structural:expansion, structural:summarization, structural:reformatting
Sexual dimorphism

Crabs often show marked sexual dimorphism. Males often have larger claws, a tendency that is particularly pronounced in the fiddler crabs of the genus Uca (Ocypodidae). In fiddler crabs, males have one greatly enlarged claw used for communication, particularly for attracting a mate. Another conspicuous difference is the form of the pleon (abdomen); in most male crabs, this is narrow and triangular in form, while females have a broader, rounded abdomen. This is because female crabs brood fertilised eggs on their pleopods.