Zopheromimus auriborussiensis, Alekseev & Nabozhenko, 2023

Alekseev, Vitalii I. & Nabozhenko, Maxim V., 2023, News from Baltic amber: a new tribe of extinct Paleogene ironclad beetles (Coleoptera: Zopheridae: Zopherinae), Zootaxa 5297 (3), pp. 435-445 : 438-442

Zopheromimus auriborussiensis sp. nov.

( Figs 1–6 )

Type material. Holotype: No. KAM 8325/2 [KRAM] (ex. coll. Konstantin Andruschenko), adult, sex unknown. Complete beetle inclusion in a transparent, yellow, polished amber piece with approximate dimensions 46×16× 8 mm; preserved without supplementary fixation. Syninclusion: absent.

Type strata. Baltic amber from Eocene amber-bearing Blue Earth layers.

Type locality. Yantarny settlement (formerly Palmnicken), Sambian (Samland) peninsula, the Kaliningrad region, Russia .

Derivatio nominis. The specific epithet “ auriborussiensis ” used as an adjective, is a compound word derived from the Medieval Latin aurum borussiense (the gold of Prussia) and referring to the German metaphoric names of Baltic amber (“das Gold Ostpreussens” or “das deutsche Gold”).

Description. Measurements: body length about 5.3 mm; maximum width across both elytra 1.4 mm; pronotal length 1.5 mm, pronotum maximum width 1.15 mm; elytral length about 3.5 mm, elytron maximum width 0.7 mm. Body elongate, subcylindrical, moderately convex dorsally. Integument uniformly black. Body vestiture consisting of (1) short, recumbent, scale-like, elongate-oval light setae, and (2) curved, semirecumbent, bristle-like dark setae. Dense light oval scales forming patterns on the dorsum (median stripe on pronotum and diagonally striped pattern on elytra) and almost entirely covering head and ventral side of the body.

Head. Prognathous, almost as long as wide, finely granulate, covered with oval scales and semirecumbent bristles. Anterior margin of epistoma widely rounded. Genae narrower than eyes. Frons flat, with elevated lateral sides near antennal insertions (frontal ridges) and near inner eye margins. Compound eyes lateral, protruding, hemispherical, without interfacetal setae, widely separated, with entire and straight anterior margin, finely faceted. Antennal grooves absent. Labrum with concavity on anterior margin. Terminal maxillary palpomere oval, twice as long as preceding palpomere, apex truncate; terminal labial palpomere elongate, spindle-shaped. Submentum with small round tubercle. Antennal insertions concealed under a lateral expansion of the frons and not visible in dorsal view. Antenna 11-segmented, almost moniliform, with weak club, reaching posteriorly to anterior one-third of pronotum. Club 2-segmented, setose, relatively short and stout. Scape nearly spherical. Pedicel subcylindrical, slightly longer than wide, longer than scape.Antennomeres 3–8subquadrate, as long as wide, subequal.Antennomeres 9–10 slightly transverse. Antennomere 11 rounded, as long as wide.

Thorax. Pronotum weakly elongate, about 1.3× as long as wide, with maximum width at midlength, pronotal base distinctly narrower than elytral base; pronotal disc slightly convex, with well-developed elongate median impression, consisting of three parts (small rounded anterior area, large oval central area, and triangular posterior area). Lateral pronotal sides weakly serrate, rounded, with moderately protruded and convex anterior part at middle. Lateral margins of anterior impressed part with bean-shaped callosities. Pronotum weakly bisinuate at the base, with weakly rounded middle lobe, not margined posteriorly; evenly arcuate anteriorly. Anterior angles obtuse; posterior angles widely rounded. Pronotal surface uniformly and finely granulated; each granule bearing a single curved semirecumbent bristle-like dark seta. Median impression covered with elongate-oval, recumbent, scale-like light setae.

Prothoracic notosternal suture well-visible, complete. Prosternum and hypomeron densely covered with oval scale-like setae, hiding the punctation. Hypomeron impressed basally, with raised posterior edge. Procoxae separated by elongate intercoxal prosternal process (as wide as procoxal diameter), distinctly widened apically and forming posterolateral projections extending to posterior margin of procoxae. Prosternal process with two fine parallel lines. Procoxal cavity posteriorly closed by projection of hypomeron and posterolateral projection of intercoxal prosternal process in the ratio 50:50 of its diameter.

