Don described the adult abdomen as having somewhat triangular brown markings on the tergites, that became progressively wider on successive segments.
Don Forsyth's original drawing of the abdomen of C 'castaneum'.
DNA and cytological data indicate that there was more than one taxon initially included under this name.
Fourth instar larva: A salinarius-type larva, length 15.2-15.7 mm (female); 14.7-14.8 mm (male). Anal tubules short and narrowing to a rounded point, only about twice as long as wide.
Frontoclypeus and posterior half to two thirds of gula, dark to very dark, sometimes with some slight darkening at posterior of head capsule.
Mentum width about 0.63 to 0.8 of VHL; with 4th lateral reduced to about the level of the 5th laterals (type II), c1 tooth of mentum broad (type IIa), 6th laterals turned out.
Ventromentum with about 35-43 striae, which reach almost to the anterior margin, particularly at the lateral edges.
Premandible with outer tooth generally shorter, inner tooth about 2-3x wider than outer.
Pecten epipharyngis with about 10-14 teeth narrowing towards the edges. Distance between antennal bases less than the distance between the S4 setae.
Antennae with basal segment about 2.5-3.1 times longer than wide, AR 1.8-2.6; Ring organ about one third to 2/5 (0.30-0.45) up from base of segment; proportions (µm) 132 : 33 ; 9 : 15 : 8 ; A3 shorter than A4, but longer than A5.
Mandible type generally type IIB, but sometimes 3rd inner tooth darker and more distinct IIC, with about 15-24 grooves on outer surface near base, and 11-14 setae in Pecten mandibularis.
Cytology: 4 polytene chromosomes, with the pseudothummi group arm combination (BF, CD, EA, G).
Distinguished by two nucleoli in chromosome 1 (1 proximal in F and one proximal in B). Arm A with a sequence differing from A4 of C. oppositus by a simple inversion which is also found in C. forsythi; arm E commonly differs from E1 of Australian species by a large inversion, although E1 appears to be present in Poutu Canal population. Arm F1 appears identical to that of oppositus F3 and australisF1. Arm G often partly unpaired. Polymorphic in arms A, B, C, D, E and F.
casA1: 1a-e, 2e - 3, 1f - 2c, 10 - 11, 2d, 8 - 9, 3f-i, 12c-a, 4 - 7, 13 - 19 as zeaA1 & forA2
casA3: 1a-e, 12a-c, 3i-f, 9 - 8, 2d, 11 - 10, 2c - 1f, 3 - 2e, 4 - 7, 13 - 19 from casA1
casB1: Nucleolus just distal to 4 characteristic bands (groups 24 - 26), and puff with distal dark bands (groups 8-7) near distal end, i.e. as nzlB2
casB2: Inversion of distal third of arm, as nzlB3, bringing puff and proximal dark bands (groups 7-8) close to nucleolus.
casC1: Characteristic band groups 3-4, with 5 distal, near distal end. as as nzlC1, tepC1.
casD1: as forD1
casD2: as forD2
casD3: small proximal inversion from casD1.
casE1: 1 - 3e, 10b - 3f, 10c - 13 i.e. as E1 oppositus
casE2: 1a-e, 3f - 10b, 3e - 2a, 10c - 13 i.e. as forE2
casF1: 1 - 2a, 10 - 2c, 15c - 11a, 2b, 15d - 23 i.e. as F1 of novae-zelandiae, F3 of oppositus, australis
casG1: with subterminal nucleolus
Lake Karapiro, South Auckland (NZ.77.1) (Sofia Ibarrarán) 27-viii-2007
Lake Okaro, nr. Rotorua, South Auckland (NZ.10.9) (Sofia Ibarrarán) 14-ix-2008
Lake Okareka, Wellington District (NZ.82.1) (Sofia Ibarrarán) 28-viii-2007
Poutu Canal, Lake Rotoaira (NZ.70.1) (D.J.Forsyth) 8-x-1990 (Forsyth's type locality)
Lake Rotoaira South Auckland (NZ.70.2) (Sofia Ibarrarán) 14-ii-2007
Lake Rotoaira (NZ.70.3) (Sofia Ibarrarán) 27-viii-2007
There is evidence from the cytology for the presence of more than one species:
At the type locality there is A1 and A2; B1 and B2; C1; mainly D2 with D1 and D3; E1 and E2; F1; and G1.
At Haast there is A2; B1 and B3; C2; D1; E1; F1; and G2.
Some sequence is in the BOLD database.