Do you know what this is?

[SandyFeet]

I just bought a previously owned Nano Cube (24 gallon)
I was moving some sand around and this little bulby type thing popped up out of the sand. if anyone knows what this might be, I'd love to know.
Thanks!

 

[melosu58]

'Bubble' Alage: Selected Descriptions, Controls and Comments by Horge Cortes-Jorge, Jr. - Reefkeeping.com

Welcome aboard.

 

[trackfast]

Hi! Remove it w/o popping it or else spores will be released.

 

[SandyFeet]

Thank you!!!!!!!