how do terrestrial and aquatic animals breathe?

Dear Student

Aquatic animals breathe air or oxygen that dissolved in water through specialised organs called gills or directly through the skin. 

Terrestrial vertebrates exhibit the process of respiration through their lungs.While invertebrates exhibits other means of respiration like in  earthworms , respiration occurs through the surface of their skin. The skin of an earthworm is moist and slimy. Gases directly diffuse into its tissues through the skin.

Aquatic animals breathe at a faster rate than the terrestrial animals because the amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the air. To meet the oxygen need aquatic animals breathe faster to intake more oxygen.
The oxygen concentration in water is 21% less than the concentration of oxygen in the air.

Hope this helps,
Regards.