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80-585: [REDACTED] Look up jaw  or jaws in Wiktionary, the free dictionary. Jaws or Jaw can refer to: Anatomy [ edit ] Jaw , an opposable articulated structure at the entrance of the mouth Mandible , the lower jaw Arts, entertainment, and media [ edit ] Jaws (James Bond) , a character in The Spy Who Loved Me and Moonraker Jaws (novel) ,

160-619: A lower jaw . The vertebrate jaw is derived from the most anterior two pharyngeal arches supporting the gills, and usually bears numerous teeth . The vertebrate jaw probably originally evolved in the Silurian period and appeared in the Placoderm fish which further diversified in the Devonian . The two most anterior pharyngeal arches are thought to have become the jaw itself and the hyoid arch, respectively. The hyoid system suspends

240-1072: A 1987 American film Music [ edit ] Jaws (soundtrack) Jaws (album) , a 1958 album by Eddie "Lockjaw" Davis JAWS (band) , an English surf pop/alternative rock band from Birmingham "Jaws", a song by BAE173 from Intersection: Blaze "Jaws", a song by Lights from Pep "Jaws", a song by Lemon Demon from the EP Nature Tapes People [ edit ] Jaw (Ćehu′pa) (c. 1850–1924), Hunkpapa Lakota winter count keeper and ledger art artist Jaw Shaw-kong , Taiwanese media personality and politician Aaron Homoki , American professional skateboarder Ron Jaworski , American football quarterback Joe Jordan (footballer) , Scottish footballer and coach Colin Lloyd , English darts player Darrell Waltrip , American race car driver Computing [ edit ] JAWS (screen reader) , for blind and vision-impaired computer users JAWS Scripting Language ,

320-421: A characteristic ladder-like appearance. The brain is in the head, encircling and mainly above the esophagus. It consists of the fused ganglia of the acron and one or two of the foremost segments that form the head – a total of three pairs of ganglia in most arthropods, but only two in chelicerates, which do not have antennae or the ganglion connected to them. The ganglia of other head segments are often close to

400-455: A common ancestor that was itself an arthropod. For example, Graham Budd 's analyses of Kerygmachela in 1993 and of Opabinia in 1996 convinced him that these animals were similar to onychophorans and to various Early Cambrian " lobopods ", and he presented an "evolutionary family tree" that showed these as "aunts" and "cousins" of all arthropods. These changes made the scope of the term "arthropod" unclear, and Claus Nielsen proposed that

480-605: A different system: the end-product of nitrogen metabolism is uric acid , which can be excreted as dry material; the Malpighian tubule system filters the uric acid and other nitrogenous waste out of the blood in the hemocoel, and dumps these materials into the hindgut, from which they are expelled as feces . Most aquatic arthropods and some terrestrial ones also have organs called nephridia ("little kidneys "), which extract other wastes for excretion as urine . The stiff cuticles of arthropods would block out information about

560-399: A lower, segmented endopod. These would later fuse into a single pair of biramous appendages united by a basal segment (protopod or basipod), with the upper branch acting as a gill while the lower branch was used for locomotion. The appendages of most crustaceans and some extinct taxa such as trilobites have another segmented branch known as exopods , but whether these structures have

640-474: A means of locomotion that was not dependent on water. Around the same time the aquatic, scorpion-like eurypterids became the largest ever arthropods, some as long as 2.5 m (8 ft 2 in). The oldest known arachnid is the trigonotarbid Palaeotarbus jerami , from about 420  million years ago in the Silurian period. Attercopus fimbriunguis , from 386  million years ago in

720-468: A modular organism with each module covered by its own sclerite (armor plate) and bearing a pair of biramous limbs . However, whether the ancestral limb was uniramous or biramous is far from a settled debate. This Ur-arthropod had a ventral mouth, pre-oral antennae and dorsal eyes at the front of the body. It was assumed to have been a non-discriminatory sediment feeder, processing whatever sediment came its way for food, but fossil findings hint that

800-424: A muscular tube that runs just under the back and for most of the length of the hemocoel. It contracts in ripples that run from rear to front, pushing blood forwards. Sections not being squeezed by the heart muscle are expanded either by elastic ligaments or by small muscles , in either case connecting the heart to the body wall. Along the heart run a series of paired ostia, non-return valves that allow blood to enter

