race features:
Retreat to Shell: Using an action, you can pull your head and limbs into your shell for up to an hour. While retreating, you are prone, your speed is 5 feet and you are immune to non-magical piercing, slashing, and bludgeoning damage. Once used you cannot use this feature against until you complete a short or long rest.
Shell Resistance: You shell has adapted to be able to take hits. You have resistance to piercing and slashing damange.