The first record of a cupped oyster species Crassostrea dianbaiensis in the waters of Japan

With a combination of our mitochondrial and nuclear DNA data, we evidenced the occurrence of a Crassostrea oyster hitherto unrecognized in Japan. This species, C. dianbaiensis (named Sumizome-gaki in Japanese), was very recently described as a new tropical oyster, although we located it in a temperate water zone (southwestern coast of Shikoku Island, Japan). Our specimens bore a morphological resemblance to the slipper cupped oyster C. bilineata (syn. C. iredalei), consistent with their close phylogenetic relationship. Some of the shell characteristics represented in the original species description were not applicable to our specimens, especially in terms of the pattern of their inner-shell coloration. Our novel finding of C. dianbaiensis in Japan updated the taxon list of Japanese Crassostrea species.