Shell to 120 mm, trigonal to rounded, with commarginal ("concentric") ridges on outer surface. It differs from its closest relative (and local native species), the Southern Quahog, Mercenaria campechiensis by smaller maximum size, violet-color tinges on the internal surface of its valves (lacking in the southern quahog), and lack of commarginal ridges on central part of the external shell surface. Given its commercial value, this is one of the best studied species of bivalves on the planet. The aquaculture industry has introduced the northern quahog to the bays and protected waters of Southwest Florida: the species was chosen over the native Mercenaria campechiensis because of the very short shelf life in this latter species. Both species can be found in the local areas invaded by M. mercenaria, and hybrids are not uncommon.