Help Id

This guy started growing under my green leather just after I brought it home does any one know what it is? It is dark purple on the inside with bright green on the outside and has a very strange texture like a bunch of hexigons. It dosent seem to be encrusting the rock it seems to be growing outwords like a brain or a favia. Any clues?

 

a sponge probably.
harmless

 

Ive got other sponges in the tank but this one has tiny polyps that come and go and also it dosent grow at the rate that the sponges do.

 

I have dibs on a sponge. Doesnt look harmful. How fast is it growing/spreading? Is it growing over anything you dont want it to?

 

It almost looks like some sort of coral growth. I had bought a leather a while back and it never came out and eventually died off. But there was a tiny patch of some hard/ hair coral on the rock that ended up covering the whole thing. If it is a sponge it looks pretty cool.

 

Well, to my knowledge, sponges don't have polyps so I am thinking a Coral.

 

grows very slow but definetly has polyps