In most cephalopods the siphuncle is central or ventral, the primtive condition as found in plectronocerids, ellemerocerids, and endocerids, e.g. being ventral. In some such as the Trocholitidae (Tarphycerida) and in a few pseudorthocerids it is instead dorsal of the center, in some along the dorsum. Any ideas as to the significance of this difference. Does it indicate anything about the orientation of the animal with respect to the shell and what evolutionary pressures might have influenced it.