Chironomus samoensis Edwards

Original Description of C. samoensis: Insects of Samoa Part VI. Fasc. 2, Nematocera.
                "59.            Chironomus (s. str.) samoensis, sp. n.
Male Female    Head ochreous, palpi and antennal flagellum rather darker; plumes of male antennae pale.    Frontal tubercles present, of moderate size.    Last segment of m antennae quite three times as long as 2-11 together.    Thorax greenish; scutum with three reddish-orange stripes, the areas between the stripes dusted with silvery-grey.    Postnotum not darker than the scutal stripes.    Pronotum slightly emarginate in middle.    Abdomen of male (when not discoloured) green, tergites 2-4 each with a more or less diamond-shaped brown spot near base, 5 brownish, 6-8 darker brown, hypopygium pale.    Seen very obliquely from in front the segments are rather distinctly silvery-grey at the base; seen obliquely from behind the silvery dusting is on the posterior margins of 2-5 and nearly the whoile of 6-7.    Hypopygium with anal point moderately long and slender; claspers slender, not much enlarged at base; upper basal appendage rather small with a downward curved point; the structure almost as figured by Kieffer for Ch. imberbis.    Abdomen of female without distinct markings.    Legs greenish-yellow; tarsi a little darker, first two segments narrowly and rather indistinctly brown at tip.    No darkening on femora, nor on front tibiae.    First segment of front tarsi about 1.8 times as long as tibiae.    No tarsal beard.    Wings hyaline; r-m slightly darkened; venation as in other members of the dorsalis group.    Halteres pale.

            Length of body (male) 4.5-5 mm.; wing 3-3.5 mm.

Chironomus samoensis is very closely related to a number of described Australasian species, such as C. subdolus Skuse and C. imberbis Kieff, of the cosmopolitan dorsalis group.    It does not quite agree with specimens of C. subdolus in the British Museum, and is not represented in the collections from the Society Is. and Fiji.    From C. hawaiiensis Grim, it differs chiefly in the absence of dark preapical rings on the femora."

The description of the upper basal appendage (SV), and the list of species to which this species is compared, is important here - all of these species have a D type SV, whereas, Tokunaga (1964) (although noting the hypopygium is of the dorsalis type) illustrates it with a triangular apex which can be misinterpreted as an S-type.    The specimens described by Tokunaga from Micronesia are probably C. samoensis, and the illustration is presumably intended to depict the somewhat beaked SV seen in some specimens.    The misinterpretation of this illustration may be partly responsible for the identification of C. samoensis in other locations, which have an S type SV. However, they also differ in other characters and are misidentifications. mis-identifications.

While the females are largely dismissed as 'like the male apart from the usual sexual differences', the relative lengths of the fore leg segments appear to be useful in separating the species of this group.
Tokunaga makes the important point that the fore tarsus has Ta4 far longer than Ta3, and slightly longer than Ta2, although examination of a pharate female from Tutuila, American Samoa, suggests that Ta2 and Ta4 can be about equal in length.