Esolus fodingshanus Jiang, Jach & Chen 2026, sp. nov.

Esolus fodingshanus Jiang, Jäch & Chen sp. nov. Figs 1 A, 1 B, 2, 3 Chinese name. 佛顶山单脊溪泥甲. Type material (23 exs.): Holotype: China • ♂, labeled ‘ China: Guizhou (贵州), Tongren City (铜仁市), Shiqian County (石阡县), Fodingshan Nature Reserve (佛顶山自然保护区), Ganxi Gelao and Dong Township (甘溪仡佬族侗族乡), Shaixi Village (晒溪村), 27°22'57.9"N, 108°04'35.8"E, H: ~ 620 m, 20. VI. 2023, Ri-Xin Jiang, Hai-Tao Li, Lan Jia, Pin Li & Yu-Hao Zhang leg. ’ (GUGC). Paratypes: (9 ♂♂, 4 ♀♀, 9 exs.): • 3 ♂♂, 2 ♀♀, with the same label data as the holotype (GUGC); 1 ♀, same label data as holotype, but collected on 15. V. 2023, Ri-Xin Jiang leg. (GUGC); • 2 ♂♂, same label data as holotype, but collected on 28. VI. 2023 (GUGC); 6 exs., same label data as holotype, but collected on 15. VII. 2025, Mao-Heng Du & Ri-Xin Jiang leg. (GUGC); 3 exs., labeled ‘ China: Guizhou (贵州), Tongren City (铜仁市), Shiqian County (石阡县), Fodingshan Nature Reserve (佛顶山自然保护区), Pingshan Township (坪山乡); Fodingshan Village (佛顶山村), near Yaoshang (尧上), 27°19'45.5"N, 108°08'22.8"E; H: ~ 720 m, 05. VII. 2024, Ri-Xin Jiang & Hai-Tao Li leg. ’ (GUGC); 4 ♂♂, 1 ♀, labeled ‘ China: • Guizhou (贵州), Tongren City (铜仁市), Yinjiang Tujia and Miao Autonomous County (印江土家族苗族自治县), Fanjingshan Nature Reserve (梵净山国家级自然保护区), Muhuang Town (木黄镇), Shibanzhai Village (石板寨村), 27°59'14.0"N, 108°40'00.7"E, H: ~ 1050 m, 28. VI. 2023, Ri-Xin Jiang & Xiu-Dong Huang leg. ’ (GUGC). Description. Male (Figs 1 A, 2, 3 A – D, 3 F). Body long oval (Fig. 1 A), black to dark brown, antennae, distal parts of legs and sometimes anterior margin of pronotum yellowish brown. Dorsal surface shiny with weak metallic luster, covered with sparse short setae. Head (Fig. 2 B) wider than long, surface microreticulate, covered with sparse small punctures, each puncture bearing a short seta. Eyes large, oval. Clypeus covered with sparse small punctures, each puncture bearing a short seta, anterior margin with sparse long setae. Labrum transverse, shorter and narrower than clypeus, with long bristles at anterior portion; anterior margin straight and anterolateral angles rounded. Antenna (Fig. 2 A) 11 - segmented, slightly longer than pronotum; scape about as long as wide, weakly expanded at middle; pedicel longer than scape, longer than wide and weakly expanded at middle; antennomeres 3–9 similar, longer than wide, widest near apex; antennomere 10 longer than antennomere 4, expanded at apex; antennomere 11 fusiform, apically acuminate. Pronotum (Fig. 2 C) wider than long, widest at base. Surface shiny and finely covered with small punctures; each puncture bearing a short seta. Anterior margin convex, anterior angles produced and curved inwards. Lateral margins slightly curved. Basal margin convex at middle, concave laterally; posterior angles slightly produced and acute. Sublateral carinae distinct. Prosternum (Fig. 2 E) medially glabrous, sparsely covered with small punctures and setae; lateral parts of prosternum and hypomera covered by plastron; apex of prosternal process rounded. Scutellum (Fig. 2 D) elongate subtriangular, ca. twice as long as wide; lateral margins slightly curved; apex acute; surface glabrous, without punctures or setae. Elytra (Fig. 2 D) elongate, less than twice as long as wide, widest at middle. Surface glabrous, sparsely covered with short setae. Lateral margins subparallel from base to 3 / 5 of elytra; humeri not developed. Punctures of elytral striae very distinct in basal half, but very small or obsolete subbasally and in apical half; punctures in striae II – IV larger and more widely spaced from each other in basal 3 / 5. Punctures of elytral striae V and VI small, more or less fused in most anterior and posterior third; sublateral elytral carina therefore situated on interval 6 anterior of elytral declivity. Hind wings (Fig. 3 F) short. Metaventrite (Fig. 2 F), disc shiny and sparsely micropunctate; each puncture bearing a short yellowish seta. Median sulcus (discrimen) absent; a pair of curved carinae demarcating lateral margins of metaventral discal, extending from meso- to metacoxae. Lateral