What are some evolutionary advantages of animals with complete digestive tube?
The complete digestive tube permits animals to continuously feed themselves without waiting for residuals to be eliminated before starting the digestion of new foods. In this way the absorption of larger amount of nutrients is possible and thus bigger and more complex species can develop. Digestive tubes with two openings also make digestion more efficient as they give different sites with different physical and chemical conditions (mouth, stomach, bowels) for the action of dissimilar complementary digestive enzymatic systems.