The shell is very convex and narrower towards the front. The edges are initially ragged while the rear part has well-developed teeth which the crab uses to retract its thoracic appendages. The enormous claws are flat on the inside and have tubercles and a toothed crest on the outer side. The top of the shell is characterized by longitudinal cleavages and tubercles and is yellowish in colour with a mottled red pattern on its carapace and claws.
The box crab is also known as the bashful or shamefaced crab because when he wraps his claws around his body for protection it appears that he is hiding or being bashful. Egg laying females have been spotted between June and September. The crab feeds mainly on molluscs and larger specimens appear to protect their young under their claws.