Eusphalerum bukejsi Shavrin, 2021

Shavrin, Alexey V. & Kairišs, Kristaps, 2021, A new species of Eusphalerum Kraatz, 1857 from the Eocene Baltic amber (Coleoptera, Staphylinidae, Omaliinae), Zootaxa 4966 (4), pp. 469-475 : 470-474

† Eusphalerum bukejsi Shavrin , sp.n.

( Figs. 1−20 )

Type material examined. Holotype: male, complete specimen in a piece of medium-sized yellow Baltic amber (with a little drilled hole on the narrowest side), 2.40 mm × 1.40 mm × 0.40 mm in size ( Figs. 1–2 ), with glued small paper on large plastic envelope labeled “9408 | JDC | Baltic amber”, with two colour photographs of habitus of the beetle (dorsal and ventral view) and with labels within a small plastic envelope: “6724 [ MAIG] | (ex. coll. Jonas Damzen | JDC 9408)” <printed>, “HOLOTYPE | Eusphalerum | bukejsi sp. nov. | Shavrin A. V. 2021 ” <red, printed> ( MAIG).

Preservation. The specimen is poorly visible in details because from the dorsal side the amber has shrunken defect covering left side of the body including head, most of the pronotum, left elytron and abdomen ( Fig. 3 ), and from the ventral side it is partially covered with white cloud of microbubbles ( Fig. 4 ).

Locality and horizon. Baltic amber from Yantarny settlement, Sambian Peninsula, Kaliningrad Area, westernmost Russia; mid-Eocene (ca 44 Ma; Wappler 2005).

Description. Measurements: maximum width of head including eyes: 0.52; length of head (from base of labrum to neck constriction along head midline in dorsal view): 0.34; ocular length: 0.18; length × width of segments III and IV of maxillary palpi: III: 0.06 × 0.03, IV: 0.07 × 0.02; length of antenna: ~0.90; length of pronotum: 0.48; maximum width of pronotum: 0.60; sutural length of elytra from the apex of scutellum to the posterior margin of sutural angle: 1.09; length of elytron from basal to apical margin: 1.18; maximum width of elytra: 1.01; length of metatibia: 0.21; length of metatarsus: 0.23; maximum width of abdomen (at segment IV): 0.90; length of aedeagus (from base of the median lobe to apex of parameres): 0.60; length of forebody: 2.00; total length (from anterior margin of clypeus to apex of abdomen): ~2.60.

Body suboval, convex ( Figs. 3 , 6–8 ); body laterally as in Figs. 9–10 ; body ventrally as in Figs. 12–14 ; forebody as in Figs. 11 , 15 . Head, antennae, pronotum, legs and abdomen brown; elytra yellow-brown; mouthparts and tarsi yellow. Body glossy, glabrous, without visible setation.

Head 1.5 times as wide as long ( Fig. 15 ); middle portion flattened, with indistinct occipital line and median impressions, and with moderately short grooves in front of ocelli, narrowly converging apicad, reaching about level of middle length of eyes ( Figs. 9 , 15 ); postocular carina smooth and indistinct. Punctation irregular, moderately dense and fine, denser in middle, infraorbital ridges and mediobasal portion in front of neck. Microsculpture poorly visible, but middle portion of head seems to be with transverse fine microreticulation. Eyes large and convex ( Figs. 8, 11–12, 15 ). Ocelli large, situated about at level of posterior margins of eyes ( Fig. 15 ), distance between ocelli about as long as distance between ocellus and posterior margin of eye ( Fig. 7 ). Apical segment of maxillary palpi slightly longer and narrower than preceding segment. Gular sutures with rounded apical parts widely separated from each other ( Fig. 12 ). Antenna ( Fig. 5 ) moderately short, reaching basal margin of pronotum, with antennomeres more or less progressively widened apicad and antennomeres 4–9 about equal length, each antennomere with long apical setae; basal antennomere wide and oblong, antennomere 2 elongate, distinctly narrower than basal antennomere, 3 narrower and shorter than 2, 4 indistinctly broader and longer than 3, 5 slightly broader than 4, 6–7 distinctly broader than 5, 8–9 slightly broader than 7, 10 slightly broader than 9, about equal in length and wide, apical antennomere slightly more than twice as long as 10, gradually narrowed from middle toward subacute apex.

Pronotum with widely elevated middle portion, moderately short, 1.2 times as wide as long, slightly broader than head, widest in middle, distinctly more narrowed posterad than anterad, with slightly concaved laterobasal nargins in front of subacute posterior angles ( Figs. 11 , 15 ); apical margin widely concaved, significantly narrower than basal margin; anterior angles widely rounded, strongly protruded anterad ( Fig. 11 ); lateral margins with very fine, moderately regular crenulation; lateral portions narrowly explanate, each laterobasal portion with wide and deep impression ( Fig. 15 ). Punctation moderately large and deep, sparser in middle. Median portion with distinct, transverse microsculpture. Prosternum with narrow and long intercoxal process ( Fig. 14 ). Mesoventrite with very long intercoxal process with subacute apex, reaching about middle of mesocoxae ( Fig. 14 ). Scutellum large, moderately wide, with several fine punctures in middle ( Fig. 6 ). Metaventrite moderately convex ( Fig. 9 ), with wide and deep metacoxal cavities and wide metaventral process, contacting with apex of mesosternal process ( Fig. 14 ). Median part of prosternum and metaventrite with moderately regular and dense, fine punctation ( Fig. 14 ).

