61-458: Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tail" in Greek ), which typically have a very short projecting tail -like abdomen , usually hidden entirely under the thorax . They live in all the world's oceans, in freshwater , and on land . They are generally covered with a thick exoskeleton . They generally have five pairs of legs, and they have pincer claws on
122-423: A Scottish animal welfare group, stated in 2005 that "scientific evidence ... strongly suggests that there is a potential for decapod crustaceans and cephalopods to experience pain and suffering". This is primarily due to "The likelihood that decapod crustaceans can feel pain [which] is supported by the fact that they have been shown to have opioid receptors and to respond to opioids (analgesics such as morphine) in
183-409: A fraction of tagged individuals were recovered. More convenient, therefore, are electronic devices such as radio-tracking collars that can be followed by radio, whether handheld, in a vehicle or aircraft, or by satellite. GPS animal tracking enables accurate positions to be broadcast at regular intervals, but the devices are inevitably heavier and more expensive than those without GPS. An alternative
244-474: A greater scale (in both space and time) than its normal daily activities; seasonal to-and-fro movement of a population between two areas; and movement leading to the redistribution of individuals within a population. Migration can be either obligate , meaning individuals must migrate, or facultative, meaning individuals can "choose" to migrate or not. Within a migratory species or even within a single population, often not all individuals migrate. Complete migration
305-493: 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
366-419: 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
427-497: A similar way to vertebrates." Similarities between decapod and vertebrate stress systems and behavioral responses to noxious stimuli were given as additional evidence for the capacity of decapods to experience pain. In 2005 a review of the literature by the Norwegian Scientific Committee for Food Safety tentatively concluded that "it is unlikely that [lobsters] can feel pain," though they note that "there
488-478: 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 pleopods . Crabs attract
549-416: A true migration, and not just a local dispersal or irruption, the movement of the animals should be an annual or seasonal occurrence, or a major habitat change as part of their life. An annual event could include Northern Hemisphere birds migrating south for the winter, or wildebeest migrating annually for seasonal grazing. A major habitat change could include young Atlantic salmon or sea lamprey leaving
610-568: A variety of causes. As such, there is no simple accepted definition of migration. One of the most commonly used definitions, proposed by the zoologist J. S. Kennedy is Migratory behavior is persistent and straightened-out movement effected by the animal's own locomotory exertions or by its active embarkation on a vehicle. It depends on some temporary inhibition of station-keeping responses, but promotes their eventual disinhibition and recurrence. Migration encompasses four related concepts: persistent straight movement; relocation of an individual on
671-429: Is advantageous in birds that, during the winter, remain close to the equator, and also allows the monitoring of the auditory and spatial memory of the bird's brain to remember an optimal site of migration. These birds also have timing mechanisms that provide them with the distance to their destination. Tidal migration is the use of tides by organisms to move periodically from one habitat to another. This type of migration
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#1732801753402732-470: Is apparently a paucity of exact knowledge on sentience in crustaceans, and more research is needed." This conclusion is based on the lobster 's simple nervous system. The report assumes that the violent reaction of lobsters to boiling water is a reflex response (i.e. does not involve conscious perception) to noxious stimuli. The earliest unambiguous crab fossils date from the Early Jurassic , with
793-439: 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 tidal and light/dark diurnal 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
854-588: 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 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. Once crabs have become juveniles, they still have to keep moulting many more times to become adults. They are covered with
915-410: Is often a chief concern. 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. Whether crustaceans as a whole experience pain or not is a scientific debate that has ethical implications for crab dish preparation. Crabs are very often boiled alive as part of the cooking process. Advocates for Animals,
976-439: Is often used in order to find food or mates. Tides can carry organisms horizontally and vertically for as little as a few nanometres to even thousands of kilometres. The most common form of tidal migration is to and from the intertidal zone during daily tidal cycles. These zones are often populated by many different species and are rich in nutrients. Organisms like crabs, nematodes, and small fish move in and out of these areas as
1037-823: 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 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
