Thick-legged Fiddler Crab

Description:

Wikipedia: Male fiddler crabs use the major claw to perform a waving display as a form of female courtship. Females choose their mate based on claw size and also quality of the waving display. In many fiddler crab species, the female occupies the burrow of their mate while she lays her clutch of eggs. Research shows that the male major claw size is also correlated with burrow width; the width of the burrow influences incubation temperature. Therefore, the female will choose a male mate whose claw size indicates the best burrow environment for her clutch of eggs. Male versus male competition also occurs as a fighting with the major claws. If a male loses his larger claw, the smaller one will begin to grow larger and the lost claw will regenerate into a new (small) claw. For at least some species of fiddler crabs, however, the small claw remains small, while the larger claw regenerates over a period of several molts, being about half its former size after the first molt.

Habitat:

Near mangroves at Pasir Perawan Beach, Pari Island, Thousand Islands Marine National Park

Notes:

I think the color of the carapace is depends on the age..