Trisinus cavernosus, Ding & Niu & Yin, 2025

Ding, Mei-Lin, Niu, Xiao-Ling & Yin, Zi-Wei, 2025, A new species group of Trisinus Raffray (Coleoptera: Staphylinidae: Pselaphinae), with description of two new species from the Tianmu Mountains, China, Zootaxa 5590 (2), pp. 256-262 : 257-259

Trisinus cavernosus sp. nov.

Chinese common name: ëǎñaȃş

( Figs 1 , 3 )

Type material (56 exx.). HOLOTYPE: CHINA: ♂, ‘ China: Zhejiang, Linan Dist., W. Tianmu Mt., Gaolingtou , 30°24'7"N, 119°30'15"E, 1000 m, 4.ix.2024, Peng, Yin, Ding & Zhang leg. ṽũ临aex天năü头DZĸDz ’ ( SNUC) . PARATYPES: CHINA: Zhejiang: 12 ♂♂, 6 ♀♀, ‘ China: Zhejiang, Linan Dist., W. Tianmu Mt., Niling to Pingxi , 30°24'22"N, 119°27'41"E, 950–1000 m, 7.ix.2024, Yin, Ding, Zhang leg. ṽũūm临aex天nāü - ṿã ’ ; 1 ♂, 1 ♀, ‘ China: Zhejiang, Linan Dist., W. Tianmu Mt., Niwuli to Xianrentai , 30°22'10"N, 119°29'27"E, 550–1200 m, 6.ix.2024, Peng, Ding, Zhang leg. ṽũ临aex天n坭坞¶-仙人台 ’ ; 1 ♂, 2 ♀♀, ‘ China: Zhejiang Prov., Hangzhou City, Mt. Wuchaoshan , alt. 200 m, 11-IV-2011, Peng & Zhu leg.’ ; 1 ♂, 8 ♀♀, ‘ China: Zhejiang Prov., Linan City, Mt. East Tianmushan , alt. 370–500 m, 12-IV-2011, Peng & Zhu leg.’ ; 1 ♀, ‘ Longwangshan, Zhejiang Prov., 300–500 m, 23-IV-2004, Jing-wen Zhu leg.’ ; 2 ♀♀, ‘ China: Zhejiang Prov., Anji, Longwangshan Mt., Qianmutian , 29.vii.2011, 700–1350 m, Yu-Hong Pan leg.’ ; 2 ♂♂, 3 ♀♀, ‘ China: Zhejiang, Anji County, Longwang Shan N. R., Pingxi, creek valley , 1000–1100 m, 09.vi.2012, Hu & Yin leg.’ ; Jiangxi: 2 ♂♂, 1 ♀, ‘ China: Jiangxi, Nanchang City, Wangjia Mountain , 28°46'1"N, 115°46'59"E, 80 m, 10.x.2024, sifted, Jing-Zhe Du leg. ũ xâ南ēǖdzüĩNJƜữŝẽī ’ ; 5 ♂♂, 1 ♀, ‘ China: Jiangxi, Nanchang City, Wangjia Mountain , 28°45'56"N, 115°47'5"E, 190 m, 3.xi.,2024, leaf litter, sifted, Ming-Zhe Liu & Jing-Zhe Du leg. ũx南ēdzüĩNJƜữŝẽ 刘ẹẽ ’ ; 3 ♂♂, 3 ♀♀, ‘ China: Jiangxi, Nanchang Botanical Garden , 28°45'51"N, 115°46'7"E, 325 m, 7.xi.2024, sifted, Jing-Zhe Du leg. ũxâ南ēäń园ữŝẽī ’ (all in SNUC) .

Diagnosis. Male. Body length approximately 1.7–1.8 mm. Head sub-rectangular; vertex greatly modified, with large V-shaped cavity between roundly denticulate lateral projections, inside cavity one lingulate protuberance surrounded by four tufts of long setae; antenna simple, lacking modifications. Pronotum in addition to sulci with weak longitudinal discal carinae. Discal striae of elytra extending posteriorly to approximately apical 4/5 of elytral length. Aedeagus greatly asymmetric, ventral stalk composed of one elongate structure with two macrosetae and one broad, membranous part, dorsal lobe thin and serrate at apex. Female. Body length approximately 1.7 mm, head simple, lacking modifications, antenna shorter than for male, genitalia as in Fig. 1J .

