AUSTRALIAN CHIRONOMUS SPECIES

Compiled by Jon Martin
Genetics Department, 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.

This listing is also available in pdf format (6.2 MB)(Updated 7 January 2014).

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
Chironomus 'februarius' - currently nomen nudum, but described in Martin 1966
Chironomus nepeanensis Skuse
Chironomus 'pseudoppositus' - currently nomen nudum, but described in Martin 1966
Chironomus tepperi Skuse

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

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

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

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


In the adult descriptions 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 SV 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 SV 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 SV 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

    1.    Wing with dark spot over cross vein and with fuscous clouds, particularly in cell R5. . . . . . . . . . . . . . . . . . . . . C. pallidinubeculosus
          Wing with at most some darkening of cross vein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.


    2.    Legs shorter than usual, posterior LR about 0.5; male hypopygium enlarged, anal point deep and laterally flanged . . . 3.
          Posterior LR about 0.7 or higher; male hypopygium of normal type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.


    3.    Thorax dull grey, pits of dorsocentral setae very distinct; inferior volsella of male very swollen . . . . . . . . . . . . . . C. tepperi
          Thorax greenish with brown stripes, pits normal; inferior volsella of male not swollen . . . . . . . . . . . . . . . . . . C. magnivalva


    4.    Wing length greater than 5 mm; anterior tarsi of males bearded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.
          Wing length less than 5 mm; anterior tarsi of males bearded or unbearded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.


    5.    Distributed on east of the continent, including Tasmania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.
          Distributed on the west of the continent, including Northern Territory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. occidentalis


    6.    Mid femur more than 1.12 times the anterior femur (likely to be) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. duplex
          Mid femur shorter than the anterior femur (likely to be) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. australis


    7.    Blackish species. Male with bearded anterior tarsi and spatulate superior volsella . . . . . . . . . . . . . . . . . . . . . . . C. 'timmsi'
          Paler species, at most brown.  Male tarsi not bearded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.


    8.    Thorax pale, anterior femur and tibia pale, tarsi with dark pattern, anal point long and tubular . . . . . . . . . . . . . . . . . . . . 9.
          Thorax partly pale but with lateral vittae darker, legs pale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. 'queenslandicus'


    9.    Tarsi darkened at both apex and base, anal point tubular. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. javanus
          [Tarsi darkened only at distal ends, anal point larger and narrowed at base, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. nr. samoensis
          [superior volsella boot shaped or beaked
Chironomus cloacalis (Abdominal tergites generally dark with pale posterior band, but may have saddle spots; AR 3.34 - 4.24; LR 1.44 - 1.78), Chironomus 'februarius' (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.), Chironomus '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: Chironomus oppositus (LR 1.5 - 1.8; wing length 2.8 - 3.6, Chironomus maddeni (AR 2.55 - 2.86; LR 1.6 - 1.8; wing length 2.4 - 3.36 mm), Chironomus '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).
- need to be inserted at 8.
Norfolk Island species: Species 1 may be near C. samoensis, superior volsella closest to Strenzke's type D(d), LR about 1.54 (i.e. lower than C. nr. samoensis, but in range of C. samoensis itself).
Species 2 has an superior volsella that is closest to Strenke's type D(f), but appears to have a flattened end. LR about 1.27.

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

VENTROMENTAL PLATE RATIO - 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

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

Provisional Key to 4th Instar Larvae

    1.     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) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
          Medium sized larvae, length up to about 19 mm, ventral head length less than 400 µm.
          (bathophilus- or plumosus-type larvae with pale to moderately darkened gular or
          frontoclypeal regions) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

    2.    Head capsule heavily darkened, bathophilus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
          Head capsule only slightly darkened on the gular region, slender plumosus-type . . . C. nepeanensis

    3.    Distributed on east side of the continent only (NSW, VIC, SA, Tas) . . . . . . . . . . . . . . . . . . . . . . 4
          Distributed on west of continent only (WA & perhaps NT) . . . . . . . . . . . . . . . . . . . . C. occidentalis

    4.    Teeth of mentum rounded (when not worn), side teeth of centre trifid tooth
        only partially distinct from central tooth. Four polytene chromosomes . . . . . . . . . . . . . . . . C. australis
        Teeth of mentum square sided and pointed, side teeth well separated from
        central tooth. Three polytene chromosomes, inversion polymorphism . . . . . . . . . . . . . . . . . . C. duplex

    5.    Larvae with lateral tubules (NB. often polymorphic) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
          Larvae without lateral tubules, ventral tubules reduced to some extent . . . . . . . . . . . . . . . . . . . . . . 12
          (NB. often polymorphic)

    6.    Larvae of the true plumosus type (posterior VT coiled) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
          Larvae of the melanotus or semi-reductus type (posterior VT bent) . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    7.    Head capsule generally darkened on both the gula and frontoclypeus . . . . . . . . . . . . . . . . . . . . . . . . 8
          Head capsule darkened in gular region only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

    8.    Both gula and frontoclypeus quite heavily darkened . . . . . . . . . . . . . . . . . . . . . C. cloacalis (majority)
          Gula and frontoclypeus slightly to moderately darkened, tropical species . . . . . . . . . . . . . . . . . . . . . 9

    9.    c2 teeth of mentum sharp and well separated (type II) . . . . . . . . . . . . . . . . . . . . . . . . . C. nr. samoensis
          c2 teeth of mentum only partially separated (type I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. magnivalva

   10.    Lateral tubules tending to be more ventrally placed, premandible with 7 teeth . . . . . . . . C. javanus
            Larvae not as above, premandible with the normal 2 teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

   11.    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

          Basal segment of antenna more than 4 times as long as wide:
            C. 'februarius' (Central trifid tooth type I); C. circumdatus (Central trifid tooth type III);
            C. bicoloris (Central trifid tooth type IV, but could appear to be Type II if worn);
            C. 'queenslandicus' (Central trifid tooth type I) (in part); and the pale headed C. cloacalis
            (Central trifid tooth type I).

   12.    Larvae of the halophilus-type (i.e. ventral tubules reduced, often only
            the posterior pair developed), head capsule pale.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. tepperi
            Larvae of the bathophilus-type (i.e. both pairs of ventral tubules developed,
            but short and not coiled).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

   13.    Head capsule pale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
            Head capsule with at least some darkening on the gula and frontoclypeus . . . . . . . . . . . . . . . . . . 15

   14.    Basal segment of antenna 3 to 3.5 times as long as wide; four polytene chromosomes . . . C. 'timmsi'
            Basal segment of antenna about 4 times as long as wide; . . . . . . . . . . . . . . . . . . . . C. sp. Bakers Beach
            three 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 5 times as long as
            wide; and four polytene chromosomes)

   15.    Antennal ratio A2/A1 more than 0.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. sp. (bathophilus-type)
            Antennal ratio A2/A1 less than 0.3
          C. oppositus forms;    C. 'pseudoppositus';    C. maddeni;    C. 'jacksoni'.

   16    Lateral tubule over 200 micron; antennal ratio A2/A1 more than 0.3; inner margins of
            ventromental plates separated by only about 0.2 of mentum width . . . . . . . . . . . C. 'queenslandicus'
          Lateral tubules less than 200 micron; antennal ratio A2/A1 less than 0.3
          C. oppositus forms oppositus, and whitei; and C. 'tyleri'.

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