Any Idea What This Is?

[revhtree]

I was rearranging some LR, and came across this one rock that these patches on it. It's the only rock that has it, and it is on the underside of the rock to. Looking closely at it, it looks to be rigid, or somewhat pourous. It is a deep purple color, it is soft, and it has that slimy film on it like corals do. Any idea what it may be??

Thanks!

PS. The picture is bad in part to all the debris floating around from my aquascaping!

 

[Fluff]

I would say a sponge. Especially if it is growing on the underside of your rock.

 

[MACATUA]

Pretty though!

 

[SeriousDude5]

Maybe a shroom