Genus Cyclina is recorded as one species in South Korea. In South Korea, it is recorded as Cyclina sinensis. However, inaturalsit records it as 3 types.

So I brought a few from Anmyeondo Island in Taean, South Chungcheong Province, South Korea. I should have filmed it while it was collected, but I couldn't record it. And when I boiled it to make the noodle soup, the black skin turned white. The color of the shell changes depending on various circumstances, such as heat and time. I don't know how to distinguish between the three types.