| Summary: | This study deals with the biodiversity and distribution of cavernicolous Amphipoda in caves of the Arabika massif (Western Caucasus). The Sarma, Trojka and Orlinoe Gnezdo caves were explored during speleological expeditions over the years 2011–12. Two new species of Amphipoda were found: a sub-surface dweller <em>Zenkevitchia sandroruffoi</em> sp. nov. is reported from the Sarma, Trojka and Orlinoe Gnezdo caves at depths from -30 m to -350 m; the second one, a deep dweller <em>Adaugammarus pilosus</em> gen. et sp. nov. is reported from the Sarma Cave at depths of -1270 to -1700 m. <em>Adaugammarus</em> gen. nov. shares similarities with <em>Typhlogammarus</em> Schäferna, 1907 and <em>Zenkevitchia</em> Birstein, 1940. The species <em>Anopogammarus birsteini</em> Derzhavin, 1945 is also re-described herein based on new samples that suggest close affinity of this species with the family Gammaridae. The original taxonomic combination is resurrected for <em>Zenkevitchia revazi</em> Birstein & Ljovuschkin, 1970, comb. resurr. (from <em>Anopogammarus</em> Derzhavin, 1945). To accommodate morphologically different species in the genus <em>Zenkevitchia</em>, two new groups are proposed. These are the <em>admirabilis</em>-group (<em>Z. admirabilis</em> Birstein, 1940 and <em>Z. yakovi</em> Sidorov, 2015) and the <em>sandroruffoi</em>-group (<em>Z. sandroruffoi</em> sp. nov. and <em>Z. revazi</em>). An updated molecular (mt-cox1) phylogeny, an identification key to the genera and a distribution map for the typhlogammarid amphipod species of Transcaucasia are provided.
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