As there are more than 1200 species of barnacles and my knowledge of coastal flora and fauna is virtually non-existent, I’m afraid I have no idea which barnacle species this is.
It is, however, one of the 25% of species that occupy the intertidal zone, that area of the coast line that is covered by water at high tide but out of the water at low tide, and this means it has to be able to protect itself from dehydration. To this end, the barnacle has developed an impermeable shell and a system of secure plates to effectively seal its top opening.
Although they are active swimmers in their larval stages, once they clamp on to their particular piece of coastal rock in adulthood and secrete the calcium mix that becomes their shell, barnacles never move again. When the tide comes in and covers them, they feed on minute organisms suspended in the water, using their hairy legs as filters and gatherers.