|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. (The current classification system can be found here.) |
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, the karyotypic studies of Jon Martin, and DNA studies with Ian Hogg, we have concluded that there are at least fifteen species of Chironomus in New Zealand. (Note that this only includes one of the two species described by Sublette & Wirth (1980) from the subantarctic islands), and includes an Australian species that may be a recent migrant. DNA studies are suggesting some of these are groups of closely related species as is common in other parts of the world.
Seven of the currently recognised species have a salinarius-type larva, and seven 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 larva of the fifteenth species is unknown.
(based on data of D.J. Forsyth)
|1a||Anal point stout||C. analis|
|1b||Anal point narrower||2a|
|2a(1b)||Abdominal tergites with dark saddle spots||5a|
|2b||Abdominal tergites with bands or patches covering most of the segment||3a|
|3a(2b)||Anterior tergites with a band over only about two thirds of the segment||4a|
|3b||Anterior tergites with band over most of the segment||C. 'thermarum'|
|4a(3a)||Pigmentation of the anterior tergites narrowing to the posterior edge||C. 'castaneum' (North Island)|
|4b||Pigmentation of anterior segments covering whole width of segment||7a|
|5a(2a)||Anterior LR generally above 1.5; only short sparse beard||C. forsythi (part)|
|5b||Anterior LR below 1.5; may or may not have beard||6a|
|6a(5b)||Lacking a beard||C. nr.'castaneum'|
|6b||Dense short beard and sparse long beard||C. zealandicus|
|7a(4b)||Anterior LR generally above 1.5; only short sparse beard (BR <3)||C. forsythi (part)|
|7b||Anterior LR probably just below 1.5, at least some longer beard (BR 3-7)||8a|
|note: *C. nr. antipodensis would also fit here, but LR not known|
|8a(7b)||Dense short beard and sparse longer beard (BR 4-7)||C. novaezelandiae|
|8b||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.
The Australian species C. 'pseudoppositus' has been recognized in New Zealand on the basis of mtCOI sequence, but the morphology has not been compared with that of Australian specimens.
SV typeIn 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).
|1a||Larva a salinarius-type||2a|
|1b||Larva with at least some development of ventral tubules||8a|
|2a(1a)||More than 60 striations on Ventromental plate||C. zealandicus (= C. species a)|
|2b||Less than 60 striations on Ventromental plate||3a|
|3a(2b)||Anal tubules relatively long sometimes with slight constriction near middle||C. forsythi|
|3b||Anal tubules relatively short, pointed or rounded||4a|
|4a(3b)||Frontoclypeal region of head pale or only slightly darkened||5a|
|4b||Frontoclypeal region very dark||6a|
|5a(2a)||c1 tooth of mentum broad and flattened, c2 teeth relatively separated (not type I)||sp. NZ9|
|5b||c1 tooth of mentum narrower, c2 teeth only partially separated (type I)||C. 'thermarum' (in part)|
|6a(4b)||c1 tooth of mentum broad (type IIA)||C. 'castaneum' group, 7a|
|6b||c1 tooth of mentum generally narrower.(usually type 3)||C. analis|
|7a(6a)||Teeth of mentum rounded||C. 'castaneum' and C. nr. 'castaneum'|
|7b||Teeth of mentum sharp||sp. NZ14|
|8a(1b)||Slight development of posterior ventral tubules only||C. 'thermarum' (in part)|
|8b||Two pairs of ventral tubules present||9a|
|note: for 8a, in thermal waters (but C. zealandicus, species 10 and sp. 12 can be also)|
|9a(8b)||Anal tubules relatively long, as in C. forsythi||sp. NZ8|
|9b||Anal tubules shorter and rounded||10(a)|
|10a(9b)||Head somewhat narrower, ratio mentum width/VHL less than 0.65, ventral tubules sometimes longer than 1.0 mm.||C. novaezelandiae|
|Note: Frontoclypeus generally darkened but sometimes pale or only slightly darkened (which group would include C. "spilleri"; C. sp. NZ10; and C. sp. NZ12). Variability possibly reflecting presence of more than one species.|
|10b||Head broader, ratio mentum/VHL above 0.65; with darkened frontoclypeus, ventral tubules about 0.5-1.0 mm.||C. sp. NZ7|
|Note: not in North Island|
Reference is also made to the mentum and mandible types originally devised by Webb & Scholl (1985) and Vallenduuk & Moller Pillot (1997) and Proulx et al. (2013), as well as a ventromental plate character. The previous classifications were made for relatively small numbers of species, but 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:
The mentum may be further classified by the characters of the central trifid tooth:
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).
Antennal ratio (AR) - measured on only the length of the sclerotized region of the segments, since the unsclerotized regions can expand to different extents in different specimens. Measured in this way the AR is usually higher.
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.
Type I - tooth fused
Type II - tooth partially free
Type III - tooth completely separated
Type A - tooth pale
Type B - some degree of pigmentation
Type C - as dark as other inner teeth
Chironomus zealandicus Hudson, 1892There 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).
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).