The connectivity of groundwater aquifers is lower compared to surface waters. Consequently, groundwater species are expected to have smaller distributional ranges than their surface relatives. Molecular taxonomy, however, unveiled that many species comprise complexes of morphologically cryptic species, with geographically restricted distributional ranges in subterranean as well as in surface waters. Hence, the range sizes of surface and groundwater species might be more similar in size than hitherto thought. We tested this hypothesis by comparing the range size of surface amphipods of the genus Gammarus and subterranean amphipods of the genus Niphargus in Iran. We re-analyzed the taxonomic structure of both genera using two unilocus species delimitation methods applied to a fragment of the COI mitochondrial marker, to identify molecular operational taxonomic units (MOTUs), and assessed the maximum linear extent (MLE) of the ranges of MOTUs from both genera. Genus Gammarus comprised 44–58 MOTUs while genus Niphargus comprised 20–22 MOTUs. The MLEs of the two genera were not significantly different, regardless the delimitation method applied. The results remained unchanged also after exclusion of single site MOTUs. We tentatively conclude that in this case there is no evidence to consider that groundwater species are geographically more restricted than surface species.

This study was conducted to describe and illustrate two new species of groundwater amphipods from the northern parts of the Zagros Mountains in West Azerbaijan Province, Iran. Mitochondrial (COI) and nuclear (28S rDNA) fragments as well as several morphological traits were used to characterize Niphargus urmiensis sp. nov. and Niphargus fiseri sp. nov. The phylogenetic analyses showed that the nucleotide differences between the recently described species and their close allies are attributed to their distinctiveness. The molecular analysis also introduced that the new species are placed within the clade comprising Iranian species as a sister taxon. The genetic distances between N. urmiensis sp. nov. and N. fiseri sp. nov. are 7.6% and 1.6%, respectively based on the COI and 28S rDNA gene fragments.