Integrative taxonomy of the groundwater amphipod <i>Niphargus bihorensis</i> Schellenberg, 1940 reveals a species-rich clade

<p dir="ltr">The genus <i>Niphargus</i> is the most diverse subterranean amphipod genus in the western Palearctic region but, owing to the presence of cryptic species and homoplasy, its taxonomy and biogeographic scenarios are complex, making molecular methods essential to understand its evolution. We conducted a study combining DNA-based taxonomy with traditional morphotaxonomy to investigate <i>Niphargus bihorensis</i> Schellenberg, 1940, known from the Western Alps and Carpathians. We redescribed the type material of <i>N. bihorensis</i> from Bihor County, Romania, and revealed the presence of a cryptic species, <i>N. absconditus</i> n. sp., in the same karstic area (Pădurea Craiului Mountains). Additionally, the Alpine populations previously attributed to <i>N. bihorensis</i> turned out to belong to a new, not so closely related species, <i>N. tizianoi</i> n. sp. Phylogenetic analyses based on a concatenated dataset of one mitochondrial and two nuclear markers suggest that the <i>N. bihorensis</i> species complex belongs to a strongly supported clade, together with several species distributed from Switzerland to Iran.</p>