Petromyzontidae
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Petromyzontidae are a family of lampreys native to the Northern Hemisphere, comprising the vast majority of living lampreys.<ref name="McEachran Fechhelm 1998">Template:Cite book</ref> Petromyzontids have the highest number of chromosomes (164–174) among vertebrates.<ref>{{#invoke:Cite taxon|main|fishbase|genus=|species=|subspecies=}}</ref>