crazy creature found?!

[jrock77]

I am in the mist of transferring my tank into a reef and I have bought my lights and started the wet* dry. Tonight I was arranging my base rock and underneath a piece of rock was a creature, something I haven't seen before. I didn't buy him or I haven't purchased any new rock in well over six months.
Regardless, it looks like a caterpillar, I fuzzy white caterpillar about 4-5 inches in length and 1* 4" to 1* 2 in width, and it is relatively flat.
Is this thing a good or bad?! my fish all seem to be fine, my mushrooms and leather coral are fine as well. One fish did just die though, but it was one that I have had from the get go and has survived two moves. Water tests are all within normal or better.
any help? thanks!

 

[jrock77]

Well that is a good question! I have never seen until tonight and well I saw it when I only had the atinic lights on, I was introducing a greek goddess slug into my tank and while I was moving the rock around I found it.
I was looking through one if my books about marine problem solving and it sounds like its a bristleworm? I don't know if this is correct, but it goes on to describe it and it almost sounds the same, but not 100%. It says that practically every tank will possess one or two speciments, which my be acceptable because it sifts through detritus searching for algee and pieces of food that haven't been eaten.
The algee makes sense if it is because I have had mass amounts of algee growth due to the new PC lights, still trying to get it under control!