词条 | Shark anatomy |
释义 |
Shark anatomy differs from that of bony fish in a variety of ways. Variation observed within shark anatomy is a potential result of speciation and habitat variation SkeletonThe skeleton of a shark is mainly made of cartilage. In particular, the endoskeletons are made of unmineralized hyaline cartilage which is more flexible and less dense than bone, thus making them expel less energy at high speeds. Each piece of skeleton is formed by an outer connective tissue called the perichondrium and then covered underneath by a layer of hexagonal, mineralized blocks called tesserae.[1] FinsMost sharks have eight fins: a pair of pectoral fins, a pair of pelvic fins, two dorsal fins, an anal fin, and a caudal fin. The members of the order Hexanchiformes have only a single dorsal fin. The anal fin is absent in the orders Squaliformes, Squatiniformes, and Pristiophoriformes. Shark fins are supported by internal rays called ceratotrichia. TailThe tail of a shark consists of the caudal peduncle and the caudal fin, which provide the main source of thrust for the shark. Most sharks have heterocercal caudal fins, meaning that the backbone extends into the (usually longer) upper lobe. The shape of the caudal fin reflects the shark's lifestyle, and can be broadly divided into five categories:
Integument{{main|Dermal denticle}}Unlike bony fish, the sharks have a complex dermal corset made of flexible collagenous fibres 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. A similar arrangement of collagen fibres has been discovered in dolphins and squid. Their dermal teeth give them hydrodynamic advantages as they reduce turbulence while swimming. CamouflageSharks may have a combination of colors on the surface of their body that results in the camouflage technique called countershading. A darker color on the upper side and lighter color on the underside of the body helps prevent visual detection from predators. (For example, white on the bottom of the shark blends in with the sunlight from the surface when viewed from below.)[3][4] Countershading can also be accomplished through bioluminescence in the few shark species that produce and emit light, such as the kitefin shark, a species of dogfish shark. The species migrates vertically and the arrangement of light-producing organs called photophores provides ventral countershading.[5][6] Some species have more elaborate physical camouflage that assists them with blending into their surroundings. Wobbegongs and angelsharks use camouflage to perform ambush predation.[7] {{clear}}Circulatory systemSharks possess a single-circuit circulatory system centered around a four chambered heart. Blood flows from the heart to the gills where it is oxygenated. This oxygen-rich blood is then carried throughout the body and to the tissues before returning to the heart. As the heart beats, deoxygenated blood enters the sinus venosus. The blood then flows through the atrium to the ventricle, before emptying into the conus arteriosus and leaving the heart.[8] Respiratory systemLike other fishes, sharks extract oxygen from water as it passes over their gills. The water enters through the mouth, passes into the pharynx, and exits through the gill slits (most sharks have five pairs, the frilled sharks, cow sharks, and sixgill sawshark have six or seven pairs). Most sharks also have an accessory respiratory opening called a spiracle behind their eyes. In bottom-dwelling sharks such as angel sharks, the spiracle allows them to take in water to breathe without having to open their mouths {{citation needed|date=May 2014}}. There are two mechanisms that sharks can use to move water over their gills: in buccal pumping, the shark actively pulls in water using its buccal muscles, while in ram ventilation, the shark swims forward, forcing water into its mouth and through its gills. As buccal pumping is more energy-intensive than ram ventilation, the former is generally used by sedentary, bottom-dwelling sharks while the latter is used by more active sharks. Most sharks can switch between these mechanisms as the situation requires. A few species, such as the great white shark, have lost the ability to perform buccal pumping and thus will suffocate if they stop moving forward.[9] {{clear}}See also
References1. ^{{cite journal |last1=Dean |first1=Mason N. |last2=Mull |first2=Chris G. |last3=Gorb |first3=Stanislav N. |last4=Summers |first4=Adam P. |title=Ontogeny of the tessellated skeleton: insight from the skeletal growth of the round stingray Urobatis halleri |journal=Journal of Anatomy |date=September 2009 |volume=215 |issue=3 |pages=227–239 |doi=10.1111/j.1469-7580.2009.01116.x |url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2750757/ |accessdate=22 February 2019}} {{Shark nav}}{{anatomy}}2. ^{{cite journal |author1=Thomson, K.S. |author2=Simanek, D.E. |year=1977 |title=Body form and locomotion in sharks |journal=American Zoologist |volume=17 |issue=2 |pages=343–354 |doi=10.1093/icb/17.2.343}} 3. ^{{Cite book |title=Whale sharks |last=Murphy |first=Julie |date=2013 |publisher=Cherry Lake Pub |isbn=9781624314490 |location=Ann Arbor, Mich. |pages=12 |oclc=829445997 }} 4. ^{{Cite journal |last=Heithaus |first=M. |last2=Dill |first2=L. |last3=Marshall |first3=G. |last4=Buhleier |first4=B. |date=October 5, 2001 |title=Habitat use and foraging behavior of tiger sharks (Galeocerdo cuvier) in a seagrass ecosystem |journal=Marine Biology |volume=140 |issue=2 |pages=237–248 |doi=10.1007/s00227-001-0711-7 |issn=0025-3162}} 5. ^{{Cite journal |last=Reif |first=Wolf-Ernst |date=June 1985 |title=Functions of Scales and Photophores in Mesopelagic Luminescent Sharks |journal=Acta Zoologica |volume=66 |issue=2 |pages=111–118 |doi=10.1111/j.1463-6395.1985.tb00829.x |issn=1463-6395 }} 6. ^{{cite WoRMS |author=Bailly, Nicolas |year=2014 |title=Dalatias Rafinesque, 1810 |id=105774 |accessdate=February 16, 2018 |db=FishBase}} 7. ^{{cite web|url=http://elasmo-research.org/education/shark_profiles/orectolobiformes.htm|title=Order Orectolobiformes: Carpet Sharks—39 species|last=Martin|first=R. Aidan|publisher=ReefQuest Centre for Shark Research|accessdate=2009-08-29}} 8. ^{{Cite book|title=Comparative Vertebrate Anatomy: A laboratory dissection guide|last=Kardong, K. Zalisko, E.|publisher=McGraw-Hill Companies|year=2006|isbn=|location=New York, NY|pages=|quote=|via=}} 9. ^{{cite web |url=http://science.howstuffworks.com/zoology/marine-life/shark-drown.htm |title=Will a shark drown if it stops moving? |author=Edmonds, M. |publisher=HowStuffWorks |accessdate=April 28, 2013|date=2008-06-09 }} 1 : Sharks |
随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识,基本涵盖了大多数领域的百科知识,是一部内容自由、开放的电子版国际百科全书。