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.
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.
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.
Key to the Siberian species of Gammarus (based on adults of both sexes)
Gammarus barnaulensis Schellenberg, 1937 is not included in the key as the original description does not provide appropriate morphological features.
1. Body and appendages ordinary, length more than 8.0 mm............................................................... 2
– Body compact, appendages shortened, length up to 8.0 mm (burrowing group *).......................... 9
2. Species with dense setation on pereopods III–IV and uropod III (pulex group).............................. 3
– Species with poorly setose pereopods III–IV and uropod III (balcanicus group)............................ 8
3. Pereopod dactyli long, slender.......................................................................................................... 4
– Pereopod dactyli short, stout............................................................................................................. 5
4. Urosomal segments moderately armed.................................................. G. lacustris G.O. Sars, 1863
– Urosomal segments richly armed............................................................... G. hanhi Safronov, 2006
5. Uropod III endopodite inner face with setae.................................................................................... 6
– Uropod III endopodite inner face naked........................................... G. teletzkensis Martynov, 1930
6. Epimeral plates II–III, ventral margins without setae, with spines.................................................. 7
– Epimeral plates II–III, ventral margins with a row of long setae........ G. angulatus Martynov, 1930
7. Antenna I slightly more than half of body length.............................. G. korbuensis Martynov, 1930
– Antenna I distinctly less than half of body length....... G. dabanus Tachteev & Mekhanikova, 2000
8. Antenna I, main flagellum up to 28 articles....................................... G. angustatus Martynov, 1930
– Antenna I, main flagellum with 34–35 articles.................................. G. pellucidus Gurjanova, 1930
9. Telson, lobes apically with 4 spines................................................... G. koshovi (Bazikalova, 1946)
– Telson, lobes apically with 1 or 2 spines................................... Gammarus sp. in Gurjanova (1930)
* Conventionally proposed group to which we additionally assign Gammarus sp. in Gurjanova (1930).
Key to the Siberian species of Gammarus (based on adults of both sexes)
Gammarus barnaulensis Schellenberg, 1937 is not included in the key as the original description does not provide appropriate morphological features.
1. Body and appendages ordinary, length more than 8.0 mm............................................................... 2
– Body compact, appendages shortened, length up to 8.0 mm (burrowing group *).......................... 9
2. Species with dense setation on pereopods III–IV and uropod III (pulex group).............................. 3
– Species with poorly setose pereopods III–IV and uropod III (balcanicus group)............................ 8
3. Pereopod dactyli long, slender.......................................................................................................... 4
– Pereopod dactyli short, stout............................................................................................................. 5
4. Urosomal segments moderately armed.................................................. G. lacustris G.O. Sars, 1863
– Urosomal segments richly armed............................................................... G. hanhi Safronov, 2006
5. Uropod III endopodite inner face with setae.................................................................................... 6
– Uropod III endopodite inner face naked........................................... G. teletzkensis Martynov, 1930
6. Epimeral plates II–III, ventral margins without setae, with spines.................................................. 7
– Epimeral plates II–III, ventral margins with a row of long setae........ G. angulatus Martynov, 1930
7. Antenna I slightly more than half of body length.............................. G. korbuensis Martynov, 1930
– Antenna I distinctly less than half of body length....... G. dabanus Tachteev & Mekhanikova, 2000
8. Antenna I, main flagellum up to 28 articles....................................... G. angustatus Martynov, 1930
– Antenna I, main flagellum with 34–35 articles.................................. G. pellucidus Gurjanova, 1930
9. Telson, lobes apically with 4 spines................................................... G. koshovi (Bazikalova, 1946)
– Telson, lobes apically with 1 or 2 spines................................... Gammarus sp. in Gurjanova (1930)
* Conventionally proposed group to which we additionally assign Gammarus sp. in Gurjanova (1930).