Crabs & Claws

Most populations of fiddler crabs are equally divided between right and left handers. This guy has the huge signalling claw on the left. The small feeding and grooming claw is on the right.  Handedness is determined genetically.

  The red land crab, Gecarcinus, has more or less equal sized claws. That may mean that they are ambidextrous but one claw is always a little larger than the other -- and that’s the one that gets you!
This gray-blue land crab is clearly right handed but scary as it may be, the claw is not a weapon of war but of propaganda, a potent signal to rivals, and enticement to the ladies.  
  This monster Tasmanian king crab is another righty. I guess somebody has to take them out of the crab traps but not me, thank you.
And this little lobster from Nova Scotia would pose a bit of a challenge. In my research I worked the lobsters boats on the coast of Maine but was never confronted with one like that. And, incidentally, that one is right handed. Right or left handedness is determined after larval life according to the use of the claws. It is an epigenetic phenomenon.  

Pistol shrimps use their large claw to stun their prey. If they lose or damage it, they go hungry. In that case the remaining claw replaces the pistol at the next molt. They change handedness. This, too, is an epigentic process, controlled by the circumstances of use.