The females of many octopus species outgrow their male counterparts, a strategy that seems to work for their non-social system. These reclusive cephalopods live alone and, when the time to mate comes, the females are found carrying an entire clutch of eggs while the males "only" contribute with the sperm, which comes in small packets called spermatophores. The bigger the female, the more eggs she is able to carry, and this translates into better odds at continuing the genetic line.
To mate with their large female counterparts, who might carry around 100,000 eggs, the males secrete their spermatophores into a pouch on their specialized third right arm (the hectocotylus) and leave it in or on the body of the female, where it will be used to fertilize the eggs when she is ready to lay. The male is assumed to die soon after he has made his contribution, while the female carries the eggs in a long strand until they hatch.
But both males and small females have an additional and surprising option for defence. These octopuses are apparently immune to the sting of Portuguese man-o-wars (Physalia Physalis) and have been known to collect stinging tentacles from the poisonous jellyfish-like creature to wield them like weapons for fending off predators.