Intraspecific variation in preserved specimens of the fiddler crabs Uca panacea and Uca pugilator (Decapoda: Ocypodidae)

The fiddler crabs Uca panacea Novak & Salmon, 1974 and Uca pugilator (Bosc, 1802) are closely related North American species that are sympatric along the north coast of Gulf of Mexico. Since U. panacea was described, there has been confusion in the identification these two species. Morphological differences between these two fiddlers have been pointed out in recent years, mainly regarding the presence of a pigment spot and granulations on the dorsal margin of carapace in U. pugilator. We report herein some intraspecific differences between the two species that we believe to be useful in avoiding misidentification among preserved specimens of these two fiddler crabs, such as the absence of the pigment spot in U. pugilator and the presence of the pigment spot and granulations on dorsal margin of carapace in U. panacea as well. Our results have also revealed that 65% of the U. pugilator specimens examined possess a gape pile in the major chela, which is not a reliable diagnostic character, but could be useful when present. The gonopods of both species were analyzed using SEM, confirming the previous statement that the sub-terminal thumb is shorter in U. panacea than in U. pugilator. Finally, as important morphological characters are missing in the original description of U. panacea, a redescription of this species is also provided.