The maximum length of the carapace in U. rapax is about 2.1 cm (Crane 1975, Kaplan 1988), although most specimens collected are between 7 and 18 cm (Koch et al. 2005). The major claw in male fiddlers is must larger than the carapace, with a maximum length of 6.3 cm (Crane 1975). As in other Uca species, the lifespan of the mudflat fiddler is relatively short, lasting only about 1.4 years (Koch et al. 2005).
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