Chelonarium dingansich Alekseev and Bukejs, 2021

Alekseev, Vitalii I., Mitchell, Jerit, McKellar, Ryan C., Barbi, Mauricio, Larsson, Hans C. E. & Bukejs, Andris, 2021, The first described turtle beetles from Eocene Baltic amber, with notes on fossil Chelonariidae (Coleoptera: Byrrhoidea), Fossil Record 24 (1), pp. 19-32 : 24-29

Chelonarium dingansich Alekseev and Bukejs sp. nov.

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Figs. 6–7 , 8a

Derivatio nominis

The specific epithet “ dingansich ” is derived from the German word combination “ Ding an sich ” (in English: “thing in itself”), a well-known philosophic concept introduced by Immanuel Kant. The species name is dedicated to this famous Königsberg (now Kaliningrad)-native Prussian philosopher and thinker, in the run-up to the 300-year anniversary of his birth in 2024. The name is used as a noun in apposition.

Type material

Holotype: collection number “6696” [ MAIG] (ex. coll. Jonas Damzen JDC 7210) , “ Holotype / Chelonarium dingansich sp.

26 V. I. Alekseev et al.: The first described turtle beetles from Eocene Baltic amber

nov./Alekseev and Bukejs des. 2021” [red printed label] [ MAIG]; adult, sex apparently female. Almost complete beetle (antennomeres 4–11 of both antennae lacking) included in a transparent, yellow amber piece with approximate dimensions of 40 mm × 20 mm and a maximum thickness of 10 mm; preserved without supplementary fixation. Syninclusions: four very small stellate trichomes and a few small gas vesicles.

Type stratum

Baltic amber from Eocene amber-bearing Blue Earth layers; a predominantly Bartonian age has been interpreted for the extinct central European resin-producing forests ( Bukejs et al., 2019).

V. I. Alekseev et al.: The first described turtle beetles from Eocene Baltic amber 27

Type locality

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

Description

Measurements: body length 6.2 mm, maximum body width 2.7 mm; pronotum length 1.4 mm, maximum pronotum width 2.3 mm; elytra length 4.9 mm, maximum combined elytra width 2.7 mm.

Body elongate oval, biconvex; total body length / maximum body width equal to 2.3; integument unicolorous dark brown (as preserved). Pubescence dark, with small patches of denser and paler setae on elytral disc: dorsum covered with short, semierect setae in moderate density; lateral sides of elytra and pronotum with slightly

28 V. I. Alekseev et al.: The first described turtle beetles from Eocene Baltic amber

longer, distinctly curved setae; elytral vestiture simple, without any trichome-like structures; venter and legs with dense, recumbent, almost straight setation, setae shorter than setae of dorsum.

Head declined, not visible from above, slightly convex; densely covered with small punctation; distance between punctures smaller than diameter of one puncture. Clypeus not distinct; frontoclypeal suture absent. Eyes small, entire, almost round, slightly convex, finely facetted, without interfacetal setation; interocular frontal distance equal to about 2× diameter of one eye. Antennal insertions hidden. Antennae rather long; scape hidden; pedicel short, about 0.4× as long as antennomere 3; antennomere 3 longest, flattened.

Pronotum transverse, 1.6× as wide as long, widest at base; densely covered with small punctuation; distance between punctures less than diameter of one puncture. Posterior angles of pronotum acute. Anterior edge of pronotum almost semicircular in dorsal view; posterior edge bisinuate and crenulate. Pronotum margined anteriorly and laterally, with sharp, raised carina dividing pronotum into upper (moderately convex dorsally) and lower (inclined posteriad) parts. Lower pronotal area, between prominent anterior carina and posterior edge of concealed head, wider than protibial width. Pro- and mesosternum with deep, elongate, intercoxal median excavation for reception of basal antennomeres. Hypomeron excavated to receive profemora; meso- and metaventrite with excavations for receiving meso- and metafemora and tibiae.

Scutellum subpentagonal, almost as long as wide, densely covered with semierect, pale setae. Elytra moderately convex, forming elongate oval about 1.9× as long as combined width; slightly wider than pronotal posterior margin, about 3.6× as long as pronotum. Elytral punctation irregular, small, dense and round, with distance between punctures less than diameter of one puncture; interspaces almost flat. Epipleura narrow, reaching abdominal ventrite 1. Metepisternum wide, about 2× as wide as epipleural maximum width; with dense, small punctation. Metaventrite slightly convex laterally, with almost flat disc; densely covered with small punctation; distance between punctures smaller than diameter of one puncture; interspaces slightly convex; discrimen distinct in anterior half of metaventrite.

Legs rather short, flattened; densely covered with small punctures; distance between punctures smaller than diameter of one puncture. All coxae distinctly separated; procoxa nearly round; mesocoxa oval; metacoxa narrow, strongly transverse, excavate, with short metacoxal plates and with triangular outer edge. Femora and tibiae subequal in length; pro- and mesofemora comparatively wider than metafemur. Tibiae narrower than femora, protibia about 0.6× as wide as profemur, mesotibia about 0.3× as wide mesofemur, metatibia about 0.6× as wide as metafemur; protibia spinose along inner margin. Tarsi 5 segmented, tarsomere 3 apparently with membranous lobe ventrally, tarsomere 4 minute. Tarsal claws with denticle basally.

Abdomen with five visible ventrites; abdominal sutures entire, slightly concave to almost straight; ventrite 5 simple, with widely triangular apical margin; finely and densely punctate; distance between punctures equal to 0.5–1.0× diameter of one puncture. Relative length ratios of abdominal ventrites 1–5 equal to 6: 4: 4: 3.5: 7 (medially).

Differential diagnosis

Chelonarium dingansich sp. nov. differs from Ch. andabata sp. nov. in possessing longer and distinctly curved setae on elytral and pronotal lateral sides (setae comparatively shorter and almost straight in Ch. andabata sp. nov.); an elytral disc with small patches of paler setae (without small patches of paler setae in Ch. andabata sp. nov.); a widely rounded, semicircular apical margin of abdominal ventrite 5 (widely triangular in Ch. andabata sp. nov.); and a distinctly more elongate oval body: less transverse pronotum, 1.6× as wide as long (2.1× as wide as long in Ch. andabata sp. nov.), and more elongate elytra, 1.9× as long as combined width (1.4× as long as combined width in Ch. andabata sp. nov.).

Remarks

The sex of the examined specimen is determined based on micro-CT results. There is no sclerotized aedeagus-like structure present inside the abdomen; therefore, the specimen appears to be female.

Figures

Figure 6. Photomicrographs of Chelonarium dingansich Alekseev and Bukejs sp. nov., holotype, 6696 [MAIG], habitus: (a) dorsal view, (b) ventral view and (c) left lateral view. Scale bar = 1.0 mm.

Figure 7. X-ray micro-CT renderings of Chelonarium dingansich Alekseev and Bukejs sp. nov., holotype, 6696 [MAIG], habitus: (a) dorsal view, (b) ventral view and (c) right lateral view. Scale bar = 1.0 mm.

Figure 8. Elytral vestiture and setation shape in fossil Chelonarium: (a) Ch. dingansich Alekseev and Bukejs sp. nov., right elytron, and (b) Ch. andabata Alekseev and Bukejs sp. nov., left elytron. Scale bars = 0.5 mm. Abbreviation: pa – patches of paler and denser setae.