10. Chironomus species 10

Likely to be conspecific with C. 'thermarum'

Currently in Bold Bin BOLD AAJ0168 with C. 'thermarum' and C. novaezelandiae, but see comments below.

Adult:


The adult of this species is amongst specimens that D.J. Forsyth called C. 'spilleri' (specimens now in the care of Ian Boothroyd).  These maless were similar to those of C. species NZ12 in having bands across the anterior two thirds of abdominal segments 2 to 6 and on four fifths of segments 7 and 8.  A pupa with a pharate male (see right) is available, from which the following characters could be determined:

Anal point (a, right) narrow at base, but appears turned down at the end which is broader
Superior volsella (b, right) with just a small hook at the tip (D-type, as e of Strenzke 1959).
Inferior volsella (a, right) extending to about middle of gonostylus with setae simple (c, right).
Gonostylus (a, right) moderately broad but narrowing only slightly at distal end, about 4+1 setae at tip.


Pupa: about 6.9mm (1 male) - 8.3 mm (1 female) long; inner margin of wing case about 1.44-1.66 mm. Cephalic tubercle about 85-114 Ám long.  Basal ring about 115-145 µm long and 57-65 µm wide, HR 1.77-2.56.  Thorax and muscle scars yellow-brown, otherwise pale.
Shagreen on posterior half of segment II, increasing to whole of segments IV-VI, little on segments VII & VIII.  Hook row with 70-92 hooks, occupying about 0.6-0.8 of segment width.  Pedes spurii B on segs II and III; pedes spurii A of sement IV large (202-218 µm long, 101-145 µm wide) and about 0.26-0.28 length of segment.
Caudolateral spurs of segment VIII with about 2 or 3 spines, at least 1small.  68-93 taeniae on each side of anal lobe, mostly in a single row, but some double at posterior end.


Fourth instar larva: bathophilus-type larva.  Generally smaller due to growing at higher temperature (but larger when reared in the lab at lower temperatures), length about 10-16 mm.  Head capsule with pale or very slightly darkened frontal apotome, some darkening in posterior region of gula.  Ventral tubules approximately equal in length, anterior 0.63 (0.44-0.96) mm and posterior 0.64 (0.32-1.01) mm.  Anal tubules about equal in size and 1.5 times to twice as long as wide (abt. 250 x 135 µm).
Head relatively narrow, mentum width about 0.56-0.6 of VHL.
Mentum (Fig. b) with 4th lateral reduced to about level of 5th laterals (type II); centre trifid tooth with distinct, small c2 teeth (i.e. Type IB).
Ventromentum (Fig. c) with about 33-41 striae.  Pecten epipharyngis (Fig. a) with about 11-16 rather uneven teeth (type B).
Basal segment of antenna (Fig. d) about 3-4 times as long as wide, RO about 20-40% up from base; 4th segment relatively short, only about 20% longer than segment 3; AR about 1.8-2.7; proportions (micron) 132 : 28 : 7.5 : 10 : 7.
Premandible with 2 teeth, inner tooth about 2-2.3 times the width of the outer tooth.
Mandible (Fig. e) with 3rd inner tooth darkened and somewhat separated (i.e type II, tending to type IIIC); about 7-16 furrows on outer surface near the base; 10-14 taeniae in Pecten mandibularis.

Cytology: 4 polytene chromosomes with the pseudothummi cytocomplex arm combination (AE, BF, CD, G).
Arm G without a nucleolus, but with a large subterminal BR, and another may be developed about the middle of the arm.  The nucleolus is in arm F.
Arm A has the sequence identical to A4 of oppositus and A1 of C. 'thermarum'.
Arms B, C, D, E, F and G appear identical to B1, C1, E1, F1 and G1 of C. 'thermarum', while D appears similar to that of C. novaezelandiae. C. novae-zelandiae.  No polymorphism known.

Arm A1:    1a-e, 11 - 10, 2c - 1f, 3e - 2d, 8 - 9, 3f-i, 12c-a, 4 - 7, 13 - 19        ie. as A4 oppositus and A1 of 'thermarum'
Arm B1:    Derived from nzlB1 by a long inversion of the distal region.  Puff with proximal dark bands (groups 7-8) towards distal end.        ie. as 'thermarum'
Arm C1:    Appears similar to C1 of tepperi, 'pseudoppositus', nzlC1 -    ie. as 'thermarum'
Arm D1:    1 -2, 16 - 11, 4c - 9, 3d-a, 4ba - 3e, 10a-c, 17 - 24                as D3 of novaezelandiae
Arm E1:    1 - 3e, 10b - 3f, 10c - 13                                                          ie. as E1 oppositus, 'thermarum', etc.
Arm F1:    1 - 2a, 10 - 2c, 15c - 11a, 2b, 15d - 23                                    ie. as oppositus, 'thermarum', etc.as F3 oppositus, & F1 of 'thermarum'
Arm G1:    subterminal BR            as 'thermarum'?

Localities:
North Island:
    Lake Ngahewa (38.31°S, 176.37°E), South Auckland (NZ.76.1) (S. Ibarraran) 28-viii-2007.
    Lake Rotowhero (38.30°S, 176.40°E), c.24 Km s. Rotorua, South Auckland (NZ.11) (D.J. Forsyth & Jon Martin) 1970-1973; (NZ.11.6) (S. Ibarraran) abt 15-ii-2007.
    Queen Elizabeth Park (37.94°S,175.56°E), South Auckland (NZ.80.1) (S. Ibarraran) abt 15-ii-2007.

This species may be confined to thermal lakes.  Lake Rotowhero varies in temperature from 29.5 to 38oC during the year.

Initially included with C. novaezelandiae, but shows consistent differences in the lighter larval head colour and some unique banding patterns.  It is very similar in cytology to C. 'thermarum', differing mainly in the better development of the ventral tubules.  Phylogenetic analysis of the mitochondrial COI sequence places it in a cluster along with C. 'thermarum'.

See also C. novaezelandiae, C. 'thermarum',  and C species NZ12.

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Modified: 8 September 2020
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