Pörtner calculates that jetting around so much takes five to 10 times the amount of oxygen that fishy swimming does. Also, “they’re not just the jet set; they’re blue bloods,” he says. When oxygenated, their blood turns blue with the reactions of hemocyanin molecules. These bulky oxygen-carrying molecules have only a third to a fifth of the capacity of the hemoglobin that does the same job in vertebrate blood.

Offsetting these disadvantages, thin skin lets squid take in some 60 to 80 percent of their oxygen directly from surrounding water, Pörtner and colleagues have found. And the muscles that most need the oxygen lie just under the skin.