Description. Male. Body ( Fig. 1A ) length 1.72–1.77 mm; color reddish-brown, with tarsi and mouthparts lighter. Dorsal surface finely punctate, covered with relatively long pubescence.

Head ( Fig. 1B, C ) sub-rectangular, almost truncate at base, much wider than long, length 0.43 mm, width across eyes 0.49–0.50 mm; vertex heavily modified, densely and coarsely punctate, lacking foveae (dorsal tentorial pits) and sulci due to modification; with large, roughly V-shaped central cavity between two large, roundly denticulate lateral projections; inside cavity one small, thin, lingulate protuberance, with two setose tufts at middle of anterior margin and two similar tufts at middle of posterior margin of cavity; lateral margins of cavity densely setose; tempora much shorter than eyes; antennal tubercles weakly raised, with setose postantennal foveae; frons broadly impressed between antennal tubercles, impunctate and glabrous at middle, anteriorly fused with clypeus; clypeus finely punctate, anterior margin carinate and moderately raised; lacking ocular-clypeal carinae. 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 relatively short, lacking modifications, length 0.90–0.92 mm; indistinct club loosely formed by slightly enlarged apical three antennomeres; antennomere 1 thick, subcylindrical, 2–10 each submoniliform, 11 largest, slightly longer than 9 and 10 combined (19:16), sub-conical.

Pronotum ( Fig. 1B ) slightly shorter than wide, length 0.36–0.37 mm, width 0.40–0.42 mm, widest approximately at middle; semi-circular lateral sulci extending from dorsal surface laterally and anteriorly; disc weakly convex, coarsely punctate, median longitudinal sulcus longer than lateral sulci, with pair of thin discal carinae, 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. 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 0.53–0.57 mm, width 0.62–0.66 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 vestigial.

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 0.41–0.51 mm, width 0.57–0.58 mm. Tergite 1 (IV) ( Fig. 1E ) dorsally longer than 2–4 (V–VII) combined, basal sulcus interrupted by two pairs of basolateral foveae, discal carinae distinct, with complete and oblique inner marginal carinae; tergite 2 (V) slightly longer than 3 (VI), 4 (VII) 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 pair 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) with one pair of punctiform basolateral foveae, 5 lacking foveae, sternite 6 (VIII) transverse, posterior margin sinuate at middle, sternite 7 (IX) ( Fig. 1F ) suboval, weakly sclerotized, apex rounded and with few long setae along apical margin.

Aedeagus ( Fig. 1G–I ) 0.27 mm long, weakly sclerotized, dorsoventrally greatly asymmetric; median lobe with large basal capsule and moderately oval 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 projection broadest at base and narrowing apically; dorsal lobe much thinner than ventral stalk, narrowed at middle and broadening apically and basally, with serrate apex; parameres fused and reduced to ventral membrane.

Female. General external morphology similar to male; antenna shorter; head lacking modifications; legs simple; each eye composed of about 18 ommatidia; humeri moderately prominent; metathoracic wings lacking. Measurements (as for male): body length 1.71–1.74 mm, length/width of head 0.36 mm / 0.47 mm, pronotum 0.37– 0.38 mm / 0.41–0.42 mm, elytra 0.49–0.51 mm / 0.63–0.64 mm, abdomen 0.52–0.54 mm / 0.60–0.62 mm; length of antenna 0.80 mm; genitalia transverse ( Fig. 1J ), 0.24 mm wide, posterior margin convex at middle.

Comparative notes. This and the following species represent the first members of the genus exhibiting significantly modified male cephalic structures. These species demonstrate apparent close relatedness based on similar external morphological characteristics and aedeagal structures. The primary distinguishing features lie in the configuration of the male vertex. Trisinus cavernosus sp. nov. displays a V-shaped central cavity with greatly projected lateral portions, whereas T. qingliangmontis sp. nov. exhibits a U-shaped central cavity with distinctly impressed lateral portions.

Distribution. East China: Zhejiang, Jiangxi ( Fig. 3A ).

Etymology. The specific epithet ‘ cavernōsus (- a, - um)’ (full of hollows or cavities) is a Latin adjective, referring to the remarkably modified male head with a large cavity of this species.

Figures

FIGURE 1. Morphology of Trisinus cavernosus 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 3. Type localities of Trisinus cavernosus sp. nov. (A) and Trisinus qingliangmontis sp. nov. (B). A. Gaolingtou, West Tianmu National Nature Reserve. B. Luminyougu, Qingliangfeng National Nature Reserve.