Diversity, taxonomy and phylogenetic relationships of the Niphargus borutzkyi ingroup (Crustacea: Amphipoda: Niphargidae) in Western Georgia, SW Caucasus

Two new Caucasian species of the genus Niphargus Schiodte, 1849 (Crustacea: Amphipoda: Niphargidae), N. rachalechkhumensis sp. nov. andN. tvishiensis sp. nov., are described from the stygobiotic habitats of the Racha-Lechkhumi and Kvemo Svaneti karst systems in Western Georgia. Both newly described species belong to the southwestern Caucasian Niphargus borutzkyi ingroup related to the European carphaticus species complex and can be clearly separated from the congeners by morphological features, mostly in uropod III and epimeral plates, and genetically. Identification key for all known species to the Niphargus borutzkyi ingroup is provided, as well as their phylogenetic relationships, the estimated time of the origin and the current distribution of the ingroup in the Colchis lowland of the southwestern Caucasus are also discussed.

Automated summary

Two new Caucasian species of the genus Niphargus belonging to the southwestern Caucasian Niphargus borutzkyi ingroup were discovered in underground habitats in Western Georgia. They are morphologically and genetically distinct from other known species, particularly in uropod III and epimeral plates. The study provides an identification key for the Niphargus borutzkyi ingroup and discusses their phylogenetic relationships, estimated time of origin, and current distribution in the Colchis lowland of the southwestern Caucasus.