Box Crab

About

Found across Indo-Pacific reef systems from Japan and Sri Lanka down to Australia, Calappa lophos is a box crab recognized by its broad, rounded carapace and large claws that fold neatly up against the front of the shell like a pair of doors. This folded posture is not just for show. It seals the crab's vulnerable face and gills behind a wall of chitin, giving the animal a boxy, almost geometric silhouette when at rest. In the wild it occupies reef-associated habitats from fairly shallow water down to around 100 meters, spending much of its time partially buried in sandy or rubble substrate. Despite being labeled freshwater in some hobbyist listings, this species is genuinely marine, requiring saltwater conditions consistent with a reef environment. The water parameters it needs reflect that. Stable salinity and alkaline, well-buffered chemistry are non-negotiable. In an aquarium context it needs space to move and dig, and a sandy bottom to accommodate its burrowing tendencies. Its omnivorous diet makes feeding relatively straightforward, though its intermediate care rating reflects the importance of maintaining consistent marine water quality. Specific behavioral details in captivity are not well documented, so this one suits a keeper willing to observe and learn as they go.