Patricia Richardson, age 12 of Ottawa, nt., for her question:

What is a mollusk?

A mollusk belongs to the vast animal family Mollusca ‑ the softies. All the mollusks have soft, boneless bodies. Many of them guard against this weakness by building themselves sturdy armor. A number of the animals we call shellfish are mollusks. Clams, mussels and oysters are soft bodied mollusks who live safely within their shells.

Most of the mollusks are water dwellers, equipped with gills. The snail, however, is a land dwelling mollusk, as are slugs who do not build shells. Cuttlefish are sea dwelling mollusks who do not build shells. The majority of mollusks are smallish animals. The giant clam several feet across the shell, is an exception and so is the big cuttlefish.