Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be 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.There are about 38 known extant species of lampreys and five known extinct species. They are classified in three families: two species-poor families in the Southern Hemisphere and one speciose family in the Northern Hemisphere; phylogenetic studies indicate a mid-Mesozoic divergence for all three, underlying the separation of Laurasia and Gondwanaland. The occurrence of modern lampreys only since the Mesozoic (with significant genus & species radiations only...