Marin I.N., Palatov D.M. 2021. Volgonyx gen.n. and Pontonyx gen.n., two new genera of the family Crangonyctidae (Crustacea: Amphipoda) from the southeastern Europe // Arthropoda Selecta. Vol.30. No.1: 43–61 [in English].
ABSTRACT. Two new Palaearctic genera are proposed within the family Crangonyctidae (Crustacea: Amphipoda), including species previously assigned to the Western Palearctic “Synurella dershavini”-group: Volgonyx gen.n. for Synurella dershavini Behning, 1928, and Pontonyx gen.n. for Synurella odessana Sidorov et Kovtun, 2015 and Synurella osellai Ruffo, 1972. New genera can be clearly distinguished from all Eurasian crangonyctid genera by a combination of morphological features, such as 1) a large elongated non-pigmented (troglomorphic) body; 2) males noticeably larger than females, with distinct sexual dimorphism in body size and morphology of uropod I; 3) absence of the calceoli on antenna II; and 4) more than 4 coupling hooks in retinacules of pleopods. Each of these genera is also characterized by several specific morphological features: greatly unequal rami of uropod I in males and a different number of coupling hooks in retinacules of pleopods (3–4 in females and 6–8 in males) in Volgonyx gen.n.; and the presence of characteristic terminal “squamous knob” on endopodite of uropod III, 5–6 coupling hooks in retinacules of pleopods and telson with a deep U-shaped notch reaching almost 1/3 of its length in Pontonyx gen.n. A combination of morphological features and molecular genetic analysis based on COI mtDNA gene marker easily separates these new genera from the genus Synurella s.str., with the type species Synurella ambulans (F. Mьller, 1846), as well as any of crangonyctid genera in both the Holarctic and Palaearctic. According to our phylogenetic reconstructions, Volgonyx gen.n. and Pontonyx gen.n. belong to the Stygobromus-clade, but they occupy well-isolated distant positions, which indicates the relic origin of these lineages, obviously correlated in time with the breakup of Laurasia in the Cretaceous (about 135–60 Mya). Volgonyx dershavini (Behning, 1928) comb.n. is also re-described based on topotypic material and the neotype is selected, since the type material is now lost.
KEY WORDS: Crustacea, Amphipoda, diversity, relic, epigean, stygobiotic, Russia, Palaearctic.