Five subspecies of the Dorogostaiskia parasitica complex (Dybowsky) (Crustacea: Amphipoda: Acanthogammaridae), epibionts of sponges in Lake Baikal

Based on morphological and molecular characters, the gammaroid amphipod Dorogostaiskia parasitica, living as an epibiont on sponges in Lake Baikal, Siberia, is here split into five parapatrically or allopatrically distributed subspecies: D. p. parasitica (Dybowsky, Horae Societatis Entomologicae Rossicae 10(Beiheft):1–218, 1874), D. p. kamaltynovi subsp. nov., D. p. hanajevi subsp. nov., D. p. ushkaniensis subsp. nov., and D. p. stenocephala subsp. nov. Diagnostic differences are described in the shape of dorsal keels, shape of head, length of antenna 1, number of segments of accessory flagellum, shape and armature of coxal plates, relative lengths of pereopod segments, and body coloration. Each subspecies is characterized by a distinct mitochondrial lineage, differing from others by 5–11% in the sequence of the COI gene, while they do not differ in nuclear 28S rRNA gene sequence. The question of taxonomic ranks for members of intralacustrine species complexes is considered and an argument is presented for a use of the subspecies rank for parapatrically distributed population segments that are distinguished by multiple independent geographically congruent character differences. This usage sorts out a pattern of systematic diversity lower than one based on documented reproductive isolation (e.g., sympatry) of full species but stronger than that based on single-gene genealogies alone.