what is this?

[KLG2015]

hey, does anyone know what this is? It appears and disappears whenever, it is bright orange and kind of cool. Before today we thought it was some sort of coral/mushroom but today it was on the glass and it's a snail! but no shell?
If you know what it is, is it harmful to fish or corals etc?
Thanks!

 

[Kristin1234]

Look like some type of nudibranch.

 

[1guydude]

That's really kool actually. Looks like an abalone to me. Hths
D

 

[bang guy]

I need a picture of the other side. I'm going to guess "Bubble Snail" based on what I see so far.