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Crabs are decapod
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
s of the infraorder Brachyura, which typically have a very short projecting " tail" ( abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the world's oceans, in
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
, and on land, are generally covered with a thick exoskeleton, and have a single pair of pincers. They first appeared during the Jurassic Period.


Description

Crabs are generally covered with a thick exoskeleton, composed primarily of highly mineralized
chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
, and armed with a pair of
chelae A chela ()also called a claw, nipper, or pinceris a pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds. ...
(claws). Crabs vary in size from the pea crab, a few millimeters wide, to the Japanese spider crab, with a leg span up to . Several other groups of crustaceans with similar appearances – such as king crabs and porcelain crabs – are not true crabs, but have evolved features similar to true crabs through a process known as carcinisation.


Environment

Crabs are found in all of the world's oceans, as well as in
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
and on land, particularly in tropical regions. About 850 species are
freshwater crabs Around 1,300 species of freshwater crabs are distributed throughout the tropics and subtropics, divided among eight families. They show direct development and maternal care of a small number of offspring, in contrast to marine crabs, which relea ...
.


Sexual dimorphism

Crabs often show marked sexual dimorphism. Males often have larger claws, a tendency that is particularly pronounced in the fiddler crabs of the genus ''Uca'' ( Ocypodidae). In fiddler crabs, males have one greatly enlarged claw used for communication, particularly for attracting a mate. Another conspicuous difference is the form of the pleon ( abdomen); in most male crabs, this is narrow and triangular in form, while females have a broader, rounded abdomen. This is because female crabs brood fertilised eggs on their
pleopod The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...
s.


Reproduction and lifecycle

Crabs attract a mate through chemical ( pheromones), visual, acoustic, or vibratory means. Pheromones are used by most fully aquatic crabs, while terrestrial and semiterrestrial crabs often use visual signals, such as fiddler crab males waving their large claws to attract females. The vast number of brachyuran crabs have internal fertilisation and mate belly-to-belly. For many aquatic species, mating takes place just after the female has moulted and is still soft. Females can store the
sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
for a long time before using it to fertilise their eggs. When fertilisation has taken place, the eggs are released onto the female's abdomen, below the tail flap, secured with a sticky material. In this location, they are protected during embryonic development. Females carrying eggs are called "berried" since the eggs resemble round berries. When development is complete, the female releases the newly hatched
larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...
into the water, where they are part of the plankton. The release is often timed with the tidal and light/dark diel cycle. The free-swimming tiny zoea larvae can float and take advantage of water currents. They have a spine, which probably reduces the rate of predation by larger animals. The zoea of most species must find food, but some crabs provide enough yolk in the eggs that the larval stages can continue to live off the yolk. Each species has a particular number of zoeal stages, separated by moults, before they change into a megalopa stage, which resembles an adult crab, except for having the abdomen (tail) sticking out behind. After one more moult, the crab is a
juvenile Juvenile may refer to: *Juvenile status, or minor (law), prior to adulthood *Juvenile (organism) *Juvenile (rapper) (born 1975), American rapper * ''Juvenile'' (2000 film), Japanese film * ''Juvenile'' (2017 film) *Juvenile (greyhounds), a greyho ...
, living on the bottom rather than floating in the water. This last moult, from megalopa to juvenile, is critical, and it must take place in a habitat that is suitable for the juvenile to survive. Most species of terrestrial crabs must
migrate Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
down to the ocean to release their larvae; in some cases, this entails very extensive migrations. After living for a short time as larvae in the ocean, the juveniles must do this migration in reverse. In many tropical areas with land crabs, these migrations often result in considerable
roadkill Roadkill is an animal or animals that have been struck and killed by drivers of motor vehicles on highways. Wildlife-vehicle collisions (WVC) have increasingly been the topic of academic research to understand the causes, and how it can be mi ...
of migrating crabs. Once crabs have become juveniles, they still have to keep moulting many more times to become adults. They are covered with a hard shell, which would otherwise prevent growth. The moult cycle is coordinated by hormones. When preparing for moult, the old shell is softened and partly eroded away, while the rudimentary beginnings of a new shell form under it. At the time of moulting, the crab takes in a lot of water to expand and crack open the old shell at a line of weakness along the back edge of the
carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
. The crab must then extract all of itself – including its legs,
mouthparts Mouthparts may refer to: * The parts of a mouth ** Arthropod mouthparts *** Insect mouthparts {{disambig ...
, eyestalks, and even the lining of the front and back of the digestive tract – from the old shell. This is a difficult process that takes many hours, and if a crab gets stuck, it will die. After freeing itself from the old shell (now called an
exuvia In biology, exuviae are the remains of an exoskeleton and related structures that are left after ecdysozoans (including insects, crustaceans and arachnids) have moulted. The exuviae of an animal can be important to biologists as they can often b ...
), the crab is extremely soft and hides until its new shell has hardened. While the new shell is still soft, the crab can expand it to make room for future growth.


