This is the largest of the limpets, often exceeding seven inches in length. The flesh on the underside of the foot is yellow, and the shell is nearly covered by a black mantle. The shell is grooved by many small radiating ridges that converge on the "keyhole" or opening on the top of the shell. A vegetarian by diet, the keyhole limpet is frequently found in deep pools or between rocks in the mid- and low-tide zones and along protected seawalls and breakwaters in bays.