Arthromelodes torus, 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 : 62-64

Arthromelodes torus sp. nov.

( Figs 26 , 79C , 93C, E )

Chinese common name: 瘤únjà甲

Type material ( 20 exx.). HOLOTYPE: CHINA: ♂, ‘China: Xizang, Dinggyê County, pass to Zhêntang Town , 27°53’58”N, 87°27’21”E, 3060 m, 28.vi.2021, Yin & Zhang leg., ƱẪŤĠ县ĿƋ沟公ḡṅðff ’ ( SNUC). PARATYPES: CHINA: 6 ♂♂, 8 ♀♀, same data as that of holotype; 5 ♂♂, also from Zhêntang, except ‘ Xiuxiongma Vill., 27°54’11”N, 87°22’42”E, 2700-3000 m, 25.vi.2021, Z. Peng, Z. Yin & W. Zhang leg., ƱẪU喀NJŤĠ县Ŀ ƋWšŏ玛村 ’ (all paratypes in SNUC).

Diagnosis. Male. Body length over 2.6 mm. Head subtruncate at base; vertex with transverse sulcus between antennal tubercles and long mediobasal carina, vertexal foveae relatively small and asetose; antenna elongate, lacking modifications; antennomeres each slightly elongate, 8 smallest, 11 slightly shorter than 9 and 10 combined. Discal stria of elytron thin and shallow, extending posteriorly to approximately apical 2/5 of elytral length. Fore and hind legs simple, mesotrochanter with setose tuft on ventral margin, mesotibia with large apical spine. Abdomen with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; tergite 1 with strongly raised protuberance at middle. Aedeagus strongly asymmetric, median lobe with large basal capsule and oval foramen, ventral stalk narrowed and protruding, dilated at apex, dorsal lobe elongate, forked at apex, parameres reduced and forming single membranous structure. Female. Body length slightly over 2.5 mm, legs and abdomen lacking modifications, genitalia as in Fig. 26I .

Description. Male. Body ( Fig. 26A ) length 2.64 mm; color reddish-brown, tarsi and mouthparts slightly lighter. Dorsal surface of body covered with short pubescence.

Head ( Fig. 26B ) subtruncate at base, approximately as long as wide, length 0.52–0.55 mm, width across eyes 0.54–0.55 mm; vertex finely punctate, with relatively small, asetose vertexal foveae (dorsal tentorial pits), with distinct transverse sulcus between antennal tubercles, mediobasal carina extending from head base anteriorly to sulcus, antennal tubercles moderately raised; frons broadly and shallowly impressed medially, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and moderately raised; ocular-mandibular carina present, thin carina present below posteroventral articulation of mandible. Venter with tiny gular foveae (posterior tentorial pits) in single small pit, median carina extending from fovea anteriorly to mouthpart, with thin basal half and thick apical half. Eyes moderately prominent, composed of approximately 25 ommatidia. Antenna 1.34–1.38 mm long, lacking modifications; antennomere 1 thick, subcylindrical, 2–8 each elongate, 8 smallest, much shorter and slightly narrower than 7, 9 longer but narrower than 10, 11 largest, shorter than 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 26B ) slightly longer than wide, length 0.60–0.62 mm, width 0.58–0.59 mm, widest at middle; lateral margins rounded; disc moderately convex, finely punctate, with median longitudinal sulcus as long as 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 0.81–0.82 mm, width 0.91–0.94 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 approximately apical 2/5 of elytral length; subhumeral fovea absent, marginal stria extending posteriorly from posterior to middle 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 broadly 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. 26C ) with moderately long setose tuft on ventral margin, mesotibia ( Fig. 26D ) with long spine at apex.

Abdomen slightly narrower than elytra, widest at lateral margins of tergite 1 (IV), length 0.77–0.79 mm, width 0.85–0.86 mm; with modified tergite 1 (IV). Tergite 1 ( Fig. 26E ) longer than tergites 2–4 (V–VII) combined, with single, strongly raised projection at middle, degree of development of projection slightly varying among individuals, basal impression broken by mediobasal and basolateral foveae, with pair of short discal carinae, with incomplete outer marginal carina; tergites 2 and 3 (V and VI) subequal in length along midline, 4 (VII) slightly longer than 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 short lateral carinae; midlength of sternite 2 (IV) as long as 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. 26F ) slightly oval, moderately sclerotized, apex rounded and with few long setae along apical margin.

Aedeagus ( Fig. 26G, H ) 0.42 mm long, strongly asymmetric; median lobe with large basal capsule and oval foramen, basoventral projection short, ventral stalk protruding and in lateral view dilated at apex; dorsal lobe recumbent, apically forked into two lobes; 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 23 ommatidia; humeral angle rounded. Measurements (as for male): body length 2.53–2.61 mm; length/width of head 0.53–0.54/ 0.53 mm, pronotum 0.56–0.57/ 0.56 mm, elytra 0.72–0.76/ 0.89–0.90 mm; abdomen 0.77–0.80/ 0.85–0.87 mm; length of antenna 1.26–1.27 mm; maximum width of genitalia ( Fig. 26I ) 0.30 mm.

Comparative notes. Arthromelodes torus is morphologically most similar to A. alpitorus by sharing most external characters, as well as a similar male tergal modification and the form of the aedeagus. The new species can be separated by the smaller body size (2.64 mm vs. 2.80–2.88 mm for male; 2.53–2.61 mm vs 2.66–2.80 mm for female), a much longer median longitudinal sulcus of the pronotum, the male having a thinner and slightly curved spine at the apex of the mesotibia, the median projection of tergite 1 (IV) with single posteromedial corner (with acute posterolateral angles in A. alpitorus ), the area posterior to the projection flat along the midline (raised in A. torus ), and a less expanded apex of the median lobe of the aedeagus. These two species appear to be well isolated by altitudinal barriers. Arthromelodes torus is also close to A. angulatus , A. aniqiao , A. complexus , A. lage , and A. langjicuo , sharing with them a setose male mesotrochanter, as well as a similar general form of the aedeagus. The male of the new species can be readily separated by the unique presence of a large central projection on tergite 1 (IV), as well as the long apical spine of the mesotibia.

Distribution ( Fig. 92 ). Dinggyê County, Tibet, SW China ( Figs 79C , 93C, E ).

Etymology. The new species name ‘ torus (swelling, protuberance)’ is a Latin noun referring to the protuberant male tergite 1 (IV).

Figures

FIGURE 26. Morphology of Arthromelodes torus sp. nov. (A–H. Male. I. Female). A. Dorsal habitus. B. Head and pronotum. C. Mesotrochanter. D. Mesotibia. E. Tergite 1 (IV). F. Sternite 7 (IX). G, H. Aedeagus, lateral (G) and ventral (H). I. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B; 0.2 mm in C–E; 0.1 mm in F–I.

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 92. Environment of Zhangmu Valley (樟木沟). Environment of Youyiqiao (友谊桥) (A, B), Lixin Village (ĒẾ村) (C) and Qu Township (DZ乡) (D). Photo Credit: A, B by Jian-Qing Zhu; C, D by Wen-Xuan Bi.

FIGURE 93. Environment of and collecting sites at Zhêntang Valley (ĿƋ沟). Slopes at altitudes of 3700 m (A), 4000 m (B), and 3050 m (C). D. Nadang Village (Ḅ当村). E. Road to Xiuxiongma Village (šŏ玛村). F, G. Environment of Ganma Zangbo Valley (HḼẪ布河ě). Photo Credit: F, G by Zhong Peng.