101-749: A sawshark or saw shark is a member of a shark order ( Pristiophoriformes / p r ɪ s t i ˈ ɒ f ɒr ɪ f ɔːr m iː z / ) bearing a unique long, saw-like rostrum (snout or bill) edged with sharp teeth, which they use to slash and disable their prey. There are eight species within the Pristiophoriformes, including the longnose or common sawshark ( Pristiophorus cirratus ), shortnose sawshark ( Pristiophorus nudipinnis ), Japanese sawshark ( Pristiophorus japonicas ), Bahamas sawshark ( Pristiophorus schroederi ), sixgill sawshark ( Pliotrema warreni ), African dwarf sawshark ( Pristiophorus nancyae ), Lana's sawshark ( Pristiophorus lanae ) and
202-426: A heterocercal caudal fin in which the dorsal portion is usually noticeably larger than the ventral portion. This is because the shark's vertebral column extends into that dorsal portion, providing a greater surface area for muscle attachment. This allows more efficient locomotion among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a homocercal caudal fin. Tiger sharks have
303-421: A C shape (see image). The location of anatomical structures can also be described in relation to different anatomical landmarks . They are used in anatomy, surface anatomy, surgery, and radiology. Structures may be described as being at the level of a specific spinal vertebra , depending on the section of the vertebral column the structure is at. The position is often abbreviated. For example, structures at
404-754: A brownish grey color and becomes white along the ventral side. Little else is known about the African Dwarf Sawshark as it is a newly discovered species. The shortnose sawshark ( Pristiophorus nudipinnis ) is similar to the longnose sawshark; however, it has a slightly compressed body and shorter more narrow rostrum. It has 13 teeth in front of its barbels and 6 behind. The shortnose sawshark tends to be uniformly slate grey with no markings on its dorsal side and pale white or cream on its ventral side. Females reach around 124 cm (49 in) long, and males reach around 110 cm (43 in) long. These sharks can live to be up to 9 years old. Like other sawsharks,
505-415: A cell similar to hair cells present in the vertebrate ear that interact with the surrounding aquatic environment. This helps sharks distinguish between the currents around them, obstacles off on their periphery, and struggling prey out of visual view. The shark can sense frequencies in the range of 25 to 50 Hz . Shark lifespans vary by species. Most live 20 to 30 years. The spiny dogfish has one of
606-418: A constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species. The respiratory and circulatory process begins when deoxygenated venous blood travels to
707-495: A few known exceptions, such as the bull shark and the river sharks , which can be found in both seawater and freshwater, and the Ganges shark , which lives only in freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics . They have numerous sets of replaceable teeth. Several species are apex predators , which are organisms that are at
808-509: A group of elasmobranch fish characterized by a cartilaginous skeleton , five to seven gill slits on the sides of the head , and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii ) and are the sister group to the Batoidea ( rays and kin). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with
909-423: A large upper lobe , which allows for slow cruising and sudden bursts of speed. The tiger shark must be able to twist and turn in the water easily when hunting to support its varied diet, whereas the porbeagle shark , which hunts schooling fish such as mackerel and herring , has a large lower lobe to help it keep pace with its fast-swimming prey. Other tail adaptations help sharks catch prey more directly, such as
1010-416: A long blade-like snout. Although they are similar in appearances, saw sharks are distinct from sawfish . Sawfish are not sharks, but a type of ray . The gill slits of the sawfishes are positioned on the underside like a ray, but the gill slits of the saw shark are positioned on the side like a shark. Sawfish can have a much larger size, lack barbels, and have evenly sized teeth rather than alternating teeth of
1111-438: A long surface area, requiring food to circulate inside the short gut until fully digested, when remaining waste products pass into the cloaca . A few sharks appear fluorescent under blue light, such as the swell shark and the chain catshark , where the fluorophore derives from a metabolite of kynurenic acid . Sharks have keen olfactory senses, located in the short duct (which is not fused, unlike bony fish) between
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#17328521293581212-450: A long, thin, and flattened snout. Midway down the snout, nasal barbels protrude on both sides of the snout. Near the barbels, the longnose sawshark possesses a pair of ampullae of Lorenzini. It is unique among the sawshark family by having a longer snout than any of its counter species. The longnose sawshark is not very large with lengths ranging from around 14 inches at birth to 38 inches in males and 44 inches in females. They can also grow to
1313-414: A pair of long barbels about halfway along the snout. They have two dorsal fins , but lack anal fins . Genus Pliotrema has six gill slits , and Pristiophorus the more usual five. The teeth of the saw typically alternate between large and small. Saw sharks reach a length of up to 5 feet and a weight of 18.7 pounds, with females tending to be slightly larger than males. The body of a longnose saw shark
