Bacanius gorskii, Alekseev & Bukejs, 2021

Alekseev, Vitalii I. & Bukejs, Andris, 2021, A new Eocene Bacanius species (Histeridae: Dendrophilinae) from Baltic amber, Fossil Record 24 (1), pp. 93-99 : 94-97

Bacanius gorskii sp. nov.

urn:lsid:zoobank.org:act:16B458B1-640B-4AB0-86FC-F34B4E4AA2B8

Figs. 1–3

Type material

Holotype: no. 8619 [CAG], “ HOLOTYPE / Bacanius gorskii sp. nov. /des. Alekseev V.I. and Bukejs A. 2021”; adult, female. A complete beetle with partially exposed hind wings is included in a transparent, yellow amber piece with dimensions of 15 × 9 mm and maximum thickness of 1.5 mm and preserved without supplementary fixation. Syninclusions: few stellate Fagaceae trichomes.

Type stratum

A predominantly Bartonian age (41.3–37.9 Ma) is interpreted for the extinct central European resin-producing forests, which produced the amber that has eroded out of the Eocene blue earth layers ( Bukejs et al., 2019). However, the vast majority of Baltic amber derives from the geological amber-bearing strata that have been assigned a Priabonian age (37.8–33.9 Ma) ( Sadowski et al., 2017, 2020).

Type locality

Baltic Sea coast, Gdańsk, northern Poland.

Description

Measurements: body length 1.14 mm, body maximum width 0.83 mm; pronotum length 0.40 mm, pronotum maximum width 0.74 mm; elytra length 0.86 mm, elytra maximum width 0.83 mm.

Body widely oval, rather convex; integument unicolorous black (as preserved).

Head large, partially retracted into prothorax, apparently covered with fine punctation, epistoma without coarse punctures. Frontal stria distinct, complete, slightly arcuate inwardly to vertex. Mandibulae large, curved, apparently bifid. Eyes small, rounded, slightly convex. Antennae clavate, nine-segmented; short, about as long as protibial length, densely covered with minute punctation, with few short setae. Scape large, elongate oval; pedicel widely oval; antennomeres 3 and 8 slightly trapezoidal, oblong; antennomeres 4–7 subquadrate; antennal club without sutures, widely oval, with rounded apex, largest, about as long as antennomeres 3–8 combined, rather densely covered with long and erect setae.

Pronotum transverse, 1.85 times as wide as long, widest at base; punctation indistinct, very sparse and fine, with more distinct small punctures at posterior margin; lateral margins widely rounded, anterior and posterior margins convex. Antescutellar stria absent. Prohypomera impressed, sparsely covered with fine punctation. Prosternal lobe wide, convex, without distinct punctation. Suture between prosternal lobe and prosternal keel indistinct. Prosternal keel with concave base. Scutellum not visible.

Elytra nearly as wide as long, widest medially, completely covering abdomen, not truncate; basal margin concave, as wide as pronotal posterior margin; elytral punctation indistinct: disc apparently impunctate, with fine and sparse punctures conspicuous laterally; dorsal elytral striae absent; subhumeral stria incomplete, shortened and indistinct in apical one-third of elytron length; epipleural stria developed, sinuate.

Mesosventrite almost flat, narrow, about 2.8 times as wide as long, without distinct punctures. Meso-metaventral suture distinct, straight, without punctures. Metaventrite with flat, apparently impunctate disc; with coarse and dense punctation laterally, distance between punctures about 0.5–1.5 times the diameter of one puncture; postmesocoxal stria semicircular; posterior margin slightly convex.

Legs rather long. Femora flattened, slightly widened mesally. Tibiae nearly as long as femora. Protibiae flattened and strongly widened in apical portion, each with one widely triangular outer tooth and two thin apical spurs. Meso- and metatibiae narrower, slightly dilated apically, with two thin, apical spurs. All tarsi pentamerous, long, slender; relative length of metatarsomeres 1–5 equal to 10: 8: 8: 7: 15. Tarsal claws thin, free, simple.

