Trisinus tangliangi, Ding & Ming & Yin, 2025

Ding, Mei-Lin, Ming, Liang & Yin, Zi-Wei, 2025, A third species of the Trisinus cavernosus group (Coleoptera: Staphylinidae: Pselaphinae), Zootaxa 5632 (2), pp. 395-400 : 396-398

Trisinus tangliangi sp. nov.

Chinese common name: ĿƂIJssȃş

( Figs 1 , 2 )

Type material (45 exx.). HOLOTYPE: CHINA: ♂, ‘China: Guangdong, Shenzhen, Wutong Mt. , 22°34’36.12”N, 114°12’19.27”E, 570 m, 7.vi.2019, sifted, Tang, Huang, Shuai, Zhao & Cai leg. Ḟ东ŝẍ圳ṪÑAEƜNJƜ ª ’ ( SNUC) . PARATYPES: CHINA (all from Wutong Mountain): 3 ♂♂, 3 ♀♀, same collecting data as for holotype’ ; 3 ♂♂, 4 ♀♀, ‘ 22°35’50.94”N, 114°10’47.96”E, 284 m, 18.xi.2018, Cheng, Shuai, & Zhao leg.’; 2 ♂♂ ‘ 22°35’50.94”N, 114°10’47.96”E, 900 m, 26.iii.2019, Tang, Shuai, Zhao, Zhou & Xia leg.’; 12 ♂♂, 10 ♀♀, ‘ 22°35’50.94”N, 114°10’47.96”E, 400 m, 27.iii.2019, Tang, Shuai, Zhao, Zhou & Xia leg.’; 3 ♂♂, 22°34’36.12”N, 114°12’19.27”E, 159 m, 28.iv.2019, Cheng, Miao, Xia & Zhang leg.’; 2 ♂♂, 1 ♀, ‘ 22°34’55.24”N, 114°11’59.97”E, 286 m, 30.iv.2019, Cheng, Miao, Xia & Zhang leg.’; 1 ♀, ‘ 22°34’56.35”N, 114°12’52.70”E, 19.vi.2020, Lin, Xia, Yin & Zhang leg.’ (all in SNUC) .

Diagnosis. Male. Body length approximately 1.8 mm. Head greatly transverse; vertex distinctly modified, with large Y-shaped cavity between markedly laterally expanded projections, one arrow-like protuberance and one small, dark tubercle inside cavity; antenna simple, lacking modifications. Pronotum in addition to sulci with weak longitudinal discal carinae, lateral margins expanded at middle. Discal striae of elytra extending posteriorly to approximately apical 4/5 of elytral length. Aedeagus greatly asymmetric, ventral stalk composed of one elongate plate with two macrosetae and another broad, apically truncate plate, dorsal lobe narrowed at apex. Female. Body length approximately 1.7 mm, head simple, lacking modifications, antenna shorter than for male, genitalia as in Fig. 1J , membranous, sub-triangular.

Description. Male. Body ( Fig. 1A ) length 1.78–1.83 mm; color reddish-brown, with tarsi and mouthparts lighter. Dorsal surface of pronotal and elytral discs and abdomen finely punctate, covered with relatively long pubescence.

Head ( Fig. 1B, C ) greatly transverse, broadly truncate at base, much wider than long, length 0.37–0.39 mm, width across vertexal projections 0.59 mm; vertex heavily modified, densely and coarsely punctate, lacking foveae (dorsal tentorial pits) and sulci due to modification; with large, roughly Y-shaped central cavity between markedly expanded lateral projections; inside cavity one thin, arrow-like protuberance and one small, dark, apically-narrowing tubercle, with two setose tufts at middle of anterior margin of cavity; tempora shorter than eyes; antennal tubercles weakly raised, with distinct postantennal foveae; frons broadly and greatly impressed between antennal tubercles, glabrous at middle, completely demarcated from clypeus by transverse ridge; clypeus with smooth surface, anterior margin carinate and moderately raised; ocular-clypeal carinae complete. Venter with two small gular foveae (posterior tentorial pits) in single pit, lacking median carina. Eyes prominent, each composed of approximately 25 ommatidia. Maxillary palpus with palpomere 1 minute; 2 elongate, curved, pedunculate basally and enlarged apically; 3 short, sub-triangular; 4 fusiform, widest near middle. Antenna moderately long, lacking modifications, length 0.95–0.98 mm; indistinct club loosely formed by slightly enlarged apical three antennomeres; antennomere 1 thick, subcylindrical, 2 larger than 3, 3–8 each slightly elongate, 9 and 10 each submoniliform, 11 largest, slightly longer than 9 and 10 combined (19:17), sub-conical.

Pronotum ( Fig. 1B ) slightly shorter than wide, length 0.40 mm, width 0.47 mm, widest at middle, anterior half of disc finely punctate; lateral margins distinctly expanded laterally; lateral sulci weakly developed, present as shallow impressions at pronotum’s basal half; disc weakly convex, coarsely punctate along short discal carinae, median longitudinal sulcus short, extending from base anteriorly slightly beyond middle of pronotum, lacking median antebasal fovea and mediobasal impression, lateral antebasal foveae connected by transverse antebasal sulcus, lacking antebasal tubercles; outer and inner pair of basolateral foveae present; basal collar coarsely punctate. Prosternum with basisternal (precoxal) portion slightly longer than procoxal rests; with small lateral procoxal foveae; oblique hypomeral grooves present at basal halves, lacking lateral antebasal hypomeral impressions; hypomeral ridges close to coxal cavities.

