Integrative taxonomy of insular land snails of the genus Sicradiscus Páll-Gergely, 2013 (Gastropoda, Plectopylidae) with description of a new species

Many land snail taxa have undergone speciation in the Ryukyu Islands and Taiwan in East Asia. We examined the shell, radular, and genital morphology, and mitochondrial phylogeny of two described Sicradiscus species distributed in Miyako Island and Taiwan, and the newly discovered Sicradiscus pallgergelyi sp. nov. from Iriomote Island. Canonical variate analysis based on adult shell measurements indicated that S. pallgergelyi sp. nov. and the Taiwanese Sicradiscus ishizakii had more similar shell measurements, whereas S. pallgergelyi sp. nov. shared common characteristics of shell sculpture with the Japanese Sicradiscus hirasei. The leave-one-out cross-validation results correctly classified 100%, 71.4%, and 88.0% of S. hirasei, S. ishizakii, and S. pallgergelyi sp. nov., respectively. The radular and genital morphology was similar in these three species. Moreover, molecular phylogenetic analyses showed monophyly of the three species, although the Japanese lineages were more closely related to each other than to the Taiwanese species. Accordingly, the characteristics of shell sculpture are common traits of the two Japanese species, and these findings indicate that shell morphology has significantly diverged in Japan. The different apertural callus lengths among the three species may be an adaptation to predators, and shell flatness may reflect interspecific differences in microhabitats.