The second pair of appendages for organisms in the subphylum Chelicerata (which include horseshoe crabs and arachnids). The chelicerae (first pair of appendages) and the pedipalps may be modified to perform a range of functions including food manipulation and sensing, locomotion, defense, and reproduction.
Results from our forum
... pretty common: http://www.springerlink.com/content/q966617t331652k1/ (Note: the "mating only once" idea was based on observations of pedipalp damage, which apparently affects but doesn't preclude future matings) http://www.blackwell-synergy.com/doi/abs/10.1111/j.1439-0310.2005.01114.x ...
See entire post