Thing inside live rock

[PurplePolyp]

I was staring at my tank and in the shadows of my live rock this thing comes out. It was red with white feathery tentacles all over it. It looks like a brittle star leg but if it is, this thing is huge. The arm was about 2" long and 1/4" thick. I enhance the photo because it was in the shadows. I tried reaching for a flashlight to get a better photo and he moved when I moved.

 

[PurplePolyp]

Here's a better photo. This is the original

 

[Leonardo7689]

Looks like a bristle worm

 

[PurplePolyp]

How big so they get and do they move? Are they bad? I can't find him now, even with the flash light.

 

[Krollo]

Def a bristle worm...good and part of CUC. Do not touch the sides have bristles that will stick in your skin like fiberglass

 

[Leonardo7689]

It varies, they are CUC. They live inside the holes in the LR and everywhere they can squeeze in. They eat scraps of foods the fish missed and dead organisms in the tank. Avoid touching their hair like bristles coz they can irritate your skin. As long as they remain small they're good IMO.