880-421: A narrow category of " true bugs ", insects of the order Hemiptera . Arthropods are invertebrates with segmented bodies and jointed limbs. The exoskeleton or cuticles consists of chitin , a polymer of N-Acetylglucosamine . The cuticle of many crustaceans, beetle mites , the clades Penetini and Archaeoglenini inside the beetle subfamily Phrenapatinae , and millipedes (except for bristly millipedes )

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960-421: A novel by Peter Benchley Jaws (ride) , a theme park attraction based on the film series Jaws (video game) , a 1987 NES video game, based on the film Films [ edit ] Jaws (franchise) Jaws (film) , a 1975 American film directed by Steven Spielberg based on the novel by Peter Benchley Jaws 2 , a 1978 American film Jaws 3-D , a 1983 American film Jaws: The Revenge ,

1040-406: A pair of mechanical jaws Hydraulic rescue tools , of which one brand is known as the "Jaws of Life" Open jaw , or open-jaw, ticket, an airline return ticket whose destination and origin differ All pages with titles containing Jaw All pages with titles containing Jaws Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with

1120-536: A proprietary programming language Java Web Start or JAWS, a system for launching Java applications outside of a web browser Other uses [ edit ] Jaws (beach) , a big-wave surfing area in Hawaii Japan Anthropology Workshop , abbreviated JAWS Jaffe Wins Above Replacement Score (JAWS), a sabermetric tool for evaluating a baseball player's Hall of Fame worthiness See also [ edit ] Grab (tool) ,

1200-539: A single origin remain controversial. In some segments of all known arthropods the appendages have been modified, for example to form gills, mouth-parts, antennae for collecting information, or claws for grasping; arthropods are "like Swiss Army knives , each equipped with a unique set of specialized tools." In many arthropods, appendages have vanished from some regions of the body; it is particularly common for abdominal appendages to have disappeared or be highly modified. The most conspicuous specialization of segments

1280-453: A superphylum Ecdysozoa . Overall, however, the basal relationships of animals are not yet well resolved. Likewise, the relationships between various arthropod groups are still actively debated. Today, arthropods contribute to the human food supply both directly as food, and more importantly, indirectly as pollinators of crops. Some species are known to spread severe disease to humans, livestock , and crops . The word arthropod comes from

1360-463: A total metamorphosis to produce the adult form. The level of maternal care for hatchlings varies from nonexistent to the prolonged care provided by social insects . The evolutionary ancestry of arthropods dates back to the Cambrian period. The group is generally regarded as monophyletic , and many analyses support the placement of arthropods with cycloneuralians (or their constituent clades) in

1440-507: A wide field of view, and can detect fast movement and, in some cases, the polarization of light . On the other hand, the relatively large size of ommatidia makes the images rather coarse, and compound eyes are shorter-sighted than those of birds and mammals – although this is not a severe disadvantage, as objects and events within 20 cm (8 in) are most important to most arthropods. Several arthropods have color vision, and that of some insects has been studied in detail; for example,

1520-400: Is copper -based hemocyanin ; this is used by many crustaceans and a few centipedes . A few crustaceans and insects use iron-based hemoglobin , the respiratory pigment used by vertebrates . As with other invertebrates, the respiratory pigments of those arthropods that have them are generally dissolved in the blood and rarely enclosed in corpuscles as they are in vertebrates. The heart is

1600-502: Is also biomineralized with calcium carbonate . Calcification of the endosternite, an internal structure used for muscle attachments, also occur in some opiliones , and the pupal cuticle of the fly Bactrocera dorsalis contains calcium phosphate. Arthropoda is the largest animal phylum with the estimates of the number of arthropod species varying from 1,170,000 to 5~10 million and accounting for over 80 percent of all known living animal species. One arthropod sub-group ,

1680-438: Is encased in hardened cuticle. The joints between body segments and between limb sections are covered by flexible cuticle. The exoskeletons of most aquatic crustaceans are biomineralized with calcium carbonate extracted from the water. Some terrestrial crustaceans have developed means of storing the mineral, since on land they cannot rely on a steady supply of dissolved calcium carbonate. Biomineralization generally affects

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1760-859: Is in the head. The four major groups of arthropods – Chelicerata ( sea spiders , horseshoe crabs and arachnids ), Myriapoda ( symphylans , pauropods , millipedes and centipedes ), Pancrustacea ( oligostracans , copepods , malacostracans , branchiopods , hexapods , etc.), and the extinct Trilobita  – have heads formed of various combinations of segments, with appendages that are missing or specialized in different ways. Despite myriapods and hexapods both having similar head combinations, hexapods are deeply nested within crustacea while myriapods are not, so these traits are believed to have evolved separately. In addition, some extinct arthropods, such as Marrella , belong to none of these groups, as their heads are formed by their own particular combinations of segments and specialized appendages. Working out

