A gastropod mollusc endemic to the western Mediterranean, it is considered the most endangered marine invertebrate in the basin. It lives firmly attached to rocks in the intertidal zone, feeding on the microscopic algae covering the substrate; adult specimens can exceed 8 cm in diameter.
Collection, even occasional, and trampling of the rocky shores frequented by bathers have drastically reduced the species along much of the Mediterranean coast. Sardinia retains some of the largest surviving populations. The species is protected under Annex IV of Habitats Directive 92/43/EEC: removing or damaging it is prohibited throughout the Marine Protected Area.