Calappa (crab)

Overview

Calappa Temporal range:
Calappa hepatica
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Infraorder:	Brachyura
Family:	Calappidae
Genus:	Calappa Weber, 1795
Species
41 extant species: see text

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.

Description

Calappa are benthic and found on sandy, shelly, and muddy sea beds at a wide range of depths. These crabs can be found from the shore to depths around 150 meters (500ft), with some species even being found deeper at around 250 meters (820 ft). This genus of crabs commonly inhabit reef areas, seagrass beds, and sandy flats where they can easily burrow and camouflage with the surrounding environment to avoid predation. 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 regions 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 Atlantic Ocean, Mediterranean Sea, and off the coast of Venezuela. Other species have also been found in different areas of Central America.

Physical Appearance

This genus is usually easily recognized by their distinctive appearances and specialized adaptation for their benthic lifestyles. Calappas are generally medium sized crabs that can range in size from about 4 cm to 15 cm across their carapaces. Of course sizing does range from species to species.

Most Calappas have a broad, rounded, and convex carapace, giving them their signature "boxy" look and where the common name "box crabs" comes from. They also have asymmetrical and highly specialized claws, usually with one being larger than the other for crushing the shells of their prey. The broad, flat claws' shielding posture gives rise to the other common name for this genus of crabs, "shame-faced crabs".

Calappas also exhibit a wide variation in carapace coloration and texture but many species are difficult to distinguish at various developmental stages. While maintaining a conserved morphology that is characterized by a broad, convex carapace and large chelae, individual species display a wide range of surface textures, from smooth and polished to coarsely granulated or finely ridged. One example would be the Calappa hepatica, which possesses a mottled grey-brown carapace that is adorned with small tubercles, that help to enhance its camouflage when it is semi-submerged in sandy substrate. Similarly, Calappa sulcata exhibits a range of coloration from pink to dark brown, with lateral margins featuring spines. These variations in texture and coloration are believed to enhance crypsis, which allows individuals to effectively blend into their specific benthic environments such as sandy substrates, coral rubble, and seagrass beds. These morphological differences reflect adaptations to localized habitat conditions and predator avoidance strategies across the genus.

Behavior and Adaptations

Calappas are known to be efficient burrowers that can dig into sediment rapidly. They alternate by pushing the sharp edge and sides of their carapaces down and backward in the sediment, they then shove their flattened claws forward against the sand. Once they have buried themselves, their claws are held tightly against the front of their bodies and since research is limited on specifics to Calappas, it can be inferred from other research on marine crustaceans with hairy appendages indicate that such structures play a role in manipulating water flow for respiration and feeding.

The mottled and variations in the coloring of their carapaces help them to blend in with their surrounding environment, making them difficult to be seen by predators unless they move. Some also have extensions along the sides of the carapace that cover their walking legs. Their large flattened claws also help to protect the head and delicate feeding structures from predators and abrasive sediment while they are burrowed.

The Calappas claws are specialized for feeding on mollusks, marine snails, and bivalves. Both of their claws are usually equally sized, with certain species one can be slightly larger than the other, but they are designed differently. The right claw has a large hook and heavy crushing knobs, which are used to crush and peel away pieces of shell from their prey until the soft body is exposed. After which, the left claw, which is more delicate with a pointed, moveable pincer, is used to pick off flesh from their crushed prey.

Like most crustaceans, Calappas are most active during the night. During this time they can be found hunting and scavenging for food. They can sometimes be found moving around during the day, likely due to disturbances to their burrows and changes in the tides. Like other burrowing crustaceans, the greater part of their lifespan is spent beneath the sand and inactive.

Ecological Role

Calappas play important roles in benthic ecosystems, as they help to control the populations of their prey and by recycling nutrients. By consuming dead and decaying organic matter on the ocean floor through scavenging, Calappas help to prevent the buildup of waste and recycle the nutrients back into their environments. By burrowing, Calappas help aid in nutrient redistribution and also help facilitate foraging opportunities for other species within their ecosystems. Their scavenging, nutrient cycling, and burrowing behaviors help to promote a healthy ecosystem where energy and nutrients are redistributed throughout their food chains.

Species

There are 43 extant species in the genus:

• 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 tortugae Rathbun, 1933
• Calappa torulosa Galil, 1997
• Calappa tuberculata (Fabricius, 1793)
• Calappa tuerkayana Pastore, 1995
• Calappa undulata Dai & Yang, 1991
• Calappa woodmasoni Alcock, 1896
• Calappa yamasitae Sakai, 1980

• 
  Calappa calappa
• 
  Calappa flammea
• 
  Calappa gallus
• 
  Calappa granulata
• 
  Calappa hepatica
• 
  Calappa japonica
• 
  Calappa lophos
• 
  Calappa philargius
• 
  Calappa sulcata

Extinct species

A further 18 species are known only from fossils.

• Calappa chungii Hu and Tao 1985
• Calappa costaricana Rathbun 1918
• Calappa earlei Withers 1924
• Calappa heberti Brocchi 1883
• Calappa lanensis Rathbun 1926
• Calappa laraensis Van Straelen 1933
• Calappa madoerensis Van Straelen 1938
• Calappa oboui Hu and Tao 1996
• Calappa pavimenta Schweitzer et al. 2006
• Calappa praelata Lorenthey 1929
• Calappa protopustulosa Noetling 1901
• Calappa restricta Milne-Edwards 1873
• Calappa robertsi Ross 1964
• Calappa sahelensis Van Straelen 1936
• Calappa sangiranensis Van Straelen 1938
• Calappa sexapinosa Morris and Collins 1991
• Calappa zinsmeisteri Feldmann and Wilson 1988
• Calappa zurcheri Bouvier 1899

Fossil of Calappa 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).