1840-501: Is largely taken by a hemocoel , a cavity that runs most of the length of the body and through which blood flows. Arthropods have open circulatory systems . Most have a few short, open-ended arteries . In chelicerates and crustaceans, the blood carries oxygen to the tissues, while hexapods use a separate system of tracheae . Many crustaceans and a few chelicerates and tracheates use respiratory pigments to assist oxygen transport. The most common respiratory pigment in arthropods

1920-481: Is sometimes by indirect transfer of the sperm via an appendage or the ground, rather than by direct injection. Aquatic species use either internal or external fertilization . Almost all arthropods lay eggs, with many species giving birth to live young after the eggs have hatched inside the mother; but a few are genuinely viviparous , such as aphids . Arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo

2000-586: Is substantially simplified compared to fish. Most of the upper jaw bones ( premaxilla , maxilla , jugal , quadratojugal , and quadrate ) have been fused to the braincase, while the lower jaw bones ( dentary , splenial , angular , surangular , and articular ) have been fused together into a unit called the mandible . The jaw articulates via a hinge joint between the quadrate and articular. The jaws of tetrapods exhibit varying degrees of mobility between jaw bones . Some species have jaw bones completely fused, while others may have joints allowing for mobility of

2080-545: Is the Devonian Rhyniognatha hirsti , dated at 396 to 407 million years ago , its mandibles are thought to be a type found only in winged insects , which suggests that the earliest insects appeared in the Silurian period. However later study shows that Rhyniognatha most likely represent a myriapod, not even a hexapod. The unequivocal oldest known hexapod and insect is the springtail Rhyniella , from about 410  million years ago in

2160-555: Is the analogue of blood for most arthropods. An arthropod has an open circulatory system , with a body cavity called a haemocoel through which haemolymph circulates to the interior organs . Like their exteriors, the internal organs of arthropods are generally built of repeated segments. They have ladder-like nervous systems , with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of

2240-459: Is widespread among arthropods including both those that reproduce sexually and those that reproduce parthenogenetically . Although meiosis is a major characteristic of arthropods, understanding of its fundamental adaptive benefit has long been regarded as an unresolved problem, that appears to have remained unsettled. Aquatic arthropods may breed by external fertilization, as for example horseshoe crabs do, or by internal fertilization , where

2320-590: The American lobster reaching weights over 20 kg (44 lbs). The embryos of all arthropods are segmented, built from a series of repeated modules. The last common ancestor of living arthropods probably consisted of a series of undifferentiated segments, each with a pair of appendages that functioned as limbs. However, all known living and fossil arthropods have grouped segments into tagmata in which segments and their limbs are specialized in various ways. The three-part appearance of many insect bodies and

2400-568: The Burgess Shale fossils from about 505  million years ago identified many arthropods, some of which could not be assigned to any of the well-known groups, and thus intensified the debate about the Cambrian explosion . A fossil of Marrella from the Burgess Shale has provided the earliest clear evidence of moulting . The earliest fossil of likely pancrustacean larvae date from about 514  million years ago in

2480-490: The Cambrian , followed by unique taxa like Yicaris and Wujicaris . The purported pancrustacean/ crustacean affinity of some cambrian arthropods (e.g. Phosphatocopina , Bradoriida and Hymenocarine taxa like waptiids) were disputed by subsequent studies, as they might branch before the mandibulate crown-group. Within the pancrustacean crown-group, only Malacostraca , Branchiopoda and Pentastomida have Cambrian fossil records. Crustacean fossils are common from

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2560-624: The Devonian period, bears the earliest known silk-producing spigots, but its lack of spinnerets means it was not one of the true spiders , which first appear in the Late Carboniferous over 299  million years ago . The Jurassic and Cretaceous periods provide a large number of fossil spiders, including representatives of many modern families. The oldest known scorpion is Dolichophonus , dated back to 436  million years ago . Lots of Silurian and Devonian scorpions were previously thought to be gill -breathing, hence