1414-428: A prize catch. They dwell in the rage of 37–500 m, preferring to stay in the warmer water. They have between 5 and 7 pups from 7–17 eggs. They have these young in the range of 37–50 m deep to make sure the pups are warm. The longnose sawshark aka the common sawshark ( Pristiophorus cirratus ) is one of 9 species within the family Pristiophoridae. It has unique physical characteristics which include
1515-445: A row behind the head. A modified slit called a spiracle lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active pelagic sharks. While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure
1616-596: A shark-like morphology, such as hybodonts . Shark-like chondrichthyans such as Cladoselache and Doliodus first appeared in the Devonian Period (419–359 million years), though some fossilized chondrichthyan-like scales are as old as the Late Ordovician (458–444 million years ago). The earliest confirmed modern sharks (selachimorphs) are known from the Early Jurassic around 200 million years ago , with
1717-405: A similar mechanism for maintaining an elevated body temperature. Larger species, like the whale shark, are able to conserve their body heat through sheer size when they dive to colder depths, and the scalloped hammerhead close its mouth and gills when they dives to depths of around 800 metres, holding its breath till it reach warmer waters again. In contrast to bony fish, with the exception of
1818-555: A single type of cone photoreceptor sensitive to green and, seeing only in shades of grey and green, are believed to be effectively colorblind. The study indicates that an object's contrast against the background, rather than colour, may be more important for object detection. Although it is hard to test the hearing of sharks, they may have a sharp sense of hearing and can possibly hear prey from many miles away. The hearing sensitivity for most shark species lies between 20 and 1000 Hz. A small opening on each side of their heads (not
1919-407: A small number of well-developed young as opposed to a large number of poorly developed young. Fecundity in sharks ranges from 2 to over 100 young per reproductive cycle. Sharks mature slowly relative to many other fish. For example, lemon sharks reach sexual maturity at around age 13–15. Rostral (anatomical term) Standard anatomical terms of location are used to describe unambiguously
2020-642: A species of sawshark that inhabits the Philippine coast. It was discovered in 1966 by Dave Ebert, who distinguished it as a new species of sawshark based on its number of rostral teeth. Lana's sawshark was named after Lana Ebert on the occasion of her graduation from the University of Francisco. It has a dark uniform brown color on the dorsal side and a pale white on the ventral side. It is slender bodied, has five gills on each side, and can grow to be around 70 cm. The African dwarf sawshark ( Pristiophorus nancyae )
2121-414: A standard set of terms to communicate clearly the position of a structure. Standard anatomical and zoological terms of location have been developed, usually based on Latin and Greek words, to enable all biological and medical scientists, veterinarians , doctors and anatomists to precisely delineate and communicate information about animal bodies and their organs, even though the meaning of some of
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#17328521293582222-403: A state in which a part further away is abnormally placed towards (varus) or away from (valgus) the midline. The terms proximal (from Latin proximus 'nearest') and distal (from Latin distare 'to stand away from') are used to describe parts of a feature that are close to or distant from the main mass of the body, respectively. Thus the upper arm in humans
2323-400: A tissue called tapetum lucidum . This tissue is behind the retina and reflects light back to it, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Many sharks can contract and dilate their pupils , like humans, something no teleost fish can do. Sharks have eyelids, but they do not blink because
2424-462: A weight of 18.7 pounds. They are known to swim in the waters off the southern coast of Australia's continental shelf. They can also be found in the eastern portion of the Indian Ocean. The longnose sawshark prefers to swim in both the open sea and coastal regions from the surface to a depth of 600m. The longnose Sawshark is known to mainly prey on small crustaceans. It uses its barbels to detect prey on
2525-452: A wound on the upper arm, but proximal to a wound on the lower arm. The terms are also applied to internal anatomy, such as to the reproductive tract of snails . Unfortunately, different authors use the terms in opposite senses. Some consider "distal" as further from a point of origin near the centre of the body and others as further from where the organ reaches the body's surface; or other points of origin may be envisaged. This terminology
2626-674: Is bipedal or quadrupedal . Additionally, for some animals such as invertebrates , some terms may not have any meaning at all; for example, an animal that is radially symmetrical will have no anterior surface, but can still have a description that a part is close to the middle ("proximal") or further from the middle ("distal"). International organisations have determined vocabularies that are often used as standards for subdisciplines of anatomy. For example, Terminologia Anatomica for humans and Nomina Anatomica Veterinaria for animals. These allow parties that use anatomical terms, such as anatomists , veterinarians , and medical doctors , to have
