Types
The North Atlantic is home to a wide range of cold water shellfish, including the famous oysters and clams, as well as mussels, snails, whelks, limpets and more unusual creatures like the mottled red chiton. You may also be able to find the dried bodies of nudibranches, as well as creatures with fanciful names, including the Arctic paper bubble, Noah's puncturella and the prickly jingle shell.
Habitat
All shorelines have distinct zones, and shellfish are more likely to live in some than in others. According to Andrew J. Martinez, urchins and starfish often live in what's called the red zone--the lowest intertidal area on the shore, which is out of the water only a few hours each day. Shellfish may also live in the tidal pools, especially the ones that are regularly refilled by the waves. Other shell-bearing animals live in the shallow parts of the ocean itself or in salt marshes.
Size
In general, North Atlantic shells are smaller than the shells of creatures from tropical waters. That doesn't mean that you can't find impressive specimens, though. Shells in the North Atlantic region range from the tiniest, such as the ¼ inch cancellate nut shell, through medium specimens like the 1-inch sea gooseberry and Atlantic awning clam, to surprisingly large shells, like the 4- to 6-inch northern horse mussel.
Locations
You can collect shells in many different locations, such as public beaches, state parks and island beaches. Each beach will have its own complement of shellfish, and will provide a different variety. Take some time to determine whether a beach offers shells that are of interest to you. The most popular beaches are often poor places to get shells; specimens are often crushed or taken before you arrive.
Warning
Be careful about what you collect. Not all creatures native to the North Atlantic should be collected. Mollusks and other shell-bearing animals may be threatened in their environment. Avoid collecting shells that still have a living animal inside, and take the time to learn the laws and regulations in your area. It's important not to disturb the environment that produces such beautiful seashells.