Go ahead, count ’em. Since there were some comments about octopuses with an odd number of arms, here’s an example. Males of this species have a highly modified arm (the one they use for sex) that is tucked away in a pouch, so they have the appearance of a seven-armed octopus.
Figure from Cephalopods: A World Guide (amzn/b&n/abe/pwll), by Mark Norman.