exchange of gases  between organism and environment
avilability
differs amongst air and water and earth

exchange    and cellular respiration

diffusion
relationship  between volume and area
respiratory structures
circulatory  structures
open and closed
auxilliry pigments  and cells

protists--simple diffusion
porifera--colonial protists--simple diffusion
cnidaria--low metaboic rate ssimple diffusion
platyhelminthes--low metabolic rates thin simple diffusion
nematodes--simple diffusion
annelids--oligochaetes
polychaetes--
haemoglobin, chlorcruorin, hemcyanin

used haemoglobin, chlorcruorin used as accessory pigments