The volcano barnacle is a relatively tall barnacle which can grow quite large in southern waters. For a long time, this species was only found attached to washed up objects originating from more southerly seas. Since 1990, it has also been found living directly on hard substrate along the Dutch coast. The Dutch version of the volcano barnacle is smaller (up to 15 mm) than its southern brothers. The volcano barnacle has various names in English: perforated, rock and rough barnacle all refer to the same volcano barnacle. To make it even more confusing, being one of the various acorn barnacles, you may even run into this name. However, the most common (and native) barnacle in the North Sea is also called the acorn barnacle!