Neomida groehni Nabozhenko et Bukejs, 2020

Nabozhenko, Maxim V., Kairišs, Kristaps & Bukejs, Andris, 2020, The oldest fossil darkling beetle of the genus Neomida Latreille, 1829 (Coleoptera: Tenebrionidae) from Eocene Baltic amber examined with X-ray microtomography, Zootaxa 4768 (3), pp. 435-442 : 436-441

Neomida groehni Nabozhenko et Bukejs sp. nov.

( Figs 1–4 )

Type material. Holotype: “C 1450”, deposited in the GPIH; adult, male. Complete beetle is included in transparent,

yellowish, subtriangular amber piece with dimensions of 20×21× 21 mm and maximum thickness 8 mm, without supplementary fixation. Specimen is visible only in lateral view; characters of head, venter and legs are poorly visible using traditional light microscopy. Syninclusions: one specimen of Crepidodera tertiotertiaria Bukejs, Biondi et Alekseev, 2016 ( Chrysomelidae , Coleoptera ), one poorly visible specimen of cf. Cathartosilvanus siteiterralevis Alekseev, Bukejs et McKellar, 2019 ( Cucujidae , Coleoptera ), two indet ant specimens ( Hymenoptera : Formicidae ), nine indet specimens of Nematocera (Diptera), few stellate Fagaceae trichomes, and small pieces of organic material.

Type strata. Baltic amber from Eocene Blue Earth layers (a mostly Bartonian age is interpreted for the extinct Central European resin-producing forests according to Bukejs et al. 2019).

Type locality. Baltic Sea coast, Yantarny settlement (formerly Palmnicken), Sambian (Samland) Peninsula, Kaliningrad Region, Russia .

Description. Measurements: body length 2.9 mm, body maximum width 2.1 mm; pronotal length 0.7 mm, maximum pronotal width 1.2 mm; elytral length 2.1 mm, maximum combined elytral width 1.5 mm.

Body elongate, moderately convex, with subcylindrical elytra ( Figs 2 A–E); integument uniformly brown (as preserved), dull, glabrous.

Head prognathous, widest at eye-level; apical margin of epistoma weakly rounded; labrum not preserved; head densely covered with small punctures (about as large as one eye facet), with distance between punctures subequal to one puncture diameter, interspaces flat ( Fig. 3B ), with microreticulation. Epistoma widely and slightly impressed, with slightly elevated posterior angles, and with very small, poorly visible marginal tubercles ( Figs. 3A,B ). Vertex slightly and evenly convex dorsally. Frons with two small, symmetrical horns at upper eye level near middle, and slightly impressed between these horns ( Figs. 2F , 3A,B ). Compound eyes large, slightly prominent, with large facets, reniform, with deep antero-medial emargination. Ratio of head width (at eye-level) to distance between eyes dorsally is 1.95, ventrally is 1.66. Apical maxillary palpomeres cylindrical, not securiform. Gular suture present in posterior portion. Mentum with round, elevated tubercle, with fovea in middle ( Figs. 2B,E ). Antennae moderately long, extending towards elytral base; forming 7-segmented club ( Fig. 3A ), rather stout, slightly clavate (antennomeres 4–10 widen gradually); scape subcylindrical, distinctly wider and longer than pedicel; pedicel cylindrical, as long as wide, short, about 0.6× as long as antennomere 3; antennomere 3 cylindrical, elongate, 1.4× as long as wide; antennomeres 4–5 nearly as long as wide, dilated apically; antennomeres 6–10 transverse, 1.3–1.4× as wide as long, distinctly dilated apically; antennomere 11 ovoid, 0.9× as wide as long; relative length ratios of antennomeres 1–11 equal to 12-7-12-12-12-12-13-14-14-14-21. Antennomeres 5–10 slightly asymmetrical, transverse.

Prothorax. Pronotum transverse ( Fig. 2A ), 1.7× as wide as long, widest in posterior one-third of pronotal length, slightly narrowed anteriad; densely covered with fine, sparse punctures in middle, and with coarse, denser punctures on lateral sides, with distance between punctures 0.5–2.0× diameter of one puncture, and microreticulate flat interspaces; disc slightly convex ( Figs. 2C,D,F ), with two small round impressions in the middle, two longitudinal elongate impressions on either lateral side, two narrow transverse impressions along base, and with lateral margins narrowly and slightly flattened. Pronotum lateral margins distinctly bordered, widely rounded, undulate; anterior margin almost straight medially (in dorsal view), arcuate (in frontal view), not bordered medially; posterior margin bisinuate, narrowly bordered. Anterior pronotal angles orthogonal, apically rounded, slightly prominent in dorsal view; posterior angles nearly right, with distinct angulate apex. Prothoracic hypomera impressed baso-laterally, densely covered with coarse punctures, with distance between punctures about 1.0–2.0× diameter of one puncture; prosternum convex, more sparsely and finely punctured than prohypomera, and distance in front of procoxal cavities nearly as long as transverse diameter of procoxa; prosternal process not beaded, rather narrow, about 0.45× as wide as transverse diameter of procoxa, with sharp, longitudinal carina medially, slightly projecting posterior to procoxae, with apical tubercle at level of basal part of coxae ( Fig. 3C ).