Behaviour

Crabs typically walk sideways (a behaviour which spawned the term crabwise), because of the articulation of the legs which makes a sidelong gait more efficient. Some crabs walk forward or backward, including raninids, '' Libinia emarginata'' and '' Mictyris platycheles''. Some crabs, like the Portunidae and Matutidae, are also capable of swimming, the Portunidae especially so as their last pair of walking legs are flattened into swimming paddles. Crabs are mostly active animals with complex behaviour patterns such as communicating by drumming or waving their pincers. Crabs tend to be aggressive toward one another, and males often fight to gain access to females. On rocky seashores, where nearly all caves and crevices are occupied, crabs may also fight over hiding holes. Fiddler crabs (genus ''Uca'') dig burrows in sand or mud, which they use for resting, hiding, and mating, and to defend against intruders. Crabs are
omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutr ...
s, feeding primarily on algae, and taking any other food, including
mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
s, worms, other
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
s, fungi,
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
, and
detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
, depending on their availability and the crab species. For many crabs, a mixed diet of plant and animal matter results in the fastest growth and greatest fitness. Some species are more specialised in their diets, based in plankton, clams or fish. Crabs are known to work together to provide food and protection for their family, and during mating season to find a comfortable spot for the female to release her eggs.


Human consumption


Fisheries

Crabs make up 20% of all marine
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
s caught, farmed, and consumed worldwide, amounting to 1.5 million tonnes annually. One species, '' Portunus trituberculatus'', accounts for one-fifth of that total. Other commercially important taxa include '' Portunus pelagicus'', several species in the genus '' Chionoecetes'', the blue crab ('' Callinectes sapidus''), ''Charybdis'' spp., '' Cancer pagurus'', the Dungeness crab (''Metacarcinus magister''), and '' Scylla serrata'', each of which yields more than 20,000 tonnes annually. In some crab species, meat is harvested by manually twisting and pulling off one or both claws and returning the live crab to the water in the knowledge that the crab may survive and regenerate the claws.


