Unlike bony fish, sharks have no ______________________________; their skeleton is made of cartilage, which is a tough, fibrous substance, not nearly as hard as bone. Sharks also have no swim bladder (unlike bony fish).

There are many different species of sharks that range in size from the size of a person's hand to bigger than a bus. Fully-grown sharks range in size from 7 inches (18 cm) long (the spined pygmy shark), up to 50 feet (15 m) long (the ______________________________ shark, which is also the biggest fish).

There are about 368 different species of sharks, which are divided into 30 families. These different families of sharks are very different in the way they look, live, and eat. They have different shapes, sizes, color, fins, teeth, habitat, diet, personality, method of reproduction, and other attributes. The spiny dogfish shark is the most common ______________________________.

Sharks have a variety of body shapes. Most sharks have streamlined, torpedo-shaped bodies that glide easily through the ______________________________. Some bottom-dwelling sharks (like the angelshark) have ______________________________ bodies that allow them to hide in the sand of the ocean bed. Some sharks have an elongated body shape (like cookiecutter sharks and wobbegongs). Sawsharks have elongated snouts, thresher sharks have a tremendously elongated upper ______________________________ fin which they use to stun prey, and hammerheads have extraordinarily wide ______________________________.