Account
What the sources say about this taxon, as written.
discussion · 
Plazi
Remarks In East Asia , this species was reported first by Tokunaga (1938: 319) based on specimens from Kyoto and Osaka in Palaearctic Japan , under the name Spaniotoma ( Trichocladius ) chalybeata Edwards, 1929 . The species was transferred to Rheocricotopus subsequently and recorded by several authors: e.g., Sasa & Kawai (1987a: 36 ; 1987b: 43 ); Sasa & Hasegawa (1988: 239) ; Sasa et al. (1988: 47) ; Sasa (1989: 67) ; Sasa & Okazawa (1992: 103) ; Sasa & Suzuki (1993: 114 ; 2000a: 6 ; 2001c: 21 ); Ree (2013: 219) ; and Liu et al. (2014a: 22) . The male has the following features: antennal ratio ca 1.0; thorax with large humeral pits; scutum without acrostichal setae; wing with a right-angled anal lobe and a short costal extension; legs with well-developed pulvilli; superior volsella thin, triangular: inferior volsella double-layered with an apically rounded dorsal lobe; and gonostylus sharply bent upward at the apex, with a small preapical crista dorsalis. Further, the abdomen tergites II–V have 3 to 5 paired longitudinal rows of setae as illustrated in Sasa (1990: 156 fig. 17i) and Sasa & Suzuki (2000b: 115 fig. 24i). Detailed re-examinations of the syntypes of R. okifoveatus Sasa, 1990 , and the holotypes of R. tedorisecundus Sasa, 1994 , R. shofukutertius Sasa, 1998 , R. isigadeeus Sasa & Suzuki, 2000 , R. yakulemeus Sasa & Suzuki, 2000 , R. inaquereus Sasa, Kitami & Suzuki, 2001 , R. inaxeyeus Sasa, Kitami & Suzuki, 2001 , Paratrichocladius yamasiroprimus Sasa, 1994 and Eukiefferiella toneefea Sasa & Tanaka, 2000 show those are junior synonyms of R. ( P. ) chalybeatus ( Edwards, 1929 ) . We found no significant difference among them. Yamamoto & Yamamoto (2018: 518) wrote: “ Rheocricotopus okifoveatus strongly resembles R. chalybeatus in many morphological characters. The former is separable from the latter by having a distinct crista dorsalis.” Almost all male specimens examined, including Chinese material, have a more or less distinct crista dorsalis. Occasionally, the crista dorsalis on the right and left differ in size and / or prominence. We found no corresponding pupal type with a similar size of the crista dorsalis as in the associated males, showing this is individual variation of the crista dorsalis. Likewise, we judged R . ( P .) taiwanensis Wang, Yan & Maa, 2004 as a junior synonym of R . ( P .) chalybeatus , although the holotype from Taipei wetland in Oriental China was not examined. Wang et al. (2004: 239) described R . ( P .) taiwanensis , believing that the bare wing veins and the preapical, semicircular crista dorsalis were sufficient to separate it from the other members of this subgenus. After evaluating our extensive material from wide geographical populations, such features can be regarded as intraspecific variation. In the original description of R. tedorisecundus , the author ( Sasa 1994: 52 ) wrote: “inner lobe of gonocoxite is absent, gonostylus without preapical tooth, and ninth tergite with a pair of highly chitinized finger-like processes at the base of anal point.” A re-examination of the holotype revealed that the crista dorsalis is small, and the inferior volsella is crushed by the coverslip and the dorsal lobe is transformed into a finger-like process beneath the base of anal point. Such errors often occur in the descriptions of Sasa and his coworkers. Also, when putting a label on the holotypes of R. fukuabeus Sasa & Tanaka, 2001 , R. inaxeyeus and Paratrichocladius yamasiroprimus , Sasa and co-authors made several errors. According to Sasa & Tanaka (2001: 54) , the holotype of R. fukuabeus , collected from the Tone River in Gumma Pref. on July 31, 2000 , should be given the registration number 393: 62, but our re-examination of the specimen (NSMTI-Dip 5339) revealed that this number actually is assigned to a specimen of Polypedilum ( Tripodura ) masudai ( Tokunaga, 1938 ) , with a label written, “ Tripodura , Kahokugata Lagoon, Ishikawa