Crab

Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) (Greek: βραχύς, translit. brachys = short,[2] οὐρά / οura = tail[3]), usually entirely hidden under the thorax. They live in all the world's oceans, in fresh water, and on land, are generally covered with a thick exoskeleton and have a single pair of pincers. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs.

Crab
Temporal range: Jurassic–Recent
Liocarcinus vernalis
Grey swimming crab
Liocarcinus vernalis
Scientific classification
Kingdom: Animalia
Phylum: Euarthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Linnaeus, 1758
Sections and subsections[1]

Description

Crabs are generally covered with a thick exoskeleton, composed primarily of highly mineralized chitin,[4][5] and armed with a single pair of chelae (claws). Crabs are found in all of the world's oceans, while many crabs live in fresh water and on land, particularly in tropical regions. Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 metres (13 ft).[6]

About 850 species of crab are freshwater, terrestrial or semi-terrestrial species;[7] they are found throughout the world's tropical and semi-tropical regions. They were previously thought to be a monophyletic group, but are now believed to represent at least two distinct lineages, one in the Old World and one in the New World.[8]

Evolution

The earliest unambiguous crab fossils date from the Jurassic,[9] although Carboniferous Imocaris, known only from its carapace, may be a primitive crab.[10] The radiation of crabs in the Cretaceous and afterward may be linked either to the break-up of Gondwana or to the concurrent radiation of bony fish, crabs' main predators.[11]

Sexual dimorphism

Pachygrapsus marmoratus male female
The underside of a male (top) and a female (bottom) individual of Pachygrapsus marmoratus, showing the difference in shape of the abdomen

Crabs often show marked sexual dimorphism. Males often have larger claws,[12] a tendency which is particularly pronounced in the fiddler crabs of the genus Uca (Ocypodidae). In fiddler crabs, males have one claw which is greatly enlarged and which is used for communication, particularly for attracting a mate.[13] 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.[14] This is because female crabs brood fertilised eggs on their pleopods.

Reproduction and lifecycle

Crab (Pachygrapsus marmoratus) on Istrian coast (Adriatic sea)
Crab (Pachygrapsus marmoratus) on Istrian coast, Adriatic Sea

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 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 into the water, where they are part of the plankton. The release is often timed with the tides. 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.

Xantho poressa 2009 G1
Female crab Xantho poressa at spawning time in the Black Sea, carrying eggs under her abdomen

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, 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.[15]:63–77

Most species of terrestrial crabs must migrate 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 of migrating crabs.[15]:113–114

Once crabs have become juveniles, they will 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. The crab must then extract all of itself – including its legs, mouthparts, 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), 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.[15]:78–79

Behaviour

Crabs typically walk sideways[16] (a behaviour which gives us the word crabwise), because of the articulation of the legs which makes a sidelong gait more efficient.[17] However, some crabs walk forwards or backwards, including raninids,[18] Libinia emarginata[19] and Mictyris platycheles.[16] Some crabs, notably the Portunidae and Matutidae, are also capable of swimming,[20] the Portunidae especially so as their last pair of walking legs is flattened into swimming paddles.[15]:96

Crabs are mostly active animals with complex behaviour patterns. They can communicate by drumming or waving their pincers. Crabs tend to be aggressive towards one another, and males often fight to gain access to females.[21] On rocky seashores, where nearly all caves and crevices are occupied, crabs may also fight over hiding holes.[22] Fiddler crabs (genus Uca) dig burrows in sand or mud, which they use for resting, hiding, and mating, and to defend against intruders.[15]:28–29, 99

Crabs are omnivores, feeding primarily on algae,[23] and taking any other food, including molluscs, worms, other crustaceans, fungi, bacteria and detritus, 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.[24][25] However, some species are more specialised in their diets. Some eat plankton, some eat primarily shellfish like clams, and some even catch fish.[15]:85

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.[26]

Human consumption

Fisheries

Sorting Crabs Ffionphort
Fishermen sorting velvet crabs at Fionnphort, Scotland

Crabs make up 20% of all marine crustaceans 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.[27]

In some species, crab meat is harvested by manually twisting and pulling off one or both claws and returning the live crab to the water in the belief the crab will survive and regenerate the claws, thereby making it a sustainable industry.[28][29][30][31]

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, as well as on the eastern, Chesapeake and southern coasts of the United States.

