Two New Species of Stygobiotic Amphipod Niphargus (Amphipoda: Niphargidae) and their Phylogenetic Relationship with Other Congeners from Iran.

Two new amphipod species from Iran, Niphargus sahandensis sp. nov. and Niphargus chaldoranensis sp. nov., are described based on their morphological characteristics and molecular analyses. Bayesian inference analyses of COI and 28s rDNA sequence data provided evidence for the validity of the two species and their placement in the Niphargus genus. N. sahandensis sp. nov. primarily differs from similar species by having more than two hook-like retinacles on the inner surface of pleopods I-III, the presence of two spines at the base of uropod I and rectangular-shaped propodi in both gnathopods. N. chaldoranensis sp. nov. is distinguished by the trapezoidal-shaped propodi in gnathopods I to II, the equal sizes of pereopods V and VI, and the proportional size of periopod VII in relation to the total body (60%). Morphological descriptions with illustrations of the new species, as well as a DNA-based phylogeny generated from analyses of a multigene dataset, are provided to better understand species relationships.