A genetic fingerprint of Amphipoda from Icelandic waters – the baseline for further biodiversity and biogeography studies

Amphipods constitute an important part of Icelandic deep-sea zoobenthos in terms of abundance. However, the knowledge of their diversity, especially at the molecular level is scarce. The present work aims to use molecular methods to investigate genetic variation of Amphipoda collected during two IceAGE expeditions. The mitochondrial cytochrome oxidase subunit 1 (COI) of 167 individuals originally assigned to 76 morphospecies was analysed. The study resulted in 81 Barcode Identity Numbers (BINs) (of which >90% were published for the first time), while Automatic Barcode Gap Discovery revealed the existence of 78 to 83 Molecular Operational Taxonomic Units (MOTUs). Six nominal species (Rhachotropis helleri, Arrhis phyllonyx, Monoculodes tenuirostratus, Paroediceros propinquus, Metopa boeckii, Astyra abyssi) appeared to have a molecular variation higher than the 0.03 threshold of both p-distance and K2P usually used for amphipod species delineation. On the other hand, two taxa of Oedicerotidae regarded as separate ones clustered together with divergences in the order of intraspecific variation. The incongruence between the BINs associated with presently identified species and the publicly available data of the same taxa was observed in case of Paramphithoe hystrix and Amphilochus manudens. All those findings underline the necessity of supplementing the molecular studies by thorough analyses of species morphology