Cookery

Crabs are prepared and eaten as a dish in many different ways all over the world. Some species are eaten whole, including the shell, such as soft-shell crab; with other species, just the claws or legs are eaten. The latter is particularly common for larger crabs, such as the snow crab. In many cultures, the roe of the female crab is also eaten, which usually appears orange or yellow in fertile crabs. This is popular in Southeast Asian cultures, some Mediterranean and Northern European cultures, and on the East, Chesapeake, and Gulf Coasts of the United States. In some regions, spices improve the culinary experience. In Southeast Asia and the Indosphere,
masala Masala, Massala or MASALA may refer to: Spice * Masala (spice), any of the many spice mixes used in South Asian cuisine ** Masala chai, a flavoured tea beverage ** Masala incense, Indian incense using a spice mix ** Masala dosa, an Indian dish Pl ...
crab and chilli crab are examples of heavily spiced dishes. In the Chesapeake Bay region, blue crab is often steamed with Old Bay Seasoning. Alaskan king crab or snow crab legs are usually simply boiled and served with garlic or lemon butter. For the British dish dressed crab, the crab meat is extracted and placed inside the hard shell. One American way to prepare crab meat is by extracting it and adding varying amounts of binders, such as egg white, cracker meal, mayonnaise, or mustard, creating a
crab cake A crab cake is a variety of fishcake that is popular in the United States. It is composed of crab meat and various other ingredients, such as bread crumbs, mayonnaise, mustard (typically prepared mustard, but sometimes mustard powder), eggs, and ...
. Crabs can also be made into a bisque, a global dish of French origin which in its authentic form includes in the broth the pulverized shells of the shellfish from which it is made. Imitation crab, also called
surimi is a paste made from Fish as food, fish or other meat. The term can also refer to a number of East Asian cuisine, East Asian foods that use that paste as their primary ingredient. It is available in many shapes, forms, and textures, and is ofte ...
, is made from minced fish meat that is crafted and colored to resemble crab meat. While it is sometimes disdained among some elements of the culinary industry as an unacceptably low-quality substitute for real crab, this does not hinder its popularity, especially as a sushi ingredient in Japan and South Korea, and in home cooking, where cost is often a chief concern.Daniel P. Puzo (February 14, 1985
Imitation Crab Draws Criticisms
''Los Angeles Times''
Indeed, surimi is an important source of protein in most East and Southeast Asian cultures, appearing in staple ingredients such as fish balls and fish cake.


Pain

Whether crustaceans as a whole experience pain or not is a scientific debate that has ethical implications for crab dish preparation. Crabs are often boiled alive as part of the cooking process.


Evolution

The earliest unambiguous crab fossils date from the Early Jurassic, with the oldest being ''
Eocarcinus ''Eocarcinus praecursor'' is a Jurassic species of decapod crustacean, sufficiently distinct from its relatives to be placed in its own family (Eocarcinidae). Often considered the oldest true crab, it was considered by a 2010 study to be an ear ...
'' from the early Pliensbachian of Britain, which likely represents a stem-group lineage, as it lacks several key morphological features that define modern crabs. Most Jurassic crabs are only known from dorsal (top half of the body)
carapaces A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the ...
, making it difficult to determine their relationships. Crabs radiated in the Late Jurassic, corresponding with an increase in reef habitats, though they would decline at the end of the Jurassic as the result of the decline of reef ecosystems. Crabs increased in diversity through the Cretaceous and represented the dominant group of decapods by the end of the period. The crab infraorder Brachyura belongs to the group Reptantia, which consists of the walking/crawling decapods ( lobsters and crabs). Brachyura is the sister clade to the infraorder Anomura, which contains the hermit crabs and relatives. The cladogram below shows Brachyura's placement within the larger
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Decapoda The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is esti ...
, from analysis by Wolfe ''et al.'', 2019. Brachyura is separated into several sections, with the
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...
Dromiacea diverging the earliest in the evolutionary history, around the Late Triassic or Early Jurassic. The group consisting of Raninoida and Cyclodorippoida split off next, during the Jurassic period. The remaining
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term ...
Eubrachyura then divided during the Cretaceous period into Heterotremata and Thoracotremata. A summary of the high-level internal relationships within Brachyura can be shown in the cladogram below: There is a no consensus on the relationships of the subsequent superfamilies and families. The proposed cladogram below is from analysis by Tsang ''et al'', 2014:


Classification

The infraorder Brachyura contains approximately 7,000 species in 98 families, as many as the remainder of the
Decapoda The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is esti ...
. The evolution of crabs is characterised by an increasingly robust body, and a reduction in the abdomen. Although many other groups have undergone similar processes, carcinisation is most advanced in crabs. The telson is no longer functional in crabs, and the uropods are absent, having probably evolved into small devices for holding the reduced abdomen tight against the sternum. In most decapods, the gonopores (sexual openings) are found on the legs. Since crabs use their first two pairs of
pleopod The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...
s (abdominal appendages) for sperm transfer, this arrangement has changed. As the male abdomen evolved into a slimmer shape, the gonopores have moved toward the midline, away from the legs, and onto the sternum. A similar change occurred, independently, with the female gonopores. The movement of the female gonopore to the sternum defines the
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term ...
Eubrachyura, and the later change in the position of the male gonopore defines the Thoracotremata. It is still a subject of debate whether a monophyletic group is formed by those crabs where the female, but not male, gonopores are situated on the sternum.


