Octopus
The octopus sucks in water through a cavity. The water is used to get oxygen to the blood. The gills circulate the bood to where the blood dumps waste. The water is then pushed out by a siphon and the cycle repeats.
Gastropods
Gastropods use a pair of gills to get oxygen. Fresh water species and many other species use a pallial lung to get in oxygen. Once they take in air they use it for a repiratory preotien hemocyanin.
Squids
Squids have a complex respespiratory system. They have two branchial hearts at there base of the gills that pumps unoygenated blood throught the gills. The blood then goes to the final ventricular heart where it pumps oxygenated blood throughout the body.