Septal necks are straight; connecting rings cylindrical, thin, and strongly contracted where they meet the necks.
32.
The siphuncle is achoanitic, having virtually no septal necks, segments formed all but entirely by connecting rings.
33.
Septal necks flair outwardly, segments are inflated ventrally and are straight dorsally, a character of the family.
34.
Those of " Solenochilus " have more strongly inflated siphuncle segments and more tightly curved septal necks.
35.
Septal necks are short, never quite reaching the previous septum and may vary in length ontogenically within a species.
36.
The juvenile segments in early genera are straight and tubular, with short orthochoantic septal necks inherited from the Bassleroceratidae.
37.
Plectronoceratina consist of forms in which siphuncle material is expanded into the chambers where unbounded by septal necks, forming siphuncular bulbs.
38.
Septal necks are retrosiphonate, characteristic of their nautlloid ancestors, and are commonly very long, forming an almost continuous siphunclular tube.
39.
The siphuncle is central, with orthochaonitic septal necks and segments which are slightly expanded between septa, giving it a beaded appearance.
40.
Later forms include those with cyrochoanitic septal necks ( curved outward ) and segments that may be slightly to strongly expanded into the chambers.
