Tubuca signata

Tubuca signata, the signalling fiddler crab, is a species of fiddler crab that is found in Australia from Queensland to northwestern Australia.

Description
Tubuca signata males have one claw that is significantly larger than the other, while females have two equal-sized smaller claws. The male adult upper claw (pollex) is smooth and bright white while the lower claw (dactyl) has a single groove along its length. The wrist (manus) is red. The male carapace is typically up to 17 mm wide (95% of individuals are this size or smaller), with females slightly smaller.