Calomicrus eocenicus Bukejs et Bezděk, 2014

Bukejs, Andris, Bezděk, Jan, Alekseev, Vitalii I., Kairišs, Kristaps & McKellar, Ryan C., 2020, Description of the male of fossil Calomicrus eocenicus Bukejs et Bezděk (Coleoptera: Chrysomelidae: Galerucinae) from Eocene Baltic amber using X-ray microtomography, Fossil Record 23 (1), pp. 105-115 : 106-111

Calomicrus eocenicus Bukejs et Bezděk, 2014

Figs. 1–4

Material examined

Collection number RSKM _ P3300.139 , male. A complete beetle is included in an elongate, transparent, yellow amber piece with dimensions of 41 mm × 19 mm × 8 mm, and preserved without supplementary fixation. Syninclusions: one specimen of Hymenoptera, a few stellate Fagaceae trichomes, numerous small detritus particles and gas vesicles .

Strata

Baltic amber from Eocene amber-bearing Blue Earth layers (a primarily Bartonian age is interpreted for the extinct central European resin-producing forests, according to Bukejs et al., 2019).

Locality

Yantarny settlement (formerly Palmnicken), Sambian (Samland) Peninsula, Kaliningrad region, Russia.

Note

Specimen RSKM _ P3300.139 is morphologically similar to the female holotype of Calomicrus eocenicus and is identified as male, showing sexually dimorphic characters of abdominal ventrite 5 and a distinctly smaller body size (see Discussion) .

Description of male

Measurements: total body length 3.5 mm; pronotum length 0.75 mm, pronotum maximum width 1.0 mm; elytra length 2.7 mm, elytra maximum width 1.9 mm.

Body elongate, slender, slightly convex dorsally and ventrally; reddish-brown as preserved, shiny, with weak metallic lustre; glabrous dorsally, with very fine, short, recumbent setation ventrally (distinctly visible on pygidium and abdomen).

Head hypognathous, relatively small, without distinct punctures; head together with eyes slightly wider than anterior margin of pronotum; vertex slightly convex. Compound eyes directed laterad, oval in outline, moderately large, prominent, entire, with distinct facets; vertical diameter 1.3× transverse diameter. Distance between eyes equal to about 1.4× transverse diameter of one eye. Antennal calli wide and elongate, slightly oblique, apparently contiguous; supracallinal sulcus distinct. Frontal ridge narrow, and sharp. Clypeus strongly transverse, with anterior margin concave. Labrum transverse, about 1.4× length of clypeus; anterior margin almost straight. Antennae filiform, slender, with 11 antennomeres; covered with fine, pale, semierect setae; antennae rather long, extending to reach posterior one-third of elytral length; antennomeres cylindrical, elongate; scape

110 A. Bukejs et al.: Description of the male of fossil Calomicrus eocenicus Bukejs et Bezděk

1.4× times as wide as antennomere 3; pedicle shortest, about 0.9× as long as antennomere 3; antennomeres 3–10 slightly dilated apically; antennomere 11 nearly spindle-shaped, with pointed apex, 3.3× as long as wide. Relative length ratios of antennomeres 1–11 equal to 9: 6: 7: 8: 8: 8: 8: 8: 9: 8: 11. Antennal insertion positioned posterior to anterior border of eyes. Distance between antennal sockets nearly equal to diameter of one socket.

Prothorax. Pronotum transverse, about 1.33× as wide as long, widest in anterior one-third of pronotal length, and slightly narrowed both anteriad and posteriad. Lateral margins widely rounded, with pronounced bordering; posterior margin slightly convex, with narrow bordering; anterior margin straight in dorsal view, arcuate in frontal view. Pronotal disc impunctate; lateral regions with sparse, very fine and effaced punctation (distinctly smaller than elytral punctures). Posterior angles distinct, nearly orthogonal; anterior angles indistinct, not protruding laterally. Anterior and posterior setiferous pores bearing long setae. Prohypomera and prosternum without distinct punctation; procoxal cavities open posteriorly; prosternal process sharp, very narrow, about 0.1× as wide as transverse diameter of procoxa.