1098-581: Is separated into several sections, with the basal 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 Eubrachyura then divided during the Cretaceous period into Heterotremata and Thoracotremata . A summary of
1159-464: Is the Argos Doppler tag, also called a 'Platform Transmitter Terminal' (PTT), which sends regularly to the polar-orbiting Argos satellites; using Doppler shift , the animal's location can be estimated, relatively roughly compared to GPS, but at a lower cost and weight. A technology suitable for small birds which cannot carry the heavier devices is the geolocator which logs the light level as
1220-460: Is the movement of various species from one habitat to another during the year. Resource availability changes depending on seasonal fluctuations, which influence migration patterns. Some species such as Pacific salmon migrate to reproduce; every year, they swim upstream to mate and then return to the ocean. Temperature is a driving factor of migration that is dependent on the time of year. Many species, especially birds, migrate to warmer locations during
1281-412: Is the relatively long-distance movement of individual animals , usually on a seasonal basis. It is the most common form of migration in ecology. It is found in all major animal groups, including birds , mammals , fish , reptiles , amphibians, insects , and crustaceans . The cause of migration may be local climate, local availability of food, the season of the year or for mating. To be counted as
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#17328017534021342-441: Is when all individuals migrate, partial migration is when some individuals migrate while others do not, and differential migration is when the difference between migratory and non-migratory individuals is based on discernible characteristics like age or sex. Irregular (non-cyclical) migrations such as irruptions can occur under pressure of famine, overpopulation of a locality, or some more obscure influence. Seasonal migration
1403-480: The Antarctic and back again each year, a distance of at least 19,000 km (12,000 mi), giving it two summers every year. Bird migration is controlled primarily by day length, signalled by hormonal changes in the bird's body. On migration, birds navigate using multiple senses. Many birds use a sun compass, requiring them to compensate for the sun's changing position with time of day. Navigation involves
1464-548: The Late Ordovician around 455 million years ago, with the Dendrobranchiata (prawns) being the first group to diverge. The remaining group, called Pleocyemata , then diverged between the swimming shrimp groupings and the crawling/walking group called Reptantia , consisting of lobsters and crabs . High species diversification can be traced to the Jurassic and Cretaceous periods, which coincides with
1525-527: The Serengeti 'great migration' , an annual circular pattern of movement with some 1.7 million wildebeest and hundreds of thousands of other large game animals, including gazelles and zebra . More than 20 such species engage, or used to engage, in mass migrations. Of these migrations, those of the springbok , black wildebeest , blesbok , scimitar-horned oryx , and kulan have ceased. Long-distance migrations occur in some bats – notably
1586-641: The pea crab , a few millimeters wide, to the Japanese spider crab , with a leg span up to 4 m (13 ft). 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 . Crabs are found in all of the world's oceans, as well as in fresh water and on land , particularly in tropical regions. About 850 species are freshwater crabs . Crabs often show marked sexual dimorphism . Males often have larger claws ,
1647-498: The "white shrimp", Litopenaeus setiferus . The Pleocyemata include the remaining groups, including "true shrimp". Those groups that usually walk rather than swim (Pleocyemata, excluding Stenopodidea and Caridea) form a clade called Reptantia. This classification to the level of superfamilies follows De Grave et al. Order Decapoda Latreille, 1802 [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Animal migration Animal migration
1708-475: 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
1769-564: The North Atlantic ocean. The capelin, for example, spawn around the southern and western coasts of Iceland; their larvae drift clockwise around Iceland, while the fish swim northwards towards Jan Mayen island to feed and return to Iceland parallel with Greenland's east coast. In the ' sardine run ', billions of Southern African pilchard Sardinops sagax spawn in the cold waters of the Agulhas Bank and move northward along
1830-517: The ability to detect magnetic fields . Most fish species are relatively limited in their movements, remaining in a single geographical area and making short migrations to overwinter, to spawn , or to feed. A few hundred species migrate long distances, in some cases of thousands of kilometres. About 120 species of fish, including several species of salmon , migrate between saltwater and freshwater (they are 'diadromous'). Forage fish such as herring and capelin migrate around substantial parts of
1891-511: The bird flies, for analysis on recapture. There is scope for further development of systems able to track small animals globally. Radio-tracking tags can be fitted to insects, including dragonflies and bees . Before animal migration was understood, various folklore and erroneous explanations were formulated to account for the disappearance or sudden arrival of birds in an area. In Ancient Greece , Aristotle proposed that robins turned into redstarts when summer arrived. The barnacle goose
