Barnacle, << BAHR nuh kuhl, >> is the only crustacean that stays in one position during its adult life. Crustaceans, which include barnacles, lobsters, and shrimp, are a type of animal with a shell and jointed legs. Adult barnacles attach themselves to a hard surface, such as a rock, the hull of a ship, or even a whale. Because a build-up of barnacles can slow a ship, shipowners use toxic paint to keep the animals off hulls.
There are around 1,000 species of barnacles. These species are divided into two main groups, barnacles with stalks, called goose barnacles, and barnacles without stalks. Goose barnacles, often found on ships, grow to 30 inches (75 centimeters) in length. Stalkless barnacles range from 3/5 inch to more than 3 inches (1.5 to 8 centimeters) in diameter.
Barnacles live in oceans throughout the world. Young barnacles go through a series of immature forms called larval stages that are different from the adult form. A barnacle hatches into a microscopic larva called a nauplius. The nauplius swims and drifts great distances, finally changing into a shelled, bean-shaped form called a cypris. The cypris settles out of the water onto a solid object, where it clings. The barnacle then sheds its larval shell and begins to form a set of hard, fixed plates.
A barnacle eats by extending its bristly cirri (tentacles) through the top of its shell. The animal waves them through the water to gather tiny organisms called plankton for its food.
