Rhizotrogus ruzzantei, a new species from southwestern Sardinia (Italy), with biogeographic considerations on the Sulcis-Iglesiente subregion and Scarabaeoidea endemics of Sardinia (Coleoptera: Scarabaeidae: Melolonthinae: Rhizotrogini)

The taxonomic placement of Rhizotrogus genei Blanchard, 1851 (Scarabaeidae: Melolonthinae: Rhizotrogini) is critically reassessed, leading to its reclassification under the genus Rhizotrogus Latreille, 1825, rather than Geotrogus Guérin-Méneville, 1842. A new species of Rhizotrogini from southwestern Sardinia (Italy) is described and named Rhizotrogus ruzzantei Sabatinelli, Cillo & Bazzato, sp. nov. The morphology of both male and female specimens is illustrated and compared with that of the closely related R. genei. Rhizotrogus ruzzantei sp. nov. exhibits significant differences in tarsal length—particularly in the anterior tarsus—which are not associated with protibial dimensions, thereby supporting its taxonomic distinction. While R. genei is widespread across Sardinia, Capraia Island (Tuscany) and Corsica (France), R. ruzzantei sp. nov. is restricted to the Lower Sulcis region, between Villa San Pietro and Sant’Antioco, occurring sympatrically with R. genei. The discovery underlines the biogeographic significance of the Sulcis-Iglesiente as a hotspot of endemism, driven by its ancient geological isolation and ecological heterogeneity. This study also provides an updated overview of Sardinian endemic Scarabaeoidea and highlights the role of the Sulcis-Iglesiente subregion in the diversification of endemic lineages.