The abalone demonstrates the basic body plan of molluscs. A foot is used for movement. A radula is a scraping tongue, and a mantle secretes the shell. [1:22]

Numerous tentacles, a funnel that evolved from the foot, a mantle that secretes the shell, and a pair of jaws with a radula- these all clearly show the nautilus mollusc design. Spiraling through the shell, a tube called the siphuncle...

The mantle deposits calcium into a protein matrix to make the shell. The inner crystalline structure prevents cracks from breaking the shell, and the mantle continually repairs the shell from the inside. [1:32]

The squid's body plan has developed for fast action. The shell is reduced to a thin "pen." The mantle wall has elastic fibers that intensify the jet propulsion. Giant nerves allow a fast reflex and three hearts pump oxygen to the gills....