But note:
The plural form of octopus is octopuses (or occasionally octopodes). Although it is often supposed that octopi is the ‘correct’ plural of octopus, and it has been in use for longer than the usual Anglicized plural octopuses, it in fact originates as an error. Octopus is not a simple Latin word of the second declension, but a Latinized form of the Greek word oktopous, and its ‘correct’ plural would logically be octopodes.
http://wiki.answers.com/Q/What_is_the_plural_of_octopus