It’s a great question! I thought the definition included both mollusks and crustaceans... but nothing with fins.This may sound like a silly question but what is included in the term 'shellfish'? I had not thought of prawns (shrimp) and lobster as shellfish but I think in culinary terms they are included?
Would crayfish be included?
and most kinds have an external calcareous shell.
Squid is a mollusk... like octopus, who doesn’t have an external shell either. Is confusing, huh. Some shellfish have no shells and none are fish.