I was asked last week, "What is a cockle?"
My answer was, "I don't really know. Its probably some kind of shellfish seafood." But my World Citizen Families deserve more of an answer than that so I did a little research.
Cockle is the name given to a group of small, edible salt water clams. They live in sandy, sheltered beaches throughout the world and have heart shaped shells. Technically to be a true cockle, the little buggers have to belong the the bivalve family Cardiidae, though bivalves from the Veneridae (Venus clams) and the Arcidae (ark clams) families are oftenly mistakingly called cockles.
Incidentally, there is also a Scottish candy called the Berwick Cockle, so named for its cockle like shape. However, since she's a fishmonger from Dublin, I think its safe to assume that Molly Malone was selling mussels and small salt water crabs, not candy.