An Unusual Pair

Marine scientists diving at night in deep water off Australia’s Great Barrier Reef recently experienced their first-ever encounter with a live male blanket octopus. What was so unusual about this?

For good reason, the blanket octopus is described as “the world’s most sexually size-dimorphic large animal.” The female grows up to six feet [2 m] in length and weighs up to 22 pounds [10 kg]. But the male is only one inch [3 cm] long and weighs one hundredth of an ounce [0.3 g]! In fact, the male is about as big as the pupil of the female’s eye. That means the female can outweigh the male by up to 40,000 times, a difference in size that appears to be the most extreme in nonmicroscopic animals. This octopus is pelagic, that is, it lives in the open sea, and until now only females and dead males caught in fishing nets have been observed.

How do these two creatures, so vastly different in size, reproduce? One of the male’s eight arms is hollow. After the male locates a female, the arm is filled with sperm. It then breaks off and enters the female’s mantle cavity, the large space inside her body. There it stays until she fertilizes her eggs by squeezing the sperm over them.

To compensate for his size, the male defends himself with tentacles that he apparently steals from the Portuguese man-of-war jellyfish and holds in the suckers of his upper arms. Even these tentacles do not save him, however, for when his duty to his mate is done, he dies. No wonder the scientists were amazed by their find!

Whatever the reason for the huge difference in size between these unusual octopuses, the words of the Bible are surely true: “As for this sea so great and wide, there there are moving things without number, living creatures, small as well as great.”​—Psalm 104:25.

[Pictures on page 31]

Female: length up to six feet; weight 22 pounds

Male: length one inch; weight one hundredth of an ounce

Actual size relative to the female

[Credit Lines]

Female: Photo P. Wirtz; male: Photo: D. Paul