What is this weird plated slug/worm?

[flyersix]

Hi - Hoping you all can help me to identify this weird plated slug i have recently spotted in my reef tank. i have had my tank for over 3 years and have never seen this guy. also have not added anything new to the tank in over a year. Kinda looks like a plated flatworm or nudibranch. hope it's not a bad guy!

 

[Overlook reef]

That is a Chiton.

Good guy!

 

[flyersix]

Hey thanks for the info!

 

[this is me]

Chiton. Good algae cleaner on rocks.

 

[Bobbofin]

Got a couple those in the rubble in my fuge along with those hated little star fish that I keep throwing away.