any one of a large
group of animals
having no
backbone, soft bodies not composed of segments, and usually covered with a
hard shell of one or more parts. The shell of mollusks is secreted by a covering
mantle and is formed on snails, clams, oysters, whelks (large, often edible,
marine snails) and mussels.
Slugs, octopuses and squids have no shell.
—Handbook for Preclears Glossary (app 9.7.90)