Sick Humbug Photo-HELP

[artista]

This is a photo of my Humbug Damsel. Whe I got him he looked fine but shortly there after got a transparent whitish lump. Now he is very weak and as you can see it is open. Can anyone tell me what it is and if it has now spread to the rest of my tank. He is now in seperate quarters but I don't know if he is going to make it.

 

[artista]

Is it a fungus or parasite? My blue damsel in with him is now getting it. If I were to remove them both, how long before it is out of my tank and safe for other fish? Those were the only two "fish" in the tank. I have a few snails, crabs and shrimp but I don't think they will be affected.
Thank You
Christy