Yantaroxenos Nabozhenko, Kirejtshuk et Merkl, 2016

Alekseev, Vitalii I. & Nabozhenko, Maxim V., 2023, News from Baltic amber: a new tribe of extinct Paleogene ironclad beetles (Coleoptera: Zopheridae: Zopherinae), Zootaxa 5297 (3), pp. 435-445 : 442

Genus Yantaroxenos Nabozhenko, Kirejtshuk et Merkl, 2016

Type species: Yantaroxenos colydioides Nabozhenko, Kirejtshuk et Merkl, 2016

Comment: The extinct monotypic genus Yantaroxenos Nabozhenko, Kirejtshuk et Merkl, 2016 was originally described from Baltic amber as a presumed representative of the tribe Belopini ( Tenebrionidae : Lagriinae ). The holotype was studied by optical microscopy. Since some important characters were not observed, the original description states: “parts of the integument of the specimen with milky cover,” “mesoventrite, meso- and metepisterna and metepimera not visible,” and “ Yantaroxenos has unclear combination of tribal characters because diagnostic structures of the head are poorly visible” ( Nabozhenko et al. 2016).

The familial placement of Yantaroxenos (with two logical alternatives, Zopheridae or Tenebrionidae ) was initially the cause of much concern during the study of Nabozhenko et al. (2016). Finally, placement in the tribe Belopini was considered the most appropriate for this extinct Baltic amber beetle. One important character of Yantaroxenos , however, was regrettably misinterpreted: In reality, all abdominal ventrites in Yantaroxenos are unfused and apparently connected by narrow membranes ( Fig. 7 ), as is the case for Zopheromimus auriborussiensis sp. nov. ( Fig. 5 ). Darkling beetles have connate abdominal ventrites 1 and 2. Ventrites 3–5 can be hinged in the middle or laterally, and membranes between ventrites 3–5 are visible in almost all representatives of tenebrionoid branch having defensive glands ( Matthews & Bouchard 2008, Matthews et al. 2010). By lacking any connate ventrites, Yantaroxenos should be excluded from the family Tenebrionidae .

The new species Zopheromimus auriborussiensis sp. nov. allowed examination of the ventral side of the thorax and head in this group of beetles. Our findings supported the assignment of Zopheromimus gen. nov. to the new tribe within the subfamily Zopherinae . Yantaroxenos colydioides shares with Zopheromimus auriborussiensis sp. nov. all of the external characters that are interpreted here to have tribal-level significance (including the paired preapical grooves on abdominal ventrite 5, which was not mentioned in original description, but is present, see Fig. 7 ). The main differences between these two genera are in the pronotal shape and number of antennomeres. The features described above led us to conclude that the extinct genus Yantaroxenos should be transferred from the tribe Belopini ( Tenebrionidae : Lagriinae ) to Zopheromimini trib. nov. ( Zopheridae : Zopherinae ).

Figures

FIGURES 5–7. Representatives of the tribe Zopheromimini trib. nov. (microphotographs): 5—head of Zopheromimus auriborussiensis; 6—abdomen of Z. auriborussiensis; 7—abdomen of Yantaroxenos colydioides. Abbreviations: mem— membranes between non-connate ventrites; pag—preapical groove on abdominal ventrite 5.