Cave crab shells varied along a spectrum between white and translucent, and housed circular pockets of bacteria that produced dots of white bioluminescent light. Their two claws were asymmetrical. The right one was much larger, and they favored it when attacking their prey. Their eyes were six times the size of an ordinary crab. Cave crabs of the ancient variety could be three feet long at their widest point.
They dwelt in brackish water pools within seaside caves, and they could go years between meals. Their metabolism was slow and they rested in a state of motionless hibernation, but an opportunity to eat sent them in to an aggressive frenzy.