2727-481: Is a pale yellow to white. This deep water dwelling fish is located off the Northeastern shore of Australia, in depths up to 176–405 m. It averages in size at about 95 cm. Other than its location and appearance little is known of the creature; it is hard to catch due to its ability to travel into the depths of the ocean. The Japanese sawshark ( Pristiophorus japonicus ) is a species of sawshark that lives off
2828-419: Is a small five-gill sawshark that lives off the coast of Mozambique. It was first discovered in 2011 when a specimen was caught off the coast of Mozambique at a depth of 1,600 ft. The African dwarf sawshark has since then been spotted off the coasts of Kenya and Yemen. It can be distinguished from other sawsharks by its location, and by having its barbels closer to its mouth than the end of its rostrum. It has
2929-413: Is also employed in molecular biology and therefore by extension is also used in chemistry, specifically referring to the atomic loci of molecules from the overall moiety of a given compound. Central and peripheral refer to the distance towards and away from the centre of something. That might be an organ, a region in the body, or an anatomical structure. For example, the central nervous system and
3030-410: Is covered in tiny placoid scales: modified teeth covered in hard enamel. The body is a yellow-brown color which is sometimes covered in dark spots or blotches. This coloration allows the saw shark to easily blend with the sandy ocean floor. These sharks typically feed on small fish, squid , and crustaceans , depending on species. The function of the sawshark barbels are not well understood, and neither
3131-648: Is debated. Some believe that electro- and chemoreception are more significant, while others point to the nictating membrane as evidence that sight is important, since presumably the shark would not protect its eyes were they unimportant. The use of sight probably varies with species and water conditions. The shark's field of vision can swap between monocular and stereoscopic at any time. A micro-spectrophotometry study of 17 species of sharks found 10 had only rod photoreceptors and no cone cells in their retinas giving them good night vision while making them colorblind . The remaining seven species had in addition to rods
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3232-668: Is divided into the superorders Galea (or Galeomorphii ), and Squalea (or Squalomorphii ). The Galeans are the Heterodontiformes , Orectolobiformes , Lamniformes , and Carcharhiniformes . Lamnoids and Carcharhinoids are usually placed in one clade , but recent studies show that Lamnoids and Orectoloboids are a clade. Some scientists now think that Heterodontoids may be Squalean. The Squaleans are divided into Hexanchiformes and Squalomorpha. The former includes cow shark and frilled shark , though some authors propose that both families be moved to separate orders. The Squalomorpha contains
3333-409: Is high, species of sharks from the family Carcharhinidae have smaller olfactory bulbs. Sharks found in deeper waters also have larger olfactory bulbs. Sharks have the ability to determine the direction of a given scent based on the timing of scent detection in each nostril. This is similar to the method mammals use to determine direction of sound. They are more attracted to the chemicals found in
3434-530: Is how they use their rostrum. It is possible they use it in a similar fashion as sawfishes, and hit prey with side-to-side swipes of the saw, crippling them. The saw could also be utilized against other predators in defense. The saw is covered with specialized sensory organs ( ampullae of Lorenzini ) which detect an electric field which is given off by buried prey. Saw sharks life history is still poorly understood. Mating season occurs seasonally in coastal areas. Saw sharks are ovoviviparous meaning eggs hatch inside
3535-455: Is known for its six pairs of gills located on its sides close to the head. They are pale brown in color, with a white underbelly. Along with their color, their size sets them apart from the other types of sawfish: The females are around 136 cm where the males are around 112 cm. Sixgill sawsharks feed on shrimp, squid and bony fish. They are located around the southern portion of South Africa, and Madagascar. Where found, they are considered
3636-581: Is limited, so sharks employ dynamic lift to maintain depth while swimming. Sand tiger sharks store air in their stomachs, using it as a form of swim bladder. Bottom-dwelling sharks, like the nurse shark , have negative buoyancy, allowing them to rest on the ocean floor. Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility . Researchers use this condition to handle sharks safely. Like other fish, sharks extract oxygen from seawater as it passes over their gills . Unlike other fish, shark gill slits are not covered, but lie in
3737-434: Is observed in the cookiecutter shark . Tooth shape depends on the shark's diet: those that feed on mollusks and crustaceans have dense and flattened teeth used for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey such as mammals have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. The teeth of plankton-feeders such as
3838-402: Is proximal and the hand is distal. "Proximal and distal" are frequently used when describing appendages , such as fins , tentacles , and limbs . Although the direction indicated by "proximal" and "distal" is always respectively towards or away from the point of attachment, a given structure can be either proximal or distal in relation to another point of reference. Thus the elbow is distal to
