Evolutionary Systematics of Two Co‐Occurring Paludomid Freshwater Gastropods in Thailand (Cerithioidea: Paludomidae)

Paludomidae is a diverse family of limnic gastropods in the Cerithioidea, with a distribution range including most of tropical sub‐Saharan Africa, the Nile Valley, Madagascar, the Seychelles, as well as South and Southeast Asia. Its systematics and taxonomy are currently in a state of confusion, with Thailand being inhabited by probably two distinct species, viz. Paludomus petrosa (Gould, 1843) and Paludomus siamensis Blanford, 1903. We examined available type material and used qualitative and quantitative shell characters in combination with multivariate ratio analysis (MRA), as well as molecular species delimitation approaches on the basis of mitochondrial and nuclear markers, that is, phylogenetic tree reconstructions, automated barcode gap discovery (ABGD) and the Bayesian variant of the general mixed Yule‐coalescent (bGMYC) approach, to test the validity of these two species. Our results confirm the presence of two morphologically distinct species in Thailand. Furthermore, we show that MRA allows us to translate the results of multivariate statistics into relations of body ratios that, along with qualitative characters, can be used to reliably identify these two species. The mitochondrial and nuclear sequence data, as a second line of evidence, corroborate our morphological findings. Paludomus petrosa and P. siamensis are re‐described, and regional distribution patterns of these species in Thailand are discussed, with a focus on the potential role of the Isthmus of Kra in separating these populations at an earlier stage.