Discovery of a New Helicarionoidean Land Snail Genus Siamopotaxis gen. nov. (Eupulmonata: Helicarionidae) from Thailand Based on Molecular Phylogenetic and Morphological Evidence

The new helicarionoidean land snail genus Siamopotaxis Pholyotha, gen. nov. is described for two new species, Siamopotaxis principalis Pholyotha, sp. nov. and Siamopotaxis thailandensis Pholyotha, sp. nov., both from Thailand. The new genus is characterised by a medium-sized, globose, high-spired, cream-coloured shell, with one or two supraperipheral bands, a rounded last whorl, a short epiphallic caecum, an elongated dart apparatus, and many radular teeth with pectiniform cusps. Siamopotaxis principalis sp. nov. differs from S. thailandensis sp. nov. by the presence of one spiral band, whereas the latter species has two spiral bands. A DNA sequence analysis of mitochondrial COI and 16S DNA, and nuclear 28S DNA gene fragments, supports the systematic placement of these new taxa and confirms that Siamopotaxis gen. nov. as a distinct clade within the Helicarionidae.