Organism X existed for a short period of time. I really like geology so trust me, I am 100% sure about this question.
(Mark me as the brainiest if this answer helps you!)
They both contain nucleus.
Lungs take in gas from the Atmosphere, where the Oxygen is diffused into the blood cells, which take the Oxygen to different organs/places that need it. . .
Gills take in dissolved oxygen from the water, and then use diffusion like lungs.