Possible coral or sponge? Can it move?

[stevelikesfish]

Please see pic below.. This is what I thought was a small coral or sponge growning on my new LR. Today I got up and it was gone... not fallen out, not in the hole (unless deep) and nowhere else in the tank...

Could anyone explain its dissapearance? The tank it currently maturing, so no fish, although I have 3 porcelain crabs in there, but I dont think they could eat that thing in one sitting?

Anyways, over to you guys!

 

[seafan]

Look at the Montipora topic, it has the same encrusting algae.