Elytra convex, indistinctly longer than wide, 1.8 times as long as pronotum ( Figs. 6–8 ), slightly widened toward apical third, reaching middle of abdominal tergite IV ( Figs. 9–10 ); apical margins without modification, widely rounded. Punctation about as that on pronotum, but more irregular, larger in mediobasal portion and along suture, finer and sparser in middle and apical portions ( Figs. 3 , 6–8 ). Microsculpture missing. Hind wings fully developed ( Figs. 9–10 ).

Legs with wide femora. Moderately short tibiae, gradually widened apicad. Tarsomeres 1–4 with dense elongate setae ventrally ( Figs. 9–10 , 12–13 ). Metatrochater narrow, elongate ( Figs. 12–13 ). Apical metatarsomere slightly longer than previous tarsomeres together.

Abdomen slightly narrower than elytra ( Figs. 6–7 , 16 ), with very narrow palisade fringe on apical margin of tergite VII. Punctation very fine and dense, without visible microsculpture.

Male. Apical margins of abdominal tergite VIII ( Fig. 16 ) and sternite VIII ( Figs. 12–14 ) widely concaved. Aedeagus with wide basal part, gradually narrowed toward median lobe, with sub-trapezoidal apical portion, sharply narrowed toward rounded apex; parameres very long, significantly exceeding apex of median lobe, with very wide apical portions, without visible setation ( Figs. 17, 19 ); internal sac long and narrow ( Figs. 19–20 ). Lateral aspect of aedeagus as in Figs. 18, 20 .

Female unknown.

Etymology. Patronymic, the new species is named to honour our colleague Andris Bukejs (Daugavpils).

Remarks. Regarding the general shape, size and coloration of the body, the new species is similar to the overwhelming majority of species of the genus Eusphalerum . Based on the shape of the aedeagus with subtrapezoidal apical portion of the median lobe and very long parameres, Eu. bukejsi sp.n. is similar to some East Asian species of the pollens (e.g. Taiwanese Eu. cariniphallum Zanetti, 1998 , Japanese Eu. poroshiriense Watanabe, 1990 ) and japonicum (e.g. Eu. hapalaraeoides Zanetti, 1998 ) groups (Zanetti 1998, Watanabe 1990). Besides that, the new species has slightly transverse pronotum and short elytra without microsculpture as these in species of the pollens group. Usually, species of pollens and japonicus groups have many short setae on the entire surface of the setiferous lobe of the parameres, sometimes with a lot of very long apical setae. Unfortunately, the tomography has not shown these tiny structures. From species of the japonicum group, Eu. bukejsi sp.n. differs by the absence of long pubescence on the pronotum and the elytra. From both groups, Eu. bukejsi sp.n. also can be distinguished by the significantly widened apical parts of the parameres and by the shape of the modified metatrochanter ( Figs. 12–13 ). In general, the modified metatrochanters are known in males of some Caucasian species of the foveolatum group ( Zanetti 1993). From extinct Eu kanti Shavrin & Yamamoto, 2019 , the new species can be distinguished by the paler coloration, absence of visible grooves in front of ocelli, narrower pronotum, significantly shorter elytra without modified apical margins, and other details of the body. In comparison with four undescribed species of the genus in Shavrin & Yamamoto (2019), that also have somewhat shortened elytra, the new species differs by the paler body, proportions of antennomeres, shorter pronotum, more irregular and finer punctation of apical half of the elytra and some other morphological features.

Figures

FIGURES 1–5. Amber specimen with inclusion (Figs. 1–2), habitus (Figs. 3–4) and right antenna (Fig. 5) of Eusphalerum bukejsi sp.n.: 3–dorsal view, 4–5–ventral view. Scale bars: 1.0 cm (Figs. 1–4), 0.1 mm (Fig. 5).

FIGURES 6–11. Habitus (Figs. 6–10) and forebody (Fig. 11) of Eusphalerum bukejsi sp.n., X-ray micro-CT renderings: 6–8, 11–dorsal view, 9–10–lateral view. Scale bar: 0.5 mm.

FIGURES 12–16. Habitus (Figs. 12–14) and body parts (Fig. 15: head and pronotum, Fig. 16: abdomen) of Eusphalerum bukejsi sp.n., X-ray micro-CT renderings: 12–14–ventral view, 16–dorsal view. Scale bar: 0.5 mm.

FIGURES 17–20. Aedeagus of Eusphalerum bukejsi sp.n.: 17, 19–parameral view, 18, 20–lateral view. Scale bars: 0.1 mm.