Pterothorax. Scutellar shield large, triangular, transverse, 1.6× as wide as long, with sparse, small punctures. Elytra elongate-oval ( Fig. 2A ), 1.4× as long as wide, 3.0× as long as pronotum, subparallel-sided, weakly convex, with sutural area elevated along entire length ( Figs. 2F,G ); humeral callosity not prominent; each elytron with 9 distinct striae composed of round, coarse punctures (coarser than those on pronotum), with striae becoming indistinct in posterior one-third of elytra, and distance between punctures 0.5–1.5× diameter of one puncture; scutellary striole very short, indistinct, consisting of approximately 4 punctures; intervals flat, with fine and dense secondary punctation and microreticulation, with interstriae 2.0–3.0× diameter of one puncture. Laterally inflected sides of elytra wide, completely visible dorsally. Epipleura wide, slightly narrowed posteriorly, almost reaching elytral apex, covered with small punctures ( Figs. 2B,E ). Mesoventrite with moderately dense and coarse punctation on sides; posterior part with Y-shaped elevation and deep, bordered fovea between mesocoxae ( Fig. 3C ). Mesepimeron covered with moderately coarse, denser punctures. Metaventrite with disc flat and longitudinal medial sulcus extending from posterior to nearly anterior margin; sparsely covered with coarse punctation (punctures smaller, sparser, and less distinct on disc and posteriorly). Metepisternum narrow, slightly dilated anteriorly, about 4.9× as long as wide anteriorly, covered with dense and moderately coarse punctation, with almost straight lateral margins.

Legs long and slender ( Figs. 2B,D ), sparsely covered with very fine punctation, and short, recumbent setae. Mesotrochantine present, mesocoxal cavities closed by mesepimeron, trochantin, and metaventrite. Procoxae transversely oval, 1.2 × as wide as long; mesocoxae subhemispherical; metacoxae narrowly oval, strongly transverse, 2.6× as wide as long, with small impression at middle; all coxae not contiguous, narrowly separated ( Fig. 1E ). Femora simple, not clavate, slightly flattened, with wide groove ventrally in apical portion; metafemora distinctly longer than pro- and mesofemora. Tibiae almost straight, narrow, nearly parallel-sided, about as long as femora, with weak, longitudinal carina externally. Tarsi moderately long, but shorter than tibiae, with moderately dense setation on plantar surface, not dilated; metatarsus 1.3× as long as protarsus, and 0.9× as long as mesotarsus, metatarsomere 1 slightly longer than metatarsomeres 2–3 combined, equal in length with terminal metatarsomere; relative length ratios of mesotarsomeres 1–5 equal to 11-6-6-6-19; relative length ratios of metatarsomeres 1–4 equal to 35-14-14-35. Claws simple.

Abdomen with five visible ventrites, punctures nearly identical to those on metaventrite (ventrites 4 and 5 with denser punctation); intersegmental membranes present between abdominal ventrites 3–5 ( Figs. 2B,E ); intercoxal process of ventrite 1 triangular, narrow, about 0.25× as wide as transverse diameter of metacoxa; ventrite 5 with apical margin rounded, not beaded; relative length ratios of ventrites 1–5 equal to 23-19-15-9-12 (medially).

Aedeagus narrow; apical piece shorter than very long basal piece; apical piece elongate, with narrowly rounded apex; aedeagus curved in lateral view, alae of apical piece absent ( Fig. 4 ).

Differential diagnosis. Neomida groehni sp. nov. possesses a glabrous body, similar to the extant Neotropical Neomida species subgroup with epipleura extending towards the elytral apex. This new fossil species differs from all known extant and extinct congeners based on its very weakly convex pronotum with undulate lateral margins (other Neomida have a strongly convex pronotum in the transverse plane, with evenly rounded lateral margins), distinct (not rounded) orthogonal posterior angles, and elevated sutural area of elytra.

Derivatio nominis. The species is named in honour of Carsten Gröhn (Glinde, Germany), who provided the holotype specimen for examination.

Figures

FIGURE 1. Neomida groehni sp. nov., holotype, photomicrograph: A – habitus, latero-dorsal view; B – details of forebody, dorsal view; C – habitus, ventral view. Not reproduced to the same scale.

FIGURE 2. Neomida groehni sp. nov., holotype, habitus, X-ray micro-CT rendering: A – dorsal view; B – ventral view with legs; C – lateral view, without legs and antennae; D – the same, with legs an antennae; E – ventral view without legs and antennae; F – anterior view; G – caudal view. Scale bars represent 1 mm.

FIGURE 3. Neomida groehni sp. nov., holotype, X-ray micro-CT rendering:A – details of forebody, dorso-lateral view, arrows show marginal epistomal tubercles; B – head, dorsal view, arrows show marginal epistomal tubercles; C – pro-mesothoracic junction, ventral view. Abbreviations: Pstr – prosternal process, MstrE – mesosternal Y-shaped elevation, MstrF – mesosternal intercoxal fovea, Mtrch - mesotrochantine. Not reproduced to the same scale.

FIGURE 4. Neomida groehni sp. nov., holotype, aedeagus, X-ray micro-CT rendering: A – ventral view; B – dorsal view; C – lateral view; D – apical piece. Abbreviations: ap – apical piece, bp – basal piece, ml – median lobe.