The Southern Marsh Clam, Polymesoda floridana (Conrad, 1846), is a species of bivalve mollusk found locally, mostly in the back-bay areas, including the Caloosahatchee estuary and mangrove habitats. This species has a broad tolerance for changes in salinity. Its adult shell measures from 1 to 1.5 inches; the shell is roughly triangular, with rounded ventral (bottom on the photos) and pointed posterior (left on photos) margins. The shell sculpture is restricted to irregular growth lines. The color whitish with purple or pinkish-purple tints. Internally purple or white with a wide purple margin.
The Southern Marsh Clam, Polymesoda floridana, from San Carlos Bay, Lee County, Florida. Photo by José H. Leal.