AUSTRALIAN CHIRONOMUS SPECIES

Compiled by Jon Martin
Genetics, Genomics & Development, Schhool of Biosciences, The University of Melbourne, Victoria, 3010, Australia


When Freeman (1961) revised the Australian Chironomidae he recognized six species of the genus Chironomus (s.s.): C. alternans Kieffer, C. australis Skuse, C. nepeanensis Skuse, C. tepperi Skuse and C. vitellinus Skuse.  However, even at that stage it was known that adults of C. alternans could be produced from distinct larval types, and with quite distinct polytene chromosomes, which appeared to be distinct species.  Bugledich et al. (1999) 'Family Chironomidae' from Zoological Catalogue of Australia, recognize 12 species of Chironomus in Australia, with another nine species that are Incertae cedis.  Only two of these latter nine, which are currently nomena nuda, are considered here.
There is also one species of Einfeldia in Australia, E. australiensis (Freeman) which Freeman placed in Chironomus (Xenochironomus).  This species is included here as the relationship of Einfeldia to Chironomus has been subject to much discussion.

This listing is also available in pdf format (6 MB)(Updated 24 February 2020).


In general, the morphological terminology used in this document follows Sæther (1980), Webb & Scholl (1985) and Vallenduuk & Moller Pillot (1997).



1. Adult morphology

Species with an Australia-wide distribution
Chironomus cloacalis Martin, 1971
Chironomus 'februarius' - currently nomen nudum, but described in Martin 1966
Chironomus nepeanensis Skuse, 1889
Chironomus 'pseudoppositus' - currently nomen nudum, but described in Martin 1966
Chironomus tepperi Skuse, 1889

Species with a tropical distribution
Chironomus bicoloris Tokunaga, 1964
Chironomus circumdatus (Kieffer, 1916)
Chironomus 'orientalis'
Chironomus javanus Kieffer, 1924
Chironomus pallidinubeculosus Tokunaga, 1964
Chironomus magnivalva Kieffer, 1917
Chironomus 'queenslandicus' - manuscript name
Chironomus sp. (bathophilus type)

Species with a south eastern distribution
Chironomus australis McQuart, 1847
Chironomus duplex Skuse, 1889
Chironomus 'jacksoni' - manuscript name
Chironomus maddeni Martin & Cranston
Chironomus oppositus Skuse, 1889:
form connori
form oppositus
form whitei
Chironomus 'timmsi' - manuscript name
Chironomus 'tyleri' - manuscript name (formerly C. oppositus f. tyleri)
Einfeldia australiensis

Species with a western distribution
Chironomus occidentalis Skuse, 1889
C. oppositus f. edwardi

Species from Norfolk Island
Chironomus 'februarius' (?)
Chironomus species NI 1 (may be as Chironomus nr. samoensis)
Chironomus species NI 2

The description of Chironomus alternans Walker and the synonyms listed by Freeman (1961) are also included, although they are considered as uncertain.  Further description is provided for those where the types are still available:

C. alternans

C. januarius

C. subdolus



In the descriptions of adult males reference is made to the types of superior volsella shape as recognized by Strenzke (1959).  This is a helpful initial classification, but experience has shown that the types are not discrete, but are part of a continuum.  The three categories as described by Strenzke are:
S-type: The SVo is shoe shaped, i.e. it is drawn out distal-medially into a broad, rounded lobe (Fig. a-c, below) (Strenzke's figure suggests the most distal point will be at the toe of the shoe).
D-type: The SVo is ribbon-like: distally it may have a weakly thickened shoulder (Fig. d, below) (most distal point is not at the internal margin), or bent in a shallow sickle-shape (Fig. e-f, below).
E-type: The SVo has the form of an elephant's tusk; distally it is sharply graded to a point, or with an expanded knob (Fig. g-i, below) (line from base to most distal point goes outside the limits of the SV).

