Euconnus (Euconnus) dulcis Sharp 1886
Creators: name: Jałoszyński, Paweł
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Euconnus
Euconnus dulcis

description: Euconnus (Euconnus) dulcis Sharp
Euconnus dulcis Sharp, 1886: 47. Redescribed by Hoshina, 2019c: 201.
Euconnus (Euconnus) dulcis Sharp; Csiki, 1919: 47.
(Figs 1–8)
Type material studied. Lectotype (here designated): ♂ (Figs 1–2), mounted on thick cardboard with annotation: “ Euconnus / dulcis Type / D.S. / Nagasaki / 28.5.81. Lewis”, with three labels: “Sharp Coll. / 1905-313” [creamy white, printed], “Type / H.T.” [round white label with red margin, printed], “SYN- / TYPE” [round white label with blue margin] (NHM). Paralectotype: ♂, mounted in a similar way as lectotype and with same annotation on mounting card, with two labels: “Sharp Coll. / 1905-313” [creamy white, printed], “SYN- / TYPE” [round white label with blue margin] (NHM).
Additional material studied. HONSHU: Ibaraki Pref.: 2 ♂♂, 1 ♀, Ishige-machi ad Tsukuba-shi, banks of Kokai-gawa River, 17.05.2003, sifted flood debris, leg. P. Jałoszyński (cPJ). One more male from Saga Prefecture (Kyushu) was also seen (NSMT).
Emended diagnosis. Among Japanese species, E. dulcis can be identified by: tiny anteromedian clypeal denticle present in both sexes; thick setae distributed on tempora and sides of pronotum; antennae with loose tetramerous club, in both sexes with elongate antennomeres 1–7, in males also 8–11 elongate, in female each about as long as broad; pronotum sub-parallel in posterior half, anteriorly strongly narrowing, with a pair of lateral antebasal pits connected by transverse groove (in one studied specimen groove vestigial); abdomen in male strongly modified, with a pair of lateral teeth directed posteromesad on sternites 6 and 7, posterior margin between teeth concave, additionally region between teeth on sternite 6 with two transverse, dense lateral groups of peg-like cuticular projections directed caudad and slightly unevenly and asymmetrically distributed; aedeagus with median lobe in ventral view broadest in subapical region, with conspicuously narrow median apical projection, symmetrical endophallic structures, and monstrously modified parameres, each strongly broadened, strongly bent in lateral view, with asymmetrical apex and bearing two groups of subapical lateral (outer) setae, in ventral view apex of each paramere developed as subtriangular projection directed distomesad.
Redescription. Body of male (Fig. 1: lectotype) slender, strongly convex, BL 1.45–1.69 mm; cuticle glossy, pigmentation moderately light brown, vestiture of setae light brown.
Head rhomboidal, slightly transverse and broadest at eyes, HL 0.28–0.33 mm, HW 0.33–0.38 mm; tempora in dorsal view distinctly longer than 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 with tiny anteromedian subtriangular tubercle (Fig. 3; arrowhead). Eyes moderately large, finely faceted, distinctly but not strongly projecting laterad from the head silhouette, in lateral view oval. Punctures on vertex and frons inconspicuous, fine and sparse; setae short and sparse, suberect, tempora densely covered with thick bristles directed laterocaudad. Antennae slender and loosely assembled, AnL 0.80–0.88 mm; all antennomeres distinctly elongate, club tetramerous but antennomere 7 distinctly longer and broader than 6 so that club is not sharply delimited.
Pronotum bell-shaped, with widest site variable, but close to middle (in some specimens indistinctly behind middle, in some indistinctly in front of middle), PL 0.35–0.41 mm, PW 0.38–0.41 mm; anterior margin arcuate and much shorter than posterior margin, anterior corners not marked, sides of pronotum in anterior 1/3–1/2 rounded and strongly converging anterad, sides in posterior half weakly convex and sub-parallel or indistinctly convergent posterad; posterior corners indistinctly obtuse-angled, distinctly marked; posterior margin nearly straight. Pronotal base with long transverse groove connecting lateral pair of minute and shallow pits, a pair of short but distinct longitudinal sublateral carinae and a pair of outer antebasal pits situated just laterad each carina, barely discernible in dorsal view and elongate. Disc dorsally covered with fine, inconspicuous punctures and moderately dense thin suberect setae, sides with dense thick bristles.
