What is this coral-like growth?

[Trevorvano]

I’ve recently started noticing a few of these guys popping up in my tank. They look like some sort of anemone like coral but not one I ever put in there.
It’s kind of a small orange sphere shape with bright green points on small arms and then longer arms/tendrils with white specks on the end. I haven’t noticed anything being harmed by these but I don’t think it’s safe to just assume they’re fine.
Any ideas? I haven’t had much look on Google!
Thanks!
Trevor

 

[Crabs McJones]

Ball anemone Generally harmless, but can multiply quickly and bother coral if their numbers get out of hand. I have a few in my tank, they mainly stick to the shadows and don't bother anything

 

[Trevorvano]

Thanks for the quick response! I think they’re kind of cool so I suppose I won’t worry about them.
They do seem to have had a fairly sudden spurt in numbers, what would I do to keep them modest?
Also, around some of them there seems to be some white, cottony, almost cobweb-like substance. Is this anything to be concerned about?

 

[Crabs McJones]

Thanks for the quick response! I think they’re kind of cool so I suppose I won’t worry about them.
They do seem to have had a fairly sudden spurt in numbers, what would I do to keep them modest?
Also, around some of them there seems to be some white, cottony, almost cobweb-like substance. Is this anything to be concerned about?

Likely a sponge, best way to control their numbers is to make sure there isn't any excess nutrients in the tank. So don't feed heavy, feed just enough for your fish to consume