Flat periwinkles are smaller than common periwinkles, but stand out due to their bright colors. The shell can vary between yellow, orange, brown or green, and even blue-gray fossils are found. Of all periwinkle species, this species is the least resistant to dehydration during low tide. Therefore, it lives deeper than other periwinkles in order to avoid lying exposed during low tide. Should that happen, it crawls at its fastest snail rate under a seaweed or stone.