Ocean Runner Nichole is curious about the perfect little round holes she has seen on empty periwinkle, mussel and clam shells. Seacoast Science Center’s Ashley Stokes explains how some snails are herbivores (plant eaters) and some, omnivores (meat eaters). Omnivores, such as dog whelks and moon snails, use their radula to “drill” a hole in its prey, then uses its proboscis to suck the contents out.