Species Diversity, Diagnostic Characters, and Distribution of Tubenose Gobies of the Genus Proterorhinus (Gobiidae): A new Species from the Caspian Sea Basin

Molecular analysis of tubenose gobies of the genus Proterorhinus from different populations identified a distinct lineage that includes haplotypes of specimens from the Caspian Sea basin (Vostochniy Manych River and the Volga’s estuary). This lineage is most closely related to the Black Sea lineages of P. semilunaris (COI p-distance = 0.020 ± 0.005) and P. victori (COI p-distance = 0.021 ± 0.006). The comparative morphological study of genetically identified samples revealed a complex of morphological features that distinguish the tubenose gobies of the Vostochniy Manych River and the Volga’s estuary from the other known species of the genus Proterorhinus. Based on the results obtained, a new species of tubenose gobies, Proterorhinus scythicus sp. nov. is described. The mitochondrial phylogeny and geographical distribution of new species highlights the ancient connection between Black and Caspian Sea basins and more recent connection between the Manych and Volga rivers. Remarkably, that the Volga’s estuary is inhabited by three of four Caspian Proterorhinus species—P. nasalis, P. semipellucidus and P. scythicus sp. nov. It makes the Volga’s estuary a richest zone in number of Proterorhinus species within the whole genus range.