Why are frogs considered the "mosses" of the animal kingdom?
Mosses are plants that are not fully adapted to a terrestrial lifestyle in the same way that Amphibians, including frogs, are not. Mosses are Bryophytes. Although they resemble higher order flowering plants, they do not have true vascular or conducting tissue. Because of this, they must live in a very moist environment. Frogs can live on land, but are still tied to the water. They must keep their bodies moist because they can actually use their entire body as a respiratory surface. Although they have tiny sac-like lungs for respiration, their body is also used for absorbing oxygen. Also, they reproduce in freshwater and must be able to return to the water for that purpose.