Discription Slide 9-15
As already mentioned, some sharks hardly swim but lay on the bottom. However, laying on the bottom is less common among sharks than continuously swimming. Video: Caribbean reef shark.
Locomotion happens through a continuous contraction of small muscle groups arranged along the flank. Contraction starts with the first segment (in the gill area) followed by the second one, the third one and so on... The results is an undulating motion.
Sharks do not possess a bony skeleton but one build entirely from cartilage. Cartilage is the same material that humans have in their noses, their ears etc. Muscles are mostly attached to the vertebrae but also directly attached to the skin.
A shark's kin consists of very small teeth which are built identical to the teeth in a shark's mouth, as well quite similar to the ones humans have. The tips of these small teeth that cover a shark's body, called placoid scales, point towards the tail hence why touching a shark when it passes feels very smooth but do so against its locomotion feels like sandpaper.
Sharks possess more sensory organs than e.g. dogs, cats or birds. The following description highlight the functions of all the sensory organs a shark has. Picture: White shark.
The eyes of most sharks are slightly far-sighted (exceptions are e.g. the nurse sharks which are near-sighted). Sharks that live in the top layers or the oceans or the shallow areas are able to see colors. As humans, they have pupils which are small when the surroundings are bright, large during low light hours (dusk, dawn, night).
As humans, they have all the common eye colors: blue, brown, green but likewise yellow and silver. Compared to human eyes, sharks can see better than we do in low light due to a special layer in the eye that reflects the incoming light, similar to dogs and cats when caught in some headlights. Picture: Eye of a blacktip shark.