Please Help Identify

[ninthmuse]

I moved a rock in my tank & found this creature! No idea what it is, where it came from or if it’s a threat to my ecosystem! Please help identify this guy

 

[ninthmuse]

It’s the small, pink bony & spiny looking thing. Thanks.

 

[ninthmuse]

 

[lmforbis]

Bristle worm. Good for the tank just don’t touch them.