Previously Chaetolabis nr. atroviridis (sp. 2h) of Martin.
Pupa: (Largely based on European specimens) Length about 10.1-10.2 mm. Conspicuous pedes spurii B on segment II; hook row with about 70 hooks. Caudolateral spur of segment VIII with about 2 equally long spines, on North American specimen (below), but only one on European specimens.
Larva a medium to large thummi-type (length about 17.8-18.0 mm). Anterior ventral tubules shorter than posterior pair (ant. 1.24 mm; post. 1.32 mm). Anal tubules long (abt. 530-710 µm) with a median constriction, about 3.5-5.5 times longer than wide; ventral pair possibly slightly longer and thicker. Gula dark on posterior half, frontoclypeus slightly darkened.
Mentum (Fig. b) as in Chironomus; central tooth relatively broad with short parallel sides (or possibly diverge slightly), side teeth well developed (type III, or II), 4th laterals slightly reduced (type I-II).
Ventromentum (Fig. c) with about 40 striae. Pecten epipharyngis (fig. a) with about 16 irregular teeth.
Antenna (Fig. d) with AR about 1.8; basal segment about 3x as long as wide.
Mandible (Fig. e) with third inner tooth relatively well separated and darkened (type IIIC).
Cytology: 3 polytene chromosomes with the modified thummi arm combination AB, CD, GEF.
Nucleolus subterminal in arm G. No nucleoli in other chromosomes.
Polymorphic in arms A, B, D and F chromosomes.
bitA1: as in Palearctic specimens; olive not obvious.
bitA2: Inversion of central part of the arm. as atrA2?
bitB1: Typical bands near the centromere still present but quite contracted in available material.
bitB2: Inversion of almost half the arm, beginning about 1/5 from centromere.
bitC1: as in Palearctic specimens, but typical bands (groups 3-4) not as obvious and may be nearer the centromere. as atrC2?
bitD1: Available specimens are heterozygous, but may be identical to the Palearctic sequence.
bitD2: Inversion of about 2/3 of the arm.
bitE1: as in Palearctic specimens, bands 10-13 obvious near the centromere.
bitF1: Available specimens heterozygous, but bands 20-23 obvious near the centromere; as in Palearctic specimens.
bitF2: Inversion of about the distal half of the arm. as atrF2?
bitG1: tandem fusion with arm E; subterminal nucleolus followed by two BRs.
Found: Ontario - Costello Creek, Algonquin Provincial Park, Nipissing Co. (45.58; -78.32); Beaver swamp near Dunrobin, Carleton Co. (45.45; -76.00); Cranberry Creek, abt. 1.5 km n. Kars, Carleton Co. (45.13; -75.63).
Also found in Palearctic Venetjärvi, FINLAND (Type locality); Sweden.
Morphology described by Wiederholm (1979) and Langton & Vallenduuk (2013). Cytology of European specimens described by Wülker (1989) (as C. macani), of Neartic specimens by Martin (2014).
The shared chromosome banding patterns and the extremely similar coxI DNA sequence to that of C. atroviridis suggests that recent hybridization has occurred and may still be occurring.