3939-402: Is rarely used in human anatomy, apart from embryology, and refers more to the front of the face than the superior aspect of the organism. Similarly, the term "caudal" is used more in embryology and only occasionally used in human anatomy. This is because the brain is situated at the superior part of the head whereas the nose is situated in the anterior part. Thus, the "rostrocaudal axis" refers to
4040-481: Is roughly symmetrical. To do this, distinct ends of an organism are chosen, and the axis is named according to those directions. An organism that is symmetrical on both sides has three main axes that intersect at right angles . An organism that is round or not symmetrical may have different axes. Example axes are: Examples of axes in specific animals are shown below. Several terms are commonly seen and used as prefixes : Other terms are used as suffixes , added to
4141-492: Is still evidential in several species termed " dogfish ," or the porbeagle . The etymology of the word shark is uncertain. The most likely etymology states that the original sense of the word was that of "predator, one who preys on others" from the Dutch schurk , meaning 'villain, scoundrel' ( cf. card shark , loan shark , etc.), which was later applied to the fish due to its predatory behaviour. A now disproven theory
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4242-736: Is that it derives from the Yucatec Maya word xook ( pronounced [ʃoːk] ), meaning 'shark'. Evidence for this etymology came from the Oxford English Dictionary , which notes that shark first came into use after Sir John Hawkins ' sailors exhibited one in London in 1569 and posted " sharke " to refer to the large sharks of the Caribbean Sea . However, the Middle English Dictionary records an isolated occurrence of
4343-458: Is to the head or tail of an animal. To describe how close to the head of an animal something is, three distinct terms are used: For example, in horses , the eyes are caudal to the nose and rostral to the back of the head. These terms are generally preferred in veterinary medicine and not used as often in human medicine. In humans, "cranial" and "cephalic" are used to refer to the skull, with "cranial" being used more commonly. The term "rostral"
4444-434: Is to the midline, or the medial plane. Lateral (from Latin lateralis 'to the side') describes something to the sides of an animal, as in "left lateral" and "right lateral". Medial (from Latin medius 'middle') describes structures close to the midline, or closer to the midline than another structure. For example, in a human, the arms are lateral to the torso . The genitals are medial to
4545-665: The Devonian . Anachronistidae , the oldest probable representatives of Neoselachii, the group containing modern sharks (Selachimorpha) and rays (Batoidea) to the exclusion of most extinct elasmobranch groups, date to the Carboniferous . Selachiimorpha and Batoidea are suggested by some to have diverged during the Triassic . Fossils of the earliest true sharks may have appeared during the Permian , based on remains of " synechodontiforms " found in
4646-704: The Squaliformes and the Hypnosqualea. The Hypnosqualea may be invalid. It includes the Squatiniformes , and the Pristorajea, which may also be invalid, but includes the Pristiophoriformes and the Batoidea . There are more than 500 species of sharks split across thirteen orders , including several orders of sharks that have gone extinct: Shark teeth are embedded in the gums rather than directly affixed to
4747-478: The anatomy of animals , including humans . The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position . This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes . The meaning of terms that are used can change depending on whether an organism
4848-438: The anterior superior iliac spine , the medial malleolus or the medial epicondyle . Anatomical lines are used to describe anatomical location. For example, the mid-clavicular line is used as part of the cardiac exam in medicine to feel the apex beat of the heart . Special terms are used to describe the mouth and teeth. Fields such as osteology , palaeontology and dentistry apply special terms of location to describe
4949-463: The bull shark , which has developed a way to change its kidney function to excrete large amounts of urea. When a shark dies, the urea is broken down to ammonia by bacteria, causing the dead body to gradually smell strongly of ammonia. Research in 1930 by Homer W. Smith showed that sharks' urine does not contain sufficient sodium to avoid hypernatremia , and it was postulated that there must be an additional mechanism for salt secretion. In 1960 it
5050-504: The clade Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes . The Elasmobranchii also include rays and skates ; the Chondrichthyes also include Chimaeras . It was thought that the sharks form a polyphyletic group: some sharks are more closely related to rays than they are to some other sharks, but current molecular studies support monophyly of both groups of sharks and batoids. The clade Selachimorpha
5151-441: The coelacanth , the blood and other tissue of sharks and Chondrichthyes is generally isotonic to their marine environments because of the high concentration of urea (up to 2.5% ) and trimethylamine N-oxide (TMAO), allowing them to be in osmotic balance with the seawater. This adaptation prevents most sharks from surviving in freshwater, and they are therefore confined to marine environments. A few exceptions exist, such as
