I have a worm.

[rulesmith]

not sure what kind, too fast for a picture. He is about 3inches long and red with lots of little things maybe legs? off of his sides. He was climbing around on my live rock under my mushrooms. Is this a bristle worm?

Is he harmful?

What can I tell you that might make it easier for you to tell me what he is?

[romunov]

Anything like here?
Polychaete Annelid Identification (http://reefkeeping.com/issues/2003-03/rs/index.htm)
Polychaete worms (http://reefkeeping.com/issues/2003-04/rs/index.htm)

[EdKruzel]

Sounds like a Bristle or possibly a Fireworm; either case it is most likely harmless to tank inhabitants. (Some larger fireworms can be a threat to certain corals).

Fireworms with a thickness close to a pencil may be a concern in some cases, but all Bristles are a benefit.

They do not have mandables and feed upon detritus and other rotting material in the tank.

With the placement of LR you have most likely intorduced numerous worms, bristles and other species as well.

Ed

[greenbean36191]

Fireworms with a thickness close to a pencil may be a concern in some cases, but all Bristles are a benefit.
You got that sort of backwards. "Bristleworms" covers all of the polychaetes, not all of which are beneficial (eunicids for example). All of the fireworms except H. carunculata are beneficial, regardless of size.

[bertoni]

Yes, I've been trying to get better about using the terms "fireworm" and "bristleworm". It's good to clean up the terminology we use, IMO.