So, from recently reading Peter Godfrey-Smith's OTHER MINDS: THE OCTOPUS, THE SEA, AND THE DEEP ORIGINS OF CONSCIOUSNESS (?2016), combined with my subsequently dipping into the much lighter Mather-Anderson-Wood volume OCTOPUS: THE OCEAN'S INTELLIGENT INVERTEBRATE (2010), I've learned several things I didn't know.
#1. the plural of 'octopus' is 'octopuses', not 'octopi'. The latter is a hypercorrection put forth in the eighteenth century by someone who cdn't tell his Latin from his Greek.
#2. octopuses are wicked smart -- by one measure, about as smart as a dog, or half as smart as a cat. They also have individual personalities. Oddly enough though, they are v. short-lived (a year or so for most species, no more than three or four for the longest-lived).
#3. there are at least seventy-two octopuses in Puget Sound, according to a count-the-optopuses survey done by divers at the same time each year.
There was also quite a lot about intelligence and the emergence of consciousness in the Godfrey-Smith book. I wish Mr. Barfield was still around: I'd be fascinated to see what he wd think of it.
Finally, I learned about a geological era I hadn't known about before: the Ediacaran Age. It's part of the PreCambrian, the time just before the Cambrian Explosion. Remarkably enough, none of the animals whose fossils they've found from that period had means to attack other animals or defend themselves from attacks: no horns, armor, pinchers, &c. They seem to have gone about their lives, pretty much ignoring each other.* The Cambrian introduced something new: predation, after which animals had to play careful attention to each other to either catch prey or avoid becoming prey. Which, by a long and eventful route, led to creatures like us.
current reading: Ben Aaronovitch's THE HANGING TREE (the latest in the Rivers of London series)
*although there's one inferred piece of evidence that challenges that: the Cnidarians (jellyfish and anemones) have toxic stingers and are thought on genetic grounds to date back before the Cambrian era.