Valves of the Florida prickly cockle are rough on the outside, especially near the edges. These bivalves grow to about 50 mm in maximum length.

On the outside they are speckled with brown on a beige background. On the inside they are a rich dark maroon shading to a dark orangey-red.

Because Sanibel has such astonishingly large numbers of shells in the beach drift, with diligent searching over a few days time, it is also usually possible to find a pure-white, albinistic valve of this species.