2640-568: The Greek ἄρθρον árthron ' joint ' , and πούς pous ( gen. ποδός podos ) ' foot ' or ' leg ' , which together mean "jointed leg", with the word "arthropodes" initially used in anatomical descriptions by Barthélemy Charles Joseph Dumortier published in 1832. The designation "Arthropoda" appears to have been first used in 1843 by the German zoologist Johann Ludwig Christian Gravenhorst (1777–1857). The origin of

2720-703: The Ordovician period onwards. They have remained almost entirely aquatic, possibly because they never developed excretory systems that conserve water. Arthropods provide the earliest identifiable fossils of land animals, from about 419  million years ago in the Late Silurian , and terrestrial tracks from about 450  million years ago appear to have been made by arthropods. Arthropods possessed attributes that were easy coopted for life on land; their existing jointed exoskeletons provided protection against desiccation, support against gravity and

2800-465: The chelicerates , including spiders and scorpions ; the crustaceans; and the uniramia , consisting of onychophorans , myriapods and hexapods . These arguments usually bypassed trilobites , as the evolutionary relationships of this class were unclear. Proponents of polyphyly argued the following: that the similarities between these groups are the results of convergent evolution , as natural consequences of having rigid, segmented exoskeletons ; that

2880-668: The insects , includes more described species than any other taxonomic class . The total number of species remains difficult to determine. This is due to the census modeling assumptions projected onto other regions in order to scale up from counts at specific locations applied to the whole world. A study in 1992 estimated that there were 500,000 species of animals and plants in Costa Rica alone, of which 365,000 were arthropods. They are important members of marine, freshwater, land and air ecosystems and one of only two major animal groups that have adapted to life in dry environments;

2960-410: The ova remain in the female's body and the sperm must somehow be inserted. All known terrestrial arthropods use internal fertilization. Opiliones (harvestmen), millipedes , and some crustaceans use modified appendages such as gonopods or penises to transfer the sperm directly to the female. However, most male terrestrial arthropods produce spermatophores , waterproof packets of sperm , which

3040-443: The phylum Arthropoda . They possess an exoskeleton with a cuticle made of chitin , often mineralised with calcium carbonate , a body with differentiated ( metameric ) segments , and paired jointed appendages . In order to keep growing, they must go through stages of moulting , a process by which they shed their exoskeleton to reveal a new one. They form an extremely diverse group of up to ten million species. Haemolymph

3120-645: The therian mammal , the premaxilla that constituted the anterior tip of the upper jaw in reptiles has reduced in size; and most of the mesenchyme at the ancestral upper jaw tip has become a protruded mammalian nose . Sea urchins possess unique jaws which display five-part symmetry, termed the Aristotle's lantern . Each unit of the jaw holds a single, perpetually growing tooth composed of crystalline calcium carbonate . Arthropod Condylipoda Latreille, 1802 Arthropods ( / ˈ ɑːr θ r ə p ɒ d / ARTH -rə-pod ) are invertebrates in

3200-691: The Devonian period, and the palaeodictyopteran Delitzschala bitterfeldensis , from about 325  million years ago in the Carboniferous period, respectively. The Mazon Creek lagerstätten from the Late Carboniferous, about 300  million years ago , include about 200 species, some gigantic by modern standards, and indicate that insects had occupied their main modern ecological niches as herbivores , detritivores and insectivores . Social termites and ants first appear in

3280-650: The Early Cretaceous , and advanced social bees have been found in Late Cretaceous rocks but did not become abundant until the Middle Cenozoic . From 1952 to 1977, zoologist Sidnie Manton and others argued that arthropods are polyphyletic , in other words, that they do not share a common ancestor that was itself an arthropod. Instead, they proposed that three separate groups of "arthropods" evolved separately from common worm-like ancestors:

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3360-423: The adult body. Dragonfly larvae have the typical cuticles and jointed limbs of arthropods but are flightless water-breathers with extendable jaws. Crustaceans commonly hatch as tiny nauplius larvae that have only three segments and pairs of appendages. Based on the distribution of shared plesiomorphic features in extant and fossil taxa, the last common ancestor of all arthropods is inferred to have been as

3440-470: The animal cannot support itself and finds it very difficult to move, and the new endocuticle has not yet formed. The animal continues to pump itself up to stretch the new cuticle as much as possible, then hardens the new exocuticle and eliminates the excess air or water. By the end of this phase, the new endocuticle has formed. Many arthropods then eat the discarded cuticle to reclaim its materials. Because arthropods are unprotected and nearly immobilized until

