Euconnus (Euconnus) japonicus
Creators: name: Jałoszyński, Paweł
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Euconnus
Euconnus japonicus

description: Euconnus (Euconnus) japonicus (Sharp)
Scydmaenus (Euconnus) japonicus Sharp, 1874: 127. Aedeagus illustrated in Hoshina et al. 2020: 76.
Euconnus (Euconnus) japonicus Sharp; Csiki, 1919: 49.
Euconnus (Euconnus) ohnoensis Hoshina, 2006: 44; syn. n. Aedeagus illustrated also in Hoshina et al., 2020: 76.
(Figs 58–63)
Type material studied. Lectotype of Scydmaenus japonicus Sharp (here designated): unknown sex (Fig. 58), mounted on a simple, thin and not annotated card, with four labels (Fig. 59): “Sharp Coll. / 1905-313.” [darkened white, printed], “ Scydmaenus / japonicus / Type. D.S.” [white with black frame, handwritten and printed], circular label “Type / H.T.” [white with red margin, printed], circular label “SYN- / TYPE” [white with blue margin, printed], and “ Japan / G. Lewis. ” [white with orange horizontal line, printed] (NHM). Paralectotype of S. japonicus: ♂, mounted on modern card, same labels as lectotype but without the red-margined “Type / H.T.” (NHM).
Emended diagnosis. Among Japanese species, E. japonicus can be identified by: nearly asetose head, densely setose pronotum with thick bristles, and sparsely but distinctly setose elytra with long, erect setae longer than spaces between their insertions; slender, loosely assembled and gradually thickened antennae with all antennomeres elongate; pronotum widest at base, with one pair of somewhat transverse antebasal pits, connected by a barely discernible trace of transverse groove and with a pair of short but distinct sublateral carinae; legs in male unmodified; and aedeagus strongly elongate, with a pair of elongate and recurved distolateral projections flanking long dorsodistal plate forming strikingly long median distal projection with slightly broadened and truncate apex.
Redescription. Body of male and female (Fig. 58: lectotype) moderately slender, strongly convex, BL 1.60; cuticle glossy, pigmentation light brown with umbra or slightly reddish hue, vestiture of setae and bristles slightly lighter than cuticle.
Head rhomboidal, slightly transverse and broadest at eyes, HL 0.25 mm, HW 0.30 mm; tempora in dorsal view about as long as eyes (but in lateral view shorter) and strongly converging posterad, nearly straight; vertex and frons confluent, weakly and evenly convex, posterior margin of vertex rounded, posteriorly convex, not bulging posterodorsad; supraantennal tubercles feebly marked; frons between antennae steeply declining; clypeus unmodified. Eyes large and moderately coarsely 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 long setae on vertex, thick bristles lacking. Antennae slender and loosely assembled, gradually thickening distad, AnL 0.85– 0.88 mm; all antennomeres distinctly elongate, antennomere 11 twice as long as broad.
Pronotum subconical with rounded sides, widest at base, but dense vestiture obscures the shape, PL 0.43 mm, PW 0.38 mm; anterior margin slightly arcuate and much shorter than posterior margin, anterior corners indistinct, sides of pronotum strongly rounded and strongly converging anterad; posterior corners strongly obtuse-angled, well-marked; posterior margin weakly arcuate. Pronotal base with one pair of minute lateral antebasal pits each situated in small transverse impression, transverse groove developed as vestigial, barely discernible superficial impression, sublateral carinae sharply marked. 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 in front of middle, EL 0.93 mm, EW 0.70–0.73 mm, EI 1.28–1.32; basal impressions shallow but distinct, humeral calli prominent and elongate, each delimited from adscutellar region by elongate impression running posterolaterad, suture near base distinctly elevated and narrow adsutural area delimited by shallow longitudinal groove; elytral apices separately rounded. Punctures on elytral disc inconspicuous; setae erect, long and sparse, but distributed on entire surface and much longer than distances between their insertions. Hind wings long, functional.
Legs moderately long and slender, unmodified.
Abdomen unmodified.
