Jeremy Pierson, age 11, of Beaumont, Tex., for his question:

ARE THERE DIFFERENT KINDS OF BARNACLES?

Barnacles are crustaceans or shellfish that attach themselves to rocks, ships or other hard surfaces and then remain attached for the rest of their lives. There are a great many different kinds of barnacles.

When hatched, barnacles are freely swimming creatures. They actually resemble small crabs at birth and can swim well. But soon they attach themselves to convenient surfaces and grow hard shells. Then only their feathery antennae, or tentacles, of which each has six pairs, still move. They wave and reach out for smaller water creatures for food.

At low tide along the ocean shore you can sae thick crusts of barnacles on piers, rocks and breakwater walls. Different kinds of barnacles pick out different locations on which to settle.

These same creatures attach themselves to the hulls of ships. Ocean steamships must be scraped at intervals to get rid of the barnacles. The can also damage smaller craft.