New Zealand Chironomus

NEW ZEALAND CHIRONOMUS SPECIES
Larval types and Karyotypes

Integration of data of Jon Martin¹ and Don Forsyth
¹ Genetics Department, University of Melbourne, Victoria, 3010, Australia

When Freeman (1959) revised the New Zealand Chironomidae he recognized two species of the genus Chironomus (s.s.): C. zealandicus and C. analis. However, even at this stage it was known that adults of C. zealandicus could be produced from two distinct larval types, a salinarius-type (lacking ventral tubules) or a so-called "thummi-type" (with ventral tubules)(Forsyth, 1971), although in fact the latter are a bathophilus-type. Analysis of the polytene chromosomes further indicated that there were different chromosome number forms of both the salinarius- and the thummi-type larvae ( Lentzios et al., 1980), which appeared to be distinct species. With the integration of the morphological and ecological analyses of Don Forsyth, and the karyotypic studies of Jon Martin, we have concluded that there are at least twelve species of Chironomus in New Zealand. (Note that this does not include the two species described by Sublette & Wirth (1981) from the subantarctic islands).
Five of these species have a salinarius-type larva, the six others are bathophilus-type, although one is polymorphic for ventral tubule development, some having only slight development of the posterior pair of ventral tubules (halophilus-type). The current classification system can be found here.

This listing is also available in pdf format (2.1 MB)(Updated 29 March 2011).

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

Provisional Key to Adult Males
(based on data of D.J. Forsyth)

1. Anal point stout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. analis
Anal point narrower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Abdominal tergites with dark saddle spots . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 5
Abdominal tergites with bands or patches covering most of the segment . . . . . . . . . . . . . . . . 3

3. Anterior tergites with a band over only about two thirds of the segment . . . . . . . . . . . . . . . . 4
Anterior tergites with band over most of the segment . . . . . . . . . . . . . . . . . . . . C. 'thermarum'

4. Pigmentation of the anterior tergites narrowing to the posterior edge . . . . . . . . C. 'castaneum'
Pigmentation of anterior segments covering whole width of segment . . . . . . . . . . . . . . . . . . . 6

5. Anterior LR generally above 1.5; only short sparse beard . . . . . . . . . . . . . . . . C. forsythi (part)
Anterior LR below 1.5; dense short beard and sparse long beard . . . . . . . . . . . C. zealandicus

6. Anterior LR generally above 1.5; only short sparse beard (BR <3) . . . . . . . . . C. forsythi (part)
Anterior LR probably just below 1.5, at least some longer beard (BR 3-7) . . . . . . . . . . . . . . . 7

7. Dense short beard and sparse longer beard (BR 4-7) . . . . . . . . . . . . . . . . . . C. novae-zelandiae
Moderate beard (BR 3-4) (based on only 1 specimen) . . . . . . . . . . . . . . . . . . . . . C. sp. NZ12

Note that the adults of some species are unknown.
The adults of C. 'spilleri', C.sp. NZ10 (not known), and C.sp. NZ12 are assumed to be similar to those of C. novae-zelandiae since Don Forsyth included them all under that name.

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).

Provisional Key to Larvae

1. Larva a salinarius-type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Larva with at least some development of ventral tubules. . . . . . . . . . . . . . . . . . . . .7

2. More than 60 striations on Ventromental plate. . . . . . . . . . . . . . . . .C. zealandicus (= C. species a)
Less than 60 striations on Ventromental plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

3. Anal tubules relatively long sometimes with slight constriction near middle . . . . . .C. forsythi
Anal tubules relatively short, pointed or rounded. . . . . . . . . . . . . . . . . . . . . . . . . . . .4

4. Frontoclypeal region of head pale or only slightly darkened. . . . . . . . . . . . . . . . . . . . 5
Frontoclypeal region very dark, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5. c1 tooth of mentum broad and flattened, c2 teeth relatively separated (not type I). . . . sp. NZ9
c1 tooth of mentum narrower c2 teeth only partially separated on shoulders of c1 (type I).C. 'thermarum' (in part)

6. c1 tooth of mentum broad (type II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. 'castaneum'
c1 tooth of mentum generally narrower.(usually type 3) . . . . . . . . . . . . . . . . . . . . . . . C. analis

7. Slight development of posterior ventral tubules only. . . . . . . . . . . . . . . . . . . . .C. 'thermarum' (in part)
In thermal waters (but C. zealandicus/species 10 and sp. 12 can be also)
Two pairs of ventral tubules present. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

8. Anal tubules relatively long, as in C. forsythi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .sp. NZ8
Anal tubules shorter and rounded. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

9. Head somewhat narrower, ratio mentum width/VHL less than 0.65 . . . . . . . . . . . . . . C. novae-zelandiae
with frontoclypeus generally darkened but sometimes pale or only slightly darkened
(which group would include C. 'spilleri'; sp. NZ10; and sp. NZ12)

Head broader, ratio mentum/VHL above 0.65; with darkened frontoclypeus.. . . . . . . . . . . . . sp. NZ7
Not in North Island.

In the following descriptions, reference is made to the mentum and mandible types as described for European Chironomus species by Webb & Scholl (1985) and Vallenduuk & Moller Pillot (1997)
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 A - c2 teeth only partially separate from c1, i.e. as shoulders on c1 (fig. a).
Type B - c2 teeth slightly more separated (fig. b).
Type II - c1 broad, c2 teeth distinctly separated (fig. c). (fig. d often due to wear).
Type III - c1 tooth relatively narrow and much higher than the separated c2 teeth (figs. e and f)
Type D - C2 teeth well separated (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.
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

This figure shows IA; IIB; IIIC respectively

Chironomus zealandicus Hudson, 1892

There have been several attempts to relate C. zealandicus to one of the cytologically known species, and it has been suggested at different times that it was either species 1 (Forsyth, 1978 and Martin, 1998) or C. species a (Martin, 1996).
However, species 1 can be ruled out because there is an entry in Hudson's journal that he reared the specimens of C. zealandicus from larvae without ventral tubules. Forsyth therefore thinks that C. species a is the species that corresponds to Hudson's C. zealandicus. This is supported further by the fact that C. species a is the largest of the reared species, about the size of Hudson's C. zealandicus specimens.
The name is therefore used in this sense in this work.

Chromosome banding patterns have been published using the Australian standard system of Martin (1964), but are in process of being switched to the more universally used (although more difficult to uniquely specify bands) system of Keyl (1962) and Devai et al. (1989).

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