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.
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.
Crab