Is a fully unidirectional respiratory system possible for a terrestrial animal? What are the advantages and di

Question

I need some help on this.. this is in regards to the respiration of vertebrate animals. thanks so much to those who'll send some good ideas about this.

Answer 1

I know of none in terrestrial animals, certainly not vertebrates. There are external gill structures on amphibians but I only recall them on aquatic stages, (tadpoles & juvenile salamanders - aquatic or very moist enviornments).
Such a system would require more structure, and entail more moisture loss in respiration than a lung type system.
Earthwrms do breath through the skin, (again moist enviornment). Though I doubt if that would qualify.
Interesting thought though.........

Answer 2

Respiration implies gas exchange. This is done most efficiently in vertebrates by being directional. O2 in and CO2 out. I do not see any other realistic possibility for the size animals vertebrates are; even at their smallest.