Xyletinus (s. str.) barsevskisi, Alekseev & Bukejs, 2019

Alekseev, Vitalii I. & Bukejs, Andris, 2019, Two new species of Xyletinus Latreille (Ptinidae: Xyletininae) in Eocene Baltic amber, Zootaxa 4668 (4), pp. 525-534 : 528-532

Xyletinus (s. str.) barsevskisi sp. nov.

( Figs 4–8 , 10 )

urn:lsid:zoobank.org:act:01820480-4755-4918-AD6F-C47D4AD99672

Material examined. Holotype: No. 057 [ CAB]. Adult, sex unknown. The complete beetle inclusion is preserved in a small piece of transparent, yellow amber with approximate dimensions 18×7× 4 mm without any further fixation. Syninclusions: few stellate fagacean trichomes, and small gas vesicles.

Type horizon. Baltic Amber, Upper or mid-Eocene.

Type locality. The Samland (Sambian) Peninsula, the Kaliningrad region, Russia .

Description. Total body length about 4.0 mm; elytra length 2.65 mm, combined maximum width of elytra 1.8 mm; pronotum length 1.35 mm, pronotum maximum width 1.9 mm. Body elongate, subparallel, convex; pubescence homogenous, fine, moderately dense, recumbent; unicolorous dark-brown with tarsi and antennae paler (as preserved).

Head hypognathous, turned downwards and not visible in dorsal view; covered with fine, dense punctures (punctation sparser anteriorly), punctures smaller than one eye facet; with microreticulation; pubescence very fine, recumbent; frons wide, almost flat, without carina or longitudinal impression. Compound eyes relatively small, slightly convex, entire, oval (slightly vertical, vertical diameter 1.3× as large as transverse diameter), with small distinct facets, without ommatidial setae; widely separated, frontal distance between compound eyes nearly equal to 2.5× transverse diameter of one eye. Antennae 11-segmented, serrate, short (reaching about posterior one-third of pronotum); scape elongate, suboval, covered with fine punctation; antennomeres 2–10 serrate; antennomere 2 subtriangular, with widely rounded right lateral margin; antennomeres 3 subequilaterally triangular, narrower than antennomere 4; antennomeres 4–6 short, narrowly triangular, strongly tranverse, about 2.5× as wide as long; antennomere 7 transverse, 1.6× as wide as long; antennomeres 8–10 triangular, slightly transverse, about 1.2× as wide as long; antennomere 11 elongate-oval, with slightly pointed apex, 3.3× as long as wide. Relative length ratios of antennomeres 1–11 equal to 17(?)–8–9–6–6– 6–9–11–11 –11–25. Terminal labial palpomere triangular. Terminal maxillary palpomere triangular, slightly widened.

Pronotum convex, transverse, 1.4× as wide as long; margined; pubescence fine, dense, recumbent; covered with moderately dense, fine punctures (like head punctation) on disc and with small, dense granulation antero-laterally, distance between granules about 0.5–1.5× diameter of one granule. Anterior pronotal angles subrectangular, rounded, not visible in dorsal view; posterior pronotal angles widely rounded and barely marked. Lateral margins apparently not visible in dorsal view; posterior margin convex medially; anterior margin arcuate in frontal view.

Scutellar shield moderately large, triangular with slightly rounded apex, transverse, about 1.5× as wide as long; densely covered with fine, recumbent setae and fine punctation.

Elytra moderately short, 1.5× as long as wide, subparallel-sided, slightly tapered posteriad; humeri distinct; with very dense microgranulation, interspaces between granules convex, forming rugosity (distinctly visible in humeral area); covered with microreticulation; elytral pubescence dense, fine, recumbent, directed backwards. Elytral disc without striae; each elytron with two shallow, impunctate striae laterally: inner stria interrupted in anterior portion of elytra, shortened, not reaches humeri, outer stria complete, striae joined at elytral apex. Metathoracic wings not apparent. Mesoventrite microreticulated, located at lower level than metaventrite. Metathorax with dense, fine punctuation and microreticulation. Metepisternum strongly widened and slightly impressed in anterior one-third. Metaventrite convex; with anterior margin bisinuated and slightly upturned; without excavation for reception of mesothoracic legs; with sharp medial carina in anterior one-fourth, and with medial groove in posterior three-fourth; posterior intercoxal process narrow, bifid; anterior intercoxal process rounded.

Legs slender, comparatively short, pentamerous, covered with fine, semierect setation. Procoxae contiguous, meso- and metacoxae separated; mesocoxae small, suboval, transverse, about 1.6× as wide as long, metacoxae elongate, narrow, strongly transverse, about 5.3× as wide as long. Femora with deep ventral groove for tibia reception; meso- and metafemora not extending beyond elytral lateral margins. Tibiae straight, about as long as femora. Tarsi short, distinctly shorter than tibia; tarsomere 1 longest, nearly as long as tarsomeres 2 and 3 combined. Tarsal claws simple, thickened basally, falcate, symmetrical.

Abdomen with five freely articulated, visible ventrites, without excavation for reception of metathoracic legs; ventrites finely and densely punctured; pubescence dense, fine, recumbent; ventrite 5 with widely rounded apical margin. Relative length ratios of ventrites 1–5 equal to 5-6-5-4-7 (medially).

Differential diagnosis. The new fossil species belongs to the genus Xyletinus based on following morphological characters: head deflexed; metathoracic ventrite and abdomen without excavation for reception of mesothoracic and metathoracic legs; antennae serrate; eyes widely separate; elytra striate; three terminal antennomeres not long in comparison with preceding segments. The combination of the following features allows the assignment of Xyletinus barsevskisi sp. nov. to the nominate subgenus: eyes comparatively small, oval, not strongly prominent; frons wide; ultimate maxillary and labial palpomeres triangular, widened; tarsi short; and elytral pubescence directed backwards.

Xyletinus (s. str.) barsevskisi sp. nov. differs from extinct X. (s. str.) besseli sp. nov in: (1) antennomeres 2–10 serrate and antennomere 11 elongate-oval; (2) elytra without striae on disc, with two striae lateraly; (3) pronotum with fine, moderately dense punctation, and with small, dense granulation antero-laterally; (4) pronotal anterior angles not visible in dorsal view; and (5) larger body size (4.0 mm in contrast to 3.1 mm in X. besseli sp. nov.).

Xyletinus (s. str.) barsevskisi sp. nov. resembling recent European species of the genus and the subgenus, but differs in almost flat frons without carina or longitudinal impression, elytral disc without distinct striae, short femora, pronotum with dense punctation medially and granulation laterally, shape of antennomeres, and unicolorous elytra.

Derivatio nominis. Patronymic, this new species is named in honor of our colleague Dr. Arvīds Barševskis (Daugavpils, Latvia) as well known specialist in Cerambycidae and Carabidae (Coleoptera) .

Figures

FIGURES 4–6. Xyletinus barsevskisi sp. nov., holotype, No. 057 [CAB]: 4—habitus, dorsal view; 5—habitus, left lateral view; 6—habitus, right lateral view. Scale bars represent 1.0 mm.

FIGURES 7–8. Xyletinus barsevskisi sp. nov., holotype, No. 057 [CAB]: 7—head and prothorax, lateral view; 8—details of elytra and pronotum, dorsal view. Not reproduced to the same scale.

FIGURES 9–10. Reconstruction of antennae: 9—Xyletinus besseli sp. nov.; 10—X. barsevskisi sp. nov. Not reproduced to the same scale.