Many assume that the plural for octopus is octopuses that is incorrect. The correct one is octopodes. This is because octopus is greek and the plural therefore is octopodes. Although, to my understanding, either version can be used along with octopi. C:
It doesn't really matter which it is, like an argument one of my teachers classes have been having for two years about whether it's osprey (Os-pre) or osprey (Os-pray). Might take up that osprey osprey argument though...
Some authorities consider "octopi" an objectionable hypercorrection, feeling the form arose from the incorrect assumption that "octopus" is a Latin second-declension form. However, "octopus" is a scientific Latin third-declension noun with a plural of octopodes. Nevertheless, the Oxford English Dictionary (2008 Draft Revision) lists "octopuses", "octopi", and "octopodes" (in that order), labelling "octopodes" 'rare' and noting that "octopi" derives from the misapprehension that octōpus is a second-declension Latin noun. The book further maintains that if the word were native to Latin, it would be third declension octōpēs (plural: octōpedes) after the pattern of pēs ("foot", plural pedēs). The original Latin word for octopus and other similar species is polypus, from Greek polýpous (πολύπους, "many-footed"); again, usually the inappropriate plural polypī is used instead of polypodēs.
Fowler's Modern English Usage states, 'the only acceptable plural in English is "octopuses"', that "octopi" is 'misconceived', and "octopodes" 'pedantic'. Chambers 21st Century Dictionary and the Compact Oxford Dictionary list only "octopuses", although the latter notes that "octopodes" is 'still occasionally used'. The descriptivist Merriam-Webster 11th Collegiate Dictionary lists "octopuses" and "octopi" in that order; likewise, Webster's New World College Dictionary lists in order "octopuses", "octopi", and "octopodes".
This from the Complete Oxford English Dictionary (we've got the compact one that needs a magnifying-glass):
OCTOPUS. Greek (όκτώπους), pl. "octopodes", anglicized "octopuses". It cites the "ses" usage to H.M. Leathes, who mentioned in Rough Notes Na. Hist. 1884 that "...enormous octopuses existed on the west side of Panama, in the Pacific Ocean."
So it's pods, podes or puses, but not pi. This is pi: Π. Or something with apples in it.
Well anywhich way can be used, 'octopods' (and option you didn't even mention) is actually the correct term for a non-singular non-specific set of multiple when it comes to an octopus. In some cased you can also use the singluar as the plural 'octopus'.
This is one of those lovely words which actually has multiple different ways of being used correctly. (But to my understanding in so much as language rules go, apparently octopods is the most underused correct form of an animal plural to date. XD )
Grammar dictates octopuses. So I tend to go with that. That being said English has basically accepted both as correct thanks to the popularity of octopi. I find myself using octopi when I'm not thinking about it. Maybe I'll change to Octopodes.
Octopodes (pronounced Octop-o-dees) is technically correct because Octopus is Greek and Octopodes would be the correct plural form from Greek, whereas octopuses is English, and Octopi is Latin (if I'm remembering correctly). But, because we, the people who speak the English language, are extremely lazy, we just say that all forms are correct and say whatever the heck we feel like, because we can. ^___^
... *hmm* Suppose, technically, it should be octopoi (since the plural in Greek [for -us] is "-oi" not "-i",) but, in reality, whatever makes you happy to say.... octopusses is fun to say, even if horribly incorrect, gramatically-speaking...