Class Bivalvia Linnaeus, 1758 - bivalves Subclass Autobranchia Grobben, 1894 Superorder Heteroconchia Gray, 1854 Clade Palaeoheterodonta Newell, 1965 Order Unionida Gray, 1854 Superfamily †Trigonioidoidea Cox, 1952 Family †Trigonioididae Cox, 1952 Subfamily †Martinsonellinae Sha, 1993