A systematic review of the snakes allied to Amphiesma pryeri (Boulenger) (Squamata: Golubridae) in the Ryukyu Archipelago, Japan

External characters, hemipenial morphology, karyotype, and reproductive mode were examined for the three subspecies of the endemic Ryukyu natricine, Amphiesma pryeri . Results revealed that populations of the Yaeyama Group, currently regarded as comprising a subspecies, A. p. ishigakiense , have several unique features such as the brownish ground colour of head, termination of sulcus spermaticus in the crotch between apical lobes of the hemipenis, terminal location of centromeres in the largest microchromosome pair, and the viviparous mode of reproduction. In the other populations, ground colour of head is black or dark greyish tan; sulcus spermaticus terminates near the tip of the left lobe of the hemipenis; the largest microchromosome pair is metacentric; and the reproductive mode is oviparous. Of these, however, the Miyakojima population, which currendy consists solely of the subspecies, A. p. concelarum , differs from the nominotypical subspecies from the central Ryukyus in having only 94–102 subcaudal scales and telocentric W chromosome; A. p. pryeri has 112–130 subcaudal scales and submetacentric W chromosomes. These strongly suggest that the two subspecies have also substantially diverged from each other, constituting distinct evolutionary lineages. We thus accord full-species status to each of pryeri, concelarum and ishigakiense , and revise their definitions on the basis of the present results. A dichotomous key to the Japanese species and subspecies of Amphiesma is provided.