“Eight Strange and Wonderful Facts About Octopuses” from Shedd Aquarium (Sept 6, 2023). 

Key Facts

Blue blood 

Octopuses use copper-based hemocyanin rather than the iron-based haemoglobin we have, which gives their blood a blue colour and helps with oxygen transport in cold or low-oxygen environments. 

Three hearts 

They have three hearts: two pump blood through the gills, and one circulates blood through the rest of the body. Notably, the systemic heart stops beating while the octopus swims, which is one reason they prefer crawling. 

Ink jet defence 

Many octopuses can release a cloud of ink (containing melanin and tyrosinase) to obscure predators’ vision and impair their senses of smell/taste, allowing the octopus to escape. 

Venomous 

All octopuses (and all cuttlefish plus some squids) are venomous; while only a few species are dangerous to humans (notably the blue-ringed octopus), octopus venom helps paralyse prey and kick-start digestion. 

Master camouflage / colour & texture change 

Even though their eyes would suggest they’re colour-blind, octopuses can rapidly change colour, pattern and texture of their skin to hide or communicate. There’s research suggesting their eye structure (shape-changing pupils) might help detect wavelength/focus shifts. 

Multitasking arms 

An octopus’s eight arms each contain a “mini-brain” of sorts (nerve clusters) at their base, and each arm has many suction cups that can independently taste, smell and feel. Two-thirds of an octopus’s neurons are in its arms (not just in its central brain). 

High intelligence 

Octopuses are exceptional among invertebrates: they can solve problems, remember, use tools, open jars, and respond to training/enrichment (as done at Shedd Aquarium). 

Land visits / tide-pool forays 

Some shore-dwelling species occasionally leave the water at low tide (for short hunts on land or in tide pools). However, being out of water is energetically expensive (because their high oxygen needs and boneless body make movement and respiration less efficient on land) so these trips are brief. 

Why it matters

These facts show how octopuses combine unusual anatomy (three hearts, blue blood, arms with independent control) with remarkable behaviour (camouflage, tool use, intelligence) — making them among the most fascinating animals in the ocean. The article emphasises that they’re “stranger than fiction” yet very much formed by Earth’s deep evolutionary history.