identification help!

[Powertec]

Looks like your nem is Lta...and i believe they have been called curly q's...depends on who you ask.
It will be fine in your tank as long as it stays happy.Don't place corals near it so it can touch them as it will sting them. They don't move around as much as a bta. They like the sand bed and good lights.You can feed it meaty chunks of scallops,shrimp etc once a week or so and that will also keep him healthy. Just don't feed him more than about a piece the size of a pencil eraser as it will make him grow awfully darn fast.

As for whats in your rock i cant see it in the pic but it sounds like a a sea star. I have tonnes of them living in my rocks. They eat all the nasty stuff.
Good clean up crew member.