How do cephalopods protect themselves?

Cephalopods have a number of very effective methods of defense.  Jet propulsion is one such method, which allows the cephalopod to move quickly.  Many cephalopods, especially octopuses, are very adept at hiding and can rapidly change not only their color, but their texture too, in order to blend in with their surroundings.  This camouflage is incredibly effective.  In addition to this, many cephalopods, including all squid and some octopuses, excrete a kind of ink, which is produced by a gland in the digestive system of the animal.  This ink confuses any predators so the squid or octopus can get away and it is also used by some octopuses to confuse their own prey so they can more easily sneak up on it from behind.