What's this 'shroom in my tank?

[zephyrlily]

I'm wondering if this is a type of cyano although I've had that before as a purplish sheet of slime growing all over my rocks. This is just a single growth I've had for a couple months and it's nowhere else in the tank. It started off as a dark brown/purple flat velvet growth and has bulged out since then appearing more like a mushroom, super soft, its diameter has never really increased (about 1/2") just slowly grown in height.

 

[heartben]

if its a mushroom it looks like a "blue" mushroom to me.
but, im no expert. just go to the coral section on the website and click it and take a look.

 

[zephyrlily]

No corals, it's not a reef tank, the same rocks have been in there for 4+ years. The only other thing added to the tank besides fish were a couple of medium size snails from tidepools, one had some nice coraline spots on its shell, maybe something else hitched on it. Any guesses?

 

[clay12340]

The picture isn't detailed enough to offer much, but it could be a sponge of some type or a mushroom coral. They are easily spread and if a fragment was attached to something you added to the tank it could have floated off and attached there. I'd be more inclined to think it is a sponge as a mushroom would look more like an umbrella than a lump, but based on the picture the best I can say is that you've got something purple.