This guide is designed for identification “in the field” where you might be looking at live crabs by eye or through binoculars or from photographs. I will generally try to avoid characters that will require you to physically catch the crab, although I may mention a few for secondary verification. It does not include the more strict taxonomist-style characters that may only be visible under a microscope or via dissection. It is also assumed that the individuals are living, as death (and even capture) can cause dramatic color change.
This is a guide to the fiddler crabs of Uruguay and Argentina. There is only one fiddler crab species in this entire region, so identification is easy.
Leptuca uruguayensis is the southernmost fiddler crab in the world and the only American species that extends south of Brazil into Uruguay and northern Argentina.
