Squid Respiration
Squid's respiration process is similar to the octopus'. They have gills because they live underwater. Since the oxygen has to pass the water and go into the blood. They do this by putting the blood next to the water using a thin wall. The wall is one cell thick and is called ctenidium (two are called ctenidia). The ctenidium is found on either side of the siphon. A siphon is a tube bent to form two legs of unequal length by which a liquid can be transferred to a lower level over an intermediate elevation by the pressure of the atmosphere in forcing the liquid up the shorter branch of the tube immersed in it while the excess of weight of the liquid in the longer branch when once filled causes a continuous flow. Lastly, the contraction of the mantel makes oxygen-rich water continually push past the ctenidia.