Cutaneous oxygen uptake, which is described as the acquisition of oxygen molecules from the surrounding environment into an organism's skin, has been thought to account for as far as 20% of total oxygen uptake in squids, however this is not the case.  The proportion of total O2 uptake across the skin is actually far lower than this, as squid’s skin is not a net source of O2 but instead partially dependent on blood-borne oxygen (Birk et al., 2018).   Squid skin is also thinner than Octopus skin and is not vascularized like its counterparts.  Respiratory functioning in Squid’s are primarily handled through three key components, these being that of the mantle, gills, and siphon, all of which have effects on the breathing processes of these organisms.  Water entry takes place through the cavity known as the mantle, entering the mantle opening.  The mantle acts as a sort of “tube sock” covering for the squid body, the gills of the squid being hidden within the mantle itself.  The gills contained within squids are said to be feathery structures positioned in the mantle cavity, and are ventilated through muscular contractions rather than through the beating of cilia.  In contracting their mantle, squids have the ability to suck water into the mantle cavity and then drive it out through a ventral funnel, resulting in jet-propulsion.  This jet-propulsive force is able to occur due to incurrent openings in the squid, and through this powerful and vigorous force, the gills are properly ventilated.  Following the pumping of water to the gills, the oxygen contained within the water is then transported to the entirety of their cardiovascular system, including the heart, arteries and various veins, where the heart system then pumps blood throughout the body.  This method of jet-propulsion is also how the locomotion of the squid occurs, as the outer mantle expelling seawater takes place through a moveable siphon which propels the organism in the opposite direction.  One study also analyzed the oxygen-binding properties of squid’s respiratory protein, finding high oxygen affinity, strong temperature dependence, pronounced pH sensitivity, all of which contributing to squid’s reliance on night-time foraging and supporting suppressed oxygen demand in hypoxic waters at greater depths in the daylight hours (Young et al., 2013).  Perception of the surrounding environment through vision and other sensory neurons being key in signaling fight or flight decision making, which will spur this method of movement to evade predators and seek prey.  

Squids have been studied to display very small venous oxygen (O2) reserves when they are at rest (Hill et al., Page 654).  Inactive squid are shown to use eighty to ninety percent of the available O2 in their arterial blood, and thus have minimal room to increase unloading of O2 from their hemocyanin.  Due to this, squid must meet a heightened O2 demand, in which they do so by increasing their rates of circulation, all of which play a factor into the squid's ability to exercise as high demands rests on their hearts alone.  This small venous O2 reserve also limits their ability to live in bodies of water that are poorly aerated because this will cause them to be unable to properly oxygenate their arterial blood.  This is due to the fact that squid differ from other senses in the fact that they cannot compensate for the O2 poor waters by deoxygenation of the venous blood contained, as venous blood is already deoxygenated to great levels in aerated waters (Hill et al., Page 654).  This all gives reason as to why Squid are so highly particular of the waters that they can exist within and why squids are notoriously intolerant of low-oxygenated environments.