For a variety of reasons, including preferences of taste and the possibility of food allergies, it’s a good idea to know which foods contain shellfish. Indeed, crustaceans are one of the eight major food allergens, the others being milk, eggs, fish, wheat, tree nuts, peanuts and soybeans. By law, the US Food and Drug Administration requires that any packaged food product with shellfish as an ingredient list the name of the shellfish on the label. Shellfish appear in meals both as whole foods and in the sauces and seasonings that adorn them.

Crustaceans include shrimp, crab, crawfish and lobster, but often the presence of these foods will be disguised under other names, both in food packaging and on restaurant menus. "Prawn" and "crevette" are both commonly substituted for shrimp, while "crayfish" and "ecrevisse" are alternative names for crawfish. Lobster goes by other names, including "langouste," "langoustine," "scampo," "coral" and "tomalley," according to the Food Allergy Initiative. Soups with "chowder" or "bisque" in their names also likely contain crustaceous species.

Mollusks are another type of shellfish, although not all mollusks have shells. Despite this, many people who are allergic to common crustaceans are also allergic to mollusks, advises the Food Allergy Initiative. Mollusks include abalone, clams, cockles, mussels, oysters, octopi, scallops, snails -- also known as esgargot -- and squid, or calamari. Fried calamari is a popular restaurant appetizer, and scallops are frequent additions to pasta dishes in authentic Italian restaurants. Dishes containing octopus and squid are commonly served as part of sushi platters.

Condiments and sauces may contain shellfish products. Fish stock, for example, may contain the shells of shrimp with ingredients like celery, onion and bay leaf. Some Japanese brands of miso, a fermented soybean paste very widely used in daily Japanese cuisine, contain fish stock, according to the International Vegetarian Union. A common ingredient in Thai home cooking is shrimp paste, made from salt, fish and shrimp; it is used to add flavor to sauces and curries.

Spices and seasonings are another potential source of shellfish in foods. Restaurants may use a variety of powdered ingredients derived from shellfish. Among these are clam broth base powder, crab extract powder, shrimp powder, scallop extract powder, oyster juice powder and lobster extract powder, varieties of which are made by Nikken Products. When dining at Asian restaurants, ask if any of these dry items are used as seasonings.