3520-440: The brain and function as part of it. In insects these other head ganglia combine into a pair of subesophageal ganglia , under and behind the esophagus. Spiders take this process a step further, as all the segmental ganglia are incorporated into the subesophageal ganglia, which occupy most of the space in the cephalothorax (front "super-segment"). There are two different types of arthropod excretory systems. In aquatic arthropods,

3600-462: The class was already quite diverse and worldwide, suggesting that they had been around for quite some time. In the Maotianshan shales , which date back to 518 million years ago, arthropods such as Kylinxia and Erratus have been found that seem to represent transitional fossils between stem (e.g. Radiodonta such as Anomalocaris ) and true arthropods. Re-examination in the 1970s of

3680-439: The dentary, quadrate, or maxilla. The snake skull shows the greatest degree of cranial kinesis , which allows the snake to swallow large prey items. In mammals, the jaws are made up of the mandible (lower jaw) and the maxilla (upper jaw). In the ape , there is a reinforcement to the lower jaw bone called the simian shelf . In the evolution of the mammalian jaw, two of the bones of the jaw structure (the articular bone of

3760-449: The details of their structure, but generally consist of three main layers: the epicuticle , a thin outer waxy coat that moisture-proofs the other layers and gives them some protection; the exocuticle , which consists of chitin and chemically hardened proteins ; and the endocuticle , which consists of chitin and unhardened proteins. The exocuticle and endocuticle together are known as the procuticle . Each body segment and limb section

3840-520: The direction from which light is coming, using the shadow cast by the walls of the cup. However, the main eyes of spiders are pigment-cup ocelli that are capable of forming images, and those of jumping spiders can rotate to track prey. Compound eyes consist of fifteen to several thousand independent ommatidia , columns that are usually hexagonal in cross section . Each ommatidium is an independent sensor, with its own light-sensitive cells and often with its own lens and cornea . Compound eyes have

3920-469: The end-product of biochemical reactions that metabolise nitrogen is ammonia , which is so toxic that it needs to be diluted as much as possible with water. The ammonia is then eliminated via any permeable membrane, mainly through the gills. All crustaceans use this system, and its high consumption of water may be responsible for the relative lack of success of crustaceans as land animals. Various groups of terrestrial arthropods have independently developed

4000-415: The epidermis. Setae are as varied in form and function as appendages. For example, they are often used as sensors to detect air or water currents, or contact with objects; aquatic arthropods use feather -like setae to increase the surface area of swimming appendages and to filter food particles out of water; aquatic insects, which are air-breathers, use thick felt -like coats of setae to trap air, extending

4080-403: The evolutionary stages by which all these different combinations could have appeared is so difficult that it has long been known as "The arthropod head problem ". In 1960, R. E. Snodgrass even hoped it would not be solved, as he found trying to work out solutions to be fun. Arthropod exoskeletons are made of cuticle , a non-cellular material secreted by the epidermis . Their cuticles vary in

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4160-504: The exocuticle and the outer part of the endocuticle. Two recent hypotheses about the evolution of biomineralization in arthropods and other groups of animals propose that it provides tougher defensive armor, and that it allows animals to grow larger and stronger by providing more rigid skeletons; and in either case a mineral-organic composite exoskeleton is cheaper to build than an all-organic one of comparable strength. The cuticle may have setae (bristles) growing from special cells in

4240-502: The females take into their bodies. A few such species rely on females to find spermatophores that have already been deposited on the ground, but in most cases males only deposit spermatophores when complex courtship rituals look likely to be successful. Most arthropods lay eggs, but scorpions are ovoviviparous : they produce live young after the eggs have hatched inside the mother, and are noted for prolonged maternal care. Newly born arthropods have diverse forms, and insects alone cover

4320-425: The form of membranes that function as eardrums , but are connected directly to nerves rather than to auditory ossicles . The antennae of most hexapods include sensor packages that monitor humidity , moisture and temperature. Most arthropods lack balance and acceleration sensors, and rely on their eyes to tell them which way is up. The self-righting behavior of cockroaches is triggered when pressure sensors on

4400-406: The ganglia of these segments and encircle the esophagus . The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong. Arthropods use combinations of compound eyes and pigment-pit ocelli for vision. In most species, the ocelli can only detect the direction from which light is coming, and the compound eyes are

4480-410: The gut and the body wall that accommodates the internal organs. The strong, segmented limbs of arthropods eliminate the need for one of the coelom's main ancestral functions, as a hydrostatic skeleton , which muscles compress in order to change the animal's shape and thus enable it to move. Hence the coelom of the arthropod is reduced to small areas around the reproductive and excretory systems. Its place

