Why does a turtle live in a shell?

The turtle's shell is really part of its skeleton. Some turtles have shells that are rounded. Others have shells that are flat. The shell is a bony box that protects a turtle from its enemies. When a water turtle gets into the water, it can paddle aound or zoom down into the water like a submarine, shell and all. Some turtles can pull in their hands, neck, legs and tail and close the shell tight when danger threatens.