Juvenile with distinct sutures between plates. On rock exposed to strong wave action, with low profile and an oval aperture like Chthamalus stellatus. Distinguished by a wide rostral plate (1) [actually rostral plate fused with rostro-lateral plates], and carino-lateral plates tapering (2) towards the aperture. Carinal plate (3). Lateral plate (4). Lleyn Peninsula, Wales. September 2009.