Shedding light on a cryptic cavernicole: a second species of Zenkevitchia Birstein (Crustacea: Amphipoda: Typhlogammaridae) discovered via molecular techniques

The Abkhazian region, in the southern foothills of the Caucasus Mountain Range, comprises a unique natural environment containing numerous subterranean habitats with relict and endemic lineages of obligate stygofauna. We aimed to assess the molecular phylogenetic relationships of Typhlogammaridae species from Balkan and Transcaucasian caves using the mitochondrial cytochrome c oxidase I (COI) in hopes of discovering previously undetected biodiversity. Our results showed molecular divergence within the genus Zenkevitchia Birstein, with two distinct groups located in the karstic regions Gudauta-Sukhumi and Gulripshi, respectively. These data indicated the existence of a new species (sequence divergences between groups of >14.3%) within the hitherto monotypic genus Zenkevitchia and allowed us to estimate the taxonomic relationship between Zenkevitchia admirabilis and Z. yakovi sp. n., based on examined morphological features and molecular phylogenetic relationships. We were unable to detect reliable morphological differences between Z. yakovi sp. n. and Z. admirabilis, highlighting the cryptic nature of the new species and the value of inclusion of molecular data in taxonomic studies.