Reviewing the Atlantic-Mediterranean Bursa scrobilator (Linné, 1758) complex
The Atlantic-Mediterranean Bursa scrobilator s. l. (Linné, 1758) “complex”, represented by three morphologically distinct forms, the Recent B. scrobilator and Ranella coriacea Reeve, 1844, and the Fossil Bursa nodosa (Borson, 1823), is here reviewed integrating morphological, molecular and paleontological data. On the base of molecular analysis using the mitochondrial COI marker, the two Extant “scrobilator” and “coriacea” forms have been proposed as two subspecies: Bursa scrobilator scrobilator n. subsp., with Atlantic-Mediterranean distribution, and Bursa scrobilator coriacea n. subsp., with western African geographical dispersal. The evolutionary relationship with B. nodosa, most probably the ancestor of these Recent subspecies, is also discussed. Furthermore, it is reported the surprising discovery of three Recent specimens of B. scrobilator s.l. with three tuberculate spiral cords, the typical shell sculpture feature of the Fossil form B. nodosa, collected from three different geographical spots of the north-eastern Atlantic Ocean (Azores Islands, Madeira Island and Morocco). This is a rare case of evolutionary throwback of an ancestral lost trait, as far as we know never described in molluscan shell.