In some regions, spices improve the culinary experience. In Southeast Asia and the Indosphere, masala 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. 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 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.[32] 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

Crabs are often boiled alive. In 2005, Norwegian scientists concluded that crustaceans could not feel pain.[33] However, a study by Bob Elwood and Mirjam Appel of Queens University in Belfast, found that hermit crabs reacted to electric shocks. This may indicate that some crustaceans are able to feel and remember pain.[34][35]

Classification

The infraorder Brachyura contains 6,793 species in 93 families,[20] as many as the remainder of the Decapoda.[36] 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. However, since crabs use the first two pairs of pleopods (abdominal appendages) for sperm transfer, this arrangement has changed. As the male abdomen evolved into a narrower shape, the gonopores have moved towards the midline, away from the legs, and onto the sternum.[37] A similar change occurred, independently, with the female gonopores. The movement of the female gonopore to the sternum defines the clade Eubrachyura, and the later change in the position of the male gonopore defines the Thoracotremata. It is still a subject of debate whether those crabs where the female, but not male, gonopores are situated on the sternum, form a monophyletic group.[36]

Superfamilies

Numbers of extant and extinct (†) species are given in brackets.[20] The superfamily Eocarcinoidea, containing Eocarcinus and Platykotta, was formerly thought to contain the oldest crabs; it is now considered part of the Anomura.[38]

A crab divination pot in Kapsiki
A crab divination pot in Kapsiki, North Cameroon.

Cultural influences

Both the constellation Cancer and the astrological sign Cancer are named after the crab, and depicted as a crab. William Parsons, 3rd Earl of Rosse drew the Crab Nebula in 1848 and noticed its similarity to the animal; the Crab Pulsar lies at the centre of the nebula.[39] The Moche people of ancient Peru worshipped nature, especially the sea,[40] and often depicted crabs in their art.[41] 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.[42]

The Kapsiki people of North Cameroon use the way crabs handle objects for divination.

References

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External links

Callinectes sapidus

Callinectes sapidus (from the Greek calli- = "beautiful", nectes = "swimmer", and Latin sapidus = "savory"), the Blue Crab, Atlantic Blue Crab, or regionally as the Chesapeake blue crab, is a species of crab native to the waters of the western Atlantic Ocean and the Gulf of Mexico, and introduced internationally.

C. sapidus is of significant culinary and economic importance in the United States, particularly in Louisiana, North Carolina, the Chesapeake Bay, and New Jersey. It is the Maryland state crustacean and is that state's largest commercial fishery.

Cancer (astrology)

Cancer (♋️) is the fourth astrological sign in the Zodiac, originating from the constellation of Cancer.

It spans from 90° to 120° celestial longitude. Under the tropical zodiac, the Sun transits this area between approximately June 21 and July 23, and under the sidereal zodiac, the Sun transits this area between approximately July 21 and August 9.In astrology, Cancer is the cardinal sign of the Water trigon, which is made up of Cancer, Pisces, and Scorpio. It is one of the six negative signs. Though some depictions of Cancer feature a lobster, the sign is most often represented by the crab, based on the Karkinos, a giant crab that harassed Heracles during his fight with the Hydra.

Coconut crab

The coconut crab (Birgus latro) is a species of terrestrial hermit crab, also known as the robber crab or palm thief. It is the largest land-living arthropod in the world, and is probably at the upper size limit for terrestrial animals with exoskeletons in recent times, with a weight up to 4.1 kg (9.0 lb). It can grow to up to 1 m (3 ft 3 in) in length from leg to leg. It is found on islands across the Indian Ocean, and parts of the Pacific Ocean as far east as the Gambier Islands and Pitcairn Islands, mirroring the distribution of the coconut palm; it has been extirpated from most areas with a significant human population, including mainland Australia and Madagascar.

The coconut crab is the only species of the genus Birgus, and is related to the terrestrial hermit crabs of the genus Coenobita. It shows a number of adaptations to life on land. Like other hermit crabs, juvenile coconut crabs use empty gastropod shells for protection, but the adults develop a tough exoskeleton on their abdomens and stop carrying a shell. Coconut crabs have organs known as branchiostegal lungs, which are used instead of the vestigial gills for breathing, and they will drown if immersed in water for long. They have an acute sense of smell, which has developed convergently with that of insects, and which they use to find potential food sources.

