Microhygrodromicus exiguus, Shavrin, 2024

Shavrin, Alexey V., 2024, Review of Hygrogeus Mulsant & Rey, 1880 and Trichodromeus Luze, 1903, with descriptions of three new genera from the eastern Palaearctic Region (Coleoptera: Staphylinidae: Anthophagini: Omaliinae), Zootaxa 5531 (1), pp. 1-62 : 55-56

Microhygrodromicus exiguus sp. n.

( Figs 125 , 127–135 , 141 )

Type material examined. Holotype ♂ ( Fig. 125 ; dissected): ‘ CHINA: YUNNAN PROv. | Gongshan Co., | Dimaluo vil., | 27°56.82’N, 098°41.97’E, 1900 m | D. Král & J. Růžička leg.’ <printed>, ‘ 6.vii.2019. [Y05], | individually under | bark of fallen trunks, | ruderals near road in the village, | above’ <printed>, ‘ HOLOTYPE | Microhygrodromicus | exiguus sp. n. | Shavrin A.V. des. 2024’ <red, printed> ( NMPC).

Description. Measurements: HW: 0.55; HL: 0.42; OL: 0.12; LT: 0.10; AL: 1.42; PL: 0.48; PWmax: 0.60; PWmin: 0.36; ESL: 0.92; EW: 1.00; MTbL: 0.62; MTrL (holotype): 0.27 (MTrL 1–4: 0.19; MTrL 5: 0.08); AW: 1.05; AedL: 0.58; BL: 2.71.

Habitus as in Fig. 125 . Forebody indistinctly bronze, dark-brown, with blackish abdomen; antennae and legs yellow-brown; mouthparts yellow. Apical portion of clypeus with dense transverse microreticulation, middle part with indistinct transverse diagonal meshes, infraorbital portions with fine subdiagonal reticulation, more visible around each ocellus, mediobasal portion between ocelli and neck with transverse and coriaceous sculpture; neck with dense and fine transverse microreticulation; medioapical portion of pronotum with indistinct transverse meshes, and mediobasal part with distinct isodiametric microreticulation; scutellum with fine isodiametric meshes; abdomen with very dense and fine isodiametric microsculpture. Pubescence of body dense, yellowish, suberect, moderately long, slightly finer on abdominal tergites.

Head 1.3 times as broad as long, with slightly elevated median portion in front of level of eyes and strongly elevated infraorbital portions; supra-antennal prominences narrow, elongate and markedly convex; anterio-median depression moderately deep and wide, distinctly narrowed posteriad and connected with interocellar depression; interocellar depression wide and deep (deeper between median level of eyes), from widest apical portion gradually narrowed posteriad. Temples convex, moderately long, slightly shorter than longitudinal length of eyes, slightly protruded posteriad. Distance between ocelli 1.7 times as long as distance between ocellus and posterior margin of eyes. Punctation irregular and moderately large, denser in middle, sparser and slightly deeper on infraorbital portions; mediobasal portion in front of neck with dense and fine punctation; neck with indistinct and very sparse punctation. Labrum as in Fig. 127 . Mandibles as in Fig. 128 . Labium and mentum as in Fig. 130 . Maxillary palpi as in Fig. 129 ; last maxillary palpomere long, but shorter than penultimate segment. Basal antennomere wide, more than three times as long as broad, antennomere 2 narrower and shorter than basal antennomere, 3 slightly shorter and narrower than 2, 4 shorter than 3, 5–8 slightly longer than 4, 9–10 slightly shorter than 8, apical antennomere 1.7 times as long as 10, from apical third gradually narrowed toward subacute apex.

Pronotum 1.2 times as broad as long, distinctly broader than head; lateroapical portions gradually and widely rounded apicad, not forming protruded portions; lateral margins distinctly crenulate, markedly stronger along latero-basal margins; posterior angles obtuse; anterior margin widely rounded, about as long as somewhat straight posterior margin. Punctation dense and moderately deep, slightly larger than that in head, sparser in medioapical and denser in middle; mediobasal portion without distinct punctures. Scutellum with several very fine punctures.

Elytra convex, about twice as long as pronotum. Punctation denser and deeper than that in pronotum, finer around scutellum.

Metatarsus about twice shorter that metatibia; apical metatarsomere about twice shorter than preceding four metatarsomeres.

Abdomen indistinctly broader than elytra. Punctation dense and fine.

Male. Posterior margin of abdominal tergite VIII straight ( Fig. 134 ). Posterior margin of abdominal sternite VIII widely concave ( Fig. 135 ). Genital segment as in Fig. 133 . Aedeagus with moderately wide basal portion and median lobe, gradually narrowed in apical third, with widely rounded apical part; parameres narrow, slightly not exceeding apex of median lobe, with two long and two short apical setae; internal sac complicated, moderately wide, with large V-shaped slerotized medio-apical and narrow elongate structures in about middle, with very long narrow flagellum, spirally folded in basal portion ( Fig. 131 ). Lateral aspect of aedeagus as in Fig. 132 .

Female unknown.

Comparative notes. Microhygrodromicus exiguus sp. n. can be distinguished from M. politus sp. n. by the smaller body, paler abdomen, stronger punctation of the head, shorter temples, which are slightly protruded posteriad, narrower apical part of pronotum with presence of lateral crenulation and absence of a mediobasal depression, longer elytra, shape of the rounded apical part of median lobe and other details of the morphology of the aedeagus

Distribution. The species is known only from the type locality in Gongshan, Yunnan, China ( Fig. 141 ).

Bionomics. The holotype was possibly found under bark of fallen trunks at elevation 1900 m a.s.l.

Etymology. The specific epithet is the Latin adjective exiguus , - a, - um (small). It alludes to the small body of the species.

Remarks. Microhygrodromicus exiguus sp. n. is the smallest species of the Hygrogeus complex in the Palaearctic Region. In the Nearctic Region, the smallest species is Microedus rogersi Hatch, 1957 (2.6–2.8 mm; see Hatch 1957).

Figures

FIGURE 141. Distribution of Microhygrodromicus exiguus (circle) and M. politus (square) in Yunnan, China.

FIGURES 125–126. Habitus of Microhygrodromicus: 125—M. exiguus (holotype), 126—M. politus (holotype). Scale bar: 1.0 mm.

FIGURES 127–130. Mouthparts of Microhygrodromicus exiguus (holotype): 127—labrum (dorsal view), 128—mandibles (left and right, dorsal view), 129—maxilla (dorsal view), 130—labium (ventral view). Scale bar: 0.1 mm.

FIGURES 131–135. Microhygrodromicus exiguus: 131—aedeagus, parameral view, 132—aedeagus, lateral view, 133—male genital segment, 134—male tergite VIII, 135—male sternite VIII. Scale bars: 0.1 mm.