Trisinus sp.

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 : 178-190

Trisinus sp.

( Figs 76 , 99F )

Material examined (1 ex.). 1 ♀, ‘ China: Mêdog County, pass from Bari Village to Renqingbeng Temple, 29°18’45”N, 95°21’27”E, ca. 1830 m, 19.iii.2017, X.-B. Song leg. [ƱẪẸṘ县巴U村 -仁ů崩寺]’ ( SNUC) .

Description. Male. Unknown.

Female. Body ( Fig. 76A ) length 1.68 mm; head, pronotum and elytra dark brown, elytra dark reddish-brown, legs and antenna reddish brown, tarsi and mouthparts light reddish-brown. Dorsal surface of body covered with relatively long pubescence, antenna and abdomen with scattered exceptionally long setae.

Head ( Fig. 76B ) subtruncate at base, much broader than long, length 0.32 mm, width across eyes 0.42 mm; vertex at middle smooth, roughly punctate anterior and lateral to deep U-shaped sulcus that connects relatively small, asetose vertexal foveae (dorsal tentorial pits), sulcus at middle of anterior margin extending anteriorly towards apical part of frons, mediobasal carina faint, extending from near head base anteriorly to level of foveae, 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 moderately raised; ocular-mandibular carina complete. Venter with two tiny gular foveae (posterior tentorial pits) in small, round opening, with thin median carina extending from fovea anteriorly to mouthparts. Eyes slightly prominent, composed of approximately 16 ommatidia. Antenna 0.76 mm long, club formed by apical three moderately enlarged antennomeres; antennomere 1 thick, subcylindrical, 2–5 and 7 each elongate, 6 and 8 smallest, slightly shorter than 7, 9–11 successively larger, 11 largest, slightly longer than 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 76B ) approximately as long as wide, length 0.39 mm, width 0.40 mm, widest at middle; lateral margins rounded; disc weakly convex, sparsely with 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 0.42 mm, width 0.58 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 barely 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 moderately elongate, simple.

Abdomen slightly narrower than elytra, widest at lateral margins of tergite 1 (IV), length 0.57 mm, width 0.57 mm. Tergite 1 (IV) approximately as long as tergites 2–4 (V–VII) combined, finely and sparsely punctate; lacking basal sulcus, with two mediobasal foveae and one pair of large basolateral foveae, discal carinae thin and short, with complete and oblique inner marginal carinae; tergite 2 (V) slightly longer than 3 (VI), 4 (VII) ( Fig. 76C ) more than twice length of 3 but shorter than 2 and 3 combined, with strongly protruding projection at middle of posterior margin, tergite 5 (VIII) ( Fig. 76D ) transverse, posterior margin impressed at middle, tergite 3–5 (V–VIII) each with one pair of small basolateral foveae, 5 with thin marginal carinae. Sternite 2 (IV) with large, transverse mediobasal and distinct basolateral foveae, lacking basal impression or sulcus, with pair of moderately long lateral carinae; midlength of sternite 2 (IV) approximately as long as 3–5 (V–VII) combined, 3–5 each with one pair of small basolateral foveae, sternite 6 (VIII) ( Fig. 76E ) transverse, posterior margin broadly emarginate, sinuate.

Genitalia ( Fig. 76F ) membranous, maximum width 0.22 mm.

Distribution. Mêdog County, Tibet, SW China.

Remarks. The dark body color, the smooth middle part and the faint mediobasal carina of the vertex, and the shorter discal longitudinal sulci of the pronotum indicate a distinct species. An associated male from the same locality is required to determine the sexual dimorphism of this species.

Figures

FIGURE 76. Morphology of Trisinus sp., female. A. Dorsal habitus. B. Head and pronotum. C. Apex of abdomen. D. Tergite 5 (VIII). E. Sternite 6 (VIII). F. Genitalia. Scale bars: 0.5 mm in A; 0.2 mm in B; 0.1 mm in C–F.

FIGURE 99. Environment of and collecting sites at Nyingchi area. A. Beibeng Township (Ü崩乡). B. Road near Gelin Village (格ff村). C. A bridge at Yarang (亚ü). D. A village near Guoguotang Great Bend (果果Ƌkm弯). E. Environment near Mêdog County (ẸṘ县). F. Path to Renqingbeng Temple (仁ů崩寺). G. An overall view of Guoguotang Great Bend. Photo Credit: E, F by Xiao-Bin Song.