Chelonarium andabata 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 : 21-23

Chelonarium andabata Alekseev and Bukejs sp. nov.

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Figs. 1–5 , 8b

Derivatio nominis

The specific epithet “ andabata ” is a Latin word meaning “a type of gladiator who fought blind because of a restrictive helmet” and refers to the strongly declined head of the beetle, which is concealed from above. The specific epithet is used as a noun in apposition.

Type material

Holotype: collection number “ RSKM _ P3000.141 ”, “ Holotype / Chelonarium andabata sp. nov. /Alekseev and Bukejs des. 2021” [red printed label] [ RSKM]; adult, male. Almost complete beetle (right antennomeres 10–11 lacking) included in a transparent, yellow amber piece with approximate dimensions of 8 mm × 16 mm and a maximum thickness of 8 mm; preserved without supplementary fixation. The dorsal part of the specimen is partially obscured by milky amber. Syninclusions are absent.

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).

Type locality

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

Description

Measurements: body length 5.6 mm, maximum body width 3.2 mm; pronotum length 1.2 mm, maximum pronotum width 2.5 mm; elytra length 4.3 mm, maximum combined elytra width 3.2 mm.

Body ovoid, widely oval, biconvex; total body length / maximum body width equal to 1.75; integument unicolorous dark brown (as preserved). Pubescence unicolorous and dark: dorsum covered with short, semierect setae in moderate density; elytral vestiture uniform, simple, without any trichome-like structures, setae almost straight to slightly curved; setae at elytral lateral sides slightly stouter; venter and legs with dense, short recumbent setae.

Head declined, not visible from above, rounded pentagonal, slightly convex; densely punctate; punctures round and small, distance between punctures equal to 0.2–0.5× 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, rounded and short; pedicel and antennomeres 3–11 flattened; antennomere 3 longest, antennomere 4 shortest; antennomeres 2–3 and 11 elongate, antennomeres 5–10 triangular in outline. Relative length ratios of antennomeres 1–11 equal to 1.5: 3: 7: 0.7: 1.8: 2: 2: 2.2: 2.2: 2: 3.4.

Pronotum transverse, 2.1× as wide as long, widest at base, with fine and dense punctation. 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 as well as tibiae.

Scutellum subpentagonal, almost as long as wide. Elytra moderately convex, widely oval, about 1.4× as long as combined width; distinctly wider than pronotal posterior margin, about 3.6× as long as pronotum. Elytral punctation irregular, dense and round along sides, sparser and finer on disc, distance between punctures equal to 0.3–3.0× diameter of one puncture, interspaces flat. Epipleura narrow, reaching abdominal ventrite 1. Metepisternum wide, about 2× as wide as maximum epipleural 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; pro- and mesocoxae widely oval, slightly transverse, about 1.3– 1.4× as wide as long; metacoxae narrow, strongly transverse, excavate, with short metacoxal plates and with triangular outer edge. Femora and tibiae subequal in length; pro- and mesofemur comparatively wider than metafemur. Tibiae narrower than femora, protibia about 0.5× as wide as profemur, mesotibia about 0.5× as wide mesofemur, metatibia about 0.6× as wide as metafemur; protibia spinose along inner margin. Tarsi 5 segmented, tarsomere 3 with long membranous lobe ventrally, tarsomere 4 minute. Relative length ratios of mesotarsomeres 1–5 equal to 15: 10: 7: 4: 25. Pretarsal claws with denticle basally.

Abdomen with five visible ventrites; abdominal sutures entire, slightly concave; ventrite 5 simple, with widely rounded, semicircular 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 7: 4.5: 4: 3.5: 6.5 (medially).

Aedeagus robust, with widely rounded base and gradually narrowed apically ( Fig. 5 ).

Differential diagnosis

The genus Chelonarium is very species-rich but poorly documented: it is in need of revision for many of its inadequately illustrated and briefly described species. The Eocene taxon Ch. andabata sp. nov. is similar to one Recent North American chelonariid species, Ch. lecontei Thomson , in its general antennal structure, but it differs in having smaller eyes (inte-

V. I. Alekseev et al.: The first described turtle beetles from Eocene Baltic amber 23

rocular distance in Ch. lecontei is slightly less than one eye diameter), denser head punctation and uniform elytral vestiture (without maculae). The newly described fossil species can be distinguished from the westernmost Palaearctic Ch. vartianae Mandl ( Afghanistan) based on having a pronotum without transverse impression. Chelonarium andabata sp. nov. clearly differs from Ch. ornatum Klug in its ratio of four basal antennomere lengths; it differs from Ch. kurosawai Satô in possessing unicolorous elytra; and it differs from Ch. beauvoisi Latreille , Ch. convexum MØquignon and Ch. cupreum MØquignon in its smaller body size. The combination of characteristics mentioned in the species description, additional characteristics of body part ratios, and details of vestiture and punctation should distinguish the new fossil species from all Recent congeners.

Figures

Figure 1. Photomicrographs of Chelonarium andabata Alekseev and Bukejs sp. nov., holotype, RSKM_P3000.141 [RSKM]: (a) ventral habitus view; (b) right lateral habitus view; (c) detail of head with antenna (horizontal arrow) and protarsi (inclined arrows) in ventral view; and (d) detail of legs in ventral view with pro-, meso-, and metatarsus indicated by horizontal arrows (from top to bottom of view). Scale bars = 1.0 mm.

Figure 2. X-ray micro-CT renderings of Chelonarium andabata Alekseev and Bukejs sp. nov., holotype, RSKM_P3000.141 [RSKM], habitus: (a) dorsal view, (b) ventral view and (c) left lateral view. Scale bar = 1.0 mm.

Figure 3. X-ray micro-CT renderings of Chelonarium andabata Alekseev and Bukejs sp. nov., holotype, RSKM_P3000.141 [RSKM], habitus: (a) ventral view without legs, showing depressions for legs reception; (b) ventral view with antennae and legs in different colours; (c) frontal view; and (d) caudal view. Scale bar = 1.0 mm.

Figure 4. Antennae of Chelonarium andabata Alekseev and Bukejs sp. nov., holotype, RSKM_P3000.141 [RSKM]: (a) X-ray micro-CT rendering and (b) reconstruction. Abbreviations: a1–a11 – antennomeres 1–11 respectively.

Figure 5. X-ray micro-CT renderings of Chelonarium andabata Alekseev and Bukejs sp. nov., holotype, RSKM_P3000.141 [RSKM], aedeagus: (a) dorsal view, (b) lateral view and (c) ventral view. Scale bar = 0.1 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.