Centrophorus spp. and the mystery of the deep-sea: how many species in the Mediterranean?

The current shift of fisheries efforts towards deep seas is raising concern about the vulnerability of deep-water sharks which are often poorly studied and characterized by problematic taxonomy. In the Mediterranean Sea the taxonomy of genus Centrophorus (Müller & Henle, 1837) has not been clearly unravelled yet. Since a proper identification of species is fundamental for their correct assessment and management, in this study we try to clarify the taxonomy of this genus in the Mediterranean basin using integrated taxonomy technique to identify the species of the genus occurring in the basin. 281 samples were analysed obtaining sequences from three mitochondrial markers (COI, ND2 and 16S). All sequences were compared with those obtained from public databases (GenBank and BOLD) to delineate discrete taxonomic units and assess inter and intra-specific genetic diversity and variability. Molecular techniques were integrated with traditional and landmark-based morphometry to assess morphological variability and provide useful diagnostic characters for the discrimination of species. Molecular analyses show a low sequence variability for all the three markers analysed. A principal haplotype occurs through all the locations despite several private and shared haplotypes, excluding a clear geographical segregation. In phylogenetic trees the sequences cluster in a highly supported branch with other sequences deposited as C. granulosus, C. uyato, and C. zeehaani. From morphometric analyses, both traditional and landmarks-based, specimens cluster in a unique group representing a single morphotype. Both molecular and morphological results confirm the presence of a unique species of Centrophorus in the Mediterranean. Genetically, all specimens result in one clade ascribable to C. cf uyato. This finding is confirmed by morphological analyses that grouped all the specimens in a unique group representing a single morphotype.