How do organisms in the Phylum Porifera Cnidaria Ctenophore Platy Helminthes and Nematode dispose of waste exchange gases?

the Porifera, Cnidaria, Ctenophore, Platy helminthes, and Nematode phylums all exchange gas and eliminate waste through diffusion. They tend to be small and/or have a large surface-to-body ratio.