Plastus Plastus rhombicus Wu & Zhou

Wu, Jie & Zhou, Hong-Zhang, 2010, Taxonomic study of subgenus Plastus s. str. (Coleoptera, Staphylinidae, Osoriinae) in China, with descriptions of five new species, ZooKeys 51, pp. 17-32 : 25-28

Plastus Plastus rhombicus Wu & Zhou sp. n. Figs 38131819

Type material.

Holotype male, Yunnan: Tengchong: Jietou (25°41.820'N 098°40.835'E), 1865 m, 14.v.2006, H.B. Liang coll. (IZ-CAS). Paratypes (2 spp.): 2 females, same data as for holotype (IZ-CAS).

Description.

Measurement. Body length: 10.43-11.78 mm. HL: 0.56-0.70 mm; HW: 1.43-1.52 mm; PL: 1.46-1.67 mm; PW: 1.99-2.22 mm; EL: 2.01-2.21 mm; EW: 2.09-2.25 mm.

Coloration. Head black with labrum red-brown (Fig. 8), mandibles black with inner side red-brown. Pronotum, elytra and abdomen black (Fig. 3). Antennae dark brown. Femora black, tibiae black at base and gradually become red-brown apically. Tarsi brown.

Structural attributes. Head (Fig. 8) transverse, about twice as long as wide, sides slightly divergent anteriorly; frontal impression deep and rhomboid, with anterior margin medially convex and slightly turned up, posterior margin slightly convergent posteriorly, about 3 times as wide as long; lateral teeth blunt with apices slightly divergent forward, on apical 1/3 of ventral side with triangularly convex subsidiary denticle (in front of which, additional small denticle present in one examined female specimen), on inner side with row of 5-7 long setae, not extending onto anterior margin of frontal impression; along external side of lateral tooth, lateral impression very short and narrow, not extending to front angle of head, bearing 2-4 short setae, anterior margin of frontal angle of head rounded; median sulcus on vertex almost twice as long as median length of frontal impression, gradually broadened posteriorly, the posterior end of which is almost 2 times as wide as middle; clypeus elongate and rounded anteriorly, with shallow depression behind anterior margin, along lateral side with 4 or 5 long setae scattered; eye glabrous and convex, occupying about 3/5 of side of head; vertex strongly convex near frontal angle, central disc polished and covered with fine micropunctures, along lateral and postero-lateral margin with some scattered punctures and long setae, at each side of posterior end of median sulcus with indistinct fovea bearing 2 or 3 long setae.

Antennae subgeniculate, antennomere I baculiform and apically slightly depressed to form shallow sulcus on dorsal side, antennomere II smallest, slightly transverse; antennomere III elongate about 1.5 times as long as II; antennomeres IV–VI slightly quadrate; VII–X gradually more transverse apically; antennomere XI elongate, apically rounded, about 1.5 times as long as X. Mentum trapeziform (Fig. 13), frontal angle slightly rounded, anterior margin weakly depressed in middle, with indistinct median denticle, ventral surface setose, with three wrinkled ridges, last posterior one less distinct than anterior two, disc surface with 4 large setiferous punctures along posterior margin, space between those punctures slightly rugose.

Pronotum transverse (Fig. 3), distinctly wider than head, anterior margin weakly bisinuate, sides rounded and slightly convergent anteriorly, median longitudinal sulcus deep and narrow, slightly broadened posteriorly, not reaching either anterior or posterior margins; lateral marginal area with 24-37 setiferous punctures, punctures on upper half slightly larger than those on lower half, disc polished, with fine micropuncture evenly distributed.

Protibiae externally furnished with 11-14 denticles, which gradually become shorter basally.

Elytra almost quadrate, epipleural line absent, setiferous punctures on lateral marginal side sparser and less distinct than those on side of pronotum.

Abdomen cylindrical, along anterior and posterior margin of III–VI segments respectively with row of setae, disc of each segments densely punctured, except for broad glabrous region near posterior margin, basal distinctly denser than apical, seg ments VII and VIII densely setose and punctured, with longitudinal glabrous region in central.

Male: aedeagus almost membranous (Figs 18, 19), basal part of median lobe strongly bulbous and curved behind basal orifice; posterior part baculiform, distinctly narrower than basal part, sides almost parallel, only ventral side sclerotised; parameres elongate and strongly curved with apices far below level of basal protruding apices, anterior margin near base rounded; basal parts protruding ventrally, apically weakly separated below basal orifice.

Remarks

. This species can be distinguished from other members of subgenus Plastus s. str. by the rhomboid shape of frontal impression of head (Fig. 8). The anterior margin of frontal impression in this species is convex upward in middle. This structure is slightly similar in position to the central tooth in the subgenus Eutriacanthus , but never pointed and protruding anteriorly as the single central tooth in the latter. Thus, this new species has a clinal morphological characteristics between subgenera Eutriacanthus and Plastus s. str.

Distribution.

Known from the type locality in Yunnan, elevation of 1865 m.

Etymology.

The species name derived from a Latin word ‘rhombicus’ (rhombic) to indicate the shape of its frontal impression.