Snorkel snails (genus Rhiostoma) are widely distributed in Indo-China and on the Malay Peninsula. The shell morphology is traditionally used for species identification yet in Thailand, the common snorkel snail, Rhiostoma housei, shows considerable variation in shell morphology within and between populations. Therefore species identifications and delimitations are difficult. We used two mitochondrial DNA fragments (COI and 16S rRNA) and morphological characters to delimit species and infer phylogenetic relationships of Rhiostoma housei s.l. from eight localities in Thailand, representing potential cryptic species suggested by earlier allozyme and karyological data. Results revealed four distinct clades from different geographic areas in Thailand. Species delimitation analyses confirmed the clades as four separate species and a geometric morphometric analysis demonstrated subtle but consistent conchological differences between the four clades. The high COI sequence divergences among the four clades (mean: 14.8%; range: 10.3–16.5%) further supported the species level recognition. As a consequence, three new species are described from Thailand: R. khoratense, sp. nov., R. nakwangense, sp. nov. and R. phunangense, sp. nov.

ZooBank: urn:lsid:zoobank.org:pub:EE534749-9346-4972-BF2E-3B5D0EB8AED8