Shark presentation3414


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Shark presentation3414

  1. 1. In this presentation, you will learn about: -What is a shark? -Skeleton -Respiration -Teeth -Evolution -Reproduction -Shark senses Vivek A. Bheeroo - Form 2 I
  2. 2. Sharks are fish with a full cartilaginousskeleton. They respire with the use of fiveto seven gill slits. Sharks have a coveringof dermal denticles to protect their skinfrom damage and parasites; they alsohave replaceable teeth. Vivek A. Bheeroo - Form 2 I
  3. 3. The skeleton of a shark is very different frombony fishes such as cod. Sharks and theirrelatives, skates and rays, have skeletons madefrom rubbery cartilage, which is very light andflexible. But the cartilage in older sharks cansometimes be partly calcified, making it harderand more bone-like. The sharks jaw is variableand is thought to have evolved from the first gillarch. It is not attached to the cranium and hasextra mineral deposits to give it greater strength. Vivek A. Bheeroo - Form 2 I
  4. 4. Like other fish, sharks extract oxygen fromseawater as it passes over their gills. Shark gillslits are not covered like other fish, but are in arow behind its head. Some sharks have amodified slit called a spiracle located just behindthe eye, which is used in respiration. Whilemoving, water passes through the mouth of theshark and over the gills -- this process is knownas "ram ventilation". While at rest, most sharkspump water over their gills to ensure a constantsupply of oxygenated water. Vivek A. Bheeroo - Form 2 I
  5. 5. The teeth of carnivorous sharks are not attachedto the jaw, but embedded in the flesh, and inmany species are constantly replacedthroughout the sharks life; some sharks canlose 30,000 teeth in a lifetime. All sharks havemultiple rows of teeth along the edges of theirupper and lower jaws. New teeth growcontinuously in a groove just inside the mouthand move forward from inside the mouth on a"conveyor belt" formed by the skin in which theyare anchored. Vivek A. Bheeroo - Form 2 I
  6. 6. The fossil records of sharks extends back over 450million years - before land vertebrates existed and beforemany plants had colonised the continents. The firstsharks looked very different from modern sharks. Themajority of the modern sharks can be traced back toaround 100 million years ago.Mostly only the fossilized teeth of sharks are found,although often in large numbers. In some cases piecesof the internal skeleton or even complete fossilizedsharks have been discovered. Estimates suggest thatover a span of a few years a shark may grow tens ofthousands of teeth, which explains the abundance offossils. Vivek A. Bheeroo - Form 2 I
  7. 7. The sex of a shark can be easily determined. The maleshave modified pelvic fins which have become a pair ofclaspers. The name is somewhat misleading as they arenot used to hold on to the female, but fulfill the role of themammalian penis.Mating has rarely been observed in sharks. The smallercat sharks often mate with the male curling around thefemale. In less flexible species the two sharks swimparallel to each other while the male inserts a claspersinto the females oviduct. Females in many of the largerspecies have bite marks that appear to be a result of amale grasping them to maintain position during mating.The bite marks may also come from courtship behaviour:the male may bite the female to show his interest. Insome species, females have evolved thicker skin towithstand these bites. Vivek A. Bheeroo - Form 2 I
  8. 8. The three senses of the shark I am goingto talk about in this presentation are:Sense of smellSense of sightSense of hearing Vivek A. Bheeroo - Form 2 I
  9. 9. Sharks generally rely on their superior sense ofsmell to find prey, but at closer range they alsouse the lateral lines running along their sides tosense movement in the water, and also employspecial sensory pores on their heads (Ampullaeof lorenzini) to detect electrical fields created byprey and the ambient electric fields of the ocean. Vivek A. Bheeroo - Form 2 I
  10. 10. Shark eyes are similar to the eyes of other vertebrates,including similar lenses, corneas and retinas, thoughtheir eyesight is well adapted to the marine environmentwith the help of a tissue called tapetum lucidum. Thistissue is behind the retina and reflects light back to theretina, thereby increasing visibility in the dark waters.The effectiveness of the tissue varies, with some sharkshaving stronger nocturnal adaptations. Sharks haveeyelids, but they do not blink because the surroundingwater cleans their eyes. To protect their eyes some havenictitating membrane. This membrane covers the eyesduring predation, and when the shark is being attacked.However, some species, including the great white sharkdo not have this membrane, but instead roll their eyesbackwards to protect them when striking prey. Vivek A. Bheeroo - Form 2 I
  11. 11. Sharks also have a sharp sense of hearing andcan hear prey many miles away. A smallopening on each side of their heads (not to beconfused with the spiracle) leads directly into theinner ear through a thin channel. The lateral lineshows a similar arrangement, as it is open to theenvironment via a series of openings calledlateral line pores. This is a reminder of thecommon origin of these two vibration- andsound-detecting organs that are groupedtogether as the acoustico-lateralis system. Inbony fishes and tetra pods the external openinginto the inner ear has been lost. Vivek A. Bheeroo - Form 2 I
  12. 12. Vivek A. Bheeroo - Form 2 I