Clams and scallops are two kinds of shellfish.
Barnacle is a shellfish.
A Nautilus is one shellfish whose name begins with an N.
There is no specific scientific name for shellfish because shellfish is a non-scientific way of describing a large number of invertibrate food items such as lobster, scallops, muscles and shrimp. Mostly 'shellfish' are either molluscs or crustaceans.
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Sally and Dave
crustacean, shellfish
A bivalve.
Calamari (squid) is not typically thought of as a shellfish but it is a mollusc - in the same family as oysters and mussels. People with a shellfish allergy could have a potentially life-threatening reaction to calamari.
This could be cioppino, which is a shellfish and fish stew where the shellfish often are still in the shell. It can include fish, shrimp/prawns, clams, crab legs, or whatever else is fresh or available. It is typically cooked in a thick, tomato-based base. A variation on this is bouillabaisse where the shellfish are out of the shell, making it easier to eat without making a big mess (but the mess is part of the fun!).
Oyster
abalone
lobster