How are Sharks Different From Other Fish?

Sharks are unique in several different ways:

1. They are made up entirely of cartilage which makes establishing a fossil history of these fish impossible.

2. Their skin is covered with denticles, which are tooth-like projections from the skin instead of scales.

3. They have no swim bladder. A very oily liver also provides buoyancy
to compensate for the lack of a swim bladder.

4. The jaw of a shark can be unhinged to open very wide while feeding. They also can
have as many as 8 rows of teeth.

5. Whenever a shark loses a tooth, another one moves up to take its
place. A shark can go through up to 2,400 teeth a year.

Source:http://bcrc.bio.umass.edu/vifishandwildlife/Education/FactSheet/PDF_Docs/30Sharks.pdf

Can you give examples of shark reproduction?

Sharks can be oviparous, ovoviviparous, and viviparous.

In oviparous sharks, a gland secretes a shell, or case, around the egg as it passes through the oviduct, protecting the shark until it hatches. The mother deposits the egg cases in the sea. Examples in this group include horn sharks and swell sharks.

In ovoviviparous sharks, the shell is often just a thin membrane. Sometimes there is more than one egg in the membrane; this group of eggs is called a candle. The mother retains the egg, and the embryo soon sheds the membrane and develops in the mother's uterus. An example of a shark that develops in this manner is a sand shark.

In viviparous sharks, the embryo receives all its nutrients from the mother. Tissues of the embryo and the mother are in intimate contact and nutrients are passed directly from the tissues of the mother to the tissues of the developing embryo.A hammerhead shark is an example of a viviparous fish.

Source:http://www.seaworld.org/animal-info/info-books/sharks-&-rays/birth-&-care.htm