Cryptic diversity in a widespread land snail: revision of the genus Xanthomelon Martens, 1860 from the Australian Monsoon Tropics (Pulmonata, Camaenidae)

Abstract

The camaenid genus Xanthomelon is widely distributed throughout the Australian Monsoon Tropics and eastern Queensland, with nine species currently being recognised in Australia based exclusively on shell features. Due to the combination of poor taxonomic descriptions and considerable variation in shell characters, considerable confusion surrounds the number of species in the Northern Territory (NT), their key characteristics and distributions. To uncover the full taxonomic diversity of Xanthomelon in the NT, we employed molecular phylogenetics and comparative studies of morphology/anatomy. Based on the patterns of mitochondrial differentiation as well as comparative shell and penial anatomy, we demonstrate that previous studies failed to correctly delineate species. We recognise five species in the NT, of which two (X. darwinense n. sp. and X. arnhemense n. sp.) are newly described. These species have distributions that range from narrowly endemic to most widely distributed throughout most of the Australian Monsoon Tropics. The ranges of multiple species overlap extensively with each other, which is a rather unusual phenomenon amongst the Australian Camaenidae.