Rheocricotopus (s. str.) togapeniculus Sasa & Okazawa, 1992 Figs 28–29, Table 25 Rheocricotopus (Rheocricotopus) togapeniculus Sasa & Okazawa, 1992: 104. Rheocricotopus kamimonji Sasa & Hirabayashi, 1993: 364. Syn. nov. Rheocricotopus kurocedeus Sasa, 1996a: 19. Syn. nov. ? Rheocricotopus fuscipes [nec Kieffer, 1909] – Hirabayashi et al. 1998: 805. Rheocricotopus (Psilocricotopus) kamimonji – Sasa & Tanaka 1998: 38. — Saether et al. 2000: 161. — Ashe & O’Connor 2012: 565. — Yamamoto & Yamamoto 2014: 297. Rheocricotopus (Psilocricotopus) kurocedeus – Saether et al. 2000: 161, misspelled as R. (Psilocricotopus) kurodeceus. — Ashe & O’Connor 2012: 565. — Yamamoto & Yamamoto 2014: 297 — Fu et al. 2016: 264. Rheocricotopus (Rheocricotopus) togapeniculus – Saether et al. 2000: 161. — Ashe & O’Connor 2012: 572. — Yamamoto & Yamamoto 2014: 298. — Fu et al. 2016: 273. Rheocricotopus (Rheocricotopus) eminellobus [nec Saether, 1969] – Makarchenko & Makarchenko 2005: 130. Type material Holotype of Rheocricotopus (s. str.) togapeniculus JAPAN – Toyama • ♂; Toga, Toga River; 16 Apr. 1990 (emerged 24 Apr. 1990); T. Okazawa and M. Sasa leg.; NSMT, NSMT-I-Dip 4709 [No. 181: 29]. Holotype of Rheocricotopus kurocedeus JAPAN – Toyama • ♂; Lake Kurobe; 14 Oct. 1994; M. Sasa leg.; NSMT, NSMT-I-Dip 4988 [284: 31]. Type specimen of R. kamimonji was not examined. Other material examined JAPAN – Fukushima • 1 ♂; Naraha, Kido River; 37°16′ N, 140°58′ E; 28 m; 24 Oct. 1991; H. Niitsuma leg.; PCHN • 1 ♂ with 1 Pe; Iwaki, Hisanohama, Obisa River; 37°08′ N, 140°58′ E; 18 m a.s.l.; 11 Apr. 1991; H. Niitsuma leg.; PCHN • 3 ♂♂ with 3 Pe, 4 ♀♀ with 3 Pe; Iwaki, Yaguki; 37°8′ N, 140°54′ E; 123 m a.s.l.; 3 Jan. 1997 (emerged 6–21 Jan. 1997); H. Niitsuma leg.; PCHN • 4 ♂♂ with 4 Pe; same data as for preceding; 2 Jan. 1998 (emerged 26 Jan. – 7 Feb. 1998); PCHN • 1 ♂ with 1 Pe; same data as for preceding; 20 Mar. 2000 (emerged 26 Mar. 2000); PCHN • 1 ♂ with 1 Pe; same data as for preceding; 15 Aug. 2001 (emerged 29 Aug. 2001); PCHN • 1 ♂ with 1 Pe; same data as for preceding; 14 Oct. 2002 (emerged 25 Oct. 2002); PCHN. – Kanagawa • 1 ♂ with 1 Pe; Kiyokawa, Miyagase; 35°30′ N, 139°12′ E; 290 m a.s.l.; 7 Feb. 1998 (emerged 28 Mar. 1998); H. Niitsuma leg.; PCHN. – Miyagi • 1 ♂ with 1 Pe; Shiroishi, Yukawa River, Kamasaki Hot Spring; 38°15′ N, 140°34′ E; 189 m a.s.l.; 1 Jan. 1997 (emerged 19 Jan. 1997); H. Niitsuma leg.; PCHN. – Nagano • 1 ♂ with 1 Pe; Kawakami; 35°58′ N, 138°34′ E; 1220 m a.s.l.; 20 Jun. 1991 (emerged 28 Jun. 1991); H. Niitsuma leg.; PCHN. – Shizuoka • 1 ♂ with 1 Pe and 1 Le, 1 ♂ with 1 Pe; Ikawa, Dainichi Pass, stream; 35°11′ N, 138°15′ E; 1100 m a.s.l.; 4 Mar. 2000 (emerged 9 Mar. 2000); H. Niitsuma leg.; PCHN • 1 ♂ with 1 Pe and 1 Le; same data as for preceding; 28 Mar. 2001 (emerged 9 Apr. 2001); PCHN • 1 ♂ with 1 Pe; Aoi-ku, Ikawa, River Well Ski Area; 35°12′ N, 138°16′ E; 1400 m a.s.l.; 15 Nov. 1997 (emerged 15 Feb. 1998); H. Niitsuma leg.; PCHN • 2 ♀♀ with 2 Pe; Aoi-ku, Kadoya River; 