The first time I had steamed mussels was at a wonderful little restaurant called the Sail Loft (don't know if it's still there) in Rockport, Maine. This is going back about 30 years. They were on the appetizer list but I ordered a second bowl as my main course. What a relvelation! My Maine family thought of them as trash, but then they felt the same way about lobster bodies and sea urchins. In those days they were "wild" mussels and preparation took some time since they had to be debearded. Today they're mostly cultivated and have almost no beards at all.
You REALLY don't want to get me started on barnacles, around which I planned a trip to Portugal!