Lamprey

Lampreys (sometimes inaccurately called lamprey eels) 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" (lambere "to lick" + petra "stone"), though the etymology is uncertain. "Lamprey" is sometimes seen for the plural form. About 38 extant species of lampreys are known, with around seven known extinct species. They are classified in three families—two small families in the Southern Hemisphere (Geotriidae, Mordaciidae) and one large family in the Northern Hemisphere (Petromyzontidae). Genetic evidence suggests that lampreys are more closely related to hagfish, the only other living group of jawless fish, than they are to jawed vertebrates, forming the superclass Cyclostomi. The oldest fossils of stem-group lampreys are from the latest Devonian, around 360 million years ago, with modern-looking forms only appearing during the Jurassic, around 163 million years ago, with the modern families likely splitting from each other sometime between the Middle Jurassic and the end of the Cretaceous. Modern lampreys spend the majority of their lives in the juvenile "ammocoete" stage, where they burrow into the sediment and filter feed. Adult carnivorous lampreys are the most well-known species, and feed by boring into the flesh of other fish (or in rare cases marine mammals) to consume flesh and/or blood; but only 18 species of lampreys engage in this predatory lifestyle (with Caspiomyzon suggested to feed on carrion rather than live prey). Of the 18 carnivorous species, nine migrate from salt water to fresh water to breed (some of them also have freshwater populations), and nine live exclusively in fresh water. All noncarnivorous forms are freshwater species. Adults of the noncarnivorous species do not feed; they...