Key to Adults

Adult males:
1a Yellow/green species. Anal point stout 2a
1b Anal point longer or tubular 3a
     
2a(1a) Anal point bulky and strongly turned down, abdomen greenish Einfeldia australiensis
2b Anal point not bulky or strongly turned down, abdomen dark C. 'queenslandicus'
     
3a(1b) Wing with dark spot over cross vein and with fuscous clouds, particularly in cell R5 C. pallidinubeculosus
3b Wing with at most darkening of cross vein 4a
     
4a(3b) Cross vein strongly darkened, LR about 1.5, wing length 4-5 mm; ant TA4 longer than Ta3 C. nepeanensis(northern),C. atchleyi(southern)
4b Cross vein not strongly darkened 5a
     
5a(4b) Legs shorter than usual, posterior LR about 0.5; male hypopygium enlarged, anal point deep and laterally flanged 6a
5b Posterior LR about 0.7 or higher; male hypopygium of normal type 7a
     
6a(5a) Thorax dull grey, pits of dorsocentral setae very distinct; inferior volsella of male very swollen C. tepperi
6b Thorax greenish with brown stripes, pits normal; inferior volsella of male not swollen C. magnivalva
     
7a(5b) Wing length greater than 5 mm; anterior tarsi of males bearded 8a
7b Wing length less than 5 mm; anterior tarsi of males bearded or unbearded 10a
     
8a(7a) Distributed on east of the continent, including Tasmania 9a
8b Distributed on the west of the continent, including Northern Territory C. occidentalis
     
9a(8a) Mid femur more than 1.12 x the anterior femur (likely to be) C. duplex
9b Mid femur shorter than the anterior femur (likely to be) C. australis
     
10a(7b) Blackish species.  Male with bearded anterior tarsi and spatulate superior volsella C. 'timmsi'
10b Paler species, at most brown.  Male tarsi not bearded 11a
     
11a(10b) Thorax pale, anterior femur and tibia pale, tarsi with dark pattern 12a
11b Thorax pale to brown, legs unbanded (mainly members of the 'C. alternans' group) 13a
     
12a(11a) Tarsi darkened at both apex and base, anal point tubular C. javanus
12b Tarsi darkened only at distal ends, anal point larger and narrowed at base, LR above 1.80, anterior tarsus 5 at least 0.35 times the length of the tibia, SV often beaked C. 'orientalis'
     
13a(11b) Wing length over 4 mm. 14a
13b Wing length less than 4 mm 15a      
14a(13a) Abdomen generally greenish with saddle markings on the anterior segments, gradually extending in length from about 5th tergite to occupy most of segment by 8th tergite (AR 2.9-3.2) . LR 1.53-1.66 C. 'tyleri'
14b Abdominal tergites generally dark with pale posterior band, but may have saddle spots;.(AR 3.3-4.25); wing length up to 4.6 mm. LR 1.44-1.78 C. cloacalis in part
15a(13b) C. oppositus type
15b Abdominal tergites generally dark, may have pale posterior band, saddle spots, or dark band across the centre of the segment 16a      
16a(15b) as 14a, but wing length from 2.6 mm C. cloacalis in part

(Abdominal tergites may be as C. cloacalis, or may have dark band across the centre of the segment; AR 2.9-3.4; LR 1.56 - 1.65.), C. 'pseudoppositus' (Abdominal tergites as in C. cloacalis AR 2.5-3.1; LR 1.5-1.8; superior volsella less curved than in other members of the oppositus-group)
Abdomenal tergites with saddle spots: C. oppositus (LR 1.5-1.8; wing length 2.8-3.6, C. maddeni (AR 2.55-2.86; LR 1.6-1.8; wing length 2.4-3.36 mm), C. 'jacksoni' (AR 2.4-3; LR ); Chironomus 'tyleri' (AR 2.9-3.2; LR 1.53-1.66; wing length 4.3-4.5 mm).

Norfolk Island species

1a LR about 1.5, superior volsella closest to Strenzke's type D(d); may be near C. samoensis. LR is lower than C. nr. samoensis from other regions, but in range of C. samoensis itself). Species 1
1b LR about 1.27, superior volsella closest to Strenke's type D(f), but appears to have a flattened end Species 2

Adult females
No key to the females currently exists but some of the characters common to both sexes can apply, as well as additional characters from the antennae, the shape of segment X and the shape of the cercus. Also, the dorsocentral setae begin more anteriorly than in males, the additional setae anterior to the parapsidal suture are the humeral setae and their arrangement can be useful as a taxonomic character.


2. Larval types and Karyotypes

In the following descriptions, reference is made to the mentum and mandible types originally devised by Webb & Scholl (1985), Vallenduuk & Moller Pillot (1997), and Proulx et al. (2013).  These classifications were made for relatively small numbers of species, but with the much larger number of species, such as in the North American fauna, they do not cover all the variability seen in these characters and so further modification has been necessary.

