The hidden diversity of the genus Lyurella Derzhavin, 1939 (Crustacea: Amphipoda: Crangonyctidae): four new species from the subterranean habitats of the northwestern Caucasus

Four new species of the Palaearctic crangonyctid amphipod genus Lyurella Derzhavin, 1939 (Crustacea: Amphipoda: Crangonyctidae), L. mikhailovi sp. n., L. fanagorica sp. n., L. fontinalis sp. n. and L. asheensis sp. n., are described based on an integrative approach from the subterranean habitats of the southwestern foothills of the Greater Caucasian Ridge (the north-eastern Black Sea coast). Despite the relative proximity of the habitats, the interspecific genetic divergence (by COI mtDNA gene marker) between the newly outlined Caucasian species of the genus varied from 11 to 21%, demonstrating a long-term isolation and lack of gene flow for at least 37Mya, starting from the Pliocene. The lowest genetic divergence between L. shepsiensis Sidorov, 2015 and L. asheensis sp. n., estimated as 4%, is also considered species-specific due to the presence of distinct morphological differences. We discuss the phylogeny, morphology, and distribution and provide a key for all known species of Lyurella. DNA barcoding data for all species, including the type species of the genus, Lyurella hyrcana Derzhavin, 1939, are presented for the first time.