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. There are about 38 known extant species of lampreys and five known extinct species. Lamprey is sometimes seen for the plural form. 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. The adult lamprey may be characterized by a toothed, funnel-like sucking mouth. Lampreys / ˈ l æ m p r eɪ z/ (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes / ˌ p ɛ t r oʊ m ɪ ˈ z ɒ n t ɪ f ɔːr m iː z/, placed in the superclass Cyclostomata. Sea lamprey, Petromyzon marinus Mouth of a sea lamprey, Petromyzon marinus Lateral cross-section of Lamprey demonstrating internal anatomy Microscopic cross section through the pharynx of a larva from an unknown lamprey species Petromyzontidae Risso, 1827 (Northern lampreys).
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