Sharks are boneless fish with have an anatomical structure that differs from other marine fish. Sharks have skeletons made of flexible cartilage and have several fins located on their bodies. Most sharks have a pair of dorsal, pelvic and pectoral fins. Anal and caudal fins are located near the rear of the shark. The front of the shark is comprised of the nostrils, snout, eyes, spiracles, gills and mouth.
Modified placoid scales comprise a shark's teeth and skin. The teeth can be replaced as they are worn out or damaged. Shark skin is rough and extremely thick. The skin protects the shark and works to decrease friction in the water.
Like most fish, sharks have a brain, heart, digestive system, liver, spleen, kidneys, reproductive systems, respiratory system, urinary bladder and pancreas. The intestines are short and have adapted to absorb nutrients in a short time.
The gills are a part of the shark's respiratory system, which extracts oxygen from the water. A shark has gills on each side of the body located in front of the pectoral fins that extract oxygen from water. Sharks do not have a swim bladder, but they possess an oily liver that aids in buoyancy. Sharks can detect electrical fields with their electroreceptive system.