Unlike P. globularis (Hanley in Thorpe, 1844), sicana has a rather small protoconch. « … the diameter of the first half whorl is 420 µm in globularis, versus 150 µm in sicana. Prior to the publication of this clearly distinctive characteristic, the distinction was probably mainly made by the more globose shape of globularis, which is not reliable at all, and sicana was frequently misidentified as globularis or “littorina”. Therefore sicana is so not a rare species, as sometimes mentioned… » – R. Kapeller: p.c. – Confer J.J. van Aarsten: “The Assimineidae of the Atlantic-Mediterranean seashores”, Basteria vol.72, september 2008, p.165-181.