Why do they call a box turtle a "box" turtle?

Question

Why do they call a box turtle a "box" turtle?

Answer 1

they call it a box turtle because when the turtle is in danger or threatened it will pull its head and legs into it's shell and the lower shell moves up creating a tight fitting box around the turtle, keeping it safe from predators, not even raccoons can get into the shell once it has closed up

Answer 2

Shell pattern.  

Answer 3

Box turtles have a movable hinge in their lower shell that allows them to completely close up with their head and legs inside to protect themselves. That is where the name is derived from.