You may crawl into your shell as a reaction on a DEX save of 7

when in your shell you get a plus 10 to your AC

you can’t attack with weapons while in your shell and can’t use spell components 

your movement changes to 50 as you slide around

you can move into another creature and they make a CON saving throw of DC 12 or fall prone

Tortles live till about 200 years old and mature at 30

You have advantage on history and arcana checks 

you have a plus 3 to wisdom and intelligence 

You can breath both air and water