Worm inside the rocks - what is it?

[servus]

1 year old tank, rocks have been in it since the beginning, here's what I found while breaking 2 rocks today. Can you help me identify it? Is it a harmful parasyte? Should I expect more of these to invade my tank now?

 

[Zach B]

Looks like a bristle worm

 

[xxkenny90xx]

Bristle worm. Good guy!

 

[servus]

Lol, wasn't sure it it's a good guy or a bad guy. Got it, thanks! I guess it'll take years to learn everything about this hobby this was a... weird surprise for me ( I HATE worms and caterpillars!).

 

[xxkenny90xx]

Lol, wasn't sure it it's a good guy or a bad guy. Got it, thanks! I guess it'll take years to learn everything about this hobby this was a... weird surprise for me ( I HATE worms and caterpillars!).

You will never learn everything about this hobby. I've been learning new things everyday for 10 years!