We were shipped one a few weeks back, it looks like an over inflated sand dollar. It slowly wasted away in our tanks, it burries itself in the sand, so i assume that it goes after the sand bed fauna like a sand sifting star. IMO, i'd treat it like a large sand sifting star, best left in the ocean. But, of course, we could be talking about different things...
I attempted to feed it several times, but w/ no success. Good luck with it, although you really should have posted this before you put it into your tank.