Anyone know what this is?

[Lee]

This little (dime/nickel size) hard coral has been in my tank for years now. It came on a piece of live rock that I put in my tank when I first set up the tank. In the past, while aquascaping, I have grabbed the rock not realizing that I was squishing this little guy. It has at times looked completely dead, leaving a hard circular skeleton on the rock. Over time it has come back and recently had to be moved because it was stinging a nearby frag. Any idea what it is?

 

[fishman1069]

It looks like an acan from the pic but I'm thinking it might be a ball anemone

 

[Lee]

It looks like an acan from the pic but I'm thinking it might be a ball anemone

Thanks for the suggestions, but I don't think it's a ball anemone because it has a hard skeleton. I also don't think it's an acan because it is only a single polyp. I have acans in my tank that have grown to about 4 times their original size and have been in the tank less time than this hitch hiker. Whatever it is, it's very slow growing and very resilient.

 

[Lee]

Some more pictures

 

[tomtoothdoc]

cup coral

http://www.arkive.org/devonshire-cup-coral/caryophyllia-smithii/

http://www.reefsanctuary.com/forums/aquarium-corals/29797-care-hidden-cup-coral.html

 

[Lee]

cup coral

http://www.arkive.org/devonshire-cup-coral/caryophyllia-smithii/

http://www.reefsanctuary.com/forums/aquarium-corals/29797-care-hidden-cup-coral.html

Thank you Tom. I think that's it.