Eating Nose to Tail

Having a few good oysters when the mood strikes you is one of the best parts of living in New England.  After picking up a dozen or so at a reputable fishmonger, I pop open the first one to find this.
Has anyone ever seen anything like this?  For those that don't have the best eyesight that's a tiny, vaguely see-through crab inside my oyster.

Oysters by nature are a all-or-nothing creature.  Anything that's not the shell goes down that hatch - I'm not too sure about this little guy though.  Glad I noticed him before I got an extra crunchy bit in my oyster.