Freshwater MusselsUnionidaUnionida (freshwater mussels) is an order in the class Bivalvia, containing 899 described species.Scientific classificationRankTaxonDomainEukaryotaKingdomAnimaliaPhylumMolluscaClassBivalviaOrderUnionidaFamiliesUnionidae719Hyriidae76Mycetopodidae48Iridinidae37Margaritiferidae16Etheriidae3