The arm that gets all the fun –
Come mating season
Most male cephalopods (octopus, squid, cuttlefish, nautilus) have an arm dedicated to reproduction called the hectocotylus. Essentially a tube of muscle, the arm passes sperm packets to the female during mating. The structure of the hectocotylus can be species specific, making it a handy tool in helping classify an organism. The arm was named when one was found detached from the male after mating and still left in the female, thus being confused for a parasitic worm. Sadly, cephalopds are generally short-lived and most die after mating.