Reef Box Crab

Calappa hepatica, commonly known as the reef box crab, is a prevalent benthic species found in tropical and subtropical regions of the 🇮🇳 Indian and 🌊 Pacific Oceans, as well as the 🌊 Red Sea.

This species attains a carapace width of approximately 4 centimeters (1.6 inches), with a length that is consistently less than two-thirds of its width. The posterior part of the carapace features broad extensions with multiple blunt marginal teeth, which effectively conceal the walking legs. The carapace and the exposed sections of the chelae (pincers) exhibit a mottled greyish-brown hue and are adorned with numerous small, raised tubercles of varying sizes. This morphological adaptation provides excellent camouflage when the crab is partially buried in the sand. The chelae are substantial and robust, tailored to the crab's diet, which primarily consists of molluscs.

Calappa hepatica inhabits the tropical and subtropical Indo-Pacific region, with its distribution spanning from the 🌊 Red Sea to Hawaii (🇺🇸 United States), 🇵🇫 French Polynesia, 🇨🇨 Cocos Island (🇦🇺 Australia), and northern 🇦🇺 Australia. Its preferred environments include sandy or shelly sand seabeds, reef habitats, and seagrass meadows, at depths reaching up to approximately 150 meters (500 feet).

During daylight hours, Calappa hepatica tends to remain buried in the sand with only its eye area exposed. It emerges nocturnally to forage for prey and can efficiently re-bury itself if threatened. This species is predominantly a predator, feeding on bivalve and gastropod molluscs, as well as hermit crabs. The right chela is specifically adapted for breaking open mollusk shells, featuring a large accessory tooth at the base of the claw's hinged part, which works in conjunction with a flat plate on the fixed part, functioning similarly to a vice. After breaching the shell, the crab utilizes its left pincer, which is longer and more pointed, to extract the soft tissues.