Aedeagus (Figs 60–63) strongly elongate, AeL 0.50 mm; median lobe in ventral view broadest near middle, barrel-shaped, ventral apical plate with median distal projection short, subtriangular and rounded at apex, dorsal apical plate with strikingly long and slender median distal projection narrowing slightly towards apex, but very short apical region broadened and truncate; median lobe with a pair of elongate, slender and recurved distolateral projections; endophallic structures symmetrical, with elongate median tubular structure and a pair of arcuate sclerites in subapical region. Parameres slender and moderately long, not reaching apex of median lobe, in ventral view apex of each paramere distinctly, gradually broadened and truncate, in lateral view parameres strongly curved in proximal half, each with two long apical setae.
Female. Lectotype was not dissected, and the male paralectotype does not bear any observable male secondary sexual characters; they are both of nearly identical measurements. Female, therefore, is either not known, or externally indistinguishable from male.
Distribution. Japan: Honshu, Kyushu.
Remarks. This species can be easily distinguished from its Japanese congeners by characteristic body form (strikingly small head with nearly straight tempora about as long as eyes, small pronotum and large elytra), slender, gradually thickened and loosely assembled antennae with all antennomeres elongate, setal pattern (nearly asetose head, sparsely setose elytra with long and erect setae longer than spaces between their insertions, and pronotum densely covered with setae and bristles), and unique aedeagus with a pair of long lateral subapical projections flanking strikingly long and truncate at apex distomedian projection of the dorsal plate.
Although Sharp (1874) stated that this species is “common in marshes, especially at Urakami, Nagasaki ”, only two syntypes are preserved at NHM (Urakami is a northern area of the Nagasaki City, the ground zero of the 1945 atomic bomb explosion). Additional specimens studied by Hoshina (2006) (as E. ohnoensis) come from Tsumadaira Wetland in Fukui Prefecture, which supports close association of E. japonicus with marshes.
Hoshina (2006) described Euconnus ohnoensis and stated that this new species was similar to E. japonicus, but smaller (BL 1.4 vs. ~ 1.6 mm in E. japonicus), pigmentation reddish brown (vs. “light brown to brown”), and the median lobe of the aedeagus was “robust, 1.8 times as long as wide in ventral view”, vs. in E. japonicus slender, ~2.5 times as long as wide. The aedeagi of E. ohnoensis and E. japonicus were illustrated on one page in Hoshina et al. (2020), which allows for direct comparisons. My conclusions are: (1) the aedeagus of E. ohnoensis is illustrated with a fully erected endophallus, which strongly distorts the shape of the median lobe, and therefore using the feature of more robust vs. slenderer aedeagus is unreliable; (2) all endophallic structures, although erected and displaced in E. ohnoensis, can be easily homologized with those illustrated in the resting position for E. japonicus, especially a pair of long outer arcuate sclerites and a pair of much smaller, also elongate inner sclerites are clearly the same; (3) differences seen in the shapes and lengths of ventral and dorsal apical plates are results of opening the ostium by flipping the ventral plate ventrad, and therefore the perspective is changed for the apical structures when the aedeagus is observed in ventral view; (4) the aedeagus illustrated by Hoshina et al. (2020) for E. japonicus is drawn inaccurately, especially the general shape of the median lobe, the shape of the ventral apical plate and dorsal apical plate with its distomedian projection, and to a lesser extent the shape and lengths of the lateral subapical projections, endophallic sclerites and parameres differ from those in the paralectotype male illustrated in the present paper (Figs 60‒63); (5) differences in pigmentation and the body length ranging from 1.4 to 1.6 mm, which means the mean BL equals 1.5 ± 0.1 mm, are not unusual within a species. Adding to these observations the same antennal structure, body form, nearly straight tempora, the same setal pattern and antebasal pronotal sculpture, Euconnus ohnoensis must be regarded as a junior synonym of E. japonicus.
description: Published as part of 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), pp. 1-37 in Zootaxa 5093 (1) on pages 16-18, DOI: 10.11646/zootaxa.5093.1.1, http://zenodo.org/record/5901006