Fun fact: octopus does not come from Latin, which would give the plural an -i ending. It comes from Greek, which means that if you want to be particularly correct about your plurals, then the plural is octopodes.
That's fun. Octopii rolls off the tongue though, doesn't it? Since we have survived both the Greek and Roman cultures, and have absorbed aspects of both into languages now widely distributed, I'd like to propose that we seed the path of a true lingua franca and declare the plural of octopus to be octopii.
It's no worse than inserting greek words (octopodes) into English language.
It's no worse than inserting greek words (octopodes) into English language.