First insights into the hyporheic crustaceans of the mountainous rivers of the Crimean Peninsula, with the description of two new species of the genus Niphargus Schiödte, 1849 (Malacostraca, Amphipoda, Niphargidae)

The riverine hyporheic amphipod fauna of the Crimean Peninsula are studied for the first time. Unique and obviously endemic representatives of the amphipod genera Niphargus Schiödte, 1849 (Niphargidae) and Litorogammarus Marin, Palatov & Copilaș-Ciocianu, 2023 (Gammaridae) were discovered in the middle and lower parts of the pre-mountainous Kacha, Alma, and Belbek rivers on the southwest coast, as well as the Ulu-Uzen, Demerdzhi, and Uchan-Su rivers in Alushta and Yalta, on the southern coast of Crimea.

The discovery of a specialized and unique hyporheic crustaceans in Crimean rivers, which were previously unknown and undocumented, is the most significant result of our research. Furthermore, two new species of the genus Niphargus, Niphargus almensis sp. nov. and Niphargus uchansi sp. nov., are described from the hyporheic habitats of the Alma and Uchan-Su rivers, representing the first true riverine hyporheic niphargids recorded from Crimea.

Both newly discovered species belong to the “ tarkhankuticus ” ingroup, whose species are distributed along the coastal areas of the Black Sea, including the Crimean Peninsula, the southern Caucasus, and the northern coast of the Republic of Türkiye (Turkey). The newly discovered species are closely related to N. tarkhankuticus Marin, Turbanov, Prokopov & Palatov, 2022, which is known from wells and subterranean watercourses on the Tarkhankut Upland.

Morphological differences between these species include the presence / absence of eyes and yellow spot on the head, differences in the armature of the epimeral plates and the telson, as well as differences in the proportions and armature of uropods I – III. Molecular genetic analysis has revealed that the divergence between the Crimean representatives of the “ tarkhankuticus ” ingroup occurred from the middle Pliocene to the early Pleistocene.

The “ youngest ” species (N. almensis sp. nov. and N. tarkhankuticus) probably diverged during the Pleistocene, approximately 2–1.5 Mya, due to the transgression of the Black Sea level and the increase in its water salinity, which led to the separation of the paleo-rivers in western Crimea and the loss of gene flow between the inhabitants of these rivers. This discovery emphasizes the importance of protecting riverbed ecosystems, as careless economic and human activities can lead to the irreversible loss of these ancient and unique animals, along with their genetic diversity.