what is this?

[tangafish]

i just found this in my tank this morning, i have never seen it before, unfortunately my camera doesnt take the best pics, but the edges are kindy ruffly and it is tan w/brown spots all over it, almost reminds me of a sea hare coloration but is completely flat. any ideas?

 

[figuerres]

sounds like and looks like a type of flatworm.
generaly I do not think they live a long time in a tank
I do think that I have read that some of them may feed on corals.

I have seen them a few times but never seen damage from them.