Really the plural is "eight-foots" because octopedus is just "eight feet" but you're successfully attempting to sound pretentious by saying it in someone else's words instead of your own.
Of course technically eight-foots have no feet at all, only arms. Hence, successfully calling it the incorrect pretentious name.
The pre-bureaucrat name for the eight-foot is devilfish, by the way. So there's that too.