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

description: Euconnus (Psomophus) debilis (Sharp)
Scydmaenus debilis Sharp, 1874: 127. Aedeagus illustrated in Kurbatov, 2006: 29.
Euconnus (Microscydmus) debilis (Sharp); Csiki, 1919: 55.
Euconnus (Psomophus) debilis (Sharp); Kurbatov, 2006: 27.
(Figs 72–78)
Type material studied. Lectotype of Scydmaenus debilis Sharp (here designated): ♂ (Fig. 72), mounted on simple and not annotated card, with six labels (Fig. 73): “Sharp Coll. / 1905-313.” [darkened white, printed], “ Scydmaenus / debilis / 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], “ Japan / G. Lewis. ” [white with orange horizontal line, printed], and “ Euconnus / debilis (Sharp) / det. S. Kurbatov, 1994” [white, handwritten] (NHM). Paralectotypes (3 exx): 2 ♂♂ and 1 ex. of unknown sex (with legs bent under body), same labels as for lectotype except without the circular red-margined one (NHM).
Additional material studied. HONSHU: Fukushima Pref.: ♂, Numayama Moor (700 m), Shimagô-machi, Aizu, 18.10.2003, S. Nomura leg. (cPJ); Hiroshima Pref.: ♀, Yawatabara, Geihoku-chô, 27.06.1987, S. Nomura leg. (NSMT); Wakayama Pref.: ♂, Hoihoi-dani (riverside), Mt. Ohto, 06.05.1994, S. Nomura leg. (NSMT); SHIKOKU: Ehime Pref.: ♂, Syukuno-machi, Matsuyama-shi, 05.05.2002, T. Kurihara leg. (EUMJ); Kôchi Pref.: ♂, Usa, Tosa City, 16– 18.08.1970, Ken Itô leg. {correctly identified as E. debilis by S. Hisamatsu in 1984} (EUMJ);
Tokushima Pref.: ♂, Akui, 25.09.1965, M. Sakai leg. (EUMJ). RUYUKYUS: Kagoshima Pref.: 19 exx, Tokara Islands, Takarajima Island, Oh-ike, 20- 23.03.1992, S. Nomura leg. (NSMT, cPJ). Additionally, two specimens from Kyushu, Saga Pref. were seen (NSMT).
Emended diagnosis. Small-bodied Psomophus (Bl ~ 1.2 mm) with slender antennal club, antennomere 11 slightly less than twice as long as broad; pronotum broadest behind middle, with one pair of small lateral antebasal pits connected by distinct transverse groove, and with short but distinct sublateral carinae; punctures on head, pronotum and elytra inconspicuous; protibiae in male with strongly bent apical regions; aedeagus in ventral view pear-shaped, broadest in sub-basal region, with broadly rounded sides and distinctly delimited apical region composed of shorter ventral apical plate with short, median subtriangular distal projection, and much longer and slenderer dorsal apical plate with sides rounded and strongly converging distad toward subtriangular and blunt apex; endophallus with conspicuous submedian elongate oval median structure; parameres in lateral view almost evenly curved, each with two long apical setae.
Redescription. Body of male (Fig. 72: lectotype) moderately slender, strongly convex, BL 1.16–1.20 mm; cuticle glossy, pigmentation light brown, in fully pigmented specimens antennal club slightly to distinctly darker than rest of body, vestiture of setae and bristles slightly lighter than cuticle.
Head rhomboidal, as long as broad or indistinctly transverse, broadest at eyes, HL 0.23–0.25 mm, HW 0.25 mm; tempora in dorsal view about 1.5 times as long as eyes and strongly converging posterad, weakly rounded or 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 moderately large and finely faceted, weakly projecting laterad from the head silhouette, in lateral view oval. Head with fine and inconspicuous punctures; setae moderately dense and long, suberect, directed posterad, thick bristles distributed on tempora and relatively sparse. Antennae slender and moderately compactly assembled, with distinct trimerous clubs, AnL 0.53–0.55 mm; antennomeres 1–2 distinctly elongate, 3–10 each about as long as brad, 11 slightly less than twice as long as broad, indistinctly broader than 10.