Elytra wider than long, length 0.53 mm, width 0.64–0.66 mm; roundly quadrate, truncate at bases, dorsal surface with relatively long pubescence; each elytron with two distinct, asetose basal foveae; discal striae long, extending from outer basal foveae posteriorly to 4/5 of elytral length; humeri denticulate, with tiny subhumeral foveae, sulcate marginal striae extending from foveae to posterior margins of elytra. Metathoracic wings fully-developed.

Mesoventrite short, laterally fully demarcated from metaventrite by oblique ridges; median mesoventral foveae narrowly separated, originating from shared setose, transverse opening, lateral mesoventral foveae large and setose, forked internally; prepectus broadened, collar-shaped; mesoventral intercoxal process short, apically acute. Metaventrite slightly and broadly impressed at middle, with pair of large, setose lateral mesocoxal foveae and setose lateral metaventral foveae, metaventral intercoxal process narrowly and shallowly emarginate at middle.

Legs moderately elongate; mesotibia ( Fig. 1D ) with small blunt tubercle at apex.

Abdomen slightly narrower than elytra, widest at lateral margins of tergite 1 (IV), length 0.44–0.46 mm, width 0.57–0.58 mm. Tergite 1 (IV) ( Fig. 1E ) longer than 2–4 (V–VII) combined, basal sulcus interrupted by two pairs of basolateral foveae, discal carinae short and distinct, with complete and oblique inner marginal carinae; tergite 2 (V) slightly longer than 3 (VI), 4 (VII) slightly shorter than 2 and 3 combined along middle, tergite 5 (VIII) transverse, posterior margin roundly emarginate at middle, tergite 2–4 (V–VII) each with one pair of small basolateral foveae. Sternite 2 (IV) densely setose at base, with large, transverse mediobasal and two pairs of basolateral foveae, lacking basal impression, with moderately long lateral carinae extending for almost half of sternal length; midlength of sternite 2 longer than 3–5 (V–VII) combined, 3–5 each short at middle, 3 and 4 (VI) each with one pair of punctiform basolateral foveae, 5 lacking foveae, sternite 6 (VIII) transverse, posterior margin sinuate at middle, sternite 7 (IX) ( Fig. 1F ) weakly sclerotized, apex rounded and with few long setae.

Aedeagus ( Fig. 1G–I ) 0.28 mm long, moderately sclerotized, greatly asymmetric; median lobe with large basal capsule and suboval foramen, ventral stalk composed of one elongate structure gradually narrowing apically and curved rightward (orientation according to Fig. 1H ), with two long macrosetae at middle, and another shorter, truncate projection broadest at base and narrowing apically; dorsal lobe much thinner and shorter than ventral stalk, narrowed at apex; parameres fused and reduced to ventral membrane.

Female. Externally similar to male in general; antenna distinctly shorter; head lacking modifications; mesotibia lacking apical tubercle; each eye composed of approximately 18 ommatidia; humeri moderately prominent, denticulations less distinct; metathoracic wings lacking. Measurements (as for male): body length 1.66–1.71 mm, length/width of head 0.32–0.34 mm / 0.47–0.49 mm, pronotum 0.37 mm / 0.43–0.44 mm, elytra 0.44 mm / 0.59–0.60 mm, abdomen 0.47–0.55 mm / 0.56 mm; length of antenna 0.80–0.82 mm; genitalia transverse ( Fig. 1J ), 0.20 mm wide, posterior margin convex at middle.

Comparative notes. This third species of the Cavernosus group is distinguished by the significantly more laterally protruding head and pronotum compared to both known congeners from Zhejiang and Jiangxi. Additional diagnostic characters include relatively longer antennae, a notably shorter median longitudinal sulcus of the pronotum, and the absence of serration at the apex of aedeagal dorsal lobe.

Distribution. South China: Guangdong ( Fig. 2 ).

Etymology. The species epithet is dedicated to Liang Tang for his extensive support to the field work in Shenzhen. The name is a noun in the genitive case.

Remarks on male wing dimorphism. Among the 24 examined males, two individuals exhibit complete absence of hind wings, suggesting intraspecific behavioral dimorphism within this species. All 21 female specimens are flightless, entirely lacking hind wings. While wing dimorphism in male Pselaphinae has been documented across multiple lineages, its underlying mechanisms and adaptive significance at the species level remain poorly understood. This phenomenon parallels patterns observed in other insect groups where wing reduction correlates with ecological specialization or resource-dependent phenotypic plasticity (e.g., Braendle et al. 2006; Kotyk & Varadínová 2017; Roff & Fairbairn 1993; Zhang et al. 2019; Ziabari et al. 2022).

Figures

FIGURE 1. Morphology of Trisinus tangliangi sp. nov. (A–I. Male. J. Female). A. Dorsal habitus. B. Head and pronotum. C. Head. D. Apex of mesotibia. E. Tergite 1 (IV). F. Tergite 7 (IX). G–I. Aedeagus, lateral (G), ventral (H) and dorsal (I). J. Genital complex. Scale bars: 0.5 mm in A; 0.2 mm in B, C, E; 0.05 mm in D, F; 0.1 mm in G–J.

FIGURE 2. Distribution of Trisinus cavernosus group species.