Pref. , 26.7.2000 , Sumida, 393: 62”. Although R. fukuabeus had been synonymized with R. ( P. ) chalybeatus by Ashe & O’Connor (2012: 562) and Yamamoto & Yamamoto (2014: 296) , the holotype may be lost. Further, after re-examination of the holotype of R. inaxeyeus , NSMT-I-Dip 5376 (No. 401 (2): 79), we found that the specimen possesses a label written “ Rheocricotopus inaquereus , Lake Inawashiro , 5-VIII-2000 , K. Kitami, L.T., 401 (2): 79, #43-10”. The features of the specimen are almost consistent with the original description of R. inaxeyeus rather than R. inaquereus , in the morphometric data, especially in the numbers of antepronotal, dorsocentral, and squamal setae. The authors ( Sasa et al. 2001: 19 ) possibly mistook the name R. inaquereus for the name R. inaxeyeu s in labelling. The true holotype of R. inaquereus is the specimen NSMT-I-Dip 5353 (No. 397: 10). Although the specimen NSMT-I-Dip 4860 (No. 227: 98) was labeled “ Holotype , Paratrichocladius yamasiroensis ”, the features are well consistent with the original description of Paratrichocladius yamasioiprimus . The author ( Sasa 1994: 30 ) evidently made a spelling mistake. In the descriptions of Paratrichocladius yamasiroprimus and Eukiefferiella toneefea , the authors ( Sasa 1994: 30 ; Sasa & Tanaka 2000: 40 , respectively) undervalued several features: well-developed humeral pit, large pulvilli in the legs and superior volsella in the gonocoxite, which is a combination peculiar to Rheocricotopus , rather than to Paratrichocladius and Eukiefferiella . Judging from the original descriptions ( Wang & Zheng 1989: 311 ), the features of R. ( P. ) emeiensis Wang & Zheng, 1989 and R. ( P. ) nigrus Wang & Zheng, 1989 are well consistent with those of R. ( P. ) chalybeatus . Additionally, photographs of the holotype males of R. ( P. ) emeiensis and R. ( P. ) nigrus taken by X. Lin (pers. comm. 2022) show that the superior volsella is plate-like, thin, triangular, and much resemble that of R. ( P. ) chalybeatus . Although we have not directly examined these holotypes , the Chinese species R. ( P. ) emeiensis and R. ( P. ) nigrus undoubtedly are junior synonyms of R . ( P. ) chalybeatus . Rheocricotopus nemoacrostichalis Chaudhuri & Sinharay, 1983 was described from India . The male resembles that of R. ( P. ) chalybeatus in the antennal ratio of 0.81, the scutum without acrostichal setae, the wing with a well-developed anal lobe and a slight costal extension, the gonocoxite with a double-layered, apically blunted inferior volsella, and the gonostylus with a sharply bent apex. According to the original description, however, the scutellum has setae in two rows, and the vein R 2+3 ends closer to R 1 than to R 4+5 , which are unusual features in Rheocricotopus . Further, the authors ( Chaudhuri & Sinharay 1983: 403 fig. 2f) drew the superior volsella as somewhat projecting posteriorly, with an acute-angled apex. As we have not examined the holotype , we cannot confidently synonymize the species with R. ( P. ) chalybeatus . Here, R nemoacrostichalis is treated as a questionable junior synonym of R. ( P. ) chalybeatus . Rheocricotopus (s. str.) heterochros Liu, Song & Wang, 2014 was described based on males from Xinjiang Uygur Autonomous Region in Palaearctic China . According to the authors ( Liu et al. 2014b: 102 ), the male is characterized by a bicoloured abdomen: tergite I entirely yellow; II–III yellow, posteromedially with a triangular brown patch; IV–V largely brown, laterally with yellow patches; remaining tergites entirely brown. Almost all features of the male agree with those of R. ( P. ) chalybeatus bicoloratus Caspers & Reiss, 1989 from Turkey . Although both holotypes of R. (s. str.) heterochros and R. ( P. ) chalybeatus bicoloratus are not examined here, we confirm that this colour pattern is mixed with the standard form in specimens collected from various geographical regions. The pattern varies between individuals in distinctness (see Fig. 3A ) and is considered intraspecific variation.