Principles of systematics and the system of bivalves

The systems of the class Bivalvia accepted in recent manuals are discussed. The system proposed by L.A. Nevesskaja, O.A. Skarlato, Ya.I. Starobogatov, and A.G. Eberzin (1971) is substantiated and updated. Morphological characters important for the establishment of taxa of different ranks are listed. Three superorders and 17 orders are established; two orders, which are restricted to the Cambrian and the beginning of the Ordovician, are placed outside the accepted superorders.