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#17328521293585252-461: The cranium . The jaw's surface (in comparison to the shark's vertebrae and gill arches) needs extra support due to its heavy exposure to physical stress and its need for strength. It has a layer of tiny hexagonal plates called " tesserae ", which are crystal blocks of calcium salts arranged as a mosaic. This gives these areas much of the same strength found in the bony tissue found in other animals. Generally sharks have only one layer of tesserae, but
5353-452: The electric fields they produce. Ocean currents moving in the magnetic field of the Earth also generate electric fields that sharks can use for orientation and possibly navigation. This system is found in most fish, including sharks. It is a tactile sensory system which allows the organism to detect water speed and pressure changes near by. The main component of the system is the neuromast,
5454-414: The great white shark ) are homeothermic and maintain a higher body temperature than the surrounding water. In these sharks, a strip of aerobic red muscle located near the center of the body generates the heat, which the body retains via a countercurrent exchange mechanism by a system of blood vessels called the rete mirabile ("miraculous net"). The common thresher and bigeye thresher sharks have
5555-449: The head . Anterior (from Latin ante 'before') describes what is in front, and posterior (from Latin post 'after') describes what is to the back of something. For example, for a dog the nose is anterior to the eyes and the tail is considered the most posterior part; for many fish the gill openings are posterior to the eyes but anterior to the tail. These terms describe how close something
5656-648: The neuraxis is different between the two groups, and so is what is considered the standard anatomical position , such as how humans tend to be standing upright and with their arms reaching forward. Thus, the "top" of a human is the head, whereas the "top" of a dog would be the back, and the "top" of a flounder may be on either the left or right side. Unique terms are also used to describe invertebrates as well, because of their wider variety of shapes and symmetry. Because animals can change orientation with respect to their environment, and because appendages like limbs and tentacles can change position with respect to
5757-467: The pectoralis major muscle). In radiology , an X-ray image may be said to be "anteroposterior", indicating that the beam of X-rays, known as its projection, passes from their source to patient's anterior body wall first, then through the body to exit through posterior body wall and into the detector/film to produce a radiograph. The opposite is true for the term "posteroanterior," while side-to-side projections are known as either "lateromedial" (from
5858-415: The peripheral nervous systems . Central (from Latin centralis ) describes something close to the centre. For example, the great vessels run centrally through the body; many smaller vessels branch from these. Peripheral (from Latin peripheria , originally from Ancient Greek ) describes something further away from the centre of something. For example, the arm is peripheral to
5959-462: The southern sawshark ( Pristiophorus nudipinnis ) is found in south-eastern Australian waters. Much of its distribution overlaps with that of the Common sawshark, however, it seems to occur less frequently. This species is similar in size as the common sawshark, but has a broader rostrum (saw) and a more even brown coloration. It also grows to be heavier than the common sawshark. Since the color pattern of
6060-1036: The Early Permian of Russia, but if remains of "synechodontiformes" from the Permian and Triassic are true sharks, they only had low diversity. Modern shark orders first appeared during the Early Jurassic, and during the Jurassic true sharks underwent great diversification. Selachimorphs largely replaced the hybodonts , which had previously been a dominant group of shark-like fish during the Triassic and Early Jurassic. Batoidea [REDACTED] Heterodontiformes [REDACTED] Orectolobiformes [REDACTED] Carcharhiniformes [REDACTED] Lamniformes [REDACTED] Hexanchiformes [REDACTED] Squatiniformes [REDACTED] Pristiophoriformes [REDACTED] Squaliformes [REDACTED] Sharks belong to
6161-511: The Short Nose lives a benthic lifestyle and feeds on benthic invertebrates. It uses its barbels to detect life on the ocean floor which it then paralyzes with its rostrum. The species is ovoviviparous and tends to give birth to a litter of 7–14 pups biannually. It inhabits ocean floors off the coast of Australia. The Bahamas sawsharks ( Pristiophorus schroeder ) have very little information on them. Studies are being done daily to learn more about
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#17328521293586262-417: The anterior and posterior nasal openings, with some species able to detect as little as one part per million of blood in seawater. The size of the olfactory bulb varies across different shark species, with size dependent on how much a given species relies on smell or vision to find their prey. In environments with low visibility, shark species generally have larger olfactory bulbs. In reefs, where visibility
6363-568: The basking shark are small and non-functional. Shark skeletons are very different from those of bony fish and terrestrial vertebrates . Sharks and other cartilaginous fish ( skates and rays ) have skeletons made of cartilage and connective tissue . Cartilage is flexible and durable, yet is about half the normal density of bone. This reduces the skeleton's weight, saving energy. Because sharks do not have rib cages, they can easily be crushed under their own weight on land. The jaws of sharks, like those of rays and skates, are not attached to
