Derolathrus hainanensis Jiang, Chen & Yang 2025, sp. nov.

Derolathrus hainanensis Jiang, Chen & Yang sp. nov. Figs 1, 2, 3 Chinese name. 海南宽颈短跗甲. Type material. Holotype: CHINA • ♂, ‘ China: Hainan, Ledong Li Autonomous County (乐东黎族自治县), Jianfengling Area of National Park of Hainan Tropical Rainforest (海南热带雨林国家公园尖峰岭片区), MingfengGu (鸣凤谷), under bark of a dead broadleaf tree, 18°44'28"N, 108°50'38"E, H: ~ 940 m alt., 2025.III.28., Jiang Ri-Xin leg. ’ (GUGC). Paratypes: CHINA • 7 ♂♂, 8 ♀♀, with the same label data as the holotype (5 ♂♂, 6 ♀♀, GUGC; 2 ♂♂, 2 ♀♀, IZAS). Diagnosis. Winged species; integument of head and pronotum with polygonal reticulation, the polygons more or less squared; surface of head and pronotum covered with sparse large punctures; disc of head with a shallow and flat longitudinal depression; eyes developed and large; pronotal disc with distinct longitudinal impression extending approximately half the pronotal length; each elytron with an entire sutural stria and one reduced second stria, which is connected at base at a shallow pit, the second elytral stria very short, less than 1 / 10 of the elytral length; metaventrite very long, about as long as combined length of ventrites I – V; aedeagus slender, symmetrical, with parameres distinctly medially curved and apically rounded. Description. Male. Body (Fig. 1 A) shape subcylindrical, narrowly elongate, reddish-brown, surface slightly shiny. Winged species. BL: 0.93–0.98 mm. Head (Fig. 2 A), nearly squared, wider than long, widest across eyes, HL: 0.15–0.16 mm, HW: 0.20–0.21 mm. Dorsal surface covered with micro-polygonal netting and sparse large punctures, each puncture bearing a short seta, the diameter of the puncture larger than that of ommatidia. Disc of head with a shallow and flat longitudinal depression, less than half the length of head, about twice as wide as the diameter of punctures on the head surface. Frons slightly concave between antennal tubercles. Antennae (Fig. 2 D) with 11 antennomeres; longer than length of pronotum, surface covered with sparse long setae; antennomere I partially hidden by the lateral margin of head; antennomere II expanded, longer than wide; antennomeres III – IX moniliform, short and transverse; antennomeres X – XI fused and forming a club, expanded; antennomere XI slightly longer and narrower than antennomere X, with apex rounded. Pronotum (Fig. 2 B), nearly trapezoid, about as long as wide and as wide as head, widest at anterior 1 / 4, PL: 0.20–0.22 mm, PW: 0.20–0.21 mm. Pronotal surface with micro-polygonal netting, the polygons more or less squared and covered with sparse large punctures, each puncture bearing a short seta. Disc of pronotum with a distinct longitudinal depression, about as long as 1 / 2 pronotal length; width of the longitudinal depression about as wide as twice the diameter of punctures on the pronotum surface. Anterior margin weakly curved, anterior angles rounded; lateral margins finely curved at anterior 3 / 4 and distinctly narrowed at posterior 1 / 4; posterior margin curved, posterior angles obtuse. Prosternal process (Fig. 2 C) with wide and round apex. Elytra. About twice as long as wide (Fig. 3 A), widest before mid-point, EL: 0.57–0.60 mm, EW: 0.25–0.27 mm. Elytral sutural stria I is distinct and long, extending from the elytral base, but not extending to the apex; stria II strongly reduced, less than 1 / 10 of the elytral length. Elytral surface covered with irregular micro-polygonal netting and rows of tiny and sparse punctures; punctures of elytra smaller than that of head and pronotum. Scutellum not visible. Metaventrite (Fig. 3 B), very long, about as long as of the combined length of abdominal ventrites 1–5, surface covered with sparse small punctures, lateral portions with longitudinal micro polygonal netting. Abdomen (Fig. 3 B) with five ventrites, ventrite 6 sometimes partially visible. Ventrite 1 about as long as ventrite 5, with lateral portions bearing polygonal netting and posterior margin nearly straight; ventrites 2–4 about the same in length, with surfaces bearing polygonal netting and sparse short setae, the posterior margin of ventrite II weakly curved and distinctly curved in ventrites 3–4. Ventrites 3–5, each with a row of round depressions at near anterior margins; posterior part of ventrite 5 with several long setae. Legs. Femora (Fig. 2 E – G) clavate, narrowed at the base, and gradually wider to apex; tibiae (Fig. 2 E – G) narrower than femora, constricted at basal portions, apex with a small tooth; surface of femora and tibiae with sparse short setae; all tarsi (Fig. 2 E – G) with three tarsomeres, the first and second tarsomeres short and minute, the third elongate, slightly curved in lateral view, much longer than combined length of two remaining tarsomeres. Aedeagus (Fig. 3 C) slender, symmetrical; parameres distinctly longer than median lobe, distinctly curved at middle, apex of parameres rounded. Female. Morphologically similar to male, without distinct sexual character in habitus. Measurements of female: BL: 0.93–0.97 mm; HL: 0.16–0.18 mm; HW: 0.19–0.20 mm; PL: 0.20–0.21 mm, PW: 0.21–0.22 mm; EL: 0.55–0.59 mm, EW: 0.26–0.28 mm. Distribution. Only known from the type locality: Jianfengling Area of National Park of Hainan Tropical Rainforest, Hainan Province, China. Biology. All adults were found under the bark of a dead broadleaf tree. The dead tree had not rotted away yet; adults of this species congregate in the damp sections under the bark, accompanied by adjacent fungal hyphae colonisation (Fig. 4). Etymology. The specific epithet refers to the type locality: Hainan Province, China; the name is treated as an adjective. Comparative notes. This species is morphologically very close to D. foveiceps Théry, 2023, both species possessing a longitudinal depression at the disc of the head and pronotum. The new species can be separated from the latter species by the surface of the pronotum without rows of setiferous depression at each side of the median depression, while the pronotum has at least 4 rows of setiferous depressions at each side of the median depression in D. foveiceps. List of known Derolathrus species (†: fossil species) D. abyssus Yamamoto & Parker in Yamamoto et al. 2016 † D. anophthalmus (Franz, 1969) D. atomus Sharp in Sharp et Scott (1908) D. capdoliensis Tihelka, Peris, Cai & Perrichot, 2022 † D. cavernicolus Peck, 2010 D. ceylonicus (Sen Gupta, 1979) D. foveiceps Théry, 2023 D. groehni Cai, Leschen, Liu & Huang, 2016 † D. hainanensis Jiang & Chen, sp. nov. D. insularis (Dajoz, 1973) D. parvulus (Rücker, 1983) D. sharpi Grouvelle in Grouvelle and Raffray (1912) D. subtilis Théry, 2023 D. troglophilus (Sen Gupta, 1979)