I was wondering about this spot on my wall hammer. (It is the round spot sticking out towards the back). It is about the size of half a dollar and if you get near it, it sinks back into the skeleton. Is this possibly new growth? I know they are very slow growing, and can grow in crazy ways. Also, does coralline algae grow on the skeleton of these? On the other side, it looks like some has started to grow on it. It is growing on the glass near it, so I am pretty sure that is what it is. (You can't see it in this photo really. You might can see some in the reflection on the glass).