A review of Rheocricotopus (Psilocricotopus) chalybeatus species group from China, with the description of three new species (Diptera, Chironomidae)

Abstract The Rheocricotopus (Psilocricotopus) chalybeatus species group from China is reviewed. Three new species, R. (P.) brochus sp. n., R. (P.) rotundus sp. n. and R. (P.) serratus sp. n. are described as adult males. R. (P.) imperfectus Makarchenko & Makarchenko, 2005, R. (P.) robacki (Beck & Beck, 1964) and R. (P.) valgus Chaudhuri & Sinharay, 1983 are recorded from China for the first time and annotated. The diagnosis for the species group is emended and a key to adult males of the species group in China is presented.


Introduction
The genus Rheocricotopus was erected by Thienemann and Harnisch (1932). Originally, Edwards (1929) treated it as a group of the genus Spaniotoma Philippi, 1865. Brundin (1956 reaffirmed the valid generic status of Rheocricotopus to be followed by Lehmann (1969) and other workers. It can be separated from other orthoclad genera by the following combination of characters: hairy eyes; without dorsomedial extension; developed pulvilli; acrostichals beginning near antepronotum; plate-like superior volsella and pointed anal point with posterolaterally directed setae. The immature stages of Rheocricotopus can be collected in streams and rivers, rarely in the littoral zone of lakes (Cranston et al. 1989). So far, 70 species (Ashe and O'Connor 2012) were recorded in all zoogeographic regions in the world. Saether (1985) reviewed the genus Rheocricotopus Thienemann & Harnisch, 1932 in the world and divided the genus into two subgenera (Rheocricotopus sensu stricto and Psilocricotopus Saether) including six species groups (atripes species group, chalybeatus species group, godavarius species group, tuberculatus species group, fuscipes species group and effusus species group). Wang and Saether (2001) erected orientalis, a new species group. The Rheocricotopus chalybeatus species group can be distinguished from other species groups by the following combination of characters: gonostylus either with pronounced, preapical, triangular crista dorsalis or with apically sharp upward bend fused with apparent crista dorsalis; humeral pit moderately large, ovoid or circular, if large and somewhat rectangular gonostylus bent sharply upwards distally; superior volsella rounded, relatively small, never with projection. To date, 22 species were recorded in the chalybeatus species group (Saether 1985;Caspers 1987;Chaudhuri and Sinharay 1983;Hazra and Chaudhuri 2004;Johannsen 1932;Makarchenko and Makarchenko 2005;Sasa 1990Sasa , 1991Sasa and Suzuki 2000;Wang andZheng 1989, 1991;Wang et al. 2004).
Based on specimens from China, in this paper, three new species are described, and a key to the Chinese species of chalybeatus group is presented.
Female and immature stages unknown. Diagnosis. This species can be separated from its congeners by the following combination of characters: AR 0.89-1.15; R with 2-4 setae; squama with 8-14 setae; Costa not produced or scarcely produced.

Rheocricotopus
Remarks. The additional specimens mainly agree with the description of Lehmann and other workers. But costal extension of specimens from Oriental Region (35-40 μm long) longer than from Palearctic Region (0-15 μm long).
Distribution Diagnosis. This species can be separated from other members of the group by the following combination of characters: R bare; anal point short, pointed distally.
Remarks. The additional specimens are similar to the description of Wang and Zheng (1989 Diagnosis. The species is characterized by having a relatively high AR (1.14-1.24), very weak and short acrostichals, 8-14 dorsocentrals, reduced number of bristles on squama, anal tergite extending beyond tip of anal point, superior volsella triangular, crista dorsalis triangular, apex pointed.
Remarks. Chinese specimens mainly agree with the description of Saether (1969Saether ( , 1985. It is recorded in Palearctic Region for the first time. Chinese specimens have lower body length (2.55-3.13 mm) and lower AR 1.07 than species from Nearctic Region (total length 3.10-3.30 mm, AR 1.18).
Remarks. The new species resembles R. (P.) notabilits Caspers, 1987 in the following combination of characters: low AR; humeral pit medium, ovoid; the shape of anal point. But the new species can be separated from latter species on the basis of following characters: (1)  Coloration. Head and abdomen yellow, thorax dark brown.
Remarks. The new species resembles R. (P.) himalayensis Chaudhuri & Sinharay, 1983 in the triangular anal point, but it can be separated from the latter species on the basis of following characters: (1) costal extension of the new species much longer (50-88 μm), than R. (P.) himalayensis Chaudhuri & Sinharay (25 μm); (2) humeral Diagnosis. This species can be separated from other members of the group by the following combination of characters: R without seta; tergites I, II and anterior part of tergite V pale brown, tergites IV and VIII brown, anal point with 4-5 setae on each side and 1 seta at the base; gonocoxite with a prominent triangular basal lobe bearing 3-4 setae.
Remarks. The Chinese specimens generally agree with the original description by Chaudhuri and Sinharay (1983), though some measured differences between the Chinese specimens and those of Chaudhuri and Sinharay (1983) are shown in Table 5.