Description:
<jats:p>With only 43 described stygobionts and only two isopod species the obligate groundwater fauna of Iran, a vast country with over 10% of limestone surface, is inadequately known. Here, we report the discovery of <jats:italic>Asellus ismailsezarii</jats:italic> sp. nov. from Zagros mountains, the first eyeless and depigmented asellid isopod from Iran. The new species is morphologically similar to <jats:italic>Asellus monticola</jats:italic> Birstein, 1932, but it is eyeless and fully depigmented, has a slightly curved pereopod IV and does not bear any setae on proximal margins of exopodite of pleopods IV and V. Species phylogenetic relationships using original and datamined mitochondrial DNA and nuclear rDNA, and estimation of molecular divergences with other <jats:italic>Asellus</jats:italic> species, suggest that <jats:italic>A. ismailsezarii</jats:italic> sp. nov. is sister to a larger clade that also contains the European <jats:italic>A. aquaticus</jats:italic> species complex. Surface populations of <jats:italic>Asellus</jats:italic> have colonized groundwater at multiple occasions and localities, both in Europe and Asia, giving rise to species and subspecies that have evolved troglomorphisms, such as depigmentation and loss of eyes. Of the 37 formally described species and subspecies of <jats:italic>Asellus</jats:italic>, 15 are from groundwater, including <jats:italic>A. ismailsezarii</jats:italic> sp. nov. We predict that many more obligate groundwater <jats:italic>Asellus</jats:italic> taxa are yet to be discovered in Asia.</jats:p>