A Krabi, Thailand, showing O. intermedia at the overhang of an intertidal cave (indicated by white arrow). B Hey or Coral Island, Phuket, showing that O. intermedia occur on shaded rocks. C O. intermedia can occupy up to 100% cover under a shaded rock in Thailand. D Octomeris intermedia, showing partially eroded samples, with longitudinal furrows at the base of the shell plates. E O. intermedia, eroded samples, showing shell with a smooth surface. F O. intermedia, uneroded samples, showing longitudinal furrows on the surface. G O. brunnea on Lanyu, Taiwan. Shell is more conical than O. intermedia. Eroded sample with smooth shell plates.