Species u.  C. species 2u.

Adult:

Wing length about 4.2-4.8 mm, VR about 0.86-0.97; anterior wing veins and crossvein slightly darkened.  AR probably quite high (perhaps 5?)
Thorax dark brown, vittae, scutellum, sternoplueron, legs, etc., blackish; postnotum pale.
Abdomen dark brown with a narrow pale band distal on segmentes VI and VII, sometimes very narrow on preceding segments.
Approximate leg proportions (micron)

	Fe	Ti	Ta1	Ta2	Ta3	Ta4	Ta5	LR	F/T	BR
PI	1615	1530	-	-	-	-	-	-	1.05	-
PII	1580	1500	1000	630	475	315	210	0.63	1.03-1.05
PIII	1775	2000	1260	940	645	410	290	0.78	0.89

Male genitalia of Chironomus species 2u (in order, left to right) hypopygium, superior volsella, inferior volsella, anal point .
Apparently a small number of setae (perhaps 6 in individual pale areas) on TIX.  Anal point stout (above, right) narrowing slightly to a rounded point, Superior volsella most similar to D(d) of Strenzke (1959).  Setae of inferior volsella simple, shorter than anal point and to about midpoint of the gonostyle, which narrows relatively gently over posterior third.

Female: - Wing length about 5 mm, VR about 0.95.  Generally dark color; vittae, scutellum and postnotum and sternoplueron blackish.  Abdominal sternites brown with yellowish posterior band.  Photos suggest femurs are lighter brown.

Pupa: Cephalic tubercles about 1.3 times longer than wide.  Caudolateral spurs of segment VIII with about 3 (1-4) closely applied spines.  Fringe of anal lobe with about 62 taeniae in a double row on each side.

Fourth instar larva a medium size plumosus-type 13.7 (11.5-16.5) (female 12.7-16.5 mm); lateral projections about 305 (200-440) µm; anterior ventral tubules 2.0 (1.10-2.48) mm, posterior 2.15 (1.30-2.13) mm, posterior pair generally longer but some variability in Saskatchewan larvae.  Anal tubules about 442 (405-500) µm (dors), 434 (359-600) µm (vent) and 2-3 times longer than wide with dorsal pair relatively longer (2.3-3.1 times) than the ventral pair (1.9-2.6 times).
Gular region generally dark on posterior third to half, and higher at outer edges, widest up from posterior margin, and in rare cases reduced to a "V"; slightly dark to dark frontoclypeus, often just a thick stripe. Ventral Head Length 356 (295.5-396) µm with overlap between sexes.
Salivary reservoir 79.5 (63-91) µm in length and 3.66 (2.27-4.5) times longer than wide.
Mentum (Fig. c) abt 0.53-0.63 of VHL with relatively rounded teeth; central trifid tooth usually type IB but may also be IIA; 1st laterals sloping outwards, 4th laterals reduced (type I-II), sometimes only slightly in Calgary specimens, but generally almost to level of 5th laterals in Saskatchewan.
Ventromental plates (Fig. d) 229.4 (210-245) µm wide and 3.63 (3.26-3.91) times wider than deep, 1.13 (1.06-1.26) times wider than mentum; separated by about 0.3 to 0.4 of the width of the mentum, with 45.5 (37-52) striae; VMR about 0.35 (0.29-0.43).
Pecten epipharyngis (Fig. a) with about 12.3 (9-14) relatively broad teeth (type B).
Premandible (Fig. a) with inner tooth 3.1 (2-4.5) times wider than the outer tooth, both coming to relatively sharp points, perhaps type B2.
Antenna (Fig. b) only 0.35-0.45 of VHL; with basal segment abt 3.5 (2.9-4.0) times longer than wide, RO a third to a half way up from base of segment; AR about 2.0 (1.72-2.63); antennal proportions (micron) 139 : 36 : 11 : 13 : 7.
Distance between the antennal bases, about 155 (142-187) µm, generally less than that between the S4 setae, about 172 (163-197) µm, but occasionally much greater.  S4 setae separated by 0.87 (0.80-0.94) of FC width at that point.  S5 setae may be slightly anterior, level or sl. posterior to nearby RO.
Mandible (Fig. e) generally with 3rd inner tooth partly to well developed and at least partly darkened (type IIB-IIIB/C), about 19.2 (14-22) furrows on outer surface near base, about 13.1 (10-16) taeniae in Pecten mandibularis; Mdt-Mat 25-33 µm, MTR 0.28-0.42.