Superfamilies

Numbers of extant and extinct (†) species are given in brackets. The superfamily Eocarcinoidea, containing ''
Eocarcinus ''Eocarcinus praecursor'' is a Jurassic species of decapod crustacean, sufficiently distinct from its relatives to be placed in its own family (Eocarcinidae). Often considered the oldest true crab, it was considered by a 2010 study to be an ear ...
'' and ''
Platykotta ''Platykotta akaina'' is a species of decapod crustacean from the Triassic of the United Arab Emirates. It is the oldest known fossil from the infraorder Anomura, and is most closely related to '' Eocarcinus praecursor''. Stratigraphy The holo ...
'', was formerly thought to contain the oldest crabs; it is now considered part of the Anomura. * Section †
Callichimaeroida ''Callichimaera perplexa'' is a species of small crabs known from the Cretaceous Churuvita Group of Colombia and the Frontier Formation of the United States. Because it possesses a strange combination of anatomical features, it is said to be th ...
** † Callichimaeroidea (1†) * Section Dromiacea ** † Dakoticancroidea (6†) ** Dromioidea (147, 85†) ** Glaessneropsoidea (45†) ** Homolodromioidea (24, 107†) ** Homoloidea (73, 49†) * Section Raninoida (46, 196†) * Section Cyclodorippoida (99, 27†) * Section Eubrachyura ** Subsection Heterotremata ***
Aethroidea The Aethridae are a family of crabs in their own superfamily, Aethroidea. It contains these genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hie ...
(37, 44†) ***
Bellioidea Belliidae is a family of crabs of the order Decapoda. They respond to predators by hyper-extending all of its limbs and remain in this position for varied amounts of time (Hazlett). Species Seven species belong to the family Belliidae : *'' ...
(7) ***
Bythograeoidea The Bythograeidae are a small family of blind crabs which live around hydrothermal vents. The family contains 16 species in six genera. Their relationships to other crabs are unclear. They are believed to eat bacteria and other vent organisms. ...
(14) *** Calappoidea (101, 71†) ***
Cancroidea Cancroidea is a superfamily of crabs, comprising the families Atelecyclidae and Cancridae. http://boletinsgm.igeolcu.unam.mx/bsgm/vols/epoca04/6502/%2810%29Osso.pdf Four other families have been separated into new superfamilies: Cheiragonidae int ...
(57, 81†) ***
Carpilioidea Carpilioidea is a superfamily of crabs containing a single extant family, Carpiliidae and three extinct families. The modern range of the family includes the Indo-Pacific, Western Atlantic and Caribbean Sea. The fossil record of the group ext ...
(4, 104†) ***
Cheiragonoidea Cheiragonidae is a small family (biology), family of crabs, sometimes called ''helmet crabs'', placed in its own Taxonomic rank, superfamily, Cheriagonoidea. It comprises three extant species, ''Horsehair crab, Erimacrus isenbeckii'', ''Telmessus ...
(3, 13†) ***
Corystoidea Corystidae is a family of crabs, in its own superfamily, Corystoidea. It includes what was once thought to be the oldest Eubrachyuran fossil, '' Hebertides jurassica'', thought to be dating from the Bathonian ( Middle Jurassic); the species was ...
(10, 5†) *** †
Componocancroidea ''Componocancer roberti'' is an unusual species of fossil crab described in 2008. It lived in the Albian age (Early Cretaceous) in what is now Montana. The species is unlike any other described crab, and is therefore placed in its own family and ...
(1†) ***
Dairoidea Dairoidea is a superfamily of crabs, comprising two families which each contain a single genus: Dairidae (the living fossil '' Daira'' ) and Dacryopilumnidae ('' Dacryopilumnus'') . Species ; Dairidae *''Daira americana'' Stimpson, 1 ...
(4, 8†) ***
Dorippoidea Dorippoidea is a superfamily of crabs. The earliest fossils attributable to the Dorippoidea date from the Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the ge ...
(101, 73†) ***
Eriphioidea Eriphioidea is a superfamily of crabs, containing the six families Dairoididae, Eriphiidae, Hypothalassiidae, Menippidae, Oziidae and Platyxanthidae. They are united by a number of characters, including a marked difference in size between t ...
(67, 14†) ***
Gecarcinucoidea Gecarcinucoidea is a superfamily of freshwater crabs. Its members have been grouped into families in various ways, with some authors recognizing families such as "Deckeniidae", "Sundathelphusidae", and "Parathelphusidae", but now only the family ...
(349) ***
Goneplacoidea Goneplacoidea is a superfamily of crabs containing 11 extant families, and two families known only from fossils (marked "†"). * Acidopsidae * † Carinocarcinoididae * Chasmocarcinidae * Conleyidae * Euryplacidae * Goneplacidae * Litoche ...
(182, 94†) ***
Hexapodoidea Hexapodidae is a family of crabs, the only family in the superfamily Hexapodoidea. It has traditionally been treated as a subfamily of the family Goneplacidae, and was originally described as a subfamily of Pinnotheridae. Its members can be ...
(21, 25†) ***
Leucosioidea Leucosioidea is a superfamily of crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entire ...
(488, 113†) *** Majoidea (980, 89†) ***
