Knowledge of the following terms is important for understanding the freshwater mussel species accounts.
- Anterior end: the shorter end of the shell as measured from the umbo; also considered the front end
- Beak: the raised part of the dorsal margin of the shell; also called the umbo
- Beak cavity: the depression or pocket on the inside of each valve leading into the beak
- Beak sculpture: the raised loops, ridges, or bumps on the umbo
- Chevron: a V-shaped marking
- Compressed: flattened or pressed together laterally
- Concentric: having a common center
- Distal: away from the center or origin
- Dorsal: referring to the top part of the shell where the hinge is located
- Elliptical: having the form of an ellipse, or oval
- Elongate: long or extended
- Extirpated: locally extinct
- Growth lines: darkened lines on the surface of the shell indicating periods of rest during growth
- Hinge: the elastic part of the shell that unites the valves along the top of the shell
- Inflated: swollen or expanded
- Interdentum: a flattened area between the pseudocardinal and lateral teeth
- Iridescent: exhibiting rainbow colors
- Lateral teeth: the elongated teeth along the hinge line of the shell
- Left valve: the left half of the shell when the dorsal edge or hinge is facing up and the anterior end is directed forward (away from the collector)
- Nacre: the interior layer of the shell, usually white, pink, salmon, or purple and iridescent
- Oblong: having the shape of or resembling a rectangle or ellipse
- Ovate: egg-shaped
- Pallial line: a linear depression on the inside of the shell
- Periostracum: the outside layer or covering of the shell
- Plications: folds
- Posterior end: the longer end of the shell as measured from the umbo; also considered the back end; also the end with the siphons, usually sticking above the stream bottom
- Posterior ridge: the ridge on the back half of the valve running from the umbo to the posterior ventral edge
- Posterior slope: the area along the dorsal part of the shell between the posterior ridges of the valves
- Pseudocardinal teeth: the triangular, often serrated, teeth located on the anterior-dorsal part of the shell
- Pustule: a bump or raised knob on the outside surface of the shell
- Quadrate: square
- Right valve: the right half of the shell when the dorsal edge or hinge is facing up and the anterior end is directed forward (away from the collector)
- Serrated: notched or grooved
- Shell margin: the circumference of a valve outline when laid flat; also known as the edge
- Solid: thick or heavy
- Striated: marked with lines or grooves
- Sulcus: a shallow depression or furrow on the outside surface of the shell
- Truncate: having the end shortened or squared off
- Tubercle: a pointed, rounded, or knoblike projection on the shell
- Umbo: the inflated dorsal part of the shell; also called the beak
- Valve: one of the two halves of the shell
- Ventral: referring to the bottom edge of the shell