I'm kinda going out on a limb here because i don't really know what I'm talking about
but could it be a Cryptodendrum adhaesivum, AKA pizza anemone?
There is something about the frilly outside edges of yours that reminds of pictures I've looked at and the foot does look similar to some of the ones in this link
http://www.carlosreef.com/AnemoneFAQ.pdf