Actually you are wrong. Due to common belief, most people do not know that platypi is actually not the right terminology. If the word, platypus, derived from Latin, then yes, it would be platypi, but because it derives from the Greek, the original being platopous, the correct plural form would be platypodes, or, as is accepted in the english language, platypuses. The same applies to octopus, because it also comes from the Greek, that being oktopous.
Further arguing, Latin has five different suffixes for pluralisation, such as the -i ending, and it is a common mistake to apply this to other words even though they are not from the Latin.
Platypi has been used so many times (wrongly, but still) that is has become acceptable in the english language but is still incorrect.
So...
-cough-
platypodes*
:D