Tretoceras is represented by depressed orthocones with closely spaced septa and what has been described and two (2)
siphuncles, one a large marginal subcylinctral tube, the other a small tubular structure about halfway between the center and venter. Neither surface nor interior nor real nature of the 2 "siphuncles" are well known. Foeste (1928) suspected a symbiotic relationship between the cephalopod animal and whatever produced the internal structure. Flower (1952) noted similar internal structures in 4 species of different ages.
[ibid ref]. The larger, outer, "siphuncle" may simply be an artifact of preservation. ==References==