The MENTUM TYPE is defined only by the degree of development of the 4th lateral teeth:


Type I - height in same line as the rest of the lateral teeth;
Type II - 4th laterals reduced, height about equal to that of the 5th laterals;
Type III - 4th laterals further reduced, height less than that of the 5th laterals.


The mentum may be further classified by the characters of the CENTRAL TRIFID TOOTH:
Type IA - c2 teeth only partially separate from c1, i.e. as shoulders on c1 (figure a).
Type IB - c2 teeth slightly more separated (figure b).
Type IIA - c1 broad, c2 teeth distinctly separated (figure c).
Type IIB - c1 very broad, c2 less separated (figure d).
Type III - c1 tooth relatively narrow and much higher than the separated c2 teeth (figs e and f).
Type IV - c2 teeth well separated, not much lower than the relatively narrow c1 tooth (figs g and h).




The MANDIBLE TYPE is defined by the degree of darkening and separation of the 3rd inner tooth:
It seems better to consider the two characters separately.

This figure shows IA; IIB; IIIC respectively

Separation:
Type I - tooth fused
Type II - tooth partially free
Type III - tooth completely separated
Color:
Type A - tooth pale
Type B - some degree of pigmentation
Type C - as dark as other inner teeth

Mandible length and Mdt-Mat:
Hirvenoja and Michailova (1998) illustrated that the distance between the tip of the dorsal tooth and the apical tooth could differ between related species (Mdt-Mat) (blue line in figure below).


However for different sized species it may be preferable to divide this value by the length of the mandible (black line in figure above) to obtain the MTR.

Ventromentum
There are several measures that can be made from the ventromental plates including distance between inner margins of the plates (VPA) and the number of striae.  Two others need some explanation:

VENTROMENTAL PLATE RATIO (VMR) - ratio of the width of the marginal region of ventromentum (usually seen as a granular band under light microscopy) (a in figure below) to the distance from the anterior margin to the base of the striae (b in figure below).


VMR = a/b

'b' also serves as a measure of the depth of the VM for the ratio of length to depth of the VM plates.
VM length (VML) is measured directly from inner margin to outer margin:

This seems preferable to the sometimes used 'horizontal length' which can be subject to parallax error and to the effects of rotation of the plates under pressure during slide mounting.

PECTEN EPIPHARYNGIS -
Proulx et al. (2013) recognised 4 types of PE in North American species.  These are useful if the teeth are not worn down, as they often are in older larvae.  Type D does not occur in any known Australian species.

Type A - fine sharp rather uniform teeth.



Type B - teeth broader but still sharp.  Sometimes with one or two fine smaller teeth interspersed.


Type C - rounded and rather uniform.  Worn type B teeth may be mistaken for this type.


Type D - rounded teeth with smaller teeth interspersed (generally found in the subgenera Lobochironomus or Chaetolabis).

ANTENNAL RATIO (AR) - length of A1 divided by the sum of legths of A2-A5, measured on the basis of the chitinised part of each segment only, as the inter-segmental regions can extend to different extents during mounting. For this reason the AR will usually be higher than that obtained by simply measuring the total length from base of A2 to tip of A5.

Relationship on the Frontoclypeus (FC) of the distance between antennal bases and distance between S4 setae
This character gives some indication of the shape of the anterior region of the FC: the amount and extent of the narrowing at the anterior end near the antennal bases, and where the S4 setae are in relation to the broadening of the clypeus (see figure below).  This relationship can be further characterized by the distance of the S4 setae from the margins of the FC most easily expressed by the fraction of the FC width between the two S4 setae.  This has two components: how far the setae are from the FC margin, and how close they are to the widest point of the FC.


Frontoclypeus with approximately equal distance between antennal bases and S4 setae.
Note also the barely visible 'ring organ' of Yamamoto et al. (2015), (more obvious at top) immediately opposite the S5 setae. This is a characteristic of species of Chironomus.

Larval types referred to in Key and in descriptions are defined here.

Provisional Key to 4th Instar Larvae

1a Larger larvae, length up to about 23 mm.  (Either thick bathophilus-type larvae with large, very darkly pigmented heads, or a slim plumosus-type larva with a small, pale head capsule) 2a
1b Medium sized larvae, length up to about 19 mm, head length less than 400 mm. 5a
     
2a(1a) Head capsule heavily darkened, bathophilus-type 3a
2b Head capsule pale, except NT and Vic where slight darkening of the gula & frontoclypeus occurs, slender plumosus-type C. nepeanensis.
     