35°3′ N, 138°22′ E; 85 m a.s.l.; 21 Dec. 1997 (emerged 11 Jan. 1998); H. Niitsuma leg.; PCHN • 1 ♂; Aoi-ku, Ashikubo, stream; 35°2′ N, 138°22′ E; 77 m a.s.l.; 4 Apr. 1987; H. Niitsuma leg.; PCHN • 3 ♂♂ with 1 Pe; same data as for preceding; 15 Feb. 1996 (emerged 22–26 Feb. 1996); PCHN • 1 ♂ with 1 Pe; Aoi-ku, Kujiragaike Pond, unnamed stream; 35°02′ N, 138°23′ E; 80 m a.s.l.; 27 Nov. 1987 (emerged 15 Nov. 1987). H. Niitsuma leg.; PCHN. – Tochigi • 1 Pe; Ichikai, Miage; 36°36′ N, 140°7′ E; 116 m a.s.l.; 13 Apr. 1989; H. Niitsuma leg.; PCHN. Description Male (n = 26) Total length 2.0–3.4, 2.5 mm. COLOURATION. Thorax dark brown. Abdomen brown, usually somewhat darker on T V–IX. Legs uniformly brown. HEAD. Temporals 3–7, 4. AR 0.89–1.20, 1.01. Clypeus with 8–16, 10 setae. Lengths (μm) of Pm 1–5: 25–44, 34 (24); 44–62, 52 (24); 86–135, 110 (24); 86–135, 113 (24); 160–231, 195 (24), respectively. Pm 4 /Pm 3 1.0–1.2, 1.0 (24); Pm 5 /Pm 4 1.5–1.9, 1.7 (24). Pm 3 with 2–6, 4 (25) SCl; Pm 4 occasionally with 1 (6) SCl. THORAX. Lateral Aps minute, 0–3, usually absent (25). Ac 14–30, 20 (23), and longest 11–24, 17 μm long; Dc 4–8, 6 (25); H absent; Pa 2–5, 3; Scts 4–10, 6. HP (Fig. 28A) composed of fused several small holes, occasionally invisible. WING (Fig. 28B). Length 1.6–2.5, 2.0 (25) mm. C extension slightly to moderately long, 25–66, 45 (24) μm. VR 1.1–1.2, 1.1 (25). R with 4–16, 8 setae; R 1 with 0–1 seta, usually bare, and R 4+5 with 0–6, 1 (25) seta. AnL obtuse. Sq with 2–14, 6 (25) setae. LEGS. P 1 with ti spur 38–54, 44 μm long; P 2 with 2 ti spurs 15–23, 19 and 15–20, 18 μm long; P 3 with 2 ti spurs 38–51, 44 and 16–20, 18 (25) μm long. P 2–3 usually without Sch, each rarely with 1 (1) Sch on ta 1. P 3 with ti comb of 11–16, 13 (25) bristles. Lengths and proportions of legs as in Table 25. ABDOMEN. Hypopygium (Fig. 28C) with AnP pointed apically, bearing 4–12, 7 (25) lateral setae. Gc145– 192, 169 μm long with SVo (Fig. 28D) right-angled at apex to somewhat roundly protruded inwardly; IVo double-layered, dorsally with narrow dorsal protrusion. Gs (Fig. 28E) 59–79, 68 μm long, roundly convex in outer margin; CD absent. HR 2.19–2.84, 2.48 (25). Female (n = 6) Total length 2.2–2.7, 2.4 (5) mm. COLOURATION. Similar to male. Sca dark brown HEAD. Temporals 4–8, 6. Antenna 5-segmented; Fm 5 91–108, 98 μm long, shorter than combined length of Fm 3 and Fm 4; AR 0.36–0.43, 0.38. Clypeus with 9–14, 12 setae. Lengths (μm) of Pm 1–5: 37–44, 41 (4); 52–62, 58 (4); 108–128, 115 (4); 123, 123 (3); 209–234, 222 (4), respectively. Pm 4 /Pm 3 1.1, 1.1 (3); Pm 5 /Pm 4 1.7–1.8, 1.8 (3). Pm 3 with 3–7, 5 (5) SCl. THORAX. Lateral Aps 2–3, 2 (5). Ac 16–29, 23 (4); Dc 9–15, 12 (5) including 1–4, 2 (5) H; Pa 2–6, 4. Sct 6–7, 7. WING. Length 1.8–2.3, 2.1 mm. C extension moderately long. VR 1.0–1.1, 1.1. R with 14–23, 20; R 1 with 6–13, 10; R 4+5 with 25–40, 35 setae. Sq with 7–10, 8 setae. LEGS. P 1 with ti spur 23–28, 26 μm long; P 2 with 2 ti spurs 18–23, 20 and 16–20, 18 μm long; P 3 