Unknown crustacean..? What is this thing?

[MrSpiffy]

I managed to find another crazy thing in my tank that I have no idea what it is. It's roughly an inch long, and maybe a half-inch wide. It looks to have segments of some sort, almost like a lobster tail has a segmented shell. Here are a couple pics. It's right in the middle of both pics. Any ideas as to what this thing is? I've only seen it a couple times with a flashlight when the lights are off. I hit it with my scraper and it was pretty hard and didn't move at all. I figured it was a fossil. But the next morning it was gone.

[CrystalAZ]

Looks like a chiton.

Crystal

[minimalist]

I agree.

[MrSpiffy]

I assume that it's not harmful. Wikipedia mentions that it eats algae and diatoms. I'm thinking it'd be a good thing to leave in the tank.

[Paintbug]

just a harmless chiton, lucky you!!

[MrSpiffy]

Sweet! Thanks everyone! I agree that it's a chiton. I got an algae-eating mollusk for free!