mcgraw-hill encyclopedia of science & technology, 10th edition, volume 13 (par-plan)

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1、PPParablastoidea—Plantsofsalineenvironmentsternalfolds(cataspires)toporesthatopenbetweenParablastoideathesingleambulacralplatesattheedgeofeacham-Asmallextinctclassofrelativelyadvancedblas-bulacrum;presumablytheywererespiratoryorgans.tozoanechinodermscontainingfivegenera(threeShort-to-longbiserialbra

2、chioleswereattachedtothenamed),rangingfromthemiddleEarlyOrdovicianedgesofthefiveambulacraandservedasthemaintotheearlyLateOrdovicianineasternCanada;food-gatheringstructures;whennotfeeding,thebra-northeastern,eastern,south-central,andwesternchiolesfoldedintolieagainstahighT-shapedambu-UnitedStates;sou

3、thandnorthWales;andnearSt.lacralcrestinthecenterofeachambulacruminthePetersburg,westernRussia.Parablastoidshaveabud-best-knowngenus.Astemwithone-piececolumnalsshapedthecaorbodywithwell-developedpentam-attachedthethecatotheseafloor,suggestingthateralsymmetry.Thecalplatesincludebasals,smallorparablast

4、oidswereattached,medium-tohigh-level,largeradials,andsometimesothersmallplatesinthesuspensionfeeders.Someparablastoidsarefoundinlowertheca;largedistinctivetriangular-to-parabolicbankorreefdeposits,suggestingtheymayhavebeendeltoidsbetweentheambulacraintheupperthecaadaptedforrough-waterconditions.Alt

5、houghthey(seeillustration);andsmalloralplatesandanoralconvergedonblastoidsinthecaldesignandwayofcrestsurroundingandcoveringthemouthonthelife,parablastoidshaddifferencesintheirplating,summit.Parablastoidshavesingleormultipleslitsambulacra,andrespiratorystructuresthatindicatethroughthelowerdeltoidsth

6、atareconnectedbyin-aseparateoriginandevolutionaryhistory.Thisjus-tifiesassigningparablastoidsandblastoidstodiffer-entblastozoanclasses.SeeBLASTOIDEA;ECHINODER-MATA;ORDOVICIAN.JamesSprinkleBibliography.R.O.Fay,Parablastoids,pp.S293–brachiolesS296inR.C.Moore(ed.),TreatiseonInverte-bratePaleontology,Pa

7、rtS:Echinodermata1(1),GeologicalSocietyofAmerica,Boulder,andUni-versityofKansas,Lawrence,1968;C.R.C.Paul,Thephylogenyofthecystoids,pp.199–213inC.R.C.PaulandA.B.Smith(eds.),EchinodermPhy-logenyandEvolutionar