Calappa calappa. These crabs show some variation in color. The video also shows a smaller one that is white with darker spots. They tend to live buried in sand by day, coming out only at night. They use those large, strong pincers to break up had seashells, eating the animals that live within. The crabs also use the claws to bury  themselves in the sand. The video has a sequence showing how quickly these crabs can disappear in this manner. Because of the shape of the carapace, we like to call these the "Darth Vader Crabs."