Shell- round to somewhat oblong, greatly inflated, and thin in the young, to moderately thick in adults. The anterior and posterior ends of the shell are rounded. Umbros are greatly inflated, elevated, and turned inward. The beak sculpture has a few faint ridges, most are only visible in younger shells.
Young mussels have a small posterior wing.
Shell surfaces are usually very smooth and shiny. They are rayless, yellow, yellowish tan, or olive in color. They become darker in older individuals. Pseudocardinal teeth are thin, compressed, and elevated. They contain two in each valve.