5. Chironomus 'thermarum'  Manuscript name by D. J. Forsyth.

In Bold Bin: BOLD:AAJ0168 or BOLD:ABZ5458

Forsyth describes the abdominal tergites of the adult male as largely dark with only a narrow pale posterior margin.

Fourth instar larva: halophilus-type, i.e. with some development of posterior pair of ventral tubules (length about 120 µm), or sometimes salinarius-type.  Smaller species (temperature effect?), length about 11.3 mm (male 9.2 mm).  Anal tubules from 1.5-2.1 times longer than wide.
Head capsule with frontoclypeus generally pale or slightly darkened, gula generallydarkened.
Mentum (below) usually type IIA;  c1 tooth relatively narrow for a type II, with c2 teeth only partly separated on its shoulders; 4th laterals only slightly reduced (type II).  Mentum width about half VHL.
Ventromentum (below) with about 45-55 striae.  Pecten epipharyngis with about 11-14 irregular teeth.  Basal antennal segment about 3.27-3.68 times as long as wide; AR 2.48 (2.22-2.66); segment proportions (micron): 124 : 23 : 8 : 12 : 7.
Distance between antennal bases less than that between the S4 setae
Mandible (below) with third inner tooth only partly separated and relatively pale (type IIB), with about 13-15 furrows near base.


a. Mentum of type II; b. Ventromentum with about 45 striae; c. Mandible of type IIB.

Cytology: 4 polytene chromosomes, pseudothummi-complex arm combination (BF,CD,EA,G).
Arm G normally closely paired with a subterminal nucleolus; another large nucleolus on arm F.  Only one Balbiani ring (BR), in the middle of arm G, was visible in the specimens examined.
Arm A with sequence A4 as found in Australian species; arm E with sequence E1 of Australian species, and arm C appears to have the same sequence as C1 of C. forsythi (ie. as C1 of the Australian species).
No polymorphism was seen in the available specimens.
thmA1:    1a-e, 11-10, 2c-1f, 3e-2d, 8-9, 3f-i, 12c-a, 4-7, 13-19                 ie. as A4 of oppositus, nzlA1, AnlA1, forA1
thmB1:    Puff (group 7) hardly developed, with proximal dark bands (group 8) near distal end.
thmC1:    as C1 of forsythi and oppositus?
thmD1:    1 - 2, 16c-a,17e-a, 10c-a, 3e - 9, 3d-a, 10d -15, 18 - 24
thmE1:    1 - 3e, 10b - 3f, 10c - 13                                                  ie. as oppositus E1
thmF1:    appears to be 1 - 2a, 10 - 2c, 15c - 11a, 2b, 15d - 23                      ie. as oppositus E1
thmG1:    Subterminal nucleolus and a median BR.

Molecular:Mt COI: Sequences suggest that C. 'thermarium' may be an ecologically plastic species that can live in thermal habitats as well as habitats with lower water temperatures.  At normal temperatures the larvae are a bathophilus type, with the ventral tubules, particularly the anterior pair, reducing in size with higher temperatures (see below).

Localities:
North Island:
    Kerosene Creek (thermal), South Auckland (38.94°S, 176.56°E) (NZ.78.1) (S.Ibarraran) 27-viii-2007
    Lake Rotowhero, South Auckland (39.30°S, 176.40°E) (NZ.11.3) (D.J. Forsyth and Jon Martin) 23-xii-1973
    ?Lake Rotowhero, South Auckland (39.30°S, 176.40°E) (NZ.11.6) (S. Ibarraran) abt. ii-2007
    Waiotapu Stream (thermal), South Auckland (38.38°S, 176.35°E) (NZ.69.1) (D.J.Forsyth) 14-vi-1983
    Waiotapu Stream (thermal), South Auckland (38.38°S, 176.35°E) (NZ.69.2) (D.J.Forsyth) 25-iii-1998

Very similar in cytology to C. species NZ10, from which it is mainly differentiated by the reduction of the ventral tubules.  This may be a temperature effect and the two may be different morphologies of the same species.

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Modified: 3 September 2020
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