Cytology:  4 polytene chromosomes with the thummi arm combination AB, CD, EF, G.  Centromeres moderately heterochromatic.
Arm G mostly unpaired, with a virtually terminal nucleolus and a Balbiani ring (BR) (possibly 2 close BRs) near the other end.
No nucleoli in the long chromosomes.  Arm B with a BR near the 4 characteristic bands.
A small distal inversion in arm D heterozygous in one specimen.

Arm A1:    perhaps as piger i.e. 1 - 19?
Arm B1:    Puff (group 7) with distal dark bands near distal end of arm.    Possibly by simple inversion from B2 of C. atrella; close to aberratus.
Arm C1:    Groups 3-4 near middle of arm, possible inversion 3 - 6.
Arm D1:    Groups 15 - 16 near middle of arm.    Probably as aberratus, etc.
Arm D2:    Small inversion in distal third.
Arm E1:    1 - 3e, 5 - 10b, 4 - 3f, 10c - 13;                        i.e. as aberratus, cucini, etc.
Arm F1:    1, 5 - 2, 6 - 10, 17 - 11, 18 - 23    i.e. inv2-5 from aberratus, sororius, etc.
Arm G1:    Partly unpaired, virtually terminal nucleolus, large BR near other end.

Found: Alberta – Edmonton (53.508°N, -113.486°W); Wood Bison Trail, Elk Island Natl. Park (53.567°N, -112.851°W); Ecole Agnes Davidson
            ES, Lethbridge (49.672°N, -112.813°W); New Horizons School, Ardrossan (53.558°N, -113.259°W); Spruce View School, Innifail
            (52.028°N, -113.948°W); nr Jasper Lake, Jasper Natl. Park 53.193°N, -117.954°W); (all BOLD); Huntington Hills, Calgary
            (51.08°N, -114.08°W).
            British Columbia – New Afton Mine, 10 km W Kamloops 50.643°N, -120.517°W) (BOLD).
            Manitoba – Churchill (58.771°N, -93.851°W); Shoal Lake School 50.438°N, -100.591°W); Wapusk Natl. Park (58.723°N, -93.46°W);
            Grasslands Natl. Park (all BOLD); abt 8 Km nw Theodore (51.75°N, -102.95°W).
            Nunavut – Water Lake, Kitikmeot (69.132°N, -105.063°W) (BOLD)
            Ontario – 4 ml e. Sudbury (44.88°N, -78.27°W).
            Saskatchewan – Frenchman River, Grasslands Natl. Park (49.149°N, -107.53°W); Lucky Lake School (50.98°N, -107.135°W); St. Peters
            School, Unity (52.444°N, -109.153°W); M.C.Knoll Elementary School, Yorkton (51.217°N, -102.433°W); Vanscoy
            School (52.003°N, -106.977°W); Whitewood School (50.328°N, -102.258°W); Yellow Grass School (49.671°N, -103.864°W);
            Wapusk Natl. Park (58.723°N, -93.46°W); (all BOLD); abt. 8 Km. w. Theodore (51.75°N, -102.95°W).
            Yukon Territory – Auriol Trail, Kluane Natl. Park and Reserve (60.714°N, -137.432°W); Shallow Bay, Lake Laberge (60.958°N,
            -135.184°W); Nilsson-Lammers Research Forest, n. Whitehorse (60.841°N, -135.208°W) (all BOLD).
    A related species occurs in South Dakota – About 5 Km. w. Yankton, Yankton Co. (abt 42.88°N, -97.40°W) (see C. species nr. sp. u)

Molecular sequences:
mtCOI: Sequence is available from the known localities, other than the South Dakota variant.

Although the adult is similar to C. hyperboreus amongst North American species, the larvae and cytology are different and the cytology and mtCO1 sequences suggest a closer relationship to C. sp. 2u and Palearctic species such as C. aberratus Keyl 1961 and C. sororius Wülker 1973.