Niphargus Schiödte, 1849 (Crustacea, Amphipoda, Niphargidae) is a new component of the biotic community in the deep pebble beach habitats of the northern Black Sea region

A new species of the genus <i>Niphargus</i> Schiödte, 1849 (Crustacea: Amphipoda: Niphargidae) is described from the deep pebble beach interstitial habitats along the northern Black Sea coastline, revealing a new type of environment for this amphipod genus and providing new insight into the diversity of this unusual biotope. <i>Niphargus primoricus</i> <b>sp. nov.</b> belongs to "<i>stygius</i>-<i>longicaudatus</i>" species group corresponds to a distinct phylogenetic lineage, recently called "<i>tarkhankuticus</i>" ingroup (clade), which currently includes several species from the coastal areas of the Black Sea (Crimean Peninsula, southern Caucasus, and northern coast of the Republic of Türkiye [Turkey]). Molecular genetic analysis revealed that the speciation within this ingroup started in the Pliocene, approximately 5.76-3.6 Mya, and correlated with the Black Sea transgression. The divergence of the "<i>tarkhankuticus</i>" clade from the related European congeners probably occurred in the Late Miocene (~ 11-10 Mya), and is likely related to the separation of the Paratethys into different basins (Euxinian, Alpine and Pannonian). The new species has a wide distribution, currently inhabiting nearly 190 kilometers along the Black Sea coastline, from Gelendzhik to Khosta, and is characterized by a low level of genetic divergence between populations. The deep pebble interstitial coastal biotopes in the area are also inhabited by specific gammarid amphipods, for example, <i>Dursogammarus dromaderus</i> Marin & Palatov, 2022 and <i>Litorogammarus dursi</i> Marin, Palatov & Copilaş-Ciocianu, 2023 (Amphipoda: Gammaridae), whose biology has not been studied, and it is unknown how they spread along the coastline.