abstract:Pteriomorphia is a subclass of saltwater clams, marine bivalve mollusks. It contains several major orders and suborders: the Arcoida, Ostreoida, Pectinoida, Limoida, Mytiloida, and Pterioida, and it also contains some extinct and probably basal families, such as the Evyanidae, Colpomyidae, Bakevelliidae, Cassianellidae and Lithiotidae.