Arthromelodes cylindricus, 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 : 30-32

Arthromelodes cylindricus sp. nov.

( Figs 11 , 78A , 96E, F )

Chinese common name: Ñ型njà甲

Type material (19 exx.). HOLOTYPE: CHINA: ♂ , ‘ China: Xizang, Nyingchi City, Shejila, nr. Sheji’ema , 29°36’50”N, 95°41’34”E, 4340 m, 05.vii.2018, leaf litter, sifted, Cheng, Peng & Shen leg. [ƱẪffż市DzĻŃ]’ ( SNUC) . PARATYPES: CHINA: 9 ♂♂, 4 ♀♀, same data as that of holotype; 2 ♂♂, 3 ♀♀, also from Shejila, except ‘ Lulang Tourist Center , 29°37’01”N, 94°41’55”E, 4300 m, 14.vii.2021, Peng, Yin & Zhang, DzĻŃ游Β中 心北坡 ’ ( SNUC) .

Diagnosis. Male. Body length over 2.60–2.67 mm. Head subtruncate at base; vertex with transverse sulcus between antennal tubercles and long mediobasal carina, vertexal foveae moderately large and asetose; antenna long, antennomeres each slightly elongate, lacking modifications. Discal stria of elytron extending to approximately apical 1/4 of elytral length. Fore legs simple, mesotrochanter with small tuft of setae on ventral margin, mesotibia with distinct apical spur, metafemur with dorsal setose patch at apex. Abdomen with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; tergite 1 (IV) with deep central cavity. Aedeagus strongly asymmetric, median lobe protruding apically, ventral stalk in dorsal view broad, dorsal lobe laterally strongly curved at middle, parameres reduced and forming single semi-sclerotized structure.

Description. Male. Body ( Fig. 11A ) length 2.60–2.67 mm, habitus generally cylindrical; color reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with moderately long pubescence.

Head ( Fig. 11B ) subtruncate at base, as long as broad, length and width across eyes 0.50–0.51 mm; vertex, frons and clypeus roughly punctate; vertex with moderately large, asetose vertexal foveae (dorsal tentorial pits), with curved transverse sulcus between antennal tubercles, mediobasal carina extending from near head base anteriorly to sulcus, antennal tubercles moderately raised; frons broadly and shallowly impressed medially, confluent with clypeus, with short frontal-clypeal carinae at sides; clypeus with anterior margin carinate and moderately raised; ocular-mandibular carina thick and complete. Venter with gular foveae (posterior tentorial pits) originating from shared opening, with distinct median carina extending from fovea anteriorly to mouthparts. Compound eyes prominent, composed of approximately 19 large ommatidia. Antenna with loosely formed club, lacking modifications, length 1.23–1.24 mm; antennomere 1 thick, subcylindrical, anterolateral margin slightly impressed and filled with short setae (but not to form prominent trichome), 2–11 each elongate, 8 smallest, 11 largest, much shorter than 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 11B ) approximately as long as wide, length and width 0.55–0.56 mm, widest at middle; lateral margins rounded; disc slightly convex, finely punctate, with median longitudinal sulcus shorter than semicircular lateral sulci in dorsal view; lacking median antebasal fovea, with complete transverse antebasal sulcus connecting lateral antebasal foveae, with additional pair of marginal antebasal foveae; outer and inner pair of basolateral foveae distinct. Prosternum with anterior part slightly longer than coxal part, with distinct 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 0.73–0.74 mm, width 0.82 mm, constricted at bases; each elytron with two large, asetose basal foveae, lacking subbasal fovea; humerus lacking prominence or denticle; discal stria extending from outer basal fovea to approximately apical 1/4 of elytral length; subhumeral fovea absent, marginal stria extending posteriorly from basal 1/3 to apex. Hind wings absent.

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 moderately separated, lateral mesoventral foveae large and setose, not forked internally. Metaventrite broadly and shallowly impressed at middle, with pair of setose lateral metaventral foveae, posterior margin with small and narrow split at middle.

Legs elongate, fore simple. Mesotrochanter with small setose tuft on ventral margin, mesotibia with distinct apical spur; metatrochanter setose on ventral margin, metafemur ( Fig. 11C ) with dorsal sensory area covered with short, dense setae at apex.

Abdomen narrower than elytra, widest at basolateral margins of tergite 1 (IV), length 0.75–0.78 mm, width 0.73–0.74 mm. Tergite 1 (IV) ( Fig. 11D ) strongly modified, much longer than tergites 2–4 (V–VII) combined; with deep central cavity, inside cavity with ‘ ± ’-shaped thick ridge, with broad, truncate projection posterior to cavity, areas lateral to projection markedly concave; setose basal sulcus separated by mediobasal and one pair of basolateral foveae, lacking discal carinae; tergites 2–4 (V–VII) each with one pair of basolateral foveae, tergite 4 (VII) slightly longer than 2 and 3 combined along middle, tergite 5 (VIII) semicircular, posterior margin roundly emarginate at middle. Sternite 2 (IV) with mediobasal and basolateral foveae in broad setose basal impression, with pair of short lateral carinae, with thin marginal carinae much longer than lateral ones; midlength of sternite 2 (IV) approximately 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. 11E ) with moderately sclerotized, rounded apex and few long setae along apical margin.

Aedeagus ( Fig. 11F, G ) 0.51 mm long, strongly asymmetric; median lobe with large basal capsule and foramen, basoventral projection short, ventral stalk protruding and in dorsal view broad, apex narrowly and shortly split; dorsal lobe in lateral view elongate and bent at middle, in dorsal view strongly curved rightwards (position in figure) at apical 1/5, gradually narrowing apically and with pointed apex; parameres reduced to single semi-membranous structure.

Female. Similar to male in external morphology; antenna slightly shorter; legs and abdomen lacking modifications; each compound eye composed of approximately 19 ommatidia; humeral angle rounded. Measurements (as for male): body length 2.56–2.57 mm; length/width of head 0.51–0.52/ 0.50–0.51 mm, pronotum 0.55–0.58/ 0.55–0.58 mm, elytra 0.70–0.72/ 0.85–0.87 mm; abdomen 0.75–0.80/ 0.80 mm; length of antenna 1.17 mm; maximum width of genitalia ( Fig. 11H ) 0.36 mm.

Comparative notes. The new species can be readily separated from all known congeners by the relatively large body size and a generally cylindrical habitus, combined with the unique sensory patch of the male metafemur and the structure of the abdominal modifications.

Distribution. Chagyib District (Nyingchi), Xizang, SW China ( Figs 78A , 96E, F ).

Etymology. The specific epithet ‘ cylindricus (- a, - um)’ is a Latin adjective (of Ancient Greek origin) referring to the cylindrical habitus of this species.

Figures

FIGURE 11. Morphology of Arthromelodes cylindricus sp. nov. (A–G. Male. H. Female). A. Dorsal habitus. B. Head and pronotum. C. Metafemur. D. Tergite 1 (IV). E. Sternite 7 (IX). F, G. Aedeagus, dorsal (F) and lateral (G). H. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B, D; 0.1 mm in C, E, H; 0.2 mm in F, G.

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.