siphuncle A long tube present in those cephalopods (Cephalopoda) that possess external shells. It runs internally, through all the chambers, and contains the siphuncular cord of body tissue, extending from the visceral mass through a perforation in each septum of the shell. The siphuncle releases gas into the unoccupied chambers of the shell, making the animal buoyant.

siphuncle A long tube present in those cephalopods (Cephalopoda) that possess external shells. It runs internally, through all the chambers, and contains the siphuncular cord of body tissue, extending from the visceral mass through a perforation (foramen) in each septum of the shell. The siphuncle releases gas into the empty chambers of the shell, making it buoyant.