An animal (such as a human) that grows fur or hair from out of its skin. The females provide milk to feed their young who are usually born live.

The fin on the back of a fish or whale. For example, the triangular fin on the back of a shark or dolphin, or the fins that stick up on the back of a fish. A fish can have up to three dorsal fins. The dorsal fin helps the animal with sudden turns and stops, and prevents them from rolling.

The tail of a dolphin or whale which moves up and down like a paddle to push the animal through the water. In some whale species, flukes are so unique that scientists use them like fingerprints to tell whales apart. Whales can use their flukes to kick food into their mouths, and flukes can also be used to control the body temperature (by changing blood flow or releasing heat).

The pair of fins on each side, just behind a fish's head. Pectoral fins help to control an animals direction while moving in the water.