Bit of a mystery. I'm stumped.

[MacDracor]

My LFS has this in one tank. No one knows what it is, it just appeared and started growing. Any thoughts?
It's squishy and when you wave a finger right next to it, it's surface ripples with the water flow.

 

[bettaowner]

It looks almost like a sponge but sponges are solid I believe so I have no idea.

 

[Sniperhank]

New too me, but cool.

 

[54seaweed]

looks like barnacles but you said it was soft
so I'm clueless