Morphology and zoogeography of the burrower-like gammarid Gammarus koshovi (Bazikalova, 1946) (Crustacea, Amphipoda, Gammaridae) - An overlooked and poorly known species in the Siberian fauna Author Sidorov, Dmitry 55C1264F-67C0-4C3F-8E6B-ECE1E821457B Federal Scientific Center of the East Asia Terrestrial Biodiversity, Russian Academy of Sciences, Vladivostok 690022, RF. biospeorossica@gmail.com Author Yalysheva, Elena 88AB67D2-1F97-4A2C-8121-362132FCF07C Municipal State Educational Institution “ Osinovskaya shkola ”, Osinovyy Mys 663457, RF. ona_vita@rambler.ru Author Sharyi-Ool, Mariana 9DE31FF0-0660-4980-B819-63305D609CAC Federal Scientific Center of the East Asia Terrestrial Biodiversity, Russian Academy of Sciences, Vladivostok 690022, RF. sharyiool@biosoil.ru text European Journal of Taxonomy 2021 2021-10-13 774 178 199 http://dx.doi.org/10.5852/ejt.2021.774.1541 journal article 4025 10.5852/ejt.2021.774.1541 bc28e8d7-56ea-4318-86bc-834a0fdb87c8 2118-9773 5567144 F8F78338-FF22-4E48-91FA-6EB1A9EC76EB Gammarus lacustris G.O. Sars, 1863 Gammarus lacustris G.O. Sars, 1863: 207 (original description). Gammarus pulex sibiricus – Kiseleva 1920: 15 (lakes of Ob’ basin). Gammarus pulex – Sars 1901: 133 (NE Mongolia ); 1903: 233–261 (Siberia, Kazakhstan , Mongolia , Tibet). — Pirozhnikov 1929: 70 (Yenisey, upstream of Krasnoyarsk). — Lepneva 1930: 135 (around Biysk); 1933: 151 (Altay lakes). — Karaman 1991: 38 (see for full synonymy). Material examined (new records) RUSSIA – Tuva Republic • 3 ♀♀ (oostegites developed, some brooding the eggs), 15 ♂♂ (BL = up to 14.0 mm); small freshwater lake , southward of Shara-Nur Lake, near shepherd’s camp ; 50°13′29.4″ N , 94°32′32.1″ E ; 2–5 m depth ; 12 Aug. 2011 ; E.N. Yalysheva leg.; yellowish silt, sapropelic mud with smell of hydrogen sulfide, plant residues ( Phragmites australis ) ; DAS 16-014 • 1 ♀ (BL = 17.0 mm); ‘ Dashtyg’ taiga lake, upper reaches of Yenisey (source of Dashtyg-Aryg Stream) , Todzha ; 53°25′12.2″ N , 96°51′52.7″ E ; 0.5 m depth ; 4 Aug. 2010 ; E.N. Yalysheva leg.; middle of lake, boulders, rubble, fouling, depressions between stones slightly silted ; DAS 16-015 . Remarks Considering the outstanding morphogenetic polymorphism ( Sket et al. 2019 ) and the very wide distribution of Holarctic/Sino-Indian G. lacustris in the water bodies of Siberia (Tuva) and Mongolia ( Fig. 1 ), it is highly probable that juveniles of this species can be misidentified as small species, such as G. koshovi . However, G. lacustris was absent in our samples from Tore-Khol, which we associated, first of all, with partial acidification of waters in the Russian part owing to the increased anthropogenic pressure because of intensive grazing, fishing, and other economic activities. It was previously reported that G. lacustris critically avoids water environments with pH <5 ( Moiseenko & Yakovlev 1990 ). However, the exact reasons for this observation remain to be solved. Distribution and ecology Mostly inhabits the pluvial lakes of the region ( Fig. 1 ), though it is also observed in lakes of the Baikal Rift Zone (previous indications in Baikal are accidental, in Stom & Timofeev 1999 ; but see Vereshchagina et al. 2021 ). Kamaltynov (2009) reported the following data: common at depths of 0–7 m , on pebbles with sand and detritus, silted sand, flooded woods, remains of vegetation, and abundant in aquatic plant thickets. Inhabits thermal springs with temperatures up to 23°С and mineralization up to 340.5 mg /L. Inhabits small lakes and rivers of the Baikal basin, in the Baikal and Transbaikal regions (including the Irkutsk and Bratsk reservoirs), adjoining water bodies of the Yenisey and Ob’, lakes in the Vilyui region of Yakutiya, lakes in the interfluve of the Lena and Aldan rivers, Bauntovskye lakes, lakes in Mongolia (Khubsugul and Selenga basin, lakes and streams of Darhat Valley, Uvs Nuur Basin, Great Lakes Depression, and Valley of Lakes) ( Dybowsky 1901 ; Sars 1901 ; Greze & Greze 1958 ; Bezmaternykh 2008 ; Kamaltynov 2009 ; Østbye et al. 2018 ; Tolomeev et al. 2018 ). Paul (2012) indicated that G. lacustris inhabits the Mongolian part of Tore-Khol Lake.