Octopuses have alien brains and three hearts

A single heartbeat pulses, strong and steady, through most of the animal kingdom. But beneath the ocean's sun-dappled surface, an octopus moves with three. Each beat propels a cerulean current, a visible divergence from the crimson flow of terrestrial life.

Two hearts, aptly named branchial hearts, dedicate their rhythm to driving blood through the octopus's gills, optimizing oxygen uptake from the water. A third, larger systemic heart, then circulates this richly oxygenated blood to the body's tissues. This triple-pump system is inefficient during high-speed swimming; the systemic heart actually stops beating during intense activity, causing the octopus to tire quickly as its tissues lose oxygen circulation.

The blood itself takes on a striking blue hue due to hemocyanin, a copper-based protein. Unlike the iron in hemoglobin that binds oxygen in vertebrates, copper proves more efficient at low temperatures and reduced oxygen concentrations, conditions common in many marine environments.

This specialized circulatory architecture, alongside a unique oxygen-carrying compound, represents a profound evolutionary adaptation. It allows octopuses to maintain high metabolic rates in their often demanding aquatic habitats, powering their complex behaviors and remarkable intelligence.

Octopuses are highly efficient at extracting oxygen, pulling up to 90% of available oxygen out of the water through their gills.