Help with ID (urchin? Sunflower star?)

[Fiver]

I first saw this last night in the dark and today it's basically in the same place it was last night. It's purple, about pea-sized, kind of flat with arms radiating all around its side. No arms/spines sticking up from the disc.

Thoughts? Thanks!

[Dkuhlmann]

If you're talking about the thing on the right side it's a sea urchin. Pretty cool hitchhiker

[flananuts]

I have one just like that that was the size of an eraser head when I started my tank. I also got a
Nice sized green pincushion with my live sand from Florida. It constantly decorates itself with shells, snails, and some Palys before I glued them down. Nice live rock btw

[Fiver]

Yes, that thing. Thanks for the ID. Any sense of what type?

My first guess was urchin, but I was thrown off by the fact that it's so flat and didn't have spines sticking up. Still new to the hobby.

[Fiver]

I have one just like that that was the size of an eraser head when I started my tank. I also got a
Nice sized green pincushion with my live sand from Florida. It constantly decorates itself with shells, snails, and some Palys before I glued them down. Nice live rock btw

Thanks! It's TBS rock. How big did the urchin get?

[sam.basye]

Looks like a Rock boring urchin.
It will get to be about the size of a golf ball. They don't decorate themselves and they like to eat small pieces of shrimp. Every once in a while I will put a tiny piece of raw shrimp on a skewer and let it grab it with its spines and watch it use is tube feet to bring it around to its mouth. The spines will grow back if broken and I've never noticed any rocks that look like they have been chewed on..
I have 2; a purple and a tan, for almost a year now.

[Betta132]

They're cool, harmless little critters. You want him.

[Fiver]

Thanks for the great input, everyone!