Trisinus quadrilobus, 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 : 176-178

Trisinus quadrilobus sp. nov.

( Figs 75 , 87 , 67C , 100A )

Chinese common name: Żú幻Ɵà甲

Type material (14 exx.). HOLOTYPE: CHINA: ♂ , ‘ China: Xizang, Nyingchi City, Pailong Village , 30°01’11”N, 95°00’01”E, 2069 m, 15.iii.2017, X.-B. Song leg. [中ǞƱ Ẫffż 市ḦË乡]’ ( SNUC) . PARATYPES: CHINA: 7 ♂♂, 3 ♀♀, same data as that of holotype; 1 ♂, 2 ♀♀ , ‘ China: Xiang , Mêdog County, nr. 80K, 29°41’09”N, 95°30’10”E, alt. 2330 m, mixed leaf litter, sifted, 09.vii.2018, Cheng, Peng & Shen leg. (中ǞƱẪẸṘ县 80K ṉ ữ)’ (all paratypes in SNUC) .

Diagnosis. Male. Body length approximately 1.85–1.90 mm. Head subtruncate at base; vertex with complete reversed U-shaped sulcus connecting small, asetose foveae, sulcus extending anteriorly at middle towards frons, with moderately long mediobasal carina; antenna elongate, lacking modifications, with scattered exceptionally long setae; all antennomeres slightly elongate, club moderately distinct. Pronotum with five longitudinal striae. Discal stria of elytron thin, extending posteriorly to approximately apical 2/5 of elytral length. Fore and hind legs simple, mesotrochanter with thin protuberance on ventral margin, mesotibia with distinct triangular spine at apex. Abdomen with long tergite 1 (IV) long, as long as tergites 2–4 (V–VII) combined; tergite 2 with two admesal and two lateral projections; sternite 2 (IV) with lamellar process at middle. Aedeagus strongly asymmetric, horn-shaped; ventral stalk broad at base, narrowing apically, dorsal lobe membranous at apex and strongly twisted and extended at basal portion. Female. Body length slightly over 1.85 mm, antenna shorter than male, legs and abdomen lacking modifications, genitalia as in Fig. 75I .

Description. Male. Body ( Fig. 75A ) length 1.86–1.91 mm; color dark reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with relatively long pubescence, antenna with scattered suberect, exceptionally long setae (up to 0.17 mm).

Head ( Fig. 75B ) subtruncate at base, approximately as long as wide, length 0.40–0.41 mm, width across eyes 0.44–0.46 mm; vertex roughly punctate, with relatively small, asetose vertexal foveae (dorsal tentorial pits), with deep reversed U-shaped sulcus connecting foveae, sulcus at middle of anterior margin extending anteriorly towards apical part of frons, mediobasal carina extending from near head base anteriorly to level of anterior margin of eyes, antennal tubercles slightly raised, with setose postantennal foveae; frons broadly and shallowly impressed medially, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and strongly raised; ocular-mandibular carina complete. Venter with two tiny gular foveae (posterior tentorial pits) in single opening, with thin median carina extending from fovea anteriorly to mouthparts. Eyes moderately prominent, composed of approximately 25 ommatidia. Antenna 0.94–0.97 mm long, lacking modifications, club formed by apical three antennomeres; antennomere 1 thick, subcylindrical, 2–7 each elongate, 8 smallest, much shorter and narrower than 7, 9–11 successively larger, 11 largest, approximately as long as 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 75B ) approximately as long as wide, length 0.44 mm, width 0.43–0.48 mm, widest at middle; lateral margins rounded; disc weakly convex, sparsely with sparse large punctures, with median longitudinal sulcus shorter than semicircular lateral sulci in dorsal view, with pair of discal longitudinal sulci; lacking median antebasal fovea, with complete, deep transverse antebasal sulcus connecting lateral antebasal foveae, small antebasal tubercles present; 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 broader than long, length 0.61–0.62 mm, width 0.70–0.72 mm, truncate at bases; each elytron with two moderately-sized, widely separated basal foveae, subbasal fovea absent; humerus slightly prominent; discal stria extending from outer basal fovea to apical 2/5 of elytral length; subhumeral fovea present, marginal stria extending posteriorly from fovea 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 narrowly separated and originating from shared central opening, lateral mesoventral foveae large and setose, forked internally. Metaventrite broadly impressed at middle, with pair of large lateral mesocoxal foveae and setose lateral metaventral foveae; area mesal to metacoxa longitudinally carinate, posterior margin broadly emarginate, lacking split at middle.

