Revision of the genus complex Gibbula: an integrative approach to delineating the Eastern Mediterranean genera Gibbula Risso, 1826, Steromphala Gray, 1847, and Phorcus Risso, 1826 using DNA-barcoding and geometric morphometrics (Vetigastropoda, Trochoidea)

The trochoid genus, Gibbula, is abundant and diverse in the Mediterranean Sea but problematic to identify and delineate. This is due to highly variable shell morphology, vague original descriptions, and missing or unspecific type material. In recent studies, COI barcoding yielded satisfactory results for species delineation. In the present study, a combination of geometric shell morphometric methods and COI barcoding was used to assess the most abundant species of the Eastern Mediterranean. All relevant identification characters were captured via standardised images of the shells in both lateral and ventral views. Agreeing with previous studies, Gibbula was recovered as paraphyletic in the molecular analysis and thus is restricted to the clade encompassing the type species Gibbula magus (Linnaeus, 1758). The geometric morphometric analyses and the barcoding approach clearly distinguish the remaining species into two groups: the genus Steromphala Gray, 1847 and the genus Phorcus Risso, 1826. Type material was used for the geometric morphometric analyses whenever possible. Based on re-examination of the original type descriptions, lectotypes were designated. The joint application of DNA-barcoding and geometric morphometrics not only effectively delineated the sister genera Steromphala and Phorcus but also delineated all analysed species in the Gibbula-Steromphala-Phorcus genus complex. The additional use of geometric morphometrics enables researchers to compare barcoded material with fossil specimens or dry collections in an objective way.