Carstenium, Alekseev & Bukejs, 2024

Alekseev, Vitalii & Bukejs, Andris, 2024, A new extinct genus of the tribe Hedobiini (Coleoptera: Ptinidae) from Baltic amber, Baltic Journal of Coleopterology 24 (2), pp. 223-230 : 224-225

Genus Carstenium gen. nov.

Type species: Carstenium kensbargense sp. nov., by present designation.

Differential diagnosis. Carstenium gen. nov. is characterized by the following combination of characters: (1) procoxae completely separated by prosternal process (in contrast to all extant genera of Eucradinae with contiguous or almost contiguous procoxae in Anhedobia , Clada , Eucrada , Hedobia , Neohedobia and Ptinomorphus ); (2) median longitudinal ridge in basal half of pronotum absent (in contrast to the representatives of Anhedobia , Eucrada , and Ptinomorphus ); (3) lateral pronotal carina absent (in contrast to Anhedobia ); (4) longitudinal costae on elytra absent and interspaces between arranged in rows punctures weakly convex only (in contrast to most species of Clada ); (5) antennae filiform with antennomeres not compressed (in contrast to the strongly serrate or pectinate antennae in Clada and Eucrada ); (6) antennae comparatively short, extending about to anterior one-fifth of elytra length (in contrast to majority of Eucradinae with antennae longer, extending to at least one-third of elytral lenght); (7) antennomeres 3–4 not equal in size and shape (in contrast to subequal, nearly spherical antennomeres 3–4 in Neohedobia ); (8) elytral punctation arranged in subregular striae (in contrast to completely irregular elytral punctation in Ptinomorphus ); and (9) pronotal disc weakly convex, without dorsal protuberance or elevation (in contrast e.g. to some species of Clada and Hedobia ).

Carstenium gen. nov. shows external similarity to extant West Palaearctic representatives of Hedobia ( H. olexai Zahradník, 2015 ; H. pubescens (Olivier, 1790) ; and H. unicolor Pic, 1897 ), but the new fossil genus differs in presence of prosternal process separating the prothoracic coxae, antennae filiform, maxillary palpomere 4 nearly securiform, tarsomere 5 long, dorsal pubescence sparse, and pronotum weakly convex in mediobasal part.

Within the known extinct Eucradinae , Carstenium gen. nov. is similar to Eucrada macleani (Abdullah et Abdullah) , with which it shares e.g. the longitudinally arranged elytral punctation and tribal characters 1–7 mentioned above in taxonomic assignment. However, the new genus can be distinguished by the shorter, non-serrate antennae and by the pronotum shape, which is “hood-like” in E. macleani according to the original description (Abdullah & Abdullah 1967). The interpretation of E. macleani and Carstenium gen. nov. (both found as inclusion in Baltic amber) as conspecific specimens belonging to the sexually dimorphic taxon is recognized as impossible. Original description of Eucrada macleani (Abdullah & Abdullah, 1967) states verbatim as follows: (1) eyes finely hairy (not as in Carstenium gen. nov.), (2) central portion of pronotal disc slightly elevated like a large tubercle (not as in Carstenium gen. nov.), (3) maxillary palp filiform, apical segment pointed at apex (not as in Carstenium gen. nov.), and (4) elytra coarsely, densely punctate (not as in the specimen under study).

Additionally, Carstenium gen. nov. can be distinguished from the Mesozoic genus Granulobium Li, Philips et Cai in having punctate head and pronotum (both densely granulate in Granulobium ), elytral punctation partially arranged in subregular striae (elytral punctation completely irregular in Granulobium ), equally long abdominal ventrites 2–4 (ventrite 4 relatively short in Granulobium ), larger body size (body length 5.1 mm in the new genus and about 2.0 mm long in Granulobium ) etc. However, Carstenium gen. nov. shares with Mesozoic Granulobium the prothorax unmodifed ventrally, and the procaxa separated by prosternal process.

Derivatio nominis. The new genus is named after Mr. Carsten Gröhn (Glinde, Germany), recognizing his support of this study. The gender is neutral.

Remarks. The new genus is monotypic. Therefore, the generic diagnosis is currently identical to that of the type species.