Arthromelodes gyamda, Yin, 2022

Yin, Zi-Wei, 2022, The Batrisini of Tibet: unveiling an enigmatic ant-loving beetle diversity at Earth’s “ Third Pole ” (Coleoptera, Staphylinidae, Pselaphinae), Zootaxa 5111 (1), pp. 1-211 : 34-36

Arthromelodes gyamda sp. nov.

( Figs 13 , 78A , 96A, D )

Chinese common name: ȕḭnjà甲

Type material (10 exx.). HOLOTYPE: CHINA: ♂ , ‘ China: Xizang, Gongbo'gyamda, near Gaduogang vil., 29°53’60”N, 93°14’22”E, 3620 m, mixed leaf litter, sifted, 18.vii.2018, Cheng, Peng & Shen leg. [工布ȕḭ]’ ( SNUC) . PARATYPES: CHINA: 4 ♂♂, 4 ♀♀, same data as that of holotype; 1 ♂, China: Xizang, Nyingchi City, valley nr. Jiare Vill., Chongge, 30°03’19”N, 93°46’46”E, 3500–3750 m, 08.vii.2021, Peng, Yin, Zhang, ƱẪffż ẘ热村ṗẋ ’ (all paratypes in SNUC) .

Diagnosis. Male. Body length over 2.1 mm. Head subtruncate at base; vertex with shallow, slightly curved transverse sulcus between antennal tubercles and moderately long mediobasal carina, vertexal foveae relatively small and asetose; antenna elongate, lacking modifications; antennomeres 1–7 each slightly elongate, 8 smallest, 9 and 10 approximately as long as wide, 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 ventral protuberance, mesofemur with short ventral spine, mesotibia with small apical denticle. Abdomen with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; tergites 1–4 each modified (IV–VII). Aedeagus strongly asymmetric, median lobe relatively short, ventral stalk in dorsal view broad, dorsal lobe elongate, apex strongly twisted, parameres reduced and forming single membranous structure. Female. Body length slightly over 2.0 mm, legs and abdomen lacking modifications, genitalia as in Fig. 13I .

Description. Male. Body ( Fig. 13A ) length 2.17–2.28 mm; color light reddish-brown, tarsi and mouthparts slightly lighter. Dorsal surface of body covered with short pubescence.

Head ( Fig. 13B ) subtruncate at base, approximately as long as wide, length 0.43–0.44 mm, width across eyes 0.44 mm; vertex finely punctate, with relatively small, asetose vertexal foveae (dorsal tentorial pits), with shallow and thin, slightly curved transverse sulcus between antennal tubercles, mediobasal carina extending from near 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 two 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 18–20 ommatidia. Antenna 1.01–1.02 mm long, lacking modifications; antennomere 1 thick, subcylindrical, 2–7 each elongate, 8 smallest, much shorter and narrower than 7, 9–11 successively larger, 11 largest, slightly shorter than 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 13B ) slightly longer than wide, length 0.48–0.49 mm, width 0.46 mm, widest at middle; lateral margins rounded; disc moderately convex, finely punctate, with median longitudinal sulcus 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 0.61–0.63 mm, width 0.76–0.78 mm, constricted at bases; each elytron with two moderately-sized, widely separated basal foveae, lacking subbasal fovea; humeral angle rounded; discal stria extending from outer basal fovea to apical 1/2 of elytral length; subhumeral fovea lacking, 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. 13C ) with long protuberance at base, mesofemur ( Fig. 13C ) with short ventral spine, mesotibia with small denticle at apex.

Abdomen approximately as broad as elytra, widest at lateral margins of tergite 1 (IV), length 0.64–0.71 mm, width 0.75–0.77 mm; with modified tergites 1–4 (IV–VII) ( Fig. 13D ). Tergite 1 (IV) longer than tergites 2–4 (V–VII) combined in dorsal view, with small, median protuberance near posterior margin, which is decorated with dense golden setae admesally; setose basal sulcus separated by mediobasal and one pair of large basolateral foveae, with very short discal carinae; tergites 2 and 3 (V and VI) each with median protuberance and dense golden setae along posterior margin, tergite 4 (VII) much longer than 2 and 3 combined along middle, with large median projection, area anterior projection strongly impressed, tergites 2–4 (V–VII) each with one pair of small basolateral foveae, tergite 5 (VIII) semicircular, posterior margin roundly emarginate at middle. Sternite 2 (IV) with large mediobasal and broad basolateral sockets, lacking obvious basal impression or sulcus, with pair of moderately long lateral carinae; midlength of sternite 2 (IV) approximately as long as sternites 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. 13E ) slightly oval, moderately sclerotized, apex rounded and with few long setae along apical margin.

Aedeagus ( Fig. 13F–H ) 0.40 mm long, strongly asymmetric; median lobe with large basal capsule and slightly oval foramen, basoventral projection short, ventral stalk short and in dorsal view dilated at apex; dorsal lobe elongate and gradually narrowing from middle towards apex, strongly twisted at apex; parameres reduced to single membranous structure.

Female. Similar to male in external morphology; antenna shorter; legs and abdomen lacking modifications; each compound eye composed of approximately 18 ommatidia; humeral angle rounded. Measurements (as for male): body length 2.13–2.16 mm; length/width of head 0.44/ 0.43–0.44 mm, pronotum 0.46–0.50/ 0.45–0.46 mm, elytra 0.59–0.60/ 0.78 mm; abdomen 0.66–0.67/ 0.76–0.79 mm; length of antenna 0.96–1.00 mm; maximum width of genitalia ( Fig. 13I ) 0.27 mm.

Comparative notes. The males of the new species can be readily separated from those of all congeners by the relatively small head and short antennae, the unique modifications of tergites 1–4 (IV–VII), as well as the form of the aedeagus.

Distribution. Gongbo'gyamda County, Tibet, SW China (78A, 96A, D).

Etymology. The specific epithet ‘ gyamda ’ is taken from Gongbo'gyamda County, the type locality of the new species.

Figures

FIGURE 13. Morphology of Arthromelodes gyamda sp. nov. (A–H. Male. I. Female). A. Dorsal habitus. B. Head and pronotum. C. Mesotrochanter and mesofemur. D. Tergites 1–4 (IV–VII). E. Sternite 7 (IX). F–H. Aedeagus, dorsal (F), lateral (G) and ventral (H). I. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B, C; 0.2 mm in D, F–H; 0.1 mm in E, I.

FIGURE 78. Distribution of Tibetan Batrisini. A. Arthromelodes cylindricus sp. nov. (circle), A. flosculus sp. nov. (triangle) and A. gyamda sp. nov. (square). B. A. intricatus sp. nov. (circle), A. lage sp. nov. (triangle) and A. langjicuo sp. nov. (square). C. A. latithorax sp. nov. (circle), A. lebus sp. nov. (triangle) and A. lotus sp. nov. (square).

FIGURE 96. Environment of and collecting sites at Nyingchi area (ffż地区). A. Gongbo'gyamda (工布ȕḭ). B. Zhongzhe Village (ΦĖ村). C. Kading Valley (ϮŤ沟). D. Chongge Cuo (ṗẋś). E, F. A slope near Serjila mountain pass (DzĻŃ山 口). Photo Credit: A, B, E, F by Zhong Peng.