It could be any of the species listed above in my copy and pasted list of known species... I do not have the technology to give the op a DNA test to prove which species it is taxonomically speaking. Since that is really the only true way to distinguish between certain Zoanthus species. With the exception of Z. Gigantus, which is easily distinguishable.... Hence why it was not listed above.
If I had to make a guess to narrow the list down I would say Z. pacificus, Z. sociatus, Z. vietnamensis, or Z. sansibaricus. As these are some of the most commonly collected Zoanthus...