not been described. T. unisulcatus is clearly rare and it is doubtful whether anything more than dead shells has been found. It has been recorded in dredgings from soft bottoms off Plymouth, the north coast of Ireland and the west coast of Scotland. Abroad it ranges from the Channel coast of France to the Mediterranean.