Taxonomic, ecological and morphological diversity of Ponto-Caspian gammaroidean amphipods: a review Author CopilaČ™-Ciocianu, Denis Author Sidorov, Dmitry text Organisms Diversity & Evolution 2022 New York, N. Y. 2022-01-07 22 2 285 315 http://dx.doi.org/10.1007/s13127-021-00536-6 journal article 10.1007/s13127-021-00536-6 1618-1077 13366423 Key to species of Onisimus 1. Antenna 1 peduncle article 1 longer than head, accessory flagellum 6-segmented, postero-ventral corner of 3 rd epimere almost straight ................................. O. platyceras 2. Antenna 1 peduncle article 1 shorter than head, accessory flagellum 4-segmented, postero-ventral corner of 3 rd epimere sharp ..................................................... O. caspius