Turtle
Turtles are parted into two groups from the way they hide their heads into their shells. The Cryptodira (hidden neck turtles) pull their heads straight into their shells by folding their necks back under their spines. They have very small necks. The Pleurodira (side-necked turtles), now found only in fresh water environments in the Southern hemisphere, fold their necks to the side, as its name states. The important adaptation of hiding their heads evolved twice from turtles in the past which were not able to do this. Obviously, this adds to their defence against predators.