A Study of the Normal and Aberrant Sexual Types of the Venezuelan Fiddler Crabs Uca Cumulanta and U. Rapax

Wild populations of two species of Venezuelan fiddler crabs, Uca cumulanta and U. rapax, were examined to determine the occurrence of normal and aberrant sexual types, sex ratios, and frequencies of right- and left-handed males. Several grades of sexuality occur. Young U. cumulanta, measuring 1.5 to 5.0 mm, can be identified as: sexuality undifferentiated symmetricals, females, right-handed males (dextrals), left-handed males (sinistrals), “exceptional” males with two small claws, and females with narrow abdomens beside other doubtful forms. Males and females of U. cumulanta can be distinguished in some cases as small as 1.7 mm carapace width. Supermales with two large claws, which have been reported to occur in other species of Uca, were not found in either of the two species. The dextral and sinistral males were about equally represented in different size classes from the two species. Sinistral males in some cases were slightly but not significantly in excess. Both merely appear to be alternative forms of each other. Males and females occur in approximately equal numbers in smaller size classes but males outnumber females in the large size classes, possibly because adult females avoid capture by burrowing deeper.