Austronausibius aenigmatista, Alekseev & Bukejs, 2022

Alekseev, Vitalii I. & Bukejs, Andris, 2022, Extant genus of flat bark beetle (Coleoptera: Silvanidae) with a present-day Australian-southern South American disjunction discovered in Eocene Rovno amber, Zootaxa 5129 (1), pp. 137-144 : 138-142

Austronausibius aenigmatista sp. nov.

( Figs. 1–2 )

Type material. Holotype: No. 6816 [ MAIG] (ex coll. Jonas Damzen No JDC-10169 R); “* Holotype / Austronausibius / aenigmatista sp. nov. / Alekseev et Bukejs des. 2021” [red handwritten label]; adult, possible female (genae not produced; metafemur as well as all tibiae simple, without secondary sexual characters, i.e., not curved and without tooth). A complete, well-preserved beetle is included in a transparent, yellow amber piece with approximate dimensions of 51× 14 mm and a maximum thickness of 14 mm; preserved without any supplementary fixation. The scutellar shield area, right side of the inclusion and several ventral portions of thorax are partially obscured by “milky” opacity. Syninclusions: stellate trichomes of Fagaceae and detrital particles.

Type stratum. Rovno amber, late Eocene ( Perkovsky et al. 2007) .

Type locality. Rivne Oblast (region), Ukraine .

Description. Body length (from apex of labrum to apex of elytra in preserved position) about 4.1 mm, maximum width (greatest width of combined elytra) 1.1 mm; head length (from apex of labrum to neck) 0.7 mm, head width (including eyes) 0.86 mm; pronotal length (along median line) 1.1 mm, pronotal maximum width (including denticles) 0.9 mm; elytral length 2.3 mm. Habitus elongate, nearly parallel-sided, weakly convex dorsally and ventrally; glabrous ( Fig. 1 ). Dorsum and appendages with fine, short, weakly curved, semi-erect pubescence ( Fig. 2A ). Body and appendages unicolored, rufous (as preserved).

Head slightly transverse (measured including eyes), slightly convex, with two symmetrical oval impressions above antennal insertions; finely punctate, punctures rounded, dense, each puncture about as large as an eye facet ( Figs. 1A , 2C ). Genae not expanded or raised. Frontoclypeal suture absent. Compound eyes relatively small and prominent, hemispherical, with coarse facets; without interfacetal setation; eyes widely separated, with distance between eyes about 5× transverse diameter of one eye. Temple short, length about 0.25× eye length ( Figs. 1A , 2B ). Antennal grooves beneath head absent. Maxillary palpi short; terminal palpomere elongate, spindle-shaped, truncate. Antenna short, extending to middle of pronotum, weakly flattened, gradually thickening toward apex; with 11 antennomeres, with rather distinct loose club composed of 3 antennomeres; sparsely covered with fine semi-erect setae; antennomere 1 subcylindrical, 1.5× as long as wide; antennomeres 2–5 equal in size, conical, slightly dilated apically, elongate, about 2.0× as long as wide, slightly shorter and narrower than antennomere 1; antennomeres 6–8 trapezoidal, nearly as long as wide; antennomeres 9–10 subequal in shape and size, transverse, about 1.6× as wide as long, with concave anterior margin, dilated apically; antennomere 11 rounded, as long as wide, without small process apically; relative length ratios of antennomeres 1–11 equal to 9-7-7-6-5-5-5-5-5-5-8.

Pronotum slightly elongate, 1.2× as long as wide, subparallel-sided; pronotal punctation rounded, fine (each puncture slightly smaller than compound eye facet), dense (distance between punctures about 0.5–1.0× diameter of one puncture); disc evenly convex ( Fig. 2C ). Anterior and posterior pronotal edges arcuate. Each pronotal side with six denticles ( Figs. 1A , 2B ): anterolateral denticle most prominent, denticle at posterior angle sharp, four lateral denticles equal in form, weak and obtuse.

