Class : Chondrichthyes - Sharks and Rays

1. Class: Chondrichthyes - Sharks and Rays The shark’s skeleton is entirely composed of cartilage. The skin is covered with tiny scales called denticles. They are similar in structure to teeth and cause the skin to be very abrasive if rubbed in the wrong direction. Most have gray, brown, white or black coloring; are not camouflaged but may be counter-shaded. Only predators are toothed whales and man. Puffer fish can accidentally suffocate a shark by blocking water from entering the gills resulting in death for both.

2. Predation: Efficient, top carnivore of the sick, weak, old and injured. Sharks will not eat Moses sole. Jaw is lined with rows of teeth like a conveyor belt (modified scales). Teeth can be replaced every 24 hours and are used to identify species. Jaw can be extended out of the mouth for extra reach. Mote Marine Laboratory in Sarasota, FL is a leading research center in shark immunology.

3. Circulation: 2 chambered heart; cold-blooded Respiration: Gills are located in muscular slits (gill slits, no operculum) behind the mouth. They exchange oxygen from the water into the blood. Sharks lack swim bladders (have oily livers) and must constantly swim upwards to balance their weight. They do sleep.

4. Senses: Vision is good in clear water. Eyelids close from the bottom upwards to prevent injury during an attack. Smell is excellent. Olfactory lobes compose 2/3 of the brain. Sharks can detect a drop of blood 1/4 mile away in the water and can determine the direction of the source. Hearing is excellent. Sound vibrations can be detected by the lateral line from 3,000 feet away. The electrical impulses of breathing from a prey can be picked up through pores in the face (ampullae of Lorenzini).

5. Reproduction: sexual, internal fertilization. Most sharks have live births - dogfish have 4-10 pups, tiger sharks may have 80-100 at one time. A few species lay eggs.

6. Shark attacks on humans are rare, but with more people in the water the odds are increased. Sharks may be looking for new food sources due to over fishing. Most attacks occur in less than 6 feet of water, at dawn or dusk, during summer months. Risks are also increased for surfers and swimmers in water with reduced visibility. A surfer in black wet-suit, paddling out on a board, may look enough like a seal to interest a shark.

7. Most attacks occur in Florida, California, Australia, and Africa. Florida has 4 times the number reported in California. Most attacks are not fatal. Sharks only kill about 10 people worldwide per year. Bees kill hundreds of people and crocodile/alligator - related deaths number nearly 1000. People have done far greater damage to the shark population.

8. The whale shark is over 50 feet long. It is a filter-feeder with baleen instead of teeth. Largestshark Most dangerous Great White sharks are found in the temperate and tropical oceans worldwide.

9. Largestray Manta Rays may have a 25 foot wide wing span. Most dangerous Sting Rays have a venomous stinger in their tail. Shuffle your feet when wading to avoid stepping on it.