Also known as percebes, the gooseneck or goose barnacle is an expensive rarity, chipped off dangerous rocky shorelines by intrepid collectors. At this price you can understand their motivation, so pay up and be grateful! You’ll get between 10 and 30 per pack. A large one is about 7cms long. Toss into boiling water for two minutes, peel and suck. We should tell you that you will get a certain amount of genuine rock (as in cliff) in your pack because the barnacles are very firmly attached to it and would be damaged if removed before cooking.
Here's a bit of background on this rare item.
Goose Barnacles Tapas Style
The F Word