Amphibians are small vertebrates that need water, or a moist environment, to survive.

The species in this group include frogs, toads, salamanders, and newts. All can breathe and absorb water through their very thin skin.

All fish share two traits: they live in water and they have a backbone—they are vertebrates.

Apart from these similarities, however, many of the species in this group differ markedly from one another. Fin fish like salmon have gills, are covered in scales, and reproduce by laying eggs. Eels, by contrast, have worm-like bodies and exceedingly slimy skin. Lungfish gulp air. Whale sharks, the largest fish, give birth to live young and eat only tiny fish, squid, and plankton. Some species, such as the weedy sea dragon, are so bizarre they seem almost unreal.