Goose barnacles are marine crustaceans but, unlike many other members of their class, they are hermaphrodites, meaning that the animal has both male and female sexual organs. Their eggs hatch into free-swimming larvae, which drift with the ocean currents as one of the immense number of animals that comprise zooplankton.
As they develop, the larvae attach themselves to an object by way of a strong stalk or ‘peduncle’. Once they have attached themselves to an object, they do not move again unless torn off by accident. As they grow they develop a feathery feeding apparatus, which filters particles of food from the water as the current passes over it. This filter can be speedily withdrawn inside the hard capitulum when the barnacle feels threatened.
If barnacles grow in sufficient numbers on the hull of a ship, they increase the vessel’s drag though the water and have to be removed when the ship is dry-docked. However, they were considered a great delicacy in some parts of the world. Even in Cornwall, if a boat arrived with clusters of barnacles attached to the hull, they were scrapped off and sold for food.