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1952-551: The bulk of the remainder. The earliest fossils of the group date to the Devonian . Decapods can have as many as 38 appendages, arranged in one pair per body segment. As the name Decapoda (from the Greek δέκα , deca- , "ten", and πούς / ποδός , -pod , "foot") implies, ten of these appendages are considered legs. They are the pereiopods , found on the last five thoracic segments. In many decapods, one pair of these "legs" has enlarged pincers, called chelae , with
2013-538: The cladogram above, the clade Glypheidea is excluded due to lack of sufficient DNA evidence, but is likely the sister clade to Polychelida , within Reptantia . Classification within the order Decapoda depends on the structure of the gills and legs, and the way in which the larvae develop, giving rise to two suborders: Dendrobranchiata and Pleocyemata . The Dendrobranchiata consist of prawns, including many species colloquially referred to as "shrimp", such as
2074-434: The class Malacostraca , and includes crabs , lobsters , crayfish , shrimp , and prawns . Most decapods are scavengers . The order is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp (about 3,000 species) and Anomura including hermit crabs , porcelain crabs , squat lobsters (about 2500 species) making up
2135-463: The crab may survive and regenerate the claws. 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
2196-688: 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. 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
2257-588: The desert locust, Schistocerca gregaria , flew westwards across the Atlantic Ocean for 4,500 kilometres (2,800 mi) during October 1988, using air currents in the Inter-Tropical Convergence Zone . In some migratory butterflies , such as the monarch butterfly and the painted lady , no individual completes the whole migration. Instead, the butterflies mate and reproduce on the journey, and successive generations continue
2318-468: The east coast of South Africa between May and July. Some winged insects such as locusts and certain butterflies and dragonflies with strong flight migrate long distances. Among the dragonflies, species of Libellula and Sympetrum are known for mass migration, while Pantala flavescens , known as the globe skimmer or wandering glider dragonfly, makes the longest ocean crossing of any insect: between India and Africa. Exceptionally, swarms of
2379-426: 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 , living on the bottom rather than floating in the water. This last moult, from megalopa to juvenile,
2440-531: 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
2501-425: The ends of the frontmost pair. They first appeared during the Jurassic period, around 200 million years ago. Crabs are generally covered with a thick exoskeleton , composed primarily of highly mineralized chitin . Behind their pair of chelae (claws) are six walking legs and then two swimming legs. The crab breathes through gills on its underside; gills must be at least moist to work. Crabs vary in size from
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2562-436: 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
2623-458: 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
2684-722: The hermit crabs and relatives. The cladogram below shows Brachyura's placement within the larger order Decapoda , from analysis by Wolfe et al. , 2019. Dendrobranchiata (prawns) [REDACTED] Stenopodidea (boxer shrimp) [REDACTED] Procarididea Caridea ("true" shrimp) [REDACTED] Achelata (spiny lobsters and slipper lobsters) [REDACTED] Polychelida (benthic crustaceans) Astacidea (lobsters and crayfish) [REDACTED] Axiidea (mud shrimp, ghost shrimp, and burrowing shrimp) Gebiidea (mud lobsters and mud shrimp) [REDACTED] Anomura (hermit crabs and allies) [REDACTED] Brachyura ("true" crabs) [REDACTED] Brachyura
2745-698: The high-level internal relationships within Brachyura can be shown in the cladogram below: Dromiacea Raninoida Cyclodorippoida Heterotremata Thoracotremata 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: Dromiidae (may be paraphyletic) Dynomenidae Homolidae (paraphyletic) Latreilliidae Decapoda Dendrobranchiata Pleocyemata See text for superfamilies. The Decapoda or decapods ( lit. ' ten-footed ' ) are an order of crustaceans within
2806-459: The legs being called chelipeds. In front of the pereiopods are three pairs of maxillipeds that function as feeding appendages. The head has five pairs of appendages, including mouthparts , antennae, and antennules. There are five more pairs of appendages on the abdomen. They are called pleopods . There is one final pair called uropods , which, with the telson , form the tail fan. A 2019 molecular clock analysis suggested decapods originated in
2867-433: 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. Crabs typically walk sideways (hence
2928-455: The mass migration of the Mexican free-tailed bat between Oregon and southern Mexico. Migration is important in cetaceans , including whales, dolphins and porpoises; some species travel long distances between their feeding and their breeding areas. Humans are mammals, but human migration , as commonly defined, is when individuals often permanently change where they live, which does not fit
