What is this flower like growth?

[Bham]

I'm currently cleaning up a hair algae problem in my tank and I noticed this growing on my Halloween hermit. I tried googling it and looking up algae and I can't find anything about it. Not concerned bit curious as to what it is.

 

[Billdogg]

octocoral of some sort.

 

[Bham]

octocoral of some sort.

Could that show up after months of not adding anything to the tank? I have no corals and did not use live rock.

 

[Billdogg]

Sure. They were probably nearly invisible specks on it's shell when you got it. That's how tthe name "hitchhikers" came into use!!! Don't worry - as time goes on more will appear seemingly from nowhere. Most will be benign, some not so much. I've been at this for over 30 years and still find new things from time to time. It is one of the aspects of this hobby that I find so amazing.