Orithyioidea ''Orithyia sinica'', sometimes called tiger crab or the tiger face crab, is a "singularly unusual" species of crab, whose characteristics warrant its separation into a separate genus, family and even superfamily, having previously been included ...
(1) ***
Palicoidea Palicoidea is a superfamily of crabs, comprising the two families Crossotonotidae and Palicidae. Together, they contain 13 genera, including two genera in the Palicidae known only from fossils. The two families were previously treated as two ...
(63, 6†) *** Parthenopoidea (144, 36†) ***
Pilumnoidea Pilumnoidea is a superfamily of crabs, whose members were previously included in the Xanthoidea. The three families are unified by the free articulation of all the segments of the male crab's abdomen and by the form of the gonopods. The earlies ...
(405, 47†) *** Portunoidea (455, 200†) *** Potamoidea (662, 8†) ***
Pseudothelphusoidea Pseudothelphusidae is a family of freshwater crabs found chiefly in mountain streams in the Neotropics. They are believed to have originated in the Greater Antilles and then crossed to Central America via a Pliocene land bridge. Parasitology Ps ...
(276) ***
Pseudozioidea Pseudozioidea is a superfamily of crabs, formerly treated in the Eriphioidea, Carpilioidea, Xanthoidea, Pilumnoidea and Goneplacoidea. A number of fossils from the Eocene onwards are known from the family Pseudoziidae. Eleven genera are rec ...
(22, 6†) ***
Retroplumoidea Retroplumidae is a family of heterotrematan crabs, placed in their own (monotypic) superfamily, Retroplumoidea. Classification Eight genera are recognised, of which all but two are only known from fossils: *'' Archaeopus'' † Rathbun, 1908 *'' ...
(10, 27†) *** Trapezioidea (58, 10†) *** Trichodactyloidea (50) *** Xanthoidea (736, 134†) ** Subsection Thoracotremata ***
Cryptochiroidea Cryptochiridae is a family of crabs known commonly as gall crabs or coral gall crabs. They live inside dwellings in corals and cause the formation of galls in the coral structure.Johnsson, R., et al. (2006)The association of two gall crabs (Bra ...
(46) ***
Grapsoidea The Grapsoidea are a superfamily of crabs; they are well known and contain many taxa which are terrestrial (land-living), semiterrestrial (taking to the sea only for reproduction), or limnic (living in fresh water). Another well-known member wit ...
(493, 28†) *** Ocypodoidea (304, 14†) *** Pinnotheroidea (304, 13†) Recent studies have found the following superfamilies and families to not be
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
, but rather
paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
or polyphyletic: *The Thoracotremata superfamily
Grapsoidea The Grapsoidea are a superfamily of crabs; they are well known and contain many taxa which are terrestrial (land-living), semiterrestrial (taking to the sea only for reproduction), or limnic (living in fresh water). Another well-known member wit ...
is polyphyletic *The Thoracotremata superfamily Ocypodoidea is polyphyletic *The Heterotremata superfamily Calappoidea is polyphyletic *The Heterotremata superfamily
Eriphioidea Eriphioidea is a superfamily of crabs, containing the six families Dairoididae, Eriphiidae, Hypothalassiidae, Menippidae, Oziidae and Platyxanthidae. They are united by a number of characters, including a marked difference in size between t ...
is polyphyletic *The Heterotremata superfamily
Goneplacoidea Goneplacoidea is a superfamily of crabs containing 11 extant families, and two families known only from fossils (marked "†"). * Acidopsidae * † Carinocarcinoididae * Chasmocarcinidae * Conleyidae * Euryplacidae * Goneplacidae * Litoche ...
is polyphyletic *The Heterotremata superfamily Potamoidea is paraphyletic with respect to
Gecarcinucoidea Gecarcinucoidea is a superfamily of freshwater crabs. Its members have been grouped into families in various ways, with some authors recognizing families such as "Deckeniidae", "Sundathelphusidae", and "Parathelphusidae", but now only the family ...
, which is resolved by placing
Gecarcinucidae The Gecarcinucidae are a family of true freshwater crabs. The family Parathelphusidae is now demoted to the rank of subfamily, as the Parathelphusinae, within the Gecarcinucidae. "Family" Parathelphusidae is now considered as a junior synonym. ...
within Potamoidea *The Majoidea families Epialtidae,
Mithracidae Mithracidae is a family of crustaceans belonging to the order Decapoda. Genera Genera: *''Ala'' *'' Amphithrax'' *''Hemus'' *'' Maguimithrax'' *'' Microphrys'' *'' Mithraculus'' *'' Mithrax'' *'' Nemausa'' *'' Nonala'' *'' Omalacantha ...
and Majidae are polyphyletic with respect to each other *The Dromioidea family
Dromiidae Dromiidae is a family of crabs, often referred to as sponge crabs. They are small or medium-sized crabs which get their name from the ability to shape a living sponge into a portable shelter for themselves.Encarta Reference Library Premium 2005 D ...
may be paraphyletic with respect to Dynomenidae *The Homoloidea family Homolidae is paraphyletic with respect to Latreilliidae *The Xanthoidea family Xanthidae is paraphyletic with respect to Panopeidae