4560-432: The heart but prevent it from leaving before it reaches the front. Arthropods have a wide variety of respiratory systems. Small species often do not have any, since their high ratio of surface area to volume enables simple diffusion through the body surface to supply enough oxygen. Crustacea usually have gills that are modified appendages. Many arachnids have book lungs . Tracheae, systems of branching tunnels that run from

4640-479: The idea that scorpions were primitively aquatic and evolved air-breathing book lungs later on. However subsequent studies reveal most of them lacking reliable evidence for an aquatic lifestyle, while exceptional aquatic taxa (e.g. Waeringoscorpio ) most likely derived from terrestrial scorpion ancestors. The oldest fossil record of hexapod is obscure, as most of the candidates are poorly preserved and their hexapod affinities had been disputed. An iconic example

4720-527: The jaw from the braincase of the skull, permitting great mobility of the jaws. While there is no fossil evidence directly to support this theory, it makes sense in light of the numbers of pharyngeal arches that are visible in extant jawed vertebrates (the Gnathostomes ), which have seven arches, and primitive jawless vertebrates (the Agnatha ), which have nine. The original selective advantage offered by

4800-598: The jaw may not be related to feeding, but rather to increased respiration efficiency. The jaws were used in the buccal pump (observable in modern fish and amphibians ) that pumps water across the gills of fish or air into the lungs in the case of amphibians. Over evolutionary time the more familiar use of jaws (to humans), in feeding, was selected for and became a very important function in vertebrates. Many teleost fish have substantially modified jaws for suction feeding and jaw protrusion , resulting in highly complex jaws with dozens of bones involved. The jaw in tetrapods

4880-490: The jaws are chitinous and oppose laterally, and may consist of mandibles or chelicerae . These jaws are often composed of numerous mouthparts . Their function is fundamentally for food acquisition, conveyance to the mouth, and/or initial processing ( mastication or chewing ). Many mouthparts and associate structures (such as pedipalps ) are modified legs. In most vertebrates , the jaws are bony or cartilaginous and oppose vertically, comprising an upper jaw and

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4960-417: The juvenile arthropods continue in their life cycle until they either pupate or moult again. In the initial phase of moulting, the animal stops feeding and its epidermis releases moulting fluid, a mixture of enzymes that digests the endocuticle and thus detaches the old cuticle. This phase begins when the epidermis has secreted a new epicuticle to protect it from the enzymes, and the epidermis secretes

5040-842: The last common ancestor of both arthropods and Priapulida shared the same specialized mouth apparatus: a circular mouth with rings of teeth used for capturing animal prey. It has been proposed that the Ediacaran animals Parvancorina and Spriggina , from around 555  million years ago , were arthropods, but later study shows that their affinities of being origin of arthropods are not reliable. Small arthropods with bivalve-like shells have been found in Early Cambrian fossil beds dating 541 to 539 million years ago in China and Australia. The earliest Cambrian trilobite fossils are about 520 million years old, but

5120-437: The lower jaw, and quadrate ) were reduced in size and incorporated into the ear , while many others have been fused together. As a result, mammals show little or no cranial kinesis , and the mandible is attached to the temporal bone by the temporomandibular joints . Temporomandibular joint dysfunction is a common disorder of these joints, characterized by pain, clicking and limitation of mandibular movement. Especially in

5200-439: The main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey. Arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many bristles known as setae that project through their cuticles. Similarly, their reproduction and development are varied; all terrestrial species use internal fertilization , but this

5280-518: The name has been the subject of considerable confusion, with credit often given erroneously to Pierre André Latreille or Karl Theodor Ernst von Siebold instead, among various others. Terrestrial arthropods are often called bugs. The term is also occasionally extended to colloquial names for freshwater or marine crustaceans (e.g., Balmain bug , Moreton Bay bug , mudbug ) and used by physicians and bacteriologists for disease-causing germs (e.g., superbugs ), but entomologists reserve this term for

5360-430: The new cuticle has hardened, they are in danger both of being trapped in the old cuticle and of being attacked by predators . Moulting may be responsible for 80 to 90% of all arthropod deaths. Arthropod bodies are also segmented internally, and the nervous, muscular, circulatory, and excretory systems have repeated components. Arthropods come from a lineage of animals that have a coelom , a membrane-lined cavity between

