It kinda looks like a sponage...

[Ben Henwood]

So I had an elegance that jumped ship a few months ago and I left the skeleton in my tank and it has this growing on it...anyone know what it is? Kinda looks like some sort of sponage.

 

[rkpetersen]

Definitely looks like a sponge. All those tiny incurrent pores, the central large excurrent pores, and the lattice-like arrangement of spicules would be typical. What species, I have no idea.