Modiolus americanus (Leach, 1815) grows to about 100 mm (about 4 inches!) in parts of the its distribution range. The brown periostracum is heavy and flaky. This species resembles last week’s Shell of the Week, the Southern Mussel. They differ, however, by the usually larger size, much more “obese” shell, and presence of orange and pink hues internally and externally in the shell of the American Horse Mussel. The Southern Horse Mussel has a “skinnier” shell and generally bluish-purple color inside.
