A New Species of Tadpole Gobies of the Genus Benthophiloides (Gobiidae) from the Caspian Sea

The genus Benthophiloides has been regarded as a rare Ponto-Caspian goby lineage comprising B. brauneri from the Black Sea–Azov basin and B. turcomanus from the Caspian Sea. We describe Benthophiloides caspius sp. nov., a new tadpole goby from the middle Caspian Sea, based on a newly collected specimen from the coast of Cape Tokmak in Kazakhstan and a re-examined historical specimen from Apsheron Strait in Azerbaijan. Comparative morphological analysis revealed stable differences between Caspian and Black Sea material, most notably in the higher numbers of branched rays in the second dorsal fin (13½–15½ in B. caspius sp. nov. vs. 11½–12½ in B. brauneri) and anal fin (11½–12½ in B. caspius sp. nov. vs. 8½–10½ in B. brauneri), as well as in body proportions, and coloration. These data support the distinct species status of the Caspian population previously referred to B. brauneri. We also report the first genetic data (COI mtDNA) for the Benthophiloides. Phylogenetic analysis suggests sister position of B. caspius sp. nov. to the Benthophilus, but the genetic distance of B. caspius sp. nov. to both Benthophilus and Caspiosoma is almost equal. The new species appears to be a rare endemic of the middle Caspian Sea. Further studies require to uncover the diversity and phylogeny of Ponto-Caspian tribe Benthophilini.