Tribasodites grandiceps, 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 : 156-158

Tribasodites grandiceps sp. nov.

( Figs 67 , 86A , 92A, B )

Chinese common name: 巨Ħûḃà甲

Type material ( 1 ex.). HOLOTYPE: CHINA: ♂, China: Xizang, Nyalam County, Zhangmu Town , Youyi Bridge , 27°58’11”N, 85°57’47”E, leaf litter, sifted, 1800 m, 29.vii.2010, Jian-Qing Zhu leg. (ƱẪỄŃ木县樟木W友谊 桥)’ ( SNUC).

Diagnosis. Male. Body length approximately 2.0 mm. Head sub-rounded at base, distinctly broader than pronotum, tempus moderately long, with rounded posterolateral margin, vertex with shallow reversed U-shaped impression, with moderately small foveae, with distinct mediobasal carina extending from head base anteriorly to level of anterior margin of eyes, with thin lateral carina from base to posterior margin of antennal tubercle; antenna moderately elongate, lacking modifications, antennomeres each distinctly elongate. Pronotum with laterally carinate median and shallow lateral longitudinal sulci, with pair of thin longitudinal discal carinae, with pair of small antebasal and tiny marginal spines. Elytra small, basally constricted; discal stria shallow, extending posteriorly to apical 1/2 of elytral length; disc finely punctate. Mesotibia with small preapical tubercle; metafemur expanded before base. Aedeagus elongate, asymmetric; median lobe with elongate basal capsule and round foramen, ventral stalk dilated at apex, dorsal lobe strongly curved at apex, parameres fused to broad membrane.

Description. Male. Body ( Fig. 67A ) length 1.95 mm; color reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with relatively dense pubescence.

Head ( Fig. 67B ) sub-rounded at base, slightly broader than long, length 0.43 mm, width across eyes 0.47 mm; vertex smooth, with shallow reversed U-shaped impression, vertexal foveae (dorsal tentorial pits) asetose, moderately small, mediobasal carina distinct, extending from head base anteriorly to level of anterior margin of eyes, lateral carina thin; posterolateral margin rounded; frons anteriorly demarcated from clypeus by thin frontal-clypeal ridge, area between moderately raised antennal tubercles weakly impressed; clypeus with smooth surface, its entire anterior margin strongly carinate and moderately raised; ocular-mandibular carina thin, complete, branched below eye, extended ventrally and then anteriorly to posteroventral articulation of mandible. Venter with granulate surface; small gular foveae (posterior tentorial pits) in single oval pit, with thin median carina extending from opening anteriorly to mouthparts. Compound eyes weakly prominent, composed of approximately 35 small ommatidia. Antenna moderately elongate, length 1.25 mm, indistinct club formed by slightly enlarged apical three antennomeres; antennomere 1 thick, subcylindrical, antennomeres each markedly elongate, 8 shortest, 9 much wider and longer than 8, cylindrical, 10 wider but slightly shorter than 9, moderately broadened at apical 1/2, 11 largest, much longer than 9 and 10 combined, sub-conical, anterolateral margin slightly impressed.

Pronotum ( Fig. 67B ) narrower than head, slightly longer than wide, length 0.45 mm, width 0.42 mm, widest approximately at middle; lateral margins rounded at middle, convergent apically and basally; disc slightly convex, finely punctate, thin median longitudinal sulcus with slightly carinate margins, posteriorly confluent with oval antebasal impression and moderately short mediobasal carina, pair of thin discal longitudinal carinae ( Fig. 67C ) avoid additional spines, with thin lateral longitudinal sulci; with pairs of small antebasal and tiny marginal spines; lateral antebasal foveae small and asetose; with tiny outer and inner pair of basolateral foveae. Prosternum with anterior part slightly longer than coxal part, with small lateral procoxal foveae; distinct hypomeral ridge extending from base to middle of anterior part, with small antebasal pit; margin of coxal cavity slightly carinate.