6464-400: The body in a standing position with arms at the side and palms facing forward, with thumbs out and to the sides. Many anatomical terms can be combined, either to indicate a position in two axes simultaneously or to indicate the direction of a movement relative to the body. For example, "anterolateral" indicates a position that is both anterior and lateral to the body axis (such as the bulk of
6565-416: The body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses . From there venous blood re-enters the heart ventricle and the cycle repeats. Most sharks are "cold-blooded" or, more precisely, poikilothermic , meaning that their internal body temperature matches that of their ambient environment. Members of the family Lamnidae (such as the shortfin mako shark and
6666-570: The body. These terms refer to the distance of a structure from the surface. Deep (from Old English ) describes something further away from the surface of the organism. For example, the external oblique muscle of the abdomen is deep to the skin. "Deep" is one of the few anatomical terms of location derived from Old English rather than Latin – the anglicised Latin term would have been "profound" (from Latin profundus 'due to depth'). Superficial (from Latin superficies 'surface') describes something near
6767-417: The closeness to the midline of the dental arch. Terms used to describe structures include "buccal" (from Latin bucca 'cheek') and "palatal" (from Latin palatum 'palate') referring to structures close to the cheek and hard palate respectively. Several anatomical terms are particular to the hands and feet. Additional terms may be used to avoid confusion when describing
6868-452: The coast of Japan, Korea, and Northern China. It swims at a depth of 500 m. It has around 15–26 large rostral teeth in front of the barbels, which are equal distance from the gills to the snout, and about 9–17 teeth behind the barbels. Like all sawsharks, the Japanese sawshark is ovoviviparous, and feeds on crustaceans and bottom dwelling organisms. Lana's sawshark ( Pristiophorus lanae ) is
6969-405: The common sawshark may be more or less defined, the easiest way to separate this species from the common sawshark is the location of the barbels, which are closer to the mouth than the co-occurring common sawshark. Unlike the common sawshark, the southern sawshark likely feeds mainly on fishes. The tropical sawshark ( Pristiophorus delicatus ) a pale brown with a yellow hue, and an underbelly that
7070-475: The deep sea dweller. They are located near Cuba, Florida, and the Bahamas (hence their name) where they dwell in the depths of 400–1000 m. As far as their appearance they can be identified by their snouts with teeth which appear as a saw, as well as their length, they are averaged at 80 cm in length. Saw sharks and sawfish are cartilaginous fish possessing large saws. These are the only two fish that have
7171-421: The end of words: Superior (from Latin super 'above') describes what is above something and inferior (from Latin inferus 'below') describes what is below it. For example, in the anatomical position , the most superior part of the human body is the head and the most inferior is the feet. As a second example, in humans, the neck is superior to the chest but inferior to
7272-417: The hand') is commonly used to describe the front of the hand, and dorsal is the back of the hand. For example, the top of a dog 's paw is its dorsal surface; the underside, either the palmar (on the forelimb) or the plantar (on the hindlimb) surface. The palmar fascia is palmar to the tendons of muscles which flex the fingers, and the dorsal venous arch is so named because it is on the dorsal side of
7373-1168: The horny keratin in hair and feathers. Most sharks have eight fins. Sharks can only drift away from objects directly in front of them because their fins do not allow them to move in the tail-first direction. Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body. This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy. Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming. Some species of shark have pigmented denticles that form complex patterns like spots (e.g. Zebra shark ) and stripes (e.g. Tiger shark ). These markings are important for camouflage and help sharks blend in with their environment, as well as making them difficult for prey to detect. For some species, dermal patterning returns to healed denticles even after they have been removed by injury. Tails provide thrust, making speed and acceleration dependent on tail shape. Caudal fin shapes vary considerably between shark species, due to their evolution in separate environments. Sharks possess
7474-418: The inner ear has been lost. The ampullae of Lorenzini are the electroreceptor organs. They number in the hundreds to thousands. Sharks use the ampullae of Lorenzini to detect the electromagnetic fields that all living things produce. This helps sharks (particularly the hammerhead shark ) find prey. The shark has the greatest electrical sensitivity of any animal. Sharks find prey hidden in sand by detecting
7575-402: The intestines of many species, and as a result often linger near or in sewage outfalls. Some species, such as nurse sharks , have external barbels that greatly increase their ability to sense prey. Shark eyes are similar to the eyes of other vertebrates , including similar lenses , corneas and retinas , though their eyesight is well adapted to the marine environment with the help of
