This has to be one of my favorite MetaFilter posts. The community links to all manners of amazing cephalopods, highlighting the beautiful blanket octopus which I had never heard of.

These species have an extreme degree of sexual dimorphism. According to the Melbourne Museum, “there’s no other non-microscopic critter that has such a significant size difference between the male and female.” Measuring only 2.4 cm long, the male blanket octopus is incongruously smaller than the female who can grow to over 2 m. This means that the female can be 100 times larger than her mate, and up to 40,000 times heavier.

More pictures at Tree of Life.