For pedants it's octopodes because its a Greek root, but the sort of people who think that way are the worst and are responsible for screwing up English a lot,

For pedants it's octopodes because its a Greek root, but the sort of people who think that way are the worst and are responsible for screwing up English a lot, so fuck those nerds. If you're speaking English then you just add an s or es. So Octopuses is right.