Calappa is a genus of crabs known commonly as box crabs or shame-faced crabs. The name box crab comes from their distinctly bulky carapace, and the name shame-faced is from anthropomorphising the way the crab's chelae (claws) fold up and cover its face, as if it were hiding its face in shame.[2]
Calappa are benthic and found on sandy, shelly, and muddy seabeds.[citation needed] They are found from the shore to depths of around 150m (500ft), with some species being found deeper at around 250m (820ft).[citation needed] They commonly inhabit reef areas, seagrass beds,[citation needed] and sandy flats where they can easily burrow and camouflage with the surrounding environment.[citation needed] They are typically found in warm marine environments, favoring tropical and subtropical climates.[3][failed verification] Many species, like Calappa calappa and Calappa hepatica, are common in the Indo-Pacific region and can be found in areas such as the Red Sea, Hawaii, French Polynesia, Cocos Island, and northern Australia.[3][failed verification] They can be found in other parts of the world, such as Calappa granulata, which has been found in the Mediterranean Sea and off the coast of Venezuela.[4][5] Other species have also been found in Central America.[6]
Description
Calappa generally range in carapace width from about 6–15cm (2.5–6in).[3] Most Calappa have a broad, rounded, and convex carapace.[3] This in conjunction with its broad, flat, shield-like claws give the crab a box-like appearance.[3] The claws' shielding posture gives rise to the other common name, "shame-faced crabs".[3]Calappa are often difficult to distinguish based on morphology alone, and thus molecular phylogenetics are sometimes used alongside morphometrics to identify specimens with unique color patterns, size ranges, and textures.[7]
Behavior
Calappa are known to burrow in the seabed.[8] They push their chelae forward against the substratum which in turn pushes their carapace down and backward into the sediment.[9] Through this process, Calappa either submerges itself completely or leaves just its eyes exposed.[8] This burial process disturbs the substratum and has been observed to inadvertently aid fish in hunting invertebrates and small fish hiding in the seabed.[10]
Calappa's chelae are specialized for feeding on marine gastropods and bivalves.[11] A study of the feeding behavior of C. ocellata found that the chelae are of about equal size but differ noticeably in function and internal morphology.[12] The right chela has a thick, calcified apodeme, broad teeth, and greater mechanical advantage than the left.[13] It is used to crush or shear shells, but it is not robust for this task.[14] Likely to compensate for this, the outside face of the right chela additionally features a "peg and cusp" structure which is used like a can opener to break the lip of gastropod shells.[15][3] The left chela is slim, pointed in a beak-like fashion, lined with small, pointed teeth along the propodus, and fringed with setae which may be used for sensing.[16] It is used for faster or more delicate tasks such as holding a shell in place during crushing, picking flesh from crushed prey, and possibly capturing agile prey.[14]
Species
Calappa contains the following extant species:[17]
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