Maxilliped-setation in two Australian fiddler crabs, Uca perplexa (n = 104) and U. vomeris (n = 128) was studied and related to the habitats in which these crabs live. Both species were collected from the banks of Myora Springs, North Stradbroke Island, Queensland, Australia. We counted the total number of setae (both plumose and spoon-tipped) on: 1) the inner and outer surfaces of the first and second maxillipeds, and 2) the inner surface of the third maxilliped. In general, there is no distinct sexual dimorphism for both types of setae in the two species. For any given size of crab, significantly more spoon-tipped setae were present in U. perplexa than in U. vomeris, providing further quantitative evidence that fiddler crabs from sandy habitats possess more spoon-tipped setae (an adaptation for processing sandy sediments) than those living in muddy habitats. No significant difference in plumose setation between the two species was generally detected; perhaps plumose setation is of less adaptive significance in terms of habitat adaptation than spoon-tipped setation in these two species. There is generally no sexual dimorphism in the size of the three maxillipeds for both species. Uca perplexa males had longer minor chelipeds than females while U. vomeris males had minor chelipeds that are deeper in the centre than females. These results provide evidence that male fiddler crabs could compensate for their foraging handicap by having longer or deeper minor chelipeds which enable them to scoop larger amounts of substrate.
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Vol. 31 • No. 3