3a(2a) Distributed on east side of the continent only (NSW, VIC, SA, TAS) 4a
3b Distributed on west of continent only (WA & perhaps NT) C. occidentalis
     
4a(3a) Teeth of mentum rounded (when not worn), c2 teeth of centre trifid tooth only partially distinct from c1 tooth (type IIa).  Four polytene chromosomes C. australis
4b Teeth of mentum square sided and pointed, c2 teeth well separated from c1 tooth.  Three polytene chromosomes, inversion polymorphism C. duplex
     
5a(1b) Larvae with lateral tubules (species often polymorphic) 6a
5b Larvae without lateral tubules (species often polymorphic) 12a
     
6a(5a) Larvae of the true plumosus type (posterior ventral tubules coiled) 7a
6b Larvae of the melanotus- or semireductus- type (posterior ventral tubules may be bent) 16a
     
7a(6a) Head capsule generally quite heavily darkened on both frontoclypeus & gula 8a
7b Head capsule darkened on gular region only 10a
     
8a(7a) Both gula and frontoclypeus quite heavily darkened C. cloacalis (majority)
8b Gula and frontoclypeus slightly to moderately darkened, tropical species 9a
     
9a(8b) c2 teeth of mentum sharp and well separated (type III), 3rd inner tooth of mandible type IA/B C. 'orientalis'.
9b c2 teeth of mentum only partially separated (type IB), 3rd inner tooth of mandible type IIIB C. magnivalva
     
10a(7b) Lateral tubules tending to be more ventrally placed, premandible with 7 teeth C. javanus
10b Larvae not as above, premandible with the normal 2 teeth 11a
     
11a(10b) Head capsule often completely pale, but sometimes slightly darkened at posterior of gula, basal segment of antenna less than 4 times as long as wide C. pallidinubeculosus
11b Basal segment of antenna more than 4 times as long as wide: 12a
     
12a(11b) Larvae of the halophilus-type (i.e. VT reduced, often only the posterior pair ), hind prolegs sharply narrowing C. tepperi (part)
12b Larvae with VT of long or moderate length 13a
     
13a(12b) Larvae of the plumosus-type 14a
13b Larvae of the bathophilus-type 18a
     
14a(13a) Gula darkened at least on posterior half 15a
14b Gula pale or only slightly darkened on posterior third 17a
     
15a(14a) Gula dark, centre tooth of mentum of type III C. circumdatus
15b Gula moderately darkened, centre tooth of type IB pale headed form of C. cloacalis
     
16a(6b) Lateral tubule over 200 micron; inner margins of ventromental plates separated by only about 0.2 of mentum width; AR abt. 1.40-1.64; PE of type D C. 'queenslandicus'
16b Lateral tubules often less than 200 micron; ventromental plates separated by about 0.3 of mentum width, AR >1.9; PE usually type B some C. oppositus f. oppositus, C. 'edwardi' and C. 'tyleri'.
     
17a(14b) Mentum of type II; Central trifid tooth type III C. 'februarius'
17b Mentum of type I; Central trifid tooth type III C. bicoloris
     
18a(13b) Basal segment of antenna 3 to 3.5 times longer than wide; four polytene chromosomes 19a
18b Basal segment of antenna about 4 times longer than wide; three or four polytene 20a
     
19a(18a) Gula and frontoclypeus pale; antennal segments A2/A1 less than 0.3 C. 'timmsi'
19b Gula and frontoclypeus at least slightly darkened, A2/A1 more than 0.3
Accurate identification only possible from examination of the polytene chromosomes.
most members of C. oppositus complex, C. 'pseudoppositus', C. maddeni and C. 'jacksoni'
     
20a(18b) Basal segment of antenna about 4 times as long as wide; three polytene chromosomes C. sp. Bakers Beach
20b A4 hardly longer than A3, four polytene chromosomes
(some specimens of C. tepperi may key to here if they have relatively well developed ventral tubules.  They have a sharply narrowing hind proleg; basal segment of antenna up to 5 times as long as wide; and four polytene chromosomes)
C. sp. bathophilus type

Einfeldia australiensis does not fit in this key as it is a more squat larva with only one pair of ventral tubules - rather like a Kiefferulus larva.  The dorsal surface has a large heart-shaped fenestra between the S4 setae.


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Modified: 7 November 2020
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