Limpet

This is the underside of a live, freshly gathered, common limpet (Patella Vulgata) of the Pembrokeshire coast. It is a monovalve and one of the most common shellfish in the world. A quintessential "poor people food," it is every bit as edible and nutritious as a clam, but less tender. A certain expert cook I know devised a reliable recipe wherein the limpets are steamed for four minutes, the sacs removed and tossed to eager cats, and the bodies ground and made into patties with a few other flavorful ingredients.