Class Bivalvia Linnaeus, 1758 - bivalves Subclass Autobranchia Grobben, 1894 Superorder Heteroconchia Gray, 1854 Clade Palaeoheterodonta Newell, 1965 Order Unionida Gray, 1854 Superfamily Unionoidea Rafinesque, 1820 Family Unionidae Rafinesque, 1820 - pearly mussels Subfamily Modellnaiinae Brandt, 1974