Shell size to 100 mm; shell large, almost circular, compressed. Umbones at midpoint of hinge. Hinge teeth reduced under umbones. Sculpture of numerous low ribs. Margins of valves crenulated. Color white-gray, drab-gray, or tan, usually with rusty-brown markings. The periostracum is brown, velvety. The photo of the live bittersweet was taken in a research cruise in the NE Gulf of Mexico in 2021.