Jane Gadsby, age 14, of St. Catherines, Ontario, Canada for her question:

What are barnacles?

Barnacles were discovered when human sailors .first put out to sea. These small shellfish cemented their hard stony houses on the sides and bottoms of the boats. Barnacles also stick their crusty shells onto whales; sea going turtles and other marine animals. They still cement themselves to our ocean going ships and from time to time every great liner must go onto dry dock for the difficult job of scraping them away. There is a fortune waiting for the person who invents a barnacle repellant.

Sailors have been struggling with the barnacle problem for ages. But scientists did not learn the true nature of these pesky shellfish until about 100 years ago. This is because they develop through several different stages of life, somewhat like certain insects. This is not so surprising, because both barnacles and insects belong in the same enormous clan of arthropod animals. But, as usual, seeing is believing. On land we can see and believe that a grubby caterpillar becomes a glamorous butterfly. But in the sea, it is not so easy to observe a leggy little swimmer change into a stay at¬home barnacle in a stodgy shell.

There are in the world's oceans about 800 different kinds of barnacle. Their super tough shells may be shaped like grooved domes or gnarled tree stumps. The smaller species are a quarter inch wide and usually dirty white. Larger species measure two inches wide and many tint their shells with blue or yellow, red or purple.

The living barnacle stays inside his shell    standing on his head. His roof is a hinged trap door that can be closed in case of trouble. When things are fine, a feathery circle of spindly legs pokes out through the open door. They sift algae and other floating morsels of food and poke them down to the barnacle's mouth inside the shell. The legs also circulate water bearing breathable oxygen.

The adult barnacle never leaves home, so dating is impossible. However, in most cases., his body produces both male and female cells that become fertilized eggs inside the shell. When they hatch, the larvae leave home and swim away, looking like millions of tiny water fleas. Each larva has six legs and one eye. It grows and molts three times in its first week. After a fourth molt, it emerges with a new shape. It now has 24 legs, two eyes and a pair of feelers.

Soon its fat body grows as big as a marble    and the little swimmer is ready to give up his freedom. He selects a solid surface underwater, clings and anchors himself with cement secreted from his feelers. Then his body extracts limy chemicals from the water and uses them to build his one room house. His 24 swimming legs now become food gatherers and the adult barnacle loses the eyes he no longer needs.

Once fixed in place, a barnacle never strays. But you would expect his shell to fall away when he dies. Not so. In a year of ocean travel, a liner may get stuck with 30 tons of barnacles, living and dead. The extra weight and the increased water resistance require extra fuel to move the ship, and scraping away the stubborn shells is hard and costly work. This explains why marine scientists are searching for something to discourage the pesky barnacles from sticking.