Argonauta
The beaks of Argonauta species are distinctive. They  are characterised by a very small rostrum and a fold that runs to the lower edge or near the free corner. The rostrum is 'pinched in' at the sides. This makes it much narrower than in other octopuses, with the exception of the closely allied monotypic genera Ocythoe and Vitreledonella. Argonaut beaks are most similar to those of Ocythoe tuberculata and Vitreledonella richardi. They differ in 'leaning back' to a greater degree than the former and because they have a more curved jaw angle than the latter.