Scutellar shield distinct, transverse, semicircular. Elytra elongate, 2.1× as long as wide combined, subparallelsided, slightly wider than pronotum, punctate-striate, with narrowly explanate lateral margins. Elytral punctation arranged in nine strial rows of larger, round, setiferous punctures ( Figs. 2A, 2C ); shortened scutellar row absent. Inner interstriae of elytra flat, covered with minute secondary punctation ( Fig. 2C ); interstria between striae 8 and 9 raised, forming shallow declivity ( Fig. 2B ). Humeral angles with distinct sharp denticle ( Fig. 1C ). Elytral setation fine, short, weakly curved, not arranged in herringbone pattern. Epipleura well-developed, reaching abdominal ventrite 3, widest at humeri, with three rows of weakly pronounced, rounded tubercles basally. Relative length ratios of prothorax to mesoventrite to metaventrite to abdomen equal to 6:2:3:10.5. Ventral surface of thorax densely punctate; prosternal process elongate, dilated apically. Metanepisternum narrow, long, with one row of punctures, 0.5× as wide as epipleuron at broadest point.

Legs short and robust ( Figs. 1B , 2B–C ). Procoxa nearly round, mesocoxa oval, metacoxa oval, not extending laterally to meet elytron. Trochanters apparently without spines. Femora widened medially, simple (without denticles or teeth), with deep, longitudinal groove for reception of tibia. Tibiae curved, dilated apically. Tarsomeres simple (not incrassate or lobed); tarsomere 5 longest, about as long as tarsomeres 1–3 combined. Pretarsal claws simple, equal in size, long.

Abdomen ( Figs. 2A–B ) with five visible, similarly articulated and punctate ventrites; ventrite 1 with femoral line closed, moderately produced posteriorly in from of almost right triangle; ventrite 5 rounded apically. Relative lengths (medially) of ventrites 1–5 equal to 2.5:2.0:1.5:1.2:1.8.

Note. The closeness of procoxal cavities (whether internally closed or narrowly open) and the form of intercoxal process of abdominal ventrite 1 in the studied specimen is unclear due to the position of the legs and the opaque amber layer in those regions.

Etymology. The specific epithet “ aenigmatista ” is used as noun in apposition and is derived from the Latin substantive meaning “enigmatist, one that proposes or speaks in riddles”.

Differential diagnosis. Austronausibius aenigmatista sp. nov. can be distinguished from extant congeners by a combination of characters: lateral pronotal sides with six obvious denticles (in contrast to one obvious denticle at anterior angle and other lateral denticles indicated by slight undulations in A. edentatus ), pronotal disc without a shallow depression and median ridge (in contrast to shallow pronotal impression and little-developed median ridge in A. aemulus ), metafemur without a denticle (in contrast to metafemur with a denticle in A. leai ), setal pattern without herringbone arrangement (in contrast to elytra with herringbone pattern of setae on 3rd or 5th and alternate interstriae in A. leai and A. congener ), pronotal disc evenly convex, not impressed (in contrast to pronotal disc with weak impressions in A. wagneri and other species), epipleuron with three rows of tubercles basally (in contrast to 4–5 in A. aridulus and 5–6 in A. neglectus ), and narrower metanepisternum, i.e., epipleuron widest point about twice as wide as adjacent region of metanepisternum (in contrast to wide metanepisternum in A. neglectus ). Additionally, the rounded form of antennomere 11 (without a small process apically) distinguishes A. aenigmatista sp. nov. from all extant congeners.

The new species resembles Mistran ot Alekseev et Bukejs, 2016 from Baltic amber but can be distinguished from it and all other extinct mid-late Eocene Silvanidae representatives using the identification key provided below.

Figures

FIGURE 1. Austronausibius aenigmatista sp. nov., holotype, 6816 [MAIG]: A—habitus, dorsal view; B—habitus, ventral view; C—details of left posterior pronotal and anterior elytral sides, black arrow indicates humeral denticle. Scale bars represent 1.0 mm (A, B) or 0.5 mm (C).

FIGURE 2. Austronausibius aenigmatista sp. nov., holotype, 6816 [MAIG], habitus: A—right lateral view; B—left lateral view; C—fronto-lateral view. Scale bars represent 1.0 mm.