75 genera are assigned to the class HYDROZOA

OrderGenusFOPFOSLOPLOS
HYDROIDAArchaeoantennulariaDmDm
HYDROIDAArchaeocryptolariaCmmMidOm
HYDROIDAArchaeolafoeaCmuMid-mOCara-m
HYDROIDAArchaeonectrisOAshgSLdov
HYDROIDACályxhydraOLldeOLlde
HYDROIDACrucimedusinaCStepCStep
HYDROIDADiscophyllumOCara-mOCara-m
HYDROIDADrevoôellaCMosc-uCMosc-u
HYDROIDAEisenackiellaKSantKSant
HYDROIDAFlexihydraO?O?
HYDROIDAGelenptronCmmMid-uCmmMid-u
HYDROIDAHydractiniaTEo-lR 
HYDROIDAHydrallmaniaKMaes-uR 
HYDROIDAInocaulisOArenDGedi-l
HYDROIDAKristinellaK?K?
HYDROIDAKullingiaVuVN-Da
HYDROIDAMazohydraCMosc-uCMosc-u
HYDROIDAMesokylixJmJm
HYDROIDAPalaeacmeaCmTrepCmTrep
HYDROIDAPalaelophacmaeaOlKBarr-u
HYDROIDAPalaeokylixO?O?
HYDROIDAPalaeonectrisDGediDEmsi-l
HYDROIDAPalaeotubaOLlde-uOLlde-u
HYDROIDAParleriaKCenoKCeno
HYDROIDAPhilippinactiniaTOlTOl
HYDROIDAPlectodiscusSLudlTrCarn-u
HYDROIDAProtohaleciumCmmMidCmmMid
HYDROIDAProtulophilaJBajoTPlio
HYDROIDAPsammactiniaKMaes-lKMaes-l
HYDROIDARhabdohydraOLlviOAshg
HYDROIDASphenoeciumCmmMidCmmMid
HYDROIDAVeluíbrellaCmAtda-uCmmMid
LEMNISCATERINACassianastraeaTrLadi-uTrNori-l
MILLEPORINAAxoporaTEo-m-uTOl
MILLEPORINAAxoporellaTEoTEo
MILLEPORINADiamantoporaTEoTEo
MILLEPORINAHeterastridiumTrNori-uTrNori-u
MILLEPORINAMilleasterTMiQPlei
MILLEPORINAMilleporaTDaniR 
MILLEPORINAPalaeomilleporaJPlie-uJPlie-u
MILLEPORINASubaxoporaJuJu
SIPHONOPHORIDAParopsonemaCmuDFras-m
SIPHONOPHORIDAProtolyellaCmAtda-lCmm
SIPHONOPHORIDARotadiscusCmAtda-uCmmMid-l
SPHAERACTINIDACycloporidiumKCenoKCeno
SPHAERACTINIDAGlobostromaTOl-lTOl-l
SPHAERACTINIDAParkeriaKCeno-lKCeno-l
SPHAERACTINIDAParonariaKAptiKApti
SPHAERACTINIDAStromactiniaTruTru
STYLASTERINAAlloporaTOl-uR 
STYLASTERINAAstyaTDaniR 
STYLASTERINACongregoporaTDaniTDani
STYLASTERINAConoporaTDaniR 
STYLASTERINADistichoporaTEoR 
STYLASTERINAErrinaTDaniR 
STYLASTERINAincertae sedisKMaesKMaes
STYLASTERINAPliobothrusTDaniR 
STYLASTERINASporadoporaTDaniR 
STYLASTERINAStylasterTEoR 
TRACHYLINIDAAcalephaJTith-lJTith-l
TRACHYLINIDAAcsaspeditesJTith-lJTith-l
TRACHYLINIDAHydrocsaspedotaJTith-lJTith-l
uncertainDelheidiaTOlTOl
uncertainEoporpitaVuVu
uncertainGraptogeitoniaO?O?
uncertainJilluaTruTru
uncertainLikiniaCMosc-uPAsse
uncertainLovceniporaTruJ?
uncertainOvatoscutumVuVu
uncertainPlumalinaDGive-lDFras
uncertainRhizostromellaKCenoKCeno
uncertainRoseoporellaD?D?
uncertainStoliczkariaTruTru
uncertainStoliczkiellaKCenoKCeno
uncertainunknownVuVu

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FOP = Period of first occurrence
FOS = Stage of first occurrence
LOP = Period of last occurrence
LOS = Stage of last occurrence

Stage abbreviations follow Sepkoski (2002).