Northern Rock Barnacle - Semibalanus balanoides
Common, intertidal barnacles that resemble volcanoes or dragon eyes. This rock had multiple generations as you can see from the variations in size.
They have a membranous base and the outer shell consists of white, overlapping, shell-like plates that grow with the animal.
Habitat: Encrusted on rocks in the low tide zone
''Semibalanus balanoides'' is a common and widespread boreo-arctic species of acorn barnacle. It is common on rocks and other substrates in the intertidal zone of north-western Europe and both coasts of North America.