Pterothorax. Scutellar shield small, triangular, impunctate, and glabrous. Elytra weakly convex, subparallel-sided, slightly narrowed posteriad, and widest in posterior one-third of elytral length; elytral anterior margin distinctly wider than pronotal posterior margin; covered with small, irregular punctures, in moderately dense arrangement, with distance between punctures equal to 1–3× diameter of one puncture. Humeral calli well developed, prominent. Elytral apices rounded. Metathoracic wings present, but details not observable in micro-CT scan data. Epipleura wide, gradually narrowed posteriorly, not reaching elytral apex, and covered with fine punctures. Metaventrite moderately convex, with distinct median line; covered with rugosity and very fine punctures. Metepisternum with rugosity and fine punctures, about 3.7× as long as wide; anterior and posterior margins oblique, lateral margins concave.

Legs slender, moderately long; covered with short, semierect setae. Procoxae widely oval and slightly transverse, 1.3× as wide as long, very narrowly separated; mesocoxae widely oval, narrowly separated by about 0.2–0.3× transverse diameter of mesocoxa; metacoxae narrowly elongate, transverse, moderately separated by about 0.5× transverse diameter of metacoxa. Femora slightly flattened and slightly dilated medially; metafemora and metatibiae equal in length; metafemora about 3× as long as wide. Tibiae almost straight, parallel-sided, without spines apically; metatibiae about 11× as long as wide. Tarsi long; metatarsus about 0.7× as long as metatibia; all tarsomeres 3 deeply bilobed; protarsomeres 1–3 slightly dilated apically, with protarsomere 1 about 0.3× as wide as long, protarsomere 2 about 0.6× as wide as long, and protarsomere 3 about 1.1× as wide as long. Relative length ratios of metatarsomeres 1–4 equal to 12: 5: 5: 7. Claws thin, with large denticle basally.

Abdomen with five visible ventrites, densely covered with fine punctures. Ventrite 5 with deep, oval fovea medially; posterior margin trilobed (median lobe moderately narrow with rounded apical margin; incisions short). Relative length ratios of ventrites 1–5 equal to 18: 10: 5: 6: 12 (measured medially). Pygidium evenly covered with dense, fine punctures.

Aedeagus ( Fig. 4 ) lanceolate, with sharp triangular apex; in lateral view, aedeagus moderately curved, with apical one-third of length thin, and middle part wide; in ventral view, aedeagus with wide, V-shaped, longitudinal furrow in middle part of length, and with longitudinal, medial carina in apical one-fifth of length. Tegmen Y-shaped.

Figures

Figure 1. Calomicrus eocenicus Bukejs et Bezděk, RSKM_P3300.139, photomicrographs, habitus: (a) dorsal view; (b) ventral view. Scale bars = 1.0 mm.

Figure 2. Calomicrus eocenicus Bukejs et Bezděk, RSKM_P3300.139, X-ray micro-CT renderings, habitus: (a) dorsal view; (b) ventral view; (c) frontal view; (d) left lateral view. Scale bars = 1.0mm.

Figure 3. Calomicrus eocenicus Bukejs et Bezděk, RSKM_P3300.139, X-ray micro-CT renderings: (a) elytra, dorsal view, with clipping planes exposing details beneath pronotum and right elytron; (b) pterothorax without legs, ventral view; (c) habitus without legs, caudal view. Scale bars = 0.5 mm. Abbreviations: f – fovea; p – pygidium; v1–v5 – abdominal ventrites 1–5 respectively.

Figure 4. Calomicrus eocenicus Bukejs et Bezděk, RSKM_P3300.139, X-ray micro-CT renderings, aedeagus: (a) dorsal view; (b) ventral view; (c) right lateral view; (d) left lateral view. Scale bars = 0.1 mm.