7676-451: The jaw, and are constantly replaced throughout life. Multiple rows of replacement teeth grow in a groove on the inside of the jaw and steadily move forward in comparison to a conveyor belt ; some sharks lose 30,000 or more teeth in their lifetime. The rate of tooth replacement varies from once every 8 to 10 days to several months. In most species, teeth are replaced one at a time as opposed to the simultaneous replacement of an entire row, which
7777-453: The jaws of large specimens, such as the bull shark, tiger shark, and the great white shark, have two to three layers or more, depending on body size. The jaws of a large great white shark may have up to five layers. In the rostrum (snout), the cartilage can be spongy and flexible to absorb the power of impacts. Fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling
7878-512: The legs. Temporal has a similar meaning to lateral but is restricted to the head. The terms "left" and "right" are sometimes used, or their Latin alternatives ( Latin : dexter , lit. 'right'; Latin : sinister , lit. 'left'). However, it is preferred to use more precise terms where possible. Terms derived from lateral include: Varus (from Latin 'bow-legged') and valgus (from Latin 'knock-kneed' ) are terms used to describe
7979-448: The level of the fourth cervical vertebra may be abbreviated as "C4", at the level of the fourth thoracic vertebra "T4", and at the level of the third lumbar vertebra "L3". Because the sacrum and coccyx are fused, they are not often used to provide the location. References may also take origin from superficial anatomy , made to landmarks that are on the skin or visible underneath. For example, structures may be described relative to
8080-538: The longest lifespans at more than 100 years. Whale sharks ( Rhincodon typus ) may also live over 100 years. Earlier estimates suggested the Greenland shark ( Somniosus microcephalus ) could reach about 200 years, but a recent study found that a 5.02-metre-long (16.5 ft) specimen was 392 ± 120 years old (i.e., at least 272 years old), making it the longest-lived vertebrate known. Unlike most bony fish , sharks are K-selected reproducers, meaning that they produce
8181-401: The main body, terms to describe position need to refer to an animal when it is in its standard anatomical position . This means descriptions as if the organism is in its standard anatomical position, even when the organism in question has appendages in another position. This helps avoid confusion in terminology when referring to the same organism in different postures. In humans, this refers to
8282-728: The mother. They have litters of 3–22 pups every 2 years. After 12 months of pregnancy, the pups are born at 30 cm long. While in the mother, pups' rostral teeth are angled backwards to avoid harming the mother. The life expectancy of sawsharks is still poorly understood, but they are thought to live to 10 years or more. Among the different species of sawshark, all are listed on the IUCN Red List of 2017 as either data deficient or of least concern Saw sharks do not see much human interaction because of their deep habitats. There are currently ten known species of sawsharks across two genera in this family: The sixgill sawshark ( Pliotrema warreni )
8383-456: The mouth and teeth. This is because although teeth may be aligned with their main axes within the jaw, some different relationships require special terminology as well; for example, teeth also can be rotated, and in such contexts terms like "anterior" or "lateral" become ambiguous. For example, the terms "distal" and "proximal" are also redefined to mean the distance away or close to the dental arch , and "medial" and "lateral" are used to refer to
8484-470: The ocean floor which it then hits with its snout to immobilize it. Like all other sawsharks, the common sawshark has a long snout with rows of small teeth and barbels on either side. It has five gill slits on either side of its head and between 19 and 25 teeth on each side. Sawsharks appear to be one of the types of elasmobranch that are difficult or impossible to age using most commonly-used approaches that rely on vertebral banding. The shortnose sawshark aka
8585-553: The oldest known member being Agaleus , though records of true sharks may extend back as far as the Permian . Sharks range in size from the small dwarf lanternshark ( Etmopterus perryi ), a deep sea species that is only 17 centimetres (6.7 in) in length, to the whale shark ( Rhincodon typus ), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length. They are found in all seas and are common to depths up to 2,000 metres (6,600 ft). They generally do not live in freshwater, although there are
8686-400: The outer surface of the organism. For example, in skin , the epidermis is superficial to the subcutis . These two terms, used in anatomy and embryology , describe something at the back ( dorsal ) or front/belly ( ventral ) of an organism. The dorsal (from Latin dorsum 'back') surface of an organism refers to the back, or upper side, of an organism. If talking about
8787-402: The outside of the left or right side of the body toward the inside) or "mediolateral"(from the inside of that side of the body toward the outside. The same logic is applied to all planes of the body and, thus top-to-bottom or bottom-to-top X-ray projections are known as "superoinferior" and "inferosuperior," respectively. However, within the diagnostic imaging industry, for this particular example,
