ink sac

plural ink sacs

1. biologyA muscular bag found in certain cephalopods used to generate ink.

   1 more example

   The ink sac feeds into the rectum, controlled by a sphincter and in some inking events mucus from another organ, the funnel organ is ejected with water and ink through the anus and the siphon to create a cloud of ink. […] Fossils are particularly well described from the Carboniferous, Triassic, Jurassic and Cretaceous periods and have been found in the USA, England, Russia, Lebanon and Germany. Sites such as Lyme Regis in Dorset have particularly yielded number of Jurassic “squid” ink sacs and nodules (Doguzhaeva et al. 2004).

   2017 August 9, Mark Carnall, “Why do cephalopods produce ink? And what's ink made of, anyway?”, in The Guardian