Normally they live in the sand and the rarely come in on zoathind rocks. A common one that does come in on zoanthid rocks is Phymanthus spp. (rock anemone). Unlike fire anemones their sting is mild.
Most the internet pictures don't show the tentacles enough. I've had these numerous times over the years and I still know where some of the ones I gave away are. They extend just like in the first pic of the thread.
They don't get all that big. They do not seem to irritate softies, zoas, mushrooms, ricordea, etc but sps and clams do not like them that much. They do not appear to oropigate out od control and in every tank i have seen them dlread, they all lived in zoa,paly coloniez... as uf they prefered them over every where else.
Their sting is not noticiable by me but I am nit sensitive to most reef life. Bee stings hurt far worse then lionfish stings to me :lol:
When Jim was at GM he had some for sale. My friend got them, not sure if that was all if them or not.