Atomaria (Anchicera) alekseevi sp. nov.

(Figs 1–2)

Type material. Holotype: collection number No 6831 [MAIG] (ex coll. Jonas Damzen JDC-10145); adult, sex unkown. A complete beetle with partially exposed metathoracic wings is included in a transparent, yellow amber piece with dimensions of 17× 25 mm and a maximum thickness of 5 mm; preserved without supplementary fixation. Syninclusions: one Carabidae (Coleoptera) specimen, one small Nematocera (Diptera) specimen, and numerous stellate trichomes of Fagaceae.

Type stratum. Baltic amber; Middle–Late Eocene (Sadowski et al. 2017; Seyfullah et al. 2018; Bukejs et al. 2019; Kasiński et al. 2020; Iakovleva et al. 2021).

Type locality. Yantarny village (formerly Palmnicken), the Kaliningrad Region, Russia.

Description. Measurements: body length (from anterior margin of head to elytral apex along midline) about 1.54 mm, body maximum width across both elytron 0.69 mm; head length 0.23 mm, head maximum width across eyes 0.38 mm; pronotum length 0.35 mm, pronotum maximum width 0.54 mm; elytra length 0.96 mm, elytra maximum width 0.69 mm. Body broadly elongate, moderately arched, slightly convex; integument uniformly lightbrown (as preserved); sparsely covered with semierect pubescence.

Head transverse, about 1.7× as wide as long; coarsely punctate, distance between punctures nearly equal to diameter of one puncture. Compound eyes hemispherical, convex, rather large, with large facets. Antennae inserted close to eyes, under lateral margin of forehead; antennal insertions widely separated; distance between antennal insertions larger than distance between antennae and аnterior margin of eye. Antennae 11-segmented with 3- segmented loosed club, slender, rather long, reaching slightly beyond pronotal base; antennomere 1 subcylindrical, slightly elongate, 1.3× as long as wide; antennomere 2 conical, elongate, 1.6× as long as wide; antennomere 3 conical, elongate, about 2× as long as wide, distinctly narrower and slightly shorter than antennomere 2; antennomere 4 slightly elongate, 1.2× as long as wide; antennomere 5 conical, elongate, 1.5× as long as wide; antennomeres 6–8 trapezoidal, nearly as long as wide; antennomeres 9–10 trapezoidal, strongly transverse, 1.3–1.4× as wide as long; antennomere 11 widely oval, with rounded apex, 1.2× as long as wide; relative length ratios of antennomeres 1–11 equal to 10:10:7:5:6:5:5:5:6:7:13.

Pronotum transverse, 1.5× as wide as long, narrowed posteriad and anteriad, with maximum width slightly beyond middle; with convex disc; with finely margined posterior and lateral sides; lateral side borders visible from above only in basal half. Pronotal punctation coarse and dense, distance between punctures equal to 0.5-1.5× diameter of one puncture, punctation distinctly sparser in posterior half; puncture diameter subequal to eye facet diameter; pronotal punctation larger than punctation of head. Posterior angles obtuse; anterior angles obtuse, slightly projecting anteriad. Anterior edge weakly sinuate, without excision; posterior edge strongly bisinuate, lobed, with shallow depression and basal pits; lateral edges widely rounded, without callosity and teeth, with distinct crenulation. Prohypomera slightly impressed; with sparse, fine punctation. Prosternum with disc convex; sparsely covered with coarse punctation, distance between punctures distinctly larger than diameter of one puncture. Prostenal process convex, rather narrow, with straight posterior margin, slightly dilated apically. Procoxal cavities apparently closed externally.

Scutellar shield small, suboval, strongly transverse, 2.2× as wide as long, covered with fine punctation.

Elytra short-oval, moderately convex, with maximum width in anterior one-third of its length, 1.4× as long as wide and 2.7 times as long as pronotum length; completely covering abdomen; lateral sides widely rounded; humeri rounded, slightly prominent. Elytral punctation irregular, coarse and dense; punctures in basal part slightly larger than punctures on pronotal disc, and distance between punctures equal to 1.5-2.0× diameter of one puncture. Epipleura narrowed posteriorly, incomplete, extending about to abdominal ventrite 2. Metaventrite with sparse, coarse punctation; disc convex. Macropterous, metathoracic wings fully developed.

Legs slender, long, relatively similar in shape, finely and densely punctate. Procoxae large, widely suboval, transverse; mesocoxae round; metacoxae suboval, strongly transverse. Femora elongate-oval, flattened. Tibiae thin, almost straight, nearly as long as femora. Tarsi long and thin; tarsomeres simple, not lobed; tarsal formula 5-5-5.

Abdomen with five visible, freely articulated ventrites; ventrite 1 sparsely covered with rather coarse punctation, ventrites 2–5 with small and denser punctures. Relative length ratios of ventrites 1–5 equal to 31:10:10:9:11 (measured medially).

Etymology. The species is named in honor of our dear colleague Dr. Vitalii I. Alekseev (Kaliningrad, Russia), leading researcher of Coleoptera inclusions in Baltic amber.

Differential diagnosis. Atomaria alekseevi sp. nov. can be distinguished from related species by a combination of characters: antennomere 3 elongated, about 2× as long as wide, slightly shorter than antennomere 2; antennomeres 9 and 10 strongly transverse; pronotal disc convex; pronotum narrowed toward base; lateral side borders of pronotum visible from above only in basal half of its length; pronotum maximum width nearly in middle of its length. A new species can distinguished from all other extinct Eocene Atomaria representatives using the identification key provided below.