Cestodes are parasites of vertebrates, with each species infecting a single definitive host or group of closely related host species. All but amphilinids and ...CestodaFromWikipedia,thefreeencyclopediaJumptonavigationJumptosearchClassofflatwormsCestodaTemporalrange:270–0 Ma[1]PreꞒꞒOSDCPTJKPgNTaeniasaginataScientificclassificationKingdom:AnimaliaPhylum:PlatyhelminthesClass:CestodaSubgroupsSeetext.Cestodaisaclassofparasiticwormsintheflatwormphylum(Platyhelminthes).Mostofthespecies—andthebest-known—arethoseinthesubclassEucestoda;theyareribbon-likewormsasadults,knownastapeworms.Theirbodiesconsistofmanysimilarunitsknownasproglottids-essentiallypackagesofeggswhichareregularlyshedintotheenvironmenttoinfectotherorganisms.Speciesoftheothersubclass,Cestodaria,aremainlyfishparasites.Allcestodesareparasitic;manyhavecomplexlifehistories,includingastageinadefinitive(main)hostinwhichtheadultsgrowandreproduce,oftenforyears,andoneortwointermediatestagesinwhichthelarvaedevelopinotherhosts.Typicallytheadultsliveinthedigestivetractsofvertebrates,whilethelarvaeoftenliveinthebodiesofotheranimals,eithervertebratesorinvertebrates.Forexample,Diphyllobothriumhasatleasttwointermediatehosts,acrustaceanandthenoneormorefreshwaterfish;itsdefinitivehostisamammal.Somecestodesarehost-specific,whileothersareparasitesofawidevarietyofhosts.Somesixthousandspecieshavebeendescribed;probablyallvertebratescanhostatleastonespecies.Theadulttapewormhasascolex(head),ashortneck,andastrobila(segmentedbody)formedofproglottids.Tapewormsanchorthemselvestotheinsideoftheintestineoftheirhostusingtheirscolex,whichtypicallyhashooks,suckers,orboth.Theyhavenomouth,butabsorbnutrientsdirectlyfromthehost'sgut.Theneckcontinuallyproducesproglottids,eachonecontainingareproductivetract;matureproglottidsarefullofeggs,andfallofftoleavethehost,eitherpassivelyinthefecesoractivelymoving.Alltapewormsarehermaphrodites,witheachindividualhavingbothmaleandfemalereproductiveorgans.Humansaresubjecttoinfectionbyseveralspeciesoftapewormsifthey