Most cephs have the beak held in by a mass of tissue and muscle called the buccal mass. You may be able to see the tip of the beak if your octopus sits on the glass, we often can with our midget octopus. It is right in the centre of the arms. Even in live squid the beaks will not necessarily be visible, it never has been in the few live squid we've had (generally for a VERY short time ). Steve or Kat may be able to add more, as they have much more experience with live squid than I have!!!