with 2 ti spurs 44–54, 48 and 16–20, 18 μm long. P 2–3 each with ta 1 bearing 0–3, 2 Sch. P 3 with ti comb of 12–15, 13 bristles. Lengths and proportions of legs as in Table 25. GENITALIA (Fig. 28F). S VIII with 14–19, 16 setae. T IX (Fig. 28G) divided into 2 protrusions, with 11– 16, 13 setae in total. Gc IX with 7–12, 10 setae on each side. Ce 64–89, 77 μm long. No 103–119, 111 μm long. Sca 89–113, 103 (4) μm long, 1.4–1.8, 1.7 (4) × as long as broad; neck conical; ducts without loop. Pupa (n = 26) Total length 2.4–3.7, 3.0 mm. COLOURATION. Exuviae pale brown, darkened on apophyses, and central and posterior spines on abdominal tergites. CEPHALOTHORAX. FA (Fig. 29A) weakly and sparsely pebbled, with FS 73–122, 92 (16) μm long. Thoracic horn 232–310, 273 (25) μm long, 3.3–6.1, 4.2 (14) × as long as broad. Lengths (μm) of Pc 1–3: 135–197, 170 (21); 111–197, 152 (21); 44–123, 78 (21), respectively. Three precorneals arranged in triangle. Lengths (μm) of Dc 1–4: 34–74, 48; 27–79, 50; 12–42, 30; 25–74, 44, respectively. Distances (μm) of Dc 1 –Dc 2, Dc 2 –Dc 3, Dc 3 –Dc 4: 62–123, 95; 22–86, 44; 10–44, 23, respectively. Dc 2–4 usually arranged in straight line, occasionally in triangle. ABDOMEN (Fig. 29B). T I–II without spinulation. T III–V each with more or less extensive spinulation. T VI–VII with posterior spinulation. T VIII with triangular, posterior spinule patch along median line. T IX with anterior spinulation. T IV–VI each with one median, rounded patch of spines, occasionally T III (Fig. 29C) with ill-defined median spine patch. Rows of simple spines present on posterior margins of T II–VIII; posterior spines weak on T II, VII–VIII, occasionally absent on T VIII. Anteriorly directed spinules present, posterior to spine rows on T II–V. PSB somewhat low on A II–III. Usually A I with 2 L-setae; II–IV each with 3 L-setae, occasionally IV with 4 L-setae; V–VI each with 4 L-setae, occasionally 3 L-setae; VII with 4 LS-setae; VIII with 5 LS-setae. AL 177–271, 226 (24) μm long, 1.6–2.0, 1.8 (24) × as long as broad, with 8–16, 11 (24) lateral taeniae on basal ⅔–¾; male genital sac 1.1–1.3, 1.2 (9) as long as AL. Larva (n = 2) COLOURATION. Head yellow with dark brown mentum, apical ⅔ of mandible, and postoccipital margin. HEAD. PM 187–197 μm long. Dorsal surface (Fig. 29D) with frontoclypeolabrum and lateral labral sclerites. SI bifid on labrum. Antenna (Fig. 29E) 5-segmented. Lengths (μm) of 1st to 5th antennal segments: 59, 16–18, 10–11, 7–8, 8, respectively. AR 1.3–1.4. First segment 3.0 × as long as broad, with RO located 0.14 from base and 2 SA each located 0.13–0.14 and 0.28–0.31 from base; with blade 39– 41 μm long, reaching apex of 4th segment. Second segment apically with LO 10 μm long, and St 3 μm long. Labrum with Pm 62–65 μm long. Mandible (Fig. 29F) 119–127 μm long, with apical tooth shorter than combined width of 3 inner teeth; Si with 7 branches including 2 or 3 apically serrated branches. Maxilla (Fig. 29G) with PG consisting of 9 distinct teeth; anterior