Class Bivalvia Linnaeus, 1758 - bivalves Subclass Autobranchia Grobben, 1894 Superorder Heteroconchia Gray, 1854 Clade Palaeoheterodonta Newell, 1965 Order Unionida Gray, 1854 Superfamily Hyrioidea Swainson, 1840 [monotypic] Family Hyriidae Swainson, 1840 1 Subfamily Hyriinae Swainson, 1840 2 Subfamily Velesunioninae Iredale, 1934