Inkbag

Inkbag, the name of a gland in many of the Cephalopoda, such as the Pen-and-ink Fish or Squid and the Octopus, which secretes a black sepia pigment. By means of this the animal discolours the water around it so that it is hidden from an opponent. The inkbag has been found with the sepia still in perfect condition in some of the fossil Jurassic Cephalopods.