Help id

[LastingReaper]

This was attached to the live rock that was bought from a fish store and need help figuring out what it is.

 

[Tuan’s Reef]

It is called hidden cup coral.

 

[ChiCity]

ball anemone

 

[Rtaylor]

Agree it’s either a hidden cup coral (Phyllangia americana) or more likely from what I can see in your pic a ball anemone (Pseudocorynactis caribbeorum). It’s easy to tell the difference in person as the hidden cup coral has a stony skeleton.

 

[GoReefin]

Looks like a ball anemone pretty neat hitchhiker!