5440-407: The new exocuticle while the old cuticle is detaching. When this stage is complete, the animal makes its body swell by taking in a large quantity of water or air, and this makes the old cuticle split along predefined weaknesses where the old exocuticle was thinnest. It commonly takes several minutes for the animal to struggle out of the old cuticle. At this point, the new one is wrinkled and so soft that

5520-469: The old exoskeleton, the exuviae , after growing a new one that is not yet hardened. Moulting cycles run nearly continuously until an arthropod reaches full size. The developmental stages between each moult (ecdysis) until sexual maturity is reached is called an instar . Differences between instars can often be seen in altered body proportions, colors, patterns, changes in the number of body segments or head width. After moulting, i.e. shedding their exoskeleton,

5600-594: The ommatidia of bees contain receptors for both green and ultra-violet . A few arthropods, such as barnacles , are hermaphroditic , that is, each can have the organs of both sexes . However, individuals of most species remain of one sex their entire lives. A few species of insects and crustaceans can reproduce by parthenogenesis , especially if conditions favor a "population explosion". However, most arthropods rely on sexual reproduction , and parthenogenetic species often revert to sexual reproduction when conditions become less favorable. The ability to undergo meiosis

5680-529: The openings in the body walls, deliver oxygen directly to individual cells in many insects, myriapods and arachnids . Living arthropods have paired main nerve cords running along their bodies below the gut, and in each segment the cords form a pair of ganglia from which sensory and motor nerves run to other parts of the segment. Although the pairs of ganglia in each segment often appear physically fused, they are connected by commissures (relatively large bundles of nerves), which give arthropod nervous systems

5760-467: The other is amniotes , whose living members are reptiles, birds and mammals. Both the smallest and largest arthropods are crustaceans . The smallest belong to the class Tantulocarida , some of which are less than 100 micrometres (0.0039 in) long. The largest are species in the class Malacostraca , with the legs of the Japanese spider crab potentially spanning up to 4 metres (13 ft) and

5840-438: The outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact, arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly setae , respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste and smell , often by means of setae. Pressure sensors often take

5920-439: The range of extremes. Some hatch as apparently miniature adults (direct development), and in some cases, such as silverfish , the hatchlings do not feed and may be helpless until after their first moult. Many insects hatch as grubs or caterpillars , which do not have segmented limbs or hardened cuticles, and metamorphose into adult forms by entering an inactive phase in which the larval tissues are broken down and re-used to build

6000-493: The single branch serves as a leg. includes Aysheaia and Peripatus   includes Hallucigenia and Microdictyon includes modern tardigrades as well as extinct animals like Kerygmachela and Opabinia Anomalocaris includes living groups and extinct forms such as trilobites Further analysis and discoveries in the 1990s reversed this view, and led to acceptance that arthropods are monophyletic , in other words they are inferred to share

6080-433: The three groups use different chemical means of hardening the cuticle; that there were significant differences in the construction of their compound eyes; that it is hard to see how such different configurations of segments and appendages in the head could have evolved from the same ancestor; and that crustaceans have biramous limbs with separate gill and leg branches, while the other two groups have uniramous limbs in which

6160-574: The time they can spend under water; heavy, rigid setae serve as defensive spines. Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, some still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors; for example, all spiders extend their legs hydraulically and can generate pressures up to eight times their resting level. The exoskeleton cannot stretch and thus restricts growth. Arthropods, therefore, replace their exoskeletons by undergoing ecdysis (moulting), or shedding

6240-447: The title Jaws . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Jaws&oldid=1256344942 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages jaw In arthropods ,

6320-477: The two-part appearance of spiders is a result of this grouping. There are no external signs of segmentation in mites . Arthropods also have two body elements that are not part of this serially repeated pattern of segments, an ocular somite at the front, where the mouth and eyes originated, and a telson at the rear, behind the anus . Originally it seems that each appendage-bearing segment had two separate pairs of appendages: an upper, unsegmented exite and

6400-656: The underside of the feet report no pressure. However, many malacostracan crustaceans have statocysts , which provide the same sort of information as the balance and motion sensors of the vertebrate inner ear . The proprioceptors of arthropods, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. However, little is known about what other internal sensors arthropods may have. Most arthropods have sophisticated visual systems that include one or more usually both of compound eyes and pigment-cup ocelli ("little eyes"). In most cases ocelli are only capable of detecting

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