Periwinkles

My fist experience with periwinkles ( Littorina littorea) was in Scotland, when I was about 4, then again in England in my early teens. It has become an annual early spring gathering treat that I have passed on to my son. Every March we go down to the shore in Rhode Island to gather a bucket full. Periwinkles are found thru out the northern  hemisphere, along shoreline at low tide. As they are not filter feeders, but browse on algae and seaweed they can be gathered during much of the year but for me they are a late fall thru early spring food. Here in the Northeast there are both native and European species...most of the larger ones are the invasives, eat them....They are about the easiest shellfish to gather. Just pick them off of the rocks at low tide.
Periwinkles require a bit of skill to pluck from their shell, a pin is the usual in Europe, but any pointy thing will work.
To cook them, steam in a broth of white wine, garlic, butter and a little salt. Add some kelp or rock weed to the broth instead of salt, you will not be disappointed.  The taste is earthy, salty and full of the sea.
pluck them from their shell and enjoy, dipped in meted butter, or save them  for some chowder.
And for more info
http://en.wikipedia.org/wiki/Common_periwinkle