Cultural influences

Both the
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...
Cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...
and the astrological sign
Cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...
are named after the crab, and depicted as a crab. William Parsons, 3rd Earl of Rosse drew the
Crab Nebula The Crab Nebula (catalogue designations Messier object, M1, New General Catalogue, NGC 1952, Taurus (constellation), Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus (constellation), Taurus. The common name ...
in 1848 and noticed its similarity to the animal; the Crab Pulsar lies at the centre of the nebula. The Moche people of ancient Peru worshipped nature, especially the sea, and often depicted crabs in their art. In Greek mythology, Karkinos was a crab that came to the aid of the Lernaean Hydra as it battled Heracles. One of Rudyard Kipling's '' Just So Stories'', ''The Crab that Played with the Sea'', tells the story of a gigantic crab who made the waters of the sea go up and down, like the tides. The auction for the crab quota in 2019, Russia is the largest revenue auction in the world except the spectrum auctions. In Malay mythology (as related by Hugh Clifford to Walter William Skeat), ocean tides are believed to be caused by water rushing in and out of a hole in the Navel of the Seas (''Pusat Tasek''), where "there sits a gigantic crab which twice a day gets out in order to search for food". The Kapsiki people of North Cameroon use the way crabs handle objects for
divination Divination (from Latin ''divinare'', 'to foresee, to foretell, to predict, to prophesy') is the attempt to gain insight into a question or situation by way of an occultic, standardized process or ritual. Used in various forms throughout histor ...
. The term '' crab mentality'' is derived from a type of detrimental social behavior observed in crabs.


See also

* Carcinisation * Anomura


References


External links

* {{Authority control Edible crustaceans Commercial crustaceans Extant Jurassic first appearances Articles containing video clips