LCh 3.3–4.3 × as long as broad. M (Fig. 29H) with 2 simple median teeth; combined width of 2 median teeth 26–27 μm. Vmp 16 μm wide at most, with 14–16 beard setae beneath. BODY. With setae 62 μm long. Pc (Fig. 29I) 23 (1) μm long, 1.8 (1) × as long as broad, with 2 spurs and 3 anal setae. Squashed small claws (Fig. 29J) present on PP. Distribution The species is known from Palaearctic Japan and the Russian Far East. Remarks Although the holotype was badly damaged during mounting, the double-layered inferior volsella with a dorsal protrusion and the gonostylus with no crista dorsalis and rounded outer margin are recognizable in the specimen. Additionally, the small humeral pit consisting of several (10–12), partly fused holes and the wing with an obtuse anal lobe and a slight costal extension are also distinctive in the specimen. More additional features were clarified in newly collected materials from Japan. The humeral pit is invisible in some specimens. The superior volsella is thick and nearly right-angled at the apex in dorsal view, but it also looks like a rounded protrusion in other views or by different pressure from the coverslip. Rheocricotopus kamimonji Sasa & Hirabayashi, 1993 was described based on a single male from Nagano Prefecture in Palaearctic Japan. Although we have not examined the holotype, judging from the original description (Sasa & Hirabayashi 1993: 364) there is no significant difference between the males of R. (s. str.) togapeniculus and R. kamimonji. The latter species is a junior synonym of R. (s. str.) togapeniculus. The holotype of the latter may be lost. Rheocricotopus kurocedeus Sasa, 1996 was described based on a single male from Toyama Prefecture, Japan. The author (Sasa 1996a: 19) wrote: “Gonostylus simple, … with a long and stout megaseta but without preapical tooth.” Nevertheless, Fu et al. (2016: 265) wrote: “Gonostylus 70 µm long, with small triangularly pointed costa dorsalis [sic].” Our re-examination of the holotype showed a gonostylus lacking any crista dorsalis. Further, Sasa (1996a: 19) wrote: “it is closest to R. togapeniculu s Sasa et Okazawa, 1992 and R. kamimonji Sasa et Hirabayashi, 1993, in that antennae are the normal type and AR is ca 1.0, and humeral pits are small, but differs also from both in the structure of inner lobes of gonocoxite and of anal point.” We compared the holotype male of R. kurocedeus to that of R. (s. str.) togapeniculus. Although the inferior volsella of the latter is deformed by a poor mounting procedure, it is distinctly recognizable that in the former, the inferior volsella is armed with a finger-like dorsal projection, not a rounded protrusion as shown in Fu et al. (2016: 264 fig. 3b–c). Additionally, there is no significant difference between both the structures of anal point. Rheocricotopus kurocedeus undoubtedly is a junior synonym of R. (s. str.) togapeniculus. Makarchenko & Makarchenko (2005: 130) gave a brief re-description of R. (s. str.) eminellobus Saether, 1969 belonging