The article presents the first insight into the diversity and distribution of the relatively small Niphargus "tauricus" ingroup of the "stygius" species group (Crustacea: Amphipoda: Niphargidae) living in the coastal caves/springs of Dobrogea in Romania, the Crimean Peninsula and the south-western foothills of the Caucasus Mountains. Six species, namely Niphargus utrishensis Marin et Palatov sp.n., N. novorossicus Marin et Palatov sp.n., N. alisae Marin, Krylenko et Palatov sp.n., N. ashamba Marin, Krylenko et Palatov sp.n., N. malakhovi Marin et Palatov sp.n. and N. dederkoyi Marin et Palatov sp.n. are described from the Black Sea coastal foothills of the south-western part of the Caucasus Mountains. Crimean N. tauricus Birštein, 1964 is re-described based on topotypic material.Morphological diagnoses and descriptions for all species of the "tauricus" ingroup as well as the key for their identification are presented. Aside from the morphological comparisons, DNA barcode (COI mtDNA gene marker) is employed for their identification. It is assumed that these species are Euxinian relicts of the Eastern Paratethys and were settled in their current habitats at the end of the Miocene at least 5 Mya. According to the data obtained, the related species of the ingroup are confined to the same mountain ridge, which suggests that the settlement occurred by several "waves". At the same time, we suppose that the modern species distribution is shaped rather by the uplift of Caucasian coastal mountain ridges and karst fragmentation occurred during the the last 2-3 Mya (since Late Pliocene -Early Pleistocene) than the fluctuation of the sea level. Because these animals are not able to disperse actively, we believe that these unique ancient genetic lineages (species) and their biotopes (underground water habitats) are in need of especial protection.

A new species of the genus Niphargus is described from the Gelendzhik–Tuapse area of the Russian southwestern Caucasus. It belongs to the “puteanus” species group and phylogenetically related to Caucasian N. ciscaucasicus and N. talikadzei, separating from other Caucasian species of the genus by the presence of 2 hooks in retinacules on pleopods, different rami of uropod I both in males and females, and relatively large inner ramus of uropod III. Molecular study has revealed that Niphargus bzhidik sp. nov. and related N. ciscaucasicus are relicts of the Late Miocene speciation, associated with the Messinian crisis (5.96–5.33Mya) separated widespread Paratethys species, which survived in long-term genetic isolation for a long time. The new species is blind and epigean, and probably unable to spread over long distances, but this way of life probably allowed surviving in refugee during the Quaternary period with a colder climate. Analysis of stable isotopes (δ13C/δ15N) revealed that the new species is carnivorous, in contrast to another studied stygobiotic herbivorous Niphargus species (e.g., Niphargus cf. tauricus). The key to the Caucasian and Eastern Asian species of the genus Niphargus, known from the territory of the former USSR, is presented in the article. [http://zoobank.org/urn:lsid:zoobank.org:act:E0019189-2432-4B64-B153-94C43FDD93E3]

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