Arthromelodes langjicuo sp. nov.

(Figs 16, 78B, 91)

Chinese common name: 朗吉śnjà甲

Type material (60 exx.). HOLOTYPE: CHINA: ♂, ‘ China: Xizang, Gyirong County, Gyirong Valley, Langjicuo Lake, 28°24’10”N, 85°23’58”E, 4000–4100 m, 21.vi.2021, Z. Peng, Z. Yin & W. Zhang leg., ƱẪU喀NJ吉PW 朗吉śéae ’ (SNUC) . PARATYPES: CHINA: 30 ♂♂, 29 ♀♀, same data as that of holotype (SNUC) .

Diagnosis. Male. Body length over 2.3 mm. Head subtruncate at base; vertex with V-shaped transverse sulcus between antennal tubercles and moderately long mediobasal carina, vertexal foveae relatively small and asetose; antenna elongate, lacking modifications; antennomeres each slightly elongate, 8 smallest, 11 as long as 9 and 10 combined. Discal stria of elytron thin and shallow, extending posteriorly to approximately half of elytral length. Fore and hind legs simple, mesotrochanter with long setose tuft on ventral margin, mesotibia with small apical denticle. Abdomen with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; tergite 1 weakly modified, with pair of small admesal tubercles at posterior 1/4. Aedeagus strongly asymmetric, median lobe with large basal capsule and elongate foramen, ventral stalk narrowed and protruding, dilated at apex, dorsal lobe elongate, apical half thin and pointing towards apex, parameres reduced and forming single membranous structure. Female. Body length slightly over 2.3 mm, legs and abdomen lacking modifications, genitalia as in Fig. 16I.

Description. Male. Body (Fig. 16A) length 2.37–2.41 mm; color reddish-brown, tarsi and mouthparts slightly lighter. Dorsal surface of body covered with short pubescence.

Head (Fig. 16B) subtruncate at base, approximately as long as wide, length 0.52–0.53 mm, width across eyes 0.51–0.52 mm; vertex finely punctate, with relatively small, asetose vertexal foveae (dorsal tentorial pits), with distinct V-shaped transverse sulcus between antennal tubercles, mediobasal carina extending from head base anteriorly to sulcus, antennal tubercles slightly raised; frons broadly and shallowly impressed medially, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and moderately raised; ocular-mandibular carina complete. Venter with tiny gular foveae (posterior tentorial pits) in single small pit, with distinct median carina extending from fovea anteriorly to mouthparts. Eyes moderately prominent, composed of approximately 30 ommatidia. Antenna 1.33–1.37 mm long, lacking modifications; antennomere 1 thick, subcylindrical, 2–8 each elongate, 8 smallest, much shorter and narrower than 7, 9 and 10 of same length, 10 slightly broader than 9, 11 largest, as long as 9 and 10 combined, sub-fusiform.

Pronotum (Fig. 16B) slightly longer than wide, length 0.54–0.56 mm, width 0.51–0.52 mm, widest at middle; lateral margins rounded; disc moderately convex, finely punctate, with median longitudinal sulcus slightly shorter than semicircular lateral sulci in dorsal view; lacking median antebasal fovea, with complete, deep transverse antebasal sulcus connecting lateral antebasal foveae; outer and inner pair of basolateral foveae distinct. Prosternum with anterior part slightly longer than coxal part, with small lateral procoxal foveae; hypomeral ridge present at basal 1/2, with punctiform lateral antebasal hypomeral pit; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.76–0.77 mm, width 0.87–0.91 mm, truncate at base; each elytron with two moderately-sized, widely separated basal foveae, lacking subbasal fovea; humerus weakly raised; discal stria extending from outer basal fovea to approximately half of elytral length; subhumeral fovea absent, thin marginal stria extending posteriorly from basal third to posterior margin of elytron.

Mesoventrite short, demarcated from metaventrite by ridged anterior edges of impressed areas where large, setose lateral mesocoxal foveae situated at mesal margins, with pair of admesal carinae; setose median mesoventral foveae broadly separated, lateral mesoventral foveae large and setose, not forked internally. Metaventrite slightly impressed at middle, with pair of setose lateral metaventral foveae, posterior margin with small and narrow split at middle.

Legs elongate, fore and hind legs simple. Mesotrochanter (Fig. 16C) with long setose tuft on ventral margin, mesotibia (Fig. 16D) with small denticle at apex.

Abdomen slightly narrower than elytra, widest at lateral margins of tergite 1 (IV), length 0.62–0.64 mm, width 0.77–0.82 mm; with modified tergite 1 (IV). Tergite 1 (Fig. 16E) longer than tergites 2–4 (V–VII) combined, degree of modification development varying among individuals, with two small admesal tubercles at middle, posterior half longitudinally raised at middle, with pair of admesal carinae or tubercles, area surrounding tubercle weakly to strongly impressed (surface with round, small cavity), basal impression broken by mediobasal and basolateral foveae, with pair of short discal carinae; tergites 2 and 3 (V and VI) subequal in length along midline, 4 (VII) as long as 2 and 3 combined along middle, 2–4 (V–VII) each with one pair of small basolateral foveae, 5 (VIII) semicircular, posterior margin roundly emarginate at middle. Sternite 2 (IV) with two mediobasal foveae and large basolateral sockets, lacking basal impression or sulcus, with pair of moderately long lateral carinae; midlength of sternite 2 (IV) longer than 3–5 (V–VII) combined, 3–5 each with one pair of tiny basolateral foveae, sternite 6 (VIII) transverse, posterior margin sinuate, sternite 7 (IX) (Fig. 16F) slightly oval, moderately sclerotized, apex rounded and with few long setae along apical margin.

Aedeagus (Fig. 16G, H) 0.37 mm long, strongly asymmetric; median lobe with large basal capsule and elongate foramen, basoventral projection short, ventral stalk protruding and dilated at apex; dorsal lobe elongate and in dorsal view flattened at middle, apical part strongly bent rightwards and narrowing towards apex; parameres reduced to single membranous structure.

Female. Similar to male in external morphology, antenna shorter, legs and abdomen lacking spines/projections or modifications, each compound eye composed of approximately 25 ommatidia and humeral angle rounded. Measurements (as for male): body length 2.33–2.37 mm; length/width of head 0.50–0.51/ 0.51 mm, pronotum 0.53–0.54/ 0.50–0.51 mm, elytra 0.70–0.74/ 0.87–0.89 mm; abdomen 0.70–0.71/ 0.85–0.86 mm; length of antenna 1.21–1.22 mm; maximum width of genitalia (Fig. 16I) 0.26 mm.

Comparative notes. Arthromelodes langjicuo inhabits leaf litter of a Rhododendron forest at an altitude of 4,100 m, being one of the highest-dwelling species within the genus. It is close to previously described A. angulatus, A. aniqiao, and A. lage, and A. torus, sharing with them a setose tuft on the ventral margin of the male mesotrochanter, as well as the generally similar form of the aedeagus. The unique form of the male tergal modification and the aedeagus readily leads to a separation of the new species from these similar congeners.

Distribution. Gyirong County, Tibet, SW China (Figs 78B, 91).

Etymology. The new species is named after its type locality, i.e., Langjicuo Lake.