Adult coconut crabs feed primarily on fruits, nuts, seeds, and the pith of fallen trees, but they will eat carrion and other organic matter opportunistically. Anything left unattended on the ground is a potential source of food, which they will investigate and may carry away - thereby getting the alternative name of "robber crab." The species is popularly associated with the coconut palm, yet coconuts are not a significant part of its diet. Although it lives in a burrow, the crab has been filmed climbing coconut and pandanus trees. No film shows a crab selectively picking coconut fruit, though they might dislodge ripe fruit that otherwise would fall naturally. Climbing is an immediate escape route (if too far from the burrow) to avoid predation (when young) by large sea birds, or cannibalism (at any age) by bigger, older crabs.

Mating occurs on dry land, but the females return to the edge of the sea to release their fertilised eggs, and then retreat back up the beach. The larvae that hatch are planktonic for 3–4 weeks, before settling to the sea floor, entering a gastropod shell and returning to dry land. Sexual maturity is reached after about 5 years, and the total lifespan may be over 60 years. In the 3–4 weeks that the larvae remain at sea, their chances of reaching another suitable location is enhanced if a floating life support system avails itself to them. Examples of the systems that provide such opportunities include floating logs and rafts of marine, or terrestrial, vegetation. Similarly, floating coconuts can be a very significant part of the crab's dispersal options.

Crab-eating fox

The crab-eating fox (Cerdocyon thous), also known as the forest fox, wood fox, or maikong, is an extant species of medium-sized canid endemic to the central part of South America, and which appeared during the Pliocene epoch. Like South American foxes, which are in the genus Lycalopex, it is not closely related to true foxes. Cerdocyon comes from the Greek words kerdo (meaning fox) and cyon (dog) referring to the dog-and fox-like characteristics of this animal.

Crab-eating macaque

The crab-eating macaque (Macaca fascicularis), also known as the long-tailed macaque, is a cercopithecine primate native to Southeast Asia. It is referred to as the cynomolgus monkey in laboratories. It has a long history alongside humans; they have been alternately seen as agricultural pests, sacred animals in some temples, and more recently, the subject of medical experiments. The crab-eating macaque lives in matrilineal social groups with a female dominance hierarchy, and male members leave the group when they reach puberty. They are opportunistic omnivores and have been documented using tools to obtain food in Thailand and Myanmar. The crab-eating macaque is a known invasive species and a threat to biodiversity in several locations, including Hong Kong and western New Guinea. The significant overlap in macaque and human living space has resulted in greater habitat loss, synanthropic living, and inter- and intraspecies conflicts over resources.

Crab-eating raccoon

The crab-eating raccoon or South American raccoon (Procyon cancrivorus) is a species of raccoon native to marshy and jungle areas of Central and South America (including Trinidad and Tobago). It is found from Costa Rica south through most areas of South America east of the Andes down to northern Argentina and Uruguay. That it is called the crab-eating raccoon does not mean that only this species eats crabs, as the common raccoon also seeks and eats crabs where they are available.

The crab-eating raccoon eats crab, lobster, crayfish and other crustaceans and shellfish, such as oysters and clams. It is an omnivore and its diet also includes, for example, small amphibians, turtle eggs, and fruits. It resembles its northern cousin, the common raccoon, in having a bushy ringed tail and "bandit mask" of fur around its eyes. Unlike the common raccoon, the hair on the nape of the neck points towards the head, rather than backward. The crab-eating raccoon also appears to be more adapted to an arboreal lifestyle than the common raccoon, with sharper, narrower claws. It also is better adapted for a diet of hard-shelled food, with most of the cheek teeth being larger than those of the common raccoon, with broader, rounded cusps. Although the crab-eating raccoon can appear smaller and more streamlined than the common raccoon due to its much shorter fur and more gracile build, the crab-eating raccoon is of similar dimensions to the northern species. Head and body length is 41 to 80 cm (16 to 31 in), tail length is 20 to 56 cm (8 to 22 in) and height at the shoulder is about 23 cm (9 in). Weights can range from 2 to 12 kg (4 to 26 lb), though are mostly between 5 and 7 kg (11 and 15 lb). Males are usually larger than the females.

Crab Nebula

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant in the constellation of Taurus. The now-current name is due to William Parsons, who observed the object in 1840 using a 36-inch telescope and produced a drawing that looked somewhat like a crab. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by English astronomer John Bevis in 1731. The nebula was the first astronomical object identified with a historical supernova explosion.

