Niphargus dancaui sp. nov., previously referred to as Niphargus cf. stygius, was sampled from various groundwater sites in and near the town of Mangalia (SE Romania) and described with Movile Cave (a sulfidic, chemoautotrophically based ecosystem) as type locality. A short comparison with Niphargus stygius specimens from Slovenia was made, together with a morphological analysis of interpopulational variability. Males of N. dancaui sp. nov. were relatively large (17 mm), with long antennae, pereiopods and uropod III. Females were slightly smaller, with shorter antennae, pereiopods and uropod III. Interpopulational variability was noticed in the chaetotaxy of the telson lobes and uropod III. N. dancaui sp. nov. is morphologically very close to N. lessiniensis and N. tridentinus, two species present in northern Italy, but distinct genetically from them based on 28S rRNA sequences. Instead, the closest relative of N. dancaui sp. nov. sequenced so far for this marker is N. montanarius, which inhabits a sulfidic cave system in central Italy. The work presented here contributes to our knowledge of groundwater crustacean biodiversity in general and of the systematics of the genus Niphargus in particular.
28S phylogeny, hypogenic cave, interpopulational diversity, Movile Cave.