Phylum Mollusca Linnaeus, 1758 - molluscs Class Bivalvia Linnaeus, 1758 - bivalves Subclass Palaeoheterodonta Newell, 1965 see Clade Palaeoheterodonta Newell, 1965 1 Order Trigonida orth. inval. [monotypic] 2 Order Unionida Gray, 1854