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. The name calappa is associated with kelapa, the Malay word for 'coconut'.
Distribution Calappa are benthic and found on sandy, shelly, and muddy seabeds. They are found from the shore to depths of around , with some species being found deeper at around . They commonly inhabit reef areas, seagrass beds, and sandy flats where they can easily burrow and camouflage with the surrounding environment. They are typically found in warm marine environments, favoring tropical and subtropical climates. 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. 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. Other species have also been found in Central America.
Description Calappa generally range in carapace width from about . Most Calappa have a broad, rounded, and convex carapace. This in conjunction with its broad, flat, shield-like claws give the crab a box-like appearance. The claws' shielding posture gives rise to the other common name, "shame-faced crabs". 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.
Behavior Calappa are known to burrow in the seabed. They push their chelae forward against the substratum which in turn pushes their carapace down and backward into the sediment. Through this process, Calappa either submerges itself completely or leaves just its eyes exposed. This burial process disturbs the substratum and has been observed to inadvertently aid fish in hunting invertebrates and small fish hiding in the seabed.
Calappas chelae are specialized for feeding on marine gastropods and bivalves. 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. The right chela has a thick, calcified apodeme, broad teeth, and greater mechanical advantage than the left. It is used to crush or shear shells, but it is not robust for this task. 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. 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. 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.
Species Calappa contains the following extant species:
Calappa acutispina Lai, Chan & Ng, 2006 Calappa africana Lai & Ng, 2006 Calappa bicornis Miers, 1884 Calappa bilineata Ng, Lai & Aungtonya, 2002 Calappa calappa (Linnaeus, 1758) Calappa capellonis Laurie, 1906 Calappa cinerea Holthuis, 1958 Calappa clypeata Borradaile, 1903 Calappa conifera Galil, 1997 Calappa convexa Saussure, 1853 Calappa dumortieri Guinot, 1962 Calappa exanthematosa Alcock & Anderson, 1894 Calappa flammea (Herbst, 1794) Calappa galloides Stimpson, 1859 Calappa gallus (Herbst, 1803) Calappa granulata (Linnaeus, 1758) Calappa guerini De Brito Capello, 1871 Calappa hepatica (Linnaeus, 1758) Calappa japonica Ortmann, 1892 Calappa karenae Ng & Lai, 2012 Calappa liaoi Ng, 2002 Calappa lophos (Herbst, 1782) Calappa monilicanthus Latreille, 1812 Calappa nitida Galil, 1997 Calappa ocellata Holthuis, 1958 Calappa ocularia Holthuis, 1958 Calappa pelii Herklots, 1851 Calappa philargius (Linnaeus, 1758) Calappa pokipoki Ng, 2000 Calappa pustulosa Alcock, 1896 Calappa quadrimaculata Takeda & Shikatani, 1990 Calappa rosea Jarocki, 1825 Calappa rubroguttata Herklots, 1851 Calappa sebastieni Galil, 1997 Calappa springeri Rathbun, 1931 Calappa sulcata Rathbun, 1898 Calappa torulosa Galil, 1997 Calappa tuberculata (Fabricius, 1793) Calappa undulata Dai & Yang, 1991 Calappa woodmasoni Alcock, 1896 Calappa yamasitae Sakai, 1980
Extinct species Calappa contains the following extinct species:
Fossils of species within this genus can be found in sediment of Europe, United States, Mexico, Central America, Australia and Japan from Paleogene to recent (age range: 33.9 to 0.0 Ma).
See also Coconut crab References
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