i think you meant 'why'. if it is 'why', here is my answer.
aquatic animals-live on water because from the name itself, aquatic, it is lives in water because it is called 'aqua' animals.
'terrestrial' word means inhabitant of the earth.
so there you go! the reasons why it lives on land an water.
hope this helped.
i don't know if you meant 'what' but this is my answer.