Morphological Differentiation and Molting of Juvenile Fiddler Crabs (Uca Pugilator and U. Pugnax)

Abstract

Because juveniles of tbe fiddler crabs Vea pugilator and Vea pugnax have been difficult to distinguish morphologically, little comparative work has been do ne on young stages of these abundant and ecologically important inhabitants of salt marshes. Here I describe a way to differentiate early crab instars of the two species by the number of spoon-tipped setae on tbe meropodite of the second maxilliped. Several broods of each species were reared fro m eggs through the first several crab instars. By the time they rea. cbed 3-4 mm carapace wid th u. pugilator developed several spoon-tipped setae, whereas U. pugnax had none, indicating that juveniles of these species can be distinguished based on the early development of adult characteristics in U. pugi/ator. 1 also recorded m olting frequency of j uvenile U. pugi/ator through the sixth crab instar and found significant variability among broods in duration of several crab instars, a phenomenon that should be taken into account in future rearing studies.