Octopus

Different from anything else alive

Octopuses are molluscs (related to snails and clams) but their cognitive abilities are unlike any other invertebrate — closer to small mammals or birds than to most marine creatures.

Several physiological features set them apart:

• Three hearts — one main systemic heart, two branchial hearts pumping blood through gills.
• Blue blood — uses copper-based hemocyanin instead of iron-based hemoglobin (more efficient in cold low-oxygen water).
• Nine “brains” — one central brain plus a ganglion in each arm, allowing significant arm autonomy.
• No skeleton — body can squeeze through any opening larger than the beak.
• Color-changing skin — chromatophore cells produce instant pattern changes despite the octopus being colorblind.

Tool use and intelligence

Octopuses are the only invertebrates documented using tools:

• Coconut shells carried as portable shelters — gathered from sea floor, transported on swims, assembled into protective dens when needed.
• Rocks placed at den entrances as doors.
• Glass jars and plastic bottles used as shelter.

In captivity, octopuses solve complex puzzles (unscrewing jars, opening locked containers), recognize individual humans, and perform problem-solving feats normally associated with vertebrates.

The European Union legally recognized octopuses as sentient beings in 2010, requiring welfare protections in research.

Camouflage masters

Octopus skin has three types of cells working together for camouflage:

• Chromatophores — red, yellow, brown pigment cells that expand and contract.
• Iridophores — produce structural blue and green colors via light reflection.
• Leucophores — produce white, reflect ambient color.

The combination allows pattern-and-color matching of remarkable subtlety. Octopuses can mimic specific environments (coral, sand, kelp) and even other animals (lionfish, sea snakes) — all despite being colorblind themselves. They infer color from polarized light and from the colors of nearby objects.

A short, intense life

Most octopus species live only 1–2 years. They reach sexual maturity quickly, mate once, and die soon after — the female watches over her single clutch of eggs without eating, dying when the eggs hatch.

This short lifespan is unusual for an animal of such intelligence; other smart species (parrots, elephants, dolphins) typically live decades.