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Spinicaudatan clam shrimps are small and bivalved branchiopod crustaceans,which reached twice the acme of evolution and radiation during the late Palaeozoic and Mesozoic.They nowadays remain only 16 genera in three families (Zhang et al.,1976;Brtek,1997).It is believed for a long time that there is a discontinuity between fossil and living clam shrimps because of lacking of Cenozoic fossil record (Kobayashi,1972).