It's octopuses, no really

Here's a cool vid about our friend, the octopus (ws). See how I avoided using the plural form? That was how I was going to play it safe, but then curiousity got the better of me.

The plural form is not what most expect. It is in fact "octopuses" and not "octopi", though the latter is in such common usage that you can probably get away with using it.

That's because the word derives from Latinized Greek, not Latin itself. If you really want to read about second declension Latin nouns and their various endings, here's the wikipedia entry.