I have always just thought him a common pacific rock anenome, but friends and I have argued since he changes colors and he doesnt have the long trunk like rocks typically do. I just figured he doesnt like the sandbed so he never needed to grow the trunk but they disagree and say hes not a rock. Long standing argument, I actually have two of them, neither with trunks and niether like the sand bed. Both been in this tank for about 2 years