Cyclotoma nigrithorax Chang & Ren 2023, sp. nov.

Cyclotoma nigrithorax sp. nov.

(Figs 1A–C, 2A, 3A, 4A, 5)

Type material. HOLOTYPE: ♁, CHINA: SICHUAN: ‘China. Sichuan, Mianyang, Yangmaxia, N32°5′48″, E104°56′32″, 810 m, 2021.X.1, leg. Ling-Xiao Chang’ (NNHMC). PARATYPES: CHINA: SICHUAN: 9 ♁♁ 5 ♀♀, same collecting data as holotype (NNHMC); 23 ♁♁, ‘ China. Sichuan, Pingwuxian, Doukouzhen, Jinbao, 980 m, leg. Hao Xu & Xin-Yuan Zhang’ (MYNU).

Diagnosis. Cyclotoma nigrithorax sp. nov. resembles C. formosana, C. indiana, C. parvimaculata, C. simianshanensis sp. nov., and C. yingjiangensis sp. nov. in appearance. However, the black pronotum and ventral surfaces except for elytral epipleura can separate it from all these similar species. In addition, C. nigrithorax sp. nov. differs from C. formosana in the femora uniformly black (vs. femora near apical 1/2 black); from C. indiana in antennomere 4 distinctly shorter than antennomere 3 (vs. antennomere 4 elongate, hardly shorter than antennomere 3); from C. parvimaculata in three lateral elytral spots visible dorsally (vs. barely visible dorsally); antennomere 4 distinctly longer than antennomere 5 (vs. antennomere 4 nearly as long as antennomere 5); from C. simianshanensis sp. nov. in antennomere 4 distinctly longer than antennomere 5 (vs. antennomere 4 slightly longer than antennomere 5); from C. yingjiangensis sp. nov. by the antenna uniformly brownish-black (vs. antennomeres 1–9 yellowish-brown, club brownish-black); antennomere 4 distinctly shorter than antennomere 3 (vs. antennomere 4 elongate, hardly shorter than antennomere 3).

Description. Male (Figs 1A–B, 2A). Length 4.6–6.6 mm; body 1.1–1.2 times longer than wide; height 2.4–3.4 mm, about 0.5 times as high as long, smooth, strongly shiny. Dorsal surfaces yellowish-brown with head, pronotum, scutellum, suture, leg, spots on pronotum and on elytra black; ventral surfaces black with elytral epipleura yellowish-brown.

Antenna 11-segmented with scape long and stout, 4.0 times longer than pedicel; antennomere 2 distinctly longer than wide, antennomere 3 about as long as antennomere 4 and 5 combined; antennomere 4 longer than wide, and distinctly longer than antennomere 5; antennomeres 6–8 quadrate; club almost as long as remaining antennomeres combined; terminal antennomeres twice as long as wide. Maxilla with terminal palpomere elongate, weakly tapering towards apex, truncate apically.

Pronotum 1.0– 1.4 mm long, 2.0– 3.2 mm wide; about 0.4–0.5 times as long as wide; anterior and lateral edges very narrowly bordered; disc weakly convex. Pronotal surface polished between punctures, punctation rather dense and moderately coarse. Prosternal process widely separates front coxae, about 1.2 times as wide as longest coxal diameter and narrower than intercoxal process of mesoventrite, widening behind front coxae; sides weakly curved outwardly, rounded at apex. Elytra 4.4–6.0 mm long, 4.1–5.6 mm wide; 1.1 times as long as wide; 4.3–4.4 times longer than pronotum, 1.8–2.1 times wider than pronotum; sides abruptly converging from about half-length towards apex; each elytron with seven black spots of different size and shape (one humeral, three near lateral margin, three sutural); sutural spots with inner margin sometimes touching elytral suture; three lateral spots with outer margin distant from lateral margin of elytra; the first lateral spots smallest and from dorsal view barely visible. Humeri moderately prominent; elytral surface polished between punctures, punctation as large as pronotal ones, rather dense and moderately coarse.

Ventrite 1 with lines bordering edge of coxal cavity extending posteriorly (Fig. 3A); ventrite 5 weakly curved at apex. Aedeagus (Fig. 4A) long, thin, curved, curled at its base; tegmen located in apical 1/4 with large, submembranous, tegminal plate with length reaching nearly basal 1/6 of aedeagus.

Female. Habitus (Fig. 1C) similar to males. Elytra with sides gently and widely converging posteriad in apical 1/3; ventrite 5 truncate at apex.

Etymology. The name refers to the black thorax; noun in nominative case standing in apposition.

Distribution. China: Sichuan.

Biology and ecology. The adults were collected by simple searching from a large pile of dead wood in the day (Fig. 5). The adults have the habit of feigning death.

Remarks. Live or fresh specimens were observed with milky white elytra which gradually turned yellowish brown after drying. This species was also recognized as undescribed by Mr. Yu-Tang Wang (Mianyang Normal University).