Monolepta rappsilberi, Bukejs & Bezděk & Kairišs & Alekseev, 2021

Bukejs, Andris, Bezděk, Jan, Kairišs, Kristaps & Alekseev, Vitalii Igorevich, 2021, The first extinct species of Monolepta Chevrolat (Coleoptera: Chrysomelidae Galerucinae) from Bitterfeld amber, described using X-ray micro-computed tomography, Zootaxa 4995 (2), pp. 345-356 : 347-352

Monolepta rappsilberi sp. nov.

( Figs 1–13 )

LSID urn:lsid:zoobank.org:act:8C7AD06A-DBB0-4B5D-BB4E-7B419D87835E

Type material. Holotype: “T-I-K-30” [CIR], female. The complete beetle is included in a transparent, yellow amber piece embedded in a block of GTS-polyester resin with dimensions 26×20× 7 mm. Syninclusions: one stellate Fagaceae trichome, and few small pieces of organic material.

Type stratum. Bitterfeld amber (probably Upper Eocene in age) from Upper Oligocene stratigraphical horizons (Chattian, 23.0–28.1 Ma).

Type locality. Germany, Sachsen-Anhalt, Bitterfeld-Wolfen, Goitzsche Lagerstätte .

Etymology. The specific epithet is a patronym dedicated to Dr Ivo Rappsilber (Halle, Germany), an enthusiast and specialist in Bitterfeld amber, the collector of the amber piece.

Description. Female. Measurements: total body length 3.3 mm; pronotum length 0.8 mm, pronotum maximum width 1.4 mm; elytra length 2.4 mm, elytra maximum combined width 1.9 mm.

Body elongate-oval, convex; brown with antennae slightly paler (as preserved), weakly lustrous; glabrous.

Head hypognathous, relatively small, head together with eyes nearly as wide as anterior margin of pronotum; frons and vertex slightly convex, apparently impunctate; genae with very fine punctation. Compound eyes large, elongate oval in outline, strongly prominent, entire, with distinct facets; vertical diameter 1.5× transverse diameter. Interocular space narrow, equal to about 0.9× transverse diameter of one eye. Frontal tubercles wide, subquadrate, contiguous, slightly convex; supracallar and orbital sulci sharp, deep. Supraorbital sulcus straight, deep. Frontal carina short, narrow and sharp. Clypeus strongly transverse, short, with anterior margin concave and posterior margin convex. Labrum trapezoidal, transverse, about 1.8× length of clypeus; anterior margin almost straight. Maxillary palpi with 4 palpomeres; palpomere 1 smallest; palpomere 2 subtrapezoidal, 1.3× as wide as long; palpomere 3 subcylindrical, nearly as long as wide; palpomere 4 conical, elongate, 1.3× as long as wide. Labial palpi with 3 palpomeres, short; palpomere 3 conical.

Antennae filiform, slender, with 11 antennomeres; rather long, about 0.7× as long as body length, extending to reach posterior third of elytral length; sparsely covered with fine, semierect setae (antennomeres 1–3 glabrous); antennomeres cylindrical, elongate; scape curved, slightly dilated apically, longest, 1.8× as long as antennomeres 2–3 combined, about 1.3× times as wide as antennomere 2; pedicle shortest, 1.8× as long as wide, 0.25× as long as scape and 0.8× as long as antennomere 3; antennomere 3 about 2.4× as long as wide, with oblique apical margin, slightly dilated apically; antennomeres 4–6 with oblique apical margin; 7–10 slightly dilated apically, subequal in size; antennomere 11 spindle-shaped, with pointed apex, 3.6× as long as wide; relative length ratios of antennomeres 1–11 equal to 20:5:6:12:11:10:10:9:9:8:11. Antennal insertions at posterior borders of eyes. Distance between antennal sockets 0.9× diameter of one socket.

Pronotum trapezoidal, transverse, about 1.75× as wide as long, widest at base, and narrowed anteriad, without impressions. Lateral margins slightly rounded, with pronounced bordering; posterior margin rounded, with wide bordering; anterior margin slightly concave in dorsal view, without bordering. Pronotal punctation fine and dense; interspaces smooth. Posterior angles nearly orthogonal, with setigerous pore bearing short seta; anterior angles indistinct, rounded, slightly protruding laterally. Prohypomera and prosternum without distinct punctation; procoxal cavities closed posteriorly; prosternal process narrow, slightly convex in apical portion, about 0.25× as wide as maximum transverse diameter of procoxa, with parallel sides, not projecting beyond posterior margin of procoxae.

Scutellum rather large, triangular with pointed apex, glabrous, and apparently impunctate.

Elytra convex, rather short, widely oval, 1.3× as long as maximum wide combined, slightly narrowed posteriad, and widest at middle of elytral length; elytral anterior margin slightly wider than pronotal posterior margin; densely covered with small, irregular punctation, distance between punctures equal to 0.3–2.0× diameter of one puncture, punctation slightly sparser laterally and apically. Humeral calli developed, slightly prominent. Elytral apices rounded separately. Metathoracic wings present. Epipleura rather wide, gradually narrowed posteriorly, reaching abdominal ventrite 3, and densely covered with very fine punctures. Metaventrite moderately convex, apparently with discrimen, without distinct punctation. Metepisternum impunctate, wide; anterior margin oblique, posterior margin nearly straight, lateral margins subparallel.

