If you've seen My Octopus Teacher, this year's Oscar winning documentary, you will surely be fascinated by a very short French documentary, La Pieuvre, by Jean Painleve from 1928 available for free on the Cinematheque Francaise's website via their wonderful platform of goodies, Henri. Take the time to have a look. It's silent, so no translation necessary.
Released in December of 1928 for the inauguration of the Studio Diamant, the film was the first widely distributed 'biology film' of the filmmaker. Painleve (great name, translation: raised bread), the son of the minister of war, was apparently a jack-of-all-trades who established this tiny film studio at the summer home of relatives of his girlfriend. He had discovered octopuses at the age of nine in Brittany and they were the impetus for his degree in zoology.
I was devastated at first by the rough handling of this specimen (Are there multiples?) both in and out of an aquarium but remembered it wasn't until recently that we gave enough credence to the brains of species other than our own. Still, in the film’s fourteen minutes, you will become attached. (One colorized moment of the octopus scaling a children's doll is particularly haunting.)
Also for octopus lovers (I will never eat one again), a marvelous children's book that takes as it point of departure the true escape of the octopus from the aquarium in New Zealand in 2016, Inky's Great Escape (there are many versions, the one you want is by Casey Lyall).