Large squalene filled livers negates the need for a shark to have a swim bladder. The liver, up to 25% of the overall body weight, counteracts the weight of the dermal denticles, teeth and cartilage; and when combined with the lift provided by the pectoral fins allows the shark to manage its buoyancy.
Gills allow sharks to maintain their watery existence by providing a means for extracting oxygen from the water as it passes over them. The oxygen is absorbed by the blood in the gills and transported from there to the rest of the body. The number of gills ranges as well as the placement of them varies amongst species. Benthic sharks, like the Wobbegong may have a spiracle behind their eyes, or 5 gills on their flattened ventral surface. The majority of sharks however have the openings on the side of the head at about midline. Sharks can continue to pass water over their gills if stationary by opening and closing their mouths, ending the theory that they would die if they don’t swim continuously. Many sharks are however required to move to ensure that blood can continue to circulate through the contraction of muscles.
Sharks are ectotherms, deriving their heat from that of the surrounding water. This means that their internal temperature may vary as a result of changes to their environment. They have a very low metabolic rate and are slow efficient swimmers, resulting in a low energy expenditure and subsequently require very little food. There are exceptions to this in the Mako and the Great White. These sharks have a body temperature up to 8OC warmer than their surroundings and are faster swimmers. This is because they have a modified circulatory system associated with a counter current heat exchange using the red muscle. As the red muscle functions, it generates heat. Muscle generated heat warms the blood circulating though it which travels back to the heart through the veins. Thus, blood returning to the heart from the muscle is warmer than the blood travelling from the heart to the muscle. Because the arteries and veins are in close proximity to one another, heat is passed from the warmer veins to the cooler arteries rather than dissipating.
Benthic sharks like the Wobbygong and Carpet shark have developed flattened bodies, with spiracles on their upper surface through which water is inhaled and passed over their gills. This adaption means that they do not clog their gills with sand which would happen if they were to use their mouth. Camouflage patterns allow these species to blend into the substrate, both as a protective mechanism but also ones which enable them to launch surprise attacks on their prey. Sharks like the Grey Nurse shark have developed long bodies, broad petrol fins and top heavy tails. This form enables them to cruise through the water with minimal effort. Fast moving sharks such as the Mako, have developed shorter, stubbier bodies with pointed noses that allow them to move through the water like torpedoes powered by powerful matching lobed tails. Both the cruisers and the faster moving sharks rely on countershading as a form of camouflage. The lighter ventral surface blends in with the light view towards the sky when viewed from their underside, whilst the dark dorsal surface blends into the darkness of the depths when viewed from above. Shark skin is covered with enamel denticles, creating a rough surface that reduces water friction further improving the way in which they move through water.
Feeding is aided by a strong detached upper jaw which a biting shark can thrust forward and out making the mouth opening much larger whilst exposing all the teeth. Jaw muscles then...