What are the differences between aquatic animal and terrestrial animal?

Question

What are the differences between aquatic animal and terrestrial animal?

Answer 1

Aquatic animals are adapted to life in water.  Most have gills to breathe in water and modified limbs to move in water (like fins or a lot of webbing on their feet.)  Fish are probably the best example.  

Terrestrial animals live on land.  Most have lungs to breathe air and their limbs are usually stronger (it takes more strength to support body weight on land than in water) and adapted to move on land.  For an example here... think of a cheetah - highly equipped for land, but couldn't survive trying to spend its whole life in water.  

Amphibious animals are adapted to live in both environments.  Most spend a portion of their life in water then undergo a significant change in their bodies to spend rest of their life on land.  The classic example here is a frog.  There are a lot of insects (mosquitoes, dragonflies, crane flies, etc).  that are also amphibious.

Most of the time, it is fairly obvious which one an animal is, but some can be tricky (most mammalogists consider beavers to be aquatic, yet Canada Geese are usually termed as terrestrial).  If you are curious about specific animals - let us know which ones and we can try to help you out!