Abdominal ventrite 1 largest, distinctly longer than ventrites 2–5 combined, with semicircular postmetacoxal stria; without distinct punctation; sutures between ventrites 1–4 strongly arcuate. Pygidium and propygidium visible in ventral view, without distinct punctation.

Differential diagnosis

The new species is assigned to the subfamily Dendrophilinae based on (1) the prosternum with short lobe, laterally incised to receive the antennae, (2) non-costate elytra, and (3) antennal cavities on prosternum weakly defined. Placement in the tribe Bacaniini is based on a combination of the following characters: (1) the bent short propygidium (visible only ventrally) and large pygidium, (2) general habitus (small size, with round and convex body), (3) elytral disc without dorsal striae, and (4) scutellum not visible.

The specimen under study differs from representatives of the genus Cyclobacanius Müller, 1925 in that the elytra are without a distinct elliptical area on the elytral disc margined by punctation, and the metaventrite is without longitudinal lines. It differs from representatives of the genus Abraeomorphus Reitter, 1886 in lacking semicircular femoral lines on the metaventrite and from the genus Australanius Gomy, 2009 based on the absence of discal striation. The shape of the prosternal lobe in the new fossil species is similar to representatives of the anophthalmic and Sardinian endemic genus Sardulus Patrizi, 1955 (Magrini, 2005; Magrini and Fancello, 2005; Magrini et al., 2012; Magrini and Onnis, 2019); however, Bacanius gorskii sp. nov. differs from Sardulus based on the presence of eyes and elytral suhumeral stria. The new species from Baltic amber lacks an arcuate antescutellar stria on the pronotal base, in contrast to representatives of the subgenus Muellerister Cooman, 1936 (of the genus Bacanius ); of the genus Neobacanius Müller, 1925 ; or of several representatives of Abraeomorphus . The subgenus Gomyister Mazur, 1984 (genus Bacanius ) is characterized by

Derivatio nominis

Patronymic, this new species is named in honour of Andrzej Górski (Bielsko-Biała, Poland), collector of this amber piece.

Remarks

Sex of the examined specimen determined was based on micro-CT results. We were unable to identify any sclerotized structure resembling an aedeagus in the abdominal cavity, and therefore we presume the specimen in question is a female.

the presence of a complete subhumeral stria ( Mazur, 1984; Mazur and Sawoniewicz, 2008), but the new fossil species has an incomplete subhumeral stria. Based on the previously mentioned combination of characters, we tentatively place Bacanius gorskii sp. nov. in the nominative subgenus.

Bacanius (s.str.) gorskii sp. nov. differs from the Eocene Bacanius kirejtshuki Sokolov and Perkovsky, 2020 described from Rovno amber in that it possesses a straight, impunctate, finely impressed meso-metaventral suture (differing from the convex, coarsely punctate meso-metaventral suture of B. kirejtshuki ); an apically reduced subhumeral stria (complete in B. kirejtshuki ); and an impunctate prosternal lobe (sparsely punctate in B. kirejtshuki ). The new species can be easily distinguished from the other two known histerid beetles in Baltic amber, Carcinops donelaitisi Alekseev, 2016 and Xestipyge ikanti Alekseev, 2016 , based upon its convex and rounded body shape, absence of dorsal elytral striae, and distinctly smaller body size.

Figures

Figure 1. Photomicrographs of Bacanius gorskii sp. nov., holotype, 8619 (CAG): (a) habitus, ventral view; (b) habitus, dorsal view; (c) details of forebody, ventral view; (d) left antenna. Scale bars: 0.25 mm for (a)–(c); 0.1mm for (d).

Figure 2. X-ray micro-CT renderings of Bacanius gorskii sp. nov., holotype, 8619 (CAG), habitus: (a) dorsal view; (b) ventral view; (c) right lateral view. Scale bar = 0.25mm. Abbreviations: h – head; m – mandibula; msv – mesoventrite; mtv – metaventrite; pk – prosternal keel; pl – prosternal lobe; py – pygidium; s – meso-metaventral suture; shs – subhumeral stria; v1 – abdominal ventrite 1.

Figure 3. Bacanius gorskii sp. nov., outline drawing of habitus, ventral view. Scale bar = 0.25 mm.