"Barnacles are not what they seem. They are not shellfish, like cockles or winkles. They are more closely related to shrimps and lobsters, belonging to that great group of animals having jointed legs known as arthropods. Barnacles have given up the vagaries of a wandering life in favour of a sedentary, reliable existence. They are crustaceans tucked into a box made out of several calcareous plates. When currents wash over them, the valves open sufficiently for the appendages of the sequestered animals to filter out tiny edible particles, a fine soup of plankton. The delicacy of their limbs contrasts with the solidity of their stony homes, which cluster together on even the most tempest-lashed cliffs to make a white crust. Barnacles can attach themselves to whales, to boats, or to the shells of other animals in the deep sea; they are found everywhere from Antarctica to the tropics."