At an apparent magnitude of 8.4, comparable to that of Saturn's moon Titan, it is not visible to the naked eye but can be made out using binoculars under favourable conditions. The nebula lies in the Perseus Arm of the Milky Way galaxy, at a distance of about 2.0 kiloparsecs (6,500 ly) from Earth. It has a diameter of 3.4 parsecs (11 ly), corresponding to an apparent diameter of some 7 arcminutes, and is expanding at a rate of about 1,500 kilometres per second (930 mi/s), or 0.5% of the speed of light.

At the center of the nebula lies the Crab Pulsar, a neutron star 28–30 kilometres (17–19 mi) across with a spin rate of 30.2 times per second, which emits pulses of radiation from gamma rays to radio waves. At X-ray and gamma ray energies above 30 keV, the Crab Nebula is generally the brightest persistent source in the sky, with measured flux extending to above 10 TeV. The nebula's radiation allows for the detailed studying of celestial bodies that occult it. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab Nebula's radio waves passing through it, and in 2003, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula.

The inner part of the nebula is a much smaller pulsar wind nebula that appears as a shell surrounding the pulsar. Some sources consider the Crab Nebula to be an example of both a pulsar wind nebula as well as a supernova remnant, while others separate the two phenomena based on the different sources of energy production and behaviour. For the Crab Nebula, the divisions are superficial but remain meaningful to researchers and their lines of study.

Crab louse

The crab louse or pubic louse (Pthirus pubis) is an insect that is an obligate ectoparasite of humans, feeding exclusively on blood. The crab louse usually is found in the person's pubic hair. Although the louse cannot jump, it can also live in other areas of the body that are covered with coarse hair, such as the eyelashes. It is of the order Psocodea.

Humans are the only known hosts of the crab louse, although a closely related species, Pthirus gorillae, infects gorilla populations. The human parasite diverged from Pthirus gorillae approximately 3.3 million years ago. It is more distantly related to the genus Pediculus, which contains the human head and body lice and a louse that affects chimpanzees and bonobos.

Deadliest Catch

Deadliest Catch is a documentary television series produced by Original Productions for the Discovery Channel. It portrays the real life events aboard fishing vessels in the Bering Sea during the Alaskan king crab, opilio crab and bairdi crab fishing seasons.

The Aleutian Islands port of Dutch Harbor, Alaska, is the base of operations for the fishing fleet. The show's title derives from the inherent high risk of injury or death associated with the work.

Deadliest Catch premiered on the Discovery Channel on April 12, 2005, and currently airs worldwide. The first season consisted of ten episodes, with the finale airing on June 14, 2005. Subsequent seasons have aired on the same April to June or July schedule every year since the original 2005 season. The 14th season premiered on April 10, 2018. On March 7, 2019, Discovery Channel announced the series will return for a fifteenth season to premiere on Tuesday, April 9, 2019.

Diogenes heteropsammicola

Diogenes heteropsammicola is a species of hermit crab discovered during samplings between 2012 and 2016 in the shallow waters of the Japanese Amami Islands. This hermit crab species is unique due to the discovery that they use living, growing coral as a shell. Crustaceans of this type commonly replace their shell as the organism grows in size, but D. heteropsammicola are the first of their kind to use solitary corals as a shell form. Heteropsammia and Heterocyathus are the two solitary corals that this hermit species has been observed as occupying. These two coral species are also used as a home by symbiotic sipunculans of the genus Aspidosiphon, which normally occupy the corals that the crabs were found inhabiting.The discoverers of this species are Momoko Igawa and Makoto Kato of Kyoto University, Japan.

Dungeness crab

The Dungeness crab, Metacarcinus magister (the naming convention recognized by WoRMS) or Cancer magister (the naming convention recognized by ITIS), is a species of crab that inhabits eelgrass beds and water bottoms on the west coast of North America. It typically grows to 20 cm (7.9 in) across the carapace and is a popular seafood prized for its sweet, moist and tender flesh. Its common name comes from the port of Dungeness, Washington.

Hermit crab

Hermit crabs are decapod crustaceans of the superfamily Paguroidea.Most of the approximately 1,110 species possess an asymmetrical abdomen that is concealed in a scavenged mollusc shell carried around by the hermit crab.

Horseshoe crab

Horseshoe crabs are marine and brackish water arthropods of the family Limulidae, suborder Xiphosurida, and order Xiphosura. Their popular name is actually a misnomer, for they are not true crabs.

