|Cardiidae, the heart cockles, have shells that may be circular, triangular or squarish, usually well-inflated. They usually have radial ribs with spines or scales, but some are smooth. The margin of the shells are usually scalloped or serrate. They are readily recognized by being heart-shaped when viewed from either the anterior or posterior side. Teeth along the hinge are large, curving outward. The foot is angular and can be used for "jumping" away from predators. Cardiidae are usually found below the surface in sand or muddy bottoms. There are 13 species found in Texas waters.