Not a frequenter of this thread, but just thought I'd stop by and add this:
It's not uncommon for crabs to lose limbs/claws, and they are able to grow them back when they molt. The most interesting of these phenomena occurs with the fiddler crab -- that's the one with one giant claw and one tiny one.
If the giant arm of the fiddler crab falls off, then two things happen: 1) the large arm is regrown as a smaller arm, and 2) the once-smaller arm begins to grow, until it becomes the large arm.
The more you know, etc.