Lampreys are a group of jawless fish composing the order Petromyzontiformes, sole order in the class Petromyzontida. The adult lamprey is characterized by a toothed, funnel-like, sucking mouth. The common name "lamprey" is probably derived from Latin lampetra, which may mean "stone licker", though the etymology is uncertain. "Lamprey" is sometimes seen for the plural form.