A note on the plural form: Fowler's Modern English Usage states that "the only acceptable plural in English is octopuses", and that octopi is misconceived and
octopodes pedantic. Octopi derives from the mistaken notion that octopus is Latin, which it is not.
Rather, it is (Latinized) Greek, from oktopous (ὀκτώπους
, gender masculine, whose plural is oktopodes (ὀκτώποδες

. If the word were Latin, it would be octopes ('eight-foot') and the plural octopedes, analogous to centipedes and millipedes, as the plural form of pes ('foot') is pedes. In modern, informal Greek, it is called khtapodi (χταπόδι

, gender neuter, with plural form khtapodia (χταπόδια

.
That said, Merriam-Webster and other dictionaries accept octopi as a plural form. The Oxford English Dictionary lists octopuses, octopi, and octopodes (the order reflecting decreasing frequency of use), stating that the last form is rare.