David Gwatney, age 11, of Sarasota, Fla., for his question:
How do barnacles grow?
A playful scientist once described the barnacle as a marine crustacean who stands on his head and kicks food into his mouth. However, shipowners ignore his cuteness and regard him as a downright nuisance. Every few years, an oceangoing liner must retire to dry dock for the costly job of scraping off 100 tons or so of stubborn barnacle shells.
The average adult barnacle builds himself a marble dome with a trapdoor, made of superdurable limy material. He uses a life and death grip to fix his dwelling onto solid surfaces submerged in the sea. Since mankind learned to sail, crowds of barnacles plastered their stubborn shells onto his ships.
Since barnacle scraping is a tough job, people tried to find ways to discourage the pest. But for centuries nobody could trace his life story or figure out where he came from. They were used to the idea that certain insects progress through several different stages of life. At last, in 1829, it was discovered that the barnacle does this also and that the youngsters in no way resemble the adults.
The adult barnacle inside his very very permanent shell has a round body with a mouth, a couple of eyes and a dozen or so hairy legs. He stands on his head and pokes his legs through the trapdoor in the top of his dome, trawling for scraps of floating food. And, of all things, the remarkable creature is both male and female.
Female cells are retained inside the shell. Male cells are strewn into the water and fertilize their own or other barnacles in the neighborhood. In about four months, the eggs under the dome become larvas and the parent strews them out into the hungry sea.
An infant barnacle is a nauplius, a minilarva with a round head that tapers to a spiky tail, plus six legs to jerk himself through the water. As he grows, he molts his skin several times. Finally he emerges as a cypris larva, somewhat like a miniclam with 2 skinny legs. He drifts around until he grinds a suitable solid surface to spend the rest of his life.
There he settles down and oozes hard limy chemicals to build his hard limy shell. As a rule, his neighborhood is crowded with other barnacles. Together they form tough, stubborn crusts on passing ships, also on whales and other sea dwellers. And their crusty shells will remain plastered to the spot, long after the original builders are dead.
About 800 different barnacle species belong to the sea. The smaller species build grayish, quarter inch shells. Most species measure about one inch. A few giants measure two inches and their shells are tinted with reds or purples, blues or yellows.