An integrated taxonomic approach, using geometric morphometric methods, reveals the cryptic diversity of Parhyale darvishi Momtazi & Maghsoudlou, 2016 (Crustacea: Amphipoda: Hyalidae)

In recent years, morphological analyses and molecular methods have been increasingly used to describe new species of amphipods. Geometric morphometric methods are recognized as part of an integrated approach in taxonomy and are a cost-effective way to identify species, but its application is rare in Amphipoda. Taxonomically, the shape of gnathopods is important in the family Hyalidae, and species could be identified based on changes in these anatomical parts. Previously, Parhyale darvishi Momtazi & Maghsoudlou, 2016, had been described as a very scattered amphipod on a wide range of northern coasts of the Persian Gulf and the Gulf of Oman. In the present study, a geometric morphometric method based on semilandmarks was used to investigate intraspecific gnathopod's shape changes of P. darvishi population in the Persian Gulf and the Gulf of Oman. Therefore, 180 semilandmarks were selected on the propodus of first and second gnathopods of 100 male and 50 female. Data were analysed using tps package software. The results of UPGMA clustering and relative warp analysis reveal cryptic diversity in P. darvishi and show the main morphometric variations between sexes and populations. The present results, clearly separated Bushehr population samples from other studied populations of P. darvishi with concave posterio-distal margin in propodus of first and second male gnathopods and subquadrate propodus of first female gnathopod. Surveying detailed morphology of Bushehr samples confirmed geometric morphometric results. Therefore, Parhyale bushehri sp. nov. was described and distinguished from similar species by revealed propodus shape variations of geometric morphometric analyses and also having setae on the outer ramous of first and second uropods, peduncle of third uropod and some mouthparts characters. Consequently, the results show the integrated approach (numerical variations and statistical analyses along with morphological analyses) in amphipod taxonomy could reveal cryptic diversity.