Baltistena concava, Batelka & Rosová & Prokop, 2023

Batelka, Jan, Rosová, Kateřina & Prokop, Jakub, 2023, Diversity and morphology of Eocene and Oligocene Mordellidae (Coleoptera), Acta Entomologica Musei Nationalis Pragae 63 (2), pp. 451-478 : 468-469

Baltistena concava sp. nov.

( Figs 8A–F , 10D )

Type material. HOLOTYPE: PřfUK93, obtained from Jonas Damzen (original number JDC9819 ): Baltic amber.

Description. Head subglobular, frons continuously convex, posterior edge of eye near posterior margin of head, elytra convex, metacoxa broad, comb formula 6//4/3/2/0, pygidium long. Main characters: Right antenna well visible, length ratios of antennomeres as follows: 2-1.6-1-1.25- 5.8-6.25-5.8-5.8-5.8-5.8-7.5, basal antennomere robust, flagellomeres cylindrical and slightly wider apically, antennomeres V–X about 2.7× as long as wide, antennomere XI 3.75× as long as wide. Structure of maxillary palpi not discernible. Eyes with small facets. Interfacetal setae present. Form of scutellum not observable. Form of basal side of pronotum not observable. Elytra 3.0× as long as pronotal disc. Protarsomere IV deeply dilated. Structure of protibia indiscernible. Mesotarsomere IV deeply dilated. Mesotibia 1.1× as long as mesotarsus. Right metatibia with six combs, left metatibia with one additional rudimentary cluster of dark scale-like setae on the most proximal position visible. Two subequal tibial spurs on metatibia present, outer one half as long as inner one. Metatarsomere I with four short transverse combs, metatarsomere II with three short combs, metatarsomere III with two longer and more oblique combs and metatarsomere IV without combs. Pygidium 2.4× as long as hypopygium. Anterior edge of metanepisternum 2.15× as long as posterior edge, ventral edge 4.15× as long as posterior edge. Metakatepisternum fully developed; suture between metakatepisternum and metaventrite slightly concave, middle of metacoxal margin distinctly concave. Pretarsal claws long with few short and widely spaced teeth. Tip of pygidium with ring of few, long, distinct, black scale-like setae.

Lengths (in mm): pronotal disc = 1.0, elytra = 2.9, mesotibia = 1.0, metatarsomere I = 0.6, pygidium = 1.8.

Etymology. The species name refers to the concave shape of the frontal edge of the metacoxa; adjective.

Differential diagnosis. This peculiar beetle is characterized by short antennomeres I–IV and extremely prolonged cylindrical antennomeres V–XI, concave anterior metacoxal margin, and dilated pro- and mesotarsomeres IV. It is difficult to determine its generic affinities. In terms of the shape of its antennae and penultimate pro- and mesotarsomere it resembles Mordellistena virginica Steury & Steiner, 2020 from the USA, which, however, differs in almost straight anterior metacoxal margin ( STEURY & STEINER 2020: fig. 7C). The inclusion of M. virginica in Mordellistena is contrary to the definition of this genus, because ERMISCH (1950a) put Mordellistena into the Mordellistenini group of genera with pro- and mesotarsomeres apically truncate, which is not the case in M. virginica . Thus, the generic placement of M. virginica must be reconsidered, but this is outside the scope of this contribution.

The antenna is also similar to that depicted for Mordellistena erythroderes Hill, 1922 from Queensland, Australia ( HILL 1922), but the poor description of this Australian species prevents further comparison and verification of its generic placement.

Another taxon sharing the same antennal structure and shape of penultimate pro- and mesotarsomeres with B. concava sp. nov. is the genus Pulchrimorda Ermisch, 1968 from Southeast Asia, notably P. tamdaoensis Horák & Farkač, 2017 and P. fusca Horák & Farkač, 2017 ( HORÁK & FARKAĆ 2017). The male antennae in both species are almost identical with those of B. concava sp. nov., but in species of Pulchrimorda the eyes are glabrous, while in B. concava sp. nov. interfacetal setae are present.

Figures

Figs 8. A–F – Mordellistenini, Baltic amber, Baltistena concava sp. nov., holotype, PřFUK93:A, B – habitus; C – eye; D – head with antenna and thorax; E – hypopygium; F – protarsomeres IV and V and serrate pretarsal claws. Scale bars: A, B – 0.8 mm; C, E – 0.2 mm; D – 0.3 mm; F – 0.1 mm.

Figs 10. A–F – Metakatepisternum: A – Baltimorda, undescribed species A, PřfUK71. B – Palaeostena eocenica (Kubisz, 2003), PřfUK107. C – Baltistena hoffeinsorum sp. nov., holotype, PřFUK92. D – Baltistena concava sp. nov., holotype, PřFUK93. E – Baltistena brevispina sp. nov., holotype, PřFUK95. F – Baltistena atronigra sp. nov., holotype, PřFUK108. Scale bars: 0.2 mm.