8888-462: The saw shark. Clear difference is that a sawfish has no barbels and a saw shark has a prominent pair halfway along the saw. The saw shark uses these like other bottom fish, as a kind of antennae, feeling the way along the ocean bottom until it finds some prey of interest. Both the saw shark and the sawfish utilize the electroreceptors on the saw, ampullae of Lorenzini , to detect the electric field given off by buried prey. Shark Sharks are
8989-403: The shark's two-chambered heart . Here, the shark pumps blood to its gills via the ventral aorta where it branches into afferent branchial arteries . Gas exchange takes place in the gills and the reoxygenated blood flows into the efferent branchial arteries, which come together to form the dorsal aorta . The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from
9090-442: The skull, the dorsal side is the top. The ventral (from Latin venter 'belly') surface refers to the front, or lower side, of an organism. For example, in a fish, the pectoral fins are dorsal to the anal fin , but ventral to the dorsal fin . The terms are used in other contexts; for example dorsal and ventral gun turrets on a bomber aircraft. Specific terms exist to describe how close or far something
9191-413: The spiracle) leads directly into the inner ear through a thin channel. The lateral line shows a similar arrangement, and is open to the environment via a series of openings called lateral line pores . This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fish and tetrapods the external opening into
9292-414: The stomach, and instead the shark either vomits or turns its stomachs inside out and ejects unwanted items from its mouth. One of the biggest differences between the digestive systems of sharks and mammals is that sharks have much shorter intestines. This short length is achieved by the spiral valve with multiple turns within a single short section instead of a long tube-like intestine. The valve provides
9393-460: The surfaces of the hand and what is the "anterior" or "posterior" surface. The term "anterior", while anatomically correct, can be confusing when describing the palm of the hand; Similarly is "posterior", used to describe the back of the hand and arm. This confusion can arise because the forearm can pronate and supinate and flip the location of the hand. For improved clarity, the directional term palmar (from Latin palma 'palm of
9494-423: The surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes . This membrane covers the eyes while hunting and when the shark is being attacked. However, some species, including the great white shark ( Carcharodon carcharias ), do not have this membrane, but instead roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunting behavior
9595-429: The terms "cranial" (towards the head) and "caudal" (towards the tail, or, downwards, away from the head) are known interchangeable alternatives to the previous two projection terms. Combined terms were once generally hyphenated, but the modern tendency is to omit the hyphen. Anatomical terms describe structures with relation to four main anatomical planes : The axes of the body are lines drawn about which an organism
9696-404: The terms often is context-sensitive. Much of this information has been standardised in internationally agreed vocabularies for humans ( Terminologia Anatomica ) and animals ( Nomina Anatomica Veterinaria ). Different terms are used for groups of creatures with different body layouts, such as bipeds (creatures that stand on two feet, such as humans) and quadrupeds . The reasoning is that
9797-403: The thresher shark's usage of its powerful, elongated upper lobe to stun fish and squid. Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver filled with oil that contains squalene , and their cartilage, which is about half the normal density of bone. Their liver constitutes up to 30% of their total body mass. The liver's effectiveness
9898-456: The top of their food chain . Select examples include the bull shark , tiger shark , great white shark , mako sharks , thresher sharks , and hammerhead sharks . Sharks are caught by humans for shark meat or shark fin soup . Many shark populations are threatened by human activities. Since 1970, shark populations have been reduced by 71%, mostly from overfishing . Until the 16th century, sharks were known to mariners as "sea dogs". This
9999-466: The tropical sawshark ( Pristiophorus delicatus ). Sawsharks are found in many areas around the world, most commonly in waters from the Indian Ocean to the southern Pacific Ocean . They are normally found at depths around 40–100 m, but can be found much lower in tropical regions. The Bahamas sawshark was discovered in deeper waters (640 m to 915 m) of the northwestern Caribbean . Sawsharks have
10100-541: The word shark (referring to a sea fish) in a letter written by Thomas Beckington in 1442, which rules out a New World etymology. The oldest total-group chondrichthyans, known as acanthodians or "spiny sharks", appeared during the Early Silurian , around 439 million years ago. The oldest confirmed members of Elasmobranchii sensu lato (the group containing all cartilaginous fish more closely related to modern sharks and rays than to chimaeras ) appeared during
10201-553: Was discovered at the Mount Desert Island Biological Laboratory in Salsbury Cove, Maine that sharks have a type of salt gland located at the end of the intestine, known as the "rectal gland", whose function is the secretion of chlorides. Digestion can take a long time. The food moves from the mouth to a J-shaped stomach, where it is stored and initial digestion occurs. Unwanted items may never get past
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