Angelo Franceschi, age 14, of Richmond, Virginia, for his question:
How are barnacles formed?
These stubborn little shell fish are nothing but a nuisance. They were discovered ages ago, securely stuck to the very first ships that man¬kind put out to sea. All this time, every sailing generation has toiled to dislodge them and the tough scraping job continues. However, not much was learned about the barnacles themselves until about a century ago. Then the truth of their remarkable life story was discovered.
Barnacles become noticeable as adults, then they stick their stubborn shells with super cement to ships and piers, whales and other ocean going creatures. The shell of the avera. e barnacle is a small sturdy dome with a hole at the top that can be closed by a hinged door. The living barnacle pokes a tuft of spindly legs through the trapdoor and trawls for food. Drifting algae and small sea dwellers are Grabbed, pulled inside and stuffed into the barnacle's mouth.
The sea is home to about 100 barnacle species. The smaller species have greyish shells about a quarter inch wide. Some of the larger species are two inches wide and may be tinied with red or purple, blue or yellow. All of them are crustacean cousins of the crabs, shrimps and lobsters ¬and souewhat distantly related to the insects.
We are used to the idea that a tubby caterpillar develops into a winged butterfly. But until a century or so ago, nobody guessed that the barnacle also develops through several distinct life stages and the infants in no way resemble the adults.
As a rule, the adult barnacle is both male and female and fully fer¬tilized eg a are produced inside the shell. The eggs hatch and the tiny larvae swirl out and away, looking like mini water fleas. to wonder everybody failed to recognize them for so long.
A newly hatched larva has one eye and and no shell. It feeds hurrily on scraps of floating plankton, grows and molts three times during its first wee:: of life. After tile fourth skin is shed., an entirely barnacle emerges. It has two eyes, a pair of feelers and no fewer than a dozen leas.
The creature's fat round body soon ,,rows almost as big, as a marble. Then it is ready to renouce its free swimming life and settle down. It selects a submerged solid surface, such as a ship or a pier or a whale. A limy substance, extracted from sea water, oozes from one of its feelers and this is used to build the barnacle's permanent home. For the rest of its life it stays inside, standing on its head. And the shell stays stuck long after the barnacle dies.
During a year of ocean travel, a fair sized ship is plastered with perhaps 30 tons of barnacle shells. The extra tonnage slows down speed and forces the ship to use more fuel. Every few years, it retires to dry dock, where the touch and expensive job of scraping off barnacles must be done.