Ligaschonus, Alekseev & Pankowski & Bukejs, 2025

Alekseev, Vitalii, Pankowski, Madeline V. & Bukejs, Andris, 2025, A new bark-gnawing beetle (Coleoptera: Cleroidea: Trogossitidae) from Baltic amber, Zootaxa 5631 (2), pp. 380-386 : 381-382

Genus Ligaschonus gen. nov.

Type species: Ligaschonus succiniripae sp. nov., designated herein

Taxonomic assignment. The specimen examined shows a combination of characters corresponding to the subfamily Trogossitinae within the family Trogossitidae , namely: (1) elongate body, (2) asymmetrical antennal club with sensorial fields, (3) all pairs of legs with ultimate tarsomeres as long as all of the previous tarsomeres combined, (4) presence of bisetose empodium situated between simple tarsal claws, and (5) externally closed procoxal cavities.

Differential diagnosis. According to Kolibáč (2013), the tribe Trogossitini included 13 extant genera. However, a molecularly based phylogenetic study by Gimmel et al. (2019) proposed a merger of the tribe Gymnochilini with Trogossitini , resulting in eight genera being placed into Trogossitini that previously had been included in Gymnochilini . The specimen under study belongs to the tribe Trogossitini sensu Kolibáč (2013) based on the combination of the following characters: (1) eyes laterally situated, rather flat, only single pair of eyes present; (2) body surface without long hairs, scales or thick setae; (3) elytra without carinae, with regular rows of comparatively fine punctures ordered in striae; (4) pronotum without projected anteriad anterior angles; and (5) frontoclypeal suture absent. The combination of the above-mentioned five characters distinguishes the studied Baltic amber trogossitid beetle from ex-representatives of Gymnochilini , i.e., the genera Anacypta Illiger , Gymnocheilis Dejean , Kolibacia Leschen et Lackner , Leperina Erichson , Narcisa Pascoe , Phanodesta Reitter , Seidlitzella Jakobson , and Xenoglena Reitter.

Despite the apparent similarity, we conclude that the studied fossil cannot be attributed to any Trogossitini genera, and thus we propose a new genus for this fossil beetle. Ligaschonus gen. nov. clearly differs from Nemozoma Latreille and Temnoscheila Westwood in lacking conspicuous sharp longitudinal groove in frons; differs from Airora Reitter , Alindria Erichson , Corticotomus Sharp , Dupontiella Spinola , and Euschaefferia Leng in the pronotum narrowed at base and about as long as wide (not subparallel and elongate, not distinctly cordate) as well as the weakly convex and not cylindrical elytra; differs from Elestora Pascoe and Melambia Erichson in not possessing conspicuously carinate elytra; and differs from Eupycnus Sharp and Tenebroides Piller et Mitterpacher in the constricted-at-base pronotum (in contrast to subparallel or distinctly cordate pronotum of the mentioned genera) and the body including head and pronotum distinctly elongate. Ligaschonus gen. nov. bears some similiarity to the extant endemic genus of the Canary Islands, Leipaspis Wollaston (non-grooved frons, elongate body shape, posteriorly narrowed pronotum, and generally non-costate elytra), but differs based on its smaller body size (about 5 mm vs. 8.5–9.5 mm in Leipaspis ), tiny but distinct anterior pronotal angles (not extended in Leipaspis ), protibia with little spines along the outer edge (reduced in Leipaspis ), finer elytral punctation, developed metathoracic wings, and a small but distinct scutellar shield (in contrast to wingless Leipaspis having scutellar shield indistinct). The new genus shares the elytral structure with Temnoscheila Westwood , a heterogenous and especially diverse taxon in the New World with more than 100 described species ( Kolibáč 2013); however, Ligaschonus gen. nov. can be easily distinguished from Temnoscheila by the frons without longitudinal median groove, by the smaller body size (9.0–26.0 mm in Temnoscheila ), and by the form of eyes (flat, not exceeding contour of cranium in Temnoscheila ).

Ligaschonus gen. nov. represents the second known member of the tribe Trogossitini in Baltic amber. The first one, Seidlitzella hoffeinsorum Kolibáč et Alekseev, 2017 , originally described within Gymnochilini ( Kolibáč & Alekseev 2017), can be easily distinguished from the new taxon by the larger body size ( 9.7–10.5 mm long), the distinctly more flattened body, the carinate elytra with two rows of rounded punctures occurring between each pair of carinae, the projecting and acuminate anterior pronotal angles, and the protibia with four small spines along the outer side, etc.Additionally, Ligaschonus gen. nov. can be distinguished from the Cretaceous Microtrogossita qizhihaoi Li et Cai in Li et al. 2021, which has the general appearance of an aberrant Latridiidae , by the following characters: (1) presence of spines along outer margin of tibiae (absent in Microtrogossita ), (2) fine sculpture of dorsal and ventral surfaces (deeply punctate and sparsely setose in Microtrogossita ), (3) 11-segmented antennae (10-segmented in Microtrogossita ), (4) distinctly asymmetrical antennal club (weakly asymmetrical in Microtrogossita ), (5) antennal grooves present (absent in Microtrogossita ), (6) finely faceted eyes (coarsely faceted ones in Microtrogossita ), and (7) larger body size (in contrast to 1.93 mm of the Microtrogossita body length).

Etymology. The name of the new genus, ligaschonus, is derived from lygašonys (or ligusones), a caste of Prussian pagan priests that performed funeral rituals centuries ago “guaranteeing passage from this to the next world” ( Balsys 2016). The name evokes the amber’s role in carrying this beetle from its Eocene world to ours today. The gender is masculine.

Description. The new genus is monotypic. Therefore, the generic description considerably overlaps that of the type species.

Note on the presumed paleoecology of the fossil. Adults of most Trogossitini hunt for xylophagous insects (e.g., Curculionidae : Scolytinae; Bostrichidae ; and Ptinidae ) on branches and logs while larvae dwell and hunt beneath bark or in galleries of xylophagous insects like bark beetles ( Kolibáč 2013). Several ex-Gymnochiline genera are active species that fly, run, and even jump swiftly around fallen logs in forest clearings ( Kolibáč & Leschen 2010), whereas larvae and adults of cylindrical species live in galleries of small Scolytinae. For the fossil species, a similar biology, i.e., an active predatory lifestyle and dendrophilous mode of life, can be assumed. The comparatively narrow and elongate body shape suggests a probable association of the extinct bark-gnawing beetle with wood galleries of scolytine as well anobiine beetles and other wood-boring inhabitants.