Shark anatomy
[1] The five synapomorphies are pharyngeal slits, a dorsal nerve cord, notochord, endostyle, and the post-anal-tail which is depicted and labeled well on the chordates page.
In cephalochordates, the pharyngeal slit, or pharynx, are lateral to the throat of the chordate and work as filters by letting water pass over this region in order to retain nutrients and oxygen from gas exchange occurring.
The dorsal nerve cord serves as a hollow-like backbone where signals are sent throughout the body due to nervous tissue being located in this region.
[3] The endostyle is underneath the pharyngeal gill slits where proteins are trapped to eventually provide the chordate energy and sustenance.
[4] These evolved synapomorphies are crucial for the current shark's lifestyle, for example, the pharyngeal slit changed to become the jaw and gills.
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.
Most sharks have heterocercal caudal fins, meaning that the backbone extends into the (usually longer) upper lobe.
This organ helps with buoyancy since the liver stores oils, decreasing the density of the shark's body.
[15] A shark's spleen is also incredibly important because it is where red blood cells (RBC's) are derived and is also where the immune system functions to fight off pathogens.
The shark stomach also has shorter intestines than most animals, which causes food to take greater amounts of time to fully digest before being excreted from the body.
[18] At the very end of the short intestine lies the rectal gland which is important for the excretion waste from the animal.
[20] Another way that helps sharks to move through the water effortlessly is partially due to the regulation of their body temperature.
These mackerel sharks retain their blood by using a heat exchange system called rete mirabile.
[10] Unlike bony fish, the sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body.
[25] During swimming, the flexible bias of the skin that is positioned 45 degrees to the body length allows for lateral bending.
This ensures that the skin stays tight to the surface, but is also flexible, preventing wrinkling and possible turbulence in streamlines passing over the body.
In vertebrates, the epidermis produces a mucus coating to help moisten the surface of the skin and can also be used as a defense mechanism from bacterial infections.
These pores are used to sense and detect electromagnetic fields, and oftentimes these aid in navigational skills and hunting down prey.
This can be particularly important at night because sharks cannot just depend on their vision in dark settings, they need another mechanism to help them navigate.
[31] This muscle also receives a sufficient blood supply which is why sharks can swim for extended periods of time, which helps break down fat.
[33] Sharks may have a combination of colors on the surface of their body that results in the camouflage technique called countershading.
The species migrates vertically and the arrangement of light-producing organs called photophores provides ventral countershading.
Like lungs in other animals, gills are essential for sharks to breathe underwater by extracting oxygen from water.
Spiracles are cartilaginous structures located on the top of a shark's head to draw oxygenated water from above in addition to it passing over the gills.
[41] Like most fishes, sharks gill slits are located on its external surface on both lateral sides near the head.
Lamellae in the gill slits are thin, membrane folds that have access to blood supplies via arteries and are the site of gas exchange.
When oxygen-rich water enters the gills, the blood takes up the oxygen through diffusion at the site of lamellae and expels carbon dioxide.
A few species, such as the great white shark, have lost the ability to perform buccal pumping and will suffocate if they stop moving forward due to insufficient oxygen passing over their gills.