Legs elongate, fore and hind legs simple. Mesotrochanter with thin protuberance on ventral margin, mesotibia ( Fig. 75C ) with large triangular spine at apex.

Abdomen slightly narrower than elytra, widest at lateral margins of tergite 1 (IV), length 0.48–0.51 mm, width 0.63–0.66 mm, with modified tergite 2 (V) and sternite 2 (IV). Tergite 1 (IV) approximately as long as tergites 2–4 (V–VII) combined, densely punctate; lacking basal sulcus, with two mediobasal foveae and one pair of large basolateral foveae, discal carinae distinct, with complete and oblique inner marginal carinae, posterior margin with row of dense setae; tergite 2 (V) ( Fig. 75D ) heavily modified, central part strongly concave, with pairs of admesal and lateral projections, areas between projections impressed, with basolateral foveae lateral to admesal projections, surface of lateral projections with short, dense sensory setae; tergite 3 (VI) short, 4 (VII) three times as long as 3 along middle, tergite 5 (VIII) semicircular, posterior margin roundly emarginate at middle, tergite 3–5 (V–VIII) each with one pair of small basolateral foveae. Sternite 2 (IV) ( Fig. 75E ) with large, transverse mediobasal and distinct basolateral foveae, lacking basal impression or sulcus, with pair of moderately long lateral carinae, with lamellar process at middle; midlength of sternite 2 (IV) longer than 3–5 (V–VII) combined, 3–5 each with one pair of small basolateral foveae, sternite 6 (VIII) transverse, posterior margin sinuate, sternite 7 (IX) ( Fig. 75F ) suboval, moderately sclerotized, apex rounded and with few long setae along apical margin.

Aedeagus ( Fig. 75G, H ) 0.20 mm long, strongly asymmetric and horn-like, with distinct basoventral projection; ventral stalk of median lobe in lateral view broad, rounded at apex; dorsal lobe membranous and lamellar at apex, basal half strongly extended and twisted; 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 11 ommatidia. Measurements (as for male): body length 1.86–1.87 mm; length/width of head 0.41/ 0.46–0.47 mm, pronotum 0.44/ 0.43 mm, elytra 0.53–0.55/ 0.69–0.70 mm; abdomen 0.53–0.55/ 0.63–0.64 mm; length of antenna 0.87–0.89 mm; genitalia membranous, lacking obvious sclerotized structures.

Comparative notes. The male of the new species can be readily separated from those of all congeners by the roughly punctate head, the unique modifications of tergite 2 (V) and sternite 2 (IV), and the form of the aedeagus.

Distribution. Chagyib District (Nyingchi) and Mêdog County, Xizang, SW China ( Figs 87 , 67C , 100A ).

Etymology. The specific epithet refers to the presence of four projections of male tergite 2 (V).

Figures

FIGURE 67. Morphology of Tribasodites grandiceps sp. nov., male. A. Dorsal habitus. B. Head and pronotum. C. Pronotum, in dorsolateral view. D. Apex of mesotibia. E. Metatrochanter. F. Metafemur. G. Sternite 7 (IX). H–J. Aedeagus, dorsal (H), lateral (I) and ventral (J). Scale bars: 0.5 mm in A; 0.3 mm in B, F; 0.2 mm in C, 0.1 mm D, E, H–J; 0.05 mm in G.

FIGURE 75. Morphology of Trisinus quadrilobus sp. nov., male. A. Dorsal habitus. B. Head and pronotum. C. Apex of mesotibia. D. Tergite 2 (V). E. Sternite 2 (IV). F. Sternite 7 (IX). G, H. Aedeagus, lateral (G) and ventral (H). Scale bars: 0.5 mm in A; 0.2 mm in B, D, E; 0.05 mm in C, F; 0.1 mm in G, H.

FIGURE 87. Distribution of Tibetan Batrisini. Trisinus quadrilobus sp. nov.

FIGURE 100. Environment of and collecting sites at Nyingchi area (A–E) and Chamdo (ăƀ) (F). A. 80K. B. 96K. C–E. Xiachayu (T察ø). F. pass of Jueba Mountain (ẅ巴山口), Markam (Ẽ康). Photo Credit: A by Zhong Peng; B by Xiao-Bin Song; F by Wen-Xuan Bi.