One octopus, two...

A tip of the hat to Dirac for alerting me to the following:

There are three forms of the plural of octopus; namely, octopuses, octopi, and octopodes. Currently, octopuses is the most common form in the US as well as the UK; octopodes is rare, and octopi is often objectionable.

The Oxford English Dictionary (2004 update) lists octopuses, octopi and octopodes (in that order); it labels octopodes "rare", and notes that octopi derives from the mistaken assumption that octōpūs is a second declension Latin noun, which it is not. Rather, it is (Latinized) Greek, from oktṓpous (ὀκτώπους), gender masculine, whose plural is oktṓpodes (ὀκτώποδες). If the word were native to Latin, it would be octōpēs ('eight-foot') and the plural octōpedes, analogous to centipedes and mīllipedes, as the plural form of pēs ('foot') is pedes. The actual Latin word is "polypus," which does render the plural "polypi." In modern Greek, it is called khtapódi (χταπόδι), gender neuter, with plural form khtapódia (χταπόδια)…

Fowler's Modern English Usage states that "the only acceptable plural in English is octopuses," and that octopi is misconceived and octopodes pedantic.

The term octopod (plural octopods or octopodes) is taken from the taxonomic order Octopoda but has no classical equivalent. The collective form octopus is usually reserved for animals consumed for food.

Text credit to Wikipedia. The photo is of two glass models by the Blaschkas, via Octopi Press [sic].