27-459: A crab is a type of crustacean. Crab or crabs may also refer to: Crab 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
54-423: 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
81-493: 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
108-419: 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
135-498: 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
162-480: 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
189-575: A thick exoskeleton . They generally have five pairs of legs, and they have pincer claws on 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
216-471: 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
243-441: 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
270-592: 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
297-411: 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,
SECTION 10
#1732791629444324-823: 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
351-526: 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
378-647: 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 ,
405-475: 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
432-466: 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
459-693: 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
486-426: 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,
513-532: 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
540-436: 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
567-459: 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
SECTION 20
#1732791629444594-723: 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
621-571: 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 Ecdysis Too Many Requests If you report this error to
648-436: 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
675-518: 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
702-473: 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
729-1153: 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
#443556