Euconnus (s. str.) rectitibia, Jałoszyński, 2022

Jałoszyński, Paweł, 2022, Taxonomy of ' Euconnus complex'. Part XXIV. Intermediate forms between Psomophus, Eupentarius and Euconnus s. str. in the East Palaearctic fauna unify problematic subgenera (Coleoptera, Staphylinidae, Scydmaeninae), Zootaxa 5194 (3), pp. 343-391 : 349-352

Euconnus (s. str.) rectitibia sp. n.

( Figs 19–23 , 24–28 , 110 )

Type material studied. Holotype ( Japan: Saitama Prefecture): ♂, two labels: “ Shinjuku-shinden (Edogawa riverbank) / Shōwa-machi , Saitama Pref. / [ Honshu , JAPAN] / 16.xii.2004, S.Nomura lg.” [white, printed], “ EUCONNUS s. str. / rectitibia m. / P. Jałoszyński, ’22 / HOLOTYPUS ” [red, printed] ( NSMT) . Paratypes (3 exx): Saitama Pref.: ♀, same data as for holotype ; Niigata Pref.: ♂, “ Kuramitsu / Shibata C. / Niigata Pref. ” [white, printed], “ 3.vii.1998 / Hiroshi Koike” [white, printed]; Fukuoka Pref. : ♂, “[ Kyushu , JAPAN] / 12. vii. 1997 / Kenshi Otsuka leg.” [white, printed], Chikugogawa riv. / Tanushimaru-machi / Fukuoka Pref. ” [white, printed]. Paratypes with yellow “ PARATYPUS ” labels similar to that with holotype, deposited in NSMT and cPJ .

Diagnosis. Antennal club clearly trimerous and slender; head round; pronotum nearly parallel-sided in posterior half and with rounded sides in anterior third converging anterad, with one pair of antebasal pits and transverse groove reduced to slightly transverse median antebasal pit, and with distinct sublateral carinae; protibiae in males unmodified, straight; aedeagus moderately sclerotized, in ventral view drop-shaped, with subtrapezoidal dorsal apical plate and with simple endophallus with darkly sclerotized submedian elongate structure.

Description. Body of male ( Figs 19 , 24 ) elongate, moderately convex; pigmentation moderately dark umbra brown, legs and palps indistinctly lighter, antennal clubs barely discernibly darkened; body covered with setae distinctly lighter than cuticle; BL 1.15–1.23 mm.

Head broadest at eyes, indistinctly transverse, HL 0.23 mm, HW 0.25 mm; tempora in dorsal view about twice as long as eyes, behind eyes strongly and evenly convergent posterad, posterior margin of vertex weakly arcuate, not bulging posterodorsad. Frons and vertex with unremarkable, fine punctures, glossy; setae sparse and suberect, tempora with sparse thick bristles. Antennae slender, with loosely assembled and slender trimerous clubs, AnL 0.65–0.68 mm, all antennomeres elongate, 11 distinctly shorter than 9 and 10 combined, about twice as long as broad.

Pronotum equally broad between base and anterior third; PL 0.25–0.30 mm, PW 0.28–0.30 mm. Sides posteriorly nearly straight, in anterior third rounded and converging anterad, base with one pair of small but distinct pits, transverse groove reduced to slightly transverse median antebasal pit, sublateral carinae sharply marked and distinct. Punctures and setae on disc similar to those on frons and vertex; sides of pronotum with dense thick bristles, sparse bristles are also present on disc.

Elytra together oval, broadest slightly in front of middle; EL 0.65–0.70 mm, EW 0.50–0.53 mm, EI 1.29–1.40; humeral calli distinct and slightly elongate, mesally demarcated by elongate impressions; elytral apices separately rounded. Punctures distinct but very shallow, superficial and diffuse, unremarkable; setae sparse but much longer than those on pronotal disc, suberect.

Legs slender, protibiae unmodified, straight.

Aedeagus ( Figs 20–23 , 25–28 ) stout, drop-shaped, moderately strongly sclerotized, AeL 0.20 mm; median lobe in ventral view broadest near middle or in submedian proximal region, sides rounded, in lateral view median lobe distinctly curved, dorsal apical plate in ventral view elongate, subtrapezoidal, with median subtriangular projection on apical margin; endophallus lacking ring-like sclerotized structure, with tubular (flagellar?) component in subapical region (clearly visible in lateral view) and submedian elongate sclerotized structure. Parameres slender but short, not reaching apex of median lobe, each with two long apical setae. Variability in aedeagal structures is discussed in Remarks.

Female. Externally indistinguishable from male. BL 1.18 mm; HL 0.23 mm, HW 0.24 mm, AnL 0.65 mm; PL 0.28 mm, PW 0.28 mm; EL 0.68 mm, EW 0.50 mm, EI 1.35.

Distribution. Japan: Kyūshū and central Honshū (regions Kantō and Chūbu) ( Fig. 110 ).

Etymology. The epithet rectitibia (noun in apposition) refers to the unmodified, straight (Latin rectus) protibiae in males.

Remarks. Specimens from Saitama Pref. ( Figs 19–23 ) differ from those from Niigata and Fukuoka Prefectures in small details of the aedeagus. However, the illustrated aedeagi (compare Figs 23 and 26 ) seem to be in a slightly different condition—the one in Figs 20–23 is in an early stage of eversion, with swollen membranous ventral subapical region (which makes the dorsal apical plate appear shorter), and the tubular subapical endophallic structure almost perpendicular in relation to the long axis of the aedeagus, while in Figs 25–28 this tubular (flagellar?) element is oriented approximately on the coronal plane of the aedeagus. Consequently, in ventral view, this tubular structure in Figs 25, 27 is visible as an elongate subtriangular subapical component situated in the proximal half of the dorsal apical plate, whereas in Figs 20, 22 it is almost horizontal and visible as if it was a cross-section – a sclerotized cordiform spot in the same region.

According to Shûhei Nomura, the holotype and one paratype of this species were collected on a floodbank of the Edogawa River, from decaying plant debris accumulated on a concrete embankment. The type locality spelled “Shinjuku-shinden” (not to be confused with Shinjuku in Tokyo) on the label of the holotype can also be read “Shinshuku-shinden” ( Shûhei Nomura , in email to the author dated 25.05.2022) .

Figures

FIGURE 110. Distribution of Euconnus rectitibia sp. n., E. kirin sp. n., E. yaimanus sp. n., and E. uchinaanchu sp. n.

FIGURES 19‒23. Euconnus rectitibia sp. n., male (Saitama Prefecture). Dorsal habitus (19); aedeagus in ventral (20, 22) and lateral (21, 23) views.

FIGURES 24‒28. Euconnus rectitibia sp. n., male (Fukuoka Prefecture). Dorsal habitus (24); aedeagus in ventral (25, 27) and lateral (26, 28) views.