mussel morphologyFreshwater mussels have three basic characteristics which distinguish them from other animals; these include 1) a two-valved shell, 2) a soft body, and 3) a muscular foot.   The "soft" parts consist of respiratory organs, digestive organs, and other vital parts.  The foot, often seen extended from between the two valves, aids the mussel in locomotion, burrowing, and positioning in the river bottom.

The mussel"s shell contains several diagnostic characteristics which are helpful in separating the species.  The shiny layer seen from inside the shell is called the nacre or "mother of pearl."  The nacre may be white, purple, pink, or pale orange.  The outer layer is made of protein and serves to protect the shell.   Shells come in a variety of shapes, including round, elongate, oval, or tear-drop shaped.  The beak is the oldest part of the shell, and the end closest to the beak is the anterior or front.  The outer surface may be smooth or have humps, ridges, depressions, furrows, and wings.  The outer surface may also be shiny, dull or brightly colored with rays or plain.