a small crustacean that occurs in vast numbers attached to rocks, jetties, piers, etc., and on the hulls of ships and boats. The commonest on the shore are acorn barnacles (Balanus spp.), which live attached to rocks with their body enclosed within a shell formed of calcareous (limy) plates. During high tide, they open their shells and use their hairy legs to comb food particles from the water. If barnacles settle on a ship's hull in large numbers they can cause serious problems. Copper sheathing during the days of sail and now modern antifouling paints discourage fouling, but such paints are an environmental issue which has not been totally resolved. Goose barnacles (Lepas anatifera) are the worst offenders. They have long stalks, up to 10 centimetres (4 in.) long, and can grow to maturity in a matter of a couple of weeks. They normally settle on the floating debris that accumulates in slicks and appear in European waters at about the time barnacle geese (Branta leucopsis) leave on migration. This coincidence, and the superficial resemblance between their comblike legs and birds' feathers, gave rise to the medieval myth that the geese hatched from the barnacles. In 1972, the British Scientist, a BP tanker, came out of refit and sailed round the Cape to the Persian Gulf. On its return voyage the ship began to judder so violently that it had to be dry-docked in Brest. The problem proved to be a covering of 70 tonnes of goose barnacles that had grown on the ship's hull in a matter of a few weeks.