ID goody or baddy?

[ShaggyRS6]

So when I got my live rock this thing was tiny, It was about half the diameter of a cent! Today, well you can see, it’s had growth spurt !!! Anyone know what it is and if I need to get rid?

 

[DSC reef]

Looks like a type of spiny urchin

 

[Leslie Tabor]

If you are talking about the spiny thing, it would be an urchin. I love them!

 

[BloopFish]

Looks to be a rockboring urchin