2989-483: The migration. Some mammals undertake exceptional migrations; reindeer have one of the longest terrestrial migrations on the planet, reaching as much as 4,868 kilometres (3,025 mi) per year in North America. However, over the course of a year, grey wolves move the most. One grey wolf covered a total cumulative annual distance of 7,247 kilometres (4,503 mi). Mass migration occurs in mammals such as
3050-515: The oldest being Eocarcinus 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 , 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
3111-509: The open sea. Juvenile green sea turtles make use of Earth's magnetic field to navigate. Some crustaceans migrate, such as the largely-terrestrial Christmas Island red crab , which moves en masse each year by the millions. Like other crabs, they breathe using gills, which must remain wet, so they avoid direct sunlight, digging burrows to shelter from the sun. They mate on land near their burrows. The females incubate their eggs in their abdominal brood pouches for two weeks. Then they return to
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#17328017534023172-436: The patterns described here. An exception is some traditional migratory patterns such as transhumance , in which herders and their animals move seasonally between mountains and valleys, and the seasonal movements of nomads . Among the reptiles, adult sea turtles migrate long distances to breed, as do some amphibians. Hatchling sea turtles, too, emerge from underground nests, crawl down to the water, and swim offshore to reach
3233-930: The rise and spread of modern coral reefs , a key habitat for the decapods. Despite the inferred early origin, the oldest fossils of the group such as Palaeopalaemon only date to the Late Devonian . The cladogram below shows the internal relationships of Decapoda, from analysis by Wolfe et al. (2019). Dendrobranchiata (prawns) [REDACTED] Stenopodidea (boxer shrimp) [REDACTED] Procarididea Caridea ("true" shrimp) [REDACTED] Achelata (spiny lobsters and slipper lobsters) [REDACTED] Polychelida (benthic crustaceans) Astacidea (lobsters and crayfish) [REDACTED] Axiidea (mud shrimp, ghost shrimp, and burrowing shrimp) Gebiidea (mud lobsters and mud shrimp) [REDACTED] Anomura (hermit crabs and allies) [REDACTED] Brachyura ("true" crabs) [REDACTED] In
3294-536: The river of their birth when they have reached a few inches in size. Some traditional forms of human migration fit this pattern. Migrations can be studied using traditional identification tags such as bird rings , or tracked directly with electronic tracking devices. Before animal migration was understood, folklore explanations were formulated for the appearance and disappearance of some species, such as that barnacle geese grew from goose barnacles . Migration can take very different forms in different species, and has
3355-424: The sea to release their eggs at high tide in the moon's last quarter. The larvae spend a few weeks at sea and then return to land. Scientists gather observations of animal migration by tracking their movements. Animals were traditionally tracked with identification tags such as bird rings for later recovery. However, no information was obtained about the actual route followed between release and recovery, and only
3416-473: 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
3477-1141: 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 omnivores , feeding primarily on algae , and taking any other food, including molluscs , worms , other crustaceans , fungi , bacteria , and detritus , depending on their availability and
3538-473: The tidal movements. Tidal migration is often facilitated by ocean currents . While most migratory movements occur on an annual cycle, some daily movements are also described as migration. Many aquatic animals make a diel vertical migration , travelling a few hundred metres up and down the water column, while some jellyfish make daily horizontal migrations of a few hundred metres. Different kinds of animals migrate in different ways. Approximately 1,800 of
3599-403: The tides rise and fall, typically about every twelve hours. The cycle movements are associated with foraging of marine and bird species. Typically, during low tide, smaller or younger species will emerge to forage because they can survive in the shallower water and have less chance of being preyed upon. During high tide, larger species can be found due to the deeper water and nutrient upwelling from
3660-399: The winter to escape poor environmental conditions. Circadian migration is where birds utilise circadian rhythm (CR) to regulate migration in both fall and spring. In circadian migration, clocks of both circadian (daily) and circannual (annual) patterns are used to determine the birds' orientation in both time and space as they migrate from one destination to the next. This type of migration
3721-543: The world's 10,000 bird species migrate long distances each year in response to the seasons. Many of these migrations are north-south, with species feeding and breeding in high northern latitudes in the summer and moving some hundreds of kilometres south for the winter. Some species extend this strategy to migrate annually between the Northern and Southern Hemispheres. The Arctic tern has the longest migration journey of any bird: it flies from its Arctic breeding grounds to
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