Legs slender, moderately long; covered with short, semierect setae. Procoxae widely oval, long, narrowly separated; mesocoxae widely oval, apparently very narrowly separated; metacoxae elongate, transverse, about 3.6× as wide as long, very narrowly separated. Femora flattened and slightly dilated medially; metafemora and metatibiae equal in length; metafemora about 3× as long as wide, profemorae slightly shorter. Tibiae almost straight (meso- and metatibiae slightly curved); metatibiae about 12× as long as wide; pro- and mesotibiae without distinct apical spur, with fringe of spinulae apically, metatibiae with rather long (about 0.6× as long as metatibial width at apex) apical spur and fringe of spinulae. Tarsi pseudotetramerous; protarsi not wider than meso- and metatarsi; all third tarsomeres deeply bilobed. Metatarsus about 0.7× as long as metatibia; metatarsomere 1 long, about 1.7× as long as metatarsomeres 2–4 combined; relative length ratios of metatarsomeres 1–4 equal to 29:6:4:7. Claws thin, with large approximately right-angled denticle basally.

Pygidium not visible (covered by elytra). Abdomen with five visible ventrites, with sparse and very fine punctation, glabrous. Ventrite 5 with longitudinal, rather long (about 0.5× as long as ventrite 5 length) carina medially; posterior margin widely rounded. Relative length ratios of ventrites 1–5 equal to 30:12:10:7:9 (measured medially).

Diagnosis. Monolepta rappsilberi sp. nov. is characterised by: small body (3.3 mm long), transverse pronotum, metatarsomere 1 about 3× as long as metatarsomeres 2 and 3 combined, and abdominal ventrite 5 with longitudinal, rather long carina medially. The comparison with numerous recent species is very difficult due to unsatisfactory species-level taxonomy of the genus Monolepta and to absence of the male of the fossil species. However, the presence of a longitudinal carina on the female abdominal ventrite 5 is a unique character unknown in all other Monolepta species.

Monolepta rappsilberi sp. nov. clearly differs from other fossil Luperini described from Eocene amber. From Calomicroides danicus Nadein in Nadein et al. 2016 (Danish amber) it is separated by: antennomere 1 1.8× as long as antennomeres 2–3 combined (antennomere 1 shorter than antennomeres 2–3 combined in C. danicus ), epipleura not reaching sutural angles of elytra, metatibial apical spur rather long, about 0.6× as long as metatibia width at apex (minute in C. danicus ), metatarsomere 1 about 1.7× as long as metatarsomeres 2–4 combined (metatarsomere 1 not longer than metatarsomeres 2–4 combined in C. danicus ), and abdominal ventrite 1 longer than ventrites 2–3 combined (ventrites 1 and 2 subequal in length in C. danicus ). From Calomicrus eocenicus Bukejs & Bezděk, 2014 (Baltic amber) it is disinguished by: antennomere 1 1.8× as long as antennomeres 2–3 combined (antennomere 1 shorter than antennomeres 2–3 combined in C. eocenicus ), metatibial apical spur rather long (tibiae without apical spur in C. eocenicus ), metatarsomere 1 about 1.7× as long as metatarsomeres 2–4 combined (metatarsomere 1 about as long as metatarsomeres 2–4 combined in C. eocenicus ), and abdominal ventrite 5 (in female) with longitudinal carina medially (without in C. eocenicus ).

Remarks. The rounded apex of the apical abdominal ventrite shows that this fossil is a female, as males of Luperini have a well-defined apical truncate lobe on the last ventrite. The sex of the examined specimen is confirmed by micro-CT results as there is no sclerotized structure resembling an aedeagus present inside the abdominal cavity.

Figures

FIGURES 1–4. Photomicrographs of Monolepta rappsilberi sp. nov., holotype, No T-I-K-30 [CIR], female: 1—habitus, dorsal view; 2—habitus, ventral view; 3—details of abdomen; 4—tarsi. Abbreviations: ca—carina, mst—mesotibia, mtt—metatibia, prt—protibia, v1–v5—abdominal ventrites 1–5. Not reproduced to the same scale.

FIGURES 5–8. X-ray micro-CT renderings of Monolepta rappsilberi sp. nov., holotype, No T-I-K-30 [CIR], habitus: 5—dorsal view; 6—ventral view; 7—right lateral vie; 8—left lateral view. Scale bar represents 1.0 mm.

FIGURES 9–11. X-ray micro-CT renderings of Monolepta rappsilberi sp. nov., holotype, No T-I-K-30 [CIR]: 9—habitus, caudal view; 10—details of forebody, dorsal view; 11—habitus without legs, ventral view. Not reproduced to the same scale.

FIGURES 12–13. X-ray micro-CT renderings of Monolepta rappsilberi sp. nov., holotype, No T-I-K-30 [CIR]: 12—head (right antenna removed), frontal view; 13—details of forebody without legs, ventral view. Abbreviations: as—antennal sock- et, c—clypeus, fc—frontal carina, ft—frontal tubercle, l—labrum, mp3–mp4—maxillary palpomeres 3–4, os—orbital sulcus, scs—supracallar sulcus, sos—supraorbital sulcus. Scale bar represents 0.5 mm.