portions of metaventrite covered with plastron setae. Legs simple; femora clavate, widest near middle; surface of femora covered with plastron setae; surface of tibiae without plastron setae. Mesal sides of tibiae with cleaning fringes; apical half of inner side of meso- (Fig. 2 H) and metatibiae (Fig. 2 I) with a row of small teeth, being not very well developed in some specimens. Tarsi shorter than tibiae, tarsal claws simple, without basal teeth. Abdomen (Fig. 2 G) with five visible ventrites; median part shiny, covered with sparse micropuntures, each bearing a short seta; lateral parts of ventrites densely covered with plastron setae. Ventrite I with a pair of curved admedian carinae. Ventrites II – III short; ventrite V longest, about 1.5 × as long as ventrites II + III. Male genitalia. Aedeagus (Figs 3 A – C) elongate, in ventral view subparallel-sided. Median lobe in ventral view narrowed at middle; apex subtruncate with rounded corners; corona not apparent; in lateral view, median lobe curved ventrad. Phallobase longer than parameres, in ventral view more or less parallel-sided, in lateral view curved ventrad. Parameres longer than median lobe; in ventral view comprehensively emarginate basally, rather abruptly attenuate near middle; apical part slim and apically distinctly curved mediad; apices almost touching each other near apex of median lobe; in lateral view, parameres curved ventrad. Spiculum gastrale as in Fig. 3 D. Measurements of male: CL: 1.64–1.78 mm; HW: 0.24–0.25 mm; PL: 0.45–0.46 mm, PW: 0.65–0.67 mm; EL: 1.20–1.32 mm, EW: 0.68–0.70 mm. Female (Figs 1 B, 3 E): externally very similar to male, but inner side of meso- and metatibiae lacking teeth. Ovipositor as in Fig. 3 E, very small; stylus absent. Apex of coxites rounded, with several sensilla. Valvifers wide. Measurements of female: CL: 1.54–1.65 mm; HW: 0.23–0.24 mm; PL: 0.42–0.43 mm, PW: 0.61–0.64 mm; EL: 1.12–1.23 mm, EW: 0.71–0.72 mm. Comparative diagnosis. Esolus fodingshanus can be easily distinguished from E. nepalensis Jäch, 1982 by the larger body size (CL: ca. 1.5–1.8 mm in E. fodingshanus, ca. 1.2–1.4 in E. nepalensis); by the elytral punctures in striae II – IV being more widely spaced from each other in basal 3 / 5; and by the genital morphology: aedeagus longer (0.5 mm in E. fodingshanus, ca. 0.4 in E. nepalensis); median lobe much wider in apical half; parameres distinctly narrowed in apical half, and longer than the median lobe. While the aedeagus in E. nepalensis has a well-developed corona, we did not observe it in the new species. Phylogenetic relationships. The two East Palearctic species, E. nepalensis and E. fodingshanus are definitely closely related phylogenetically. They share several conspicuous synapomorphies: e. g., 1) due to fusion of elytral striae V and VI, sublateral elytral carinae placed on interval 6 (at least in anterior half of elytra) (Figs 1 A – C, 2 D); 2) phallobase longer than parameres (Fig. 3 A – C; and Jäch (1982: fig. 7)); 3) parameres in ventral view comprehensively emarginate basally (Fig. 3 A, C; and Jäch (1982: fig. 7)); and 4) ovipositor poorly developed, styli absent (Fig. 3 E; and Jäch (1982: fig. 8)). The most remarkable autapomorphic feature of these two species is the reduction of the ovipositor and the complete loss of the styli, which is, as far as we know, not known from any other Elmidae. Biology. All adults of the new species were collected from the benthos in forest streams, where they were found in riffle areas with rather strong current (Fig. 4 A – F). All specimens examined are micropterous and therefore probably unable to fly. However, hind wing polymorphism is a common phenomenon in various elmid genera, including Esolus (see Berthélemy 1979), and it therefore cannot be excluded that macropterous individuals of the new species may exist (see also Hayashi et al. 2013; Shepard 2019). Distribution. China: Fodingshan and Fanjingshan Mountains in eastern Guizhou Province (Fig. 6). Etymology. The epithet refers to the type locality, Fodingshan National Nature Reserve (佛顶山国家级自然保护区); the name is treated as an adjective.