(Figs. 1–5)
Type material. Holotype 3: Russia: Republic of Altai, Kosh-Agach district, Plateau Ukok, Lake Muzdy- Bulak env., 2400 m, 49.26 ºN, 87.65 ºE, 8.VII. 2008, Coll. A. Barkalov, sweeping on sedge along lake bank [SZM].
Diagnosis. This species is related to D. annulitarsis Ringdahl and D. planitarsis Fallén (see key above), differing mainly in antennal morphology and leg color. Antennal scape enlarged, flattened dorsoventrally; stylus nearly apical; femora almost entirely yellow; mid tarsomeres 1–4 yellow with dark apices. Based on the presence of yellow femora, the new species is included in group IV (Stackelberg 1930 a; Parent 1938) and keys to D. amginensis Stackelberg, 1928, that has simple mid tarsus and hind femur without ventral setulae, different leg setation and antennal morphology.
Description. Male: Body length: 5.5 mm, wing length: 6.5 mm, wing width: 2.4 mm, antenna length: 1.4 mm, hypopygium length: 2.2 mm.
Head: Face grey, not reaching lower eye margin, in middle wider than postpedicel height (2.0/ 1.7). Proboscis dark-brown and palpus light-brown, with black hairs. Frons shining bronze, metallic green laterally, weakly grey pollinose along eyes and antennal sockets. Antenna (Figs. 1–2) black, with somewhat elongate segments; scape enlarged, flattened dorsoventrally, with strong dorso-lateral setae; postpedicel lanceolate, with pointed apex; stylus strictly subapical, densely shortly haired, simple. Ratio of postpedicel length to its width to stylus length, 34 / 18 / 45. Lower postocular setae black. Thorax: metallic green; mesonotum grey pollinose, with two narrow brown longitudinal stripes; propleuron with 1 strong black seta below, small fine hairs in middle and short black seta above. Legs: mainly yellow; pulvilli snow-white. Coxae green, densely grey pollinose; fore coxa with black hairs. Fore femur brownish dorsally in basal half. Mid and hind femora with 1 strong anterior preapical seta; hind femur with long yellow ventral hairs, in middle as long as femora diameter. Fore tibia with 3 long and 1 short anterodorsal, 3 posterodorsal and 4 posteroventral setae, without apicoventral seta. Fore tarsus simple, slightly compressed laterally, with segments 1–2 yellow, dark at apex, and segments 3–5 black. Mid tibia with 5 antero- and 2 posterodorsal, 2 anteroventral and 1 ventral setae. Mid basitarsus without strong setae; mid tarsomeres with black ventral setulae; segments 1-4 yellow, with dark apices; segment 4 hardly thickened at apex; segment 5 black, flattened dorsoventrally, with anterior and posterior rows of strong setae. Hind tibia slightly thickened at apex, with 6–7 long strong anterodorsal, 6 posterodorsal, a row of short black ventral setae; tibial organ in form of elongate swelling, brown basally, with a row of short white hairs. Hind tarsus black, simple. Hind basitarsus with 3 strong dorsal, 2 short anterior setae. Tarsomere length ratio: fore tarsus (from first to fifth): 52 / 20 / 15 / 10 / 15, mid tarsus: 82 / 40 / 32 / 24 / 22, hind tarsus: 84 / 62 / 44 / 31 / 20. Wing: mostly hyaline, brownish anteriorly and along M 1 + 2. Costal thickening at R 1 weakly developed; Ratio of part of costa between R 2 + 3 and R 4 + 5 to that between R 4 + 5 and M 1 + 2: 31 / 13. Distal part of CuA 1 longer than m-cu (23 / 13). Hind margin of wing with emargination at CuA 1. Lower calypter yellow, with black cilia. Halter yellow. Abdomen: metallic green, laterally and ventrally grey pollinose. Hypopygium black, shining ventrally, grey pollinose dorsally. Apicoventral epandrial lobe dark-yellow, broad, angular at apex, with 1 strong seta. Cercus yellow, broadly black along distal margin, elongate-ovate, deeply serrate at apex, with long falcate marginal setae distoventrally.
Female: Unknown.
Distribution. Dolichopus tundrensis is only known from the high-mountain tundra locality in Altai Mountains, i.e. from the Plateau (Table) Ukok.
Etymology: 'Tundra' is a biome where the tree growth is hindered by low temperatures and short growing seasons.