Systematic revision of the snorkel snail genus Benson, 1860 (Gastropoda, Caenogastropoda, Cyclophoridae) with descriptions of new species.

The snorkel snail genus Benson, 1860 is comprised of terrestrial cyclophorid snails with wide-ranging species diversity and radiation in Southeast Asia. The typical characters of the genus are a depressed shell, a detached and descending portion of the last whorl with a distinctive peristomal breathing device attached, and a calcareous cup-shaped operculum. Herein, we have revised the systematics of extant species based on shell morphology combined with COI barcoding. From these thirty recognised species, twelve are described as new to science: R. ? amarapuraense, , , , , , , , , , , , and All conchological characters are provided via illustrations of type specimens and living snails, and descriptions of the shells and radulae. Phylogenetic analysis based on partial COI gene sequences strongly supports the designated morphospecies and a monophyletic , confirming that all pterocyclinid snails with a calcareous, cup-shaped operculum belong to the same clade. A high intra-specific divergence was observed in and populations from locations in close proximity, suggesting a lower dispersal and higher level of isolation. The low inter-specific divergence found in , , , and supports their recent diversification and local adaptation, and is congruent with their marked morphological differences. Finally, nine formerly -placed species were reclassified into either the genus or the genus .