The Difference Between Crustaceans and Shellfish (And Ways to Enjoy Both)

Contrary to popular belief, the terms ‘crustaceans’ and ‘shellfish’ are not interchangeable. In fact, the correlation between these two categories only goes one way: while crustaceans are always shellfish, shellfish are not always crustaceans.

If that sounds complicated, don’t worry. Allow us to explain further.

What are shellfish?

To put it as simply as possible, shellfish live in the water and have a shell (or shell-like) exterior. From that basic definition, shellfish can then be divided into two main categories: crustaceans and mollusks.

Crustaceans: Characterized by hard outer shells and segmented limbs, examples of commonly enjoyed crustaceans are shrimp, crab and lobster.

Mollusks: Defined as soft-bodied invertebrates with calcium carbonate shells, examples of commonly enjoyed mollusks are clams, mussels, scallops and oysters. 

So, to elaborate on our description above with a specific example, both crabs and scallops are shellfish, but only crabs are crustaceans. However, it’s not uncommon for people to refer to the mollusk subcategory as simply ‘shellfish,’ and distinguished from crustaceans entirely.  

Does your head hurt yet? Now that we’ve cleared that up, let’s get to the important part:

What are some of the best ways to prepare shellfish?

On the Grill

With their convenient, built-in shells, shellfish are actually perfect for grilling — with no fuss or mess to deal with. Here are a few specific tips dependent on what type of crustacean or mollusk you’re grilling:

• Lobster tails: Use kitchen shears to cut along the underside of the shell, then put directly on the grill grates to cook for about 10 minutes, flipping halfway through. Baste with butter during cooking for even more delicious flavor.
• King crab legs: Most king crab legs come precooked, and the grill is the perfect place to reheat them to get a little smoky flavor. Just put directly on the grill and warm each side for no more than five minutes each.
• Shrimp: To avoid losing any shrimp between the grill grates, consider making shrimp and vegetable skewers. Just make sure to choose vegetables that also cook quickly — like tomatoes or mushrooms — since your shrimp will be cooked in less than five minutes.
• Oysters: Just put them straight on the grill and take them off once they’ve “popped” open — it’s as easy as that. Squeeze a little lemon on top and enjoy.

Baked in the Oven

If you don’t have access or if it’s not the right season for grilling, don’t let that stop you from enjoying shellfish. Both crustaceans and mollusks can be baked in the oven with your favorite herbs and seasonings. Keep it simple by sprinkling on some Old Bay seasoning or brush with butter, squeeze over a lemon, and top with fresh dill. The flavor combinations are endless.

Boiled on the Stove

While it might be the toughest method to impart deep flavor, shellfish can also be quickly boiled or steamed on the stove. However, if you’re cooking for a group, there’s no better crowd-pleaser than a seafood boil. Begin by building a flavorful broth with water, salt, white wine, lemon and garlic. Then, add in your chosen ingredients, beginning with the items that will take the longest to cook through. A classic seafood boil uses potatoes, corn on the cob, lobster, shrimp, sausage and a mixture of seasonings, such as fresh thyme and red pepper flakes. Don’t be afraid to get creative!