Arthromelodes nepaeformis, 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 : 53-55

Arthromelodes nepaeformis sp. nov.

( Figs 22 , 79A , 95 , 96D )

Chinese common name: OE形njà甲

Type material (55 exx.). HOLOTYPE: CHINA : ♂, ‘ China: Xizang, Cona County, Lebu Valley, pass to Mama Vill. , 27°50’16”N, 91°45’48”E, 2400–2700 m, 04.vii.2021, Z. Peng, Z. Yin & W. Zhang leg., ƱẪDZḄ县勒布沟 Þ玛乡 ’ ( SNUC) . PARATYPES: CHINA : 13 ♂♂, 6 ♀♀, same data as that of holotype ; 25 ♂♂, 9 ♀♀, also from Lebu Valley , except ‘ 27°55’13”N, 91°51’16”E, 3650-4050 m, 05.vii.2021 ’; 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 Ʊ Ẫffżẘ 热村ṗẋ ’ (all paratypes in SNUC) .

Diagnosis. Male. Body length approximately 1.7–1.8 mm. Head subtruncate at base; vertex with deep transverse sulcus between antennal tubercles, lacking mediobasal carina, vertexal foveae moderately large and asetose; antenna relatively short, antennomeres each slightly elongate or moniliform, lacking modifications. Discal stria of elytron extending posteriorly to more than apical 1/3 of elytral length. Protibia strongly sinuate, protarsomere 1 with tuft of umbellate setae; mesotibia with long apical spine. Posteromedial area of metaventrite covered with dense, thickened setae. Abdomen with large Tergite 1 (IV) longer than tergites 2–4 (V–VII) combined in dorsal view, simple. Aedeagus strongly asymmetric, median lobe protruding apically, ventral stalk strongly curved in lateral view, dorsal lobe strongly curved at apex, parameres broad, weakly sclerotized. Female. Body length slightly over 1.7 mm, legs and metaventrite lacking modifications, genitalia as in Fig. 22I .

Description. Male. Body ( Fig. 22A ) length 1.73–1.82 mm; bicolored, head, maxillary palpomere 4, pronotum, most parts of protibia and abdomen dark brown, antennae, elytra and legs (other than protibia) reddish-brown, tarsi and mouthparts (other than maxillary palpomere 4) lighter in color. Dorsal surface of body covered with relatively short pubescence.

Head ( Fig. 22B ) subtruncate at base, approximately as long as wide, length 0.37–0.38 mm, width across eyes 0.38 mm; vertex finely punctate, with relatively large, asetose vertexal foveae (dorsal tentorial pits), with slightly curved, deep and short transverse sulcus between antennal tubercles, mediobasal carina absent, antennal tubercles moderately raised; frons broadly and weakly impressed medially, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and moderately raised; ocular-mandibular carina complete. Venter with small gular foveae (posterior tentorial pits) originating from shared transverse slit, with distinct median carina extending from foveae anteriorly to mouthparts. Compound eyes prominent, composed of approximately 32 moderately large ommatidia. Antenna 0.86–0.87 mm long, lacking modifications; antennomere 1 thick, subcylindrical, 2–7 each slightly elongate, 8 smallest, moniliform, 9 much larger than 8, approximately as long as wide, 10 as long as and slightly broader than 9, 11 large, as long as 9 and 10 combined.

Pronotum ( Fig. 22B ) approximately as long as wide, length 0.41–0.42 mm, width 0.40–0.41 mm, widest at middle; lateral margins rounded; disc moderately convex, finely punctate, with median longitudinal sulcus much 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 pits; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.60 mm, width 0.71 mm; each elytron with two large, widely separated basal foveae, lacking subbasal fovea; humerus weakly prominent; discal stria extending from outer basal fovea to more than apical 1/3 of elytral length; subhumeral fovea small, marginal stria extending posteriorly from middle to apex.

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, forked internally. Metaventrite ( Fig. 22C ) moderately impressed at middle, with pair of setose lateral metaventral foveae, posteromedial area covered with dense, thickened setae, with pair of angulate admesal projections, posterior margin with small and narrow split at middle.

