1. Chondrichthyes

2. Hydrodynamics  Body shape  Sharks typically have an elongate fusiform body (rounded and tapering at both ends). This body shape reduces drag and requires a minimum of energy to swim. Swimming is essential for buoyancy.

4. Caudal Fin = Propulsion  Unlike most bony fishes, the upper lobe of a shark's caudal fin is larger than the lower lobe. As the caudal fin moves back and forth to propel the shark forward, it also moves upward. As the caudal fin continues to lift, the shark's head points down. The overall effect of the motion of the caudal fin results in a forward and downward motion

5. Pectoral Fins = Lift  The pectoral fins compensate for this downward motion. One function of the rigid pectoral fins is to provide lift in the forward region of the shark's body. This counteracts the overall downward force caused by the caudal fin and results in horizontal passage through the water.

6. Pelvic Fins = balance  Also Paired  In males the median part of the pelvic fin is modified to form a clasper which is used in copulation.

7. Swimming Speed  Generally sharks swim at speeds less than 5 kph (about 3 mph). For the most part, bottom-dwelling sharks are slow- swimming. Makos are among the fastest sharks, reaching speeds up to 48 kph (30 mph). Makos are among the fastest sharks, reaching speeds up to 48 kph (30 mph).

9. Characteristics  1. Endoskeleton entirely cartilaginous. This is interesting considering they evolved from ancestors that had bone. Notochord present but reduced Vertebrae separate and complete  2. Brain of two olfactory lobes, two optical lobes, two cerebral hemispheres, cerebellum, and medulla oblongata.  3. Circulatory System 2 chambered heart.  4. Respiration: through gills, they have 5 to 7 pairs.

10. Placoid Scales  5. Skin with placoid scales. Teeth are modified placoid scales that can be replaced on a regular basis.

11. Scales Help Swimming? As a shark swims, placoid scales may create a series of vortices or whirlpools behind each scale. This enables a shark to swim efficiently.

13.  6. Digestive System with stomach and intestine with a spiral valve.  7. Body fusiform with heterocercal caudal fin. 8. Mesonephric Kidney and rectal gland: the rectal gland helps control salt concentrations in the blood by secreting a colorless fluid high in sodium chloride. 9. No swim bladder or lung. Sharks have high amounts of lipids fats in their liver that help them be bouyant.

14.  10. Separate Sexes  All sharks have Internal Fertilization but care of young varies considerably.  Oviparous: eggs released by females, development outside the mother.  Ovoviviparous: eggs develop inside mother without nourishment from parent. Hatch inside mother or immediately after laying.  Viviparous: eggs develop inside with nourishment, offspring born alive already with development.

15.  11. Lateral Line: part of its nervous system. Detects changes of current in the water, and movement of some objects in the water.  Consists of long recessed grooves along the side of the shark. Concentrated at the head area and extending posterior to the tail. The groove has a series of neuromasts.  Navigation is the primary function of the lateral line system.

16.  12. Ampullary Organs of Lorenzini  Detect bioelectric fields.  Located in the head around the eye.  Enables them to detect prey that is even buried in the sand.