Euconnus (Euconnus) impar Sharp, 1886

Jałoszyński, Paweł, 2022, Euconnus Thomson of Japan: redescriptions of species established by Reitter, Sharp and Franz, new synonyms, and summary of current state of knowledge (Coleoptera, Staphylinidae, Scydmaeninae), Zootaxa 5093 (1), pp. 1-37 : 13-15

Euconnus (Euconnus) impar Sharp

Euconnus impar Sharp, 1886: 46 .

Euconnus (Pycnophus) impar Sharp ; Hoshina & Arai 2003: 11.

Euconnus (Euconnus) impar Sharp ; Jałoszyński 2021b: 268 (implied, by placing Pycnophus as junior synonym of Euconnus s. str.).

Euconnus (Pycnophus) otorii Hoshina & S. Arai in Hoshina et al. (2003): 30. Synonymized by Hoshina & Arai 2003: 11. ( Figs 50–57 )

Type material studied. Lectotype of Euconnus impar Sharp (here designated): ♂ ( Fig. 50 ), mounted on thick cardboard ( Fig. 51 ) annotated: “ Euconnus / impar. Type / D.S. / Nagasaki / 28.5.81. Lewis”, and with three labels ( Fig. 51 ): “Sharp Coll. / 1905-313.” [darkened white, printed], circular label “Type / H.T.” [white with red margin, printed], and circular label “SYN- / TYPE” [white with blue margin, printed] ( NHM) . Paralectotypes of E. impar (3 exx): 2 ♂♂, mounted on one thick card and annotated as lectotype, with two labels: “Sharp Coll. / 1905-313.” [darkened white, printed], and circular label “SYN- / TYPE” [white with blue margin, printed] ( NHM) ; 1 ♂, mounted on a separate thick card and annotated as lectotype, with two labels: “Sharp Coll. / 1905-313.” [darkened white, printed], and circular label “SYN- / TYPE” [white with blue margin, printed] ( NHM) .

Additional material studied. HONSHU: Ibaraki Pref.: 6 ♂♂, 5 ♀♀, Shishitsuka ad Tsuchiura, 14– 23.09.2002, all collected from surface of mud under decaying plant debris on rice paddies after harvest, leg. P. Jałoszyński (cPJ). Additionally, specimens from Saga Prefecture were also seen ( NSMT) .

Emended diagnosis. Among Japanese species, E. impar can be identified by: nearly asetose head and elytra and densely setose pronotum with thick bristles; slender and loosely assembled tetramerous antennal club; pronotum lacking antebasal pits, groove and sublateral carinae, broadest indistinctly behind middle; male protarsi modified, with tarsomere 1 forming long and blunt projection directed ventrad; and aedeagus strongly elongate and with heavily sclerotized median lobe, with a pair of long rod-like distolateral projections and long ventrodistal plate slightly broadening toward truncate apex.

Redescription. Body of male ( Fig. 50 : lectotype) moderately slender, strongly convex, BL 1.60–1.80 mm; cuticle glossy, pigmentation light brown with reddish hue, vestiture of setae and bristles slightly lighter than cuticle.

Head rounded, slightly transverse and broadest at eyes, HL 0.30–0.35 mm, HW 0.33–0.38 mm; tempora in dorsal view slightly less than twice as long as eyes and strongly converging posterad; vertex and frons confluent, weakly and evenly convex, posterior margin of vertex rounded, posteriorly convex, not bulging posterodorsad; supraantennal tubercles barely marked; frons between antennae steeply declining; clypeus unmodified. Eyes moderately large, finely faceted, weakly projecting laterad from the head silhouette, in lateral view oval. Head virtually impunctate and asetose, except for sparse setae on clypeus and several on vertex; thick bristles lacking. Antennae slender and loosely assembled, with slender tetramerous clubs, AnL 0.80–0.90 mm; antennomeres 1–8 distinctly elongate, 9 and 10 each about as long as broad, 11 about 1.8 × as long as broad.

