Knuckle Coral?

I went to Gerbers today just because and came across a strange looking coral that I never seen before. At first look, it looked something like a Ball Anemone. That is, a Pseudocorynactus... something I really want.

Naturally I asked about it. Blake told me that coral was known as a Knucklebone Coral and its hollow and inside there is a worm inside it. I never, ever heard of a coral like it and know nothing about it. A search online reveals very little. Almost no videos on youtube.



So who can tell me what a Knuckle Coral is, what its requirements are, how big they get, and any other information about it.



Please and thank you.