Numerous species of limpets are characteristic of the splash zone. These small, single-shelled gastropods have a conical, lopsided shell lacking the siphon hole characteristic of some limpets in the lower tidal zones. The limpets vary in size and shell texture from the very large and smooth owl limpet to the smaller rough limpet. The limpet is a nocturnal vegetarian that scrapes the food off of the substrate with a file-like device called a radula that is common to snails and their relatives.