What is "pteriomorphia"

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

This subclass of mollusks has lamellibranch gills, and is epibenthic. Some attach to the substrate using a byssus. The foot is reduced. The mantle margins are not fused. Gills are usually large and assist in feeding. This group includes the well known mussels, scallops, pen shells, and oysters. It also includes the only members of the class bivalvia to have rudimentary eyes.