Cephalopod beak

All extant cephalopods have a two-part beak, or rostrum, situated in the buccal mass and surrounded by the muscular head appendages.

Fossilised remains of beaks are known from a number of cephalopod groups, both extant and extinct, including squids, octopuses, belemnites, and vampyromorphs.

[10][11][12][13] Composed primarily of chitin and cross-linked proteins,[14][15][16][17] beaks are more-or-less indigestible and are often the only identifiable cephalopod remains found in the stomachs of predatory species such as sperm whales.

[18] Cephalopod beaks gradually become less stiff as one moves from the tip to the base, a gradient that results from differing chemical composition.

In hydrated beaks of the Humboldt squid (Dosidicus gigas) this stiffness gradient spans two orders of magnitude.