Phylum [Mollusca] Linnaeus, 1758 - molluscs Class Bivalvia Linnaeus, 1758 - bivalves Subclass Palaeoheterodonta Newell, 1965 see Clade Palaeoheterodonta Newell, 1965 1 Order †Modiomorphoida 2 Order Unionoida see Order Unionida Gray, 1854 3 Order Trigonioida see Order Trigoniida Dall, 1889