Elytra oval, broadest slightly in front of middle, EL 0.80–0.90 mm, EW 0.63–0.68 mm, EI 1.23–1.33; basal impressions short and shallow, humeral calli prominent and elongate, each delimited from adscutellar region by elongate impression running posterolaterad, elytral apices separately rounded. Punctures on elytral disc fine, inconspicuous; setae long, sparse (but longer than spaces between their insertions) and strongly erect. Hind wings long, functional.
Legs moderately long and slender, unmodified.
Abdomen (Fig. 4) modified, with sternites 6 and 7 each with a lateral pair of tubercles directed posteromesad, posterior margin between tubercles concave, sternite 6 between tubercles with two lateral transverse groups of densely and unevenly distributed peg-like cuticular projections.
Aedeagus (Figs 5–8) stout, AeL 0.25 mm; median lobe in ventral view broadest in subapical region, ventral apical plate with slender, nearly parallel-sided distal projection truncate at apex; endophallic structures symmetrical, with small sclerotized subapical median complex composed of short median tubular structure and a pair of slender sclerites convergent distad; parameres monstrously modified, strongly broadened, in lateral view strongly bent and with asymmetrical apices, each with triangular apex in ventral view directed distomesad, and with two groups of subapical setae.
Female. Only one female was available for this study; it differs from all males in stouter elytra, antennomeres 8–11 distinctly shorter, not elongate, and unmodified abdomen. The clypeal denticle is present in female, although slightly smaller. BL 1.48 mm; HL 0.28 mm, HW 0.35 mm, AnL 0.80 mm; PL 0.38 mm, PW 0.40 mm; EL 0.83 mm, EW 0.70 mm, EI 1.18.
Distribution. Japan: Honshu, Kyushu.
Remarks. This species can be easily identified by external characters, including the unique body form, large, broad and somewhat flattened head, clypeal denticle, loose antennal structure, and conspicuous modifications of the abdomen in males. Known variability includes a wide range of body length, in males from 1.45 to 1.69 mm, proportions of the pronotum and elytra (especially the pronotum can be indistinctly longer than wide, as long as wide or indistinctly wider than long), and the pronotal sculpture: in one specimen the transverse antebasal groove connecting lateral pits was found very shallow and barely observable, with an indistinct deepening at middle that may appear as a median pit, but in fact is a rudiment of the groove.
Euconnus dulcis was redescribed by Hoshina (2019c). However, his description and illustrations are highly inaccurate. The body silhouette (Hoshina 2019c: fig. 1) is incorrect, both in proportions of body parts and in the shape of the pronotum. Moreover, each of the two syntypes have a deep and distinct antebasal transverse impression connecting the inner pair of pronotal pits, and a pair of short sublateral antebasal carinae separating inner and outer pits (the latter situated more laterally then illustrated by Hoshina and much smaller) but these features were neither illustrated nor mentioned in the redescription. The conspicuous median clypeal denticle and modified abdominal sternites, the most remarkable external features of this species, were not even mentioned. The aedeagus illustrated in Hoshina (2019c: figs 2–4) is unskillfully drawn and the shape and proportions of the apical region (especially in lateral view), the shape of parameres, and the distribution and number of parameral setae do not agree with features seen in the lectotype male and non-type specimens examined during the present study.
Euconnus dulcis was placed in the nominotypical subgenus by Csiki (1919). Hoshina (2019c) apparently did not know about this long-established placement, as he stated: “I do not put Euconnus dulcis in a subgenus at this time”. I confirm Csiki’s decision as correct. Euconnus dulcis belongs in Euconnus (s. str.) based on the tetramerous and in males unmodified antennal club, the bell-shaped pronotum with an even number of antebasal pits, and the aedeagus with non-emarginate apical region.
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 3-4, DOI: 10.11646/zootaxa.5093.1.1, http://zenodo.org/record/5901006