A NEW GENUS OF THE FAMILY CRANGONYCTIDAE (CRUSTACEA, AMPHIPODA) FROM THE PALAEARCTIC, WITH DESCRIPTIONS OF TWO NEW SPECIES FROM THE FOOTHILLS OF THE ALTAI MOUNTAINS

An overview of stygobiotic crangonyctid amphipods from the Altai Republic, Russia is presented, with the erection of the new genus Palearcticarellus Palatov et Marin gen. n. for three previously described Stygobromus-like species, as well as two new species: Palearcticarellus smirnovi Palatov et Marin sp. n. from several localities in the drainage basins of the Biya and Katun rivers, and Palearcticarellus sapozhnikovi Palatov et Marin sp. n. from the springs around Lake Kureevo. Three previously known species are transferred to the new genus: Palearcticarellus pusillus (Martynov 1930) comb. n., P. mikhaili (Sidorov, Holsinger et Takhteev 2010) comb. n., both endemic to the Altai Republic, and P. kazakhstanica (Kulkina 1992) comb. n., from the northern Tian Shan. The new genus is morphologically (but not phylogenetically) very similar to the North American Stygobromus in also demonstrating some troglomorphic features, including depigmented integuments and reduced eyes, but it can be separated by 1) the presence of coxal gills 7; 2) less than 6 plumose setae (bristles) on the inner plate of maxilla 1; and 3) the presence of 2-5 hooks in the retinacle of the pleopods. At the same time, a molecular study reveals that the new genus represents a well-isolated and well-supported sister Glade to the Eurasian Synurella-related genera: the Caucasian Lyurella, the northeastern (Siberian) Synurella (= Eosynurella), and the northwestern (European) Synurella. However, it can clearly be separated from these genera by 1) free, non-fused uronites; 2) blunt posteroventral margins of epimeral plates 1-3; as well as 3) an unpigmented body; 4) mostly reduced eyes; 5) the presence of 2-5 hooks in the retinacle of the pleopods; and 6) the armature of gnathopods 1 and 2 (palmar margins of both gnathopods being armed with a double row of bifurcate robust setae, similar to those in most of North American species, but not Palaearctic ones). The new species can easily be distinguished from each other by 1) the number of hooks in the retinacle of the pleopods; 2) the shape of both gnathopods; 3) the shape and depth of a distal notch on the telson, and 4) the armature of uropod 3. The morphology and body size of smaller species of Palearcticarellus Palatov et Marin gen. n. (e.g., P. pusillus and P. mikhaili) are assumed to be more closely related to their neotenic origins rather than troglomorphy, the latter being more characteristic of larger species (e.g., P. smirnovi and P. sapozhnikovi).