Fiddler Crab Uca annulipes male
To be honest, I am not sure that these fiddler crabs I have seen in Lembeh Island are all U. annulipes but they are Uca genus. The reason is because within the species they vary their coloration and their claw can be located in the left or the right arm. Moreover, when they loose the claw they will develop a new one on the opposite arm. I have seen crabs with a yellow claw and others with a red claw. I tried to find out if the yellow is a second claw grown after loosing the first claw, presumably red? but I could not find a color explanation. The females do not have this massive claw and are otherwise also of variable colors but without the design/pattern the males have on the carapace.
More on this here:
And here a video:
''Uca annulipes'' is a species of fiddler crab found along the coastline from South Africa to Somalia, Madagascar, India, China, Indonesia, Malaysia and the Philippines.