What are these worms and are they problematic?

[jotoole]

I moved a couple pieces of coral and all of the sudden all these little worms emerged.

 

[KC's CNC Creations]

bristle worms, some people feel they shouldnt' be in their tanks, they are just a part of the clean up crew and i've never had issues with them, even had some very large ones many moons ago.

 

[Ashish Patel]

IME they are part of the clean up crew and very beneficial to clean inside the rockwork and sand. I had a ton of them but when I removed my sandbed they slowly perished until now I have not seen any in years.

 

[vetteguy53081]

Not welcome in my tanks but harmless unless you touch them with your bare hands . Arrow crabs will eat them like candy