[squidfood]

The style guides to most scientific journals will assert "octopuses", so you're unlikely to get "octopi" past that collective editorial authority, in any case - the others are however deemed acceptable alternates in common use.

[mturmon]

... most scientific journals will assert "octopuses" ...

I saw a lecture by Peter Godfrey-Smith, the author of the book in TFA, and he also comes down on the side of "octopuses".