Mentum with 4th laterals slightly reduced, but may still be above level of 5th laterals (essentially type II); c1 tooth characteristically broad and flat on top, c2 teeth relatively well separated; 6th lateral arising at a slightly lower level than other teeth.
Ventromentum with about 36-40 striae. Pecten epipharyngis with about 14-15 relatively even teeth.
Antenna with basal segment about 3.25x longer than wide, RO about a third up from base; AR 1.92-3.10, fourth segment about 1.6x length of 3rd; antennal proportions (micron) 141 : 35 : 10 : 15 : 8.
Mandible of type II, with about 18 - 22 grooves on outer surface near the base; Pecten mandibularis of 10-14 bristles.
Gut of most larvae almost filled with sand particles.
Cytology: 4 polytene chromosomes with thummi cytocomplex arm combination (AB, CD, EF, G).
Centromeres heterochromatic. Two nucleoli, one proximal in arm F; the other about one third from the heterochromatic end of arm G. A Balbiani ring developed near distal end of arm G. Arm A with the sequence A4 found in Australian species; arm E with sequence E1 of the Australian species; and arm F as in C. oppositus F3 and C. australis.. No polymorphism in the small sample examined.
Arm A1: 1a-e, 11-10, 2c-1f, 3e-2d, 8-9, 3f-i, 12c-a, 4-7, 13-19 ie. as A4 oppositus
Arm B1: Puff (group 7) and about 2 distal dark bands (8ab) , close to 4 characteristic bands.
Arm C1: possibly 10A-10D6, 11B11-10D7, 11B12-11E; ie. as C2 of forsythi
Arm D1: 1 - 2, 16c-a,17e-a, 10c-a, 3e - 9, 3d-a, 10d -15, 18 - 24 ie. as forD1, nzlD2
Arm E1: 1 - 3e, 10b - 3f, 10c - 13 ie. as E1 oppositus, analis
Arm F1: 1 - 2a, 10 - 2c, 15c - 11a, 2b, 15d - 23 ie. as F3 of oppositus, and F1 of australis and forsythi
Lake Okaro, Rotorua area (NZ.10.8 & NZ.10.9) (D.J.Forsyth & S. Ibarrarán) 14-ix-1982 and 14-ii-2007
Lake Okareka, Rotorua area (S. Ibarraran) 15-ii-2007
Lake Hayes, c.13 km n.e. Queenstown, Westland (NZ.47.1) (Jon Martin) 7-i-1974
MtCOI sequence suggests that there may be hybridization with C. “castaneum” particularly where they occur together in the same lake. On the other hand, there is a possibility that this is a unique whole-arm translocation event with no connection to other species in the thummi-cytocomplex. At such, this species would be immediately reproductively isolated from its pseudothummi-cytocomplex parent. The limited mitochondrial DNA difference would then reflect that this event occurred relatively recently.