Amygdalum papyrium is a member of the family Mytilidae. The fragile shell of the Atlantic paper mussel is white with a glistening, smooth periostracum (thin organic layer covering the outer layer of the shell) that is bluish green to yellow in color. The shell is elongate, compressed, and wider at the posterior end. Umbones are present near, but not at, the anterior end. The interior of the shell is iridescent white with smooth margins (Mikkelsen and Bieler 2008). A. papyrium attaches to the substratum as well as to each other with byssal threads often forming dense beds that support rich faunal and infaunal invertebrate assemblages.