to the fuscipes group, based on males from Primorsky in the Russian Far East. The male of R. (s. str.) eminellobus is similar to that of R. (R.) togapeniculus in the small humeral pit and the gonostylus with no or indistinct crista dorsalis, but separable from it by the relatively thin, roundly protruded superior volsella and the somewhat broad, triangular inferior volsella (see Saether 1969: 86 fig. 43, 1971: 1250 fig. 8f). The male of R. (s. str.) eminellobus sensu Makarchenko & Makarchenko (2005: 132 figs 16–17) has nearly triangular, thick superior volsellae and narrowly projected, finger-like inferior volsellae. The species is not true R. (s. str.) eminellobus, but belongs to R. (s. str.) togapeniculus. Hirabayashi et al. (1998: 805) recorded a male of R. (s. str.) fuscipes (Kieffer, 1909) from the Oze Moor in Gunma, Japan but without any morphological account. The male of R. (s. str.) fuscipes also resembles that of R. (s. str.) togapeniculus in the small indistinct humeral pit, and the gonostylus roundly convex in outer margin, with indistinct or no crista dorsalis, but differs from it in the semicircular superior volsella, and the triangular inferior volsella without conspicuously projecting apex (Goetghebuer 1932: 57 fig. 93, as Trichocladius dispar Goetghebuer, 1913; Albu 1968: 462 fig. 8, as R. dispar; Lehmann 1969: 367 fig. 4, as R. dispar (Goetghebuer, 1913); Langton & Pinder 2007: 139 fig. 72g). So far, R. (s. str.) fuscipes has been known from Europe, North Africa and West Asia (Ashe & O’Connor 2012: 570). On the other hand, R. (s. str.) togapeniculus is distributed in Japan: Fukushima, Tochigi and Nagano Prefectures, near Gunma Prefecture. Although we have not examined their voucher specimen, there is a high possibility that the species is R. (s. str.) togapeniculus. The pupa of R. (s. str.) togapeniculus will key to that of R. (s. str.) tamahumeralis in Saether (1986). Indeed, these pupae are very similar to each other. However, the tergal spinulation of abdomen generally is weaker than that of R. (s. str.) tamahumeralis, and is absent on tergite II. The pupa of R. (s. str.) tamahumeralis has anterolateral and posteromedial spinulation on tergite II. The ventromental plate with 14–16 beard setae beneath and the antennal ratio of 1.3–1.4 does not allow the larva of R. (s. str.) togapeniculus to key beyond couplet 8 in Saether (1986). It resembles that of R. (s. str.) tamahumeralis in the number of beard setae underneath the ventromental plate and the value of antennal ratio, but differs in the fused frontoclypeolabrum. In R. (s. str.) tamahumeralis, the larva has a frontoclypeus separated from the labral sclerite.

Published as part of Niitsuma, Hiromi & Tang, Hongqu, 2026, Taxonomic review of Rheocricotopus Brundin, 1956 (Diptera: Chironomidae: Orthocladiinae) from East Asia, with descriptions of twelve new species, pp. 1-114 in European Journal of Taxonomy 1037 on pages 95-101, DOI: 10.5852/ejt.2026.1037.3157, http://zenodo.org/record/18507203