Elytra elongate (about 2.5× as long as wide), subparallel, slightly convex, punctate-striate, with weakly carinate interstriae and straight (not rounded) apices. Elytral punctures round, arranged in 9 or 10 longitudinal rows, mostly hidden by setation. Scutellary striole not apparent. Interstriae granulate, densely covered by short setae. Setae mostly flat, oval, scale-like. Dense light oval scales making a pattern in the form of diagonal and semicircular stripes. Scutellar shield transverse, oval. Metathoracic wings are not apparent on the specimen, possibly present. Epipleura narrowed posteriorly, extending posteriorly to about the middle of abdomen.

Mesoventrite punctate, metanepisternum granulate, metaventrite densely covered with oval scale-like setation and sparse dark hair-like setae. Mesocoxal cavities laterally closed by meso- and metaventrites. Mesanepisternum triangular; mesepimeron narrow, with one row of punctures; metanepisternum narrow and long; with one row of small granules. Mesocoxae narrowly separated by 1/4 mesocoxal diameter. Metaventrite with convex disc; discrimen, distinct, as long as one-half of metaventrite.

Legs. Relatively similar in shape, setose; femora and tibiae covered with dense scale-like setae. Pro- and mesocoxae hemispherical and convex, metacoxae strongly transverse. Trochanters oblique, visible on all legs. Femora slightly longer than tibiae, flattened. Tibiae straight. Tarsi about as long as tibiae. All tarsomeres narrow, simple (non-lobed). Tarsal formula 5-5-4. Relative length ratios of metatarsomeres 1–4 equal to 9:5:7:18. Tarsal claws slender, simple, without basal tooth or expansion, about 0.3× as long as tarsomere 4.

Abdomen. With five visible, freely articulated abdominal ventrites; sutures between ventrites deep and complete. Ventrites are punctured and densely covered with oval scale-like setae and sparse dark hair-like setae. Intercoxal process of abdominal ventrite 1 triangular, acute. Relative length ratios of abdominal ventrites 1–5 equal to 48:30:25:20:22 (measured medially). Abdominal ventrite 5 with two shallow, transverse preapical grooves. Apex of ventrite 5 with dense semierect pubescence.

Note: The number of antennomeres in the club was determined by using patches of dense and fine pubescence (interpreted as sensory areas) as indicators of the distal surface of a club antennomere. The apical antennomeres are not fused and all antennomeres look rather uniformly articulated, therefore the form of antennae is described as “almost moniliform.” However antennomeres 9–10 are weakly expanded in comparison to more proximal antennomeres. Only antennomeres 10 and 11 bear a finely pubescent apical surface (discernible in frontal view). Therefore, it was decided that the specimen possesses a weak 2-segmented antennal club.

Remark: The genitalia are not exposed, making definite sexual determination impossible.

Differential diagnosis. The new extinct species from Baltic amber can be easily distinguished from extinct Zopheridae from Paleogene ambers by the combination of subfamilial and tribal characters, but most obviously in 5-5-4 tarsal formula (in contrast to the 4-4-4 tarsal formula in all Colydiinae and Pycnomerus , or 4-5- 4 in Damzenia groehni Alekseev in Alekseev & Alekseev 2019).

In many respects, this new genus resembles the Baltic amber species Yantaroxenos colydioides Nabozhenko, Kirejtshuk et Merkl, 2016 , originally assigned to the tenebrionid tribe Belopini ( Nabozhenko et al. 2016) , but differs in having protruding, hemispherical eyes (eyes longitudinally oval in Yantaroxenos ), a different pronotal shape (strongly convex with protruding anterior half that covers the base of the head in Yantaroxenos ), shorter body length (8.2 mm in Yantaroxenos ), and 11-segmented antennae (antennae “with 10 visible antennomeres” in Yantaroxenos ).

Figures

FIGURES 1–2. Zopheromimus auriborussiensis sp. nov., holotype, No KAM 8325/2: 1—habitus, dorso-lateral view; 2— habitus, ventro-lateral view. Scale bar = 1 mm.

FIGURES 3–4. Zopheromimus auriborussiensis sp. nov., holotype, No KAM 8325/2, forebody, ventro-lateral view: 3— microphotograph; 4—schematic drawing. Abbreviations: A2—antennomere 2 (as long as antennomere 3); E—eye (lateral, hemispherical); PH—prothoracic hypomeron (not grooved); PC—procoxal cavity (externally closed); AP—abdominal procoxal process (triangular).

FIGURES 5–7. Representatives of the tribe Zopheromimini trib. nov. (microphotographs): 5—head of Zopheromimus auriborussiensis; 6—abdomen of Z. auriborussiensis; 7—abdomen of Yantaroxenos colydioides. Abbreviations: mem— membranes between non-connate ventrites; pag—preapical groove on abdominal ventrite 5.