Hydnobius Schmidt, 1841:193.
Hydnobius: HATCH (1929): 6 (synonymy and references); VOGT (1961): 142 (diagnosis of the genus, key to Central and North European species); DAFFNER (1983): 27 (key to Palaearctic species); DOWNIE & ARNETT (1996): 329 (key to the Northeast American species); PECK & COOK (2009): 11 (diagnosis of the genus, key to North and Central American species).
See HATCH (1929) for complete synonymy and respective references, and VOGT (1961) and PECK & COOK (2009) for the diagnosis of the genus.
Type species: Anisotoma punctatum Sturm, 1807, designated by THOMSON (1859)
Diagnostic morphological characters in Hydnobius
The shape of the male metafemur is considered an important taxonomic character for the species-level taxonomy of Hydnobius (VOGT 1961, DAFFNER 1983). In contrast, male aedeagus of almost all species shares the similar triangular pyramid-shape, and usually does not show remarkable differences between related species although parameres are often used as a diagnostic character in identification keys. Moreover, the inner sac of the aedeagus usually does not have any distinct sclerites (for example, see the aedeagus of H. akitsuensis, Figs. 3A, 3B), and therefore, also, does not provide useful taxonomic characters. PECK & COOK (2009) found that mandibles, female abdominal sternite 8, female coxites, male metafemora, and the aedeagus are useful taxonomic characters at specific level. In this study, I examined two species of Hydnobius occurring in Japan and the North Chishima Islands, and confirm that especially the female abdominal sternite 8 shows morphological differences between these species.