Pronotum bell-shaped, widest slightly behind middle, but dense vestiture obscures the shape, PL 0.40–0.45 mm, PW 0.38–0.44 mm; anterior margin strongly arcuate and much shorter than posterior margin, anterior corners indistinct, sides of pronotum strongly rounded and strongly converging anterad; posterior corners strongly obtuseangled, well-marked; posterior margin shallowly bisinuate. Pronotal base lacking pits, sublateral carinae and transverse groove. Disc virtually impunctate, densely covered with thin, suberect setae and thick, straight bristles distributed not only on sides, but also on dorsum.

Elytra oval, broadest slightly or distinctly in front of middle, EL 0.90–1.03 mm, EW 0.68–0.75 mm, EI 1.23– 1.37; basal impressions short and shallow, humeral calli prominent and only slightly elongate, each delimited from adscutellar region by elongate impression running posterolaterad, elytral apices separately rounded. Punctures on elytral disc inconspicuous; setae erect, long and very sparse, only a few can be seen, mainly on anterior half of each elytron, where setal insertions are separated by spaces subequal to lengths of setae. Hind wings long, functional.

Legs moderately long and slender, modified: profemora strongly thickened, pro- and mesotibiae weakly sinuate, protarsi ( Fig. 53 ) with tarsomere 1 forming blunt, short projection directed ventrad, all tarsomeres of fore legs with conspicuously long setae.

Abdomen unmodified.

Aedeagus ( Figs 54–57 ) strongly elongate,AeL 0.45–0.50 mm; median lobe in ventral view broadest in submedian region, ventral apical plate strongly elongate, broadening distad and with truncate apex, apical region with a pair of long and slender sclerotized lateral rod-like projections flanking median ventral plate; endophallic structures symmetrical, with a pair of elongate, approximate subapical sclerites touching each other along midline, and with lateral groups of needle-like sclerites projecting laterad beyond silhouette of median lobe; parameres slender and moderately long, not reaching apex of median lobe, in lateral view strongly curved in proximal half, each with two long apical setae.

Female. Externally easily distinguishable from males by markedly slenderer profemora ( Fig. 52 vs. 50) and unmodified tarsomere 1 of protarsi. Wings well developed, functional. BL 1.68–1.75 mm; HL 0.33 mm, HW 0.35– 0.38 mm, AnL 0.80–0.83 mm; PL 0.43 mm, PW 0.39–0.43 mm; EL 0.93–1.00 mm, EW 0.70–0.75 mm, EI 1.23– 1.38.

Distribution. Japan (Honshu, Kyushu), South Korea.

Remarks. This is one of the most remarkable Japanese species of Euconnus (s. str.), identifiable by external characters. Although adults of E. impar show some variability in the body length (the smallest studied specimen is 1.60 mm long, whereas the largest is 1.75 mm), and in proportions of body parts (especially the elytra: the elytral index in males is 1.23–1.37, and in females 1.23–1.38), their body form and setal pattern are constant and allow for easy identification. Hoshina et al. (2003) mentioned a difference in shape and thickness of femora between males and females, but overlooked the striking sexual dimorphism in the first tarsomere of fore legs ( Fig. 53 ), which is unique among Japanese Euconnus .

According to Hoshina et al. (2003), adults of E. impar were collected on Honshu (prefectures Saitama, Tochigi, and Yamanashi) in wetlands near ponds and from leaf litter in a dried riverbed, where humidity was still high. These observations agree with my experience—I have collected and observed individuals of this species walking on very wet mud under a thin layer of decomposing plant remains on drained rice paddies, surrounded by deciduous and strongly disturbed and fragmented forests in a generally agricultural countryside. It seems that E. impar may be associated with ephemeral habitats of decomposing plant debris on wet soils, and as both sexes have well-developed wings, it can be expected that they fly to actively search for new suitable places, and flight intercept traps may be effective to collect this species.

Figures

FIGURES 50–57. Euconnus impar, male (50) and female (52). Dorsal habitus (50) and annotated mounting card with historical labels (51) of lectotype; dorsal habitus of non-type specimen (52); tarsus of fore leg of male in lateral view, on dark and white background, arrowhead indicating modified tarsomere 1 (53); aedeagus in ventral (54, 56) and lateral (55, 57) views.