The soft body of the orthoceras lived in the last open-ended segment at the large end of the conical shell. As the body grew it added on to the shell. Eventually a dividing wall, called the septa grew to separate the old “home chamber” from the new one
The siphuncle is a tube that runs the entire length of the shell, through each of the chambers. This tube could serve as a bouyancy device allowing the animal to rise and lower itself to different depths.