Incorrect. Platypus is Greek in origin, not latin. Platypi would be the correct pseudo-latin pluralization, but platy means flat and pus means foot in Greek. The noun pus is irregular in Greek, pus podos, podes are the forms of it. The correct plural of platypus would be platypodes in the masculine or platypoda in the feminine. Scientists don't call them platypi. Platypus is both singular and plural in some cases although platypuses is also acceptable.
I took 4 semesters of greek and 4 semesters of latin in college and I specifically asked a biology teacher what they called multiple platypuses.
NOW THAT YOU HAVE BEEN EDUCATED I'LL CHIME IN WITH INCREDIBLE LASCIVIOUS PINEAPPLES.
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The Interplanetary League of Pinecones