What is this?

[Gareth elliott]

Found during a water change currently put in my sump in a breeder box

 

[aKlevans]

ball anemone

 

[keddre]

Ball anemone. Not sure how mug they get, but it appears harmless, I have two

 

[Gareth elliott]

Thanks, will let it back into main looked too suspicious to leave when i saw it lol.
Pseudocorynactis globulifera?

So if want to keep should reattach to a rock looks like they dont move like true anemones?

 

[Oldsalt01]

Ball 'nems generally don't get over 1/2" in diameter. Mine LOVE live brine shrimp. Yah, I intentionally feed em! If you want to keep it, find a nook in the rock. It'll settle right in, and no, they don't move around.