Sponge, Hydra, jelly fish ◦ No circulatory system ◦ 2 layers both contact with environment ◦ Diffusion @ cell membrane Flatworms use outer surface as gas exchange surface
Sponge, Hydra, jelly fish ◦ No circulatory system ◦ 2 layers both contact with environment ◦ Diffusion @ cell membrane Flatworms use outer surface as gas exchange surface