To sum up: 'octopodes' is Greek, 'octopi' isn't Latin (or is bad post-Classical Latin, and scientific New Latin always strives to use good Latin)... and 'octopuses' is English. It's an ordinary English word, not technical, so there's no reason not to use the English plural.

Thank you Nicholas, octopuses it shall be. By the way, do you know anything about a possible Etruscan origin for "Caesar"?