Barnacle, a small saltwater animal with a protective shell-like covering. There are more than 1,000 species. Barnacles attach themselves permanently to ships, wharves, and rocks, and to other marine animals. Barnacles on the hull of a ship increase friction and can reduce the vessel's speed. The ship must then be put in dry dock to have the bottom scraped. To prevent barnacles from clinging to ships, the hulls are either treated with toxic paint containing tin or copper or are coated with plastic.

Young barnacles hatch from eggs and develop into free-swimming larvae that resemble tiny crabs. The young barnacles secrete a gluelike substance and attach themselves to a suitable surface. They slowly change into jellylike creatures the size of small marbles. They then secrete layers of calcium carbonate (lime), which may be yellow, red, purple, or brown. The barnacle's legs stick out like tentacles from an opening in the top of the shell. At their tips are cirri, feathery appendages that sweep plankton and other food into the mouth.

The most common barnacles are gooseneck barnacles and acorn barnacles, named for their shape. Gooseneck barnacles have a stalk, which they use for attachment; acorn barnacles have no stalk—they attach themselves directly onto a surface. In Europe and North America, barnacles are eaten as a delicacy.

BarnaclesBarnacles attach themselves to ships, wharves, rocks, and to other marine animals.
What’s Special About a Barnacle?

Adult barnacles attach themselves to rocks and other hard surfaces. They feed on living things, or organisms (AWR guh nihz uhmz), that float in the water. Barnacles have special limbs or body parts that gather these organisms in so that the barnacle can feed on them. Because barnacles are attached to, and rarely move from, their perches, they have developed a special way to produce young without any mate.

A barnacle is called a hermaphrodite (hur MAF ruh dyt). That means that barnacles have both male and female reproductive organs. They can produce both sperm (male reproductive cells) and eggs (female reproductive cells).

This reproductive strategy allows them to fertilize themselves and produce offspring, even when there are no other barnacles nearby. If two barnacles happen to be close to one another, however, they can mate and produce young.

Barnacles belong to the class Cirripedia of the subphylum Crustacea. Gooseneck barnacles belong to the genus Lepas; acorn barnacles to the genus Balanus.