Elytra slightly wider than long, length 0.56 mm, width 0.61 mm; each elytron with three moderately large, asetose basal foveae; discal stria extending posteriorly from outer basal fovea to half of elytral length; humerus weakly prominent, subhumeral fovea present, carinate marginal stria extending from fovea to posterior margin of elytron.

Mesoventrite short, demarcated from metaventrite by transverse carinae; median mesoventral foveae narrowly separated, originating from shared transverse opening, large lateral mesoventral foveae broadly forked internally, with short mesoventral process, with complete marginal stria. Metaventrite moderately prominent admesally, inclined towards middle, with well-developed lateral mesocoxal foveae, with two lateral metaventral foveae, posterior margin roundly emarginate and with narrow split at middle.

Legs elongate; procoxa with exceptionally long seta at apex; mesotibia ( Fig. 67D ) with small preapical tubercle; metatrochanter ( Fig. 67E ) with long curved ventral protuberance, metafemur ( Fig. 67F ) broadly expanded at middle, with long setae along expansion.

Abdomen constricted near base, widest at lateral margins of tergite 1 (IV), length 0.55 mm, width 0.64 mm. Tergite 1 (IV) longer than 2 and 3 (V and VI) combined, lacking basal sulcus, with one pair of mediobasal and two pairs of basolateral foveae and pair of thin discal carinae, complete, thin inner and thickened outer marginal carinae subparallel; tergite 2 (V) slightly longer than 3 (VI), 4 (VII) shorter than tergites 2 and 3 combined, 2–4 each with one pair of small basolateral foveae and pair of thin marginal carinae; tergite 5 (VIII) semicircular, transverse, posterior margin narrowly emarginate at middle. Sternite 2 (IV) with one pair of mediobasal and three pairs of basolateral foveae, lateral two pairs in large sockets, lateral carina thick; midlength of sternite 2 more than twice length of 3 (V), 3–5 (V–VII) subequal lin length, sternites 3–5 each with one pair of small basolateral foveae, sternite 6 (VIII) transverse, posterior margin broadly emarginate, convex at middle, sternite 7 (IX) ( Fig. 67G ) composed of pair of triangular, membranous structures.

Aedeagus ( Fig. 67H–J ) 0.34 mm long, asymmetric, elongate; median lobe with laterally extended transverse basal capsule and slightly oval foramen, basoventral projection strongly enlarged, ventral stalk broad at base and apex, laterally expanded before apex and then dilated apically; dorsal lobe fusing with median lobe at base, elongate, in dorsal view bent to left at apical 1/4, then greatly curved to right and narrowing apically, parameres fused, broad and flattened, membranous.

Female. Unknown.

Comparative notes. This species is allied with a number of species centered on T. dilophus by the relatively long and rounded postocular margins, simple male antennae, and a generally elongate and slender aedeagus. It is most similar to T. prolixicornis in the lack of additional spines along the discal carinae of the pronotum, the mesally expanded metafemora of the male, and the presence of a small preapical tubercle on the male mesotibiae. These two species can be readily separated by the relatively much shorter antennae, the head being distinctly wider than the pronotum, the shorter elytra and less prominent eyes, and different forms and structures of the metafemoral expansion and the aedeagus of T. grandiceps . Tribasodites mirabilis also has modified male metafemora, but otherwise it is readily separable by the unique modification of the metatibiae and form of the aedeagus.

Distribution. Nyalam County, Tibet, SW China ( Figs 86A , 92A, B ).

Etymology. The specific epithet is a Latin adjective meaning ‘large-headed’, indicating this species has a relatively larger head among the species of Tribasodites .

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 86. Distribution of Tibetan Batrisini. A. Tribasodites dilophus sp. nov. (circle), T. elongatus sp. nov. (triangle) and T. grandiceps sp. nov. (square). B. T. gyirong sp. nov. (circle), T. kiypu sp. nov. (triangle) and T. mirabilis sp. nov. (square). C. T. prolixicornis sp. nov. (circle), T. Tribasodites pugiunculus sp. nov. (triangle) T. vertexalis sp. nov. (square) and T. yatung sp. nov. (diamond).

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.