The Atlantic Petricolid, Choristodon robustus (G.B. Sowerby I, 1834), is an inch-long clam belonging to the Venus Clam family Veneridae. The species is found from North Carolina to Brazil. Shells of other members of the Venus Clam family, such as the Southern Quahog, the Sunray Venus, and the Cross-barred Venus, to name a few, are commonly found along the beaches and bays of Southwest Florida. This is not the case with the shells of the Atlantic Petricolid: the species is present in the area, but will be found only inside limestone rocks, coral skeletons, and larger shells. An Atlantic Petricolid bores into these structures using its cheese grater-like shell combined with some chemical dissolution.
The photos show shells of the Atlantic Petricolid, on left, from Sanibel, on right, from Búzios, Brazil. Photos by José H. Leal.