Chasmatonotus yamamotoi Saigusa, 2024, sp. nov.

Chasmatonotus yamamotoi sp. nov. (Figs. 1–4) Type material. HOLOTYPE. ♂ labelled: “Nogodan 1100–1200 m [35º18’57” N, 127º35’09” E], Chili-san, Sannae Myeon, Korea, May 13, 1991, T. Saigusa col.“, “HOLOTYPE/ Chasmatonotus / yamamotoi/ Saigusa [red label]”. PARATYPES: 20 ♂, 1 ♀, same data as holotype; 23 ♂, 2 ♀, Manbokdae 1000–1200 m [35º21’14” N, 127º31’14” E], Sannae Myeon, Korea, May 14, 1991, T. Saigusa col.; 3 ♂, 1 ♀, Samjonri 1100–1300 m [35º19’52” N, 127º35’58” E], Chili-san, Sannae Myeon, Korea, May 15, 1991, T. Saigusa col. The holotype is presently preserved in Kyushu University Museum, Fukuoka and eventually should be gifted to an authorized museum in Korea. Paratypes are gifted to Kyushu University Museum, Canadian National Collection of Insects (Ottawa) and The Natural History Museum (London). All specimens of the type series were collected during field work under the co-operative insect faunal survey of Korea conducted by Kyungpook National University (Prof. Lee Chang Eon), Korea and Kyushu University (Entomological Laboratory), Japan. Diagnosis. Wing bicolored, white on basal 1/3 and almost evenly dark brown on apical 2/3, marked with an indistinct narrow pale longitudinal stripe; body blackish, with 2 anterior abdominal segments yellowish white; legs blackish; male gonostylus almost evenly narrow with a simple short subbasal process on inner surface; female 9th abdominal tergum with medially excavated posterior margin weakly produced into a median process; female laterosternite with a moderately long posterior process and lacking basal protuberance. Description. Male (Fig. 1A) Size: Body length: 1.6–2.1 mm. Wing length: 1.9–2.1 mm, width: 0.5–0.6 mm. Coloration and general aspect. Head and thorax blackish brown to black, abdomen blackish brown to dark brown with two anterior segments yellowish white. Legs blackish brown to dark brown, trochanter and basal part of fore femur paled in some specimens. Antenna and maxillary palpus dark brown. Mesonotum almost polished, thoracic pleura thinly dark pollinose; abdominal terga 7–8 and terminalia thinly greyish pollinose. Wing almost evenly dark brown with basal 1/3 white except costal area darker; narrow indistinct pale stripe in cell m 1 extending from basal white area and ending before apical 1/4 of wing. Wing veins pale on white area, brown on dark area. Halter yellowish white. Setae and setulae on body, appendages and wing brown to black. Structure. Head (Figs. 2A, B): Clypeus clothed with ca 20 setae, irregularly biserial postocular setae. Antenna (Fig. 1C) short, 300–330 μ long, with flagellum 240–270 μ long, 0.84–0.91 times as long as head width; flagellum with 5 flagellomeres, flagellomere 1 1/2 as long as 4 apical flagellomeres combined, cylindrical, 3 x as long as wide, weakly constricted in middle 1/2; flagellomeres 2–4 short, oval, slightly longer than wide; flagellomere 5 twice as long as flagellomere 4, weakly tapered to pointed apex on apical ½; flagellomeres bearing several longish setulae nearly as long as flagellomere 3. Maxillary palpus (Fig. 1E) rather long; relative lengths of segments 2–5 in one paratype 1: 1.5: 1.3: 2.4; palpal segments short, setulose, denser on segment 3, shorter and sparser on terminal segment. Thorax (Figs. 2C, D): Chaetotaxy. Antepronotum with ca 10 setae medially, several ones laterally; acrostichals minute, ca 15 in number, almost uniserial and arranged in mesonotal fissure; dorsocentrals uniserial, but partly biserial in middle of row, mostly short, but posterior 2–3 dorsocentrals strong, bristle-like; prealar area with 2–3 strong setae accompanying several shorter setulae in front; ca 10 marginal scutellars strong with a few scattered discal and marginal setulae; mesepimeron with 1–5 setulae, mesepisternum with 0–2 setulae. Wing (Fig. 1F): 3.3–3.5 times as long as wide. Venation: R 1 ending in costa at basal 2/3 (somewhat beyond middle of wing); R 2+3 faint but well traceable. Legs (Fig. 1G): Short setulose. Relative lengths of podites as in Table 1. Tarsomeres 1 and 2 each with 1–2 apical setae. Spurs or comb of mid and hind tibiae as in Figs. 1 H and I. Terminalia (Figs. 3A, B): Epandrium (Fig. 3E) trapezoidal, width of anterior part 1/2 as wide as posterior part distinctly angulate at posterolateral corners, with almost straight lateral margin; anal point (Fig. 3F) long and strongly compressed laterally, 1/2 as long as epandrium except anal point itself, in lateral aspect oval and raised dorsally. Inner process of gonocoxite simple, moderately long, situated basally. Gonostylus (Figs. 3C, D) slender in lateral aspect, tapered near apex, with straight dorsal margin and ventral margin slightly widened subbasally; inner surface of gonostylus with subbasal process short, fine, simple and not accompanying distally extending longitudinal ridge; gonostylus microtrichiose, with a few setulae. Female (Fig. 1B) Size: Body length: 2.1–2.4 mm. Wing length: 2.4–2.7 mm, width: 0.8 mm. Coloration and general aspect Similar to male. Structure Terminalia (Fig. 4): Tergum 8 weakly sclerotized in part, articulated to, but not joined with posterolateral corner of sternum 8. Tergum 9 well developed, posterior margin weakly and roundly lobate bilaterally, excavated for middle 1/3, and produced to weak median projection. Laterosternite basally fused with tergum 9, with posterior process sparsely setulose, extending to level of middle of tergum 9; no free basal projection on laterosternite. Etymology. This species is named for the late Dr. Masaru Yamamoto, an excellent chironomid systematist, who was one of the graduate students of entomology when the author was on staff at Kyushu University. We worked together on this taxon, prior to his un-timely death. Distribution. This species is distributed in the Jiri (Chiri) Mountains at 1100–1500 m, in the southern part of the Korean Peninsula.

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