Octopuses, sometimes called octopi, were solitary marine invertebrates found in tide pools, reefs, and the deep ocean alike, adapting to nearly every marine environment save the polar ice. Their soft, boneless bodies allowed them to compress themselves through gaps no wider than a coin, a trait that made them notoriously difficult to keep captive. Most species measured 30 cm to 1 m (1–3 ft) across the arms, though a few deep-water Giant Octopus species grew considerably larger. Eight arms, lined with sensitive suckers, served them for crawling, hunting, and manipulating objects with a dexterity that unsettled those Mortalkind who studied them too closely.
They were solitary hunters, feeding on fish, crustaceans, and smaller mollusks, which they subdued with a venomous bite before prying open shells with surprising patience. Octopuses possessed the ability to change the color and texture of their skin in an instant, vanishing against rock or coral, and could release clouds of ink to cover their retreat when threatened. Scholars who dissected them noted three hearts and blue-tinted blood, along with a nervous system so distributed through the arms that some questioned whether the creature thought with one mind or eight.
Octopuses were short-lived by the standards of the sea, most dying within a year or two of hatching, and females perished shortly after tending their single clutch of eggs. Despite this brevity, they were regarded by coastal folk as uncannily intelligent, capable of solving puzzles, escaping enclosures, and, by some accounts, recognizing individual faces. Sailors told wary tales of them prying open locked chests or slipping aboard ships in the night, and many considered it ill luck to eat one without first thanking the sea for its cleverness.