What is this?

[derrick.hiebert]

Any idea what this is?

I circled it in the picture

Thank you!

 

[WheatToast]

Ball “anemone” (Pseudocorynactis caribbeorum) or a similar coral. These are common hitchhikers that are generally benign and multiply much more slowly than Aiptasia

 

[derrick.hiebert]

Should I leave it there or will they eventually become a problem?

 

[WheatToast]

Should I leave it there or will they eventually become a problem?

I would leave it. Neat find!

 

[Mikedawg]

+ 1, good find and adds interest and diversity imho.

 

[vetteguy53081]

Many regard Ball anemone as a pest and a majority keep them based on their beauty and colors. While called anemone, they are actually a mushroom and get the name from the series of little balls and row of tentacles found on rock and other ornamental anemones
As Wheat Toast indicated- a good find and keeper requiring no special care