The ground beetle genus Bembidion Latreille in Baltic amber: Review of preserved specimens and first 3D reconstruction of endophallic structures using X-ray microscopy (Coleoptera, Carabidae, Bembidiini).

The ground beetle genus Bembidion is a highly diverse group of small predators with more than 1.200 described extant species. In contrast, only two representatives of Bembidion are known from the amber fossil record and their position within this mega-diverse genus is dubious. Here, we address the taxonomic position of these two extinct Bembidion species (B. succini Giebel, 1856 and B. christelae Ortuño & Arillo, 2010). Based on the insufficient description and the missing type specimen, B. succini, nomen dubium, cannot be assigned to the genus Bembidion and/or to the tribe Bembidiini with certainty. The subgenus Archaeophilochthus Ortuño & Arillo, 2010 was erected for the second extinct species, B. christelae, based on external characters. However, this species seems indistinguishable to members of the earlier described subgenus Philochthemphanes Netolitzky, 1943 which comprises about extant 10 species distributed in East and Southeast Asia. Furthermore, we describe two new species, B. bukejsisp. n. and B. alekseevisp. n., from the Eocene Baltic amber using X-ray microscopy. Based on external and genital morphology including endophallic structures, we erected the monotypic subgenus Eodontium subgen. n. for B. bukejsisp. n., which is probably related to the subgenera Andrewesa Netolitzky, 1931, the Hydrium complex, or the Odontium series sensu Maddison (2012). On the other hand, B. alekseevisp. n. can be assigned to the subgenus Eupetedromus Netolitzky, 1911. The occurrence of representatives of at least two species groups adapted to a temperate climate suggests the presence of at least locally temperate climates in Baltic amber forests.