Description: Diodora variegata (Sowerby II, 1862) - exterior view of a variegated keyhole limpet shell, 1.45 cm long. Anterior to the top and posterior to the bottom. Family Fissurellidae - limpets use their radulae to scrape algae from hard substrates. They typically occupy rock intertidal shorelines. Date: 25 February 2011, 18:04. Source: Diodora variegata (variegated keyhole limpet) (San Salvador Island, Bahamas) 1. Author: James St. John.