Balanus barnacles

Balanus perforatus is a species of barnacle in the family Balanidae, and it is one of the commonest barnacles in Greece. The species is is a large barnacle which grows up to 30 millimetres in both diameter and height. Its shape resembles a volcano with steep sloping sides. The six fused lateral calcareous plates are pale purplish-brown and often ridged vertically. They often separate near the top leaving jagged ridges. Tissue inside the operculum is brightly coloured. Two pairs of moveable plates cover the operculum which can be sealed by a purplish-brown flap when the barnacle is exposed above water or it is not feeding.[(wiki)
These barnacles were spotted while been attached in a thin piece of wood, probably a stem, in Karnagio shipyards, Pefkakia, Volos city, Greece.