Arthromelodes alpitorus, 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 : 11-13

Arthromelodes alpitorus sp. nov.

( Fig. 2 )

Chinese common name: Ṉ瘤únjà甲

Type material (60 exx.). HOLOTYPE: CHINA: ♂ , ‘ China: Xizang, Dinggyê County, pass to Zhêntang Town , 27°55’0”N, 87°29’47”E, 3500–3650 m, 26.vi.2021, Peng, Yin & Zhang, ƱẪU喀NJŤĠĿƋ沟Ḃ山杜ḁff ’ ( SNUC) . PARATYPES: CHINA: 21 ♂♂, 20 ♀♀, same data as that of holotype; 11 ♂♂, 7 ♀♀, same data as that of holotype except ‘3650-4020, 27.vi.2021 ’ (all paratypes in SNUC) .

Diagnosis. Male. Body length approximately 2.8–2.9 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 as long as 9 and 10 combined. Discal stria of elytron thin and shallow, extending posteriorly to more than apical 1/3 of elytral length. Fore and hind legs simple, mesotrochanter with setose tuft on ventral margin, mesotibia with large, curved apical spine. Abdomen with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; tergite 1 with broad, bifid protuberance at middle. Aedeagus strongly asymmetric, median lobe with large basal capsule and elongately oval foramen, ventral stalk broad and dilated at apex, dorsal lobe elongate, forked at apex, parameres reduced and forming single membranous structure. Female. Body length approximately 2.7–2.8 mm, legs and abdomen lacking modifications, genitalia as in Fig. 2I .

Description. Male. Body ( Fig. 2A ) length 2.80–2.88 mm; color reddish-brown, tarsi and mouthparts slightly lighter. Dorsal surface of body covered with short pubescence.

Head ( Fig. 2B ) subtruncate at base, approximately as long as wide, length 0.58–0.59 mm, width across eyes 0.56–0.58 mm; vertex finely punctate, with relatively small, asetose vertexal foveae (dorsal tentorial pits), with distinct, curved transverse sulcus between antennal tubercles, mediobasal carina extending from head base anteriorly to sulcus, antennal tubercle 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, additional incomplete carina present below posteroventral articulation of mandible. Venter with tiny gular foveae (posterior tentorial pits) in single small pit, median carina extending before fovea anteriorly to mouthpart, gradually thickened anteriorly. Eyes moderately prominent, composed of approximately 26 ommatidia. Antenna 1.46 mm long, lacking modifications; antennomere 1 thick, subcylindrical, 2–8 each elongate, 3 and 8 of same length, shortest, 8 much shorter and slightly narrower than 7, 9 longer but narrower than 10, 11 largest, approximately as long as 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 2B ) slightly longer than wide, length 0.65–0.66 mm, width 0.62 mm, widest at middle; lateral margins rounded; disc moderately convex, finely punctate, with median longitudinal sulcus much shorter than 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 0.85–0.87 mm, width 0.94–0.96 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 posteriorly to more than apical 1/3 of elytral length; subhumeral fovea absent, thin 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 long, narrow split at middle.

Legs elongate, fore and hind legs simple. Mesotrochanter ( Fig. 2C ) with short setose tuft on ventral margin, mesotibia ( Fig. 2D ) with thick, curved spine at apex.

Abdomen slightly narrower than elytra, widest at lateral margins of tergite 1 (IV), length 0.81–0.88 mm, width 0.85–0.86 mm; with modified tergite 1 (IV). Tergite 1 ( Fig. 2E ) longer than tergites 2–4 (V–VII) combined, with broad, strongly raised projection at middle, projection with acute posterolateral angles in fully-developed individuals, less so in few other specimens, area posterior to projection moderately raised along middle, 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 and 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 roundly emarginate at middle, sternite 7 (IX) ( Fig. 2F ) slightly oval, moderately sclerotized, apex rounded and with few long setae along apical margin.

Aedeagus ( Fig. 2G, H ) 0.45 mm long, strongly asymmetric; median lobe with large basal capsule and elongately oval foramen, basoventral projection short, ventral stalk broad and protruding, in lateral view strongly dilated at apex; dorsal lobe obliquely erect, 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 22 ommatidia; humeral angle rounded. Measurements (as for male): body length 2.66–2.80 mm; length/width of head 0.55–0.57/ 0.56–0.57 mm, pronotum 0.62–0.63/ 0.58–0.60 mm, elytra 0.77–0.79/ 0.93–0.94 mm; abdomen 0.80–0.83/ 0.87–0.88 mm; length of antenna 1.31–1.35 mm; maximum width of genitalia ( Fig. 2I ) 0.29 mm.

Comparative notes. Arthromelodes alpitorus is morphologically most similar to A. torus by sharing most external characters, as well as a similar male tergal modification and form of the aedeagus. The new species can be separated by the larger body size (2.80–2.88 mm vs. 2.64 mm in male; 2.66–2.80 mm vs 2.53–2.61 mm in female), a much shorter median longitudinal sulcus of the pronotum, the male having thicker and more strongly curved spine at the apex of mesotibia, the median projection of tergite 1 (IV) with acute posterolateral angles (with single, acute posterior corner in A. torus ), and area posterior to the projection raised along middle (flat in A. torus ), and a more expanded apex of the median lobe of the aedeagus. It is worth noting that A. alpitorus inhabits Rhododendron forests experiencing low temperatures at an altitude of 3500–3650 m, which is much colder than the mixed forests inhabited by A. torus at 3000 m. It appears that Arthromelodes alpitorus is well-isolated from A. torus by high altitude geographical barriers.

On the other hand, this species 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, but A. alpitorus can be otherwise readily separated by the unique form of the male tergal modification and the aedeagus.

Distribution. Dinggyê County, Tibet, SW China ( Figs 77A , 93A ).

Etymology. The species name is combined from ‘ Alpînus (alpine)’ and ‘ torus (swelling, protuberance)’, indicating a high-altitude distribution as well as the morphological similarity of this species to A. torus .

Figures

FIGURE 2. Morphology of Arthromelodes alpitorus 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 77. Distribution of Tibetan Batrisini. A. Arthromelodes alpitorus sp. nov. (circle), A. angulatus sp. nov. (triangle) and A. aniqiao sp. nov. (square). B. A. bicolor sp. nov. (circle), A. championi (Jeannel) comb. nov. (triangle) and A. complexus sp. nov. (square). C. A. cona sp. nov. (circle), A. crassicornis sp. nov. (triangle) and A. criniger sp. nov. (square).

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.