Legs elongate, hind leg simple. Protibia ( Fig. 22D ) strongly sinuate, surface with linear microsculpture and erect setae, protarsomere 1 apically extended and with tuft of umbellate setae at apex; mesotibia ( Fig. 22E ) with long, slightly curved spine at apex.

Abdomen much narrower than elytra, widest at basolateral margins of tergite 1 (IV), length 0.46–0.50 mm, width 0.60–0.61 mm; lacking modifications. Tergite 1 (IV) in dorsal view longer than tergites 2–4 (V–VII) combined; setose basal sulcus separated by mediobasal and one pair of basolateral foveae, with pair of thick, triangular discal carinae; tergites 2 and 3 (V and VI) lacking foveae, 4 (VII) as long as 2 and 3 combined along middle, with one pair of basolateral foveae, 2–4 each with pair of thin lateral carinae, tergite 5 (VIII) semicircular, posterior margin roundly emarginate at middle. Sternite 2 (IV) with large mediobasal and broad basolateral sockets, with pair of long, thick lateral carinae; midlength of sternite 2 (IV) as long as sternites 3–5 (V–VII) combined, 3 and 4 short, 5 slightly longer than 4, 3–5 lacking foveae, sternite 6 (VIII) transverse, posterior margin emarginate at middle, sternite 7 (IX) ( Fig. 22F ) slightly oval, moderately sclerotized, apex rounded and with few long setae along apical margin.

Aedeagus ( Fig. 22G, H ) 0.33 mm long, strongly asymmetric; median lobe with large basal capsule and subtriangular foramen, lacking basoventral projection, ventral stalk protruding, in lateral view strongly curved, narrowing towards apex; dorsal lobe elongate and strongly curved at apex; parameres fused to form broad plate, weakly sclerotized.

Female. Similar to male in external morphology; antenna shorter; legs and metaventrite lacking modifications; each compound eye composed of approximately 22 ommatidia; humeral angle rounded; tergite 4 (VII) with thickened lateral ridges. Measurements (as for male): body length 1.72–1.78 mm; length/width of head 0.35–0.37/ 0.36–0.37 mm, pronotum 0.38/ 0.38–0.39 mm, elytra 0.51–0.52/ 0.65–0.67 mm; abdomen 0.50–0.58/ 0.61–0.62 mm; length of antenna 0.73–0.77 mm; maximum width of genitalia ( Fig. 22I ) 0.21 mm.

Comparative notes. This species appears to be well isolated in the genus due to the unique bicolored body, and the oddly modified protibiae and tarsomeres 1 of the male. The setose metaventrite is shared with A. crassicornis and A. lebus , but the setae are of a different density and length.

Distribution. Cona County and Chagyib District (Nyingchi), Xizang, SW China ( Figs 79A , 95 , 96D ).

Etymology. The new species name is a combination of ‘ nepa (a crab)’ and ‘ fôrma (shape)’, referring to the crab-like habitus of the new species.

Figures

FIGURE 22. Morphology of Arthromelodes nepaeformis sp. nov. (A–H. Male. I. Female). A. Dorsal habitus. B. Head and pronotum. C. Metaventrite. D. Protibia. E. Apical part of mesotibia. F. Sternite 7 (IX). G–H. Aedeagus, ventral (G) and lateral (H). I. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B; 0.2 mm in C; 0.1 mm in D, E, G–I, 0.05 mm in F.

FIGURE 79. Distribution of Tibetan Batrisini. A. Arthromelodes markam sp. nov. (circle), A. monba sp. nov. (triangle) and A. nepaeformis sp. nov. (square). B. A. nepaeformis sp. nov. (circle), A. songxiaobini sp. nov. (triangle) and A. speciosus sp. nov. (square). C. A. torus sp. nov. (circle), A. zhangmu sp. nov. (triangle) and A. zhentangensis sp. nov. (square).

FIGURE 95. Environment of and collecting sites at Lebu Valley (勒布沟). Forests at 2400 m (A, B), and 3650 m (C, D).

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.