A senior curator at the Melbourne Museum, Mark Norman, who recently found a living specimen on the Great Barrier Reef, said that until now the male had only been discovered dead in trawls and plankton nets. His achievement in capturing and photographing a live one has been documented in a recent paper for the New Zealand Journal of Marine and Freshwater Research. According to the article, the male blanket octopus is, technically speaking, "the most extreme example of sexual size-dimorphism in a non-microscopic animal ... such dimorphism is not seen in any other animal remotely as large".



Dr Norman said: "There's no other critters on that scale that have such a significant difference between the male and female." The two-metre female weighs at least 10,000 times as much as the male, sometimes up to 40,000 times as much.

This could make the question of position rather delicate, but as it turns out it doesn't matter. The male, it seems, relies on its arm as much as its penis to have sex. This reproductive arm, known as a hectocotylus, is tucked away in a white spherical pouch between its other arms. When males mate, the pouch ruptures, the penis injects sperm into the tip of the arm, the arm is severed, and passed to the female. It stays there until used to fertilise the female's eggs, which can be weeks later.

And while the human post-orgasm is sometimes referred to as "the little death", for the male blanket octopus the term takes on literal meaning. The male dies, but the female carries on, free to have sex with more males. "It's kamikaze sex, effectively," said Dr Norman. "They've found females with up to six male arms in the gill cavity."

But how did it get that way? Males compete with each other to fertilise the female, explained Dr Norman. Being small allows the male to mature earlier, and allows for better protection using its tentacle segments.