Fishing Little Cayman

name of weird crab-like fish in Caymans?
i came across a really weird crustacean while snorkeling on the north side of Grand Cayman. Similar shell to a lobster, no tail. instead of claws, it had 2 really long sharp arms. Underneath were hundreds of little brushlike legs (or what looked like legs, they seemed to allow the thing to move), nthese legs were concealed under the lobster like shell.
i don’t have a picture to refer to, so i hope my explanation provides enough clues… Thanks!
I was a prawn, and if it was the size of a lobster it was more than likely a Tiger prawn. Heres a link….
http://en.wikipedia.org/wiki/Tiger_Prawn
Little Cayman – 2006 June – “Sealife”