Strange Sex

Male argonauts (a type of pelagic octopus) have a weird reproductive system. Their penis is a detachable arm called the hectocotylus. When mating, the male argonaut releases this arm, which autonomously swims to the female and deposits sperm. The female then stores the sperm for later fertilization.

Male argonauts are tiny compared to females -—often less than an inch long -- while females can grow up to 12 inches. Early biologists mistakenly believed the hectocotylus was a parasitic worm rather than a reproductive organ.