Help identify...

[Jose H]

I was cleaning out my sump area, removed some filtration sponge and saw this big thing just hanging out. What is it? Good or bad? It was about 3" to 4" long.

 

[Rybren]

Looks like a plain old bristle worm to me.

 

[Jose H]

I've read that they're not bad if it's still small. But eventually they can grow and eat any weak/sick fish. But what exactly is their role in the tank?

 

[Salty1962]

CUC, I'd keep it. I've never lost any livestock to them unless it was dead, if it's dead I'd rather they eat them instead of polluting your water.

 

[Jose H]

I'm sure there's some more in there, but I shouldn't worry about them then, correct?