Pronotum bell-shaped with rounded sides, in most specimens widest slightly behind middle, but dense vestiture in intact specimens may obscure the shape, which is slightly variable, PL 0.28–0.30 mm, PW 0.26–0.30 mm; anterior margin nearly straight and much shorter than posterior margin, anterior corners indistinct, sides of pronotum strongly rounded in anterior half or 1/3 and strongly converging anterad, in posterior half weakly rounded and slightly converging posterad or slightly sinuate; posterior corners strongly obtuse-angled, well-marked; posterior margin weakly arcuate. Pronotal base with distinct transverse groove connecting one pair of small lateral pits, in some specimens groove slightly shallower at middle, sublateral carinae sharply marked. Disc covered with inconspicuously fine punctures, densely covered with thin, suberect setae and thick, straight bristles distributed not only on sides, but also on dorsum (setae and bristles easily brake off during preparation!).
Elytra oval, broadest distinctly in front of middle, EL 0.60–0.70 mm, EW 0.45–0.51 mm, EI 1.27–1.42; basal impressions shallow but distinct, humeral calli prominent and weakly elongate, each delimited from adscutellar region by elongate impression; elytral apices separately rounded. Punctures on elytral disc fine, inconspicuous; setae moderately sparse and long, but much longer and thicker than those on head and pronotum, suberect, setae clearly longer than distances between their insertions. Hind wings long, functional.
Legs moderately long and slender, protibiae (Fig. 74) modified, with short apical portion strongly bent mesad.
Abdomen unmodified.
Aedeagus (Figs 75–78) moderately elongate, AeL 0.20–0.26 mm; median lobe in ventral view pear-shaped, broadest in sub-basal region, with broadly rounded sides and distinctly delimited apical region composed of shorter and subtrapezoidal ventral apical plate bearing short median subtriangular distal projection, and much longer and slenderer dorsal apical plate with sides rounded and strongly converging distad toward subtriangular and blunt apex; endophallus with conspicuous submedian elongate oval median structure; parameres slender, not reaching apex of median lobe, in lateral view almost evenly curved, each with two long apical setae.
Female. Externally similar to male but with protibiae very weakly curved; winged. BL 1.13–1.20 mm; HL 0.23 mm, HW 0.25 mm, AnL 0.50–0.55 mm; PL 0.28–0.30 mm, PW 0.28–0.30 mm; EL 0.63–0.68 mm, EW 0.48–0.50 mm, EI 1.25–1.37.
Distribution. Japan: Honshu, Kyushu, Shikoku, Ryukyus (Tokara Islands).
Remarks. Among described Japanese Euconnus species, E. debilis is the only member of the subgenus Psomophus and can be distinguished by the subgeneric feature: the trimerous antennal club. As discussed by Jałoszyński (2017c), Psomophus is a somehow problematic subgenus and it may in future be merged with the large and morphologically diverse Euconnus s. str. Additional findings in Japanese fauna support this view (Jałoszyński, in preparation), as there are more (new) species that inhabit Japanese Islands and have distinctly or indistinctly trimerous clubs, and diverse remaining characters. This problem will be treated separately. Here, however, it should be noted that there are at least 4‒5 undescribed species in Japan that highly resemble E. debilis, and at least three of them have males with the protibiae modified in a very similar way as those in E. debilis. Moreover, their distributional ranges overlap. For this reason, in order to identify any male of Euconnus with body form similar to that illustrated in Fig. 72, trimerous antennal club and bent apices of profemora, examination of aedeagus is indispensable.
Euconnus debilis has a broad distribution, currently known localities range from Fukushima Prefecture in the CN region of Honshu, through Shikoku and Kyushu and the south-western Tokara Islands. Aedeagi of specimens distributed on different islands do not show any differences that could be attributed to separate species or subspecies. However, external morphology of this species is somewhat variable, and although the body form, setal pattern and distribution of punctures are constant, adults of E. debilis can have noticeably different proportions of body parts, best visible in the elytral index, which in the small studied sample ranges 1.27‒1.42 among males and 1.25‒1.37 among females. In fully pigmented specimens the antennal club is slightly to distinctly darker than the remaining portion of antenna, but most commonly the antennae are uniformly light brown. There is another, externally similar, and yet undescribed Psomophus broadly distributed in the Ryukyus, from Tokara Islands to Okinawa-jima, which can be easily confused with E. debilis, but clearly differs in the male genitalia (Jałoszyński, in preparation).
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 22-24, DOI: 10.11646/zootaxa.5093.1.1, http://zenodo.org/record/5901006