What is this on my frag

[prohopper]

The other day I bought 2 small frags one being a mushroom. Anyways after I placed them in my tank, the mushroom kinda lifted up a bit from the water flow and noticed this white thing underneath it. Any ideas what this is? Doesn't look like part of the mushroom but I could be wrong I'm still kinda new to corals.

 

[smartorl]

It looks like it could be a sponge. Maybe someone could come along with a little better id.

 

[prohopper]

I wish I could get a better picture of it. It almost resembles a brain as in it is made up of a bunch of squiggley lines kinda reminds me of what snail eggs look like on the glass.

 

[btldreef]

It's sponge. It's harmless and they come and go in our tanks. Consider it a good little hitchhiker.