Carolina Marsh Clam (Polymesoda caroliniana Bosc, 1801)

Carolina Marsh Clam
Polymesoda caroliniana Bosc, 1801

Carolina Marsh Clam:
A Rather Well-Rounded Clam

By Patricia B. Mitchell.

The Carolina Marsh Clam is broadly ovate to almost circular in shape and may grow to a length of about 2 inches. The fairly thick bivalve shell is inflated, with fine concentric growth lines. A thin shiny brownish or greenish periostracum serves as an “overcoat” for this mollusk. Often the valve halves of Polymesoda Rafinesque, 1820, are somewhat corroded near the umbones (beaks). Underneath the noncalcareous periostracum the shell is dull white. Often the white interior is tinged with pretty purple.

Each of the two valves has three central teeth in the area where the valves join. The right valve has two tiny grooved side teeth on each side; the left valve has one. There is a small, narrow, pointed pallial sinus (a notch at the posterior end of the pallial line where the retracted siphons rest).

Polymesoda caroliniana lives in mud in warm to temperate waters. It may be found in tidal rivers, intertidally, or just below the low tide line. Its habitat (which is expanding) is anywhere from Virginia to northern Florida, and in the Gulf of Mexico to Texas.

The Carolina Marsh Clam was a large part of the diet of the Calusa Indians of southeast North America.


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