Horseshoe crabs live primarily in and around shallow coastal waters on soft sandy or muddy bottoms. They tend to spawn in the intertidal zone at spring high tides. They are commonly eaten in Asia, and used as fishing bait, in fertilizer and in science (especially Limulus amebocyte lysate). In recent years, population declines have occurred as a consequence of coastal habitat destruction and overharvesting. Tetrodotoxin may be present in Carcinoscorpius rotundicauda.Because of their origin 450 million years ago, horseshoe crabs are considered living fossils. A 2019 molecular analysis places them as the sister group of Ricinulei within Arachnida.

Japanese spider crab

The Japanese spider crab (タカアシガニ, takaashigani, "long-legged crab"), or Macrocheira kaempferi, is a species of marine crab that lives in the waters around Japan. It has the largest leg span of any arthropod. It is the subject of fishery and is considered a delicacy. Two fossil species belonging to the same genus have been found, Macrocheira ginzanensis and Macrocheira yabei, both from the Miocene of Japan.

List of crab dishes

This is a list of crab dishes. Crabs live in all the world's oceans, in fresh water, and on land, are generally covered with a thick exoskeleton and are arthropoda and have a single pair of claws. Crab meat is the meat found within a crab. It is used in many cuisines across the world.

Malus

Malus ( or ) is a genus of about 30–55 species of small deciduous trees or shrubs in the family Rosaceae, including the domesticated orchard apple (M. pumila syn. M. domestica ) – also known as the eating apple, cooking apple, or culinary apple. It is dealt with under Apple. The other species are generally known as crabapples, crab apples, or wild apples.

The genus is native to the temperate zone of the Northern Hemisphere.

Philodromidae

Philodromidae is a family of spiders commonly known as philodromid crab spiders or running crab spiders. This family is superficially similar to the "true" crab spiders in the family Thomisidae.

However, studies have shown that these families are not as closely related as previously thought. Unlike thomisids, philodromids tend to have few true setae (hairs or spines) on their bodies. They also lack the congruent eye tubercles of some thomisids. The second legs are usually the longer of the four pairs of walking legs and in the genus Ebo this is quite extreme, with the second pair of legs in some species twice as long as the first pair.

The most common genus is Philodromus which, like Ebo is widespread. Other common genera include the elongate grass-dwelling Tibellus and the widespread Thanatus, which includes the widely distributed Holarctic house crab spider Thanatus vulgaris. This species commonly captures flies on and in buildings.

The family contains over 500 species in nearly 30 genera. Most are dull colored- brown, gray, yellowish or mottled, and seldom reach above 10 mm in body length. Most have a leaf-like cardiac mark on the anterior dorsal abdomen. None of the species build webs, but they do use silk for draglines and for egg sacs.

Selenopidae

The Selenopidae are a family of araneomorph spiders, sometimes called wall crab spiders, but also wall spiders and flatties. The Selenopidae are one of several families whose English name includes the phrase "crab spider".

As at 10 February 2019, this family comprised 259 species in nine genera, of which Selenops is the best known. The Selenopidae occur worldwide and are primarily tropical and subtropical, though several species are found in deserts, and can be found from sea level to over 2500 meters. The genus Selenops is the most widely distributed, whilst the genus Anyphops is found throughout Sub-Saharan Africa. The remaining genera have more specific distributions. At least one (possibly extinct) species of Garcorops, G. jadis, is known only from subfossil copal.Selenopidae are a variety of colors including various shades of grey, brown, yellow, and orange, with darker markings on the cephalothorax and spots or mottling on the abdomen, and annulations on the legs of most species. The spiders are very flat dorsoventrally, have two tarsal claws and laterigrade legs. They are commonly found on walls or under rocks. They are exceptional in that both their running and striking speeds place them amongst the world’s fastest animals, making them difficult to capture. In addition, their coloring makes them often quite difficult to see. Like almost all Entelegynae, they have eight eyes arranged in two rows of six and two.

Thomisidae

The Thomisidae are a family of spiders, including about 175 genera and over 2,100 species. The common name crab spider is often linked to species in this family, but is also applied loosely to many other species of spiders. Among the Thomisidae, "crab spider" refers most often to the familiar species of "flower crab spiders", though not all members of the family are limited to ambush hunting in flowers.

Superfamilies of Infraclass Brachyura (true crabs)
Dromiacea
Raninoida
Cyclodorippoida
Eubrachyura
Principal commercial fishery species groups
Wild
Farmed
Edible crustaceans
Shrimp/prawns
Lobsters
(incl. slipper & spiny)
Crabs
Crayfish
Others

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