Is this an isopod or a baby bristle worm or something else?

[Seadragon]

I found out tonight some hitchhiker pests tagged along with the GSP frags and Xenia frags that I recently purchased from a local hobbyist.  My only questions are:

1. What is it?
2. Is it dangerous to my tank inhabitants?

 

Thanks in advance for any thoughts.

 

 

 

 

 

 

Any idea?

[M. Tournesol]

It looks like the armless herbivorous munnid isopods (attention some isopods are predatory or parasitic http://reefkeeping.com/issues/2006-02/bp/index.php).
In my tank, my munnid isopods are everywhere, pose no problem to my corals (Zoanthus and Pocilloporidae) and are a good source of food for my gobys (my Court Jester Goby love them). 

 

Here a good guide on pods :

http://reefkeeping.com/issues/2004-08/rs/index.php