"An atoll (/\u02C8\u00E6t\u0252l/, /\u02C8\u00E6t\u0254\u02D0l/, /\u02C8\u00E6to\u028Al/, /\u0259\u02C8t\u0252l/, /\u0259\u02C8t\u0254\u02D0l/ or /\u0259\u02C8to\u028Al/), sometimes called a coral atoll, is a ring-shaped coral reef including a coral rim that encircles a lagoon partially or completely. There may be coral islands/cays on the rim. The coral of the atoll often sits atop the rim of an extinct seamount or volcano which has eroded or subsided partially beneath the water."@en . . . .