Looks like some kind of crab to me.. maybe a deep water type, something where there is no light. I noticed the little "lights" along the appendages.
Peg
Edited;
Just a thought. When I lived in the VI there were shells everywhere on the beaches, that when assembled (if one could find enough of them) resembled a trilobite type shellfish. The shells are very hard, I still have some that I collected years ago. The animal is shaped somewhat like the one in the picture. The shells I have are sections, one lays over the other, and resemble boomerangs... except the flat is on the other angle.